4. Composite Resins: Part 1

Question 1

Types of restorative materials (5)

Answer 1

Composite resins
Amalgam
Glass ionomer
Compomers
Ceramics

Question 2

Classification of composite resins (4)

Answer 2

Filler particles (conventional, microfilmed, hybrid)
Setting (light-cured, self-cured)
Area of use (anterior, posterior)
Handling

Question 3

Ideal properties of direct filling materials (10)

Answer 3

Mechanical strength/rigidity/hardness
Bonding to tooth/compatible with bonding systems
Thermal properties
Aesthetics
Radiopaque
Handling/viscosity
Anticariogenic
Smooth surface finish/able to be polished
Low setting shrinkage
Biocompatible

Question 4

What are direct restorative materials used on (5)

Answer 4

New caries
Abrasion/erosion
Failed restorations
Secondary caries
Trauma

Question 5

Composition of composite resins (5)

Answer 5

Filler particles
Resin 
Camphorquinone 
Low weight dimethacrylates
Silane coupling agent

Question 6

Definition of filler particles

Answer 6

Microfine glass particles of various sizes and types

Question 7

Types of microfine filler particles (5)

Answer 7

Silica
Quartz
Borosilicate glass
Lithium aluminium silicate
Barium aluminium silicate.

Question 8

Definition of resins

Answer 8

Relatively soft materials made from monomers such as Bis-GMA

Question 9

What is Bis-GMA

Answer 9

Reaction product of bisphenol-A and glycidyl methacrylate

Question 10

Key characteristics of resins (3)

Answer 10

Bifunctional molecules
Contain C=C bond which facilitates cross-linking
Can undergo free radical addition polymerisation

Question 11

Definition of camphorquinone

Answer 11

Photo-activator catalyst that initiates polymerisation of resins (setting) when activated by blue light

Question 12

Functions of camphorquinone (2)

Answer 12

Produces radical molecules which initiate free radical addition polymerisation of BIS-GMA leading to changes in resin properties (increased molecular weight, so increased viscosity and strength).
Causes a degree of conversion of resin

Question 13

Function of low weight dimethacrylates

Answer 13

Added to adjust the viscosity and reactivity of the resin monomers

Question 14

Example of low weight dimethacrylate

Answer 14

TEGDMA

Question 15

Definition of silane coupling agent

Answer 15

A coupling agent is used to preferentially bond to glass and also bond to resin
Normally water will adhere to glass filler particles, preventing resins from bonding to the glass surface
In silanes, methoxy groups hydrolyse to hydroxy groups and react with absorbed water or hydroxyl in filler

Question 16

Function of silane coupling agent

Answer 16

Provide an essential bond between filler particles and the resin

Question 17

Uses for composite (7)

Answer 17

Where aesthetics is important
Class III, IV and V permanent restorations
Class II – limited occlusal wear
Labial veneers
Inlays and onlays (indirect technique)
Cores
Modified forms as luting cements (some dual cured)

Question 18

Purposes of adding filler particles to resin (7)

Answer 18

Improves mechanical properties (strength, hardness, rigidity)
Improves aesthetics
Increases abrasion resistance
Lower thermal expansion
Lower polymerisation shrinkage
Less head of polymerisation
Makes some areas radiopaque

Question 19

Types of composite resin curing (5)

Answer 19

Self-curing
Light curing
UV activation
Direct curing
Indirect/post curing

Question 20

Overview of camphorquinone reaction (2)

Answer 20

Light-cured composite resin contains camphorquinone, which is a photo initiator
When blue light (430-490nm) is applied, the camphorquinone begins the reaction, culminating in composite setting

Question 21

Advantages of light-curing systems (6)

Answer 21

Extended working time (on-demand set)
Less finishing
Immediate finishing
Less waste
Higher filler levels (not mixing two pastes)
Less porosity (not mixing two pastes)

Question 22

Definition of depth of cure

Answer 22

The depth to which the composite resin polymerises sufficiently, such that its hardness is about half of that of the cured surface

Question 23

Typical ideal increments of composite resin for a complete depth of cure

Answer 23

1.5-2mm

Question 24

Consequence of increments >2mm on depth of cure (2)

Answer 24

Results in an under-polymerised base

This results in poor bonding to teeth and early restoration failure

Question 25

Features of bulk-fill composites (2)

Answer 25

6mm depth-of-cure

Lucerin initiator as well as camphorquinone

Question 26

Feature of lucerin initiator

Answer 26

Has a different optically absorption spectrum, hence UV and blue light are needed to polymerise (cure) the material fully

Question 27

Potential problems of light-curing (5)

Answer 27

Light/material mismatch – overexposure
Premature polymerisation from dental lights (avoid exposure)
Optimistic depth of cure values – product, shade, light exposure and intensity
Recommended setting times too short – product, light used, light/material distance, contamination/damage to light guide, timer accuracy, variations in light output. Use for >30s
Polymerisation shrinkage – affects bond to tooth, potential for cuspal fracture and microleakage; use small increments (light from different angles)

Question 28

Safety considerations for light curing (3)

Answer 28

Exothermic reaction (release of heat into resin; conduction to adjacent enamel/dentine)
Divergent light beam – modern devices are brighter/more intense
Ocular damage (safety glasses/shield)