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3rd Year BDS > Dental Materials > Flashcards

Dental Materials Flashcards

1
Q

What is a dental impression used for?

A

Recording the intra-oral structures

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2
Q

What information do we receive from the dental impression?

A

Negative imprint of the oral structures from which a positive reproduction can be formed

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3
Q

What is the process of a conventional impression?

A
  1. Material is mixed
  2. Loaded into impressions tray
  3. Inserted into mouth
  4. Allowed to set
  5. Remove from mouth
  6. Permits a cast to be made
  7. Device is made of this cast
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4
Q

What are the 2 main uses for dental impressions?

A

Study casts and construction of dental appliances

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5
Q

Name some forms of dental applicances?

A
  • Orthodontic appliances
  • Removable dentures
  • Mouth guards and bleaching trays
  • Inlays and onlays
  • Crowns
  • Bridges
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6
Q

What are the requirements for an impressions tray?

A
  • Rigid and non-flexible under load
  • Extend sufficiently to support the impression material
  • Fit loosely around dental arch avoiding soft tissues
  • Adequate means of retention of impression material in tray
  • A handle
  • Decontaminated
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7
Q

Name the 2 main material types of trays?

A

Plastic and Metal

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8
Q

Problems caused by a non-rigid impressions tray?

A
  • Tray shape is altered intra-orally
  • Distorts the impression material
  • Cast inaccurate
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9
Q

Name the 2 main ways impression trays ensure the impression material stays in the tray?

A 
Trat design:
- perforations
- rim-lock
Tray adhesives:
- types
- usage
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10
Q

How do perforations ensure retention?

A

Material extruded through holes retaining the material to tray mechanically

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11
Q

How does rim-lock ensure retention?

A

Retentive feature around extent of tray

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12
Q

What are tray waves and how do they improve retention?

A
  • Periphery waves

- Helps to contain the fluid impression material in stock impression trays

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13
Q

What is greenstick and how does it improve retention?

A
  • Rigid impression material

- Contains the fluid impression material in impression tray

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14
Q

What are the chemical constituents and purposes of the constituents of greenstick?

A
  • Resin and waves for consistency control
  • Stearic acid as a plasticiser
  • CaCO3 as a filler, colouring agent and controlling rigidity
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15
Q

How is greenstick prepared?

A
  • Transition temp at 55-60C

- Softened by hot water or flame

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16
Q

What is the typical tray adhesive used with alginate?

A

10-12% toluene in 45-50% isopropanol

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17
Q

What is the mechanism of action of a tray adhesive?

A
  • Based on contact technology
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18
Q

What is the process of tray adhesive use? but, when should they never be used with?

A
  • Applied to tray and allow to dry
  • used sparingly
  • Periphery covered
    Never on metal trays
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19
Q

Name the 2 main presentations of tray adhesive?

A

Spray and paint on

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20
Q

What are the benefits of special trays?

A
  • Permits equal thickness of impression material

- Dimensional change of impression material theoretically the same in all dimensions

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21
Q

What are special trays made from?

A

Polymethylmethacrylate or Shellac

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22
Q

What are the specific spacing of the perforations according to material used?

A

3mm - alginate
2mm - C-silicone
1mm - impression paste

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23
Q

Name the 10 most important properties of impression materials?

A
  1. easy to handle
  2. compatible with oral fluids
  3. reproduce detail accurately
  4. good tear resistance
  5. no adverse effects
  6. pleasant taste
  7. easily removable
  8. easy decontamination
  9. remain dimensionally table
  10. compatible with all model construction materials
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24
Q

What is the process of impression decontamination?

A
  1. Immediately after removal rinsed under cold running water
  2. Tray and material immersed in water-based disinfection solution (MFI)
  3. Impression then rinsed gently with tap water (over-disinfection can lead to changes)
  4. impression placed in sealed polythene bag and sent to lab
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25
Q

What is alginate chemcially?

A

Irreversible hydrocolloid

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26
Q

What is a colloid?

A

A substance which is distributed evenly through a material

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27
Q

What 2 phases can alginate be in?

A

Dispersed and continuous

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28
Q

What is the chemical equation for alginate?

A

Sodium and potassium salts + alginic acid forms alginate

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29
Q

What are the chemical constituents of alginate and their function? ***

A
  • K/Na alginate - dissolves in water to form a hydrogel with Ca
  • CaSO4 dihydrate - reacts with soluble Na alginate to form insoluble Ca alginate
  • Borate - reduces inhibition of setting of plaster
  • Silicate powder - filler controls consistency and flexibility
  • NaPO4 act as a retarder by reacting with Ca
  • Na silicofluoride - controls pH
  • Glycols - reduces powder dustiness
  • Peppermint - taste
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30
Q

What is the process of alginate setting reaction?

A
  • Potassium (sodium) alginate + calcium sulphate dihydrate + water → calcium alginate + potassium (sodium) sulphate
  • NaPO4 retards setting
  • Set after PO4 runs out
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31
Q

What is the mixing, working and setting times of alginate?

A

Mixing: 45-60s
Working: 45s (fast) 75s (reg)
Setting: 1-4.5 mins

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32
Q

How to reduce permanent deformation when using alginate?

A
  • Reducing amount of compression
  • Reducing time the impression is under compression
  • Allowing time for recovery before pouring model
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33
Q

How to improve dimensional stability with alginate?

A
  • Allow the alginate to heal over bench
  • Control relative humidity
  • Proper storage
  • Syneresis (contracts on standing)
  • Imbibition (wrap in damot tissue and place in bag)
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34
Q

What are the 3 factors which affect the strength of alginate?

A
  • P/L ratio = weaker
  • insufficient spatulation (improper dissolving)
  • over speculation (disrupts formation of Ca alginate gel)
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35
Q

What are the advantages and disadvantages of alginate as an impressions material?

A 
Adv:
- easy slow
- reproduce detail
- fast set
- minimal tissue displacement
- cheap
- tolerable
Dis:
- poor dimensional stability
- poor tear strength
- distorts if unsupported
0 3mm thickness required
- easy to include air in bag
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36
Q

What are the indications of use for alginate?

A

Less accuracy and detail is required:

  • study cast
  • denture construction
  • removable ortho
  • teeth opposing an indirect cast restoration
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37
Q

How to properly prepare the alginate mixture?

A
  • shake container
  • dispense metered volumes
  • use correct bowl and spatula
  • add powder to water
  • mix in a 8-figure motion
  • swipe material against bowl side to reduce air incorporation
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38
Q

What are some useful clinical tips fr alginate use?

A
  • ensure smooth impression surface
  • smear into fissures
  • place some on palate
  • evert lips and retract cheeks
  • ensure centrality
  • hold still
  • ensure full set
  • remove quickly from mouth
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39
Q

What are the common failures of poor alginate mixtures?

A
  • Grainy
  • Treating
  • Bubbles
  • Chalky model
  • Distortion
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40
Q

What is the reason for a grainy alginate?

A
  • inadequate or prolonged mixing

- ratio too low

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41
Q

What is the reason for alginate tearing?

A
  • Inadequate bulk

- premature removal

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42
Q

What is the reason for external bubbles on alginate?

A

Air incorparation

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43
Q

What is the reason for a chalky alginate?

A
  • Inadequate cleaning
  • Excess water in impression
  • Premature removal
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44
Q

What is the reason for a distorted alginate?

A
  • Delayed pouring of impression
  • Tray movement
  • Premature removal
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45
Q

Name a commercially available alginate product?

A

Tropicalgin by Zhermack

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46
Q

How can gypsum improve the quality of an alginate impression? but what is necessary to remember?

A
  • Good surface quality and detail gain
  • Avoid water interaction with gypsum
  • Set gypsum not in contact with alginate for periods of serval hours
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47
Q

What is the defintion of a dental cast?

A

Replica of the structures in the oral cavity

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48
Q

What are dental plasters and dental stones based on?

A

Gypsum
CaSO4 dihydrate
Crystalline in form

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49
Q

Explain the process of production for Plaster of Paris?

A

Heating crystalline gypsum to between 110-130 in open vessel
Forms Beta-Ca sulphate hemihydrate
Add water reverting back to dihydrate
Highly exothermic reaction

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50
Q

Describe the appearance of beta-Ca sulphate hemihydrate?

A

Porous powder
Irregular shaped particles
Not closely packed together

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51
Q

How does the the crystalline hemihydrate from impact the plaster?

A

Determines the precise type of plaster produced

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52
Q

Explain the process of dental stone?

A

Dihydrate is heated to 125C under pressure in presence of water vapour

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53
Q

Describe the appearance of alpha-Ca sulphate hemihydrate

A

Unformorm shaped particles

Reduced porosity

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54
Q

What are the 5 chemical constituents for dental stone?

A 
CaSO4 hemihydrate
Water
KSO4
Borax
NaCl
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55
Q

What is the function of KSO4 in the dental stone mixture?

A 
2%
Accelerates setting time by half
Crystallises quickly
Encourages further crystal growth
4% decreases expansion
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56
Q

What is the function of Borax in the dental stone mixture?

A

2%
Retards the set
Leads to formation of Ca salts of the borate
Deposited on the dihydrate crystals preventing further crystal growth

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57
Q

What is the function of NaCl in the dental stone mixture?

A

Reduces expansion
Extra sites for crystal growth
Keeps crystals closer together

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58
Q

What is the function of CaSO4 dihydrate in the dentals tone mixture?

A

0.5-1%
Provides nuclei of crystallisation
Acts as an accelerator

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59
Q

Explain the dental stone setting process?

A

Water is added to hemihydrate poder
Converted to dehydrate
As solubility of dihydrate is low a supersaturated solution rapidly forms
Stability of this solution is low, the dihydrate crystals start to precipitate out
Process continues as more hemihydrate is dissolved in water

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60
Q

What are the compressive strength properties of dental stone?

A 
12-45 MPa Compressive strength
Greater porosity - Low CS
B-hemihydrate - Low CS
Further water lost to atmosphere over time
After 7% water lost - 60 MPa gained
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61
Q

What are the surface hardness and abrasion properties for dental stone?

A

Higher hardness values assoc with higher compressive strength
With water loss to atmosphere hardness also increases
Open crystal structure is stable once set but is porous permitting water up take
Leads to surface degradation of the model

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62
Q

Describe how you could increases the abrasion resistance of a dental stone cast?

A 
Impregnation:
Epoxy resin
Methylmethacrylate
Glycerin
Haderning solutions containing 30% colloidal silica (increases hardness)
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63
Q

What are the reproduction of detail properties for dental stone?

A

Not ideal for very fine detail
ISo requires 0.05mm line using a specific consistency of mixed materials
But considered sufficient for most dental applications

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64
Q

What are the hygroscopic expansion properties for dental stone?

A

Stone is immersed in water during set
Crystals can grow more freely
Degree of expansion is greater
Affect relatively insignificant

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65
Q

What are the volumetric change on setting properties fro dental stone?

A

Theoretically expected
Slight setting expansions is always observed
Expansion is due to crystal growth of dihydrate and the set materials having micro porosities
Models will be fractionally oversized and prosthesis too big

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66
Q

What is the difference in setting expansion between plaster and stone?

A

Plaster:
- 0.3-0.4%
Stone:
- 0.05-0.3%

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67
Q

What are the working and setting time properties for dental stone?

A

2-3 minute working time

2-3 minute setting time

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68
Q

What is the definition of working time?

A

The point at which the material can be manipulated into the impression satisfactorily

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69
Q

How can the manufacture manipulate the setting time for htypsum?

A

KSO4
Borax
NaCl
CASO4 dihydrate

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70
Q

Indications for dental stone (gypsum)?

A

Study casts for general diagnosis
Working casts:
- denture full and partial
- ortho appliances

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71
Q

What is the definition of a working cast?

A

Cast onto which the restoration is constructed in the lab

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72
Q

What is the definition of a study cast?

A

Cast is intended to be used for treatment planning purposes

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73
Q

How compatible is a gypsum-based material?

A

Compatible with all commonly used impression materials

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74
Q

How can you adjust the behaviour of the dental stone material?

A

P:L ratio
Water temperature
Degree of spatulation of the mixture

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75
Q

What adverse reactions to the dental stone will excess water procedures?

A

Aid mixing
Slow setting time
Weakened plaster

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76
Q

What occurs if you increases the temp of the water added to the mixture for gypsum-based impression materials?

A

Solubility of the hemihydrate and dihydrate increases
Mobility of the Ca and SO4 ions increases so set is accelerated
Results in combo of both small accelerate in rate of reaction and a reduction in setting time

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77
Q

What are the adverse reactions of changing spatulation speed and time for dental stone?

A

Particles are wetted thoroughly so a smooth mix forms
Increasing speed or time of spatulation reduces setting time, as crystal nuclei are disrupted forming more crystal sites and more rapid precip of dihydrate
Greater setting expansion

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78
Q

What is the definition of a silicone impression material?

A

Elastomeric impression material
Condensation reaction with ethyl alcohol given off
Hydrophobic

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79
Q

Name the 5 constituents of silicone impression material?

A 
Dimethyl siloxane
Colloidal silica or CuCO3
Stannous octoate
Alkyl silicate
Colloidal silica
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80
Q

What is the function of dimethyl siloxane in silicone impression material?

A

low Mr silicone which has reactive terminal hydroxyl end groups

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81
Q

What is the function of CuCO3/Colloidal silica in silicone impression material?

A

Filler, as silicone polymer is liquid

FIller particles between 5-10 um

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82
Q

What is the function of Stannous octoate in silicone impression material?

A

Accelerator

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83
Q

What is the function of Alkyl silicate in silicone impression material?

A

Accelerator

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84
Q

What is the function of Colloidal silica in silicone impression material?

A

Thickening agent

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85
Q

Explain the reaction for condensation silicones?

A

Condensation reaction with ethyl alcohol given off
3D silicone matrix is formed on setting
Marked shrinkage on polymerisation
Not as accurate as addition silicones due to setting reaction
Slight exothermic
Poured ASAP
Accurate proportioning difficult leads to variability

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86
Q

What is the function of alkyl silicate in the silicone material and what occurs if the amount is reduced?

A 
Creates cross linking
Reduced amount causes:
- weaker material
- decreased tear resistance
- increased permanent set
Moisture sensitive (setting inhibited)
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87
Q

Why does stannous octoate has a limited shelf-life? (silicone)

A

Oxidises
Alkyl silicate not stable in presence of tin ester
Minimal shrinkage as bulk of material is filler

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88
Q

How much does silicone shrink?

A

Proportional to the amount of polysiloxane present

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89
Q

Name the 3 presentation of condensation silicones?

A

Putty
Putty and light body
Paste/Paste

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90
Q

Explain the mixing technique for condensation silicone?

A

Mixed with low viscosity paste accelerator

Kneaded into mass of putty

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91
Q

Give 1 trade name for condensation silicones?

A

Lab Putty (Coltene Whaledent)

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92
Q

What are the indications for condensation silicone?

A

Where dimensional stability is not crucial:
- fixed prosthodontics (putty and light body)
- removable prosthodontics (putty) (reline and rebase)
Produce wax replicas of denture

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93
Q

Name the 2 types of impression composition materials?

A

Greenstick

Red cake

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94
Q

Give a description of greenstick?

A

Rigind non-elastic impression material
Used for border moulding of impression trays especially the post dam
Mucocompressive

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95
Q

When to avoid greenstick?

A

Allergy to colophony (asthma)

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96
Q

Give a description of red cake?

A

Thermoplastic
Impression Compound (Trade name)
Sheets or sticks
Indicated for first impression of the edentulous arch

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97
Q

What are the chemical constituents and purposes of the constituents of red cake?

A
  • Resin and waves for consistency control
  • Stearic acid as a plasticiser
  • CaCO3 as a filler, colouring agent and controlling rigidity
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98
Q

What are the properties for red cake?

A 
Transition temp between 55-60C
Hot water both or over naked flame
Overheating can create volatile compounds
Or leaching from overheating  
Full softening is essential
Mucocompression gained
Highly viscous
Dimensional stability poor 1/5%
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99
Q

Explain the process of how to use red cake chairside?

A 
Boiling water
Line dish with gause
Leave for 1 min to soften
Place into impression tray
Place back in bath to soften
Bit back
Check to see if safe for intra-oral
Place
Take impression
Cool impression to keep dimension
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100
Q

Why do we need to use occlusal registration?

A

Not possible to relate the dental arches to each other due to lack of index teeth
Casts can’t be related to each other

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101
Q

What is the aim of occulsa registratyion?

A

Records the relationship of the dental arches to each other intraorally which can then be used to relate the casts extraorally

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102
Q

Name 3 types of occlusal registration materials?

A

A-silicones/polyether
Higher methacrylates
Waxes

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103
Q

Give a description of a-silicones/polyether bite reg pastes?

A

Easy to manipulate and move
May ‘bounce’
usually syringed in a gun and allowed to set

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104
Q

Give 2 names of bite reg paste commercial products?

A

Jet Bite Blue, Coltene Whaledent, Silicone

Memosil 2, Heraeus Kulzer, Silicone

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105
Q

Give a description of higher methacrylates?

A 
Based on (poly)methylmethacrylate
Fluid/dough form
Sets to a solid
Rigid 
Highly accurate
Can get into undercuts
Used as a dough or coping + dough
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106
Q

What is the definition of coping?

A

Thin layer of material which covers the preparation to the margins

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107
Q

How to use higher methacrylates in bite registration?

A

Mix dough, place on coping, patient bites
Removed when material set
Can be replaced on model to indicate occlusal relationship

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108
Q

Give 1 example of a commercial name for a higher methacrylate?

A

DuraLay II (Reliance)

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109
Q

What can higher methacrylates show?

A

Dough, removed and measured

Indicates amount of interocclusal clearance

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110
Q

What is the definition of an addition silicone impression material

A

Elastomeric impression material
Termed after setting reaction addition polymerisation reaction
Hydrophobic

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111
Q

Name the 6 constituents for addition silicone impression materials and their functions?

A

Polymethyl hydrogen siloxane - polymer
Siloxane prepolymers - cross linking polymer
Quartz - filler
Divinyl polydimethylsiloxane - polymer
Chloroplatinic salt - catalyst
Surfactant and retards - reg of setting and aids to wetting of hydrophobic silicone

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112
Q

How can the amount of filler change the category of the addition silicone impression material?

A

Heavy
Universal
Light-body

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113
Q

What 2 pastes are needed to form an addition silicone impression material?

A

Base paste

Catalyst paste

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114
Q

What must both pastes share for an addition silicone impression material?

A

The same consistency to facilitate mixing

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115
Q

What is the function of surfactants for an addition silicone impression material?

A

Address the hydrophobicity of the polysiloxanes
Facilitates wetting of the surface of the preparation and the soft tissues
Aids pouring of the model as wet stone has an affinity for the hydrophilic surface of the impression

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116
Q

What reaction will occur if the mixture has moisture contamination for an addition silicone impression material?

A

Rolled edge of preparation margins

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117
Q

Describe the setting reaction for an addition silicone impression material?

A

Polymethyl hydrogen siloxane in one paste + vinyl-terminated polysiloxane on the other paste
Addition polymerisation reaction

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118
Q

Explain the setting reaction chemistry for an addition silicone impression material?

A

Hydrogen from the hydrogen siloxane backbone links with the vinyl group on the other siloxane chain
Forming cross-link polymer
No byproducts

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119
Q

What type of catalyst is present for an addition silicone impression material and what must you avoid interacting with it?

A

Platinum
Sulphur containing materials such as latex gloves
Results in weakened material
Latex-free gloves

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120
Q

Describe the good properties of an addition silicone impression material?

A

Highly hydrophobic
V good dimensional stability (best)
Many models can be poured

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121
Q

Describe the bad properties for the use of an addition silicone impression material?

A

Too accurate and not compensated for during the investment and casting process
Too small a die producing a small cast

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122
Q

When will the addition silicone impression material increase in stiffness and why?

A

After 2-3 hrs due to further crosslinking

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123
Q

How to mitigate the poor tear resistance of an addition silicone impression material?

A

Leave in the mouth for longer

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124
Q

How to mitigate the bad interaction of the addition silicone impression material to the oxygen inhibition layer of resin-based composite materials?

A

Apply a layers of separator on recently placed resin-based composite materials

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125
Q

Name 3 advantages and disadvantages for an addition silicone impression material?

A 
Adv:
- good detail reproduced
- excellent dimensional stability
- high patient acceptance
Dis:
- hydrophobic
- too accurate
- tear resistance poor
- expensive
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126
Q

Name the 2 indications for an addition silicone impression material?

A

Fixed and removable cast restorations
Good if distance between lap and surgery is far
Suitable for the same indications as alginate
More surface detail and long term dimensional stability

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127
Q

Name the 5 types of presentation for addition silicone impression materials?

A 
Putty
Heavy-bodied
Universal bodied
Light-bodied
Extra light-bodied pastes
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128
Q

Give 1 example of a commercially available addition silicone impression material?

A

Affinis Coltene Whaledent

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129
Q

What is the effect to a model if addition silicones release hydrogen gas as a by product?

A

Porosity on the die material

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130
Q

What can be used to absorb the hydrogen for an addition silicone impression material?

A

Palladium

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131
Q

How to pour a cast for a gypsum based material or epoxy?

A

Leave for 30 mins before pouring cast

And leave overnight if epoxy is to be sued to make the die

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132
Q

What are the 2 main constituents of an impression paste?

A

Zinc oxide

Eugenol-based impression

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133
Q

Name the 2 main indications for an impression paste?

A

Making working impression of edentulous arches

Denture relining material

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134
Q

What spacing does impression paste need in a special tray?

A

1mm

Used in thin sections

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135
Q

Name the 2 pastes used in an impression paste?

A

Base

Catalyst

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136
Q

Name the constituents for the base paste of an impression paste and their function?

A

Base:

  • Zinc oxide - reactive component
  • Inert oils - plasticiser and reduced irritation of eugenol
  • Zinc acetate - acclerator
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137
Q

Name the constituents for the catalyst paste of an impression paste and their function?

A

Catalyst:

  • eugenol - reactive component
  • Mg/CaCl - accelerator
  • Talc/Kaolin or silica - inert fillers
  • Gum rosin - binder (50%)
  • Lanolin/resinous balsam - viscosity and flow regulator
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138
Q

What is the function of gum rosin of an impression paste?

A

Binder
Gives the paste body
Reduces the risk of separation of the components
Thermoplastic and so can be softened in hot water aiding is removal from the plaster model

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139
Q

What catalyses the setting reaction for an impression paste?

A

Water

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140
Q

Describe the setting reaction of impression paste?

A

Similar to ZOE

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141
Q

Describe the process of the setting reaction of the impression paste?

A

Sets slowly passing through a thickening phase after which it is hard to manipulate
Further phases of hardening occur before the impression should be removed
Setting reaction accelerates with the increases in oral temp and humidity
Check for set on mixing pad

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142
Q

Name 3 good properties of the impression paste?

A

Rigid impression produced
Good fine detail reproduced
Mucostatic impression

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143
Q

Name 3 bad properties of the impression paste?

A

Lacks elasticity leading to breakage or distortion when removed from undercuts
Adheres to dry surfaces
Small dimensional change (0.15% shrinkage)

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144
Q

Describe the process of mixing impression paste?

A 
By hand
Using paper pad
Clarident spatula
Paste/paste system
Each paste a different colour
Ensures mixed thoroughly
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145
Q

Describe the best practice to remove the impression paste from the spatula to the tray?

A

Warm spatula above temp rosin soften and wipe

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146
Q

What strange sensations can impression paste give to a paitient?

A

Tingling or mild burning sensation intra-orally

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147
Q

How to avoid the impression paste sticking to the patients extraoral tissues?

A

Apply petroleum jelly to extraoral features

A lot

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148
Q

Give 1 example of a commercially available impression paste?

A

Impression paste by SS White

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149
Q

What material can be sued to make a working model?

A

Gypsum-based

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150
Q

How long will a gypsum-based material cast take to set?

A

At least 1 hr

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151
Q

How to remove the impression paste from the gypsum-based model?

A

Immersed in warm water to remove the impression

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152
Q

What type of cast can an impression paste only be sued with?

A

Gypsum-based model

No separating medium is required

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153
Q

What are the indications for impression plaster?

A

USed to record endentulous ridges

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154
Q

Name 5 good properties for impression plaster?

A 
Good surface detail
Tolerated by patient
Small setting expansion
Good dimensional stability
Hydrophilic
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155
Q

Name 3 bad properties for impression plaster?

A

Sets ridigly and is very brittle
Must be fractured to release it from undercuts
Pieced back together so that the cast may be poured (no recovery from deformation)

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156
Q

Describe the setting reaction and constituents for impression plaster?

A

Similar to plaster of PAris with the beta-CaSO4 hemihydrate
More KSO4 included to control expansion
Borax is needed to retard the set
KSO4 also acts as accelerator
Requires a higher water to powder ratio when used as an impression material
Runnier mix if compared to pouring a model
Setting is exothermic

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157
Q

Name 2 disadvantages of impression plaster?

A

Salivate excessively and can damage surface detail

Hard to tolerate the upper impression as material flows quite readily during early setting reaction

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158
Q

Describe the mxijgn process for impression plaster?

A

Hand
Correct P:L
Powder sifted into water and left for short time before mixing
Powder particles fully wetted

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159
Q

How must the powder for an impression paste be stored?

A

Airtight tin to stop water entering the tin

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160
Q

What sized spacing is needed for impression plaster in a special tray?

A

1mm

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161
Q

How long is the working time for impression plaster?

A

2-3 mins

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162
Q

How do you insert the tray with impression plaster as the impression material?

A

Tray moved side to side on insertion so material can flow

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163
Q

How to decontaminate impression plaster?

A

Decontamination procedure follow manufacturer’s instructions

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164
Q

When casting impression plaster what should you use as a separator?

A

A separating medium
Solution of Na alginate painted onto impression used
Prevents plaster used for model adhering to the impression plaster

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165
Q

What is the definition of a wax?

A 
Type of lipid
Insoluble in water
Soluble in non-polar solvents
Melt above 45C
Plastic at ambient temps
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166
Q

Name the 5 bases to make a wax?

A 
Animal/vegetable fat
Gums
FAs
Oils
Resins
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167
Q

What is the melting point, hardness and role in dental wax for Carnauba?

A

Organic
84-91
High
Increases melting range and hardness

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168
Q

What is the melting point, hardness and role in dental wax for Ouricury?

A

Organic
79-84
High
Increases melting range and hardness

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169
Q

What is the melting point, hardness and role in dental wax for Candelilla?

A

Organic
68-75
High
Increases hardness of paraffin wax

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170
Q

What is the melting point, hardness and role in dental wax for Beeswax?

A

Organic
62-68
Medium
Common base for many waxes

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171
Q

What is the melting point, hardness and role in dental wax for Japan Wax?

A

Organic
53
Medium/low
May be substituited for beeswax

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172
Q

What is the melting point, hardness and role in dental wax for Paraffin?

A

Synthetic
40-51
Medium
Common base wax

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173
Q

What is the melting point, hardness and role in dental wax for Ozokerite

A

65-69
Medium/high
Great affinity for oils and raises melting temp

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174
Q

What is the melting point, hardness and role in dental wax for Ceresin?

A

77-93
Medium/High
Increases melting range

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175
Q

What is the melting point, hardness and role in dental wax for Montan?

A

72-90
Medium/high
Increases melting range

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176
Q

What is the melting point, hardness and role in dental wax for Barnsdahl?

A

70-74
Medium/High
Increases melting range and hardness and reduces paraffin wax flow

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177
Q

Origin of the Carnauba wax?

A

Copernicia palm

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178
Q

Origin of Ouricury wax?

A

Feather palm

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179
Q

Origin of the Candelilla wax?

A

Euphorbia antisyphilitica

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180
Q

Origin of the Japan wax?

A

Really a fat containing glycerides of palmitic and stearic acid
From sumac tree
Lacquer

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181
Q

What is the definition of a lacquer?

A

Clear or coloured varnish that dries by solvent evaop to produce a hard and durable finish

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182
Q

Origin of Spermaceti wax?

A

Sperm whale

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183
Q

Origin of bees wax?

A

Bees

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184
Q

Why can natural waxes have very varying properties within the same wax?

A

Source difference

Time obtained

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185
Q

What is the definition of mineral waxes?

A

Derived from refining petroleum products
Available as paraffin wax
Show volumetric contraction (10-16%) during cooling and solidification

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186
Q

What is the defintion of microcrystalline waxes?

A 
Derived from heavier oil fractions produced during petroleum distillation
Higher MP
Less volumetric contraction
Tougher
Formed into plates
Oil reduces hardness
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187
Q

Give 4 examples of microcrystalline waxes?

A

Ceresin
Ozokerite
Montan
Barnsdahl

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188
Q

Which substances can you later to alter the overall properties of a wax?

A

Gums
Fats
Resins

189
Q

Why do dental waxes have a melting range?

A

As there are many different constituents on the eax which melt at different temps

190
Q

What is a key property a dental wax must have?

A

Change rapidly from solid to liquid

191
Q

What to consider when mixing a dental wax?

A

Amount and mode of thermal expansion

Ensure the properties of the wax blended is suitable for each application

192
Q

What are the physical properties of waxes?

A

Compressive strength and elastic moduli are relatively low

Beeswax weakest and carnauba wax strongest and most elastic

193
Q

How can flow of wax be adjusted?

A

Change in temperature below MP

Flow controlled by composition

194
Q

How long should be left between completion of wax pattern and investment?

A

Short as possible as, wax shouldn’t be left to stress relieve
Wax can rebound and loss its shape

195
Q

What are the indications for baseplate and modelling wax?

A 
Base of denture
Bite blocks (occlusal rim)
196
Q

Name the 5 constitients of baseplate wax?

A 
Paraffin waxes (ceresin + beeswax and some carnauba was as hardener)
Al/Cu particles as strengtheners
Resins
Oils
Colouring agents
197
Q

What are the properties of baseplate wax?

A

FLow determined by climate present in
DImensional stability not crucial
Beeswax permits surface to be smoothed and contoured
MP < 100
Residue wax on teeth can interfere with bonding and interlocking of resin with artificial teeth

198
Q

What is the only successful application of wax?

A

Bite rims to record jaw relationship

199
Q

What is the definition of shellac?

A 
Derived from insects
Thermoplastic
Rigid when solid
Waxes can be added
More stable at mouth temps
200
Q

What are the properties of an acrylic base plate?

A

More rigid
Better retention
More expesnive

201
Q

Indication for acrylic base plate?

A

Fit and retention of prototype and therefore final denture

202
Q

What is a clinical tip for using wax bite black?

A

Pass wax through cold water between spells in mouth
Reduces expansion
Returns to original size and shape

203
Q

What is the definition of Moyco beauty wax?

A

Record occlusal relationships
Strengthened to overcome distortion
Brittle

204
Q

What is the definition of sticky wax?

A

Beeswax mixed with natural resins (dammar)
Firm and brittle once cet
fracture > flex
FLows when melted
Hold casts together with metal prior to mounting

205
Q

Name 4 denture base materials?

A

Wax
Shellac
Acrylic
Metal

206
Q

Name 4 types of cast metal used for denture base?

A

Cobalt-Chromium
Nickel-Chromium
Pure titanium
Titanium

207
Q

Name 3 materials denture teeth can be constructed from?

A

PMMA (polymethylmethacrylate)
Bis-GMA
Ceramic

208
Q

What are the good properties of PMMA denture teeth?

A

Highly cross-linked resin
Good hardness and wear resistance
Resists crazing
Good abrasion resistance

209
Q

What are the optical considerations for denture teeth choice?

A 
Aesthetics are key
Need to be translucent and opalescent
Shade guide
Denture teeth should fluoresce like natural teeth under UV light
Different shapes and sizes
210
Q

Name the 2 types of construction methods for PMMA denture teeth?

A

Inject into mould

Built up in layers

211
Q

Explain the process of inject into mould construction method for PMMA denture teeth?

A

Injected into a mould (acrylic powder is softened by heating and forced into the mould under pressure
further divided into dough and injection moulded

212
Q

Explain the built up in layers construction method for PMMA denture teeth?

A

Best aesthetics

213
Q

What are the good properties of ceramic denture teeth?

A

Excellent aesthetics

Good wear resistance

214
Q

What are the bad properties of cermaic denture teeth?

A

Hard so can’t be adjusted easily
If adjusted lose surface glaze
Glaze can’t be replaced
Brittle
Unnatural chattering and clicking on contact
Retention to denture base via diatoric hole on undersurface of teeth (mechanical)
PMMA is forced into retention holes
No chemical bond between teeth and denture allowing teeth to detach during lifetime
Silane can be used to create chemical union but is unreliable

215
Q

What are the contraindications for ceramic teeth?

A

Reduced ridge support as more force is transmitted to the ridge
Need sufficient bulk for strength contraindicated where little interocclusal clearance is present

216
Q

What occurs if the denture teeth are poorly bonded to the denture base?

A

Stress concentrations
Debonding of the tooth
Better quality teeth (highly corss-linked) have a decreased ability to bond

217
Q

How can highly cross-linked teeth achieve a better bond to the denture base?

A

Build the tooth with less crosslinking in the bonding area

218
Q

How to enhance chemical adhesion for a denture tooth?

A

Resin at base of tooth can be softened with a monomer

chemicals must be compatible

219
Q

How can micromechanical retention be achieved for a denture tooth?

A

Roughening

220
Q

Which curing method is better for union between denture tooth and base

A

Heat is better

Cold is other option

221
Q

What can you treat denture teeth to enhance bond strength?

222
Q

What properties must the denture teeth and base share to enable compatibility?

A

Modulus of elasticity
Coefficient of thermal expansion
This prevents crazing and cracking around the base

223
Q

Explain the process of processing of a denture?

A 
Convert the wax prototype into finished acrylic appliance
Invested
Boiled out
Acrylic placed into plask
Cured
Flash removed
Polished
224
Q

How to flask acrylic?

A

Gypsum bonded investment material used such as binder is beta Ca SO4
Low temp

225
Q

Explain the process of flasking during the denture processing process?

A

Waxed up denture is sealed onto a master model
Invested in plaster of PAris in a splint metal flask
Plaster has set the flask is open end and boiling water is used to remove the wax
Done thoroughly to remove all traces of wax
Wax will act as a separator and stop bonding between denture teeth and denture base

226
Q

When flasking what is essential to take care with?

A

Not to disturb any teeth or clasps

Only held by mechanical interlocking or undercuts

227
Q

Why is a separator applied during the flasking stage?

A

Prevents the resin dough impregnating the gypsum which would create a rough surface
Reduces water ingress into acrylic, which would lead to crazing

228
Q

Name an example of a separator and its function?

A 
Na alginate
K alginate
NH3 alginate
Forms an insoluble Ca alginate coating on surface of plaster
Eliminates water ingress
229
Q

What is the definition of a denture adhesive?

A

It is a glue that stick the prosthesis to the supporting oral mucosa
Attempts to improve the retention and function

230
Q

Name the 3 main materials in a denture adhesive?

A

Gelatin
Pectin
Gum

231
Q

How are denture adhesives thickened?

A

With cellulose or a filler such as MgO2

232
Q

What materials can be added to a denture adhesives to give antibacterial properties and reduce surface tension?

A

Hexachlorophene

Na lauryl sulphate

233
Q

Name the 3 presentations of denture adhesives?

A

Paste from tube
Powder
Pads

234
Q

Name 2 commercially available denture adhesives?

A

Fixodent by P&G Oral Health

Poligrip by GSK

235
Q

Why is good denture hygiene important?

A

Bacteria and fungi may colonise the surfaces of a denture

Can cause infection of the soft tissues/damage

236
Q

Name the 3 main materials for a denture cleanser?

A 
Na hypochlorite (kill bacteria and fungi)
Citric acid (breakdown biofilm)
Na perborate (forms an alkaline peroxide solution when in contact with water)
237
Q

What is the function of a dental cleanser?

A

Bactericidal

Fungicidal

238
Q

Name the 3 types of presentations for denture cleansers?

A

Paste
Tablet
Powder

239
Q

What are the side effects of Na hypochlorite on the denture?

A

Bleach denture white

240
Q

Na hypochlorite ratio for denture cleansing?

A

1 tsp to a tumbler of water for 20 mins

Do not use with metal dentures

241
Q

Explain the process of cleaning a denture?

A 
To remove food debris and plaque
Soft brush with cold water
No toothpaste as abrasive
Fill sink with water to reduce risk of shattering
Toilet soap as preference
242
Q

Name 1 commercially available denture cleanser?

A

Milton Sterilising fluid by Milton

243
Q

Name the 8 requirements of a denture base resin for a dentist?

A

Adequate strength to withstand occlusal loading
Easy to manipulate and process
No toxic fumes or dust during processing
Remain unstained and unaffected by fluids and temperature changes in the oral cavity
Simple to repair
Maintain its shape, form and aesthetics in normal function
Biocompatible
Radiopaque

244
Q

Name the 6 requirements of a denture base resin for patients?

A

Fit well and be comfortable in use
Not traumatise the tissues
Easy to clean
Aesthetically pleasing both immediately on placement
and in the longer term
Allow good heat diffusion to retain normal perception
of thermal stimuli
Permit food to be tasted normally so that food can
remain appealing

245
Q

What is the GS denture base material?

A

PMMA

Polymethymethacrylate

246
Q

Name the 4 formulations of PMMA?

A

Gel
Sheet
Blank
P:L

247
Q

How is PMMA formed?

A

Polymer formed from the addition reaction of monomer methylmethacrylate

248
Q

What advantages does PMMA have in a powder and granule formulation?

A

Increases SA:V enabling more mixing

150um

249
Q

Name the 6 chemical constituents of PMMA and their functions?

A 
(Poly)methylmethacrylate (principal component)
Benzoyl peroxide (initiator)
Ti/Zn oxide (increases opacity)
Inorganic pigments
Mercuric sulphide
Cadmium sulphide
Ferric oxide
(varies colour, respectively:
Red, Yellow. Brown)
Dibutyl phthalate (plasticiser)
Dyed synthetic fibres –
nylon or acrylic
(simulate anatomical
structures such as
capillaries within the
denture base material)
250
Q

What is the alternative to dibutyl phthalate and why is it needed?

A

Potential carcinogen

Citrates or benzoate esters

251
Q

What must you ensure not to happen with the PMMA powder?

A

Not contaminated as a small amount will activate the reaction

252
Q

What is MMA?

A 
Liquid monomer
100.3C BP
Toxic if inhaled for long time
Flammable
Well-ventilated room
253
Q

What are the 4 chemical constituents of MMA and their function?

A 
Methylmethacrylate (monomer)
Hydroquinone (inhibitor – prevents monomer polymerising during storage
Ethylene glycol dimethacrylate
(substituted for the main
monomeric component)
(cross-linking agent)
Dibutyl phthalate, butyl
and octyl methacrylate
(plasticizer)
254
Q

What chemical can be added to MMA to act as an accelerator?

A

N,N dimethyl p-toluidine
N,N-dihydroxyethyl-p- toluidine
Undergo cold curing polymerisation

255
Q

What can methylmethacrylate be substituted for to remove irritation?

A

Ethyl and butylmethacrylate

256
Q

What is the function of hydroquinone?

A

React with any random free radicals to prevent premature reaction from UV or free radicals
Produces stabilised free radicals

257
Q

How to improve the wear, fracture resistance, cracking and crazing of PMMA?

A

By adding cross-linking polymers such as diethylene glycol dimethacrylate
Different monomer units can react with another growing chain, therefore linking the chains

258
Q

What are the role of plasticisers in the PMMA/MMA mixture?

A

Vary mechanical properties
Prevent interaction between polymer molecules
Causes problems when plasticiser runs out the denture becomes harder and can migrate into oral fluid

259
Q

What are the biocompatibility of phthalates?

A

Poor
Carcinogenic
Look for alternative plasticisers such as esters octyl or butyl methacrylate
Methacrylates less likely to leach, but failure of polymerisation will causes leaching and hardening of denture base

260
Q

How should PMMA sheets be stored?

A

sheets are stored in the refrigerator in

the dark before heat processing in the normal way

261
Q

Name the 3 types of PMMA acrylic polymerisation methods?

A

Cold
Chemical
Self-cure

262
Q

Explain the setting reaction of a PMMA acrylic resin?

A

Initiated by an organic peroxide such as benzoyl
peroxide
Free radicals produced either by heating or reacting with a chemical accelerator such as
an organic amine
Highly exothermic reaction
Heat is slow to dissipate as processing is carried out in a plaster mould

263
Q

What causes gaseous porosity of PMMA acrylic resin?

A 
Temperature must be
carefully controlled as the
volatile monomer may
vaporise during
processing
Gas bubbles may be
produced and can
become entrapped in the
denture base resin
264
Q

How much polymerisation shrinkage occurs for PMMA acrylic?

A

Shrinkage equates to 6% for the recommended 3:1
polymer:monomer mix
Dimensional change must be compensated for during the manufacturing process otherwise the final denture or appliance will not fit
Internal strains are set up within the material as a result

265
Q

What are the mechanical properties of PMMA?

A

Low tensile strength
Low elastic modulus
Flexes in use (fracture overtime, due to cyclic loading - fatigue fracture)

266
Q

What does cross-linking ensure for the structure of PMMA?

A

Cross-linking agents help to ensure that there is a
network of molecules rather than long chains or
branched chains that reduce the strength of the final material

267
Q

What is the fracture toughness of PMMA acrylic?

A

Low

Brittle on impact

268
Q

What are the thermal properties of PMMA?

A

High coefficient of thermal expansion
Low glass transition temp
Low thermal conductivity
Low thermal diffusivity

269
Q

Why can low glass transition temp be problematic with ceramic teeth?

A

Due to the difference in coefficient of thermal expansion

Ceramic teeth may be lost due to variations in contraction and expansion of the materials during thermal cycling

270
Q

What consequences do low heat diffusivity and gaseous porosity cause to the patient?

A

Hot food sensation reduced

Oral mucosa become less keratinised (unprotected)

271
Q

Describe the dimensional stability of PMMA?

A

PMMA absorbs fluid, causing expansion by 2%
Polymer shrinkage compensated for expansion
Keep denture wet as drying out can cause shrinkage and crazing
Water sorption cause discolour and stain
Colour stability is good

272
Q

What is the GS P:L ratio for PMMA acrylic?

A

Heat-cured process, powder:monomer ratio should be about 3

or 3.5:1 by volume or 2.5:1 by weight

273
Q

What occurs if the polymer to monomer ratio is too high for PMMA?

A

insufficient monomer

to wet the polymer a granular resin structure results

274
Q

What occurs if the monomer ratio is too high for PMMA?

A

Increased shrinkage

275
Q

What problems arise from residual monomer presence?

A

Irritant to oral soft tissues

Acts as a plasticiser softening the polymer

276
Q

What problems are caused by the plasticisier softening the denture polymer?

A

Denture base weaker and more flexible
Fracture may result
Polymer may creep under load over the long term and
deform the denture base
More marked with cold-cure acrylics and can create greater problems
Crosslinking agents may be added in an attempt to minimize this effect
Loss of material due to water solubility is low.
Presence of organic solvents such as alcohols and chloroform has an adverse effect on methacrylates

277
Q

What is the definition of crazing and what causes it?

A

Fine cracks on the surface of the acrylic
Localised areas of plastic deformation of the polymer
caused by stress relief of internal strain

278
Q

What is the definition of crack and what causes it?

A

Crack is formed as a result of brittle fracture as the walls of voids in the region are thin in the region of the fracture
Crack grows under externally applied load eventually leading to a
continuous crack
Areas filled with microscopic voids and a crack may result if the crazed area can no longer support stress

279
Q

What do tensile stresses cause in PMMA dentures?

A

Tensile stresses will also cause rupture of the polymer chains leading to a weakened denture

280
Q

What are the 4 causes of crazing?

A

Heat
Action of organic solvents
Differences in coefficients of thermal expansion around (dissimilar) inclusions that form stress concentrations
Loss of moisture (contract and expand during dry at wet cycle - reduced by crosslinking)

281
Q

Name 3 ways to prevent crazing of PMMA dentures?

A

Not allowed to dry out
Finished denture always supplied in water
Patient advised to store in water

282
Q

How are small BVs mimicked in a denture base?

A

Small fibres of red acrylic

283
Q

What shades are denture bases?

A

Mucosa-coloured

284
Q

How to increase wettability of the denture base?

A

Triethoxysilane

285
Q

When would clear acrylic be used for a denture?

A

Improved appearance for more discerning patient

Processed in 2 stages

286
Q

How is radiodensity created in a PMMA denture?

A

Originally radiolucent

Achieved by addition of 10-15% bismuth or uranyl salts

287
Q

What are the detrimental effects of increasing radiopacity?

A

Increasing transverse deflection
Increasing water sorption
Handling of the unset polymer more difficult

288
Q

What are the 6 other properties of PMMA?

A 
Low density
Light weight
Easier to wear
No taste or smell
Cheap
Easy to process
289
Q

Name the 5 types of acrylic (based on means of curing)?

A 
Heat cured
Cold cured
Light cured
Injection technique
High impact
290
Q

Explain the process of formation of heat cured acrylic?

A

Polymer and monomer are mixed to form a sand like mixture initially
Becomes tacky as polymer starts to dissolve
Left in container until dough stage is reached

291
Q

What is the dough stage for heat cured acrylic?

A

Does not stick and snaps when pulled apart

Failure to pack the mixture into the mould at the dough stage will result in the material becoming too ribbery and stiff

292
Q

What factors affect the time to achieve dough time?

A

Particle size of the polymer - smaller the bead diameter, the more rapidly the dissolution of the bead in the monomer, reaction
therefore proceeds more quickly
Molecular weight of the polymer - lower molecular weight, faster the reaction will proceed
Higher temperature produces a quicker reaction
Presence of a plasticiser - reduces the dough time
Polymer/monomer ratio - higher ratio, shorter the dough time
Type of polymer – permeation of the monomer is greater with a
granular polymer, dissolves more readily and reaction time is quicker

293
Q

How to add colour to the acrylic?

A 
Added colouring agent
Can be added to polymer beads or powder
Little needed as intense
If colour agent on polymer bead surface add slowly to the monomer
Can lead to streaking
294
Q

Explain the process of processing of heat cured acrylics?

A 
Excess of acrylic
dough is placed into
the part of the flask
containing the teeth
Flask is closed and
placed into a press
Pressure applied so
that the dough is
forced into all parts of
the mould
Excess is expressed
out of the press
295
Q

How to avoid shrinkage porosity?

A

Excess of acrylic dough is required otherwise
shrinkage porosity will result
Placed into the flask with a thin polythene sheet
Flask is opened and the excess removed
Known as trial packing
May be repeated several times until no excess is
expressed
At last closure the polythene sheet is removed with any residual excess

296
Q

Explain the process of heat-cured processing?

A

Essential that sufficient acrylic dough is tamped
into place and remains under pressure during
the processing
Otherwise any air voids incorporated during the
packing will not collapse
Leads to a source of porosity and weakness
Flask is finally closed and placed under pressure
in a water bath most commonly 73°C for 8 hours
or longer
Normally carried out in the laboratory overnight
for convenience
Temperature of the water bath is slowly raised to reduce the risk of the monomer vaporising otherwise gaseous
porosity may occur
Near complete conversion of the monomer results with a minimum amount of unreacted monomer remaining
When polymerisation cycle is complete, flask is removed from the water bath and allowed to cool slowly at room
temperature before being opened
Slow cooling prevents stresses forming by plastic
deformation within the polymer as there is a difference of
contraction between the gypsum and acrylic
Also allows some stress-relieving flow of the material
Higher the curing temperature the acrylic is more likely to
distort due to more residual stress

297
Q

What temperature is necessary for processing of heat-cured acrylic?

A

Monomer heated will become vapourised
Polymerisation is exothermic so flask hotter than water bath
Slow processing to allow dissipation
Gypsum absorbs heat
Follow manufacturer’s processing instructions

298
Q

Explain the process of divestment of the PMMA denture?

A

Denture carefully removed from the gypsum model avoiding flexure and breakage
Acrylic flash removed and non-tissue bearing surfaces are polished

299
Q

Explain the process of polishing the PMMA denture?

A

Soft brown rubber points used
Kept moving to stop heat burning or distorting the denture
Fibres removed using sharp scalpel blade
Stain resistance can be problematic
Heat can cause denture to melt, can change properties

300
Q

Explain what you would use to finish the PMMA denture?

A

Finish with rubber points and wheels or
sandpaper
Pumice slurry:
- crushed porous volcanic stone that is a
highly siliceous glass
- slurry should be made up with water to a thin
paste
- moved quickly over the surface at high speed
to prevent the build up of heat

301
Q

Explain what you would use to polish the PMMA denture?

A

Tripoli
Calcium carbonate (whiting or precipitated
chalk) used in suspension with water

302
Q

What other dental appliances are constructed with acrylic?

A

Occlusal splints

303
Q

Explain the injection technique for denture formation?

A

Designed to maintain pressure on the
acrylic as it cures in an attempt to overcome the large volumetric shrinkage of PMMA
Wax sprue which is added to the denture
Denture is flasked and the wax boiled out
High pressure injection cylinder is connected to the flask
Acrylic is mixed and placed into the cylinder.
Injected into the mould under pressure when at the
desired consistency
High pressure is maintained during the polymerisation
reaction so more material is pushed into the flask to
compensate for the polymerisation shrinkage

304
Q

Give an example of an commercially available injection moulding system?

A

Ivoclar vivadent

305
Q

What is added to PMMA to create a high-impact acrylic?

A

Butadiene-styrene rubber (reinforcing agent) is
added to confer some resistance to fracture
Rubber particles are grafted onto the MMA to
become incorporated into the acrylic matrix
Powder liquid presentation
Processed like hear cured
Longer lifespan and performance
More expensive

306
Q

What is the initiator for a cold-cured acrylic?

A

Tertiary amine

307
Q

What is the catalyst for a cold-cured acrylic?

A

N,N dimethyl-p-toluidine

Sulphinic acid are

308
Q

What is present in TII cold cure resin powder and liquid?

A 
Powder:
- polymethylmethacrylate
- benzoyl peroxide
- Pigments 
Liquid:
- methylmethacrylate
- di-n-butylphthalate
- amine
309
Q

What is present in TII cold cure resin powder and liquid?

A 
Powder:
- polyethyl methacrylate
- benzoyl peroxide
- pigments
Liquid:
- butyl methacrylate
- amine
310
Q

Indications for TII cold-cured acrylic?

A

MMA hypersensitive patients

311
Q

What is difference between TII and TI cold cured acrylic?

A

Less irritant to soft tissues
Softening temp is lower to 67C rather than 90
Greater risk of distortion

312
Q

Describe the polymerisation efficiency of TII cold cured acrylic and what does this cause?

A

Residual monomer remains
(3–5%) as polymerisation process is less efficient than heat-curing
Due to the lower molecular weight
of the polymer chains and the lack of
propagation of the chain during the polymerisation process
Residual monomer acts as a plasticiser
which softens the material
Inferior mechanical properties result
Eventually properties achieve same level as heat after all leached out
Leaching on oral mucosa is a cause of irritation
Polymer beads smaller to facilitate the monomer dissolving the polymer

313
Q

Why does TII cold cured acrylic have problems with porosity and how to minimise it?

A

Due to air dissolved in the monomer which is not
soluble in the polymer at room temperature
May be reduced by polymerising the material
under pressure
Need excess material within the mould to ensure
that the prosthesis will remain under pressure
during the curing process and ensure that porosity is minimised

314
Q

What are the mechanical properties of cold cured acrylics?

A

Cold cured acrylics are not as strong as those
that are heat cured (c80%)
Due to lower molecular weight of the formed
polymer so less conversion of the monomer to
polymer occurs
More initial deformation and creep
Slower recovery seen
Less build up of internal strain occurs as no
external heat source is used

315
Q

Describe the stability of cold-cured acrylics?

A

Poorer long-term colour stability due to presence
of tertiary amine
Only 0.1% dimensional change seen on
polymerisation
Due to the reduced level of conversion of the
monomer
Greater exothermic reaction than heat-cured
materials due to an excess of initiator
Initiator which contributes most significantly to
the exothermic reaction

316
Q

What are the indications for cold cured acrylics?

A

Removable orthodontic appliances
Minor denture repairs or relines (laboratory)
Chairside relines

317
Q

Describe light-cured acrylic presentation and constituents?

A

Cured by the application of visible light energy
Presented as a prefabricated sheet of material
which can be adapted to the surface of a model
Urethane dimethacrylate and high molecular
weight acrylic resin monomers are blended with an organic filler of acrylic beads

318
Q

How to improve handling for light cured acrylics?

A

Microfine silica is added to optimise handling
Forms an interpenetrating polymer network when
cured

319
Q

Explain the setting reaction for light cured acrylics?

A

Camphorquinone, accelerator (amines) and
pigments are also required
Supplied fully compounded in a light tight package
Technician lays down the material on the model or
denture being constructed or modified, moulding it
into the desired shape
Placed into a light box and cured for c5–10 minutes
Surface of the material must be treated with a
barrier chemical such as carboxymethylcellulose to
prevent oxygen inhibition of the polymerization
reaction as process is carried out in air

320
Q

Indications for light cured acrylics?

A

Baseplates of the denture on which a
conventional PMMA suprastructure is added
Orthodontic appliances
“Gum work” portion of metal-based partial
dentures
Repair of fractured acrylic dentures
Hard relines
Construction of special (impression) trays

321
Q

What is a flexible denture?

A

Biocompatible nylon
thermoplastic
Claimed to be flexible and
unbreakable

322
Q

Name 2 commercially available flexible dentures?

A

Sunflex partials

Valplast flexible partials

323
Q

Indications for flexible dentures?

A

Allergic to MMA

324
Q

Explain the process of formation of a flexible denture?

A

Denture is placed in very hot water for a minute prior to placement to fit the denture initially or if clasp adjustments are required
Thermoplastic material so will soften and on cooling gain its new shape
Nylon material is microscopically porous so aesthetic issues arise in
use as the denture base is more difficult to adjust and polish

325
Q

What problems can occur when using dental stone casts and an articulator?

A

Continuous expansion
Lose accuracy
Add something to stop it AE8

326
Q

Which materials to use when flasking a CD?

A

Plaster of Paris for the base
Na alginate as the separator
Dental stone as the topper

327
Q

What is the ideal space between the tray and the dental arch?

328
Q

Name 3 things metal files aim to remove?

A

Necrotic material from lumen of canals
Hard tissue from canal walls
Microorganisms that have penetrated dentinal tubules

329
Q

Name 3 barriers to fully cleaning the root canal system?

A

Complex anatomy
Biofilm
Smear layer

330
Q

What makes complex root canal anatomy hard to clean?

A

Many connection

Complex at apical 1/3

331
Q

What is the definition of biofilm?

A

Dense aggregate of cocci, rod and filamentous forms embedded in an ECM on the root canal walls
Can colonise:
- necrotic material in lumen of RC
- in dentinal tubules

332
Q

How to remove biofilm before RCT?

A

Mechanical removal via instrumentation and irrigation

Not easily disrupted

333
Q

What is the definition of the smear layer?

A

1-2um thick, amorphous, irregular and granular on dentinal surface
Composed of inorganic and organic particles, coagulated proteins, pulp tissue, blood cells and microorganisms
Caused by instrumentation of the canals

334
Q

Explain the process in removing the smear layer?

A

By using chelating agents
Recommend to remove as:
- remove bacteria and nutrients
- it impedes irrigation

335
Q

Name the 8 functions of endodontic irrigants?

A

Lubricate files to facilitate passage into canal
Wet canal walls and flush debris
Contain any dentinal shavings in suspension so facilitating their removal from canals (prevents apical impaction of debris)
Facilitate dissolution of organic mater
Remove smear layer
Aid cleaning of area inaccessible to mechanical cleansing methods
Disinfect RCS
Neutralise endotoxins

336
Q

Name the 2 groups of endodontic irrigants?

A

Clean and expose bacterial contaminates

Used to disinfect RCS

337
Q

Name 2 irrigants for cleaning?

A

EDTA

Citric acid

338
Q

What is the definition of citric acid?

A

Chelating agent
Removes calcified tissue and detach biofilms from root canal walls
10-50%

339
Q

What is the definition of EDTA?

A 
Synthetic aa or Na salt of EDTA
ethylenediamine tetra-acetic acid
Demineralise and soften root canal wall dentine by 20-50um
Neither cidal or static
Kill bacteria by starving from metal ions (chelates metal ions)
Non-toxic
Non-corrosive
Not effective against smear layer alone
15-17%
Never mix with NaOCl
340
Q

Name a commercial product of EDTA?

A

ENdo-Solution EDTA Cerkamed dental-medical

341
Q

What is the function of EDTA gel?

A

Coat endodontic files
Lubricate and removes smear layer making canal prep easier and faster
Increased viscosity is better for holding debris in suspension

342
Q

What is the definition of EDTA gel?

A

Contains carbamide or urea peroxide causing effervesce
Elevator action helps to remove debris
Bubbles when in contact with NaOCl
Oxygen kills anaerobic bacteria

343
Q

Name a commercially available EDTA gel?

A

Glyde File Prep
Dentsply Maillefer
EDTA + carbamide peroxide

344
Q

When should you not use chelating materials?

A

Initially to negotiate canals as a false can may be cut iatrogenically

345
Q

How should you use chelating materials within the root canals?

A

Thoroughly washed from RCS as retention will continue softening the dentine
Are self-limiting
Chelating + disinfecting irrigant
Provides a cleaner surface

346
Q

Name 4 types of irrigants for disinfection?

A

NaOCl
Iodine potassium iodine
Chlorhexidine
Other potent phenolic disinfecting agents
High bactericidal concentrations close to toxic dose

347
Q

What is the definition of NaOCl?

A

Potent organic tissue solvent that is proteolytic and dissolves necrotic organic material
Releases free CL which has bactericidal effects
Cl breaks peptide bonds dissolving proteins into aas
Aas degraded by hydrolysis by chloramine mol
Chloramines are antibacterial
Oxidising and hydrolysing agent
pH> 11
No effect on smear layer (Ca)
High pH denatures proteins
Hydroxyl ions damage bacterial lipid and membranes + DNA

348
Q

Explain how to use NaOCl?

A

Breaks down components during use
Must be replaced as i loses its efficacy
Dwell time of at least 30 mins
Biofilm must be disrupted to reach bacteria
Canal must be flushed long after canal prep has ceased for this disinfectant to be effective

349
Q

What are the components of the NaOCl solution?

A

No diff between 0.5-5% solutions for antibacterial effects
But efficiency of weak solutions decreases rapidly
High conc disinfecting process is faster, untoward damage can occur, as it is more toxic
More effective if solution is warmed, as more Cl is released

350
Q

What are the characteristics of NaOCl?

A

High surface tension than water, so does not wet canal well
Walls are not fully covered and the full biofilm may not by disrupted
Higher conc = thicker sol
Not effective at killing all microorganisms
Enterococcus faecalis can’t be killed

351
Q

When using NaOCl, what should you be wary about?

A

Bleaching clothes
Unpleasant taste
Irritant to eyes, skin and oral mucosa
Bleaching will lighten any stained tooth tissue

352
Q

Name 2 commercially available NaOCl?

A 
Parcan Sol (Septodont) 3%
Chlorax (CerKamed Dental-Medical) 2% or 5.25%
353
Q

What instrument to be used with NaOCl?

A

Ultrasonic instrument

Acoustic streaming enhances cleaning effect

354
Q

What are the side effects if disinfecting irrigants come in contact with anything bar root canals?

A 
Severe inflammation + tissue necrosis
Neurological damage
Facial atrophy
Anaphylaxis
Airway problems
355
Q

What are the clinical manifestations for extracanal extrusion of endodontic irrigants?

A 
Immediate serve pain
Profuse bleeding from within canal
Rapid swelling and Oedema
Ecchymosis
2nd infection
Paresthesia
Persistent pain
356
Q

Explain the 9 step process the manage extracanal extrusion?

A
  1. Stop irrigating and consider giving additional LA
  2. Immediate irrigation with sterile water or saline for 5-10 mins
  3. Dress root canal with non-setting CaOH and access cavity
  4. Analgesic advice (paracetamol 500mg)
  5. Prescribe antibiotics only if signs of systemic involvement
  6. Consider referral to oral and maxillofacial specialist for special care
  7. Fully inform patient of event and the potential sequalae
  8. Write up detailed notes
  9. DATIX form
357
Q

Explain how to reduce the risk of extracanal extrusion?

A

Use a side exiting endodontic irrigating needle
Do not bind tightly in the canal so that irrigating fluid may pass in a coronal direction
Keep needle and syringe moving while performing, slow and gentle irrigation
Use finger pressure

358
Q

What is the definition of Chlorhexidine digluconate?

A 
Cationic bis-biguanide
Wide bacterial range (greater than NaOCl)
static at 0.2% cidal at 2%
Causes cell wall decomposition leading to loss of cellular components
Not dissolve organic tissue
Negative healing effect
Increases odds of failure
Result in anaphylaxis
359
Q

Why is Chlorhexidine digluconate better than NaOCl?

A

Kills microorganisms that NAOCl can’t

Safer

360
Q

Explain how chlorhexidine digluconate works?

A

Binds to hydroxyapatite on the root canal walls
Used as final soak
Good substantivity of about 12 hrs after application

361
Q

What reaction occurs between Chlorhexidine digluconate and NaOCl?

A

Acid-base reaction seen with NaOCl forming an insoluble precipitate 4-chloroaniline
Stains dentine
Carcinogenic
Difficult to remove (can block canals)
Can be overcome by irrigating with sterile water
CHX breaks down when heated to form PCA

362
Q

Name 2 commercially alleviable chlorhexidine digluconate products?

A

R4 (Septodont) 20% in denatured alcohol

Gluco-Chex 2.0% (Cerkamed Dental-Medical)

363
Q

Name 2 forms a chlorhexidine digluconate gel?

A

Hibiscrub (Regent Medical) 4%

Gluco-Chex 2.0% Gel (Cerkamed Dental-Medical)

364
Q

What is the definition of Iodine Potassium Iodide?

A 
Organic and releases iodine
Iodine is a potent antibacterial agent with broad spectrum action
Bact/fung/tuberculo/vuru and sporicidal
Effective for 2 days
Penetrate dentinal tubules
365
Q

Explain how Iodine Potassium Iodide works?

A

Attacks proteins, nucleotides and FAs leading to cell death

Low tox, but patient allergic to iodine

366
Q

What is the formulation of Iodine Potassium Iodide?

A

Irrigating sol 2% iodine in 4% aqueous potassium iodide such as Videne (Adams)

367
Q

What is the definition of H202?

A

Degrades to form water and oxygen producing hydroxyl free radicals
Effective against bacteria, yeasts and viruses as it attack the proteins and DNA
Not reduce bacterial load in RCS significantly
Oxygen may penetrate into periarticular tissues causing surgical emphysema due to effervesce
Not used in contemporary endo

368
Q

What is the definition of hypochlorous acid?

A

Less toxic than NaOCl
Similar to NaOCl
Dissociates in sol into hypochlorite ions but the reduced level of discolouration compared to NaOCl means that any adverse effects are reduced
NaOCl is more efficient as more Cl is available between the sol of same conc

369
Q

What is the definition of electronically activated water?

A

Sol of hypochlorous acid
Generated via process of electrolysis from water and NaCl by an electrochemical device
Safer than other solution as if less irritant if extruded into he periradicular tissues
Cidal
pH 5-7
Sterilox

370
Q

Name and give characteristics of non-active irrigants?

A 
Sterile water
LA solution
Lubricate files and carries sward in sol
No disinfectant prop
Not recommended for sole irrigant
371
Q

What is the definition of a co-irrigant?

A

More than 1 irrigant to enhance effect
Usually consist of an acid or chelating agent + NaOCl
dissolve smear and assist in biofilm destruction + disinfect

372
Q

What is the definition of Ozone?

A

Sterilising of water supplies
Sterilising agent
Effective and toxic dose very close
Gas delivered down a handpiece

373
Q

Explain how the Ozone device works?

A

Area sealed from the surroundings and residual gas is drawn back to the generator and neutralised using a Pl filter
Deliver ozone down fine tip directly into canal for very short time

374
Q

Name 2 device names for Ozone?

A

Healozone CurOzone

Prozone W%H

375
Q

What is the definition of bacterial photodynamic therapy?

A

Impossible to consistently disinfect enter RCS due to:
- anatomy
- disinfectants are ineffective against some organisms
Combo of photo-sensitiser and specific wavelength is effect against all oral microorganisms

376
Q

What is the definition of a photo-sensitiser?

A

Different wavelengths of activation
Tolonium Cl (relative of toluidine blue O)
Conc between 13-80 ug/ml
Lower surface tension so can wet and penetrate into the dentinal tubules
No problem with extracanal extrusion

377
Q

What is the definition of a light source?

A 
Laser diode or LED
Red light at 635nm +/- 2nm
Light exists photo-sensitiser mols
Minimal heat
Light delivered via a tapered endodontic tip
378
Q

Explain the mechanism of action for Bacterial PDT?

A

Photo-sensitiser is preferentially taken up by rapidly dividing cells such as microorganisms
Chemical must be in contact or in very close proximity to bacteria
Taken up by the liposomes on cell walls
When light energy is applied photo-sensitiser
molecule becomes excited and free oxygen radicals
produced
Singlet oxygen species is a protoplasmic poison
which causes oxidative injury to bacterial cell wall
Leads to death of microorganism
Photo-sensitiser returns to its unexcited state -
causes no further effect when light switched off
No collateral damage seen to any surrounding
tissues
Resistant strains cannot be build up
Both light and photo-sensitiser are ineffective
when used separately.
Also viricidal and fungicidal

379
Q

Name 2 commercially available bacterial PDT?

A

CumdentPACT
Cumdente Dental Concepts Laser diode
PAD Plus Denfotex Research LED

380
Q

What is the aim of root canal preparation?

A

Remove as many microorganisms as possible
Shape root canal to provide a uniform sized dead space to facilitate its subsequent obturation using stand sixed cones of plastic material and its adaptation to root canal walls to achieve a seal
Avoid ledges, perforations zips and canal transportation

381
Q

What are metal files used for?

A

Remove:
- necrotic material from lumen of root canals
- hard tissue from root canal walls
- microorganisms that have penetrated dentinal tubule
Facilitate penetration of disinfecting agents so they reach the microorganisms in RCS

382
Q

What force to files exert onto the RCS?

A

All files tend to straighten within a curved canal and exert a lateral force on the root canal wall

383
Q

How can files be different?

A 
Shape
Tapers
Length
Cutting
Non-cutting tips
Sade edged
Colour/number coded
384
Q

name 2 types of endodontic files?

A

Hand - composed of stainless steel or nickel-titanium

Rotary - only nickel-titanium in a speed-reducing, torque controlled handpiece

385
Q

Describe the anatomy of an endodontic file?

A

Both have cutting edges along the length of the file
Handle/attachment for drill
Silicone stop

386
Q

Explain how the cutting edge of the endodontic file cuts?

A

Cuts when its radial lands are in contact with canal wall
Lead angle determines cutting efficiency
Radial land areas required for conventional helically fluted files because they prevent the file from over-engagement in the canal
Lock of radial land areas reduces friction
File may fracture if suddenly engaged
Radial lands are important for files that have +ve rake angles
Designed so that radial lands can’t screw themselves into wall
Debris directed towards coronal canal so not compacted apically

387
Q

What is the definition of a rake angle?

A

Angle of action of the cutting blade us similar to a snow plough which is forces downwards towards surface of road

388
Q

What is the definition of stainless steel files?

A

Alloy of iron, carbon and chromium + nickel
Forms an invisible passivation layer of chromium oxide on surface when exposed to air
If scratched, code later rapidly reforms preventing degrade
Prevents rusting in presence of water

389
Q

How are stainless steel files manufactured?

A

Machine shaped directly from a stainless steel wire
Machined into a blank of the desired shape
Greater # of twists greater the work hardening

390
Q

What are the stainless steel file properties?

A

Do not bend easily
Bend file prior to introduction
Bending instrument will further work harden the metal making it more brittle leading to fracture

391
Q

What is the definition of a nickel-titanium files (NiTi)

A

500% more flexible than stainless steel and 3 times stronger
Corrosion resistant
Hand and rotary instruments available

392
Q

What are the 2 NiTi temperature dependent crystal structures?

A

Austenite - high temp or parent phase, cubic structure

Martensite - low temp, monoclinic structure

393
Q

What are the properties of NiTi alloy?

A

Superelasticity and shape memory effect
Occur due to austenite to martensite transition induced by stress or temp (martensitic transformation)
Under certain other condition other phase my be present (R-phase)

394
Q

What is the definition and properties of austenite NiTi alloy?

A

Superelasticity due to austenite NiTi
Austenite can be transformed to martensite by stress, termed stress-induced martensite transformation
Allows complete recovery of deformation up to 8% strain
Stress-induced martensite state is not stable so retransformation back to austenite phase so spring back to original shape
Lower elastic modulus than stains steel
Higher torque values at fracture

395
Q

What are the indications for Austenite NiTi files?

A

Shape straight or slightly curved canals
Pathfinding instruments as compensation for the decreased torque resistance caused by small diameter files
Profile

396
Q

What is the definition and properties of martensitic NiTi alloy?

A

Softer and more ductile than austenitic
Easily deformed and exhibits shape memory effect when heated
Pseudoplastic
Fatigue crack growth resistance is higher than stable austenite
Hyflex

397
Q

What are the properties of gold and blue heat-treated instruments?

A

Heat treat martensitic alloy
Blue colour due to titanium oxide left after heat
Controlled memory effect
Enhanced flexibility and cyclic fatigue resistance compared with conventional NiTi and M-Wire
Greater angle of rotation but lower torque at fracture
Preferred un serve curved canals
Pre-bendable to bypass ledges

398
Q

Name 2 commercially available gold/blue heat treated instruments

A

Rotary system: ProTaper Gold (Dentsply Sirona)
• Reciprocating motion: Reciproc Blue (VDW) &
WaveOne Gold (Dentsply Sirona)

399
Q

Explain the manufacturing process of NiTI endodontic instruments?

A

Conventional NiTi alloys are ground to make files opposed to twisted
Lead to defects n the surface so potentially causing decreased fracture resistance, cutting efficiency and corrosion resistance
Electropolishing sometime used to remove surface defects causing by grinding (improves above problems)

400
Q

Explain how to choice between different endodontic files?

A

Rotary systems are much more efficient than
hand techniques
• Hand files sometimes preferred to negotiate very
curved root canals although newer rotaries may
be used these days
• Engine driven NiTi endodontic instruments result in significantly less canal transportations
compared to stainless steel hand instruments
• Selection of material of which file is made and its
method of construction is critical in determining
performance of instrument

401
Q

What factors do stainless steel endodontic files depend on?

A

Composition of material
Geometry of file
Way in which it is loaded

402
Q

What are the contraindication for use of a stainless steel endodontic file?

A

Anticlockwise twisting as this increases twisting resulting in brittle fracture
NaOCl and EDTA reduce cutting ability so files should be rinsed
Long prep times prolong immersion of instruments in these solutions in the canal and start process of degrad

403
Q

Name 3 ways a file may break?

A

Sharp curve - cyclic fatigue
Overuse - flexural fatigue
In rotation while instruments is prevented from moving - torsional fatigue

404
Q

What is the definition of torsional stress? how to reduce it?

A

Evert cutting action in the canal

Torque controller so that the rotation of file is stopped prior to receiving excessive torque

405
Q

Explain the decontamination process for endodontic files?

A

Debris retained on file after use is called swarf
• May contain neural tissue with prions
• Proteins that cannot be destroyed by the usual
methods of surgical disinfection
• Theoretically associated with new-variant
Creutzfeldt–Jakob disease ( nvCJD )
• Endodontic files should therefore be considered as
single use
• Incidence of instrument separation is decreased
• Autoclaving can decrease the cutting ability of some
files and may result in metal fatigue

406
Q

What are the 2 parts for inter-visist temporisation?

A

Canal medicaments

Temporary dressings

407
Q

Explain why inter-visit temporisation is necessary?

A

Signs/symptoms
Further opportunity to disinfect the RCS by placing a medicament with antimicrobial prop
Cases which require root formation to complete

408
Q

Name 6 types of inter-visit canal medicaments?

A 
Steroid/antibiotic combo
Non-setting CaOH
Chlorhexidine
Phenol or derivatives
Halogens
Formaldehyde
409
Q

Indications for steroid/antibiotic paste?

A

Irreversible pulpitis

Intracanal dressing between appointments

410
Q

Name 1 commercially available steroid/antibiotic paste and its constituents?

A

OdontoPaste (Australian Dental Manufacturing)
Ledermix

Constituents:

  • Clindamycin hydrochloride 5%
  • triamcinolone acetonide 1%
  • CaOH
411
Q

Explain how the steroid/antibiotic paste works?

A

Acts topical only killing bacteria adjacent to vital tissue
Steroid suppresses any inflamm response
Permits bacteria at a distance from surface of lesion to proliferate - leads to death of pulp

412
Q

Why can endodontic steroid paste be useful for irreversible pulpitis?

A

When sufficient analgesia can’t be gained to fully extirpate vital tissue
Only effective when it is in contact with vital tissue so rational is debatable

413
Q

What are the pros of using steroid/antibiotic paste + non-setting CaOH?

A

Ledermix
Synergistic
Placed separately - too viscous
Place steroid/antibiotic paste on a paper point to carry it into canal followed by syringing non-setting CaOH

414
Q

Give a description of non-setting CaOH?

A

Intracanal medicaments
Active chemical provided as a slurry in a water base
Methylcellulose based
Facilitate removal of the products from the canal
Radiopaque
pH is 12

415
Q

Explain how non-setting CaOH works?

A

Bactericidal:
- slow acting antimicrobial agent has therapeutic effect after being in situ at least a day
- effective disinfection in most cases of infected necrotic cases seen in a week
Neutralises acidic endotoxins
Inhibits osteoclastic activity due to high pH - useful in cases of inflamm root resorption
Hydrolyses lipid component of bacterial LPS - renders bacteria inactive and reduces toxic effect from debris
Denatures proteins in RCS
May activate CA-dependent adenosine triphosphate reaction assoc with hard tissue formation stimulation periradicular healing

416
Q

Name the 6 indications for non-setting CaOH?

A

Inter-visit intracanal medicament - disinfect canal system
Controls exudation in persistent infection
Partial pulpotomy - create a calcific barrier to maintain vitality of tooth
Apexogenesis - continue root formation in vital tooth
Apexification - induces apical closure of non-vital immature teeth
- dressing replaced every 6 weeks until hard tissue barrier forms
Resorption - inhibits activity of osteoclasts die to high pH so arresting inflamm process

417
Q

Name the 3 contraindication for non-setting CaOH?

A

Cause calcification of canal if left in situ > 6 month

Increases risk of root fracture due to denaturing the collagen

418
Q

What is the mode of delivery of non-setting CaOH?

A

Past inside a tube
Fine endodontic Needle (Navvi tip) attached to a Luer lock syringe
Deliver paste into canal
Consistency of paste must be as thick as possible to fill RCS
Can be difficult to remove
Effectively removed with citric acid or EDTA as alkaline CaOH reacts with acid

419
Q

Name 1 commercial produce for non-setting CaOH?

A

UltraCal by Ultradent

420
Q

What are the advantages of non-setting CaOH PLUS points over non-setting CaOH?

A 
Greater release of CaOH and so more effective
Points ready to use 
No mixing
Easy to apply and remove
No smearing
421
Q

Give a description of chlorhexidine?

A

Incorporated into gutta percha
Activ point (Roeko) is a 5% chlorhexidine diacetate
Placed in canal for 1-3 weeks
Conform to ISO specification for GP points for size and diameter which matches shape to that of root canal
Drop of sterile water is sued to accelerate release of the chlorhexidine
Same effects as a chlorhexidine irrigant

422
Q

Give a description of phenol?

A

Effective antimicrobials
Strong antiseptics
Short duration for effect
Protoplasmic poison and works at an optimal conc of 1-2%

423
Q

Give 3 examples of phenols?

A

Para-monochlorphenol
Thymol
Cresol

424
Q

What did studies show about the use of phenols as disinfectants?

A

Not able to fully disinfect the RCS after 2 weeks
Due to insufficient vapour released for effective antimicrobial action when the products placed on a cotton pellet in pulp chamber

425
Q

Give 1 commercially available phenol product and its constituents?

A 
Cresophene - Septodont
Constituents:
- para-chlorophenol
- dexamethasone  with thymol and camphor
High tox and carcinogenic
Obsolete in endodontic practice
426
Q

Give a description of halogens?

A

Antimicrobial
Chlorine-containing products (chloramines)
Iodine more popular such as iodine potassium iodide
Releases vapours
2% iodine prep quicker at reducing bacterial load than CaOH
Can prevent E. faecalis growth within 1-2 hrs

427
Q

Contraindications for iodine halogens?

A

Iodine hypersensitivity

428
Q

Give a description of formaldehyde?

A

Caustinerf Forte - Septodont
Toxicity of formaldehyde containing medicaments
Not justified

429
Q

Give 7 key properties needed for a good coronal temporisation?

A 
Coronal seal must be perfect - to prevent bacterial ingress
Function
Aesthetics
Strong to withstand occlusal loads
Low solubility
High wear resistance
Longevity
430
Q

Name 5 materials used for inter-visit coronal temporisation?

A 
GIC
Zinc polycarboxylate cement
Reinforced zinc oxide eugenol cement
Zinc oxide containing putties
Semi-permanent material - forming a core using a resin-mod glass ionomer cement, resin composite or amalgam
431
Q

What to consider when placing a coronal termporisation material?

A

Need to consider final restorative material viz
resin composite definitive restoration and use
of a eugenol-containing cement

432
Q

Name 2 types of coronal protection?

A

Tightly fitting copper

Orthodontic band

433
Q

What is the function of obturating material?

A

Prevents ingress of microorganisms by creating a seal at both coronal and apical ends, lateral canals and dentinal tubules
Completely fills dead space removing all air which could expand or contract in a pressurised environment

434
Q

Give a description of Gutta percha?

A

Consists of polyisoprene which comes from rubber tree
Polyisoprene has 2 isomeric forms:
- cis = rubber
- trans = GP
Trans exists in 2 phases:
- alpha phase is heated and used molten
- beta are GP points or cones used at room temperature
Mixed with other chemicals to enhance handling

435
Q

Give a comparison between alpha and beta phase for trans polyisoprene?

A

Beta phase is formed when GP cooled quickly whereas alpha phase is formed if material is cooled slowly
Alpha form is denser and has better thermoplastic characteristics

436
Q

Name the 4 constituents for GP and their functions?

A

Gutta percha
Zinc Oxide - filler and antimicrobial
Resins - Plasticiser
Metal sulphates - radiopacity

437
Q

What are the physical properties of GP?

A 
Highly biocompatible
Minimal tissue changes
Inert
Minimal toxicity
Dimensionally stable and packable
Thermoplastic softening at 60-65C and melting at 100C
Stretchable
Antibacterial
Radiopaque
No heat sterilisation
Oxidises on light exposure - degrades and becomes brittle
Lacks rigidity
Poor adaption
Shrinkage 2%
438
Q

Explain how to sterilise GP?

A

Using NaOCl

Do not use acetone or alcohol to disinfect as it can be absorbed

439
Q

What is the presentation of GP?

A

Points
Cones
Several different sizes
Different tapers

440
Q

What are the manufacturing tolerances for GP?

A

Subjected to ISO standards
Cones are made to a tolerance of +/- 0.05mm
Different products are composed of different proportions of chemicals creating variations in brittleness and stiffness

441
Q

Explain the cold obturation technique for GP?

A

GP + endodontic seal to fill root canal
Cold lateral condensation - GS
Cone which corresponds in size to canal prep is coated with a root canal prep and introduced into root canal
then pushed laterally to create space so that next cone can be placed
Other accessory cones coated with seaer are then introduced into canal one at a time
Continue until root canal is fully obturated
Adjust GP cone with scalpel blade
Use liquid GP - allows material to flow into irregularities of RCS
GuttaFlow - Roeko (GP + addition cross-linking poly(dimethyl siloxane)
30um particle size - 0.2% shrinkage

442
Q

Name the 8 chemical constituents for GuttaFlow and their functions?

A 
GP powder - obturating component
ZInc oxide - filler and radiopacity
Zirconium dioxide - filler and radiopacity
Silicone oil - binder + consistency
Paraffin ol - binder + consistency
Colloidal silver - inhibit reinfection
Hexachloroplatinic acid - catalyst
Colouring agent - colour
443
Q

Explain the technique for warm GP?

A

Used at high temperatures as pellets
Conjugation with gun
150-230C
Narrower gauge = lower temperature
Once at temp molten material can be expressed out of needle of gun into canal
Secure apical stop before suing molten GP - to prevent extrusion
Good for obturating anatomical irregularities

444
Q

What are some present techniques to cut GP?

A 
Heat used to cut GP
Heating over bunsen burner:
- naked flame
- burning other objects
- tempers steel of instrument = damage
SYstem B sears GP cleanly
Wire inside probe heats up quickly
Easy and sade
445
Q

Name 4 other obturation systems?

A

Real Seal 1 :
- good for latex sensitivity
Thermafil:
- softened GP flow into RC

446
Q

What obturation product is indicated for patients sensitive to latex?

A

Real Seal 1
Polyester with barium sulphate and silicate as radiopaque filler
Core is resin based with a Resilon outer coating
No rubber or rubber-based materials
Soluble in chloroform and my be removed like GP

447
Q

Give a description of ENdoREZ?

A

EndoREZ:

  • hydrophilic
  • dual cured resin obturation system based on UDMA and triethylene glycol dimethacrylate
  • polymerisation similar to resin composite
  • base and catalyst presentation
  • takes 20 mins can be sped up by accelerator
  • filler for radiopacity
  • master + accessory then light cure
448
Q

Give a description of SmartSeal?

A

Smartseal:

  • hydrophobic polymer,
  • swell when water absorbed,
  • hoop system prevents excess swelling
  • flexible
  • points and sealer
449
Q

What are the shortcoming of Silver points?

A

DO not fully obturate canal
Rely on RC sealer
Prone to corrosion
Corrosion products high tox and can leach
Permeate dentinal tubules
Difficult to remove as they tend to fracture
Rigid so can’t adapt to walls

450
Q

What is the definition of an endodontic sealer?

A

Paste coated onto endodontic point prior to its insertion into RC
Paste/paste presentation
Used sparingly
Prvenets extracanal extrusion and decreases amount of sealer needed

451
Q

What is the function of the endodontic sealer?

A
  • Lubricate and facilitate full placement of master point +/-
    accessory cones
    • Fills voids between obturation points
    • Fills and seals lateral canals and passes through lateral canals
    to root surface - seen radiographically as a ‘puff’ on side of root
    • Provide a disinfectant action if they contain an active component
452
Q

Name and describe the 4 physical properties all endodontic sealers must display?

A

Flow - determines ability to effectively fill voids
between master cone and accessory cones and any
accessory canals may be obturated.
• Film thickness - should be minimal as sealer is by far
most likely material to degrade
• Solubility - most sealers are soluble and are absorbed
to some extent when exposed to tissue fluid, keep to
a minimum
• Radiodensity - should also be radiopaque

453
Q

Name 6 types of endodontic sealers?

A 
Zinc oxide eugenol
Calcium hydroxide
Epoxy resin
GIC
Poly(dimethyl siloxanes)
Tricalcium silicate cements
454
Q

Give a description of Zinc oxide eugenol endodontic sealers?

A

Good results with cold techniques
Small particle size to enhance flow
Weak
Porous
Susceptible to decomposition in tissue fluids
Lose volume as eugenol and zinc oxide are released
Resins/rosins added to decrease dissolution
Can act as sensitising agent
Zinc oxide antimicrobial and cytotoxic
Other added chemicals:
- germicides - antiseptic
- Canada balsam - increases adhesion to dentine
- corticosteroids - suppress inflamm
- paraformaldehyde - antimicrobial

455
Q

Name the chemical composition of Zinc oxide eugenol endodontic sealer?

A 
Powder:
Zinc oxide - filler
Silver - radiopacity
Oleoresins - viscosity
Staybelite resin - binder
Dithymoliodide - antiseptic
Bismuth subcarbonate/subiodide/trioxide/sulphate - radiopacity
Sodium borate - filler
Thymol iodide - antiseptic
Oils and waxes
Liquid:
- eugenol - cement former
- canada balsam - viscosity
- polymerised resin - reinforcing agent
456
Q

Give a description of CaOH endodontic sealers?

A 
Dissociates into an ionic form and may confer an
antimicrobial effect and promote healing
sealer must dissolve so leaving voids
in obturated material 
Sealer is more soluble
Poor cohesive strength
457
Q

Name the chemical components for CaOH endodontic sealers?

A 
Base:
- CaOH - cement
- Zinc Oxide - cement
Activator:
- Barium sulphate - radio
- Titanium dioxide - filler/colour
- Zinc stearate - binder
458
Q

Give a description of epoxy resin endodontic sealers?

A 
Good flow and sealing ability
High dimensional stability
Low shrinkage
Sufficient working time
Adhesion to other materials and dentine
Antibacterial properties
Less porous and have greater hardness
Their lower solubility and greater film thickness may
prove problematic if the material needs to be removed
Soluble in chloroform which facilitates removal
least toxic of all
endodontic sealers
Allergy
459
Q

Name the chemical components for Epoxy resin-based endodontic sealer?

A 
Base:
- silver powder - radio
- bismuth oxide - radio
- hexamethylenetetramine - hardener
- titanium oxide - colour/filler
Catalyst:
- bisphenoldiglycidyl ether - cement former
460
Q

Explain the setting reaction for epoxy resin endodontic sealer?

A

Addition polymerisation reaction in which epoxides
and amine react to form long chains
• No residual monomer remains with no by-products
• Diamines present in cement provide high
dimensional stability
• Exothermic reaction
• Poly(addition) reaction is temperature dependent
and takes a substantial amount of time
• Extended working time provided c4 hours

461
Q

Give a description of GIC endodontic sealers?

A

Modified GICs
• Low toxicity and induce little tissue irritation
• Cytotoxic but this and any inflammatory responses
decrease with time
• Adhere to dentine but may be less good at sealing
• Physical properties are better than zinc oxide
eugenol with less coronal leakage
• Leach fluoride which is taken up by dentine
• More susceptible to dissolution if exposed to liquids
before maturation is complete

462
Q

What are the chemical constituents for polydimethylsiloxane endodontic sealers?

A 
Polydimethylsiloxane - Active component
Silicon oil - Binder
Paraffin base oil - Binder
Platinum salt-  Catalyst
Zirconium dioxide - Filler
463
Q

Give a description of polymethylsiloxane endodontic sealer?

A

Insoluble so not resorbed - contraindicated in
deciduous teeth
• Dimensionally stable although there is an initial
slight expansion on setting
• Thin film thickness and good flow characteristics
allows material to flow into tubules and fins
• Excellent biocompatibility
• Cannot bond to dentine
• No antibacterial properties

464
Q

Give 1 commercially available polydimethylsiloxane endodontic sealer

A

RoekoSeal
Difficult to use with heated
techniques as heat will
decrease working time

465
Q

Give the properties of tricalcium silicate based endodontic sealer?

A 
Bioactive
• Stimulates bone regeneration (hydroxyapatite formation)
• Promotes periradicular healing
• Mineralisation of dentine
• Biocompatible
• Adhesion to dentine and GP
• pH 11 &amp; CaOH2
release – antimicrobial
• Dimensionally stable
466
Q

Give 1 commercially available tricalcium silicate based endodontic sealer?

A 
Use with GP points
• Any obturation
technique
• BioRoot™ RCS
(Septodont)
• 1 spoon to 5 drops
• Working time c15 mins
• Setting time <4 hours
• 45µm film thickness
467
Q

Give a desctiption of formaldehyde containing obturating pastses?

A

Paraformaldehyde decomposes to give its
monomer which is a water soluble protein
denaturing agent
• Highly toxic, genotoxic, mutagenic and
carcinogenic
• Cause severe inflammatory reactions and
necrosis with direct tissue contact
• Cause permanent injury if applied to neural
tissue on extrusion outwith root canal space
May be transported to other parts of the body
• Allergenic which causes contact dermatitis and
has also caused type 1 anaphylaxis
• Leaching occurs for a long time and results in
chronic inflammation
• Prevents or delays healing and masks
inflammatory process

468
Q

Give 1 commercially available ZOE containing obturating pastes?

A

TubliSeal EWT - SybroEndo - ZOE

3rd Year BDS (21 decks)

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