Fixed Prosthesis Flashcards
What is the defintion of an extra-coronal restoration?
Is a restoration that which is outsaide or external to the crown portion of a natural tooth. (sits over remaining tooth structure)
Name 3 different types of extra-coronal restorations?
Veneer
Only
Crown (partial or full)
Name the 3 main indications for extra-coronal restorations?
Support for remaning broken down teeth
Prevention of microleakage
Aesthetics
In what order should treatment be planned?
Relief of pain/emergency Cause related therapy Intial reassessment Basic operative care Reassessment Reconstructive therapy Recall and maintance
Name the 5 main risks of extra-coronal restorations?
Pulpal inflammation Periapical periodontitis Poor plaqie contraal Restoration loss if poor occlusal management Loss of occlusal stability
Name the 3 main factors when deciding whether a patient is suitable for an extra-coronal restoration?
Patient expectations
Tolerate the procedure
Maintain their mouth for the foreseeable future
What are the 4 guiding principles for preparing an extra-coronal restoration?
Plan resto that maintains structural integrity of remaining tooth tissue
Least invasive option
Consider effect on pulp
For endo teeth provide best coronal seal and support weakened teeth
What are the alternbatives to extra-coronal restorations?
Direct resto bonding
Excellent marginal adaptation and bonding systems
Bleaching
Micro-abrasion
What are the 6 key principles of extra-coronal restoration tooth preparation?
Preservation of tooth structure Retention and resistance form Structual durability of resto Mariginal integrity Periodontal health Aesthetics
What are the principles to follow when preserving tooth structure?
Conservative preparations
Minimise pulpal damage
Restoraton should protect remaning tooth structure
Name the 9 factors in which crown preparations effect the pulp-dentine complex?
Dentinal fluid flow Smear layer Pre-exitising pulapl condition Thermal trauma LA Material irrigation Micro-leakage Luting Dehydration
How can exisiting pulpal condition affect the sucess of a future extra-coronal restoration?
Restorative procedures are injurious to the pulp
Can result in fibrosis, reduced vascualrity and tertiary dentine
Pulp less able to recover from further injury
Effect of pulp damage is cumulatiev
Can elad to pulapl necrosis
How can theraml trauma affect the sucess of a future extra-coronal restoration?
From previous light-cure or exothermic materials
Pulpal temperature is rasied during crown preps
Can reach a fatal level if inadequeatly cooled air-rota
Sub-lethal temperature can still lead to scarring, fibrosis and reduced vascualrity
How can microleakage affect the sucess of a future extra-coronal restoration?
Following tooth prep tubules are exposed
Must be adequately sealed or it will be permeable
This can cause hypersensivitiy, bacterial invasion and dehydration
How can luting affect plaque control for extra-coronal restorations?
All cements are soluble
Good marginal integrity is essential for plaque contrl and aesthetics
Good mechnical form of prep and well manaufactures corwn required to protect cement lute
How can dehydration of dentine affect the sucess of a future extra-coronal restoration?
Excessive use of the 3in1
Delays in preparation stages
Name the 9 main precaustion to preotect the long-term vitality of the pulp?
Evaluate pulp health pre-op
Lots of water spray during tooth prep
Use light and intermittent cutting forces
Sharp brus
Ensure the suction doesn’t suck the cooling water away
Avoid dehydrationg the denture tubules
Ensure good mechanical form of prep
Seal dentine ASAP
Wait 2 weeks between cutting corwn and placing final restoration
What is the defintion of resistance form?
The features of a tooth prep that enhance the stability of a restoration and resist dislogment along an axis other than the path of displacement (apically or obliquely)
What is the defintiion of retention form?
Quality inherent in the dental prostheiss acting to resist the forces of dislogment along the path of insertion (direct and indirect retention)
The more parallel the opposing wall the greater the retention
What can be done to increase retention and resistance form?
Degree of taper Grooves Boxes Pins Larger SA for luting Prep of occluso-gingival height and bucco-lingual width
What is the optimal taper for a crown prep?
6 degrees (16 more realisitc)
3 degree of inclination on each opposing wall
Less than 6 can make it hard for the lute and technician
How do grooves, boxes and pins increase resistance form?
Decrease the rotational arc of displacment
Placement of auxillary features must be parallel to the path of insertion to the crown
What are the mechanical requirement for a extra-coronal restoration? (diagram)
Small space between tooth and resto - filled with cement
Higher resistance reduces rotational arc compared to higher retention
Increased OG- height and narrow BL-width = smaller rotational arc of dispalcement (higher resistance)
Decreased OG-height and wider BL-width = larger rotational arc of displacement
For anterior teeth for resistance form what is most important?
Bucco-lingually
Limited opportunity for long parallel walls
Cut palatal wall so it is long and parallel
For posterior teeth for resistance form what is most important?
BL is parallel
MD is more limited*
How to plan path of insertion for extra-coronal teeth?
Along long axis of tooth and parallel to adjacent proximal contacts
How to balance structiral durability of an extra-coronal restoration?
Dentine removal and risk to pulp and strcutural integrity
Ensure enough space for material
Thickness for functional cusp size?
1.5mm
Thickness of extra-coronal resto?
1mm
What are the consequences for inadequate preparation?
Weak crown
Poor aestehtics
Compromised gingival and periodontal health
What are the consequences for excessive preparation?
Crown strong Good aestehtics Good perio and gingival health Tooth weak Pulpal problems
What is the defintion of a margin?
The outer edge of a crown, inlay, only or other resto, a boundary surface of a tooth prep is termed the finish line or curve.
Finisgh on sound tooth structure
Adequate sixe and thickness
Name 6 forms of finishing margins?
90 degree shoulder Deep chamfer Radial shoulder Shoulder plus bevel Knife edge Chamfer margin
What is the defintiion of the bioloigcal width
Distance from the depth of the crevice to the alveolar crest
~2mm
What are the 4 consequences of impinging on biologic width and the practical aspects?
Gingival inflamamtion Pocket formation Recession Loss of alveolar crest height (consider crown lengthining)
Practical aspects:
- difficult soft tissue management for impressions
- gingival inflammation
Why do we need a core for an extra-coronal restoration?
Provide retention and resistance form
Restoration of coronal tissue
Durable coronal seal
How can we achieve increased retention and resistance form for the crown?
Use of ferrule
Use of adhesive materials to bong to tooth tissues
How can we achieve increased retention and resistance form for the core?
Use of undercuts and grooves in remaining tooth tissue
Why are dentine pins bad?
They increase stress on tooth
Increased risk of periodontal ligament damage
Predispose tooth to fracture
What is the definition of a ferrule?
A band of iron
2mm from crown margin
1mm thick
What 4 questions shoould you think about when assessing the need for a core?
- Can the tooth provuide retentuion for its extra-coronal resto without additional material being added
- Do we need to add amterial that will aid resistance and retention, or der we just need to block out irregs
- is there sufficient remaining tooth tissue to retair and support a core?
- Can a ferrule be achieved?
What is the prognosis for an extra-coornal that extends subgingivally? Can it be improved?
Poor prognosis
Crown lengthing surgery
Electrocauterisation
What can be done to improve the chance of creating a successful ferrule?
Crown lengthing surgery
What does a coronal seal provide to a vital tooth?
Increased pulpal protection
Prevents caries at and beneath the restoration margin
What does a coronal seal provide to a non-vital tooth?
Additional luine of defense to endodontic seal
Prevents caries at and beneath the restoration margin
What are the advanatages and diadvanatges for amalgam as a core material?
Adv:
- not technique sensitive
- strong in bulk
- sealed by corrosin products
- bonded into place with cemments and resins
Dis:
- Needs 24 hour seeting before tooth prep
- weak when thin
- electrolytic action bvetween core and crown
- not intrinsucally adhaesive
- poor aesethics under ceramic restos
Indications for amalgam as a core material?
Posterior teeth
Interim resto for posterior teeth
Substitiute for dentine pin
What are the advanatages and diadvanatges for composite as a core material?
Adv: - strong - stonger than amalgam in thin sections - fast setting - no need for matrix placment Dis: - technique sensitive - essential isolation - dentine bond can be ruptured by polymerisation contraction - hard to distingish between tooth and core during prep
Indications for composite as a core material?
Build-up material for posteruiior and anterior teeth if isolation is insured
Aesthetic interim resto - longer than amalgam
What are the advanatages and diadvanatges for GIC as a core material?
Adv: - intrinsucally adhesive - fluoride release Dis: - too weak - crack - radiolucent
Indications for GIC as a core material?
Excellent filler for inlays but needs sufficient dentine to support crown
No strong enough to be a core
Exisiting crown with caries, remove the caries then fill the area with GIC
Why is it advised to remove the exisiting restoration before an extra-coronal restoration is to be placed?
Assess tooth strcutral integrity
Pulpal expopsure
Underlying caries
Unless an interim has been placed (by you)
What are the advantages and disadvanatges of using the Nayyar core technique? (endo)
Placed immediatalu after endo - reduing risk of coronal leakage
Utilises coronal tooth structure to increase retention
Reduces stressess created byt post placememnt
Easily retrievable
What is the Nayyar core technique? (endo)
Amalgam dervied, using the pulp horns and chamber for retention
Retention from coronal and radicular tooth tissue
How to plan to minimise the risk of failure for extra-coronal restorations?
Treatment planning perfect
Pt shows good OH, diet and protected occlusion
Perfect preps and impressions
Perfect lab work
Plan for failure - least invasive
Explain that the restoration will fail in time
What 3 questions to think about when a restoration has failed?
- Possible causes of the failure of the EC restoration
- How can it be prevented in the future
- Suitable strategies to remedy the situation
Name the 7 objectives to be acheived when trying to have a successful EC restoration?
- Miminaml intervention to secure patient’s OH
- Careful case selection (treat tooth with context - remaining dentition, occlusal facros, age, dexterity, diet, maintenace and expectations)
- Excellet assessment and planning (plan instages)
- Textbook standard prep and impression
- Perfectly fitting temporary
- Careful cememntation of crown
- Regular maintenance
Name the 7 main reasons for EC restoration failure?
Loss of retention Mechanical failure Caries Periodontal Endodontic Aesthetic Damage to opposing tooth
How does the loss of retention lead to EC restoration failure?
Lack of ferrule or poor retention of the core
Poor retention between core and undercuts, pits and grooves
Occulsion - axial forces only on molars, canine guidance and no deflective contacts)
How does mechanical failure lead to EC restoration failure?
Due to lack of ferrule
Forces focussed on apical terminus of post
What is the main reasons for why ceramic crowns fail?
Secondary caries Chipping due to: - metal coping too thin and flexure - oxide layer not good enough to bond to ceramic - poor occlusal planning
How can you resolve a mechanical failure in ceramic crowns?
Replace - risk iatrogenic weaking of tooth, loss vitality, cost and time Repair kit (etched with HF - very corrosive)
How can caries lead to EC restoration failure?
Aetiological factors can’t be controlled
Loss of tooth tissue and structure/integrity
Usually unrestorable
At crown margins
How can periodontal failure lead to EC restoration failure?
Poor emergence profile - poor crown contouring
Ledges at the margin - PRFs
Encroaching on biologic wifth - inflamm, PPD, recession and bone loss
Perio not controlled before crown
Plan the simpliest and least invasive option to allow more room for resolution in the future
How can endodontic failure lead to EC restoration failure?
Marginal breakdown - caries - loss vitality - root infection - apical periodontitis
Questionable marginal fit and patients OH
Failure of coronal seal leading to reinfection of RCS (remove GP to CEJ and fill with GIC for isolation)
How can aesthetic failure lead to EC restoration failure?
Gingival recession leading to expoure of unsightly margins:
- taruma to soft tissues during crown prep or insertion of retraction cord
- inflamm due to poor fitting temo; enchroaching on biologic width - uncontrolled perio disease
Poor shade matching
Need to think if crowns were neccesary rather than composite veneers
How can damage to opposing teeth lead to EC restoration failure?
Poor occlusion understanding
Damage/wear to other teeth - poor aestehtics
Porcelain is abrasive when unglazed
What are the 7 key ideas when trying to minimise failure for EC restorations?
Careful case selection - motavation, OH and appropriuateness of tooth
Excellent assessment and planning
Planning: - pulp, occlusion, periodontal support, remaining tooth structure and aesthetics
Well executed prep and impression
Well fitting temporary - to stop movememnt and inflamm
Appropriate cemment selection for specific crown
Maintenance - remediation could be necessary
What are the advanatages and disadvanatges for RMGIC for ECRs?
Adv:
- command set
- seal tubules
- bond to tooth
- variable colour
Dis:
- moisture senitive
- weak
- contains HEMA
What is the definition of temporisation?
Restores form and function to the tooth while the
definitive restoration is being constructed
What are the advantages of a good temporisation?
Facilitates subsequent stages of the procedure
Produces a better definitive restoration
Can be useful to glean information from
temporaries
What are the requirements of a good temporisation restoration?
Retained for the period of time between fitting and
placement of the definitive restoration
Removed easily at the fit appointment without damage to the preparation
Good retention for this period and ease of removal
What is the most satisfactory combination of a temporisation?
Well-prepared (mechanically retentive)
preparation with a well-constructed temporary
restoration grouted by a soft luting cement
Name 4 types of temporary restorations?
Acrylate-based materials
Dimethacrylate composites
Light-cured temporary materials
Putties
What is suggested for long term temporisation?
Indirect temporary restoration
What are preformed crowns made from?
Polycarbonate
Cellulose acetate
Aluminium
Stainless steel
What are the mechanical properties of polycarbonate crown forms?
High impact resistant polymer
Sufficiently strong to withstand occlusal forces
Linked by a variety of chemical groups (bis-GMA)
What is the clinical technique to place a polycarbonate crown?
Crown form of the approximate size selected
Acrylic bur used to adjust its size and shape
Roughen interior of the polycarbonate crown
Refined with another material (usually an acrylate)
Can trim through the polycarbonate ‘shell’ to
accommodate, if occlusion dictates
Acrylic can withstand occlusal forces if at least c1 mm
thick
Often too broad buccolingually and so require thinning
to achieve a satisfactory contour gingivally
Describe a cellulose acetate crown form?
Transparent
Packed with another material matching in shade to the
surrounding teeth (resin-based composite)
What are the disadvantages of cellulose acetate crown form?
Merely act as a matrix - must be removed after
Thickness of the crown reduces by about 0.2 mm
when removed
Leads to instability in the occlusion and movement of
adjacent teeth
Refining material may lock into undercuts
Compromises removal of the crown and the patient’s
ability to keep the (gingival) area clean
What is the main indication for cellulose acetate crowns?
Matrix to build up teeth using resin based composite
What is the main indication for metal crown forms?
Posterior teeth
Name the 2 materials avalaibale for metal crown forms?
Aluminium
Stainless Steel
What are the advantages and disadvantages of using aluminium metal crowns?
Easy to manipulate - malleable and ductile
Corrode with time as saliva can react with them
Risk of galvanism if placed adjacent to another
metal
How are aluminium metal crowns prepared?
Cut to approximate size of the preparation using
crown shears
Ability of the aluminium to be worked and shaped lends itself to this process
What are the disadvantages of aluminium corwn if the form is not refined?
Not possible to perforate the metal shell should the
occlusion dictate it
No other information gained
Wear may lead to temporary cement being exposed
with the restoration failing
Why are acrylic materials used with temporary crowns?
Enhance the fit between their internal surface and the preparation
Closeness of the fit enhances retention
What are the disadvantages of using methylmethaycrylate/polymethlymethacrylate with temporary crowns?
Disadvantage: High polymerisation shrinkage Poor mechanical strength Highly exothermic setting reaction High level of monomer release Poor wear resistance Poor aesthetics Chemical interaction with eugenol
What are the clinical impact of using methylmethaycrylate/polymethlymethacrylate with temporary crowns?
Clinical impact: Unsatisfactory fit Breakage during function Thermal trauma to the pulp Significant pulpal irritation Undesirable wear during function leading to perforation or fracture of the temporary leading to occlusal instability Unsightly restoration Non-eugenol-containing products should be used
What are the physical properties of higher methacrylates?
Lower glass transition temperature
Poly(butylmethacrylate) then distortion seen at mouth temperature
Combo no distortion at mouth temp
Tough and less brittle
Morphology changes on hot foods and liquids
Describe methylmethacrylate?
MMA monomer and PMMA polymer
Benzoyl peroxide/tertiary amine, initiator/activator curing system
Presence of a tertiary amine results in yellowing
after setting
Especially in sunlight as the solar ultraviolet
breaks down the amine
What are the properties of methylmethacrylate?
Monomer has a distinctive, unpleasant smell Relatively inexpensive Good marginal fit Good transverse strength Good polishability Durable
What are the indications for methylmethacrylates?
Inlays and Onlays
Prevents overeruption
Affords increased fracture resistance
Explain the clinical technique when refining a preformed crown with an acrylic material?
- Complete the preparation
- Select a crown form that approximately corresponds to the
tooth being temporised - Trim this crown form (using an acrylic bur for a
polycarbonate crown form and crown shears for a metal crown
form) so that the margins approximate those of the
preparation. Roughen the internal surfaces of the
polycarbonate crowns - Mix the acrylic material to the consistency of wet sand
- Fill the crown form by running the material down the sides to
ensure no air bubbles are incorporated inside the crown form - Allow the excess monomer to evaporate and watch the
surface until it turns from a shiny to matt finish - At this point fully seat the temporary crown onto the moist
preparation and remove the obvious excess using a probe or flat
plastic to prevent it setting into the undercuts so that the crown
can be removed easily later - Remove and reseat the crown several times to reduce the
effect of polymerisation shrinkage
(9. Place in hot water to accelerate the setting reaction) - Trim the margins using an acrylic bur and reseat on the
preparation to verify the margins - Check the occlusion and adjust if necessary
- Polish if necessary
- Lute the crown using a temporary luting cement
What alternative clinical technique for preformed crown with an acrylic material?
Blowdown splint made of thermoplastic resin
may also be used
Wax temporary prosthesis on a study cast
Vacuum-formed splint constructed from this
Splint filled with a methacrylate material and
inserted intraorally once the preparation has
been done
Name the 2 types of resin composite based materials for temporary restorations?
Some form of dimethacrylate resin (frequently bis-GMA and triethylene glycol dimethacrylate)
Composite-type technology which is based on the
ethylene imine derivative of bisphenol-A
Describe dimethacrylate resin?
Frequently bis-GMA and triethylene glycol
dimethacrylate
+ filler (usually inorganic and containing zirconia
and silicon dioxide)
Filler forms only 40% by weight
Describe Ethylene Imine Derivative Of Bisphenol-A?
Catalysed by an aromatic sulphonated ester
Filler is added to increase strength
Multifunctional methacrylates produce a
relatively high cross-link density early on in the
setting reaction
Rubbery stage is achieved allowing the partially
set restoration to be removed without distortion
or damage
What are the properties of Ethylene Imine Derivative Of Bisphenol-A?
Presence of filler reduces polymerisation shrinkage
As the resin monomer volume is reduced,
shrinkage is reduced in proportion
Catalyst and base
What are the advantages of dimethacrylate resins?
Good aesthetics Good colour stability Available in a range of shades including a bleach shade Good flexural strength Hard Moderately good wear resistance Moderately low exothermic reaction Polishable due to small filler particles Good tissue biocompatibility Non-irritant to the soft and hard tissues Generally radiopaque Replicates occlusal surface May be repaired Minimal shrinkage
What are the disadvantages of dimethacrylate resins?
More expensive
May be insufficient thickness for strength interocclusally
Can stain with certain foodstuffs
What are the indications for dimethacrylate composirte materials?
Temporary inlays
Temporary onlays
Temporary veneers
Temporary crowns
As a refining material for temporary crown forms
Short temporary bridges (three units maximum)
Give 1 comerically avaliable example of dimethacrylate composite material?
Protemp 4 - 3M ESPE
Descirbe the step-by-step process of the resin-replica technique?
. Preoperative impression
• Include at least one tooth on either side of the tooth
to be prepared made either in the mouth or on a
study cast
• +/- modify the shape of the crown to be temporised
prior to impression taking (e.g. thickening it to
increase the strength of the temporary crown)
• Putty v alginate
• Impression may be adjusted using a scalpel blade to
open up the interproximal areas to increase the bulk
of material and hence its strength
2. Select the shade of the temporary material to be
used (if applicable)
3. Carry out the tooth preparation
4. Syringe the first portion of material mixed on the
bracket table
5. Syringe the mixed material into the matrix keeping
the nozzle within the body of the expressed material
6. Reseat the matrix on the preparation
7. Monitor the setting material (on the bracket table)
• Remove it when it has reached a rubber stage (usually 30–90
seconds depending on the material and mouth temperature
and humidity)
• Do not delay any longer or the set material will lock into any
undercuts
8. Remove the matrix impression
• Allow the temporary restoration to self-cure for 4–5 minutes
(may be accelerated by placing it in hot water)
• Remove it from the impression
9. Trim the flash
• Use tungsten carbide or diamond burs
• Reseat on the prep(s)
10. Check the occlusion and adjust if necessary
11. Wipe the surface with a cotton wool roll to
remove the oxygen inhibition layer
12. Polish the completed restoration using
polishing instruments (e.g. discs, burs, etc.)
13. Lute the crown using a temporary luting
cement
How to repair a dimethacrylate composite material?
Resin based composite materials can bond to the dimethacrylate composite Flowable resin composite may be used to: • Repair small non-load-bearing defects • Fill voids • Refine margins • Improve contacts For newly placed material: • Remove any contamination (e.g. saliva or dust) with water • Air dry • Add the flowable composite and cure in no more than 1 mm increments
Describe light cured temporary resin materials?
Used to temporise intracoronal preparations
Rubbery in consistency
Retained in the cavity mechanically
No bonding to the cavity walls which facilitates
their subsequent removal
Reasonably easily removed at the fit appointment using an excavator
Only suitable for short term use (no more than a month)
because it slowly degrades and wears
Tend to develop a malodour due to bacterial activity over time
What is the function of CaSO4 in light cured temporary resin materials?
Harden in presence of moisture
What is the setting reaction for light cured temporary resin materials?
Primarily by light curing
Shrinking by 1.6–3%
Prepolymers added to them to decrease polymerisation shrinkage
Shrinkage is relatively low so formation of marginal
gaps, microleakage and discolouration of the
material is reduced
Depth of cure <4mm
Tend to discolour with use
Which light cured temporary resin materials is indicated for inlays?
Low-viscosity materials
Which light cured temporary resin materials is indicated for onlays?
Rigid ones are designed for onlayswhere the cavity size is larger
What are the properties of light cured temporary resin materials?
More difficult to manipulate
Place material into the cavity and the gross remove
excess prior to light curing
Surface can be finished using rotary instrumentation
If necessary
Stiffer materials offer higher strength and reduce
drifting of adjacent and opposing teeth
Easier to manipulate into the cavity as they can be
condensed into place
Radiopaque
How to manipulate light cured temporary resin materials?
Do not need to be cemented
With a temporary luting cement
Applied to the preparation walls prior to placement
of the temporary material to seal the cut dentinal
tubules
What are the indications for light cured temporary resin materials?
Temporary dressings for inlay preparations
Temporary restoration of (retentive) cavities
Inter-visit access cavity sealants during an
endodontic procedure
Relining prefabricated temporary crown forms
and bridges made of methacrylates or
polycarbonate
Sealing implant screw access openings
What are the contraindications for light cured temporary resin materials?
Allergy to one of the constituents Large (multisurface) cavities Crown or bridge material Subgingival preparations Should not remain in the mouth for more than 6 weeks
Desribe a putty?
Based on zinc oxide and zinc sulphate
Radiopaque
Placed in their soft unset state
Harden in the presence of moisture from saliva
Expand during setting
Basic setting reaction is the hydration of calcium
sulphate to form a plaster (gypsum)
What are the advantages and disadvantages of putty?
Wear resistance is poor
Create a good seal
Some products are claimed to adhere to dentine
What are the indications for putty?
Seal endodontic access cavities between visits
Temporise inlay cavities
Temporise retentive cavities
Give 1 comerically avaliable product of putty?
Cavit-G 3m ESPE (easy to remove)
What are the advantages of indirect temporary restorations?
Better marginal fit Increased strength Better wear resistance Easier to keep clean Better aesthetics and colour stability Greater occlusal reliability and stability
What are the disadvantages of indirect temporary restorations?
Greater cost implication
Failure to provide a satisfactory temporary
prosthesis may prove to be a false economy
Acrylic, Bis-GMA or acrylic bonded metal
Why do we have to retract gingiva when doing crown impressions?
Gingival tissues must not
obscure the margins of a preparation
Sufficient bulk of impression material is required to give
the impression material adequate strength
Name 1 example of a mechnical means for gingival retraction?
Retraction cord
Name 2 examples of chemical means for gingival retraction?
Astringents
Vasoconstrictor agents
Describe the retraction cord and how it works?
Usually made of cotton and placed into the gingival sulcus
Separates the marginal gingival tissues and the tooth by pushing the gingival tissues so exposing the margin of the preparation
Name the 3 types of retarction cords avaliable?
Twisted Braided Knitted - more effective at retraction as they have a springiness
Why is the knitted cord the most effective mechanical means for gingival retraction?
Hold and carry significantly more haemostatic chemicals than conventional cords
Flavoured to increase patient acceptance
How are retraction cords placed?
Packed around the
preparation using a
special instrument
What is the main fucniton of a retraction cord wetted in haemostatic chemicals?
Generally a haemostatic agent
Controls gingival haemorrhage
Facilitates a clean and dry field
Important with hydrophobic impression materials
Name 3 types of astringent haemostatic retractions chemicals?
Aluminium trichloride
Potassium aluminium sulphate
Ferric sulphate
Name 1 type of vasoconstrictor haemostatic retractions chemical?
Adrenaline hydrochloride
Why must haemostatic retraction chemicals be removed? and give an example?
Many of these chemicals adversely affect the set
of the impression material
Racestyptine (Septodont) + polyether
impression material = Gas → bubble defects in
the surface of the stone die
How do retraction chemical work mechanically? and how to remove it?
Chemicals expand either on their own or in combination with applied pressure
Injected perpendicularly into
the gingival sulcus to fill it
Removed by washing away with water from the three-in-one syringe
Which retraction method is good for implants and why?
Aluminium chloride
Useful for implants as cord may compromise the
gingival cuff around the fixture
Name 1 commercially avaliable gingival retraction material?
Ultrapak
Optident
Knitted cord that can be impregnated with 15.5% ferric sulphate
Name 1 other retraction system, describe it and how its used?
Magic Foam Cord: - addition silicone - bubbles form within material - paste/paste and injected around prep - pressure is then applied by the patient biting on a Comprecap - densely packed cotton wool roll
Name the 6 requirements of an impression tray?
Be rigid and non-flexible under load when taking the
impression
Extend sufficiently to support the impression material in
the region being reproduced
Fit loosely around the dental arch and not touch the soft
tissues
Have adequate means of retaining the impression
material in the tray
Have a robust (integral) handle
Be able to be adequately decontaminated (if not meant for single use)
Name the 10 desirable properties of impression materials?
Easy to handle
Compatible with oral fluids
Reproduce detail accurately
Have good tear resistance
Have no adverse effects on the patient
Have a pleasant taste
Easily removable from the mouth especially from undercut areas
Be able to be adequately decontaminated
Remain dimensionally stable after removal
Compatible with all model construction materials
Desribe the spacing for different types of impression materials?
3mm – Alginate
2mm – C-Silicone
1mm - Impression paste and Impression plaster
Good thing about special trays?
Permits equal thickness
of impression material
What is an addition silicone impression material?
Elastomeric impression material Termed after setting reaction (addition polymerisation reaction) Hydrophobic
How does filler affect addiition silicone impression material?
Amount of filler added will also determine the
category of material i.e. heavy, universal or light-
bodied
Which chemical in the constitiuents of addition silicone impression material is vital? and why?
Surfactant
Added to address the hydrophobicity of the polysiloxanes
Aid in the pouring of the model as the wet stone has an affinity for the hydrophilic surface of the impression
What is the reaction for an addition silicone impression material?
Poly methyl hydrogen siloxane in one paste +
vinyl-terminated polysiloxanes in the other
Addition polymerisation reaction
Forms a cross-linked polymer
What should you not use with addition silicone impression material?
Latex gloves due to sulphur residues
What are the properties of addition silicone impression material?
Dimensionally stability is very good
More than one model may be poured
May be too accurate and not compensated for during the investment and casting process
Too small a die is produced leading to a small cast
Set after 2-3 hours (cross-linking)
What is a known disadvantage of using addition silicone impression material when it comes to pouring the cast?
Some addition silicones release hydrogen gas as a by-product
• May become incorporated into the model → porosity in the die material
• Leave for 30 minutes before pouring the cast in the case of a gypsum material and overnight if epoxy is to be used to make the die
Name 1 commerically avaliable addition silicone impression material?
Affinis - Coltene Whaledent
What is the definition of a polyether impression material?
Most hydrophilic elastomeric impression material
Presented as a paste/paste system (base &
accelerator)
Used as a monophase impression technique
Non-toxic
Non-irritant
Explain the setting reaction for polyether impression material?
Cross-linking reaction between the aziridine at
the end of each polyether molecule
Chain lengthening occurs at the same time as
cross-linking between chains
Occurs by cationic polymerisation of the imine
groups on the polymer chain
Unlike other elastomeric materials the base to
accelerator paste ratio is not 1:1 but 4:1
What are the properties of polyether impression materials?
Notoriously very stiff
Good tear resistance
Good dimensional stability - leave for 30 mins
Polyether impression materials absorb water
Disadvantages of polyether impression materials?
May present some difficulty on removal: - contraindicated in a special tray - care with metal stock trays - select a slightly larger tray - block out undercuts - place soft (modelling) wax or caulk under bridge pontics Thin dies as these may fracture when the impression is removed from the casts aste being on the unpleasant side!
Indicitons for polyether impression materials?
Indirect cast restorations
Implant work
Functional impressions
Describe polysulphide impression materials?
Paste/Paste
Unpleasant smell and taste
Long set time
Name the base paste constituents for polyether impression materials?
Base paste:
Polyether polymer - 50–60% - Polymer which on initiation will crosslink further
Colloidal silica/diatomaceous earth - 5–10% - Filler
Glycoether or phthalate - 10% - Plasticiser
Name the accelerator paste constituents for polyether impression materials?
Alkyl aromatic sulphonate such as
2,5-diclorobenzene sulphonate *– Initiator of cationic ring opening polymerisation
Colloidal silica/diatomaceous earth – Filler
Glycoether or phthalate – Plasticiser
Name the base paste constituents for polysulphide impression materials?
Polysulphide polymer
(thiokol rubber) - 80–85 - Polymer, which on initiation will cross-link so setting the impression
Titanium dioxide
Silica
Copper carbonate - 16–18% - Filler (increases with viscosity of paste); particle size is in the range of 2–5 μm
Name the accelerator paste constituents for polysulphide impression materials?
Lead dioxide - 60–66% - Oxidizing agent that acts as a cross-linking agent
Dibutyl phthalate - 30–35% - Plasticising agent
Sulphur - 1–1.5% - Enhances the reaction
Oleic or stearic acid - 1–2% - Retarder
What type of reaction happens for a polysulpide imprssion material?
Condensation polymerisation reaction
Slightly exothermic with a temperature rise of
about 3–4°C
Cross-linking occurs between the polymer
chains later in the reaction
Material becomes stiffer and more resistant to
permanent deformation
What are the disadvantages of polysulphide impression materials?
Susceptible to environmental changes namely
temperature and humidity
Incompatible with moisture
Contracts slightly on setting
model will be slightly larger and creates space for the luting cement
Need to be poured as soon as possible
What are the properties of polysulphide impression materials?
Dimensionally stable
Good tear strength
Describe agar as an impression material?
Reversible hydrocolloid
Non-toxic
Non-irritant
Only true hydrophilic Impression material
What are the constituents of Agar impression material?
Agar - Dispersed phase of the colloid - 13–17%
Potassium sulphate - To counter adverse effect of borax on setting reaction of model plaster - 1.0–2.2%
Borax - To strengthen the gel - 0.2–0.6%
Alkyl benzoate - To prevent mould growth in impression during storage - 0.1–0.2%
Wax - Filler - 0.5–1.0%
Thixotropic materials - Viscosity regulators and
thickeners - 0.2–0.4%
Colours and flavouring - To enhance the taste and
appearance of the material - <0.1%
Water - Provides the continuous phase of the colloid. The amount present determines the flow properties of the sol and the physical properties of the gel phases - 79–85%
What is the setting reaction for agar impression material?
Gel may be converted to its sol state by heating to between 70 and 95°C
Known as the liquefaction temperature
Phase transformation back to the gel stage occurs at a much lower temperature (between 35 and 50°C)
Permits the gel to be heated sufficiently and placed in the sol state in an impression tray
Assembly is tempered allowing the temperature to be lowered until the patient can tolerate the material being seated in the mouth in a fluid state
Impression tray may be cooled to lower the temperature of the sol which then solidifies
What is the hardware required to carry out an impression using agar?
Hydrocolloid bath and metal trays incorporating
water cooling coils required
facilities to pour the models as soon as possible
Dimensional stability of the agar is determined
by the relative humidity and temperature
How many times can you heat up agar before it must be discarded?
May only be repeated up to four times before the material
is discarded because it becomes increasingly harder to
break down the agar structure after repeated reheating
Explain how to carry out an impression using agar impression material?
Material removed from bath and placed in syringe
Injected around prep and immediate surroundings
Another is used to fill the selected perforated tray
Connection of cooling hose
Tray is seated over dental arch
Cooling system is connected
Tray held steady in mouth - until reaches transition temp
Tray must be removed quickly
Indicaitons for agar impression maetial use?
Accuracy is very important, such as for fixed indirect restorations
Dental laboratories to duplicate models
How must the viscosity of the agar impression material be adjusted?
Viscosity should be such that it is sufficiently thick that it will be retained in the tray but not so viscous that the material will not flow around the teeth as the tray is seated
What are the properties of agar impression material?
Very little distortion
Low tear resistance
What are the disadvanatges of using agar imprssion materials?
May take up excess water and swell with this
swelling being uncontrolled in direction and
extent (imbibition)
Syneresis occurs if left for a period of time before
being cast
Impression should be kept at 100% relative humidity
Need generous thickness of material to limit the
deformation which may arise on removal especially
from an undercut
From most viscous to least viscous name the elastomeric impression material in order?
putty heavy-bodied medium (or regular/universal-bodied) light-bodied extra light-bodied
What is the defintion of thixotropy? and how else is it referred as?
‘how it flows and stays where it has been placed without dripping’
Structural viscosity
How is viscosity affected?
By temperature
What problems can viscosity cause when pouring impression materials?
Failure of the impression
material to flow will cause
irregularities in the
impression
Explain the process for a standard impression technique using heavy and light bodied impression material?
Heavy body and light-bodied wash in a
stock tray
Heavy body provides support for the light-
bodied material which on its own would distort
under load
Light-bodied material is sufficiently fluid to
reproduce the fine detail where required
Name the 4 advanatges of using heavy-bodied over a putty?
No displacement of the teeth
No deformation of a non-rigid tray
No displacement of the light bodied material from
around the preparation
No folding of the putty leaving a defect like a seam in the impression
Explain the process for a standard impression technique using universal impression material?
Injected around the
preparation and also fills the tray
Loaded tray is then seated over the syringed
material
Detail reproduction of the universal paste must be
sufficient to provide an adequate representation
of the preparation
Monophase impression
Use a non-perforated tray
What can affect the working and setting times of impression materials?
Temp
Humidity
Why do the same materials have different working and setting times? and which has the longest?
Different consistencies of the same material frequently show differing working and setting times Polysulphide
Which impression materials show the best dimenstional stability?
Polysulphide shows the next greatest shrinkage
Polyether and addition silicones show minimal shrinkage
Addition silicones are the most dimensionally stable
Why does shrinkage occur for impression materials?
Determined by their setting
reaction
Any by-product of the setting reaction causes material to shrink
What is the consequence of dimensional chnage on setting? and how can it be solved?
Die cast being larger than mouth
Increased cement lute thickness
Describe the 2 types of shirnkage?
Section of rubber will shrink toward the centre of the mass of that component
Where angled features of the preparation exist this usually leads to curling of the margins
Which elastomeitc impression material recoevrs best frim deformation from best to worst?
Addition silicone (0.05–0.2%)
• Polyether (1.5–2.0%)
• Condensation silicone (1.5–3%)
• Polysulphides (3–5%)
What is the defintiion of strain?
Flexibility of the material
Which elastometic material has the most strain?
Polysulphides
Condensation silicones are slightly more flexible
than the addition silicones while polyether is the
stiffest of the four common elastomers
Think removal from die casts
How is hardness measured and how does it measure?
Measured using a Shore hardness device
Measures the depth of an indentation in the material
created by a given force under a standard load
How does hardness change with time for elastomeric impression materials?
Polysulphide and addition silicones do not change
with time but all the other materials become harder
What proeprties form the worst combinantion for impression maetrials?
low flexibility and high
hardness values are more difficult to remove from
the mouth
WHen can high tear strength casue a problem?
High tear strength may cause problems
removing the impression
Especially when it has flowed between the teeth
or under bridge pontics
May have deformed greatly before the material
tears which may be irreversible and lead to an
inaccurate model
How is detail reproduction infleunced by filler content?
Light-bodied materials contain less filler
Also flow more readily over the preparation and
there is less likelihood of air being trapped
Filler size also determines the ability of the
impression material to record fine detail
How to apply impression material to improve the quality of the impression?
• Keep tip of syringe in the body of material at all times to prevent air becoming entrapped in the mass of material • Apply in a stirring motion to ensure good adaptation to the preparation
Why is good mositure control necessary for elastomeric impression materials? and why is it critical to remove?
All the elastomers are hydrophobic Good moisture control is essential otherwise the detail reproduction will be inadequate May be achieved using high-speed suction saliva extraction and isolation of the site with cotton wool rolls or dry guards Moisture acts as a separating medium so preventing the impression material from bonding to the tray
Name the types of failure in impressions?
Thinning of material Impression distortion Impression tearing Incomplete anatomical capturing Dragging Voids Poor margins Light body displacement Over/undermixed
What are boxing waxes used for?
used to retain the gypsum when it is poured into the impression
What are bbeading waxes used for?
used to block out undercuts
Why are waxes ideal for being used for auxillary processing?
Can be moulded easily to the shape required
Can be easily removed after the gypsum material has set
Are relatively inexpensive
What is carving waxes used for?
Demonstartion purposes (diagnostic)
Name the 3 types of inlay waxes?
Hard
Medium
Soft
Describe the properties of inlay waxes?
High level of detail and dimensional accuracy required
Soft
Not flake or fragments
Used in thin section
Flow characteristics of wax must be such that once pattern is removed from model it shows minimal stress relief
Heated to between 45 and 50°C
Thermal expansion has to be modified so that the dimensional change of the investment material during the investment process may be compensated for
What are pattern waxes used for?
Used to construct the wax “framework” which then forms the metal skeleton/baseplate
Creates specific design features
Name the 2 types of pattern waxes?
Prefabricated
Uniform thickness
Describe the properties of preformed pattern waxes
slightly stickier
very ductile as they must be adapted around teeth
What are baseplate waxes used for?
Denture base
Uniform thickness
Describe the lost wax technique?
- Wax pattern is made which corresponds to the shape of the object (designed to burn out at a temperature below 600°C)
- Sprue is then attached to the wax pattern
- Distal end of the sprue is attached to a apex of a cone shaped rubber mould (ensure that the molten alloy will flow directly into all parts of the device without damaging the investment)
- Metal casting ring is lined by a piece of lining material usually an aluminium silicate ceramic or cellulose paper liner
- Investment material is then poured into the casting ring
- When investment material has set, rubber casting base is removed and casting ring contents are placed in a burnout oven to remove the wax
- Alloy may now be introduced into the void in the casting ring to form the prosthesis
- Casting is now removed from investment material and ring
- Casting covered with surface oxides which require to be removed
- Sprue is then removed, casting finished by grinding and polishing until a high lustre is gained
Indications for the lost wax technqiue?
Used to construct fixed prosthodontic restorations such as inlays, onlays, crowns, bridges and removable prostheses
What is the definition of an alloy?
the by-product of the fusion of two or more metal elements after heating above their melting temperature
Which grain size is better and why?
It determines the properties of the alloy, and the smaller the grains are better as the more boundaries prevent dislocations in the structure
What are grain refiners and give 1 example?
They prevent dislocations in the structure, such as iridium or ruthenium
What is the definition of yeild strength?
Is the force per unit area required to permanently deform the alloy
What is the definition of yield point?
as the stress at which a material begins to deform plastically. Once the yield point is passed a proportion of the deformation will be permanent and irreversible
What is the definition of ductility?
is the ability of an alloy to deform under tensile stress
What is the definition of stiffness?
determined by its elastic modulus and the design of the casting
Why can an alloy be in different phases?
Alloys are composed of several individual metals so they have a melting range
What is the definition of liquidus?
Temperature at which the alloy liquefies on heating
What is the definition of solidus?
the temperature at which it becomes a solid again
How biocompatible are metal alloys?
Responsible for a hypersensitive reaction in approximately 12% of females and 7% of males worldwide
Nickel
Manifests clinically as an unpleasant metallic taste, irritation or allergy
Name 5 noble alloys?
Gold Platinum Rhodium Ruthenium Iridium Osmium
What is the definition of a noble alloy?
An alloy with a precious metal present as its main metal
Casting alloys?
Only metal present
Bonding alloy?
Fuses with another material, such as ceramic
Describe TI gold alloy?
Soft, used for small inlays in low-stress areas
Describe TIV gold alloy?
Increased hardness, tensile strength and yield strength
How is an increased in TIV gold alloy hardness acheived?
Copper mainly responsible due to order hardening
Copper atoms form ordered clusters instead of being randomly distributed within the alloy
Ordered atomic structure prevents movement or slippage of the layers of atoms
How much copper must be added?
11%
What is the role of zinc in alloys?
Oxygen scavenger
What are the properties that make prescribing cast gold restorations desirable?
Very strong in thin sections
Tooth tissue conserved
Wear resistance same as enamel - and so wont wear away opposing tooth
Durable in function
Dimensionally very accurate - reduces adjustment
Good longevity
Easily polished
What is the miniumum thicjness for gold?
1mm and 1.5 mm over functional cusps
When are cast gold restorations contraindicated?
Primary dental disease should be under control first
Non-tooth looking apperance
Cost
How can you bond gold alloy to the tooth?
Gold alloy has no inherent ability to bond chemically to tooth tissue
Restorations usually luted into or onto the preparation
May be heat treated so that it can bond to tooth tissue with use of adhesive resin-based cement
Forms a surface oxide layer of copper oxide to which resin-based adhesive may bond
What is the protocol for heat treating a gold alloy?
Firstly sandblast fitting surface followed by the heat treatment
400C for 9 mins
Must contain at least 11% copper
Why should you autoclave crowns coming back from the lab?
Contamination with bacteria
What is a good tip before placing the crown?
Measure the thickness of the metal to be adjusted by using an Iwannson gauge
Prevents inadvertent perforation of the surface being adjusted
Give 2 examples of commercially avaliable casting alloys?
Argenco 10S by Argen Corp TIII gold alloy
Argenco Bio2 by Argeb Corp TIV gold alloy
What is the defintion of a bonding alloy?
Tooth-coloured restorations a metal substructure may be partially or fully covered in ceramic to give the restoration the appearance of a natural tooth
Metal-ceramic
Porcelain-bonded restoration
Bonding alloy vs Casting alloy?
Bonding less metal
Casting more metal
Can we fuse noble or base metal alloys to ceramic?
Yes
Why is it necessary for the coefficients of thermal expansion of bonding alloys need to be similar?
Need to be similar otherwise expansion and contraction will occur on heating and cooling causing cracking of the ceramic
What are the dimensions needed for a bonded crown?
Under ideal circumstances minimum interocclusal clearance for a bonded crown is 1.7 mm (0.6–0.8 mm of metal coping + 0.9–1.1 mm thickness of ceramic)
Minimum thickness of 1 mm with an all-(noble)-metal occlusal surface
Name the 3 methods to fuse cermaic to metal?
Compression fit
Micromechanical retention
Chemical union
Describe the compression fit for fusing ceramic to alloy?
Ceramic shrinks when fired so it shrink fits onto metal coping
Describe the micromechanical retention for fusing ceramic to alloy?
Surface of metal coping exhibits irregularities
Micromechanical bonding of ceramic onto metal will occur as ceramic may flow during firing
May be enhanced by sandblasting metal surface prior to application of ceramic
Describe the chemical union for fusing ceramic to alloy?
Chemical bonds will form via oxide layer so connecting ceramic and metal alloy
Enhanced by inclusion of elements such as tin, gallium, indium or iridium
These elements tend to be burned out during casting so a proportion of new alloy must be used with every subsequent casting so that a sufficient amount is maintained
name the 4 categories for bonding alloys?
High gold alloys
Gold-palladium alloys
Palladium-silver alloys
High palladium alloys
Why is the melting range of the bonding alloy important?
Appreciable difference between the firing temperature of the ceramic and the melting temperature of the alloy
The solidus must be considerably higher than the fusion temperature of the ceramic
If these temperatures are too close permanent deformation of the metal substructure can occur during firing of ceramic
Indicaitons for base metal bonding alloys?
Higher bond strengths are gained to resin composite adhesive cements than with noble metal alloys
Cost
What are the advantages and disadvanatges of base metal alloys?
Adv: - good corrosion resisatnce - low creep - high modulus - high yield strength - low density Dis: - allergy to nickel - toxic due to beryllium - difficult to cast - high shrinkage - difficult to finish and polish - adhesive failure due to oxide layer
What is the definition of sandblasting?
Sandblasting creates a rough surface to facilitate micromechanical bonding
Application of an acid to the metal coping is another method
Maryland bridge
Maryland bridge?
Acid-etch bridge
What is the definition of a ceramic?
an inorganic non-
metallic solid produced
by the application of heat
which is then cooled
Why does dental ceramics have low kaolin compared to decorative ceramic?
Influences optical properties and therefore aesthetics of the final restoration
Kaolin is absent in dental ceramics because it is opaque
What are the charactersiitcs of a feldspathic ceramic?
Vitreous (glass) ceramics are made up of a silica network • Contain either potash feldspar (potassium alumino silicate) and/or soda feldspar (sodium alumino silicate - albite) • Amorphous structure
What is the definition of pyroplastic flow?
Plastic heats, melts then mixes together removing the amorphous structure
Explain for manufacture of ceramic powder?
Made by taking the raw materials and grinding to a fine powder
Blended and fired at a high temperature in a furnace
Molten mass thus produced is then rapidly cooled in cold water
Why must air be removed when creating the ceramic powder?
Very important that powder particles are very closely packed so that a dense compact structure without air inclusions is produced
Otherwise these residual voids within the ceramic are areas of weakness which will facilitate crack propagation
Minimum amount of air must be incorporated into powder slurry
during this process to avoid porosity and stress concentrations
in final product
Name 4 types of coping materials?
Metalalloy
Alumina
Spinel
Stabilised zirconia
Why are stains added to crowns?
Stains may be applied using a paint brush to characterise final
restoration
Applied to surface of restoration or become incorporated within
the ceramic
Surface stain may be lost if any adjustment is made or during
function
What is the definition of glazing?
Final stage of firing process is glazing • Produces a glassy smooth surface thus sealing it • Any small areas of porosity at surface are filled • Achieved by • very carefully re-firing restoration to fuse outer layer of ceramic completely • using glazes with lower fusing temperatures (transparent glass) which are applied as a thin layer to outer surface of restoration
Name 3 other ways to manufacture a ceramic crown?
Pressing
CAD/CAM
Combo
What are the properties of dental ceramics?
Brittle Corrosion resistance Colour stability Very smooth finish Highly translucent Highly biocompatible Chemically stable Dimensionally stable
What are the mechanical properites of dental ceramics?
Strong
High elastic modulus
Low tensile and flexural stength
Behaves like glass in tension and flexure
Describe the 3 classifications for ceramics?
Glass-matrix
Polycrystalline
Resin-matrix
What is the defintion of glass-matrix ceramics?
non-metallic inorganic
ceramic materials that contain a glass phase
What is the defintiion of polycrystaline ceramics?
non-metallic
inorganic ceramic materials that do not contain
any glass phase
What is the defintiion of resin-matrix ceramics?
polymer-matrices
containing predominantly inorganic refractory
compounds that may include porcelains,
glasses, ceramics and glass-ceramics
Name the 3 types of glass-matrix ceramics?
Feldsapthic
Synthetic
Glass-infiltared
Name the 4 types of polycrysaline ceramics?
Alumina
Stabilised zirconia
Zicornia tougened alumina
alumina toughed zirconia
Name the 3 types of resin-matrix ceramics?
Resin nanoceramic
Glass-ceramic in a resin interpenerating matrix
Zirconia-silica cermaic in a resin interpenetrating matrix
What is the definition of a leucite ceramic?
Leucite (crystalline phase of potassium aluminium
silicate) and a glass phase formed
Potassium feldspar forms leucite crystals by being
heated to a temperature of between 1150 and
1500°C
Difference between leucite and feldspar ceramics?
Leucite is the heated up version of feldspar
What is the advantages of lithium disilicate?
Small, interlocking, randomly orientated needle-
like crystals
70% crystalline in volume
c3 times stronger than a conventional feldspathic
ceramic
Very effective at preventing crack propagation (high
fracture toughness)
May be bonded to tooth structure - glass phase active allows this
What are the indications for lithium disilicate?
Veneers Inlays Onlays Crowns 3 unit anterior bridges
What are the advanatges of glass infiltrated of alumina?
Tougher crystalline material such as alumina
used to produce a strengthened coping
Alumina crystals effective crack stoppers
Prevents propagation of a crack which has
developed in the weaker superficial phase of the
material
Name the process of glass infiltarted of alumina building?
Slip casting
What are the properties of polycrystalline ceramics?
Fine-grain crystalline structure
Provides high strength and fracture toughness
Limited translucency
Chemically more inert - no glass phase (no etching potential)
What is the definition of trasnformational toughness?
When a crack propagates through the material,
strains form at the leading edge
• Results in change in phase from tetragonal to
monoclinic
• Crack closes due to pressure applied by
volumetric change
What are the properties of stabilised zirconia?
High flexural strength of 650MPa
• Low thermal conductivity
• Biocompatible
• Opaque
How to stabilise stabilised zirconia?
Tetragonal or cubic phases must be stabilised at
room temperature by the alloying pure zirconia
with oxides such as yttria, cerium, magnesium
and calcium
What is the definition of resin-matrix ceramics?
Materials with an organic matrix highly filled with
ceramic particles
Aims of resin-matrix ceramics?
Obtain a material that more closely simulates the modulus of
elasticity of dentine
• Facilitate milling and adjustment
• Facilitate repair or modification with resin composite
What are the indications for ceramic restorations
Aesthetics
Root filled teeth
Types of restorations that can be used with ceramics?
Veneers inlays onlays crowns bridges implant supra- and substructures denture teeth
What are the contraindications for ceramic restorations?
Parafunction • Unfavourable occlusion • Immature teeth • Subgingival preparations (mainly for adhesive cementation)
What ceramic would you use for an impnat substructure?
Zirconia, as it can be milled from a block
What type of marginal finish does zirconia need?
Chamfer finish
What type of marginal finish is necessary for lithium dislicate?
Radial shoulder
What can occur if the ceramics fracture?
If the unsupported ceramic is thicker than 1 mm
it will have no support from the underlying tooth
structure - risk of flexure during function and
thus fracture
Disadvantages of using metal alloy coping?
Minimum bulk of a precious metal alloy and ceramic is generally
considered to be 1.7 mm although most technicians would prefer
2.0 mm
• Allows 0.9–1.1 mm of ceramic facing and 0.6–0.8 mm of
precious metal alloy
Less conservative
Give 2 examples of commercially avaliable sinstered ceramics?
IPS InLine by Ivoclar Vivadent
IPS e.max cream by Ivoclar Vivadent
Name the probelms with ungalzed ceramics?
There is a large volumetric shrinkage so difficult to control occlusal contacts accurately
• It is abrasive in the unglazed state
What is the defintion of a biscuit try in?
Large volumetric shrinkage seen when ceramic
is fired makes the creation of exact and accurate
occlusal contacts impossible
• In order to overcome these problems, try-in
appointment in the biscuit (or unglazed) state is
recommended
• Also allows the clinician and patient to assess
the aesthetics
• Termed a biscuit try-in
Advantages of reglazing and polishing?
Reglazing:
- better result
- surface resealed
Polishing:
- done intraorally
- no further appointments
What is the definition of resin-bonded ceramics?
bonded onto tooth tissue by the use of a resin based composite adhesive if they are firstly chemically treated
Name 3 types of resin-bonded ceramic?
Fledspathic ceramic
Leucite containing feldspathic glass
Lithium disilicate and derivatives
How to construct a resin-bonded ceramic?
• Methods of construction:
• Refractory die is made and the ceramic is built up and then
sintering onto it
• Lost wax technique used and ceramic pressed onto die
• Ceramic block is milled
• Fitting surface is then etched with 5%
hydrofluoric acid for 20s and silanated prior to
being sent to the clinic for fitting
Give 1 commerically avalibale hot press ceramic product?
IPS e.max Press by Ivoclar Vivadent
How can stabilised zirconia be adjusted to bond to silanting agent?
Snadblasting, which then allows chemical bond to resin adhesives
Name 2 commercially avaliable CAD/CAMs products?
Cerec 3D by Sirona
etkon-CADCAM CS II by Straumann
Name the 17 ideal properties of an ideal luring material?
Not harm patient Adhere chemically, mechanically or micromechanically Sufficient working time Low film thickness and fluidity to allow seating of restoration Quickly form a hard mass High tensile strength High compressive strength High fracture toughness Modulus of elasticity which is appropriate for stress absorption Not dissolve Radiopaque Good seal Cariostatic Technique insensitive Easy and accurate proportioning Range of shades Easy to clean and remove excess
What is the defining of luting?
Filling up of potential gap between a cast restoration and tooth
Name the 2 types of luting materials?
Conditional cements
Luting resin composites
What are the benefits of luting resin composites compared to conventional?
Wear resistance
Aesethtic
Insoluble to oral fluids
Better mech properties
Give 8 options of luting cements?
Zinc oxide eugenol Zinc oxide EBA Zinc polycarbonate GIC RMGIC Composer Zinc phosphate Resin composite
What are the differences for cements between dressings and lutings?
Viscosity
SA:V
How to use resin adhesive systems for bonding indirect restorations?
Etch and bond used
Bonding agen forms a bond with luting material
Name 5 types of resin composite luting systems?
Chemical cure Light cure Dual cure Self-adhesive Smart
Describe how a chemically cured resin composite luting cements works?
Bond metal to tooth tissue or adhesive gold restorations
Gel applied around margins of the restoration
Setting in 4 mins
Fallen out of favour
Describe how light cured resin composite luting cements work?
Only used when the light curing unit may predicdably access the cement such as ceramic veneers
No tertiary amine stops shade shift
Indications for dual cured resin composite luting cements?
Crowns Bridges Inlays Inlays Non-metallic posts
Describe how dual cured resin composite luting cements work?
Self etch bonding agents and dual cured luting composites cant be used together
Non tertiary amine
Give 2 example of commercially avaliable dual cured resin compositeutong cements?
NX3 - Kerr Hawe
Panavia V5 - Kuraray
Describe self-adhesive resin luting materials and their advantages?
Etches the dental hard tissues Goes from hydrophilic to hydrophobic No intermediate bonding Saves time Easier to use
Describe a ‘smart’ resin luting materials?
Contains a component which facilitates the polymerisation of an unpolymerised dentine bonding agent which is applied to the tooth
Rely X ultimate and used with Scotchbond Universal
Name 2 types of restoration substrates?
Metallic alloys - NiCr, CoCr and gold
Ceramics - glass phase and polycrystalline
Explain how to bond to non-precious metal alloy?
Fitting surface treated to enhance bond by acid etching and sandblasting
Increases surface energy, roughness, surface area and wetability but decreases surface tension
Creating of a stable chemical bond to the oxide layer from the acid ester in the composite cement
Thick oxide layer is formed with alloy
Must be thinned
Sandblast prior to fitting
Explain how to bond to gold alloy?
Copper and iridium need to be added to gold alloy
Must contain at least 16% copper (TIV gold alloy)
Heat treated at 400C for 9 mins
Thin oxide layer formed
Restoration bonds by combo of chemical and micromechanical bonding
Adhesion of resin composite to gold via disulphide methacrylate which forms a methacrylate gold compound bond via sulphur atom
How does Rely X Ultimate and Panavia V5 have further chemical adhesion?
10-MDP
Describe how bonding of resin composite to glass ceramics?
Chemcially active glass phase permits chemical bonding
Surface etched with 5% hydrofluroic acid for 20s (toxic, lower time and conc)
Create microretentice etching pattern
Silane coupling agent yMPS aplled to etched surface
Bonds to silane methacrylate to form methacrylate silicate compound
Hydrolysis and condensation reaction
Created covalent bond
Increases wetability
What is silanation?
Silage coupling agent such as acetone Solvent Degrades by hydrolysis Stored in fridge Added chair side
How to sandblast resin composite to bond to glass ceramics?
Cojet
Then apply silane coupling agent
Then resin composite luting cements to dental hard tissue
Describe polycrystalline ceramics?
No glass phase
Can’t be etched
Usually luted
Explain the 3 types of protocols for polycrystalline ceramics?
Sandblast fitting surface Clean with alcohol, then dry Apply lute and seat OR Sandblast with cojet Apply silane Apply lute and seat OR Use 10-MDP
Explain how to remove temporary cement?
Flour of pumice and water slurry on rubber cup with slow handpiece
No prophy paste as it has oils
Use of try in paste?
Ascertain final shade
Matches set cement
Allows for to be assessed better
Need to be removed prior to actual seating
Deacribe the clinical procedure of cementation?
Rubber dam PTFE tape on adj teeth Mechanically clean tooth with pumice and water slurry on a brush Don't overdry tooth Apply ivoclean - cleans restoration Cement applied sparingly to axial surfaces of cast Aim to not have much excess Seat resto under gentle pressure Maintain pressure Tack cure margins Remove excess Light cured margins
What is the best to use to lute a restoration?
Reain composite based cements as they have higher strength and low solubility
Name the powder constituents for zinc phosphate cements?
Zinc oxide MgO2 - white colour and compressive strength Al2O4 - mech prop SiO2- colour and calcination process Fl - cariostatic
Name the liquid constituents for zinc phosphate?
Phosphoric acid
Water
Al - buffer, forms cements
Zn - stabilises pH and reduces reactivity, increases working time and faciliates cement mixing
What is the role of Al in zinc phosphate reaction?
Prevents crystallisation and permits the formation of an amorphous cement
What occurs during the maturation phase of zinc phosphate?
Water is bound more strongly into cement leading to a stronger and less soluble cement
Dearibe the structure of zinc phosphate cement?
Cored structure
Only surface zinc particle react
Surrounded by a matrix of zinc phosphate
How can zinc phosphate cement reaction be a risk to the teeth?
Exothermic
Heat cause pulpal trauma
How to reduce the potential risk from zinc phosphate?
Buffers in liquid compinebt
Tears powder by heating above 1000C to make it less reactive - converting to granules, then sintered with other less reactive oxides, and grounded to a fine powder
Name factors which affect the speed of setting of zinc phosphate?
Calcination Composition Cooled glass slab - mixing Condenstation on slab Varying rate of powder added to liquid Temperature
Deacribe the cement lute thickness of zinc phosphate cement?
Thinnest of all avaliable luting agents
25um
Deacribe the mode of retention of zinc phosphate cements?
Grouts only
Form tags between the microitreguaktiriws on the 2 surfaces being luted
Sandblasting increases retention
Deacribe the solubility of zinc phosphate cement?
Low
Addition of water weakness the structure
Cement erodes below 4.5 pH
How to use zinc phosphate cement to lute restorations?
To achieve optimal film thickness:
- maintain seating pressure
- vent restoration of full crown
Minimum delay
How can viscosity of zinc phosphate cement affect the pH?
Runny low as 2
Stiff high as 3
Moisturenin dentine can have a buffering effect
Name the advantages and disadvantages of zinc phosphate cement?
Adv: - easy to mix - sharpnset - acceptable properties - cheap - good track record Dis: - irritant to pulp - non bonding - brittle - no antibacterial - soluble - opaque
Name the indications and contradictions of zinc phosphate cement?
Indications:
- definitive cementation for inlays, metal based crown, metal bases bridge and ortho bands
- based
- temp restoration where adequate resto is present
Contraindications:
- definitive cementation of all ceramic crowns and bridges due to opacity
- close to pulp without lining
