Composite Resin

Question 1

what is composite used for

Answer 1

restorative material for primary and secondary caries, trauma and abrasion

Question 2

what are the ideal properties for composite

Answer 2

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

Question 3

what are the constituents of composite resin

Answer 3

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

Question 4

what is the importance of glass filler particles in composite

Answer 4

improve the mechanical properties, good mechanical strength

Question 5

what is the size of glass filler particles

Answer 5

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

Question 6

what is the importance of resin in composite

Answer 6

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

Question 7

what is the role of camphorquinone

Answer 7

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

Question 8

what is the role of dimethacrylates

Answer 8

alter viscosity and reactivity

Question 9

what is the role of silane coupling agent

Answer 9

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

Question 10

how can composite be classified

Answer 10

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

Question 11

what is the effect of having more glass filler particles

Answer 11

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

Question 12

what is meant by depth of cure

Answer 12

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

Question 13

what is an average value of depth of cure for composite

Answer 13

2mm

Question 14

how do bulk fill composites work

Answer 14

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

Question 15

what are some problems with curing

Answer 15

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

Question 16

how can polymerisation shrinkage be avoided

Answer 16

by lowering the configuration factor - small increments

Question 17

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

Answer 17

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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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

Question 21

what is an average value of bond strength for composite

Answer 21

40MPa

Question 22

what should the polymerisation contraction shrinkage be below for a composite

Answer 22

less than 5%

Question 23

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

Answer 23

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

Question 24

what is the importance of thermal expansion

Answer 24

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

Question 25

what is the configuration factor

Answer 25

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

Question 26

how does the configuration factor affect contraction shrinkage

Answer 26

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

Question 27

what are the principles of cavity preparation

Answer 27

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