Composite Resin Flashcards Preview

Dental Material Science > Composite Resin > Flashcards

Flashcards in Composite Resin Deck (27)
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1
Q

what is composite used for

A

restorative material for primary and secondary caries, trauma and abrasion

2
Q

what are the ideal properties for composite

A

high mechanical strength, high YM, high hardness, abrasive resistant, low thermal expansion and thermal diffusivity, low polymerisation contraction shrinkage, good bond strength, good aesthetics, biocompatible

3
Q

what are the constituents of composite resin

A

glass filler particles, resin, camphorquinone, low weight di-methacrylates, silane coupling agent

4
Q

what is the importance of glass filler particles in composite

A

improve the mechanical properties, good mechanical strength

5
Q

what is the size of glass filler particles

A

can vary, large and small - hybrid is a combination of sizes, large particles improve mechanical properties but small improve aesthetics

6
Q

what is the importance of resin in composite

A

Bis-GMA is normally used, opposite to glass filler, improves viscosity, has little importance for mechanical properties, but contains bifunctional molecule with C=C bond, can be broken and undergo polymerisation - increases strength and viscosity of material

7
Q

what is the role of camphorquinone

A

activated by blue light, produces free radicals which can then break the C=C in the resin and induce free radical addition polymerisation

8
Q

what is the role of dimethacrylates

A

alter viscosity and reactivity

9
Q

what is the role of silane coupling agent

A

allows a better bond between the glass filler particles and the resin material

10
Q

how can composite be classified

A

filler particles - large, microfine, hybrid
type of cure - light cure, self cure
area of use - anterior, posterior

11
Q

what is the effect of having more glass filler particles

A

improve mechanical properties, improved aesthetics, improve thermal properties, increased abrasion resistance, lower polymerisation shrinkage

12
Q

what is meant by depth of cure

A

the most superficial surface of composite receives the most blue light therefore, is always cured. however, the depth at which the blue light can penetrate through the material to produce material with 50% of the hardness of the most superficial layer is the maximum depth of cure

13
Q

what is an average value of depth of cure for composite

A

2mm

14
Q

how do bulk fill composites work

A

they have lucirin in it as well as camphorquinone. this releases free radicals at a different wave length, therefore less light has to be received to induce it - at lower areas where less light is, still have polymerisation

15
Q

what are some problems with curing

A

increases the temperature - can damage the pulp
blue light might be dangerous for patient and operator
polymerisation contraction shrinkage

16
Q

how can polymerisation shrinkage be avoided

A

by lowering the configuration factor - small increments

17
Q

give a value for compressive strength of composite and how does this compare with amalgam and enamel

A

300MPa, slightly lower than amalgams 400MPa, however, higher than enamel 250MPa

18
Q

give a value for tensile strength of composite and how does this compare with amalgam and enamel

A

50MPa, slightly lower than amalgams 60MPa, but higher than enamel 35MPa

19
Q

give a value for youngs modulus of composite and how does this compare with amalgam and enamel

A

14MPa, much lower than amalgam at 30MPa and enamel with 50MPa

20
Q

give a value for hardness of composite and how does this compare with amalgam and enamel

A

90GPa, lower than amalgam with 100GPa but enamel is much better with 350GPa

21
Q

what is an average value of bond strength for composite

A

40MPa

22
Q

what should the polymerisation contraction shrinkage be below for a composite

A

less than 5%

23
Q

compare the thermal expansion of enamel and dentine with amalgam, composite and glass ionomer

A
enamel - 8
dentine - 11
amalgam - 22-28
composite - 25-68
glass ionomer - 10
24
Q

what is the importance of thermal expansion

A

ideally, a restorative material should expand and contract at the same rate as tooth tissue when exposed to hot and cold temperatures. If not, gaps will appear between the tooth and restoration, resulting in micro leakage of bacteria, water and food - resulting in secondary caries

25
Q

what is the configuration factor

A

ratio of bonded surfaces to unbonded surfaces
high - many surfaces bonded together
low - not many surfaces bonded together

26
Q

how does the configuration factor affect contraction shrinkage

A

if a high factor, when the resin polymerisations the material shortens. If surfaces are bonded together, the resin will attempt to pull these surfaces together, will result in gaps forming between the restorative material and the tooth tissue - microleakage

27
Q

what are the principles of cavity preparation

A

identify and remove carious enamel
identify the extent of the caries at the ADJ
remove detinal caries, starting from the ADJ peripherally and moving in towards the centre of the lesion
remove caries over the pulp
outline form modification - enamel finishing
internal finishing - remove sharp internal line angles
requirements of restorative material