4. Composite Resins: Part 1 Flashcards
Types of restorative materials (5)
Composite resins Amalgam Glass ionomer Compomers Ceramics
Classification of composite resins (4)
Filler particles (conventional, microfilmed, hybrid)
Setting (light-cured, self-cured)
Area of use (anterior, posterior)
Handling
Ideal properties of direct filling materials (10)
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
What are direct restorative materials used on (5)
New caries Abrasion/erosion Failed restorations Secondary caries Trauma
Composition of composite resins (5)
Filler particles Resin Camphorquinone Low weight dimethacrylates Silane coupling agent
Definition of filler particles
Microfine glass particles of various sizes and types
Types of microfine filler particles (5)
Silica Quartz Borosilicate glass Lithium aluminium silicate Barium aluminium silicate.
Definition of resins
Relatively soft materials made from monomers such as Bis-GMA
What is Bis-GMA
Reaction product of bisphenol-A and glycidyl methacrylate
Key characteristics of resins (3)
Bifunctional molecules
Contain C=C bond which facilitates cross-linking
Can undergo free radical addition polymerisation
Definition of camphorquinone
Photo-activator catalyst that initiates polymerisation of resins (setting) when activated by blue light
Functions of camphorquinone (2)
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
Function of low weight dimethacrylates
Added to adjust the viscosity and reactivity of the resin monomers
Example of low weight dimethacrylate
TEGDMA
Definition of silane coupling agent
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
Function of silane coupling agent
Provide an essential bond between filler particles and the resin
Uses for composite (7)
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)
Purposes of adding filler particles to resin (7)
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
Types of composite resin curing (5)
Self-curing Light curing UV activation Direct curing Indirect/post curing
Overview of camphorquinone reaction (2)
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
Advantages of light-curing systems (6)
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)
Definition of depth of cure
The depth to which the composite resin polymerises sufficiently, such that its hardness is about half of that of the cured surface
Typical ideal increments of composite resin for a complete depth of cure
1.5-2mm
Consequence of increments >2mm on depth of cure (2)
Results in an under-polymerised base
This results in poor bonding to teeth and early restoration failure
Features of bulk-fill composites (2)
6mm depth-of-cure
Lucerin initiator as well as camphorquinone
Feature of lucerin initiator
Has a different optically absorption spectrum, hence UV and blue light are needed to polymerise (cure) the material fully
Potential problems of light-curing (5)
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)
Safety considerations for light curing (3)
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)
