Dental Ceramics / Dental Porcelain

25-mark university answer

Contents

1. Definition
2. Ideal requirements
3. Composition of dental porcelain
4. Classification
5. Types of dental ceramics
6. Fabrication methods
7. Properties
8. Advantages
9. Disadvantages
10. Uses / indications
11. Failure and prevention
12. Conclusion

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1. Definition

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2. Ideal requirements of a dental ceramic

• Natural translucency, fluorescence, and shade matching teeth
• High compressive strength and adequate flexural strength
• High hardness and wear resistance
• Good fracture toughness
• Resistance to dissolution and chemical degradation in saliva
• Biocompatibility and tissue compatibility
• Low thermal conductivity
• Dimensional stability during firing
• Coefficient of thermal expansion compatible with tooth structure or metal/ceramic substructure
• Ability to bond to tooth structure or suitable luting cement
• Smooth, highly polishable surface
• Minimal abrasion of opposing natural teeth

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3. Composition of conventional dental porcelain

Functions of main constituents

Feldspar

• Potassium and sodium aluminosilicate.
• On heating, it forms a glassy phase.
• Responsible for translucency and esthetics.

Quartz

• Remains largely unchanged during firing.
• Provides strength and reduces excessive shrinkage.

Kaolin

• Gives plasticity to the unfired porcelain mass.
• Present only in small quantity in modern dental porcelains.

Leucite

• Crystalline phase within a glass matrix.
• Improves strength by resisting crack propagation.
• Raises coefficient of thermal expansion, hence is useful in porcelain intended for metal-ceramic restorations.

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4. Classification of dental ceramics

A. According to fusion temperature

• High-fusing porcelains: denture teeth
• Medium-fusing porcelains: some older ceramic restorations
• Low-fusing porcelains: metal-ceramic restorations
• Ultra-low-fusing porcelains: repair porcelains and low-temperature systems

B. According to microstructure and composition

1. Glass-matrix ceramics
2. Polycrystalline ceramics
3. Resin-matrix ceramic materials

1. Glass-matrix ceramics

• Feldspathic porcelain
• Leucite-reinforced glass ceramic
• Lithium disilicate glass ceramic
• Fluorapatite glass ceramic
• Zirconia-reinforced lithium silicate

2. Glass-infiltrated ceramics

• In-Ceram Alumina
• In-Ceram Spinell
• In-Ceram Zirconia

3. Polycrystalline ceramics

• Alumina
• Zirconia, especially yttria-stabilized tetragonal zirconia polycrystal, or Y-TZP

4. Resin-matrix ceramics

• Nanoceramic resin
• Polymer-infiltrated ceramic network materials

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5. Types of dental ceramics

5.1 Feldspathic porcelain

• Excellent translucency and esthetics
• Low strength and low fracture toughness
• Brittle
• Etchable with hydrofluoric acid
• Can be bonded effectively to enamel with resin cement

• Porcelain veneers
• Veneering porcelain for metal-ceramic crowns
• Veneering porcelain for zirconia frameworks
• Characterization of ceramic restorations

5.2 Leucite-reinforced glass ceramic

• Stronger than feldspathic porcelain
• Good esthetics
• Suitable for adhesive bonding
• Moderate fracture resistance

• Veneers
• Inlays and onlays
• Anterior crowns
• Selected posterior single crowns

5.3 Lithium disilicate glass ceramic

• High esthetics and translucency
• Greater strength than feldspathic and leucite ceramics
• Can be etched with hydrofluoric acid and silanated
• Suitable for adhesive cementation
• Available as pressable and CAD/CAM forms

• Veneers
• Inlays and onlays
• Anterior crowns
• Posterior single crowns
• Short-span fixed partial dentures in selected cases

5.4 Alumina ceramic

• High hardness and strength
• More opaque than glass ceramics
• Limited ability to etch and bond
• Mostly replaced by zirconia in current practice

• Ceramic copings and frameworks
• Earlier all-ceramic crown systems

5.5 Zirconia ceramic

• A crack causes tetragonal zirconia crystals to transform to the monoclinic phase.
• This transformation causes slight expansion.
• The expansion produces compressive stress around the crack.
• Crack propagation is reduced.

• Very high flexural strength
• High fracture toughness
• Excellent wear resistance
• Biocompatible
• Radiopaque
• More opaque than glass ceramics, although newer translucent zirconias have improved esthetics
• Cannot be conventionally etched with hydrofluoric acid because it contains no silica glass phase

• Posterior crowns
• Monolithic crowns
• Fixed partial denture frameworks
• Implant-supported crowns and bridges
• Abutments
• Full-arch prostheses

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6. Methods of fabrication

A. Powder-liquid condensation and firing

1. A refractory die or metal framework is prepared.
2. Porcelain powder is mixed with water or a special liquid.
3. Porcelain slurry is applied in increments.
4. Condensation is done to remove water and reduce porosity.
5. The porcelain is dried.
6. Firing is carried out in a porcelain furnace, usually under vacuum.
7. Additional layers are added and fired.
8. Glazing and finishing are done.

B. Sintering

• Reduces porosity
• Increases density
• Improves strength

C. Heat pressing

• Pressable leucite ceramics
• Pressable lithium disilicate ceramics

D. Slip-casting and glass infiltration

E. CAD/CAM milling

• Lithium disilicate blocks
• Zirconia discs
• Leucite-reinforced ceramic blocks

F. Additive manufacturing

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7. Properties of dental ceramics

7.1 Mechanical properties

High compressive strength

Low tensile strength

Brittleness

High hardness

Fracture toughness

• Low in feldspathic porcelain
• Higher in lithium disilicate
• Highest in zirconia

7.2 Optical properties

• Translucency
• Opalescence
• Fluorescence
• Shade stability
• Ability to reproduce enamel and dentin appearance

7.3 Thermal properties

• Low thermal conductivity
• Low thermal diffusivity
• Relatively insulating to the pulp
• Thermal expansion must be compatible with a metal or ceramic framework in layered restorations

7.4 Chemical properties

• Excellent resistance to saliva and oral fluids
• Do not corrode
• Stable colour
• Acid resistance varies with ceramic type
• Glass ceramics can be etched by hydrofluoric acid
• Zirconia cannot be effectively etched with hydrofluoric acid

7.5 Biological properties

• Generally biocompatible
• Smooth glazed surfaces show low plaque accumulation
• Well-polished ceramic margins support periodontal health
• Rough, fractured, or poorly finished surfaces may retain plaque and abrade opposing teeth

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8. Advantages of dental ceramics

1. Excellent esthetics and life-like translucency
2. Stable shade with no discoloration over time
3. High compressive strength
4. High hardness and wear resistance
5. Excellent biocompatibility
6. No corrosion or metallic taste
7. Low thermal conductivity
8. Smooth glazed surface and low plaque retention
9. Radiopacity in many modern systems
10. Can be bonded to tooth structure in silica-based ceramics
11. Suitable for metal-free restorations
12. Excellent resistance to oral fluids and chemical degradation

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9. Disadvantages of dental ceramics

1. Brittle and susceptible to catastrophic fracture
2. Low tensile strength
3. Require adequate tooth reduction and material thickness
4. May wear opposing enamel if surface is rough
5. Difficult to repair intraorally
6. Technique-sensitive fabrication and cementation
7. Risk of chipping of veneering porcelain in layered restorations
8. Some ceramics, especially zirconia, have inferior translucency compared with feldspathic porcelain
9. Cost may be high
10. Ceramic restorations cannot be adjusted excessively after glazing without repolishing

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10. Uses and indications

Feldspathic ceramic

• Laminate veneers
• Esthetic layering porcelain
• Porcelain-fused-to-metal crowns
• Characterization of restorations

Leucite-reinforced ceramic

• Veneers
• Inlays
• Onlays
• Anterior crowns

Lithium disilicate

• Veneers
• Inlays and onlays
• Anterior crowns
• Posterior single crowns
• Selected short-span bridges

Zirconia

• Posterior crowns
• High-load crowns
• Long-span fixed partial dentures
• Implant-supported crowns
• Implant abutments
• Full-mouth rehabilitation
• Monolithic crowns in patients with high occlusal load

Metal-ceramic restoration

• Anterior and posterior crowns
• Fixed partial dentures
• Situations requiring combined strength of metal and esthetics of porcelain

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11. Failures of ceramic restorations and prevention

Common failures

1. Fracture of ceramic

• Inadequate thickness
• Sharp internal line angles
• Excessive occlusal load
• Parafunctional habits such as bruxism
• Poor bonding or cementation
• Defects and porosity within ceramic

• Adequate tooth preparation
• Rounded internal angles
• Correct material selection
• Adequate occlusal reduction
• Proper bonding or cementation
• Occlusal adjustment
• Night guard for bruxism patients

2. Chipping of veneering porcelain

• Improper framework support
• Mismatch in thermal expansion
• Poor cooling after firing
• Occlusal stress

• Anatomically supported framework
• Compatible veneering ceramic
• Controlled cooling
• Avoid excessive occlusal contact on veneering ceramic

3. Wear of opposing teeth

4. Debonding

• Poor surface treatment
• Contamination
• Inadequate adhesive procedure
• Incorrect cement selection

• For glass ceramics: hydrofluoric acid etching, silane application, and resin cement where indicated
• For zirconia: airborne-particle abrasion, zirconia-compatible primer containing phosphate monomer such as MDP, and appropriate resin cement when adhesive bonding is needed

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12. Conclusion

Suggested diagram for the answer sheet

Dental ceramics
│
├── Glass-matrix ceramics
│   ├── Feldspathic porcelain
│   ├── Leucite-reinforced ceramic
│   └── Lithium disilicate
│
├── Glass-infiltrated ceramics
│   ├── Alumina
│   ├── Spinell
│   └── Zirconia-alumina
│
└── Polycrystalline ceramics
    ├── Alumina
    └── Zirconia

Finishing and Polishing of Various Restorations

25-mark university answer

Contents

1. Definitions
2. Objectives and importance
3. General principles
4. Instruments and abrasives
5. Finishing and polishing of amalgam restorations
6. Finishing and polishing of composite restorations
7. Finishing and polishing of glass ionomer cement restorations
8. Finishing and polishing of metallic cast restorations
9. Finishing and polishing of ceramic restorations
10. Finishing of provisional restorations
11. Errors and precautions
12. Conclusion

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1. Definitions

Finishing

• Removal of excess restorative material
• Refinement of margins
• Establishment of anatomical contour
• Correction of occlusal discrepancies
• Removal of sharp edges and overhangs

Polishing

Difference between finishing and polishing

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2. Objectives and importance

1. Restore normal anatomical form and contour.
2. Remove excess restorative material and marginal overhangs.
3. Establish proper occlusion and proximal contact.
4. Improve esthetics by producing a smooth and glossy surface.
5. Reduce plaque retention.
6. Reduce gingival irritation and periodontal inflammation.
7. Reduce staining and discoloration of restorations.
8. Reduce wear of opposing teeth.
9. Improve patient comfort, especially to the tongue.
10. Increase the longevity of the restoration.

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3. General principles of finishing and polishing

1. Use abrasives from coarse to fine

• Coarse abrasives remove gross irregularities.
• Medium abrasives refine the surface.
• Fine and superfine abrasives provide final luster.

2. The abrasive should be harder than the material being finished

3. Use light pressure

• Produce heat
• Damage restoration margins
• Cause ditching
• Create deep scratches
• Remove excessive material

4. Use intermittent strokes

5. Use water cooling whenever necessary

6. Preserve restoration anatomy

7. Finish from tooth surface toward restoration

8. Use appropriate instruments for each surface

• Discs: facial and lingual flat surfaces
• Strips: interproximal surfaces
• Points and cups: occlusal surfaces
• Burs: contouring and gross reduction
• Paste and brush: final gloss

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4. Instruments and abrasives used

Finishing instruments

• Sharp hand instruments
• Carvers
• Scalers
• Finishing burs
• Carbide finishing burs
• Fine diamond burs
• Abrasive discs
• Abrasive strips
• Sof-Lex type discs
• Rubber points and cups
• Silicon carbide stones
• Aluminum oxide discs
• Diamond instruments

Polishing agents

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5. Finishing and polishing of amalgam restorations

Timing

• Conventional amalgam: after 24 hours
• High-copper amalgam: generally after 24 hours
• Some modern high-copper amalgams may permit earlier finishing depending on the manufacturer’s instructions

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Objectives in amalgam finishing

• Remove excess amalgam
• Correct occlusion
• Reproduce grooves, fossae, cusp inclines, and marginal ridge
• Remove sharp margins
• Improve smoothness and corrosion resistance
• Reduce plaque retention

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Armamentarium for amalgam finishing and polishing

• Sharp explorer
• Carvers
• Finishing burs
• Steel finishing burs
• Stones
• Rubber cups
• Rubber points
• Brushes
• Pumice slurry
• Tin oxide paste
• Zinc oxide paste
• Water and lubricant

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Procedure

Step 1: Check occlusion

• Use articulating paper.
• Detect premature contacts.
• Remove high spots with a finishing bur or stone.
• Preserve cusp and groove anatomy.

Step 2: Remove excess amalgam

• Remove marginal flashes and overhangs using sharp hand instruments, finishing burs, or discs.
• Interproximal excess should be removed carefully with finishing strips.

Step 3: Re-establish anatomy

• Reproduce developmental grooves, fossae, marginal ridges, and cusp slopes.
• Do not create deep grooves that weaken the restoration.

Step 4: Smoothening

• Use fine finishing burs, stones, or abrasive rubber points.
• Use light intermittent pressure.

Step 5: Polishing with pumice

• Pumice mixed with water is applied with a rubber cup or brush at low speed.
• Keep the surface wet to prevent heat generation.

Step 6: Final polishing

• Use tin oxide or zinc oxide paste with a soft brush or rubber cup.
• This produces a smooth, shiny surface.

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Advantages of polishing amalgam

• Reduces roughness and plaque retention
• Improves appearance
• Reduces tarnish and corrosion
• Decreases marginal breakdown
• Improves comfort
• Increases restoration longevity

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Precautions

• Do not polish freshly placed amalgam.
• Do not over-carve or over-polish margins.
• Avoid excessive heat.
• Avoid thinning the marginal ridge.
• Do not alter occlusal anatomy excessively.
• Use gentle pressure and adequate cooling.

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6. Finishing and polishing of composite restorations

Timing

• Immediately after curing in most composite restorations
• Delayed finishing may be done in selected situations, especially if there is concern regarding marginal integrity or polymerization stress

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Objectives

• Remove excess composite and flash
• Establish proper contour and embrasure form
• Correct proximal contact
• Reproduce surface texture
• Improve gloss
• Minimize staining and plaque accumulation
• Avoid damage to adjacent enamel and gingiva

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Armamentarium

• Fine diamond burs
• Multi-fluted carbide finishing burs
• Abrasive discs
• Aluminum oxide discs
• Finishing strips
• Interproximal abrasive strips
• Rubber cups and points
• Silicone points
• Polishing pastes
• Composite polishing brushes
• Felt wheels
• Diamond paste or aluminum oxide paste

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Procedure

Step 1: Remove gross excess

• Use a sharp blade, scalpel, fine diamond bur, or finishing carbide bur.
• Remove flash at the cervical and proximal margins.
• Protect adjacent teeth using a matrix strip or metal matrix.

Step 2: Establish contour

• Use fine finishing burs and discs.
• Facial and lingual surfaces are finished using discs from coarse to superfine.
• Maintain normal facial convexity and embrasure form.

Step 3: Finish interproximal surfaces

• Use abrasive strips.
• Start with coarse strips only if excess material is present.
• Finish with fine and superfine strips.
• Avoid damaging proximal contact.

Step 4: Finish occlusal anatomy

• Use fine diamond or multi-fluted carbide burs.
• Re-establish fissures, triangular ridges, cusps, and fossae.
• Avoid unnecessary removal of composite.

Step 5: Polishing

• Use rubber points, cups, spirals, brushes, or fine polishing discs.
• Use polishing paste for final gloss.
• Use light pressure and intermittent movement.

Step 6: Final inspection

• Marginal adaptation
• Surface gloss
• Occlusion
• Proximal contacts
• Absence of sharp edges
• Absence of damage to adjacent enamel

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Important points in composite polishing

• Use a sequence from coarse to superfine abrasives.
• Avoid overheating, which can damage the resin matrix.
• Maintain a wet field where possible.
• Do not use excessively coarse diamonds on the final surface.
• A mylar strip produces the smoothest initial surface, but this resin-rich surface may be less wear resistant and may require careful finishing.
• Final polishing improves stain resistance and esthetics.

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7. Finishing and polishing of glass ionomer cement restorations

Timing

• Conventional glass ionomer cement: usually finish after approximately 24 hours, depending on the product.
• Resin-modified glass ionomer cement: can often be finished earlier after adequate light curing, according to manufacturer instructions.

Objectives

• Remove excess material
• Establish contour
• Preserve marginal integrity
• Avoid desiccation and surface crazing
• Produce a smooth surface that resists plaque accumulation

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Procedure

Step 1: Initial contouring

• Use sharp hand instruments immediately after placement to remove gross excess.
• Avoid disturbing the setting cement.

Step 2: Delay definitive finishing

• Allow sufficient maturation.
• Protect the restoration with varnish, bonding agent, resin coat, or petroleum jelly as indicated.

Step 3: Finishing

• Use fine carbide burs, superfine diamond instruments, discs, or strips.
• Use low speed and light pressure.
• Use water spray where appropriate.

Step 4: Polishing

• Use fine abrasive discs, rubber points, cups, or polishing paste.
• Apply a protective surface coating after finishing if recommended.

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Precautions

• Do not aggressively finish immediately after placement.
• Avoid dehydration of conventional glass ionomer.
• Avoid water contamination during early setting.
• Do not use dry, high-speed instrumentation.
• Avoid over-polishing, which may expose filler particles and increase surface roughness.

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8. Finishing and polishing of metallic cast restorations

Objectives

• Remove excess cement and metal flash
• Smooth margins
• Refine occlusal and axial contours
• Produce a lustrous surface
• Reduce plaque retention
• Improve gingival health

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Instruments and agents

• Fine carbide burs
• Fine diamond burs
• Sandpaper discs
• Rubber wheels
• Rubber points
• Stones
• Pumice
• Tripoli
• Rouge
• Tin oxide
• Chromium oxide
• Felt wheel and soft brush

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Procedure

1. Remove excess luting cement with scalers and floss.
2. Check margins with an explorer.
3. Check occlusion with articulating paper.
4. Adjust high points using fine finishing burs or stones.
5. Smooth margins with rubber wheels and fine abrasives.
6. Polish with pumice or tripoli.
7. Apply rouge, tin oxide, or chromium oxide for final high luster.

Precaution

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9. Finishing and polishing of ceramic restorations

Importance

• Accumulate plaque
• Stain
• Irritate soft tissues
• Cause excessive wear of opposing enamel
• Reduce esthetics

Finishing instruments

• Fine diamond burs
• Extra-fine diamond burs
• Ceramic-specific abrasive wheels
• Silicon carbide points
• Rubber polishing points
• Diamond-impregnated rubber points
• Diamond polishing paste
• Felt wheels
• Ceramic polishing kits

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Procedure

Step 1: Minimal adjustment

• Adjust only when necessary.
• Use fine diamond burs with water spray.
• Use low pressure.

Step 2: Sequential polishing

• Use ceramic polishing kit from coarse to fine.
• Continue through medium, fine, and superfine rubber points.
• Use diamond paste with felt wheel for final gloss.

Step 3: Final evaluation

• Check surface gloss.
• Check occlusion.
• Ensure that no rough area remains in contact with opposing natural teeth.

Glazing

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Special point: Zirconia polishing

• Use fine diamonds only for necessary adjustments.
• Follow with zirconia polishing points, usually diamond impregnated.
• Finish with diamond paste if required.
• Avoid leaving a rough ground zirconia surface, as it may wear opposing teeth.

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10. Finishing and polishing of provisional restorations

Procedure

1. Trim excess material using acrylic burs or carbide burs.
2. Finish with sandpaper discs, rubber wheels, or abrasive points.
3. Polish with pumice and water.
4. Final high shine may be achieved with polishing paste and soft brush.

Importance

• Reduces plaque accumulation
• Prevents gingival inflammation
• Improves patient comfort
• Provides better esthetics
• Allows accurate evaluation of contours and occlusion

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11. Errors and precautions

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12. Conclusion

• Amalgam is generally polished after 24 hours using pumice and tin oxide.
• Composite can usually be finished immediately with discs, strips, points, and polishing paste.
• Glass ionomer cement requires gentle and often delayed finishing because of early moisture sensitivity.
• Cast metal restorations are polished with progressively finer abrasives, pumice, tripoli, and rouge.
• Ceramics require fine diamonds, ceramic polishing systems, and diamond paste after adjustment.

Newer Zirconias in Dentistry

10-mark university answer

Contents

1. Introduction
2. Conventional zirconia
3. Need for newer zirconias
4. Classification of newer zirconias
5. Composition and microstructure
6. Properties
7. Indications
8. Advantages and limitations
9. Conclusion

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1. Introduction

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2. Conventional zirconia

• 3Y-TZP
• Full name: 3 mol% yttria-stabilized tetragonal zirconia polycrystal

Features

• Predominantly tetragonal crystal phase
• High flexural strength
• High fracture toughness due to transformation toughening
• Low translucency and comparatively opaque appearance
• Suitable for posterior crowns, bridges, and frameworks

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3. Need for newer zirconias

• Chipping of veneering porcelain
• Delamination
• Increased laboratory steps
• Greater thickness requirement
• Less natural appearance in anterior teeth

• Greater translucency
• Better shade matching
• Monolithic, metal-free restorations
• Reduced need for veneering porcelain
• Improved esthetics in the anterior region

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4. Classification of newer zirconias

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5. Composition and microstructure

A. 4Y zirconia

• Contains about 4 mol% yttria.
• Has a mixture of tetragonal and cubic phases.
• Provides a useful balance between strength and translucency.
• Known as high-translucency zirconia.

B. 5Y zirconia

• Contains about 5 mol% yttria.
• Has greater cubic-phase content.
• Light scattering is reduced, producing better translucency.
• Has lower strength and fracture toughness than 3Y or 4Y zirconia.
• Called ultra-translucent zirconia.

C. 6Y zirconia

• Contains more than 5 mol% yttria.
• Has very high cubic phase and very high translucency.
• Mechanical strength is lower, so indications are more restricted.

D. Multilayered zirconia

• Shade
• Translucency
• Yttria concentration
• Strength

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6. Properties of newer zirconias

Advantages

1. Improved translucency
   Better esthetics than conventional 3Y zirconia.
2. Better shade integration
   Available in pre-shaded and multilayered forms.
3. Monolithic restorations
   Reduces the need for veneering porcelain and hence reduces veneer chipping.
4. High strength compared with glass ceramics
   Especially 4Y zirconia.
5. Biocompatibility
   Well tolerated by oral tissues.
6. Low plaque retention
   When properly polished.
7. Wear resistance
   Smooth polished zirconia is generally kind to opposing enamel.

Important drawback: strength-translucency trade-off

• Cubic phase increases
• Translucency increases
• Tetragonal phase decreases
• Transformation toughening decreases
• Flexural strength and fracture toughness decrease

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7. Indications

3Y zirconia

• Posterior crowns
• Long-span fixed partial dentures
• Implant-supported prostheses
• Bruxism patients
• High-stress areas

4Y zirconia

• Monolithic anterior and posterior crowns
• Short-span bridges
• Inlays, onlays, and table tops in selected cases
• Cases requiring a balance of esthetics and strength

5Y zirconia

• Veneers in selected cases
• Anterior crowns
• Esthetic single crowns
• Short-span anterior fixed partial dentures where indicated

6Y zirconia

• Highly esthetic anterior single crowns
• Veneers or minimally loaded restorations
• Not preferred for long-span bridges or heavy occlusal loads

Multilayered zirconia

• Esthetic monolithic anterior crowns
• Esthetic posterior crowns
• Full-contour restorations where natural shade gradient is desired

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8. Limitations and precautions

1. Ultra-translucent zirconia is not ideal for long-span bridges.
2. It may be unsuitable for patients with severe bruxism or high occlusal load.
3. Zirconia cannot be etched by hydrofluoric acid because it lacks a silica glass phase.
4. Adhesive bonding, when required, involves air abrasion and an MDP-containing zirconia primer/resin cement.
5. Excessive grinding can create surface defects.
6. After occlusal adjustment, zirconia must be polished with zirconia-specific polishing systems.
7. Cement shade can influence the final esthetic result, especially with highly translucent zirconias.

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9. Conclusion

Higher translucency means lower strength.

Dental Ceramics / Dental Porcelain

25-mark university answer

Contents

1. Definition
2. Ideal requirements
3. Composition of dental porcelain
4. Classification
5. Types of dental ceramics
6. Fabrication methods
7. Properties
8. Advantages
9. Disadvantages
10. Uses / indications
11. Failure and prevention
12. Conclusion

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1. Definition

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2. Ideal requirements of a dental ceramic

• Natural translucency, fluorescence, and shade matching teeth
• High compressive strength and adequate flexural strength
• High hardness and wear resistance
• Good fracture toughness
• Resistance to dissolution and chemical degradation in saliva
• Biocompatibility and tissue compatibility
• Low thermal conductivity
• Dimensional stability during firing
• Coefficient of thermal expansion compatible with tooth structure or metal/ceramic substructure
• Ability to bond to tooth structure or suitable luting cement
• Smooth, highly polishable surface
• Minimal abrasion of opposing natural teeth

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3. Composition of conventional dental porcelain

Functions of main constituents

Feldspar

• Potassium and sodium aluminosilicate.
• On heating, it forms a glassy phase.
• Responsible for translucency and esthetics.

Quartz

• Remains largely unchanged during firing.
• Provides strength and reduces excessive shrinkage.

Kaolin

• Gives plasticity to the unfired porcelain mass.
• Present only in small quantity in modern dental porcelains.

Leucite

• Crystalline phase within a glass matrix.
• Improves strength by resisting crack propagation.
• Raises coefficient of thermal expansion, hence is useful in porcelain intended for metal-ceramic restorations.

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4. Classification of dental ceramics

A. According to fusion temperature

• High-fusing porcelains: denture teeth
• Medium-fusing porcelains: some older ceramic restorations
• Low-fusing porcelains: metal-ceramic restorations
• Ultra-low-fusing porcelains: repair porcelains and low-temperature systems

B. According to microstructure and composition

1. Glass-matrix ceramics
2. Polycrystalline ceramics
3. Resin-matrix ceramic materials

1. Glass-matrix ceramics

• Feldspathic porcelain
• Leucite-reinforced glass ceramic
• Lithium disilicate glass ceramic
• Fluorapatite glass ceramic
• Zirconia-reinforced lithium silicate

2. Glass-infiltrated ceramics

• In-Ceram Alumina
• In-Ceram Spinell
• In-Ceram Zirconia

3. Polycrystalline ceramics

• Alumina
• Zirconia, especially yttria-stabilized tetragonal zirconia polycrystal, or Y-TZP

4. Resin-matrix ceramics

• Nanoceramic resin
• Polymer-infiltrated ceramic network materials

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5. Types of dental ceramics

5.1 Feldspathic porcelain

• Excellent translucency and esthetics
• Low strength and low fracture toughness
• Brittle
• Etchable with hydrofluoric acid
• Can be bonded effectively to enamel with resin cement

• Porcelain veneers
• Veneering porcelain for metal-ceramic crowns
• Veneering porcelain for zirconia frameworks
• Characterization of ceramic restorations

5.2 Leucite-reinforced glass ceramic

• Stronger than feldspathic porcelain
• Good esthetics
• Suitable for adhesive bonding
• Moderate fracture resistance

• Veneers
• Inlays and onlays
• Anterior crowns
• Selected posterior single crowns

5.3 Lithium disilicate glass ceramic

• High esthetics and translucency
• Greater strength than feldspathic and leucite ceramics
• Can be etched with hydrofluoric acid and silanated
• Suitable for adhesive cementation
• Available as pressable and CAD/CAM forms

• Veneers
• Inlays and onlays
• Anterior crowns
• Posterior single crowns
• Short-span fixed partial dentures in selected cases

5.4 Alumina ceramic

• High hardness and strength
• More opaque than glass ceramics
• Limited ability to etch and bond
• Mostly replaced by zirconia in current practice

• Ceramic copings and frameworks
• Earlier all-ceramic crown systems

5.5 Zirconia ceramic

• A crack causes tetragonal zirconia crystals to transform to the monoclinic phase.
• This transformation causes slight expansion.
• The expansion produces compressive stress around the crack.
• Crack propagation is reduced.

• Very high flexural strength
• High fracture toughness
• Excellent wear resistance
• Biocompatible
• Radiopaque
• More opaque than glass ceramics, although newer translucent zirconias have improved esthetics
• Cannot be conventionally etched with hydrofluoric acid because it contains no silica glass phase

• Posterior crowns
• Monolithic crowns
• Fixed partial denture frameworks
• Implant-supported crowns and bridges
• Abutments
• Full-arch prostheses

---

6. Methods of fabrication

A. Powder-liquid condensation and firing

1. A refractory die or metal framework is prepared.
2. Porcelain powder is mixed with water or a special liquid.
3. Porcelain slurry is applied in increments.
4. Condensation is done to remove water and reduce porosity.
5. The porcelain is dried.
6. Firing is carried out in a porcelain furnace, usually under vacuum.
7. Additional layers are added and fired.
8. Glazing and finishing are done.

B. Sintering

• Reduces porosity
• Increases density
• Improves strength

C. Heat pressing

• Pressable leucite ceramics
• Pressable lithium disilicate ceramics

D. Slip-casting and glass infiltration

E. CAD/CAM milling

• Lithium disilicate blocks
• Zirconia discs
• Leucite-reinforced ceramic blocks

F. Additive manufacturing

---

7. Properties of dental ceramics

7.1 Mechanical properties

High compressive strength

Low tensile strength

Brittleness

High hardness

Fracture toughness

• Low in feldspathic porcelain
• Higher in lithium disilicate
• Highest in zirconia

7.2 Optical properties

• Translucency
• Opalescence
• Fluorescence
• Shade stability
• Ability to reproduce enamel and dentin appearance

7.3 Thermal properties

• Low thermal conductivity
• Low thermal diffusivity
• Relatively insulating to the pulp
• Thermal expansion must be compatible with a metal or ceramic framework in layered restorations

7.4 Chemical properties

• Excellent resistance to saliva and oral fluids
• Do not corrode
• Stable colour
• Acid resistance varies with ceramic type
• Glass ceramics can be etched by hydrofluoric acid
• Zirconia cannot be effectively etched with hydrofluoric acid

7.5 Biological properties

• Generally biocompatible
• Smooth glazed surfaces show low plaque accumulation
• Well-polished ceramic margins support periodontal health
• Rough, fractured, or poorly finished surfaces may retain plaque and abrade opposing teeth

---

8. Advantages of dental ceramics

1. Excellent esthetics and life-like translucency
2. Stable shade with no discoloration over time
3. High compressive strength
4. High hardness and wear resistance
5. Excellent biocompatibility
6. No corrosion or metallic taste
7. Low thermal conductivity
8. Smooth glazed surface and low plaque retention
9. Radiopacity in many modern systems
10. Can be bonded to tooth structure in silica-based ceramics
11. Suitable for metal-free restorations
12. Excellent resistance to oral fluids and chemical degradation

---

9. Disadvantages of dental ceramics

1. Brittle and susceptible to catastrophic fracture
2. Low tensile strength
3. Require adequate tooth reduction and material thickness
4. May wear opposing enamel if surface is rough
5. Difficult to repair intraorally
6. Technique-sensitive fabrication and cementation
7. Risk of chipping of veneering porcelain in layered restorations
8. Some ceramics, especially zirconia, have inferior translucency compared with feldspathic porcelain
9. Cost may be high
10. Ceramic restorations cannot be adjusted excessively after glazing without repolishing

---

10. Uses and indications

Feldspathic ceramic

• Laminate veneers
• Esthetic layering porcelain
• Porcelain-fused-to-metal crowns
• Characterization of restorations

Leucite-reinforced ceramic

• Veneers
• Inlays
• Onlays
• Anterior crowns

Lithium disilicate

• Veneers
• Inlays and onlays
• Anterior crowns
• Posterior single crowns
• Selected short-span bridges

Zirconia

• Posterior crowns
• High-load crowns
• Long-span fixed partial dentures
• Implant-supported crowns
• Implant abutments
• Full-mouth rehabilitation
• Monolithic crowns in patients with high occlusal load

Metal-ceramic restoration

• Anterior and posterior crowns
• Fixed partial dentures
• Situations requiring combined strength of metal and esthetics of porcelain

---

11. Failures of ceramic restorations and prevention

Common failures

1. Fracture of ceramic

• Inadequate thickness
• Sharp internal line angles
• Excessive occlusal load
• Parafunctional habits such as bruxism
• Poor bonding or cementation
• Defects and porosity within ceramic

• Adequate tooth preparation
• Rounded internal angles
• Correct material selection
• Adequate occlusal reduction
• Proper bonding or cementation
• Occlusal adjustment
• Night guard for bruxism patients

2. Chipping of veneering porcelain

• Improper framework support
• Mismatch in thermal expansion
• Poor cooling after firing
• Occlusal stress

• Anatomically supported framework
• Compatible veneering ceramic
• Controlled cooling
• Avoid excessive occlusal contact on veneering ceramic

3. Wear of opposing teeth

4. Debonding

• Poor surface treatment
• Contamination
• Inadequate adhesive procedure
• Incorrect cement selection

• For glass ceramics: hydrofluoric acid etching, silane application, and resin cement where indicated
• For zirconia: airborne-particle abrasion, zirconia-compatible primer containing phosphate monomer such as MDP, and appropriate resin cement when adhesive bonding is needed

---

12. Conclusion

Suggested diagram for the answer sheet

Dental ceramics
│
├── Glass-matrix ceramics
│   ├── Feldspathic porcelain
│   ├── Leucite-reinforced ceramic
│   └── Lithium disilicate
│
├── Glass-infiltrated ceramics
│   ├── Alumina
│   ├── Spinell
│   └── Zirconia-alumina
│
└── Polycrystalline ceramics
    ├── Alumina
    └── Zirconia

25-mark university answer

Contents

1. Definitions
2. Objectives and importance
3. General principles
4. Instruments and abrasives
5. Finishing and polishing of amalgam restorations
6. Finishing and polishing of composite restorations
7. Finishing and polishing of glass ionomer cement restorations
8. Finishing and polishing of metallic cast restorations
9. Finishing and polishing of ceramic restorations
10. Finishing of provisional restorations
11. Errors and precautions
12. Conclusion

---

1. Definitions

Finishing

• Removal of excess restorative material
• Refinement of margins
• Establishment of anatomical contour
• Correction of occlusal discrepancies
• Removal of sharp edges and overhangs

Polishing

Difference between finishing and polishing

---

2. Objectives and importance

1. Restore normal anatomical form and contour.
2. Remove excess restorative material and marginal overhangs.
3. Establish proper occlusion and proximal contact.
4. Improve esthetics by producing a smooth and glossy surface.
5. Reduce plaque retention.
6. Reduce gingival irritation and periodontal inflammation.
7. Reduce staining and discoloration of restorations.
8. Reduce wear of opposing teeth.
9. Improve patient comfort, especially to the tongue.
10. Increase the longevity of the restoration.

---

3. General principles of finishing and polishing

1. Use abrasives from coarse to fine

• Coarse abrasives remove gross irregularities.
• Medium abrasives refine the surface.
• Fine and superfine abrasives provide final luster.

2. The abrasive should be harder than the material being finished

3. Use light pressure

• Produce heat
• Damage restoration margins
• Cause ditching
• Create deep scratches
• Remove excessive material

4. Use intermittent strokes

5. Use water cooling whenever necessary

6. Preserve restoration anatomy

7. Finish from tooth surface toward restoration

8. Use appropriate instruments for each surface

• Discs: facial and lingual flat surfaces
• Strips: interproximal surfaces
• Points and cups: occlusal surfaces
• Burs: contouring and gross reduction
• Paste and brush: final gloss

---

4. Instruments and abrasives used

Finishing instruments

• Sharp hand instruments
• Carvers
• Scalers
• Finishing burs
• Carbide finishing burs
• Fine diamond burs
• Abrasive discs
• Abrasive strips
• Sof-Lex type discs
• Rubber points and cups
• Silicon carbide stones
• Aluminum oxide discs
• Diamond instruments

Polishing agents

---

5. Finishing and polishing of amalgam restorations

Timing

• Conventional amalgam: after 24 hours
• High-copper amalgam: generally after 24 hours
• Some modern high-copper amalgams may permit earlier finishing depending on the manufacturer’s instructions

---

Objectives in amalgam finishing

• Remove excess amalgam
• Correct occlusion
• Reproduce grooves, fossae, cusp inclines, and marginal ridge
• Remove sharp margins
• Improve smoothness and corrosion resistance
• Reduce plaque retention

---

Armamentarium for amalgam finishing and polishing

• Sharp explorer
• Carvers
• Finishing burs
• Steel finishing burs
• Stones
• Rubber cups
• Rubber points
• Brushes
• Pumice slurry
• Tin oxide paste
• Zinc oxide paste
• Water and lubricant

---

Procedure

Step 1: Check occlusion

• Use articulating paper.
• Detect premature contacts.
• Remove high spots with a finishing bur or stone.
• Preserve cusp and groove anatomy.

Step 2: Remove excess amalgam

• Remove marginal flashes and overhangs using sharp hand instruments, finishing burs, or discs.
• Interproximal excess should be removed carefully with finishing strips.

Step 3: Re-establish anatomy

• Reproduce developmental grooves, fossae, marginal ridges, and cusp slopes.
• Do not create deep grooves that weaken the restoration.

Step 4: Smoothening

• Use fine finishing burs, stones, or abrasive rubber points.
• Use light intermittent pressure.

Step 5: Polishing with pumice

• Pumice mixed with water is applied with a rubber cup or brush at low speed.
• Keep the surface wet to prevent heat generation.

Step 6: Final polishing

• Use tin oxide or zinc oxide paste with a soft brush or rubber cup.
• This produces a smooth, shiny surface.

---

Advantages of polishing amalgam

• Reduces roughness and plaque retention
• Improves appearance
• Reduces tarnish and corrosion
• Decreases marginal breakdown
• Improves comfort
• Increases restoration longevity

---

Precautions

• Do not polish freshly placed amalgam.
• Do not over-carve or over-polish margins.
• Avoid excessive heat.
• Avoid thinning the marginal ridge.
• Do not alter occlusal anatomy excessively.
• Use gentle pressure and adequate cooling.

---

6. Finishing and polishing of composite restorations

Timing

• Immediately after curing in most composite restorations
• Delayed finishing may be done in selected situations, especially if there is concern regarding marginal integrity or polymerization stress

---

Objectives

• Remove excess composite and flash
• Establish proper contour and embrasure form
• Correct proximal contact
• Reproduce surface texture
• Improve gloss
• Minimize staining and plaque accumulation
• Avoid damage to adjacent enamel and gingiva

---

Armamentarium

• Fine diamond burs
• Multi-fluted carbide finishing burs
• Abrasive discs
• Aluminum oxide discs
• Finishing strips
• Interproximal abrasive strips
• Rubber cups and points
• Silicone points
• Polishing pastes
• Composite polishing brushes
• Felt wheels
• Diamond paste or aluminum oxide paste

---

Procedure

Step 1: Remove gross excess

• Use a sharp blade, scalpel, fine diamond bur, or finishing carbide bur.
• Remove flash at the cervical and proximal margins.
• Protect adjacent teeth using a matrix strip or metal matrix.

Step 2: Establish contour

• Use fine finishing burs and discs.
• Facial and lingual surfaces are finished using discs from coarse to superfine.
• Maintain normal facial convexity and embrasure form.

Step 3: Finish interproximal surfaces

• Use abrasive strips.
• Start with coarse strips only if excess material is present.
• Finish with fine and superfine strips.
• Avoid damaging proximal contact.

Step 4: Finish occlusal anatomy

• Use fine diamond or multi-fluted carbide burs.
• Re-establish fissures, triangular ridges, cusps, and fossae.
• Avoid unnecessary removal of composite.

Step 5: Polishing

• Use rubber points, cups, spirals, brushes, or fine polishing discs.
• Use polishing paste for final gloss.
• Use light pressure and intermittent movement.

Step 6: Final inspection

• Marginal adaptation
• Surface gloss
• Occlusion
• Proximal contacts
• Absence of sharp edges
• Absence of damage to adjacent enamel

---

Important points in composite polishing

• Use a sequence from coarse to superfine abrasives.
• Avoid overheating, which can damage the resin matrix.
• Maintain a wet field where possible.
• Do not use excessively coarse diamonds on the final surface.
• A mylar strip produces the smoothest initial surface, but this resin-rich surface may be less wear resistant and may require careful finishing.
• Final polishing improves stain resistance and esthetics.

---

7. Finishing and polishing of glass ionomer cement restorations

Timing

• Conventional glass ionomer cement: usually finish after approximately 24 hours, depending on the product.
• Resin-modified glass ionomer cement: can often be finished earlier after adequate light curing, according to manufacturer instructions.

Objectives

• Remove excess material
• Establish contour
• Preserve marginal integrity
• Avoid desiccation and surface crazing
• Produce a smooth surface that resists plaque accumulation

---

Procedure

Step 1: Initial contouring

• Use sharp hand instruments immediately after placement to remove gross excess.
• Avoid disturbing the setting cement.

Step 2: Delay definitive finishing

• Allow sufficient maturation.
• Protect the restoration with varnish, bonding agent, resin coat, or petroleum jelly as indicated.

Step 3: Finishing

• Use fine carbide burs, superfine diamond instruments, discs, or strips.
• Use low speed and light pressure.
• Use water spray where appropriate.

Step 4: Polishing

• Use fine abrasive discs, rubber points, cups, or polishing paste.
• Apply a protective surface coating after finishing if recommended.

---

Precautions

• Do not aggressively finish immediately after placement.
• Avoid dehydration of conventional glass ionomer.
• Avoid water contamination during early setting.
• Do not use dry, high-speed instrumentation.
• Avoid over-polishing, which may expose filler particles and increase surface roughness.

---

8. Finishing and polishing of metallic cast restorations

Objectives

• Remove excess cement and metal flash
• Smooth margins
• Refine occlusal and axial contours
• Produce a lustrous surface
• Reduce plaque retention
• Improve gingival health

---

Instruments and agents

• Fine carbide burs
• Fine diamond burs
• Sandpaper discs
• Rubber wheels
• Rubber points
• Stones
• Pumice
• Tripoli
• Rouge
• Tin oxide
• Chromium oxide
• Felt wheel and soft brush

---

Procedure

1. Remove excess luting cement with scalers and floss.
2. Check margins with an explorer.
3. Check occlusion with articulating paper.
4. Adjust high points using fine finishing burs or stones.
5. Smooth margins with rubber wheels and fine abrasives.
6. Polish with pumice or tripoli.
7. Apply rouge, tin oxide, or chromium oxide for final high luster.

Precaution

---

9. Finishing and polishing of ceramic restorations

Importance

• Accumulate plaque
• Stain
• Irritate soft tissues
• Cause excessive wear of opposing enamel
• Reduce esthetics

Finishing instruments

• Fine diamond burs
• Extra-fine diamond burs
• Ceramic-specific abrasive wheels
• Silicon carbide points
• Rubber polishing points
• Diamond-impregnated rubber points
• Diamond polishing paste
• Felt wheels
• Ceramic polishing kits

---

Procedure

Step 1: Minimal adjustment

• Adjust only when necessary.
• Use fine diamond burs with water spray.
• Use low pressure.

Step 2: Sequential polishing

• Use ceramic polishing kit from coarse to fine.
• Continue through medium, fine, and superfine rubber points.
• Use diamond paste with felt wheel for final gloss.

Step 3: Final evaluation

• Check surface gloss.
• Check occlusion.
• Ensure that no rough area remains in contact with opposing natural teeth.

Glazing

---

Special point: Zirconia polishing

• Use fine diamonds only for necessary adjustments.
• Follow with zirconia polishing points, usually diamond impregnated.
• Finish with diamond paste if required.
• Avoid leaving a rough ground zirconia surface, as it may wear opposing teeth.

---

10. Finishing and polishing of provisional restorations

Procedure

1. Trim excess material using acrylic burs or carbide burs.
2. Finish with sandpaper discs, rubber wheels, or abrasive points.
3. Polish with pumice and water.
4. Final high shine may be achieved with polishing paste and soft brush.

Importance

• Reduces plaque accumulation
• Prevents gingival inflammation
• Improves patient comfort
• Provides better esthetics
• Allows accurate evaluation of contours and occlusion

---

11. Errors and precautions

---

12. Conclusion

• Amalgam is generally polished after 24 hours using pumice and tin oxide.
• Composite can usually be finished immediately with discs, strips, points, and polishing paste.
• Glass ionomer cement requires gentle and often delayed finishing because of early moisture sensitivity.
• Cast metal restorations are polished with progressively finer abrasives, pumice, tripoli, and rouge.
• Ceramics require fine diamonds, ceramic polishing systems, and diamond paste after adjustment.

10-mark university answer

Contents

1. Introduction
2. Conventional zirconia
3. Need for newer zirconias
4. Classification of newer zirconias
5. Composition and microstructure
6. Properties
7. Indications
8. Advantages and limitations
9. Conclusion

---

1. Introduction

---

2. Conventional zirconia

• 3Y-TZP
• Full name: 3 mol% yttria-stabilized tetragonal zirconia polycrystal

Features

• Predominantly tetragonal crystal phase
• High flexural strength
• High fracture toughness due to transformation toughening
• Low translucency and comparatively opaque appearance
• Suitable for posterior crowns, bridges, and frameworks

---

3. Need for newer zirconias

• Chipping of veneering porcelain
• Delamination
• Increased laboratory steps
• Greater thickness requirement
• Less natural appearance in anterior teeth

• Greater translucency
• Better shade matching
• Monolithic, metal-free restorations
• Reduced need for veneering porcelain
• Improved esthetics in the anterior region

---

4. Classification of newer zirconias

---

5. Composition and microstructure

A. 4Y zirconia

• Contains about 4 mol% yttria.
• Has a mixture of tetragonal and cubic phases.
• Provides a useful balance between strength and translucency.
• Known as high-translucency zirconia.

B. 5Y zirconia

• Contains about 5 mol% yttria.
• Has greater cubic-phase content.
• Light scattering is reduced, producing better translucency.
• Has lower strength and fracture toughness than 3Y or 4Y zirconia.
• Called ultra-translucent zirconia.

C. 6Y zirconia

• Contains more than 5 mol% yttria.
• Has very high cubic phase and very high translucency.
• Mechanical strength is lower, so indications are more restricted.

D. Multilayered zirconia

• Shade
• Translucency
• Yttria concentration
• Strength

---

6. Properties of newer zirconias

Advantages

1. Improved translucency
   Better esthetics than conventional 3Y zirconia.
2. Better shade integration
   Available in pre-shaded and multilayered forms.
3. Monolithic restorations
   Reduces the need for veneering porcelain and hence reduces veneer chipping.
4. High strength compared with glass ceramics
   Especially 4Y zirconia.
5. Biocompatibility
   Well tolerated by oral tissues.
6. Low plaque retention
   When properly polished.
7. Wear resistance
   Smooth polished zirconia is generally kind to opposing enamel.

Important drawback: strength-translucency trade-off

• Cubic phase increases
• Translucency increases
• Tetragonal phase decreases
• Transformation toughening decreases
• Flexural strength and fracture toughness decrease

---

7. Indications

3Y zirconia

• Posterior crowns
• Long-span fixed partial dentures
• Implant-supported prostheses
• Bruxism patients
• High-stress areas

4Y zirconia

• Monolithic anterior and posterior crowns
• Short-span bridges
• Inlays, onlays, and table tops in selected cases
• Cases requiring a balance of esthetics and strength

5Y zirconia

• Veneers in selected cases
• Anterior crowns
• Esthetic single crowns
• Short-span anterior fixed partial dentures where indicated

6Y zirconia

• Highly esthetic anterior single crowns
• Veneers or minimally loaded restorations
• Not preferred for long-span bridges or heavy occlusal loads

Multilayered zirconia

• Esthetic monolithic anterior crowns
• Esthetic posterior crowns
• Full-contour restorations where natural shade gradient is desired

---

8. Limitations and precautions

1. Ultra-translucent zirconia is not ideal for long-span bridges.
2. It may be unsuitable for patients with severe bruxism or high occlusal load.
3. Zirconia cannot be etched by hydrofluoric acid because it lacks a silica glass phase.
4. Adhesive bonding, when required, involves air abrasion and an MDP-containing zirconia primer/resin cement.
5. Excessive grinding can create surface defects.
6. After occlusal adjustment, zirconia must be polished with zirconia-specific polishing systems.
7. Cement shade can influence the final esthetic result, especially with highly translucent zirconias.

---

9. Conclusion

Higher translucency means lower strength.

50-mark answer: topic map / table of contents

1. Introduction and definition
2. Objectives of restoring a badly broken tooth
3. Assessment and diagnosis
   • History and clinical examination
   • Pulpal, periodontal, and periapical assessment
   • Remaining tooth structure
   • Radiographic assessment
   • Occlusal evaluation
4. Restorability and prognosis
   • Favourable factors
   • Unfavourable factors
   • When extraction is indicated
5. Biologic principles
   • Preservation of tooth structure
   • Biologic width and supracrestal tissue attachment
   • Crown-root ratio
   • Periodontal health
6. Endodontic considerations
   • Need for root-canal treatment
   • Timing of definitive restoration
   • Coronal seal
7. Ferrule effect
   • Definition
   • Importance
   • Ideal dimensions
   • Methods to obtain ferrule
8. Methods of gaining sound supragingival tooth structure
   • Surgical crown lengthening
   • Orthodontic extrusion
   • Surgical extrusion
   • Deep margin elevation in selected cases
9. Post and core restoration
   • Indications and objectives
   • Types of posts
   • Principles of post preparation
   • Core materials
   • Failures and prevention
10. Selection of definitive restoration
    • Direct composite restoration
    • Full metal crown
    • Metal-ceramic crown
    • All-ceramic crown
    • Endocrown
11. Tooth preparation and crown design
12. Occlusal considerations
13. Special situations
    • Anterior teeth
    • Posterior teeth
    • Endodontically treated teeth
    • Teeth with subgingival fracture margins
14. Sequence of clinical management
15. Conclusion

High-level overview

Principles for Restoration of Badly Broken Teeth

50-mark university answer

Table of contents

1. Introduction
2. Objectives of restoration
3. Assessment of a badly broken tooth
4. Restorability and prognosis
5. Biological principles
6. Endodontic principles
7. Ferrule effect
8. Methods to obtain sound supragingival tooth structure
9. Post and core principles
10. Core restoration
11. Choice of definitive restoration
12. Crown preparation and occlusal principles
13. Restoration of anterior teeth
14. Restoration of posterior teeth
15. Clinical sequence of management
16. Causes of failure and prevention
17. Conclusion

---

1. Introduction

• Reduced retention for the final restoration
• Reduced resistance to fracture under occlusal forces
• Difficulty in obtaining proper margins and isolation
• Risk of violating periodontal attachment
• Difficulty in establishing a coronal seal after root-canal treatment
• Compromised esthetics, function, and prognosis

Preserve and use the remaining sound tooth structure wherever possible.

---

2. Objectives of restoration

1. Eliminate caries and unsupported tooth structure.
2. Maintain pulpal and periodontal health.
3. Restore normal anatomy, contour, contact, esthetics, and function.
4. Provide a durable coronal seal.
5. Resist masticatory and parafunctional forces.
6. Prevent fracture of the residual tooth structure.
7. Obtain adequate retention and resistance form for the final crown.
8. Respect the periodontal attachment apparatus.
9. Preserve maximum sound tooth and root structure.
10. Achieve a restoration with a predictable long-term prognosis.

---

3. Assessment of a badly broken tooth

A. History

• Pain, sensitivity, swelling, or sinus tract
• History of trauma
• Previous restoration and endodontic treatment
• Parafunctional habits, especially bruxism and clenching
• Dietary caries risk
• Oral hygiene status
• Esthetic expectations
• Medical history and periodontal risk factors

---

B. Clinical examination

1. Extent and location of tooth destruction

• Supragingival
• Equigingival
• Subgingival
• Extending below the alveolar crest
• Extending into root dentin

2. Remaining coronal tooth structure

• Number of remaining walls
• Height of sound dentin above the gingival margin
• Thickness of residual walls
• Presence of cracks
• Presence of unsupported enamel or dentin
• Whether a circumferential ferrule can be obtained

3. Pulpal and periapical status

• Pulp vitality tests
• Percussion and palpation
• Mobility
• Periodontal probing
• Radiographs

4. Periodontal status

• Plaque and calculus
• Gingival inflammation
• Probing depths
• Furcation involvement
• Mobility
• Crown-root ratio
• Width of attached gingiva
• Periodontal bone support

5. Occlusion

• Centric and eccentric contacts
• Premature contacts
• Interferences
• Wear facets
• Bruxism
• Position of tooth in the arch
• Opposing dentition

---

C. Radiographic assessment

• Root length
• Root morphology and curvature
• Number and width of canals
• Periapical status
• Quality of previous root-canal treatment
• Caries extent
• Level of alveolar bone
• Root fracture
• Internal or external resorption
• Crown-root ratio
• Post space availability

---

4. Restorability and prognosis

A. Favourable factors

• Adequate periodontal support
• Good oral hygiene and low caries activity
• Sufficient root length
• Favourable crown-root ratio
• Adequate root thickness
• Absence of vertical root fracture
• Treatable pulpal or periapical disease
• At least 1.5-2 mm of sound coronal dentin for ferrule
• Ability to obtain isolation and a sound restoration margin
• Controlled occlusion
• Cooperative patient with regular follow-up

---

B. Unfavourable factors

• Vertical root fracture
• Extensive subcrestal caries or fracture
• Severe periodontal bone loss
• Advanced furcation involvement
• Very short root or unfavourable crown-root ratio
• Root perforation that cannot be repaired predictably
• Severe root resorption
• Inadequate remaining root dentin after post preparation
• Persistent endodontic infection not amenable to retreatment or surgery
• Uncontrolled bruxism
• Inability to maintain isolation, oral hygiene, or follow-up

---

C. Indications for extraction

1. Vertical root fracture.
2. Caries or fracture extending deeply below the bone crest with no practical method to expose a maintainable margin.
3. Severe periodontal disease with poor support.
4. Non-restorable root resorption or perforation.
5. Inadequate root length after proposed crown lengthening.
6. Poor strategic value of the tooth in the treatment plan.
7. Unfavourable cost-benefit ratio compared with replacement options.

---

5. Biological principles

A. Preservation of tooth structure

• Remove only carious, infected, unsupported, or fractured tooth structure.
• Preserve sound axial walls where possible.
• Avoid excessive canal enlargement during post preparation.
• Prefer adhesive restorative procedures when appropriate.
• Use a conservative crown preparation compatible with the selected restorative material.

---

B. Periodontal attachment and margin placement

• Easier to finish and polish
• Easier to inspect
• Easier for the patient to clean
• Less likely to cause gingival inflammation
• Easier to isolate for adhesive procedures

• Persistent inflammation
• Bleeding on probing
• Gingival recession
• Pocket formation
• Alveolar bone loss
• Loss of attachment

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C. Crown-root ratio

• A favourable ratio improves resistance to lateral and rotational forces.
• Crown lengthening can improve ferrule but may worsen crown-root ratio.
• Therefore, the benefit of gaining tooth structure must be weighed against periodontal and biomechanical disadvantages.

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6. Endodontic principles

A. Need for root-canal treatment

• Irreversible pulpitis
• Pulp necrosis
• Periapical disease
• Trauma with pulpal involvement
• Extensive tooth destruction where pulp preservation is not possible
• Need for a post in a non-vital tooth, provided endodontic treatment is indicated

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B. Quality of endodontic treatment

• Adequate cleaning and shaping
• Dense obturation
• Appropriate working length
• Absence of persistent symptoms
• Satisfactory periapical status, or a clear plan for managing pathology
• Adequate coronal seal

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C. Importance of coronal seal

• The tooth should receive a sound definitive coronal restoration as early as practical.
• A provisional restoration must seal the access cavity effectively.
• Long-term exposure of obturated canals to the oral environment may require reassessment and possible retreatment.

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7. Ferrule effect

Definition

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Importance of ferrule

• Increases fracture resistance
• Reduces wedging forces from posts and cores
• Resists functional levering forces
• Improves resistance form of the crown
• Reduces risk of root fracture
• Reduces core and crown dislodgement
• Distributes stress more favourably around the cervical tooth structure

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Requirements of an ideal ferrule

• About 1.5-2 mm vertical height of sound tooth structure
• Circumferential, continuous dentin band if possible
• Adequate dentin thickness
• Crown margin placed on sound tooth structure
• Proper crown encirclement of the tooth

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When ferrule is inadequate

1. Surgical crown lengthening
2. Orthodontic extrusion
3. Surgical extrusion in selected teeth
4. Deep margin elevation in carefully selected cases
5. Extraction and replacement when the tooth cannot be predictably restored

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8. Methods to obtain sound supragingival tooth structure

A. Surgical crown lengthening

Principle

Indications

• Subgingival caries or fracture margins
• Need for ferrule
• Need to place crown margin on sound tooth structure
• Violation of periodontal attachment by a restoration margin

Advantages

• Predictable in suitable cases
• Exposes tooth structure directly
• Allows impression making and restoration placement

Disadvantages

• Removes supporting bone
• May unfavourably alter crown-root ratio
• Can expose root surfaces
• May cause sensitivity
• May produce esthetic problems, particularly in anterior teeth
• Requires healing before final restoration

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B. Orthodontic extrusion

Principle

Advantages

• Preserves alveolar bone
• Preserves periodontal attachment better than osseous resection
• Useful in the anterior esthetic region
• Can improve crown-root relation compared with excessive bone removal

Disadvantages

• Time consuming
• Requires patient compliance
• May require circumferential fiberotomy to prevent bone and gingiva from following the tooth
• Requires retention period
• Not suitable in every tooth or occlusal situation

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C. Surgical extrusion

Indications

• Selected single-rooted teeth
• Subgingival crown-root fracture
• When orthodontic extrusion is not practical

Limitations

• Technique-sensitive
• Risk of root resorption, ankylosis, and periodontal injury
• Requires careful case selection and follow-up

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D. Deep margin elevation

Advantages

• Conservative alternative in selected cases
• Improves isolation and accessibility
• May avoid surgical crown lengthening
• Facilitates adhesive indirect restoration

Limitations

• Not suitable where isolation is impossible
• Must not compromise periodontal attachment
• Requires excellent bonding technique and finishing
• Long-term maintenance and margin cleansability must be considered

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9. Post and core principles

A. Definitions

Post

Core

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B. Purpose of a post

• Retain the core when insufficient coronal tooth structure remains
• Provide retention for a crown foundation

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C. Indications for post placement

• Extensive coronal tooth structure has been lost
• The core cannot be retained by remaining tooth walls
• A crown is planned and adequate core retention is absent
• The tooth is endodontically treated and structurally compromised

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D. Contraindications

• Adequate coronal tooth structure is present for a core
• Root is short, thin, curved, or severely tapered
• Root has fracture, perforation, resorption, or poor periodontal support
• Canal preparation would leave dangerously thin dentin
• Root-canal treatment is inadequate and requires retreatment
• Tooth has poor overall prognosis

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E. Types of posts

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F. Principles of post preparation

1. Preserve apical seal

2. Length

3. Diameter

• Post diameter should be minimal.
• Preserve as much radicular dentin as possible.
• Excessive enlargement weakens the root.
• A post should not exceed roughly one-third of root diameter in many conventional guidelines.

4. Shape

• Parallel-sided posts generally give better retention than tapered posts.
• Tapered posts may be more conservative in tapered roots.
• The canal anatomy must guide preparation.

5. Anti-rotational feature

• Remaining coronal dentin
• Core extensions
• Auxiliary pins or grooves where appropriate
• Pulp chamber configuration in posterior teeth

6. Passive placement

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10. Core restoration

A. Requirements of an ideal core

• Replace missing coronal tooth structure
• Be adequately retained
• Resist compression and fracture
• Be dimensionally stable
• Permit crown preparation
• Bond to remaining tooth structure where possible
• Be compatible with the definitive luting and crown material
• Be easy to repair if necessary

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B. Core materials

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11. Choice of definitive restoration

A. Direct composite restoration

Indications

• Moderate tooth structure loss
• Adequate remaining enamel/dentin
• Low to moderate occlusal load
• When cusps are not undermined or can be selectively protected

Advantages

• Conservative
• Adhesive
• Esthetic
• Usually completed in one visit
• Repairable

Limitations

• Less suitable for severely weakened posterior teeth under heavy occlusal load
• Polymerization shrinkage and wear must be controlled
• Requires isolation

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B. Cuspal coverage restorations

• Onlay
• Overlay
• Partial crown
• Endocrown
• Full crown

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C. Full coverage crown

• Major coronal destruction exists
• Remaining cusps are weak
• Tooth has received endodontic treatment and needs cuspal protection
• A post-core foundation requires coverage
• Esthetic and functional rehabilitation is required

• Full metal crown
• Metal-ceramic crown
• All-ceramic crown
• Monolithic zirconia crown
• Lithium disilicate crown, where esthetics and adhesive bonding are appropriate

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D. Endocrown

Indications

• Endodontically treated molars
• Extensive coronal loss
• Adequate pulp chamber depth
• Short clinical crowns where conventional retention is difficult
• Cases where post placement would remove excessive radicular dentin

Advantages

• Conservative of root dentin
• Avoids post space preparation
• Simplifies treatment
• Provides cuspal coverage
• Particularly useful in molars

Limitations

• Requires adhesive isolation
• Less suitable for teeth with very shallow pulp chambers
• Case selection is essential
• Caution in severe bruxism or unfavourable occlusion

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12. Crown preparation and occlusal principles

A. Retention form

• Adequate axial wall height
• Minimal taper
• Parallel opposing walls where feasible
• Proper finish line
• Auxiliary grooves or boxes when indicated
• Good-quality luting procedure

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B. Resistance form

• Adequate wall height
• Adequate ferrule
• Proper axial reduction
• Rounded internal line angles
• Auxiliary features where required
• Controlled occlusion

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C. Occlusal reduction

• Follow natural anatomy
• Preserve functional cusp form
• Provide adequate material thickness
• Avoid excessive loss of tooth structure

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D. Functional cusp bevel

• Buccal cusps of mandibular posterior teeth
• Palatal cusps of maxillary posterior teeth

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13. Restoration of badly broken anterior teeth

Treatment options

• Direct composite build-up
• Veneer or partial coverage restoration, if adequate tooth structure remains
• Fiber post and composite core followed by crown
• Cast post and core followed by crown in selected severely damaged teeth
• Orthodontic extrusion or crown lengthening to gain ferrule
• Extraction and replacement if prognosis is poor

Principles

• Preserve facial enamel where possible.
• Maintain adequate ferrule.
• Use esthetic core and post material when a translucent all-ceramic crown is planned.
• Avoid excessive post diameter.
• Use a post only when core retention is inadequate.
• Manage palatal contacts and protrusive guidance carefully.

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14. Restoration of badly broken posterior teeth

Main principles

• Preserve remaining cusps where strong.
• Cover weakened cusps.
• Use bonded core build-up where possible.
• Use post only if the core cannot be retained by pulp chamber and remaining walls.
• Prefer a conservative adhesive cuspal coverage restoration or endocrown in selected molars.
• Use full crown coverage where structural loss and occlusal risk justify it.
• Check centric and eccentric contacts carefully.

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15. Clinical sequence of management

1. History and examination
   Assess symptoms, caries risk, periodontal condition, occlusion, esthetic needs, and patient expectations.
2. Radiographic assessment
   Evaluate root form, periapical status, bone level, restorability, and possible post space.
3. Diagnosis and treatment planning
   Decide whether the tooth is restorable and determine alternatives, including extraction and replacement.
4. Disease control
   Remove caries, treat periodontal inflammation, control caries risk, and institute oral hygiene measures.
5. Endodontic treatment or retreatment where indicated
   Ensure adequate cleaning, obturation, and a coronal seal.
6. Create or preserve ferrule
   Use existing tooth structure where possible. If insufficient, consider crown lengthening, orthodontic extrusion, surgical extrusion, or selected deep margin elevation.
7. Foundation restoration
   Place a bonded core. Use a post only if needed for core retention.
8. Provisional restoration
   Ensure it has proper seal, contour, contact, and occlusion.
9. Definitive crown or cuspal coverage restoration
   Select material according to esthetics, available space, load, and bonding requirements.
10. Cementation or adhesive bonding
    Follow material-specific protocols.
11. Occlusal adjustment and finishing
    Remove premature contacts and polish adjusted surfaces.
12. Review and maintenance
    Monitor periodontal health, marginal integrity, recurrent caries, periapical status, and occlusion.

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16. Causes of failure and prevention

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17. Conclusion

• Preserve maximum sound tooth structure.
• Ensure periodontal and endodontic health.
• Obtain a sound coronal seal.
• Provide a continuous ferrule of sound dentin whenever possible.
• Use posts only to retain cores, not to strengthen roots.
• Avoid excessive removal of radicular dentin.
• Provide cuspal coverage or full coverage when structural loss demands it.
• Control occlusal forces and maintain the restoration regularly.

The long-term success of restoration depends more on remaining sound tooth structure and ferrule than on the type of post.