5. Composite Resins: Part 2 Flashcards
Properties that affect the choice of material (10)
Mechanical Bonding Thermal Aesthetic Handling/viscosity Surface finish Polymerisation shrinkage Anticariogenic Biocompatible Radiopacity
Clinical requirements of large posterior cavity (3)
High strength
High rigidity
High abrasion resistance
Clinical requirements of deciduous restoration (4)
Strong in thin section
Wear of tooth
Bonding
Microleakage
Types of composite (3)
Conventional
Microfine
Hybrid
Features of conventional composite (2)
Strong
Problems with finishing and staining due to soft resins and hard particles
Features of microfine composite (3)
Smaller particles
Allows for smoother surfaces (better aesthetics for longer periods)
Inferior mechanical properties (elastic limit and rigidity)
Features of hybrid composites (2)
Compromise between conventional and microfine composites
Improved filler loading and coupling agents cause improvement in mechanical properties
Definition of hardness (3)
Resistance to scratching or indentation resistance
Related to material surface
Measured by the amount of surface indentation (KHN)
Definition of abrasion (2)
Abrasion occurs when the tooth grinds/slides along the opposing tooth surface (or restorative material at its surface
Abrasion leaves behind a rough surface
What does surface roughness affect (3)
Appearance
Plaque retention
Sensation when in contact with tongue (laceration)
Process of tooth wear of composite resins (4)
Resin is removed
Leaves some of the filler particle exposed
If enough resin is removed, the filler particle is dislodged, leaving a “cut” out of the resin
Process continues
Factors that affect tooth wear (2)
Material factors
Clinical factors
Material factors that affect tooth wear (5)
Filler material Filler size distribution Filler loading Resin formulation Coupling agents
Clinical factors that affect tooth wear (7)
Cavity size Cavity design Tooth position Occlusion Placement technique Cure efficiency Finishing methods
Features of material/tooth bonding (2)
Bonding to enamel occurs through acid etch technique
Bonding to dentine occurs through dentine/universal bonding agents (DBAs)
Typical bonding strength of composite to enamel/dentine
40MPa
Dependent on the surface preparation of tissue, composite brand and test method
Function of good material/tooth surface bonding (3)
Help reduce microleakage
Help to counteract polymerisation shrinkage
Help to reduce the likelihood of a gap between the restoration and tooth
Features of composite restoration placement (2)
Will not have to withstand full stress - the stress will be transferred to tooth and bone
Poor bonding to tooth concentrates stress on the restoration, so failure is more likely
Compressive strength of enamel
250MPa
Compressive strength of dentine
280MPa
Compressive strength of amalgam
350MPa
Compressive strength of (hybrid) composite
300MPa
Compressive strength of microfilmed composite
260MPa
Compressive strength relationship between materials (4)
Amalgam > composite > dentine > enamel
Elastic limit (Yield) stress of (hybrid) composite
300MPa
Elastic limit (Yield) stress of microfilled composite
160MPa
Tensile strength of enamel
35MPa
Tensile strength of dentine
40-260MPa
Tensile strength of amalgam
60MPa
Tensile strength of (hybrid) composite
50MPa
Tensile strength of microfilled composite
40MPa
Tensile strength relationship between materials (4)
Dentine > amalgam > composite > enamel
Flexural strength of (hybrid) composite
150MPa
Flexural strength of microfilled composite
80MPa
Elastic modulus of enamel
50GPa
Elastic modulus of dentine
12GPa
Elastic modulus of amalgam
30GPa
Elastic modulus of (hybrid) composite
14GPa
Elastic modulus of microfilled composite
6GPa
Elastic modulus relationship between materials (4)
Enamel > amalgam > composite > dentine
Hardness of enamel
350VHN
Hardness of dentine
60VHN
Hardness of amalgam
100VHN
Hardness of (hybrid) composite
90VHN
Hardness of microfilled composite
30VHN
Hardness relationship between materials (4)
Enamel > amalgam > composite > dentine
Thermal properties include (2)
Thermal conductivity
Thermal expansion coefficient
Ideal thermal properties of composite
Thermal conductivity should be low to avoid pulpal damage from hot and cold foods/fluids
Thermal expansion should be equal to that of the tooth, to reduce microleakage
Actual thermal properties of composite
Low thermal conductivity
High thermal expansion coefficient
Thermal expansion coefficient of enamel
11ppm/C
Thermal expansion coefficient of dentine
8ppm/C
Thermal expansion coefficient of amalgam
22-28ppm/C
Thermal expansion coefficient of composite
25-68ppm/C
Thermal expansion coefficient of GIC
10-11ppm/C
Thermal expansion coefficient of ceramic
8-14ppm/C
Thermal expansion coefficient of gold alloy
12-15ppm/C
Thermal expansion relationship between materials (7)
Composite > amalgam > gold alloy > ceramic > enamel = GIC > dentine
Components of aesthetic properties (5)
Shade range Translucency Maintenance of properties over lifetime Resistance to staining Surface finishing
Why should composite restorations be radiopaque
To allow secondary caries to be diagnosed more easily on radiographs
Handling/viscosity properties of composite (4)
Light-curing
Mixing/working times
Viscosity
User-friendly
Composite setting shrinkage
Low
Polymerisation shrinkage is still a problem as stresses develop at hard tissue surfaces, making de-bonding more likely
Bonding occurs between (2)
Filler and resin particles
Resin and hard tissues
