Restoration of Cavities with Different Materials: Differences and Similarities

Question 1

What type of teeth are by far the most likely to fracture

Answer 1

Teeth that have been previously restored

Question 2

How to fractures occur on restored teeth

Answer 2

1. there will be a deflection of the cusp as the tooth has been weakened by restoration
2. Causes an open interface between the restoration and the tooth
3. Causes microleakage
4. Recurrent caries
5. Fracture

NB doesn’t exactly have to happen in this order

Question 3

AY BAWS CAN I HABE DE NOTE PLZ

Answer 3

Cus the filling material will differ from enamel there will be higher stress at the tooth-restoration interface that can cause crack propagation

Question 4

What should you look for when forming the shape of the restoration

Answer 4

• Minimise reduction of tooth tissue to ensure maximum preservation
• Geometry of cavity - amalgam = sharp angles and flat base, composite = rounded base

Question 5

Why do we want the geometry of the cavity to be correct for the restorative material

Answer 5

Helps to keep stress level low and avoid fractures of the restored unit

Question 6

Name some general features of amalgam fillings

Answer 6

• Good longevity
• Needs mechanical retention, no chemical or micro-mechanical
• Strong
• Poor aesthetics
• Mercury toxicity

Question 7

What are the limitations of using dental amalgams

Answer 7

• Brittle, low tensile strength, susceptible to creep
• Breaks under bending force
• Important to use in bulk - avoid thin sections
• Deep cut boxes with 90 degree margin angles
• Not conservative
• Avoid sharp angles with high stress

Question 8

What are some general features of composite fillings

Answer 8

• Light cured
• 2mm increments
• Polymerisation shrinkage
• Not natively adhered - etching/bonding agent - micromechanical retention
• Good creep resistance and compressive strength
• Excellent aesthetics

Question 9

What are the limitations of Composite fillings

Answer 9

• Adhesive first and then retention
• Good quality adhesive bond
• Greater polymerisation shrinkage in large restorations
• Dentine bonding is weaker than bonding to an acid-etched enamel
• High wear in contact areas

Question 10

Name some general features of GICs

Answer 10

• Natural adherence to tooth
• No shrinkage
• Fluoride release/uptake
• Ease of placement in bulk
• Ultra conservative restoration
• Aesthetic

Question 11

What are some limitations of GICs

Answer 11

• Low strength and high wear at early stages
• Need protection from dehydration
• Low diametral tensile strength
• Low tensile strength
• Unable to withstand high tensile loads
• Restoration must be supported by tooth tissue

Question 12

Compare how restorative material distributes loads to tooth tissue

Answer 12

Materials = isotropic

Enamel and dentine = anisotropic

Question 13

Describe the photo elasticity method of looking at the stress distribution of a restored tooth

Answer 13

Based on birefringence:

• When light passes through a birefringent material it experiences 2 refractive indices
• magnitude of each refractive index directly related to the state of stresses at that point within the material

Question 14

Describe the finite element analysis of examining stress distribution in a restored tooth

Answer 14

• Computer modelling
• Mesh of complex shape
• Each element assigned the property of materials
• Distribution of stresses can be modelled

Question 15

Where are high stresses found mostly in bonded restorations

Answer 15

At the cusps

Question 16

Where are high stresses found mostly in non-bonded restorations

Answer 16

All around the cavity margins, mainly in sharp corners of cavity design

Question 17

Where will cracks occur in bonded restorations

Answer 17

At the enamel in contact with the opposing tooth as the cusps will constantly undergo flexion due to contact with opposing tooth

Question 18

Where will cracks occur in non-bonded restorations

Answer 18

On the internal line angle and the DEJ

Question 19

Where do high stresses focus in onlay/overlay restorations

Answer 19

Within in the restoration itself

If base of onlay is parallel (at a tangent sorta) to cuspal margins then there is more stress concs in these regions, but if cut at angle, stress is reduced at these regions

Question 20

AY BAWS CAN I HABE DE NOTE PLZ

Answer 20

• Avoid use of sharp edges and corners as stress will concentrate here