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BDS3 > Paper 1: BCS, CP > Flashcards

Paper 1: BCS, CP Flashcards

1
Q

Describe denture base material

A

PMMA powder + MMA liquid

  • PMMA = MMA pre-polymerised into powder via suspension polymerisation
  • acts as filler as doesn’t polymerise more

Powder + Liquid HC using Dough Technique

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2
Q

Advantages of using HC Dough Technique

A

Using MMA alone: vol. shrinkage 21% (7% linear shrinkage)
- 2/3 replace w/ PMMA vol. shrinkage 7% (~2% linear)

Exotherm red.

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3
Q

Discuss composition of denture base PMMA

A

Powder

  • PMMA spherical beads 10-200mmetre
  • benzoyl peroxide (0.2-0.5%); initiator
  • pigments (1-2%)
  • Ti/Zn oxides; opacifiers

Liquid
- MMA
— volatile, flammable
— store dark glass bottle; avoid spontaneous polymerisation = extend shelf life
- ethylene glycol dimethacrylate (10%); cross-linking monomer
— form covalent bonds b/w PMMA chains
— improve craze resistance
— too much = brittle
- hydroquinone (0.0006%); inhibitor
— react w/ FRs that form in bottle
— form stabilised FRs; can’t initiate polymerisation

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4
Q

Activation requirements for HC polymerisation

A

Initiator (benzoyl peroxide) + heat (~80)

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5
Q

Discuss stages of HC polymerisation of PMMA

A

PMMA + MMA mixed -> Dough formed which is heated (80)
FR polymerisation occurs forms cured plastic polymer

Initiation: FR attack MMA double bond
Propagation: (chain growth); MMA monomers add to chain
Termination: 2 growing chains meet; FRs combine form stable covalent bond

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6
Q

Discuss the formation of crazes in denture bases

A

Internal strains due to thermal contraction
- minimise: use acrylic teeth, allow flask to cool slowly
Relieving produce tiny defects (crazes)
- form cracks which grow = #

Form in response to;

  • heat; polishing
  • differential thermal contraction around porcelain teeth
  • attack by solvents; pt drinking alcohol
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7
Q

Discuss the formation of porosities in denture bases and why this is problematic

A

Exothermic: if over BPt (MMA 100.3)
Gaseous: incorrect curing; monomer vaporises leading voids
Contraction: flasks not kept under Constant Spring pressure during curing cycle
Granular: incorrect mixing/packing; structural deficiency due to loss of monomer

Problem

  • H2O fills voids
  • unreacted monomer (toxic) leach out
  • further voids -> more H2O absorbed
  • leads to crazes + failure
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8
Q

Advantages of HC PMMA denture base

A

Glass transition temp: 105/125 (high)
- well above temp. encountered in use
— polishing, cleaning

Specific gravity: low; doesn’t fall out

Aesthetic
Manufacture + repair easy
Good longevity: 5-10yr

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9
Q

Disadvantages of HC PMMA denture base

A

Toxicity: residual monomer (0.5%)
- contact dermatitis, mucosal irritation

Elastic modulus: 2.6GPa (low)
Impact strength: low (cracks grow), brittle
Fatigue strength: low; major cause failure
Abrasion resistance: low
Thermal conductivity/diffusivity: low; is insulator
- potentially scald as don’t feel temp.

Dimensional stability: polymerisation shrinkage

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10
Q

Discuss rubber reinforcement of HC acrylics

A

Butadiene styrene

  • introduce rubber phase
  • high impact acrylics
  • cracks stop growing when rubber domains reached
  • high degree of resistance to #
  • lower flexural modulus; long term fatigue failure due to excessive flexure
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11
Q

Discuss potential fibre reinforcements of HC acrylics

A

Carbon: difficult handling, poor aesthetic
Polyaramid plain fabric (Kevlar)
- ineffective: poor bonding b/w resin and fibres
Ultra-high MWt polyethylene (UHMPE)
- neutral colour
- biocompatible
- low density
- surface treated for bonding to resin
- fabrication T consuming
Glass: most promise
- hydrophilic glass + hydrophobic PMMA problematic
- incorporated in resin as short fibres; in cloth or loose form

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12
Q

Explain why HC PMMA dentures need to be kept in H2O

A

In storage/mouth absorbs ~2% H2O
If drys out will absorb >2% H2O
If this continues crazes form
- due to relieving IS + residual monomer leaching
- crazes -> cracks -> fail; red. longevity

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13
Q

Uses for RT PMMA

A 
Denture repair 
Relining denture bases 
Additions to denture
Special trays 
Temp. crown and bridge
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14
Q

How is RT cured acrylic mixed?

A

RT PMMA (pre-polymerised MMA) powder + RT MMA monomer liquid mixed in Dough Technique

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15
Q

Composition of RT cured PMMA

A

Powder

  • PMMA; finer particle size cf HC
  • BP; initiator
  • colour pigments
  • Ti/Zn oxides; opacifiers

Liquid

  • MMA monomer
  • hydroquinone; inhibitor
  • N,N-dimethyl-p-toluidine (DMPT); activator
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16
Q

Describe the RT polymerisation process of RT PMMA

A

Liquid + powder mixed
PMMA beads dissolve in MMA liquid
Activation: DMPT breakdowns BP liberating FRs
FRs attack MMA double bonds
- follows initiation, propagation + termination stages

~10min cure

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17
Q

How does the finer particle size of RT PMMA powder affect the curing process?

A

More rapid diffusion of MMA into PMMA beads

- rapidly gelates to hard mass

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18
Q

Advantages of RT PMMA cf HC PMMA

A

Cheaper
Less technician T; don’t have to send to lab
Chair side use

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19
Q

Disadvantages of RT PMMA cf HC PMMA

A

Physically weaker
- low MWt PMMA affect mechanical properties
- > residual monomer (3-5%) (not all able to polymerise)
— leaches -> porosities

Aesthetics: poor stability; DHPT causes yellowing
Tg: lower (70-80)

Porosity

  • more rapid gelation
  • hand mixing incorporate air

Inc. H2O uptake

  • low MWt
  • loss of residual monomer
  • porosity
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20
Q

Discuss PEMA; what it is, monomers it can be mixed with, Tg

A

Higher methacrylate (cf PMMA) powder mixed w/ (usually) higher MWt monomers using Dough Technique

Monomers

  • can’t use MMA = incoherently mixed product
  • none = tissue conditioner
  • higher MWt monomers (ethyl, butyl, hexyl)

Tg: 65 (

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21
Q

Uses of RT PEMA acrylics

A 
Tissue conditioner (no monomer)
Hard reliner
Soft lining material
Extension of special trays and dentures 
Temp. crown + bridge
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22
Q

Discuss PEMA tissue conditioners

A

PEMA mixed w/ no monomer

  • no polymerisation occurs
  • forms viscoelastic gel via polymer chain entanglement
  • short life (3d); no polymerisation, alcohol volatile, plasticiser leaching

Uses

  • denture lining; allow tissues to recover
  • maxillofacial prosthesis; obturators
  • functional impression materials
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23
Q

What is the function of PEMA powder in PEMA/EMA?

A

Same as PMMA
Acts as virtual filler
- dec. shrinkage
- lower exotherm

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24
Q

What is the purpose of soft lining materials?

A

Make denture more comfortable for pt in area has traumatised soft tissues

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25
Q

Function of plasticisers

A

Adjust viscosity of material
- make natural rigid material soft and rubbery

Lower Tg and elastic modulus

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26
Q

Dis/adv of soft lining PEMA

A 
Adv
- soft, rubbery acrylic 
- adheres well to acrylic denture base
— contains acrylic group
- Tg lowered by plasticiser
Disadvantages
- hardens w/ T as plasticiser leaches
— use as little as possible
- short life due to hardening 
- biocompatibility; phthalate (banned in EU - use citrate)
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27
Q

Function of temp. crown

A

Mimic natural tooth
Protect prep. tooth while permanent crown being made
Made @ chair side

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28
Q

Composition of crown and bridge/extension PEMA

A

Powder

  • PEMA
  • BP
  • colour pigments
  • opacifiers

Liquid

  • butyl methacrylate monomer
  • hydroquinone
  • DMPT
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29
Q

Adv of PEMA/BMA

A 
Lower exotherm cf PMMA/MMA
Less pulpal and soft tissue irritancy
Non-volatile monomer
Good handling 
Not brittle, ductile
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30
Q

Discuss light cure dimethacrylate materials

A

Uses

  • composite filling
  • temp. crown + bridge

Properties

  • high modulus
  • low exotherm
  • adequate polymerisation shrinkage

Composition; 1 paste

  • BisGMA/urethane dimethacrylate
  • camphorquinone
  • diluents
  • fillers
  • pigments
  • DMPT
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31
Q

Discuss HEMA

A

Low viscosity liquid

Dry state: forms hard resin
Wet state: soft rubbery - hydrogel
- absorbs 10-100% H2O

Uses
- RMGIC, dentine bonding agent
- unsuccessful as soft lining
— absorbed too much liquid causing to swell

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32
Q

Discuss cyanoacrylates

A

Polymerise v quickly @ body temp

Used as surgical glue
Dental uses
- PD surgery 
- adhesive for dentine (bonds to collagen)
- endodontic cement

Full strength within 24h
- higher moisture + thinner bond-line = faster cure

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33
Q

6 factors which keep dentures in place

A
  1. Saliva
  2. Muscles
  3. U and L teeth when biting
  4. Gravity (L denture)
  5. Denture clasps (direct)
  6. Denture rests (indirect)
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34
Q

Discuss how saliva can aid denture retention and the factors affecting this

A

Weak glue: b/w denture and tissues
- clinically unlikely to resist displacement

Suction: peripheral seal around denture
Factors
- dry mouth (poor)
- thin saliva layer (good)
- well-fitting denture (good); flange fills width of sulcus
Posterior ‘post. dam’ seal: artificial ridge created in denture to seal saliva
- border b/w hard and soft palate

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35
Q

Discuss how muscles and teeth can support dentures

A

Muscles

  • learn to control denture using musculature; dependent on health
  • post. tongue naturally rest on post. denture

Teeth biting together

  • uneven/stable: dentures will slide
  • correct occlusion (bite together in RCP); dentures stable
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36
Q

Define denture support, retention, stability

A

Support: ability to resist displacement towards tissue (O loading)

Retention: ability to resist displacement away from denture bearing area perp. to tissue surface at rest

Stability: ability to resist displacement in relation to underlying bone during function in any direction

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37
Q

Discuss what affects denture support and how to check support

A

Depends

  • amount of coverage of underlying tissues/denture bearing area (more = better)
  • condition (firmness) of underlying tissues/denature bearing area (firmer = better)

Check

  • press O surface bilaterally; see if moves
  • see how much area covered; denture extension ideal?
  • signs of trauma?
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38
Q

Explain why an U complete denture has better support and is less likely to cause trauma

A

Larger fit surface and covers more underlying tissue and bone (more support)
Thus O forces distributed over larger surface area (less trauma)

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39
Q

Discuss factors affecting denture retention and how to check retention

A

Depends

  • adhesion b/w denture, saliva, mucosa
  • area covered
  • adaptation to tissue
  • border seal (suction)
  • muscular control (tongue, cheek)
  • gravity (L)

Check

  • hold onto denture teeth, try to pull away from tissues
  • press incisal edge U ant.; does back lift?
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40
Q

Discuss factors affecting denture stability and how to check stability

A

Depends

  • degree of support and retention
  • degree of alveolar bone reposition
  • area covered
  • freedom to make excursive movement
  • consistency of supporting tissue
  • position of teeth and design of polished surfaces
  • correct vertical and horizontal O relationship
  • level of O plane

Check

  • history
  • press O surface unilateral
  • observe denture during function
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41
Q

Ideal properties of successful denture

A 
Comfortable
Strong enough
Tolerable
Adequate stability 
Atraumatic
Aesthetic
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42
Q

Main components of RPD

A

Saddles
Rests
Clasps
Major + minor connectors

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43
Q

Discuss RPD saddles

A

Part that covers edentulous ridge
Usually (not always) incl. replacement teeth

Note: not all edentulous ridges restored by saddles

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44
Q

Function and types of RPD rests

A

Main support provider

Function

  • transmit O forces to teeth along longitudinal axes
  • maintain O relationship of denture base to abutment teeth
  • prevent trauma to gingiva
  • provide some lat. stability
  • prevent food packing b/w abutment teeth and base

Types

  • occlusal: pre/molars
  • cingulum: canines
  • incisal: outdated
  • ring: wraps all way round tooth
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45
Q

What is a rest seat? Function

A

Any prepared surface on abutment teeth to take rest

Function

  • provide O space b/w U+L teeth to allow adequate metal thickness
  • provide more suitably inclined bearing surfaces cf natural teeth
  • provide shape of surface desirable for amount of bracing
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46
Q

How to decide where to position RPD rests?

A

Adjacent to saddle
Adequate PD attachment of abutment teeth
Equally distributed; opposite
Adequate O space

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47
Q

Function, types, components and location of clasps

A

Provide retention

Function

  • utilise resistance of metal to deformation
  • engage extra-coronal undercuts
  • usually natural undercuts

Types

  • occlusally approaching
  • gingivally approaching
  • ring

Components

  • rest
  • retentive arm; engages undercut
  • reciprocal arm; thicker, firm, doesn’t engage, resists displacement
  • minor connector

Location

  • adjacent to saddle
  • spread around arch
  • only need 2 diametrically opposed
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48
Q

Discuss Kennedy classification of dentures

A

Suggests/governs partial denture design

1: bilateral edentulous areas post. to remaining teeth; free end saddles
2: unilateral edentulous area post. to remaining teeth
3: unilateral edentulous area w/ teeth ant. + post.; bounded saddle
4: single, bilateral edentulous area ant. to remaining teeth; crosses midline

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49
Q

Discuss Applegate’s rules applied to Kennedy Classification

A

Missing 7+8 discounted if not being replaced
Most post. edentulous area determines classification
Modification spaces: additional edentulous areas (Class 2 mod 2)
Class 4: no modifications

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50
Q

Importance of denture support and how it can be gained

A

Importance

  • red. movement on loading
  • red. trauma
  • improve distribution loading
Gaining: any part of denture that sits on bearing surface 
- hard tissue: teeth, hard palate
— tolerate axial loading
— feedback prevents overloading
— as low as 20microm displacement 
- soft tissue: alveolar ridge, hard palate
— loading can cause pain/trauma
— limited feedback
— displacement >500microm
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51
Q

Ways in which denture retention can be gained w/ natural teeth

A

Frictional contact
Clasps
Sectional denture
Precision attachments

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52
Q

Discuss frictional contact, sectional dentures and precision attachments

A

Frictional Contact
- most mucosa-borne acrylic dentures req. friction b/w base + natural teeth for retention
- guide planes enhance effect
— also improve clasps; restrict path of removal to 1 path

Sectional Dentures

  • 2 parts w/ different paths of insertion
  • when seated lock together by hinge or parallel split posts
  • exploit undercuts on M and or D of abutment teeth

Precision Attachments

  • depend on friction b/w machined M and F parts
  • req. cast restorations on abutment teeth
  • usually intra-coronal; may be extra-coronal
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53
Q

Define major connector (RPD)

A

Unit of denture that connects components on 1 side of arch to the opposite side
Part of denture to which all other components are attached

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54
Q

Principles of major connector design

A

Rigidity
Must not impinge moving tissue
Avoid pressure on gingiva
Adequate relief when indicated; bony prominences, tori
Supported by rests
Borders sited and contoured for tolerance

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55
Q

Types of mandibular major connector

A

Lingual Bar
Dental Bar
Lingual Plate
Buccal Bar

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56
Q

Discuss lingual bar and space req.

A

Conventional and sub-lingual types
Kennedy connector
Not sit on gingival margins

Space

  • at least 3mm clear of gingival margins
  • clear of moving tissues of FOM
  • adequate dimensions for rigidity
  • at least 7mm b/w gingival margin and FOM
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57
Q

Discuss dental Bar/connector

A 
Sits across teeth
Req. crown height of 8mm
- 2mm clear of incisal edge; don’t see
- 2mm clear of gingival margin
- 4mm depth for rigidity (+ 2mm thickness)
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58
Q

Discuss lingual plate

A 
Only used when necessary 
Covers all gingival margins + teeth
- unfavourable 
- accumulation of plaque
- difficult to clean
Thin, wide
Contoured for intimate contact w/ lingual surface
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59
Q

Maxillary major connectors

A

Palatal Bar

  • ant., mid., post.
  • usually ant. + post.
  • narrow, thick (rigid) but bulky
  • min. palate + gingival margin coverage

Palatal Strap

  • thin, wide metal
  • lots of palatal coverage, min. gingival coverage

Palatal Plate

  • max. coverage; soft tissue hyperplasia, poor hygiene
  • most comfortable, best support, rigid

Palatal Horseshoe

  • covers gingival margin
  • avoids palatal coverage; gag reflex
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60
Q

Discuss minor connectors

A

Connect major connectors to other components

Req.

  • adequate O space
  • emerge at 90 degree to gingival margin
  • avoid sharp internal line angles
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61
Q

Discuss hygienic denture design and why it is important

A

Minimal amount of gingival margin coverage; free wherever possible

Why

  • don’t cause plaque formation
  • promote inc. in amount of plaque where gingival margin covered
  • alter quality of plaque
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62
Q

Discuss how to minimise gingival damage in RPD design

A

Provide at least 3mm relief or none at all
If <3mm; gingival hypertrophy into small spaces making difficult to clean
Thus >3mm req. or none

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63
Q

Requirements of endodontic instruments

A

Flexible
Maintain cutting edge
Not corrode

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64
Q

Discuss SS endodontic material

A

Alloy of ace and <0.8% C; some Ni and Cr
Files prepared by twisting wire or machined (Hedstrom)
Flexibility depends on geometry, diameter, taper, twists
- rhombohedral (K-flex) most flexible

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65
Q

What is the only movement twisted SS endo instruments can be used in? Why?

A

Reciprocating up to 90 degrees
As
- clockwise: untwists file -> ductile failure
- anti-clockwise: tightens twist -> brittle failure
— usually fail anti-clockwise

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66
Q

Discuss the structure of endodontic Ni-Ti

A

Can exist in 2 crystal structures w/ different properties

Martensite

  • low temp. form; body centred cubic
  • low modulus (flexible), high strain @ break

Austenite

  • high temp. form; monoclinic
  • high modulus (rigid), low strain @ break
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67
Q

Discuss shape memory of Ni-Ti

A

Unique property

Deform NiTi with v low force @ lower temp
When heated through transformation temp recover original shape
- ortho use: apply pressure to teeth as recovers shape
Remove deformations by heating to 125 degrees
- endo: curve file for canal, removed by sterilising

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68
Q

Discuss superelasticity of NiTi

A

Can be strained much higher cf conventional alloys before permanent deformation occurs
Elastic deformation up to 8% cf SS 1%

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69
Q

Discuss causes of NiTi # and how it can be improved

A 
Both ductile and brittle aspects 
Due to;
- low yield stress
- work hardening
- structural imperfections produced during manufacture
- fatigue

Improved by

  • electropolishing machined surfaces
  • ion implantation or surface coating to harden
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70
Q

Compare NiTi and SS properties

A 
Strain: 8% vs 1%
NiTi
- higher strength, lower modulus
- machines; continuous rotation
- expensive 
- better fatigue life, flexibility

SS

  • used for hand instruments
  • cheaper, can be pre-curved

Both suffer fatigue

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71
Q

Discuss 3 main irrigants used in endo

A

NaOCl (0.5-5.25%) 1%

  • dissolves proteolytic debris
  • antibacterial
  • affects instruments
  • possible toxicity

Chlorhexidine 2%

  • usually chlorhexidine deglutonate
  • alternative to NaOCl
  • antibacterial
  • adheres to dentine
  • not proteolytic

Ethylene Diamine Tetra-acetic Acid (EDTA) 10-18%

  • lubricant
  • dissolves smear layer; calcified canals
  • use in conjunction w/ NaOCl
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72
Q

Discuss endodontic medicaments

A

Non-setting Ca(OH)2 (pulpdent)

  • most common
  • alkaline pH12
  • antibacterial: OH- release -> damage bacteria preventing growth

Ledermix
- mix; cortisone derivative and broad spectrum AB
— 1% triamcinolone (anti-inflammatory)
— 3% demeclocycline (AB)
- good for pulpal or PD inflammation
- endo-Perio lesion: spread from pulp -> PD tissue

Phenolic compounds
Quaternary ammonium compounds 
- not effective
- used near toxic level
1% Iodine - 2% Potassium-Iodide 
- low toxicity, antibacterial
- staining; rinse w/ NaOCl
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73
Q

Discuss phases of gutta percha

A

60% crystalline, hard, rigid

Alpha
- high temp., cooled slowly
- softer
- thermoplastic techniques
— heated and injected into canal

Beta

  • high temp., cooled rapidly
  • rigid
  • GP points
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74
Q

Composition of GP points

A

GP 19-22%
ZnO 59-75% filler
Heavy metal salts 1-17% radio-pacifier
Wax/resin 1-4% plasticiser

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75
Q

Properties of GP

A 
Biocompatible
Insoluble
Thermoplastic
- softens 60-65
- melts 100 (can’t heat sterilise)
Light degradable (brittle)
Swells in solvents (acetone, chloroform)
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76
Q

Alternatives to GP

A

Resilon

  • thermoplastic polyurethane
  • bioactive glass + radiopaque filler
  • similar handle cf GP
  • similar filling techniques
  • softened by heat, soluble in solvents
  • req. EDTA Tx and self-etch Prime for good bond

Silver
- rigid, corrodes
- discolour
Acrylic or Ti: solve corrosion problem

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77
Q

Discuss composition of ZOE for canal sealing

A 
Powder
- ZnO (MgO)
- fillers; SiO2, Al2O3
- dicalcium phosphate
- Zn salt
Liquid
- eugenol 
- other oils; olive, cotton seed
- acetic acid (accelerate)
- H2O (essential)
Additive
- iodides: bactericidal 
- Ag, Ba, bismuth salta: radiopacity
- resins: improve adhesion to canal
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78
Q

Properties of ZOE

A 
Moisture accelerate set
Eugenol: allergy, inflammatory reaction, inhibit polymerisation 
Soluble H2O
Obtundant
Thermal insulator
Good seal
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79
Q

Composition of setting Ca(OH)2

A

Paste 1: Base
- salicylate Ester: butylene glycol disalicylate
- TiO2, CaSO4, BaSO4 (fillers)
Paste 2: Catalyst
- Ca(OH)2
- ZnO
- toluene sulphonamide, Zn stearate (plasticiser)

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80
Q

Properties of Ca(OH)2

A 
Alkaline: bactericidal 
Long working T
Biocompatible
High solubility; water weakens
Moisture accelerate set
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81
Q

Discuss resin based canal sealers

A 
Epoxy amine
- good handle
- good seal
Polyketone/Polyvinyl resin, reinforced ZOE
- cytotoxic when set
Urethane dimethacrylate/BisGMA

Properties

  • insoluble
  • polymerisation shrinkage
  • long working T
  • good flow
  • radiopaque
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82
Q

Discuss GI as canal sealer

A

Glass powder + PAA

Bonds to tooth
Short working T
Sets hard, difficult to remove

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83
Q

Discuss polydimethysiloxane canal sealer

A

Addition cured silicone (impression material)

Good working T
Smooth, homogenous mix
Good flow
Insoluble 
No bonding 
Not antibacterial
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84
Q

Discuss mineral trioxide aggregate

A

Complex reaction
- hydration of tricalcium silicate -> hydrated calcium silicate gel + Ca(OH)2

Sets hard, mixed w/ H2O
Strong
Alkaline: initial 10.2, set pH12.5
Long set: 3-4h
Expensive, difficult to handle
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85
Q

Classification of dental alloys

A

High noble

  • > 40% Au
  • > 60% noble metal; Pt, Pd

Noble: >25% noble
Base metal (Co-Cr, Ni-Cr, Ti)
- <25% noble

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86
Q

Requirements of RPD alloy

A 
Biocompatible 
Easy to cast
- high density: easily force out air of mould, fill w/ alloy
- low MPt = low shrinkage 
Low casting shrinkage 
Easy to join/solder
Easy to finish/polish
Easy to adjust
High modulus (rigid)
High yield stress
Good fatigue strength 
Good wear resistance
Good corrosion/tarnish resistance
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87
Q

Composition of Co-Cr alloys

A

Co (50-65%); strength, hardness
- interchange Ni (0-30%); inc. ductility, dec. hardness
Cr (25-30%); hardness (solution hardening), resist corrosion (passive oxide layer)
Mo (4-6%); red. grain size, hardness (solution hardening)
C (0.2-0.5%); hardness + strength
- forms carbides which precipitate on slow cooling
- excess carbides = brittle
Small amounts: Fe, W, Mn, SI

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88
Q

Dis/adv Co-Cr alloy

A

Adv

  • cheap
  • hard, abrasion resistant
  • high modulus (use in thin section)
  • high yield stress
  • low density, lightweight
  • Ni-free biocompatible
  • good thermal response

Disadv
- poor handling
— high casting temp, high cast shrinkage (~2%)
- low ductility
- rapid work hardening (can’t be adjusted)
- Ni sensitivity
- difficult to finish/polish (due to hardness)
— req. electrolytic polishing of fit surfaces

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89
Q

Composition of Ni-Cr alloys

A

Ni (60-80%); hardness, strength
Cr (10-27%); hardness (solution hardening) corrosion resistance (passive oxide layer)
Mo (2-14%)
Be (0-2%); carcinogenic
+ Al, C, Co, Cu, Mn, Ti
- fluidity, castability
- limit carbide precipitation, too much = brittle

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90
Q

Composition of T4 gold alloys

A 
Au 60-70%; lowest amount as ductile 
Ag 4-20%
Cu 11-16%
Pt 0-4%
Pd 0-5%
Zn 1-2%
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91
Q

General rules for properties of gold alloys from T1-4

A

As go from T1-4

  • hardness (Vickers), elastic modulus (rigidity), tensile strength inc.
  • ductility, elongation @ break dec.
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92
Q

Compare properties of T4 gold cast and hard

A

Vickers hardness: 130-160; 200-240VH
Tensile: 410-520; 690-830MPa
Modulus: 95; 103GPa
Elongation: 5-25; 1-6%

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93
Q

Dis/adv of T4 gold alloys

A 
Advantages
- biocompatible 
- easy to 
— cast; low MPt, shrinkage 1%
— finish/polish
— solder
- corrosion resistant
- can be heat hardened (order hardening)

Disadvantages

  • high density; uncomfortable for pt
  • low yield stress; weaker
  • low modulus; thick sections
  • expensive
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94
Q

Discuss forms of Ti/alloys

A

Commercially pure Ti

  • 4 grades of 99% Ti + varying amounts N, C, H, Fe, O
  • Inc. O, Fe: inc. strength, Dec. ductility
Alloys
- alpha: low temp., hexagonal
- beta: high temp., cubic centred body
- Ti6Al4V alpha + beta
— V toxin replaced by Nb: Ti6Al7Nb
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95
Q

Compare properties of Ti6Al4V and cpTi (G1 vs G4)

A 
Hardness: 320; 126-263VHN
Tensile: 930; 240-550MPa
Yield: 860; 170-480MPa
Modulus: 113; 102-104GPa
Elongation: 10-15; 24-15%
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96
Q

Discuss materials used for denture clasps

A

Wrought

  • pre-mode, bought clasps, soldered on to framework
  • SS, Au
  • better flexibility (esp. Au) and strength
  • Au: easy to adjust + solder, possible corrosion @ join w/ base metal

Cast

  • cast w/ framework
  • Co-Cr, T4 Au

Base metal clasps have limited adjustment (work hardening)

Aesthetic clasps

  • thermoplastic acetal resin (polyoxymethylene)
  • used w/ acrylic or Co-Cr RPDs
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97
Q

What are cold cure soft acrylics? What is their use?

A

Temporary soft lining materials
Soft, viscoelastic material

Use: Tx irritated mucosa supporting denture

  • allow recovery of inflamed tissue from ill-fitting denture
  • absorb some energy prod. by masticatory forces
  • shock absorber b/w O surface denture + underlying tissue
  • promote healing
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98
Q

Discuss properties of temporary SLM/RT soft acrylic

A

Generally inf. HC soft acrylic (long-term SLM)
3-5% residual monomer: irritant + fungal infection
Higher H2O uptake; monomer leach, space filled w/ H2O cf HC
Poorer mechanical properties cf HC
Temporary: 1-2 wk

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99
Q

Discuss composition of RT soft acrylics (temporary SLM)

A 
Powder
- PEMA
— or copolymer of butyl and ethyl methacrylate 
— or PMMA
- residual BP
- opacifiers
- pigments
Liquid
- EMA
— or BMA
— or MMA
- ethylene glycol dimethacrylate; cross-linking agent
- dibutyl phthalate (or citrate)
— phthalate = carcinogen 
— no chemical bond = leaching
- DMPT; 3ry amine activator 
- hydroquinone
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100
Q

Compare functions or short term SLM and TC

A

Similar function, differ;
Composition: polymerisable monomer; ethanol, no polymerisable monomer
Setting: FR addition polymerisation; gelation + chain entanglement
Lifespan: 1-2 wk; 3d

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101
Q

What are tissue conditioners? What are their uses?

A

Soft, viscoelastic materials
Uses
- Tx irritated mucosa supporting denture (temp. SLM)
- temp. (3d) denture liner; Tx denture stomatitis
- functional impression material; wear provisional denture 24h
- piezograph
— impression moulded by tongue, lips, cheeks over 5-10min
- maxillofacial prostheses

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102
Q

Compare composition of Viscogel and Coe-comfort (TCs)

A 
Viscogel
Powder
- PEMA
— or copolymer B/EMA
Liquid
- plasticiser
— butyl phthalyl, butyl glycollate, dibutyl phthalate 
— acetyl tributyl citrate 
- ethanol 6-15%
- no monomer = no polymerisation

Coe-Comfort
Powder
- Zn undecylenate
— Zn: red. irritation + swelling of fungal infection
— Fatty acid: prevent growth fungus
Liquid
- Benzyl Benzoate: plasticiser, preservative
- ethyl alcohol: solvent; accelerate gelation

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103
Q

Discuss setting of TCs

A

Set via gelation (chain entanglement), physical process
On mixing, polymer beads (chains) swell in alcohol
- allows penetration of plasticiser b/w polymer chains
- polymer chains move more easily
Gel formed by polymer chain entanglement

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104
Q

Discuss factors than can affect handling of TC

A

Inc. powder:liquid

  • inc. viscosity of gel
  • affect final compliance (softness)
  • inc. rate

To inc. rate

  • inc. temp
  • dec. MWt + particle size of polymer powder
  • inc. ethanol
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105
Q

Advantages and disadvantages of TC

A

Adv

  • simple
  • use chair-side
  • bond PMMA
  • compliant (soft)
  • viscoelastic

Disadv
- harden in mouth: ethanol + plasticiser leach
— ethanol lost within 24h (may be irritant)
- possible toxicity of plasticiser
- porous: ingress of microorganisms
- difficult to remove from denture

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106
Q

Discuss general properties of temporary SLM and TCs in relation to interaction w/ fluids and denture cleansers

A

Fluids
- high H2O uptake; stain, microbial colonisation
- plasticisers can leach
— inc. in presence of long-chain fatty acids, alcohol
- inc. surface roughness esp. soft acrylics
- more affected cf silicones (long term SLM)

Cleanser

  • all affect SLM and TCs
  • hypochlorite bleaches
  • alkaline peroxide roughens surface, bleaches
  • brush w/ soap
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107
Q

What are long-term SLMs? What are their functions?

A

Group polymeric materials
Last in OC >wks/mnths/yrs
Intended inc. comfort + support prosthetic Tx
Can’t red. forces transmitted by denture bearing area

Function
- evenly distribute masticatory forces + absorb some energy
— relieve mucosa from high mechanical stress
- deforms elastically, energy release as returns to original form

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108
Q

4 types of long term SLMs

A

HC addition silicone
RT vulcanised cured condensation silicone
RT vulcanised cured addition silicone
HC soft acrylic

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109
Q

Uses of long-term SLM

A 
Long-term (wks-yrs), resilient linings 
Pt can’t tolerate hard denture base
Utilise undercuts for retention
Retention of complete dentures to implants 
Obturators and other prostheses
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110
Q

Disadvantages of long term SLM

A

Expensive: HC sent to lab
Difficult to modify and polish
Dec. denture thickness, inc. rigidity/hardness
- 1mm thick hardness as support of underlying tissue comes through
More prone to #

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111
Q

Ideal properties of SLMs

A 
Nontoxic, nonirritant 
Bond PMMA
Not support growth of Candida
Permanently resilient + compliant
Low H2O uptake (similar to PMMA 2%)
Not affected by denture cleansers
Easy to clean, not easily stained
Sufficient mechanical strength + abrasion resistance 
Wetted by saliva
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112
Q

Compare the viscoelasticity of silicone-based and soft acrylic SLM

A

Silicone based recovery rate is faster

Soft acrylics can permanently deform

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113
Q

Discuss the composition and setting of HC addition silicone SLMs

A

Composition: one paste

  • vinyl terminated poly(dimethyl siloxane)
  • gamma-methacryloxypropyltrimethoxy silane (MPTS); cross-linker
  • BP: initiator
  • PMMA: filler
  • colouring agents

Setting

  • HC 100degrees for ~2hr; can be microwaved
  • addition, FR polymerisation
  • BP oxidises CH3 on neighbour siloxane chains to form cross-links
  • silane acts as cross-linker
  • methacrylate group reacts w/ denture base to form bond
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114
Q

Composition of RT vulcanised condensation silicone

A 
Similar to impression material 
Base
- silicone polymer w/ terminal OH groups
- inert filler
Catalyst
- tetraethoxy orthosilicate; cross-linker
- dibutyl tin dilaurate; catalyst 
- inert filler
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115
Q

Composition of RT vulcanised addition silicone

A 
Base
- vinyl terminated poly(dimethylsiloxane)
- H+ terminated poly(dimethylsiloxane)
- inert filler
Catalyst 
- vinyl terminated poly(dimethylsiloxane)
- Pt-based catalyst: chloroplatinic acid
- inert filler
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116
Q

Other components in silicone SLMs

A

Bonding agent/Primer (all silicones)

  • polymer in solvent
  • can contain silane
  • can contain MMA; bond PMMA denture

Glaze/Polish (RT vulcanised)

  • smooth and seal trimmed areas
  • not used in contact w/ tissue
  • unfilled AS, some w/ solvent
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117
Q

Compare general properties of SLM silicones

A

RT vulcanised AS: better mechanical and adhesion to PMMA cf CS
HC AS: best adhesion and lower H2O cf RT vulcanised

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118
Q

Advantages and disadvantages of SLM silicones

A

Adv

  • resilient
  • compliant
  • not adversely affected by OC

Disadv

  • poor adhesion to PMMA
  • poor tear strength
  • hydrophobic: not wetted by saliva
  • support growth of Candida
  • 1-paste HC req. refrigeration (short shelf-life)
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119
Q

Composition of HC soft acrylic SLMs

A 
Long-term SLM
Powder
- PEMA
— E/BMA copolymer
- residual peroxide

Liquid
- higher methacrylate monomer: E/BMA
— contribute to softness
- cross-linker: ethylene glycol dimethacrylate
- plasticiser: butyl phthalyl, acetyl tributyl citrate
— red. Tg below mouth temp

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120
Q

Discuss setting of HC soft acrylic SLM

A

As w/ HC PMMA: FR addition polymerisation on heating
Dough technique
Initiation: FR attack double bond
Propagation: monomers add to chain, chain growth
Termination: 2 growing chains meet, FRs combine forming stable covalent bond

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121
Q

Advantages and disadvantages of HC soft acrylic SLM

A

Adv

  • initial compliance is good: retains softness
  • wetted by saliva (hydrophilic)
  • bond PMMA
  • good tear resistance
  • polished if chilled

Disadv

  • hardens (plasticiser leach); toxicity
  • high H2O absorption; plasticiser leach
  • less resilient cf silicones; don’t remain soft
  • permanent deformation can occur
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122
Q

Discuss waxes and dental waxes

A

Organic crystalline compounds; natural or synthetic
Thermoplastic moulding material
- solid @ RT
- heated to liquid phase thus is mouldable
Pyrolysed; melt and/or decompose -> H2O vapour + CO2
Individual wax
- sharp, well-defined MPt
- little use
Dental
- blend 2/+ waxes
- material w/ softening temp range over which is mouldable material

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123
Q

Composition of dental waxes

A 
Wax: synthetic and 2/+ natural 
Small amount additives
- gums: gum Arabic, tragacanth
- fats: esters of FAs w/ glycerol
- fatty acids
- oils
- natural (dammar, rosin) and synthetic (shellac) resins
- pigments
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124
Q

Aim of additives in dental waxes

A

To give set of given properties of specific range of temps
Contain range of MWt that affect melting and flow properties
Chemical components of natural and synthetic waxes impart characteristic physical properties

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125
Q

7 types of natural wax

A

Paraffin: petroleum

  • straight chain HC
  • melt: 40-70

Microcrystalline: heavier petroleum fractions

  • branched HC
  • melt: 60-90

Ceresin: petroleum or lignite refining

  • melt: 61-78
  • use: inc. melting range paraffin

Carnauba: Carnauba Palm

  • melt: 84-91
  • use: inc. melting range + harden paraffin

Candelilla: small shrub

  • melt: 68-75
  • use: harden paraffin

Beeswax

  • melt: 63-70
  • use: modify paraffin

Spermaceti: sperm whale
- use: coating on floss

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126
Q

Discuss synthetic waxes w/ examples

A

Production
- combination of chemicals in lab OR
- chemical action on natural wax
Usage inc.; higher degree of refinement

Polyethylene: 100-105
Polyoxyethylene glycol: 37-63
Halogenated HC
Hydrogenated HC
Wax esters: reacting FAs + alcohol
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127
Q

Define melting range and flow (waxes)

A

Melting range
- range of temps at which each component begins to soften and then flows

Flow: movement of wax molecules which slip over each other (at high temp wax has low viscosity and flows)
- mobile as approaches melting range
- control of flow/melting range important in manipulating wax
- clinic: melting range of bite registration wax only slightly > mouth temp
— too high would be uncomfortable for pt
- lab: much higher melting range

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128
Q

Discuss excess residue and dimensional change (waxes)

A

Excess residue: wax film remaining on object after removal

  • may result in inaccuracies in item being produced
  • important in lost wax technique

Dimensional change
- waxes have greater thermal expansion and contraction cf any other DM
- important in pattern wax: duplicate restoration carved in wax
- if heated > melting range/unevenly = expansion > acceptable standards = inaccuracies
- on standing dimensional change due to release of residual stress
— invest and cast within 30 min after carving wax

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129
Q

How are stresses formed in wax?

A

Heating
Carving
Bending
Manipulating

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130
Q

Discuss types and uses of inlay wax

A

Is pattern wax
T1: medium, direct technique
T2: soft, indirect technique
- restoration made in wax -> metal/ceramic

Use: patterns for inlays, onlays, crowns

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131
Q

Ideal properties of inlay wax

A

Direct: soft, plastic > mouth temp
Indirect: solidifies < mouth temp

Carved w/o flaking or distortion
Colour contrast from tooth/die
V low residue on vaporisation (<0.1% @ 500 degrees)
Low thermal expansion (but high cf DMs)
No distortion @ moulding temp (no stress build up)
Softens w/ dry heat

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132
Q

Composition of inlay wax

A

Paraffin (60%): weak, flakes thus need additives
Carnauba (25%): inc. melting range/glossy finish
Ceresin (10%): modify toughness and carving
Beeswax (4%): red. flow @ mouth temp, red. brittleness @ RT
Dammar resin (1%): improve smoothness, crack and flake resistance, glossy finish

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133
Q

Discuss casting wax

A

Type of pattern wax
Use: patterns for partial denture framework
Composition: unknown, similar to inlay wax
Highly ductile: bend double @ 23 degrees w/o cracking

Class 1: easily adaptable 40-45
Class 2: adapts well to surface, not brittle on cooling
Class 3: burnt out w/o leaving residue

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134
Q

Discuss modelling wax

A

Use: set up artificial teeth for C denture

Composition

  • paraffin or ceresin (70-80%)
  • beeswax (12%)
  • resins: natural or synthetic (3%)
  • carnauba (2.5%)
  • microcrystalline or synthetic waxes (2.5%)

Properties

  • easily mouldable w/o cracking, flaking, tearing
  • easy to carve
  • melt and solidify repeatedly w/o changing properties
  • no residue after removal w/ boiling water and detergent
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135
Q

Discuss boxing-in wax

A

Type of processing wax

  • box wax as sheets
  • heading as ribbon

Use

  • build up vertical walls around impression before pouring
  • beading: adapt around impression borders

Properties

  • pliable @ RT
  • retain shame @ 35 degrees
  • slightly tacky
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136
Q

Discuss sticky wax

A

Type of processing wax
- adhesive wax

Use: temp joining of articles

  • align # parts of acrylic denture
  • align fixed partial denture parts before soldering

Composition

  • rosin
  • beeswax
  • dammar

Properties

  • RT: hard, brittle
  • melted: sticky, adheres closely to applied surface
  • # s on movement rather than distorting
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137
Q

Discuss impression wax

A 
Use: O registry (edentulous impression)
Composition 
- HC waxes: paraffin, ceresin, beeswax
- Al or Cu: improve integrity and shape 
Properties
- distorts when removed from undercut areas: only edentulous areas
- soft/flows @ mouth temp; rigid @ RT
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138
Q

Discuss 4 other dental waxes

A

Wax rim/Bite rim: pattern wax

  • use: restore O relationship, arrangement of teeth
  • softening temp > mouth temp
  • tough, resists #

Utility/Rope wax: adapt border of impression

Shellac denture base

  • stable @ mouth temp
  • high softening point

Base plate wax: pattern wax

  • use: preparing wax patterns for prosthesis
  • red or pink sheets
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139
Q

Compare mucocompressive and mucostatic impression materials

A

Mucocompressive/displacive
- viscous, record mucosa under load
- appliance has wider distribution of load during function (stable)
— compensates for differing compressibility of bearing area
— red. risk # due to flexion
- retention compromised as soft tissues return to original position @ rest
- examples: impression compound, high viscosity alginate/elastomer (polyether)

Mucostatic

  • fluid, displace less
  • record un-displaced tissue
  • better retention as closer adaptation to tissue @ rest
  • instability during function as tissues distort
  • examples: impression plaster, ZOE, low viscosity alginate, light body addition silicone
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140
Q

Discuss non-elastic impression materials

A

Rigid materials; little/no elasticity
Any significant deformation = permanent deformation
Use: no undercuts, edentulous pt

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141
Q

Composition, properties and handling of impression plaster

A

Composition

  • CaSO4 B-hemihydrate
  • K2SO4; accelerator, anti-expansion
  • borax; retarder (counteract K2SO4)
  • colouring agents; contrast model plaster

Properties

  • mix w/ H2O hemihydrate -> dihydrate
  • expands on set; sets hard
  • thinner mix cf model plaster
  • flows into fine details e.g. ridges
  • mucostatic
  • no trays req.
  • edentulous cases only

Handling

  • mix; load tray, position, hold till sets
  • may # on removal; retrieve and glue together
  • beading wax adapted to periphery; indicate where impression ends
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142
Q

Discuss impression compound; composition, properties, handling

A

Composition

  • resins
  • waxes
  • talc; filler
  • stearic acid; lubricant

Properties

  • thermoplastic
  • poor thermal conductivity/flow
  • not reproduce undercuts
  • mucocompressive
  • high viscosity; record full depth of sulcus if req.

Handling

  • soften by heating in H2O @ ~60 degree
  • load stock tray, position
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143
Q

Discuss ZOE impression paste; composition, properties, handling

A 
Composition 
- paste 1
— ZnO
— Zn acetate 
- paste 2
— eugenol 
— inert filler; kaolin, talc

Properties

  • brittle when sets; #s
  • accurate in thin sections
  • initial low viscosity and pseudoplasticity
  • mucostatic

Handling

  • Zn eugenolate formed on mixing
  • use v close fitting tray or existing denture

Use diminishing due to elastomers
- edentulous or relining

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144
Q

Uses of hydrocolloid impression materials

A 
C/P dentures
Ortho: base plate
Mouth protectors 
Study models, working casts
Duplicating models
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145
Q

Dis/advantages of alginates

A 
Adv
- setting behaviour 
— Na3PO4 (retarder) = viscous paste while seating
— rapid once begins = min. impression T
- cheap, reliable

Disadv
- H2O loss
— continual shrinkage post-set (cast immediately) = poor dimensional stability
— cover w/ damp gauze in plastic bag (few hrs)
- H2O/disinfectant immersion
— imbibition; initially swells
— shrinks; H2O soluble salts eluted
— prolonged immersion impractical and unsolved
- poor tear strength; large undercuts can’t be reproduced
- highly viscoelastic
— snap removal technique
— permanent deformation up to 1.5%; diminished if undercuts not deep

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146
Q

Dis/advantages of agar

A

Adv

  • easy to use
  • cheap
  • good surface detail

Disadv

  • syneresis (cast immediately) = poor dimensional stability
  • imbibition; distortion
  • poor tear strength; better cf alginate
  • compatibility w/ model materials
  • highly viscoelastic; permanent deformation up to 1%
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147
Q

Uses of elastomers

A

Accurate replica teeth + supporting tissues
- C/P denture, crown, bridge, inlay
Border moulding of special trays (polyether)
Duplicating of refectory casts
Bite reg

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148
Q

Dis/advantages of poly(dimethyl siloxane) impression material

A

Condensation silicone

Adv

  • strength, dimensional stability cf alginate
  • more elastic cf polyether/sulphide
  • tear strength, elongation @ break adequate; undercuts reproduced

Disadv

  • dimensional stability; 0.3-0.5% shrinkage 24h
  • hydrophobic; detergents incorporated (may expand)
  • mouth dry as possible
  • mainly lab use
  • erratic setting: liquid catalyst
  • limited shelf-life: liquid catalyst
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149
Q

Dis/advantages of poly(vinyl dimethylsiloxane)

A

Addition silicone impression material
Adv
- best dimensional stability; <0.05% 24h
- elastic recovery v good cf polysulphide/ether

Disadv
- free H2O (plaster) react w/ unreacted Si-H -> H2 = porous model
— wait 20-30mins before casting
- tear strength, elongation @ break adequate; less cf CS
- hydrophobic
- natural rubber retard set; S poison Pt catalyst
- poor shelf-life, long set

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150
Q

Dis/advantages of polyether

A

Adv

  • dimensional stability in air
  • quick set cf polysulphide
  • reliable
  • clean handle

Disadv

  • high modulus + low elongation @ break = tears easily (original impregum)
  • dimensional stability in H2O/vapour; disinfection problematic
  • permanent deformation
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151
Q

Dis/advantages of polysulphide

A

Adv
- strongest impression material: elongation @ break ~500%

Disadv

  • dimensional stability: 0.1-0.2% shrinkage
  • slow set
  • dirty handling, unpleasant odour
  • elastic recovery poor cf silicones, polyether
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152
Q

What are investment materials?

A

Ceramic material used to form moulds for dental castings

Used to compensate for shrinkage of alloy due to change from liquid to solid and thermal contraction

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153
Q

General requirements of investment materials

A 
Withstand high temp and pressure
Easy to manipulate, fast set
Smooth surface to give smooth finish to casting and preserve fine detail
Chemically stale @ temps used
Porous enough to allow air/gas to escape 
Easily break away from casting
Not react w/ alloy
Sufficient strength to withstand casting
Expand to compensate for shrinkage 
Inexpensive
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154
Q

3 general components of investment materials

A

Refractory: withstand temp, shrinkage compensation
- crystalline SiO2: quartz, cristobalite, tridymite
Bind: hold refractory particles together
Other additions: modify physical properties

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155
Q

Mechanisms of expansion of investment materials

A

Setting expansion of binding
- greater in presence of refractory
- interferes w/ interlocking of crystals as they form
- finer particle size = greater expansion
Thermal expansion
Inversion expansion of refractory
- all crystalline forms undergo sudden expansion as change a -> b form
- silica used singly or together to give desired expansion
Hygroscopic expansion: in contact w/ H2O during set

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156
Q

3 types of investment materials

A

Gypsum bonded
Phosphate bonded
Silica bonded

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157
Q

Composition of gypsum bonded investment

A

Refractory: a-hemihydrate CaSO4 (stone) 25-55%
Binder: cristobalite and/or quartz 55-75%
Additives: 2-3%
- C; reducing agent
- boric acid, NaCl; regulate set, expansion

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158
Q

Properties of gypsum bonded investment

A 
35% hemihydrate, 65% cristobalite: thermal expansion 1.2% @ 700
Setting expansion: max 0.6% in air
Hygroscopic expansion: 1.2-2.2%
- immersed in H2O or wet liner in casting ring
- continues setting reaction
- promote crystal growth 
Cheap
Sufficiently strong
Porous for Au alloys 
Req. metal ring for support
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159
Q

Use of gypsum bonded investment

A

Gold alloys MPt up to 700

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160
Q

Composition of phosphate bonded investment

A

Refractory: formed by acid/base reaction; 20%
Binder: cristobalite and/or quartz; 80%
C: red. agent
- not for Ag-Pd alloys >1500 as causes brittleness

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161
Q

Properties of phosphate bonded investment

A 
Mixed w/ H2O
- thermal: 1%
- setting: 0.5%
Mixed w/ colloidal silica suspension 
- thermal: 1.3-1.6%
- setting: 0.5%
Hygroscopic: possible when mixed w/ colloidal silica

Stronger cf gypsum; don’t req. metal rings
Finer particle size = smooth surface cf gypsum
Set affected by temp

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162
Q

Use of phosphate bonded investment

A

Higher MPt alloys up to 1000
- gold, base metal, metal-ceramic, all ceramic

Preferred choice as can be used for all alloys up to 1200

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163
Q

Composition of silica bonded investment

A

Powder: MgO (neutraliser)
Liquid: HCl, ethyl silicate

Refractory: cristobalite and/or quartz
Binder: formed on mixing liquids
- ethyl silicate + H2O -> silicic acid + EtOH
- mix powder: silicic acid + MgO -> silica (gel)
- dry @ 100 degrees
- heat: silica gel -> cristobalite

164
Q

Properties of silica bonded investment

A 
Shrinks when dried (remove H2O, EtOH)
No setting expansion 
High thermal expansion: 1.6%
Ethyl silicate: hazardous, short shelf life
- sodium silicate better
EtOH: hazard, flammable 
Not porous; req. vents
Complicated, expensive
165
Q

Use of silica bonded investment

A

High MPt base metal alloys up to 1200

Mainly partial dentures

166
Q

Requirements of die materials

A 
Highly accurate
Compatible w/ impression material 
Dimensionally stable 
Good # strength 
Good wear resistance
167
Q

Discuss die stones

A

Improved stone (densite): a-hemihydrate

  • T4: high strength, max expansion 0.1%
  • T5: high strength + expansion (0.1-0.3%)
  • gypsum bonded investment
  • smooth surface, denser, harder

Surface Hardened

  • filled w/ polymer
  • die hardener; colloidal silica
  • cyanoacrylate
168
Q

6 alternative die materials

A 
Filled acrylic: autopolymerised, high shrinkage
Epoxy
- some shrinkage: 0.03-0.3%
- can be filled
- hard, strong
- can be Cu plated
- can’t use w/ alginate
Polyurethane: good wear + # resistance 
Amalgam: only w/ inelastic impression material 
Flexible: silicone, polyether
169
Q

Discuss alternative technique for die formation

A 
Cu/Ag Plating
- directly plate impression w/ pure Ag/Cu
- adv
— dimensionally stable
— good abrasion resistance
— good surface detail 
— strong
- disadv
— Ag: uses AgCN
— can’t use alginate

Metal sprayed impressions: bismuth-tin alloy

170
Q

Define immediate, transitional, diagnostic and definitive denture

A

Immediate: constructed and fitted in same appt teeth XLA
Transitional: pt about to loose all/many teeth, add teeth to denture as lost
Diagnostic: test inc. OVD or aesthetics
Definitive: final set of complete dentures

171
Q

EO findings important in Tx planning denture

A 
Jaws: opening, closing 
Palpate TMJ, MoM
Smile line: happy? Change?
Lip support: req. more?
Overclosed or propped open?
Pathology: angular cheilitis 
Appearance: tooth missing, U lip support
172
Q

IO findings important in Tx planning denture

A 
All pathology noted + Tx prior to constructing dentures
OH and caries assessment
Perio health: abutment teeth
Existing restorations sound
Arches: edentulous areas described
Over-eruption
Tilting? Drifting?
Space: enough width within arch and height b/w arches for teeth
173
Q

5 stages in Tx planning for denture

A 
Relief of Symptoms
- pain resolved immediately 
- trauma common; ulcer, granuloma 
Prevention: OHI, diet, F- application 
Stabilisation 
- PD/caries paramount 
- good plaque control 
- Diagnostic
— articulate + survey study casts
— provisional denture design 
- initial denture design 
Definitive Tx Phase
- plastic/cast restorations 
- RCT
- denture construction 
Maintenance: review
174
Q

Discuss the shortened dental arch

A

Adequate oral function can be maintained w/ 10 occluding pairs of teeth
- U&L1-5

Factors affecting prognosis
- premolar c ant. teeth healthy
- tooth contacts favourable; avoid malocclusion (Class 2/3, ant. open bite)
- tooth wear likely? Young, bruxism?
— load inc. as no Ms
- caution if TMJ problems or bruxist
175
Q

6 main reasons for replacing missing teeth

A 
Appearance
Chewing
Speech
Swallowing
Occlusal maintenance
Psychological comfort
176
Q

Importance of occlusal maintenance following tooth loss

A

Teeth will over-erupt/tilt if opposing tooth lost

  • 92% of cases
  • ~30% >2mm

Factors

  • occlusal relationship
  • periodontal support
  • soft tissues

Problems may occur when restorations req. after over-eruption

177
Q

Discuss when dentures need to be provided

A

Only when req. functionally or psychologically

  • SDA may be acceptable
  • fixed options preferred?
  • benefits > risks
  • stabilised mouth
  • pt request

Indications

  • large spans
  • replacement of supporting tissue
  • obturation of defects
  • immediate replacement
178
Q

Why and when are jaw registrations used?

A 
Why
- allow articulation of master casts 
— analysis of occlusion 
— construction of denture components
— set teeth according to chosen occlusion

When: only when req.
- not enough occlusal contacts for casts to be correctly located

179
Q

Compare ICP and RCP/centric relation in choosing for denture

A

Intercuspal Position

  • sufficient teeth present
  • stable occlusion
  • conformation occlusal approach; use wherever possible

RCP/CR

  • jaw relationships not tooth
  • insufficient teeth to stabilise occlusion
  • reorganised occlusal approach; req. extensive fixed restorations
  • use: inc. OVD, edentulous pt
180
Q

Importance of denture teeth position

A

Appearance
Stability
Speech
Planning of implant placement

181
Q

What are the general principles when deciding how to position artificial teeth?

A

Denture surfaces modelled to replace part of pt’s tissue or part of existing denture
Usually, want artificial teeth to occupy same space as natural teeth

In partially dentate, position usually straightforward to determine

182
Q

Define neutral zone and denture space

A

Neutral zone: inward pressure from cheeks balanced by outward pressure from tongue

Denture space: area limited by tongue, lips, cheeks, residual alveolar ridge

183
Q

3 main clinical scenarios that may present w/ denture pt

A

Planned transition to edentulism
Pt has existing dentures
Pt is edentulous but has no existing dentures

184
Q

Tx options when plan is planned transition to edentulism

A 
Add to existing partial dentures: best Tx option
Transitional denture
- construct simple acrylic partial first
— convert to C/C later
- restores jaw relationship 
- allows period of habituation 
Immediate insertion C/C; same day as XLA
185
Q

If pt has an existing denture what is important to check with regards to tooth position?

A

Are teeth in correct position?

  • lip support
  • appropriate incisal edge
  • jaw relationship changed
  • enough space for tongue
  • dentures displaced by soft tissues
186
Q

If edentulous pt has never had dentures how do you determine the previous O relationship?

A

Check gross skeletal abnormalities; easily identified
Old photos
Anatomical landmarks; incisive papilla, palatal gingival remnant
Patterns of muscular activity
Function methods of recording denture space: piezography

187
Q

Landmarks used in determining denture tooth position

A

Incisive papilla: labial surface 1s ~10mm

Palatal gingival remnant: 10mm to buccal surface

188
Q

In new C/C denture how is O height, O anteroposterior orientation, lip support, arch width and arch contour determined on O rim?

A 
O height
- lip line
- 17-21mm below ant. nasal spine
- parallel to interpupillary line
O orientation: parallel to ala-tragal line
Lip support
- naso-labial angle
- position of incisive papilla; labial 1s 10mm ant.
Arch width: palatal gingival remnant
Arch contour: residual ridge contour
189
Q

How to assess correct OVD in new C/C cases?

A 
Aim: FWS 2-4mm
Measure: Willis Gauge or Callipers
- FWS = RVD - OVD
Assess
- observe swallowing
- watch speaking
— S sounds
— count 60-70 w/ rims in situ
190
Q

In new C/C case, discuss adjustment of L O rim after U O rim adjustment

A 
Adjust orientation of L to U
Adjust height of L
- retromolar pad
- FWS (2-4mm)
Adjust contour L
- U rim contour
- lip activity
191
Q

Problems and solution to pt who has worn same dentures for long time

A

Pt unlikely to be able to adapt to marked changes in

  • extension
  • form of polished surfaces
  • occlusal height

Solution

  • copy old denture w/ modifications
  • compensate for changes taken place since old dentures made
192
Q

Discuss use of piezography in making dentures

A

Form of functional impression
Pt has maxillary denture or adjusted O rim in
Viscogel applied to lower base and base seated
Pt sips and swallows water to mould Viscogel

193
Q

Reasons for and against acrylic partial dentures

A

For

  • cheaper; corners may be cut
  • fewer stages to construct; test pt tolerance
  • easier to add teeth to; poor prognosis teeth
Against
- difficult gaining tooth support
— uncomfortable, cause trauma
- difficult avoiding gingival margins 
— plate connectors; strength
— U arch possible; trauma 
- more bulk; is it tolerable?
194
Q

Indications for partial acrylic denture

A 
Large saddles
- influence of tooth support red.
Immediate replacement denture 
Provisional prostheses
- test pt tolerance 
- inc. OVD
195
Q

What is the desired denture relief @ gingival margins? Why?

A

3mm or none at all

Gingival hypertrophy into small areas of relief making v difficult to clean and plaque control difficult

196
Q

Dis/advantages of immediate partial dentures

A

Adv

  • maintain aesthetics
  • replicate tooth space
  • prevent tongue spread

Disadv

  • may exacerbate post-XLA complications; pain
  • loss of fit
  • may need reline/remake; resorption
  • more post-insertion appt; within 24h
197
Q

Define impression

A

-ve likeness of teeth and oral structures allowing manufacture of accurate model of structures

198
Q

Classification of impression materials

A

Properties of when set

  • Rigid: compound, plaster, ZOE
  • Elastomeric: PVS, polyether
  • Hydrocolloid: alginate, reversible hydrocolloid

Setting Reaction

  • Polymerisation: PVS, polyether
  • Thermoplastic: compound, reversible hydrocolloid
  • Gellation: reversible hydrocolloid, alginate
  • Chellation: alginate, ZOE
199
Q

Properties of alginate

A 
Stable over short period
Hydrophilic
- tolerate OC
- imbibition, syneresis
Accuracy depends on handling 
Tears easily
Elastic
Cheap
200
Q

Properties of impression compound

A 
Inaccurate 
Rigid 
Resinous taste
Hydrophobic; tolerate disinfection 
Mucodisplasive 
Cheap
201
Q

Properties of PVS

A

Poly(vinyl dimethyl siloxane) = addition silicone

Expensive 
Best dimensional stability 
Hydrophobic; disinfection good, but mouth dry as possible 
V accurate 
Elastic
Good tear resistance 
Delayed pouring possible (stable)
202
Q

Properties of polyether

A 
Hydrophilic 
Stability; good in air, expands in H2O
Good shelf-life (2yr)
Good elastic recovery 
Low setting contraction 
Tears easily 
Excellent surface detail
203
Q

ZOE impression material properties

A

Cheap
Stable
Accurate in thin sections but breaks easily
Rigid
V strong taste; eugenol (cloves)
Hydrophobic; H2O streaks surface, disinfects well

204
Q

Different impression taking techniques

A

Single stage, single phase
Single stage, dual phase
2 stage

205
Q

Discuss single stage, single phase impression technique

A

Alginate in stock tray

  • quick, easy, cheap
  • poor accuracy
  • difficult to do well

Good for 1ry impression for P/C dentures

206
Q

Discuss single stage, dual phase impression technique

A

Alginate + putty/compound

  • PVS putty fill edentulous space
  • putty extend/adapt tray
  • ensure alginate supported
207
Q

Discuss 2 stage impression technique

A

Uses 1ry and 2ry impression

1ry impression make special tray
- has predictable thickness of impression material 
2ry impression is wash impression
- min. inaccuracies 
- supports material @ borders 
— use material to extend/adapt periphery
208
Q

4 criteria for assessing impressions

A

Extension
Rolled Border
Anatomical Landmarks
Surface Detail

209
Q

Discuss extension and rolled border when judging impression

A

Extension

  • over B sulcus
  • depth and width of sulcus
  • to vibrating line

Rolled Border

  • indicate correct height and width of border
  • knife edge: under extended
  • tray showing: over extended
210
Q

Anatomical landmarks to check for on impression

A

U

  • incisive papilla, gingival palatal remnant
  • residual alveolar ridge, tuberosities
  • frenae, sulci
  • hamular notches, fovae palatini

L

  • retromolar pads
  • residual alveolar ridge
  • frenae, sulci
211
Q

What should be avoided on impression surface?

A

Air blows
Unsupported areas
Tears, drags
Saliva

212
Q

General management of occlusal errors for dentures

A

Decide O relationship @ start of Tx
- remember horizontal and vertical component
Choose O relationship reproducible in pt
- must be kept same at all stages throughout Tx
If know natural ICP and have tooth support design around natural ICP
If many post. teeth lost use RCP
Post. teeth need to intercuspate to function well

213
Q

Discuss ways to check for occlusal errors during denture try in

A 
Check tooth position on articulator
- intercuspation of post
- appearance and position 
Hold C/C together see if wobbles
High spots; shimstock
- P denture; check w/ denture in and out
214
Q

Outline process of flasking denture

A

After wax try-in

Place wax try-in on master cast
Fill 1/2 flask w/ plaster
- place cast w/ try-in in plaster
- let plaster set
Fill other 1/2 flask w/ plaster
- paint separating medium on plaster
Push 2 flasks together 
- metal MUST touch
Boil off wax; teeth MUST NOT move
- ensure all wax removed
Mix acrylic + place in flask
- push together; ensure metal touching 
- cure
— HC: H2O-bath, low heat, long time
Open flask, remove denture -> trim + polish
215
Q

5 key areas that errors during FPF can affect

A 
Fit
Aesthetics
Strength
Biocompatibility 
Deterioration/longevity
216
Q

How can FPF affect fit of denture?

A

If wax try-in correct shape and fits, denture should fit
If not = flasking errors

Use cast for fit surfaces
- impression quality important 
- cast goes in flask
Teeth held firmly throughout flasking
Wax contours on try-in replicated in acrylic
217
Q

How can FPF affect denture aesthetics?

A

All errors in flasking

Acrylic should be translucent not opaque
Polished surfaces v smooth (finishing); except where stippled
Gingiva + teeth colour natural
Teeth not moved from desired position
Characterisation; veins etc

218
Q

How can FPF affect strength of denture?

A

Errors of flasking

Acrylic base thick enough; check during try-in
Acrylic correct commotion + thoroughly set
Join b/w base + teeth strong
- ensure all wax boiled off
No porosity; mixing, heating

219
Q

How can FPF affect biocompatibility of denture?

A

Most down to polishing

Acrylic cured properly (flasking)
Ensure no sharp edges
Surfaces smooth where possible 
Disinfect before fitting
Advise don’t wear @ night
220
Q

How can FPF affect longevity of denture?

A

Acrylic maintain appearance; doesn’t absorb stains, colour stability, polished surface
- HC better cf cold cure
Easy to clean
- smooth
- no stagnation areas (deep groove where food packs, difficult to clean)

221
Q

When is tooth wear Tx w/ removable pros indicated?

A

When teeth missing
- not all teeth need replacing
Wear is so extensive that restoring is not feasible

222
Q

3 areas requiring assessment for tooth wear Tx w/ removable pros

A

Tooth restorability

  • enamel (bonding)
  • reduce lat. forces on restorations
  • resistance form

OVD

  • wear accompanied by alveolar compensation = FWS normal
  • pt over closing, no compensation = FWS inc.

Initial contact in RCP, pt slide to ICP
- difficult to guide pt into RCP
- wear facets on teeth help locate
— D last standing L + M U tooth contact

223
Q

Importance of FWS assessment for removable pros

A

If inc. FWS

  • prosthesis will restore OVD
  • well tolerated
  • Tx more simple
If FWS normal
- prosthesis inc. OVD
— use fixed appliance where possible 
- less tolerable 
- provisional appliance may be req.
— splint
224
Q

Indications and req. of provisional removable prosthesis for wear cases

A 
Indications
- inc. OVD
— maintenance of occlusal stops during restorative phase
- assess appearance
- assess tolerance 
- protect from further wear/trauma
Req.
- pt able to eat; review 1-2/12
- night wearing
— to protect restorations 
— min. gingival coverage 
- OVD inc. tooth supported 
— use on/overlays
— design similar to Michigan splint
225
Q

Discuss the definitive prosthesis for Tx tooth wear and possible alternatives

A

Provisional design completed before tooth preparation

  • allows to plan restorations of abutment teeth
  • plan design features; guide planes, rests, attachments

Alternatives

  • onlay denture
  • overlay denture
  • overdenture
  • combination
226
Q

Compare onlay, overlay and overdenture

A

Onlay: covers O and palatal occluding surfaces
- O contacts maintained

Overlay: covers O surface to level of gingival margin

Overdenture: covers O surface + flange extends beyond gingival margin
- root retention helps maintain alveolar bone + proprioception
- metal copings may be req. to prevent #
— endo Tx
- attachments incorporated onto copings; inc. retention
— req. 8mm vertical space
— good maintenance

227
Q

Common causes of failure of overlay and overdentures

A

due to failure of components

  • bruxism
  • lack of interdental space

Longevity must be factored into design

228
Q

What order is denture checked during fit appt?

A
  1. Fitting surface
  2. Flanges
  3. Occlusion
  4. Retention + stability
  5. Aesthetics
  6. Ensure pt can remove/reinsert
  7. Give pt written instructions

Review 1wk

229
Q

Before seating denture in mouth during fit appt what should be checked?

A 
Any sharp edges using straight probe
- saddle borders
- fit surfaces
Check for acrylic pearls on fit surface 
No acrylic flash over Co-Cr; where metal in direct contact w/ teeth
230
Q

How to check denture is seated correctly?

A

Rests contacting teeth, P connector contacting mucosa
Clasps in correct position
- tip in undercut
- relief under gingivally approaching
- traumatise tissue?
Relief under lingual bars; 0.5mm
Metal framework against teeth
- occlude spray rubs off @ high spots
- GHM b/w teeth + framework marks high spots
- preventable; good impression, careful planning of tooth preps

231
Q

Discuss how to check occlusion of denture

A 
Visual first
- natural teeth occlude as should w/ denture in 
Opposing tooth contacts: GHM, shimstock
Pt feedback
- meet evenly?
- fell natural teeth in contact?

Compare occlusion w/ dentures out and in
- make sure get same

232
Q

What is the medical devices directive? How does it apply to dentures?

A 
Legislation outlining what all medical devices must comply to
Instructions for dentures
Eating: smaller pieces, softer foods
Speaking: req. T to get used to 
Pain: take out, wear on day of review
Night time: remove + soak
Cleaning: warm H2O + soap over basin

Bring old + new denture to review in ~1wk

233
Q

Why are denture cleansers used? What are their requirements?

A

Why

  • remove deposits; food, calculus, bacteria, stains
  • prevent unpleasant tastes/odours
  • prevent infection: stomatitis, angular cheilitis

Req.

  • remove plaque, calculus, stains
  • non-toxic, safe to handle
  • doesn’t damage denture
  • antibacterial, antifungal
  • simple to use
234
Q

5 types of denture cleansers

A 
Soap + H2O
Denture Pastes 
Alkaline Peroxides
Dilute Acids
Alkaline Hypochlorites
235
Q

Compare denture cleansers

A

Pastes

  • mechanical cleaner
  • soft, nylon brush
  • gentle action to red. wear

Alkaline Peroxides

  • immersion cleaning
  • O2 bubbles dislodge debris
  • safe, pleasant to use
  • harmful to temp. soft lining

Dilute Acids

  • softens calculus then brushed off
  • 5% HCl: damages clothes, corrodes metal
  • sulfamic acid: less damaging
  • use infrequently; v effective

Alkaline Hypochlorites

  • v effective: remove plaque + staining
  • disinfectant: good for stomatitis
  • corrodes metal, may cause bleaching
  • suitable for silicone/temp. soft lining
236
Q

How can denture stomatitis been prevented?

A

Remove dentures at night
Good denture hygiene
Hypochlorite soaks
Topical antifungal: miconazole gel

237
Q

Possible cause of pain under denture, how to detect

A

Palpate tissues

Possibly

  • nerve
  • buried root
  • bony prominence
238
Q

Possible problems that may present at denture review

A

Localised swollen tissue under denture; uneven contact (high spot)
- occlusal problem

Loose denture

  • @ rest (retention); fit surface + border
  • during function (stability); check all
  • pt factor: saliva, muscle control

L denture lifts up

  • polished surface problem
  • lingual undercut

Pain on lat. excursion

  • polished surface problem
  • PIP rub off in lat. excursion

Cheek biting

  • polished surface problem
  • provide B overjet

Heel contacts; polished surface problem; remove

Gagging

  • U denture loose; fit/polished surface
  • excessive OVD: occlusal surface
  • lack of tongue space; polished surface
239
Q

Common causes of denture failure

A 
Flexural fatigue; usually old denture
Dropped: impact #
Midline #
- open flanged
- midline diastema
- deep frenal notch
- alveolar resorption under denture
- tooth wear -> unfavourable O forces 
Previous repair
Permanent soft lining: thins acrylic 
Denture base thinning: abrasive cleaning 
U midline P torus; relief in master cast
Bruxism, clenching
240
Q

Possible methods of repairing acrylic #s

A

If clean # (pieces locate out of mouth)

  • fix w/ sticky wax
  • pour plaster cast
  • repair w/ cold-cure acrylic

Complex #

  • alginate ‘pick up’ impression of all/some pieces to relocate
  • v difficult, remake likely
241
Q

Methods of preventing denture failure

A 
Adequate acrylic thickness
Strengtheners
- selenesse fibres, SS mesh embedded
- mechanical retention 
High impact acrylics (flex)
Incorporate Co-Cr denture base
242
Q

Tx for debonded/broken denture tooth

A

Will debond if this film wax left on tooth during boiling out
Kept tooth: lab repair w/ cold-cure
Missing tooth: impression of opposing arch, send to lab for repair

243
Q

Difference between denture reline and rebase

A

Reline: resurface tissue side to make denture fit more accurately
Rebase: refitting denture by replacing most/all denture base

244
Q

Indication for denture reline/rebase

A 
Doesn’t fit; loose, painful
Resorption: XLA, surgery
Alternative to new denture
\+ flange
\+ permanent soft lining
245
Q

Problems w/ denture reline/rebase

A

Inc. OVD; use thin wash
O errors; use closed mouth technique
Damage
Irreversible changes

246
Q

Define ant. and post. guidance

A

Ant.

  • influence of teeth on guidance
  • can be post. teeth: Class 2 Div 1, Class 3

Post.

  • influence of TMJ + MoM on guidance
  • usually only edentulous/severely depleted dentition
247
Q

Discuss mutually protected occlusion and group function

A

Mutually protected Occlusion/Canine guidance
- ICP = RCP
- multiple even contacts in ICP on all teeth
— tight contact post.
— light contacts ant.
- complete disclusion of all teeth on lat. excursion using 3s only
- complete disclusion of post. on protrusion using even contacts on all ant.
- why 3s
— longest root: crown:root favourable
— P surface morphology suits smooth guidance
— in front of masseter = weaker forces

Group function
- where 3 guidance is impossible use next teeth back to share guidance

248
Q

Discuss strategies used when deciding what Tx approach to use for Tx wear

A

Conformative

  • don’t alter current O scheme
  • teeth restored as individual units
  • ICP + RCP may/not be coincident

Reorganised

  • purposely alter O scheme
  • make ICP = RCP
  • may inc. OVD
249
Q

Discuss methods of creating space for restorations

A

Crown Lengthening

  • bone removal + repositioning of flaps apically to inc. tooth length
  • allows enough retention even when O red. complete
  • root must be long enough
Dahl Principle: restorations @ inc. OVD
- vertical ortho 
- open O by purposely making high restoration on Tx teeth 
— others move into space
- forces must be vertical
— jiggling forces = pain + loose teeth
- teeth OE into contact + Tx teeth intrude 
- 4-6/12 for teeth to re-occlude
250
Q

Define crown

A

Rigid restoration which covers part/whole of external aspects of tooth
Usually req. some form of tooth prep
Constructed in Ag, ceramic, composite or combination

251
Q

Indications for crowns

A

Protect remaining tooth structure
- weakened by caries, large restorations, wear, endo Tx
- Ferrule: req. 1.5-2mm beyond margin to protect tooth
Aesthetic demands
Abutments for fixed/RPD
Alter O plane

252
Q

5 types of crown

A 
Full Ag
Partial Ag
Ceramo-metal
All ceramic
Composite
253
Q

Compare indications for FGC and PGC

A

FGC

  • max. retention req.
  • min. aesthetic demands
  • caries/restorations on all axial walls
  • perseveration of tooth structure

PGC

  • mod. aesthetic demands
  • parts of axial walls intact
  • cuspal protection req.
  • preservation of tooth structure
254
Q

Compare indications for CMC and all ceramic crowns

A

CMC

  • max. retention req.
  • caries/restorations on all axial walls
  • high aesthetics

All ceramic

  • caries/restorations on all axial walls
  • max. aesthetic demands
  • mod. strength req.
255
Q

5 principles of tooth preparation for crown

A
  1. Preservation of tooth structure
  2. Retention + Resistance
  3. Structural durability
  4. Marginal Integrity
  5. Preservation of periodontium
256
Q

Discuss preservation of tooth structure and structural durability for crowns

A

Preservation of tooth structure

  • restoration must preserve remaining tooth structure + replace lost tooth
  • intact tooth structure preserved whenever retention + pt acceptance allow

Structural Durability

  • restorations must contain a bulk of materials that is adequate to withstand O forces + meet aesthetic demands
  • materials must be confined to space created by tooth prep
257
Q

Discuss retention and resistance of crowns

A

Retention: resist removal in direct inserted
Resistance: resist displacement apically
- interrelated, often inseparable

Prep taper inc., retention dec.
Tooth length inc., retention inc. (at least 1mm prep)

258
Q

How can retention + resistance be improved for crowns?

A

Auxiliary features: grooves, boxes

Limiting path of withdrawal

259
Q

Discuss marginal integrity and preservation of periodontium for crowns

A

Restoration will only survive in OC if margins are closely adapted to finishing of preparation

Supraginival + well defined margins

  • aid impression taking
  • health
  • accuracy in die construction

Biological width
- margins >2mm from alveolar crest
— combined width of epithelial + connective tissue attahcemtn
- encroaching in width = gingiva inflammation, loss of alveolar height, Perio pockets

260
Q

Define 4 parameters of colour

A

Hue

  • quality by which possible to distinguish one colour family from another
  • corresponds to wavelength of light

Value

  • achromatic measure of lightness or darkness of colour
  • pure black to pure white

Chroma: degree of saturation of colour

Translucency

  • high = transparent
  • low = opacity
261
Q

6 factors affecting colour of tooth

A

Lighting: look different under different light source
- colour corrected (5500K)
Value Contrast
- relative lightness of object affected by lightness of background
- lighter on darker background
Hue Contrast
- viewed on different background colour, appear to take on complementary colour of background
Matamerism
- appear same colour under 1 light source, different under different source
- due to non-matching spectral analysis curves

Opalescence: light scattering caused by fine particles
Fluorescence: emission of visible light when exposed to UV

262
Q

Physical factors affecting tooth colour

A

Natural tooth colour

  • depends on composition, thickness, structure of tissue
  • not uniform: true colour mosaic in yellowish-white range
  • mainly determined by dentine colour

Surface Texture

  • macro: developmental loves + ridges: mamelons
  • micro: surface detail
263
Q

Special Characteristics of teeth affecting their colour

A

Complex in/external features

  • # lines, fissures, cracks
  • white spots, staining

Degree of fluorescence when illuminated by UV
Degree of opalescence due to HA crystals
Translucency: depends on extent + hue

264
Q

Disadv of using shade guides for determining restoration colour

A

Subjective

Restricted + inadequate range of shades
Made from thick, high fusing porcelain: no variation in thickness
No surface texture or characteristics
Material different from ceramic restoration: different optical properties

265
Q

Adv of technology based shade matching

A

Objective measurement

No influence of surroundings/lighting conditions
Improved communication b/w lab + dentist
Reproducible
Integration w/ hardware + image enhancing software

266
Q

2 types of luting cement

A

Adhesive

Non-adhesive

267
Q

Compare 2 types of luting cements

A 
Non-adhesive
- reliant on retentive prep
— crowns
— retentive onlay
— custom cast posts
— some prefabricated posts
- ZnPO, Zn polycarboxylate, GI
Adhesive
- reliant on micro-mechanical bond
— crowns
— RBB
— on/inlay
— prefabricated posts, non-metal posts
- RMGIC, resin
268
Q

What to check when crown in die?

A 
Fit surface: defects, casting nodules, bubbles
Damage
- marginal deficiencies 
- proximal contacts of adjacent teeth
Margins
- over/under extended
- ledges
- casting should only touch margins
269
Q

Why is no LA preferred when fitting crowns?

A

Proprioception not impaired

Valuable for assessing occlusion + tight proximal contacts

270
Q

Common errors causing failure to seat crown

A

Correctable

  • tight proximal contacts
  • casting blebs on fit surface
  • no die spacer (req. sand blasting)
  • defective margins

Remake
- impression distortion
— will fit casts but not in mouth

271
Q

Types of defective margins + reasons for occurrence

A

Over-Extended

  • poor impression
  • incorrectly trimmed die
  • surplus untrained wax/ceramic

Under-Extended (ledge)

  • poor impression
  • incorrectly trimmed die
  • over-polished casting
  • difficulty identifying finish line

Over Contoured (thick): over waxed

Open Margin

  • poor impression
  • incorrectly trimmed die
  • over-polished casting
  • casting not completely seated
  • incomplete casting
272
Q

4 parameters to be checked when crown seated

A

Proximal contacts
Marginal fit
Occlusion
Aesthetics

273
Q

Discuss assessment of proximal contacts and marginal fit of seated crown

A 
Proximal contacts
- tight as others in mouth
- hold crown firmly, test w/ floss
- too tight = adjust tighter 1st
- adjust
— mark w/ articulating paper
— rubber wheel, straight hand piece, polish 
- open contact: Au solder/ceramic in lab

Marginal fit

  • 100microm opening borderline acceptability
  • over-extended: adjust crown from axial
  • deficient/ledge: remake
274
Q

Discuss assessment of crown occlusion

A

Always 1st and last thing to do
Know what trying to achieve: have idea of pattern

Assess resistance of shimstock on adjacent occluding teeth w/o crown seated
- should be same w/ crown in situ

Adjusting

  • mark high spots w/ GHM (black)
  • adjust w/ large flame diamond
  • post. hold shimstock firm, ant. light
  • check lat. excursion; remove non-working side interference
  • recheck absence of deflective contacts from RCP to ICP
275
Q

Discuss assessing aesthetics of seated crown

A

CMC: adjust using diamond bur + additional of ceramic
Shade improved by adding stains

Gross changes anticipated

  • try-in during biscuit stage
  • glaze after adjustments

Ensure pt happy before cementing

276
Q

Discuss finishing + polishing of crown before cementing

A

Use sequence of abrasives to achieve smooth surface

Au

  • finishing burs -> rubber abrasive points + white stone
  • solfex for proximal contacts

CMC/Ceramic

  • soflex, comp finishing diamonds
  • rubber abrasive points, rubber cup w/ diamond paste
277
Q

Indications, dis/advs for ZnPO as luting

A

Indications

  • single FM/CM/Li disilicate/Zirconia C w/ retentive feature
  • fixed-partial metal-ceramic denture
  • posts: material of choice as expands
  • multiple cementation

Adv

  • low film thickness
  • longest track record
  • high compressive strength
  • resistance to H2O dissolution

Disadv

  • acid dissolution
  • low tensile strength
  • no molecular adhesion to tooth or crown
  • technique sensitive; P:L, mixing
278
Q

Indications, dis/advantages of GIC for luting

A

Indications

  • single FM/CMC
  • fixed-partial metal-ceramic denture
  • high caries risk

Adv

  • F- release
  • high compressive
  • low film thickness
  • post-set: resistant to H2O
  • considerable bond to tooth

Disadv

  • acid dissolution
  • sensitive to moisture during set
  • no molecular adhesion to crown
  • low tensile
279
Q

Indications, dis/advantages of RMGIC for luting

A

Indications

  • single FM/CMC
  • fixed-partial denture
  • poor geometry of prep

Adv

  • F- release
  • high tensile + compressive
  • low film thickness
  • molecular adhesion to tooth
  • resistant to H2O dissolution

Disadv

  • short track record
  • H2O absorption: expansion + cracking on ceramic
280
Q

Indications, dis/advantages of resin luting cement

A

Indications

  • porcelain veneer, RBB metal
  • onlay: ceramic, zirconia, comp
  • Crown/FPD: ceramic, zirconia
  • FM/CMC/zirconia/FPD w/ poor prep geometry

Adv

  • high compressive + v high tensile
  • H2O + acid resistant
  • molecular adhesion: tooth + crown

Disadv

  • highly technique sensitive
  • variable film thickness
  • difficulty removing proximal + subgingival excess
  • polymerisation shrinkage = marginal leakage
  • post-op sensitivity depending on technique + materials
281
Q

Why must PD health be obtained pre-crown prep?

A 
Un-Tx gingivitis 
- swollen
- inflamed
- loose gingival tissues 
Creat difficulties w/
- assessing
- preping finish line
- moisture control
- reproducing finish lines
Leads to
- suboptimal fit -> 
— further PD deterioration 
— caries
282
Q

Discuss need for soft tissue management during impression stage + rationale

A

Need

  • assess margins: supra? in crevice? sub?
  • if some/all margins @/subgingival req. management

Rationale

  • prevent bleeding
  • act as physical barrier
  • retract soft tissue
  • allow accurate impression of margins
283
Q

Aim of soft tissue retraction + ideal properties of good retraction

A

Aim: allow reproduction of entire prep

Ideal

  • achieve haemostasis
  • effective gingival displacement
  • no irreversible damage
  • no systemic effects
284
Q

3 main types of tissue retraction

A

Mechanical
Chemomechanical
Surgical

285
Q

Discuss mechanical methods of tissue retraction

A

Retraction Cord

  • aim: sulcus enlargement, physically displace gingiva away
  • disadv: sulcular haemorrhage -> moisture control + poor impression

Cu Ring

  • aim: displace gingiva, carry impression material to ensure margins captured
  • disadv: traumatic, efficacy + impression accuracy
286
Q

Discuss use of impregnated retraction cord for soft tissue retraction

A

Chemomechanical method
Retraction cord soaked in astringent
Combine
- packing of retraction cord (sulcus enlargement)
- + chemical action (control haemorrhage)
- = accurate impression

Chemicals

  • iron sulphate 15%
  • potassium alum
  • aluminium sulphate
287
Q

Discuss duel cord technique for tissue retraction

A

Pack 2 impregnated retraction cords into sulcus

Method
- thinner cord packed 1st + remains in sulcus during impression
- larger cord placed on top: follow normal steps
— wait 4 mins, wash, remove, dry, take impression

Aim: thinner cord red. risk gingival cuff recoiling and displacing impression
Disadv: inc. inflammation + tissue damage

288
Q

Discuss use of retraction paste for soft tissue retraction

A 
Chemomechanical method
Used to create space b/w prep + sulcus
- some medicated w/ AlCl
- viscous + maintains rigidity
— displace gingiva w/o causing trauma

Method

  • express around prep directly into sulcus
  • wait 2 mins, wash, dry, take impression

Adv: quick, easier
Disadv: technique sensitive

289
Q

Discuss rotary curettage + crown lengthening methods of soft tissue management

A

Surgical methods

Rotary Curettage

  • aim: limited removal of sulcular epithelium w/ rotary while prep margin
  • adv: quick
  • disadv: trauma, haemorrhage, poor healing, inc. PD destruction
Crown Lengthening
- bone removal + gingival re-contouring 
- adv: inc. crown height + retention, create supra margin, aesthetic
- disadv
— discomfort
— furcation involvement; poor cleaning
— margins in cementum: difficulty bonding
— inc. crown:root ratio
— allow T for healing
290
Q

Discuss electrosurgery for soft tissue management

A

Aim
- controlled destruction by current from small cutting electrode
— high current + temp @ tip
- high freq. current cuts +/- coagulates tissues

Use

  • when retraction cord alone not feasible; hyperplastic gingiva
  • sulcus widening, coagulation, gingivectomy

Contraindications

  • Cardiac pacemakers
  • topical anaesthetics + flammable aerosol
291
Q

Rationale for blocking out undercuts pre-impression and where they commonly occur

A

Rationale

  • addition silicone + polyether rigid once set
  • may flow into undercuts + become lodged once set

Areas

  • B sulcus
  • PD bone loss
  • large interdental space
  • beneath BP

Method: soft wax (ribbon wax)

292
Q

Types of impression trays

A

Stock
- adapted stock
Special
Triple

293
Q

Discuss use of stock and adapted stock trays for impression taking

A

Stock

  • sized according to average curvature of arch; S-XL
  • rigid plastic; flexible bend under load + distort impression
  • commercially available + cheap

Adapted Stock
- impression of last molar
— difficult as material drags D; not well supported
— modify D using acrylic/green stick/putty to create post. dam
- arch wider than stock
— warm + soften tray using flame free heater
— mould post. B flange out
— if doesn’t work use special

294
Q

Discuss use of special and triple trays for impressions

A

Special
- use
— shape of arch/tooth alignment/anatomical feature prevent seating of stock
—- repaired cleft palate, much wider arch
— clearance allows even layer of impression around tooth
- disadv: additional lab procedure + cost
- don’t use w/ heavy body for crown; in undercuts = v difficult to remove

Triple
- impression of prep, opposing + occlusion in 1
- use: single preparation w/ stable O + opposing teeth
- disadv
— dynamic O + guidance movements for whole arch not replicated
— less accurate morphology; more O adjustment @ fit

295
Q

Importance of moisture control during impression taking and how this is achieved

A

Why

  • pt comfort
  • improved vision
  • impression accuracy: silicones are hydrophobic

How

  • 3-in-1, aspirator, saliva ejector
  • RD
  • cellulose pads
  • cotton wool rolls in B/L sulcus
296
Q

Define copy and replica denture

A

Copy

  • similar to original denture
  • some modifications made

Replica

  • exact replica of original w/o modification
  • v elderly/frail difficulty adapting to new
297
Q

Indications for copy dentures

A

Previously satisfactory denture

  • v old, now loose
  • req. many repairs due to failing material
  • O worn
  • poor aesthetics

Elderly: allow some changes from idea to allow easier adaptation

Less clinical T + pt keep denture used to

298
Q

Rationale on whether to make changes on old or new dentures

A

Old

  • all changes easily tested in mouth
  • easily removable to get original back

New

  • old denture not altered; no matter if intolerable
  • changes not easily tested
  • need another replica of changes made after
299
Q

Techniques available for copying dentures

A

Soap box

  • most commonly used as cheap + easy
  • poor results as box flexible

Dundee: stock tray + putty

  • rigid putty must be used to prevent distortion
  • more expensive cf alginate (£10 vs 8p)

Murray Wolland: metal modified flasks

  • can use alginate
  • not flexible, good impression w/ no distortion
300
Q

Describe clinical + lab stages in copying denture

A

Clinic
- complete modifications, check pt happy
- attach greenstick/thick rolled wax (unnecessary Murray/Dundee)
- fill 1/2 copy box, insert denture teeth down, set
- apply Vaseline thinly to impression material
- fill other 1/2 box, leave some to fill fit surface, close tightly
- set, remove, return denture
Lab
- molten wax poured into teeth, set
- self cure acrylic poured into mould, set
- wax teeth removed individually, replaced w/ denture teeth
Clinic
- try in: aesthetics, occlusion
— good: closed mouth impression w/ light body
— seat U 1st, seat L, close into O
Lab: remove excess, FPF

301
Q

Dis/advantages of copy dentures

A

Adv

  • less clinical T
  • pt adapt quickly; used to polished surface

Disadv

  • cost
  • more lab T
302
Q

Classify luting cements

A

H2O based

  • ZnPO
  • Zn polycarboxylate
  • GI
  • RMGI

Resin

  • composite
  • compomer
  • RMGI

Temp: ZOE/non-eugenol

303
Q

Req. of luting cements

A 
Biocompatible
Aesthetic
Insoluble
Adequate mechanical properties
Good marginal seal
Retention 
Easy handle
Radiopaque
Low film thickness
304
Q

Composition of ZnPO luting cement

A 
Powder
- ZnO 90%
- others
— MgO 10%: hardens, whitens
— Al2O3, SiO2: reinforcement
— SnF2: short-term F- release
- Zn/MgO heat Tx red. reactivity

Liquid

  • phosphoric acid 45-63% aqueous solution
    • H2O accelerate set
305
Q

Dis/advantages of ZnPO luting cement

A 
Adv
- compressive: 40-140MPa; sufficient
- bond strength: 0.5-1.5MPa
— fairly retentive via mechanical interlocking
- elastic modulus: 12Gpa; similar dentine
- film thickness: <25microm
— adequate if mixed properly
— unreacted ZnO 8microm
- low H2O solubility once set
Disadv
- tensile: 5-7MPa; brittle
- difficult handle
- linear shrinkage: 0.5%; micro-leakage
- low pH, slow neutralise
— irritation, inflammation, painful set
- solubility
— 0.04-3% H2O initially
— lactic acidosis attack soluble
306
Q

Composition of Zn polycarboxylate luting cement

A 
Powder
- ZnO: heat Tx
- others
— MgO, SnO 10%
— Al2O3, SiO2: reinforcement
— bismuth salts: modify set
— SnF2: easier mix, strength

Liquid
- polyacrylic acid 30-40%
— freeze dried
— liquid = H2O

307
Q

Dis/advantages of Zn polycarboxylate luting cement

A 
Adv
- film thickness: similar cf ZnPO
- bond strength: 1-2MPa
— chemical adhesion to tooth + some metal 
- low pH3-4, neutralises rapidly
— high MWt PAA prevent diffusion
— less irritation 
- solubility 
— H2O: 0.1-0.6%
— acid soluble: less cf ZnPO
-resistance bacteria ingress

Disadv

  • compressive: 55-85MPa; weaker
  • tensile: 8-12MPa; better
  • elastic modules: 4-6GPa
  • difficult handle
308
Q

Composition of GIC

A 
Powder
- ion leachable glass
- basic:  SiO2, Al2O3, CaF2
- other
— AlPO4, NaF
— Sr3+, Ba2+: radiopacity 
Liquid
- polycarboxylic acid: PAA 50%
— copolymer acrylic + itaconic acid
- tartaric acid 10%
- free dried; liquid = H2O
309
Q

Dis/advantages of GIC

A 
Adv
- film thickness: low, = ZnPO
- F release
- bond strength: 3-5MPa
— chemical adhesion 
— same ZnPC
- compressive: 100-160MPa
— inc. w/ age
- elastic modulus: 10GPa
- solubility: lower cf ZnPO/PC

Disadv

  • tensile: 4-5MPa; brittle
  • H2O sensitive: protected after placement
  • difficult handle
310
Q

Composition of RMGIC

A

Powder

  • ionomer glass
  • photosensitiser: DHPT
Liquid
- PAA, tartaric acid
- H2O compatible vinyl monomer (HEMA)
— OR PAA w/ pendant methacrylate groups
- photoinitator: camphorquinone
311
Q

Dis/advantages of RMGIC

A

Adv

  • compressive: 40-140MPa; sufficient
  • bond: 5-10MPa; chemical
  • tensile: 13-24MPa; better
  • F-
  • less H2O soluble
  • handle

Disadv

  • residual monomer: toxic
  • polymerisation shrinkage
  • swell in H2O: PHEMA hydrogel
312
Q

Composition of composite luting cement

A

Monomers

  • bisGMA
  • UDMA
  • diluent: TEGDMA, EDGMA

Fillers: ground quartz, colloidal silica
- aesthetics, red. shrinkage, radiopacity
- less + smaller size (<20microm)
— thinner film thickness

Additives

  • hydroquinone: shelf-life
  • DHPT/BP: RC
  • DHPT/Camphorquinone: LC
  • optical brightener, pigments
313
Q

Special component of self-adhesive resin cement

A

Adhesion promoting resin: 4-META, MDP

Phosphate (MDP) + carboxyl (4-META) promote bond to Ca2+ (tooth) and metal oxide (ceramic/metal alloy)

  • no direct bond to precious metal
  • phosphate v susceptible to O2 inhibition

Some req. primer to bond tooth, self-adhesive don’t

314
Q

Compare composition of P/L and 2 paste self adhesive resin luting cements

A

P/L

  • PMMA powder
  • MMA liquid
  • tributyl borane: catalyst
  • 4-META

2 paste

  • resin + 4-META (secure, Parkell Inc)
  • resin +MDP (panavia)
315
Q

Properties of adhesive resin cements

A 
Compressive: 180-260MPa
Tensile: 40MPa
Bond
- aesthetic: 15-20MPa
- self 20-30MPa
Insoluble 
High film thickness
Residual monomer
O2 inhibition
316
Q

Discuss composition of compomer cements

A

Powder/Liquid

  • powder: silica, strontium based glass powders
  • liquid: UDMA/bisGMA, acid resins

2 paste: mix of glass/silica fillers + resins

317
Q

Discuss bonding to ceramics; how it is achieved and when can’t be used

A

Tech with hydrofluoric acid
- only acid to dissolve silica glass
- v harmful to tooth
Silane Tx (same as comp filler)

Can’t use: high strength alumina/zirconia cores

  • acid won’t dissolve
  • silane won’t bond (no silica)
  • use self-adhesive
318
Q

Compare how to bond to base and precious metals

A

Base: etch, grit blast
Precious: Sn plating, silica coating, metal primer

319
Q

Discuss tin plating, silica coating and metal primers

A

Sn Plating
- cover surface noble metal in Sn
- bond strength: improvement depend on alloy used
— effective for self-adhesive resin, less so for comp
- technique sensitive

Silica Coating

  • silica coating + heat OR silica blasting
  • bond strength: enhance for any alloy
  • technique sensitive

Metal Primer

  • bond strength: v effective for precious metal + resin
  • simple
320
Q

Discuss resin-resin bonding

A

Use: comp inlay, fibre reinforced bridges, endo posts
Problem
- bonding uncured -> cured difficult

Micromechanical

  • grit blast remove surface layer
  • HF etch dissolve silica filler

Chemical
- silanation of surface filler or surface-embedded silica

321
Q

Req. of metal alloy for fixed appliance

A 
Biocompatible: technician, pt
Corrosion resistance: degradation, ion release
Tarnish resistance
Mechanical 
- high modulus 
- high yield stress
- not brittle
Easy handle/casting
- low melting range
- high density 
Cheap
322
Q

Composition of high Au alloys

A 
Main
- Au
- Ag
— hardening: solution + precipitation 
— whitens
— red. tarnish resistance 
- Cu
— hardening: solution + order (if >11%)
— dec. MPt
Minor
- Pd/Pt
— hardening: solution + precipitation 
— inc. MPt
— corrosion resistance 
- In, Ir, Re, Ge: fine grain size
- Zn: scavenger
323
Q

Properties of high Au which make it easy to cast

A

Low casting temp
High density
Low shrinkage: 1.4%

324
Q

Compare general properties of T1,2,3,4 Au alloys

A

T1

  • burnished: improve marginal fit, inc. hardness (cold working)
  • use: small, well supported inlay (low stress)

T2

  • burnished
  • use: larger inlay; not thin section

T3
- can he hardened
— 400degree 10min for CuO, bonds adhesive resin luting
- burnishing difficult
- use: in/onlay, FGC, short span bridge, cast cores + posts

T4

  • can he hardened
  • not burnishable
  • use: high stress; removable denture + clasps, long span bridge
325
Q

Composition of medium Au alloy

A

Au: 40-60%

Ag: 25%
Cu: 12%
Pd: 5%
- all form solid solution w/ Au

Single phase structure

326
Q

Composition of low Au alloy

A

Ag: 40-55%
Pd: 20%
Au: 10-20%
Cu: 8-14 OR In: 16-18%

327
Q

Colour of low Au alloys, effect of Cu and In on this

A

Usually white

Cu-free containing In are yellow

328
Q

Properties and use of med/low Au alloys

A

Properties: similar cf T3

  • hardness: 170-285VHN
  • yield: 340-380MPa
  • modulus: 75-90GPa
  • elongation: 4-10%
  • cheaper
  • heat harden: sufficient Cu

Use: T3; in/onlay, FGC, short span bridge, cast posts + cores

329
Q

Composition of Ag-Pd alloys

A 
Ag: 47-70%
Pd: 25-40%
Some
- Cu: dec. MPt, harden
- Zn: scavenger 
- In: grain size refiner
330
Q

Properties of Ag-Pd alloys

A

Termed white golds

Cheaper
Difficult cast: high MPt, low density
Tarnish: presence of Ag
Work harden: limited adjustment

Hardness: 55-310VHN
Yield: 500-940MPa
Elongation: 3-33%
High Pd similar to T4

331
Q

Properties of Ni-Cr alloys

A

Ni: allergen
Be: carcinogenic
High casting shrinkage

Hardness: 400VHN
Yield: 500MPa
Modulus: 200GPa
Elongation: 2%

332
Q

Dis/adv of Ti and alloys

A

Adv

  • biocompatible
  • low density (good for RPD)
  • corrosion resistance
  • fatigue limit: highest for alloy

Disadv

  • difficult cast: low density (fixed)
  • high MPt: 1700
  • high casting shrinkage 3.5%
  • react w/ investment
333
Q

Additional req. of metal-ceramic alloys

A 
Good bond to porcelain
Not react adversely w/ porcelain 
Melting range > firing temp
- would melt otherwise
Thermal expansion slightly > porcelain 
- when cooling metal retract more
- compressive force on porcelain = good bond
Low creep/sag
334
Q

Composition + properties of high Au ceramo-metal alloy

A

Au: 85%
Pt/Pd: inc. MPt
+ In, Sn: oxide layer (bond porcelain)
No Cu: red. MPt + greening of porcelain

Strong bond
Melting range low enough to cause sag
Modulus: low; min. coping thickness 0.5mm

335
Q

Composition + properties of low Au Ceramo-metal alloys

A

Au: 50%
Pd: 30%
Ag: 10%
In/Sn: 10%

Castability, accuracy of fit, corrosion resistance similar cf high Au
Cheaper
Higher MPt; inc. Pd

336
Q

Composition + properties of Ag-Pd metal-ceramic alloys

A

Pd: 60%
Ag: 30%
In and/or Sn: 10%

Cheaper alternative to high fusing gold alloy
Improved modulus
Difficult cast: high MPt
High Ag: discolour porcelain

337
Q

Composition + properties of high Pd alloy

A

Pd: 80%
+ Cu, Ga, In, Sn
No Ag

Cu doesn’t discolour porcelain; unlike in Au containing
Poor sag resistance due to creep

338
Q

Properties of Ni-Cr metal-ceramic alloy

A

Highest modulus of PFM alloy: coping thickness 0.3mm
High MPt, no sag
High casting shrinkage, poor castability
Poor porcelain bond: adhesive failure
- Cr (form passive oxide layer) only on surface
- thus only bonding to surface and not bulk material
Ni allergy

Co-Cr can be used

  • stronger, harder
  • similar casting problems
339
Q

Discuss Ti metal-ceramic alloys

A

cpTi, Ti6Al4V
High MPt, no sag
Passive oxide layer: porcelain bond

340
Q

Advantages of ceramics

A 
Aesthetics
Relatively inert
High MPt
Low thermal expansion (similar cf tooth)
High elastic modulus
341
Q

General composition of dental porcelains

A

Feldspar: soda (albite), potash (orthoclasej
- melt 600-1000degree; form glass on cooling
SiO2: glass former
- MPt 1700degree; remains unchanged
Al2O3: intermediate
Na2O, K2O: modifier

342
Q

Discuss use of fluxes in ceramics and boric oxide

A

Fluxes

  • added to red. fusing temp
  • incl. glass modifiers (Na2O, K2O) added as carbonates

Boric Oxide

  • glass former
  • add ~6% act as flux
  • red. fusing temp., doesn’t inc. thermal expansion
343
Q

Composition of feldspathic porcelain

A

Feldspars: 73-85%
- Na:K important: K dec. fusing temp., less affect on viscosity
Quartz: 13-25%
Kaolin (Clay) <4%: only high fusing temp. type

344
Q

Composition of feldspathic glass

A 
SiO2: 63%; former
Al2O3: 17%; intermediate 
Boric oxide: 7%; former
Potash (K2O): modifier
Soda (Na2O): modifier
Other oxides
- Co: blue 
- Cr/Sn or Cr/Al: pink
- Ti/Zr: opacity 
- rare earth metals: fluorescence
345
Q

How to minimise firing shrinkage of ceramics? Compare firing in air and reduced pressure

A

Use 3 different particles sizes w/ 7 fold size difference

Firing in Air

  • large particle size range
  • slow fire, allows air to escape
  • few, large porosities ~6%

Firing in Reduced Pressure

  • not total vacuum
  • mix large and small particles
  • small pores
  • helps prevent porosity ~0.6%
346
Q

Properties of feldspathic ceramic

A

Low strength: flexural 60-70MPa
- low stress areas unless used w/ high strength support
Brittle

Highly translucent: aesthetic
Ultraconservative prep

347
Q

Discuss strengthening of feldspathic ceramics

A

Prevent formation + propagation of cracks
Generally, compressive force applied to surface to close cracks
Inc. strength, red. aesthetics

348
Q

Discuss ion exchange toughening of feldspathic ceramic

A

Exchange surface Na+ -> K+
- K+ 35% larger
Put in compression due to ion crowding
Prod. ion exchange coating for ceramics

50-100% inc. strength depending on original composition

349
Q

Discuss dispersion strengthening

A

When high strength, elastic, crystalline grains added to glass matrix there is inc. strength if thermal expansion match

Strength inc. w/ inc. crystal content + dec. crystal size

350
Q

Types of reinforced ceramic cores

A

Aluminous porcelains
Glass infiltrated crystalline structure
Pure Zr/Al2O3 cores

351
Q

Discuss aluminous porcelains

A

Al2O3 reinforced feldspathic core

  • up to 50%wt fused alpha-alumina
  • 25microm

Crystals act as crack stoppers: similar thermal expansion cf glass
Surface defects left critical, glazing has little effect on strength

Can cause opacity

352
Q

Discuss glass infiltrated ceramics

A

Ceramic/glass interpenetrating phase composite

Porous crystalline (70%) infiltrated by glass (30%)
Glass enters pores = denser material
353
Q

Compare In-Ceram Spinell, Alumina, Zirconia

A

Glass infiltrated crystalline ceramics

Spinell

  • weakest: flexural 200-400MPa
  • best aesthetics: high translucency

Alumina

  • flexural: 400-600MPa
  • dec. aesthetics: poor translucency due to refractive index differences

Zirconia

  • strongest: flexural 600-800MPa
  • poor aesthetics: opacity
  • transformation strengthening from ZrO2
354
Q

Discuss pure alumina and zirconia cores

A

Type of reinforced ceramic cores
Both polycrystalline

Pure alumina

  • formed by dry pressing
  • CAD/CAM

Pure zirconia

  • crown + bridge
  • higher flexural, lower modulus cf Al2O3
355
Q

What is transformation strengthening?

A

Unique property of zirconia
Highly localised stress at crack tip causes load induced transformation of tetragonal -> monoclinic
- 3-5% expansion; squeeze crack closed

356
Q

Discuss glass ceramics

A

Glass made to crystallise by heating in presence of seed crystals/nuclei
- crystalline content 30-100%

Dispersion Strengthening: through crystal growth
- not added (reinforced ceramics)

Properties depend on size + vol. crystals
- controlled by selection of heat Tx regime

357
Q

3 main crystalline phases in glass ceramics

A

Fluoromica
Leucite
Lithium disilicate

358
Q

Discuss fluoromica glass ceramics

A

Based on growth of tetrasilicic fluoromica crystals
Fluorescence
- SiO2, Al2O3, MgO
- K2O, ZrO3, fluorides

Cast as glass, heat Tx produce needle like crystals
Flexural 2x greater cf feldspathic porcelain

359
Q

Discuss lithium disilicate glass ceramics

A

Crystalline phase in SiO2-Li2O glass ceramic system
Needle like crystals (70%): highest vol. fraction of crystalline phase

Inc. strength + toughness; sufficient for all ceramic bridge

360
Q

Compare leucite containing and leucite reinforced glass ceramics

A

Leucite Containing
- glasses heat Tx produce leucite crystals (35-50%)
— tetragonal RT; cubic >625
- use: PFM w/ matching thermal expansion w/ alloy
- low flexural, higher aesthetics cf leucite reinforced

Leucite Reinforced
- on cooling: compressive stresses inc. around crystals as > thermal expansion cf glass
— crystals crack, prod. round ended #s
— both strengthen
- high flexural, low aesthetics 
- use: single ant. unit, veneer
361
Q

Why are colouring systems req. for glass ceramics? Compare methods for leucite and lithium disilicate ceramics

A

All glass ceramics req. external colour for aesthetics
- addition of surface layer or surface staining

Leucite: layer powdered leucite reinforced ceramic sintered on surface
Disilicate: req. new apatite glass layer system due to differences in thermal expansion

362
Q

Discuss porcelains for PFM/CMC

A

Low fusing porcelain containing leucite crystals

High thermal expansion

  • ideally slightly < metal alloy
  • inc. glass modifier (alkali) content

Leucite content controlled to give req. thermal expansion

363
Q

Discuss mechanisms of metal-porcelain bond

A

Compression (main)

  • thermal expansion: glass < metal
  • cooling: metal shrinks faster, porcelain compressed
  • gripped by metal

Mechanical

  • good wetting of metal oxide by porcelain
  • surface roughness of metal oxide (sandblasting)

Molecular: metal oxide layer

  • all PFM have metal oxide layer
  • bond via oxides in porcelain

VDW’s Forces (adhesion)

364
Q

Discuss Captek

A

Core for PFM
- porous Au-Pt-Pd infiltrated w/ pure Au

No oxide layer used

  • porcelain bonder of Pt and Au micro-filaments
  • gives micromechanical bonding

Good aesthetics
Expensive

365
Q

Composition of alginate

A 
Na/K alginate
Diatomaceous earth: filler
CaSO4: cross-linker
Na3PO4/Na2CO3: retarder
Na fluorosilicate/fluorotitinate: pH controller
MgO: pH controller
366
Q

Composition of agar

A 
Agar
Borates: strength
Potassium sulphates: accelerator
Wax: filler
H2O: dispersion medium
367
Q

Composition of poly(dimethyl siloxane)

A

Condensation silicone

Base paste

  • silicone polymer w/ terminal OH
  • inert filler

Catalyst

  • tetraethoxy orthosilicate: cross-linker
  • dibutyl tin dilaurate: catalyst
  • inert filler
368
Q

Composition of poly(vinyl dimethyl siloxane)

A

Addition silicone

Base

  • silicone polymer w/ terminal vinyl
  • inert filler

Catalyst

  • silicone oligomer w/ Si-H: cross-linker
  • Pt salt catalyst
  • inert filler
369
Q

Composition of polyether

A

Base

  • polyether polymer: terminal ethylene-imine
  • filler: rigidity, dimensional stability
  • plasticisers: adjust viscosity
  • pigments, flavourings
  • triglycerides: intrinsic viscosity

Catalyst

  • sulphonium tetra borate salt: cationic starter
  • filler, pigment, plasticiser
370
Q

Composition of polysulphide

A

Base

  • polysulphide polymer: thiokol S-S
  • TiO2/ZnS: filler
  • phthalate ester: plasticiser

Catalyst

  • PbO2: cross-linker
  • S
  • stearic/oleic acid
  • filler, plasticiser
371
Q

Rationale for using elastomer impression materials for fixed pros

A

Strength + dimensional stability better cf hydrocolloid

Best accuracy

372
Q

Problems associated w/ direct composites

A

Placement T consuming
Difficulty ensuring good tooth-tooth contact
Polymerisation shrinkage + marginal adaptation
Incomplete cure due to limited DoC

373
Q

Uses of indirect composites

A

In/onlay
Veneer
Fibre reinforced composite

Suited for

  • multiple post. restorations in single Q
  • large restoration mass
374
Q

Advantages of indirect composites

A

Full DoC: 100% monomer conversion not achieved (better cf direct)
Red. polymerisation shrinkage as more polymerisation
Improved physical properties + wear resistance cf direct
Less abrasive cf ceramic inlay
Repairable
Cure: light, heat, pressure or combination

375
Q

Disadvantages of indirect composites

A

Luting cement req.
- high shrinkage stresses = bond failure
- flash = gingival irritation
Effective cure: few unreacted methacrylate groups left
- req. polishing to improve bond
Highly technique sensitive
Micro-leakage, recurrent caries
X-ray marginal diagnosis difficult: less radiopaque cf metals
Less wear resistant + durable cf ceramics
Longevity: long term studies req.

376
Q

Dis/advantages of veneers

A

Adv: colour stability cf veneering resins
Disadv
- pre-cured comp + freshly applied resin cement = weakest porting
- aesthetics: leakage @ weak interface, stain more (cf ceramic)
- req. repair

377
Q

What are fibre reinforced composites? Uses?

A

Resin composites containing fibres to improve strength and stiffness
Use: splint, bridge, crown, removable denture

378
Q

Types of fibres for reinforcing composite

A

Carbon
Glass
Polyethylene: UHMPE
Aramid

379
Q

Compare mesh/woven and unidirectional fibres

A

Mesh/woven: better general and multidirectional support

Unidirectional

  • short + long fibres, distributed in many ways in resin matrix
  • allow construction long span bridges
380
Q

Discuss carbon and glass fibres for reinforcing composite

A

Carbon

  • unaesthetic
  • inc. modulus: strain to failure dec.
  • conduct electricity

Glass
- req. binding for easy processing
- coupling agent req. to improve interfacial bond
- hazardous
— careful handle: salts, oils, grease damage
— respiratory problems

381
Q

Discuss aramid reinforced composites

A

V low resistance to axial compression

  • poor transverse properties
  • low longitudinal shear modulus

Break into small fibrils
Hygroscopic
Degrade in UV

382
Q

Discuss UHMPE reinforced composites

A

Excellent modulus and strength:weight properties
Lower density cf aramid
Excellent biocompatibility
Better impact strength cf all others

Low MPt: 150
Low surface energy + poor adhesion

383
Q

Dis/advantages of fibre reinforced composites

A

Adv
- high fibre content + good fibre wetting + coupling by resin = (cf particulate resin)
— high flexural
— high modulus
— impact resistance
- lighter, translucent, non-corrosive cf metal

Disadv

  • correct bonding system critical to success
  • lack clinical experience
384
Q

Define temporary and provisional crown, how long must they last?

A

Temporary: cover prep. whilst definitive crown manufactured; few wks

Provisional: test changes in shape/colour during function; few mnths

385
Q

Rationale for temporaries

A

Protect dentine tubules from micro-leakage
Maintain O relationship
Maintain aesthetics
Maintain interdental space + contacts
Prevent gingival hyperplasia @ margins + maintain health
Confirm enough O red. + B+L
Confirm retention

386
Q

Rationale for provisional crowns

A

As w/ temporaries +

  • check changes in O acceptable
  • check: aesthetics, phonetics, mastication
387
Q

5 methods for constructing temporaries/provisional

A 
Overimpression: alginate/putty indices 
Vacuum formed matrix: created on cast pre-prep.
Al Crown: molars
Celluloid Crown former: ant.
Polycarbonate crown: ant. + premolar
388
Q

Discuss overimpression technique

A

Impression taken in mouth or on cast
- tooth broken: wax build up on model prior
Complete prep., fill index w/ low exotherm resin, fit in mouth
Allow set to rubbery phase
- don’t set hard as difficult to remove (undercuts)
Trim margin w/ soflex disc
Add resin/flowable as req.

389
Q

Discuss vacuum formed matrix method of making temporaries

A

Stone cast of prep. + 2 teeth either side
Resin sheet heated in vacuum forming machine, pressed into place
Formed trimmed around teeth
Putty index made over formed in position on cast

Direct: complete prep., fill w/ low exotherm resin, set
Indirect: best marginal fit
- complete prep., alginate impression
- quick set stone cast, temp. made on this cast
- allows higher acrylics + comps to be used

390
Q

Discuss polycarbonate crown formers for making temporaries

A

Prefabricated tooth shapes for ant., fit where touch unless adapted

  • 1 colour, expansion, req. lots of adjustment
  • last resort

Choose fit interdental space + roughly correct height
Trimmed to correct height
- usually cut interdental space to correct shape
Crown filled w/ low exotherm resin, adapted to fit
Trimmed/polished as before

391
Q

Discuss aluminium and celluloid crown formers for temporaries

A

Aluminium

  • anatomical or flat O surface
  • size as close fit as possible, trim margins
  • pt bite to form
  • fill w/ low exotherm resin, set
  • finish

Celluloid

  • clear crown formers; useful for # tooth, req. temp. quickly
  • crown approximated w/ crown shearers, pp
  • fill w/ low exotherm resin, set
  • finish/polish
392
Q

Discuss TB: aetiology, transmission, risk, Dx, prevention, Tx

A 
Leading fatal infectious disease WW
Aetiology: mycobacterium tuberculosis 
Transmission: contaminated, airborne droplet
- eradicated by immune system 
- 1ry TB
- lay dormant
Dx: Mantoux tuberculin test; ZN stain; sputum culture 
Prevention: BGC
Tx: antimycobacterial 6/12, up to 24/12
393
Q

Clinical signs and oral manifestations of TB

A

Clinical

  • pulmonary TB: chest pain, fever, haemoptysis, weight loss, fatigue, productive cough
  • extrapulmonary: LNs, meninges, pericarditis, skin, GIT
  • disseminated: enter bloodstream, affect any organ, usually fatal

Oral: orofacial TB 2ry, disseminated from lungs
- deep, punched out ulcers w/ peri-ulcer swelling + erythema
- cervical lymphadenopathy, gland/bone involvement
- tongue + gingival lesions
— painful, solitary, well-demarcated red papule -> chronic atrophic plaque
- cartilage (ear, nose): completely destroyed

394
Q

Discuss sarcoidosis: progression, aetiology, resolution, Tx

A

Multisystem granulomatous disease

Aetiology: unknown

  • interaction b/w environmental factors + genetic determinant
  • not autoimmune: immune alteration/dysregulation
  • red. immune response: inc. infection + cancer

Affects: lungs, LN, mouth, salivary glands
Progression: slow, symptoms subtle
Resolution: spontaneous (mnths/yrs), relapse common
Tx
- symptomatic
- steroid/sparing immune modulator: azathioprine, methotrexate
- lung transplant only long term solution in red. vital capacity pt

395
Q

Clinical signs and oral manifestations of sarcoidosis

A

Clinical
- nonspecific: fever, apatite loss, fatigue, cough
- respiratory: cough, dysponea, chest pain
- skin
— lupus pernio: chronic, infuriated papule, mid-face (ala of nose)
— rash, erythema nodosum

Oral

  • multiple, asymptomatic submucosal nodules; P, B, L mucosa
  • gingival + tongue: indurated swelling
  • FOM: ranula (mucocele from sublingual gland)
  • X-ray: ill-defined radiolucencies in alveolar bone
  • parotid: bilateral, painless swelling w/ or w/o xerostomia
396
Q

What is Wegener’s Granulomatosis? Limited vs severe? Aetiology, pathogenesis, mortality, Tx

A

Rare, necrotising anti-neutrophil cytoplasmic Ab-associated vasculitides
- affects: S-M sized vessels

Aetiology: unknown
Pathogenesis: interaction b/w immune system + environmental factor w/ genetic predisposition
Limited: restricted to U+L RT; Severe: additional multi-system manifestation

Mortality: high; >90% 2yr in unTx
Tx: corticosteroids + cyclophosphamide (immunosuppressant), surgery (repair damage)

397
Q

Clinical signs and oral manifestations of Wegener’s granulomatosis

A

Clinical

  • nonspecific: fever, night sweats, lethargy, apatite loss,arthralgia
  • chronic sinusitis, rhinitis, epistaxis
  • pulmonary: cough, haemoptysis, dysponea, stridor, wheeze
  • ocular: conjunctivitis, scleritis, uveitis, proptosis
  • skin: purpura, ulcers

Oral

  • strawberry gingivitis/hyperplasia: granular enlargement + erythema
  • bone resorption, tooth loss
  • painful/less ulcers: B mucosa +/- P
398
Q

Discuss amyloidosis, clinical signs + oral manifestations

A

Fatal disease, deposition of EC and/or IC insoluble amyloid interfering w/ normal function of organ

Clinical

  • kidney: nephritic syndrome (haematuria, proteinuria, hypertension)
  • skin: wash papules, plaques anogenital/eyelids/neck
  • nails: dystrophic, brittle
  • heart: myocardial insufficiency (fatal)

Oral
- localised, soft, elastic papules
- macroglossia (20%), firm, loss of mobility
— lat. ridging due to indentation from teeth
- dysgeusia, hyposalivation, submandibular swelling

399
Q

Clinical signs + oral manifestations of anaemia

A

Clinical

  • fatigue, breathlessness
  • inc. infection
  • pale skin + nail beds, conjunctiva pallor

Oral

  • pale mucosa
  • inc: glossitis, recurrent apthae, angular stomatitis, candidiasis
400
Q

Oral signs of leukaemia

A

Pale mucosa
Spontaneous gingival bleeding + haemorrhages
Painless gingival hyperplasia
Ulcerative necrotic lesions

401
Q

Discuss Crohn’s disease: aetiology, Tx

A

Common inflammatory bowel disease
Patchy, full thickness ulcers involving any part GIT
- discontinuous involvement = skip lesions
Mortality + complications inc. w/ duration
Aetiology: unknown; genetic + environmental provoking factor
Tx: no cure, symptomatic, diet exclusion; steroids + surgery

402
Q

GI and extra-intestinal signs of Crohn’s

A

GI

  • abdominal pain
  • anal fissures, perianal fistula, abscess (30%)
  • malabsorption, weight loss, vit deficiency
  • diarrhoea, stone formation
  • child: stunted growth, delayed puberty + development

Extra-intestinal

  • rheumatological: ankylosing spondylitis, psoriatic/reactive arthritis, sacroilitis, joint/hip/back pain
  • skin: erythema nodosum, pyoderma gangrenosum
  • ocular: recurrent iritis/uveitis
  • GU: kidney stone, renal amyloidosis
403
Q

Discuss orofacial granulmatosis

A

Orofacial Crohn’s; can occur separately from Crohn’s
Signs
- lymphoedema
- multiple, non-caseating giant cell granulomas
- cobble stoned mucosa: tags, fissures, hyperplasia
- tongue: enlarged, fissures
- recurrent aphthous stomatitis,p
- aphthous-like ulcers
- uni/bilateral LMNL: recurrent -> permanent (Melkersson-Rosenthal syndrome)
- granulomatous cheilitis -> angular cheilitis (lip swelling)

404
Q

Discuss ulcerative colitis; aetiology, Tx

A

Idiopathic chronic inflammatory bowel disorder
Affects part/whole colon
Sub/mucosa not full thickness

Aetiology

  • enhanced reactivity against Ag of normal intestinal flora + certain dietary products
  • +ve family history

Tx: aminosalicylates + corticosteroids, colectomy (cures)

405
Q

Clinical signs + oral manifestations of ulcerative colitis

A

Clinical

  • intermittent pattern of acute episodes
  • bloody diarrhoea, abdominal pain
  • nutritional deficiency, weight loss, failure to thrive
  • extra-intestinal: finger clubbing, uveitis, iritis
  • rheumatological: ankylosing spondylitis, sacroilitis, arthritis
  • skin: erythema nodosum, pyoderma gangrenosum

Oral: less common cf CD

  • mucosa: erythematous w/ scattered pustules, haemorrhagic ulcers, abscesses
  • pyostinatitis vegetans: multiple friable pustules; varying severity + pain
406
Q

Discuss coeliac disease; aetiology, Tx

A

Debilitating chronic inflammatory disease of GIT
Aetiology: sensitivity to gliadin
Tx: diet restriction, corticosteroids

407
Q

Clinical signs + oral manifestations of coeliac disease

A

Clinical
- diarrhoea: oily, foul smell
- indigestion, malabsorption: weight loss, nutritional deficiency
— delayed development, failure to thrive, weakness, fatigue
- skin: dermatitis herpetiformis: symmetrical, itchy stinging small papules
- bleeding: prothrombin deficiency (impaired VitK absorption)
- hypocalcaemia: muscle weakness, paraesthesia

Oral

  • glossitis, tongue fissuring, depapillation
  • ulceration (similar aphthous stomatitis)
  • candidiasis

BDS3 (4 decks)

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