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Describe why Teeth can be seen as Compound Systems

*Different Components of a Tooth has different properties. Individually each component is not very useful however when brought together, they are stronger and act synergistically.

-Describe the different components of a Tooth that act together as a Compound System

*Teeth are fundamentally formed of Enamel & Dentine with different properties. PDL has viscoelastic properties with proprioception that feedbacks to the brain so you do not exceed occlusal loads.

Enamel is Hard & Brittle, Dentine is Softer & Toughter.

-How do we aim to restore the compound structure of a tooth (3)

*1) using a Compound System made up of Components with Desirable Properties

2) By Careful Bio-mechanical design considerations

3) By using an effective and reliable adhesive interface assembly

-List 8 Relevant Properties of Restorative Materials

*1) Elastic Modulus

2) Compressive Strength

3) Flexural Strength

4) Fracture Toughness

5) Coefficient of Thermal Expansion

6) Hygroscopic Expansion

7) Wear Behaviour

8) Fatigue Behaviour

-What is the Coefficient of Thermal Expansion of a Tooth

*10ppm Degrees C (-1)

-Define Composite Material

*A single Entity containing two or more constituent phases

-What is the Role of Composite Fillers (4)

*1) Reduce Polymerisation Shrinkage

2) Limit Fracture Propagation

3) Increase Wear Resistance

4) Improve Optical Properties

-List ideal properties for a Dentine Replacement

*1) Low Elastic Modulus

- Matching Dentine

2) Adhesive

3) Resilient to absorb shocks

4) Fluoride-releasing

5) Resistant to degradation

-List ideal properties for an Enamel Replacement

*1) High Elastic Modulus

- matching enamel

2) Tooth-coloured

3) Reliable bonding mechanism

4) High Strength

5) Abrasion matched to enamel

6) Resistant to mechanical fatigue

7) Resistant to static fatigue

-How do Block Forms work

*Work by absorbing load into mass and avoid crack propagation

-How do Shell Forms work

*work by constructional shape that avoid deformation of the crown itself

-How does Laminate Form work

*Works by bonding to underlying tooth structure

-Describe the Materials vs Design of a Full Gold Crown

*- Ductile and Easily Deformed

- 360 Degree Wrap Prevents Deformation

-Describe the Materials vs Design of an Adhesive Porcelain Crown

*- Brittle & Easily Fractured if Deformed

- Adequate Bulk Prevents Deformation

-Why are endodontically treated teeth crowned post treatment

*The tooth is weakened due to access cavity preparation. There has been a loss of structural integrity associated with loss of roof of the pulp chamber. There has been loss of dentine elasticity.

To prevent further bacterial contamination, restore function and aesthetics a crown is placed.

-When is Cuspal Protection Required in Posterior Teeth (3)

*Cuspal Protection is required if there is

1) Loss of Marginal Ridges

2) Loss of Substantial Tooth Structure

3) Heavily Restored Tooth

-How is Cuspal Protection Achieved in Posterior Teeth (3)

*Cuspal Protection can be achieved by

1) Adhesive Restorations

2) Cusp-Coverage Cast Restorations

3) Full-Coverage Restorations

-Following Crown Preparation the Pulp Tissue can die. Explain Why (5)

*1) Aggressive Insult to the tooth, dentine & Odontoblasts

2) Thermal Damage

3) Local Anaesthesia

- Adrenaline causing Vasoconstriction, reducing pulp blood flow.

4) Dessication

5) Bacterial Contamination

-What Percentage of Teeth die following crown preparation

*20%

Important to consider this as part of consent prior to crown preparation

-Give Properties of Full Gold Crowns (3)

*1) Minimal Tooth Reduction

2) Least Aesthetic Crown (Not an Issue for Posterior Teeth)

3) Can be Adjusted Intra-orally

-FGC can be made from Gold Alloys. There are 4 Gold Alloy Types. What is Type II Gold Alloy

*Type II (Medium) was less burnishable but hard enough to stand up in small, multiple surface inlays that did not include buccal or lingual surfaces

-FGC can be made from Gold Alloys. There are 4 Gold Alloy Types. What is Type III Gold Alloy

*Type III (Hard). The most commonly used type of Gold for All Metal Crowns and Bridges.

-What metals are included in a Type III Gold Alloy

*1) Gold: 75%

2) Silver: 10%

3) Copper: 10%

4) Palladium: 3%

5) Zinc: 2%

-What is the survival rates of Full Gold Crowns

*According to a Study in 2004, survival rates were 97% at 9 years and 94.1% for longer than 40 years.

FGC have extreme predictability and longevity.

-List Properties of Metal Ceramic Crowns (4)

*1) Metal Core

2) Extensive Buccal Tooth Reduction

3) Aesthetics at the cost of tooth tissue

4) Only the metal component can be adjusted intra-orally.

-List 3 PFM Alloy Types

*1) High Noble Alloys

2) Noble Alloys

3) Base-Metal Alloys

-List properties of High Noble Alloys used to make PFM

*High Noble Alloys have minimum of 60% noble metals (Gold, Palladium, Silver) and a minimum of 40% by weight of Gold.

They usually contain a small amount of tin, indium or iron which provides oxide layer formation. These metals provide a chemical bond for the porcelain

-List Properties of Noble Alloys used to make PFM

*- Gold

- Palladium

- Silver

Contain at least 25% by weight noble metal. They have relatively high strength, durability, hardness and ductility.

-Base Metal Alloys consist of Nickel and Beryllium. What is the concern of these two metals.

*These are two of the most commonly constituents of base-metal alloys and can cause allergic reactions when in Intimate Contact with the Gingiva.

-What are the Survival Rates of PFM Crowns

*5 year survival was estimated at 95.6% for Metal Ceramic Crowns

-What are the Survival Rates for All Ceramic Crowns

*93.3% 5 Year Survival

-List Properties of All Ceramic Crowns

*- High Strength Ceramic Core

- Most Aesthetic

- Low Edge Strength

- Requires Extensive Reduction

- Intra-Oral Adjustment not Possible.

-What is the Fracture Rate of All Ceramic Crowns

*5 year Fracture Rate of 4.4% irrespective of the materials used.

Molar Crowns showed a significantly higher 5 year fracture rate than premolar crowns. The difference between anterior and posterior crowns was also significant.

-What is Retention Form

*Prevents Dislodgement of the Crown in an Axial Direction

-What is Resistance Form

*Prevents Dislodgement of the Crown due to Rotation from a lateral load.

-What is the Tooth Reduction for All Ceramic Crowns

*Occlusal Reduction: 1.5mm

Above 2mm Reduction in Areas of Stress, Functional Cusps.

Margins are Rounded Shoulders.

Axial Walls should be Parallel and Slightly Tapered of 5-10 Degrees

-What is the Tooth Preparation for a PFM Crown

*Shoulder Preparation on Labial Aspect to accommodate both Metal and Ceramic. The Lingual/Palatal aspect can have lighter preparations with only chamfer margins to accommodate only metal.

The area where the labial shoulder joins the palatal chamfer is called the wing area where you can have a wing or blend them nicely into each other.

-What is the Tooth Preparation for a FGC

*Uniform Reduction with Chamfer Margins to accommodate only metal.

For Maxillary Molars, areas of stress are further reduced i.e. palatal cusp. For Mandibular Molars this is on the buccal cusps.

-Give examples of Liners and Bases used for Cementation

*GIC (Fuji IX) and RM-GIC (Fuji II)

-List Benefits of using RM-GIC as a Liner/Base

*- Ease of Use, Bulk Fill

- They help reduce the C-Factor within Composite Restorations

- They can be etched to establish strong bonds with dentine bonding agents.

- Adhere to unetched hard tissue and exhibit sustained fluoride release.

-Give Examples when it may be necessary to keep patients in Long Term Provisionals

*1) When Assessing Pulpal Health

2) During Gingival Healing from Periodontal and Oral Surgery

3) Implant Integration

4) Evaluating Aesthetic and Functional Changes in OVD

-What are the effects of Loss or Failure of the Temporary Crown (4)

*1) Pain

2) Over Eruption & Loss of Space

3) Drifting of Proximal Teeth

4) Damage to Core Preparations

-What are the Functions of Temporary Cementation

*1) Provide a Seal

2) Prevent Marginal Leakage

3) Prevent Pulpal Irritation

4) Low Strength to Allow Easy Removal

5) Protect Preparation

-List 8 Ideal Properties of a Temporary Cement

*1) Ability to Seal against leakage of Oral Fluids

2) Low Solubility

3) Biocompatible

4) Chemical Compatibility with Provisional Polymer

5) Ease of Use/Removal

6) Easy to Eliminate Excess

7) Adequate Working & Setting Times

8) Compatibility with Definitive Luting Agent

-List Common Temporary Cements used

*- Fine Particle Zinc Oxide Eugenol Cement (TempBond)

- Non Eugenol Cements (TempBond NE)

- Zinc Phosphate, Zinc Polycarboxylate and GIC (These have too high strength and can be difficult to remove without causing damage to preparation

-How Does TempBond set

*Comes as a Base and Accelerator Paste which are mixed together.

-List Advantages of Zinc Oxide Eugenol (4)

*1) Easy Removal thus Enabling Reuse of Temporary Restoration

2) Acceptable Sealing Properties

3) Obtundent (Blunts Irritation) Effect on Pulp

4) Ease of Use

-List Disadvantages of Zinc Oxide Eugenol

*1) Free Eugenol acts as Plasticiser of Methacrylate Resin and reduces surfaces hardness and strength

2) Eugenol can interfere with Bond Strength of Resin Cements

3) Eugenol inhibits the polymerisation of certain resin cements

-What is the purpose of a Definitive Cement

*To Fill the microgap between tooth structure and restorative material to assist in the retention of the restoration.

-List Properties of the Ideal Permanent Cement

*1) Adequate working time with rapid set

2) Low film thickness

3) Low solubility

4) High compressive and tensile strengths

5) Low viscosity

6) Adhesion to tooth structure and restorative materials

7) Biocompatible

8) Cariostatic

9) Translucency or opacity when required

10) Radiopaque

-How can Permanent Cements be Categorised (3)

*1) RMGIC

2) Total Etch Adhesive Resin Cements

- Self Cured, Light Cured, or Dual Cured

3) Self Etching Resin Cements

-How does RM-GIC bond to tooth structure

*Bonds to the Inorganic Phase of Dentine

-Comment on the Adhesive Ability of RM-GIC

*Adhesion to Tooth Structure or Ceramic is not strong

-Why is RM-GIC contraindicated for cementing most ceramics

*RM-GIC can cause Hygroscopic Expansion due to HEMA which can lead to fracture of ceramics

-Describe when RM-GIC can be used as a Definitive Cement

*For Cementing Metal-Based inlays, onlays, crowns and bridges

-What is the trade name for RM-GIC when it is used as a Definitive Cement

*Rely X Luting

-List the composition of RM-GIC Definitive Cement (3)

*1) Acid Soluble Glass

2) Polyacid Polymers

3) Polymerising Dimethacrylates

The Polyacid Polymers react with Calcium in the Glass Filler and the Dentine.

The Dimethacrylates polymerise into Solid Resin

-What is the Powder Composition of RM-GIC

*Ion-Leachable Glass

-What is the Liquid Composition of RM-GIC

*1) Methacrylate Resin (Bis-GMA)

2) Polyacid

3) HEMA

4) Water

-What is the Function of Bis-GMA in RM-GIC

*Enables Polymerisation Reaction

-What is the Function of Polyacids in RM-GIC

*Reacts with Ion-Leachable Glass to allow Acid Base Reaction

-What is the Function of HEMA in RM-GIC

*Enables the Resin and Acid Components to co-exist in an aqueous solution.

-What is the Function of Water in RM-GIC

*Allow Ionisation of the Acid Component so that Acid-Base Reactions can occur.

-List Advantages of RMGIC (8)

*1) Adequate Compressive Strength, Diametral Tensile Strength and Flexural Strength (but less than resin composites)

2) Easy Manipulation & Use

3) Low Film Thickness

4) Fluoride Release similar to GIC

5) Polymerisation is not significantly affected by Eugenol Containing Provisional Materials as long as it is completely removed

6) Minimal Post Operative Sensitivity

7) Some Adhesion to Enamel and Dentine

8) Resistance to Marginal Leakage and Some Moisture Resistance

-List Disadvantages of RMGIC

*1) Dehydration Shrinkage due to the Glass Ionomer component as late as 3 months after maturity with the polymerisation shrinkage

2) Stress Fractures at Exposed Cement Tooth Restoration Interface

3) HEMA is responsible for increased water sorption contraindicating their use for the cementation of all ceramic crowns and posts in non-vital teeth

4) Cement Bulk is Very Hard & Difficult to Remove

-Describe How Total Etch Adhesive Resin Cements are used as Definitive Crowns

*Pre Treatment of the Tooth Surface with 37% Phosphoric Acid and Application of a Dentine Bonding Agent prior to application of the resin cement

The Ceramic Fit Surface is Etched with Hydrofluoric Acid in order to provide a micromechanically retentive surface

The resin cement is used in conjunction with a silane applied to the HF-etched crown

This forms a micromechanical bond to both tooth and restorative material.

-Why must we isolate the operative area when using Total Etch Adhesive Resin Cements

*The ability to clinically isolate the operative area from contamination due to the presence of blood and other oral oral fluids is essential for the successful use of total-etch resin cement systems.

-What are Total Etch Adhesive Resin Cements composed of

*1) Resin Matrix of Bis-GMA or Urethane Dimethacrylate

2) Filler of Fine Inorganic Particles

-List 5 Advantages of Total Etch Adhesive Resin Cements

*1) Superior Compressive and Tensile Strengths

2) Insoluble in Oral Fluids

3) Adhesive

4) Micromechanical Bonding to Prepared Enamel, Dentine, Alloys and Glass Ceramic Surfaces

5) Available in Wide Range of Shades and Translucencies creating Excellent Aesthetics

-List 8 Disadvantages of Total Etch Adhesive Resin Cements

*1) Highly Technique Sensitive

2) High Film Thickness

3) Marginal Leakage due to Polymerisation Shrinkage

4) Severe Pulpal Reaction when applied to cut Vital Dentine

5) No Fluoride release or uptake

6) Low Modulus of Elasticity so cannot support long span prosthesis

7) Difficulty in removing hardened excess resin cement from inaccessible areas

8) Use of Eugenol Based Provisionals inhibited the complete polymerisation of the resin cement. Therefore must use TempBond

-What does Silane Coupling Agent do

*Allows Two Materials to be Bonded Together that normally do not bond together without a Coupling Agent

-Give an Example of Self Cure Resin Cements

*Panavia 21

-Give an Example of a Light Cure Resin Cement

*Calibra

-When can Dual Cure Resin Cements be used

*Can be used in ANY metal free restoration

-Give an Example of a Dual Cure Resin Cement

*Panavia F 2.0

-How do Self-Etching Resin Cements work

*Require NO pre-treatment of the tooth surface. No Etch or Primer. Less Technique Sensitive

-Which Restorative Materials can be cemented with Self-Etching Resin Cements

*1) Metallic Crowns, Inlays & Onlays

2) Ceramic Crowns, Inlays & Onlays

3) PFM Crowns

-Comment on the Bond Strength of Self Etching Resin Cements

*Bond Strengths of Self Etching Resin Cements are not as high as the Total Etch Adhesive Resin Cements.

-Why is High Bond Strength difficult to achieve with Self Etching Resin Cements

*Bonding between Resin Cements and High Strength Ceramic Substructure is difficult to achieve because of their chemical inertness and lack of silica content that makes it not susceptible to etching.

-What is the Cement of Choice for Metal/Metal Based Indirect Restorations

*RM-GIC

-What is the Cement of choice for High Strength Ceramic Substructure Restorations with Zirconia or Alumina Cores

*Unicem (Self Etched)

-What is the Cement of Choice for Glass Ceramic Restorations

*Calibra (Light Cured

-What are the indications for Crowns (8)

*1) Broken Down or Heavily Restored Teeth

2) Trauma

3) Tooth Wear

4) Hypoplastic Conditions and Atypical Shape

5) To Alter and Correct Occlusion

6) Part of Another Restoration

7) Restore Missing Function

8) Appearance

-What are the Contraindications of Placing Crowns (4)

*1) Other More Conservative Options

2) Poor Oral Hygiene

3) Very Broken-Down Tooth with Caries extending Sub-gingivally

4) Poor Periodontal Condition and Lack of Bone Support

-When the Patient is Young, What factors must be considered before planning for crowns (3)

*1) Size of the Pulp

2) Degree of Eruption of Tooth

3) Co-operation of the Patient

-Why is it important to assess oral hygiene before planning for Crowns

*Important that the patient has good oral hygiene so it increases the likelihood of success of the treatment.

This also includes assessing the status of the other teeth, the soft tissue conditions.

-What periodontal factors affect the planning for crowns

*- It is important to correct and control any inflammatory defects

- Assess the soft tissue contours

If necessary then correct with Orthodontic Correction or Surgical Correction

-In terms of Occlusion, which approach is prepared for when planning for Crowns

*Consider Conformative Approach vs Reorganisation of Occlusion approach.

-What is the Conformative Approach

*When indirect restorations are place on anterior teeth conforming to the patients existing occlusion.

-What is the Reorganisation Approach

*Where the vertical dimension and patients occlusion have been completely reorganised using indirect restorations

-Why may Crown Lengthening Surgery be required before placing Crowns

*To remove excessive gingivae to increase the length of the visible crown height

-What are the Different Types of Crowns in terms of Coverage (3)

*- Full Coverage Crowns

- Partial Coverage Crowns

- Post Core Crowns

-What are the 5 different types of Bridges

*1) Fixed-Fixed

- Fixed to an Abutment on Both Sides

2) Fixed-Moveable

- Fixed to an Abutment on one end and there is a moveable join somewhere in the middle on the pontic

3) Cantilever (Fixed on one side and other side is the pontic)

4) Resin Bonded

- bonded to adjacent teeth with a wing, fixed-fixed or cantilever

5) Implant Retained Bridges

-What are the disadvantages of Conventional Tooth Supported FPD

*- Invasive and Irreversible Approach

- Loss of Enamel, Pulp Damage but Fixed and Predictable Solution. Good Survival and Longevity

-What are the disadvantages of Resin Bonded Bridges

*Although Conservative, there is a risk of debond and some aesthetic issues due to metal wing behind the teeth.

-Radiographs are necessary to assess Abutment Teeth.

What factors are assessed on the Radiograph

*1) Periodontal Assessment

2) Periapical Assessment

3) Root Configuration

- Teeth with Conical Roots are more suitable for short-span bridge

-What are the different types of Anterior Crowns (3)

*1) Metal Ceramic

2) All Porcelain

- Porcelain Jacket Crown

- Dentine Bonded Crown

- High Strength Porcelain

- CAD/CAM

3) Other Types

- Composite Crowns

-What is the Most Popular Porcelain Crown

*PFM (Metal Ceramic Crowns)

- They have a metal core and ceramic veneer surface.

-What is the Labial Preparation dimension for a Porcelain Fused Metal Crown

*1.5mm

-What is the Palatal Preparation dimension for a PFM Crown

*0.7mm