Composite Resin Material Science

Question 1

what are the IDEAL PROPERTIES of a restorative material?

Answer 1

• good mechanical properties
• bonds to tooth/compatible with bonding systems
• aesthetics
• easy to handle/viscosity
• thermal properties
• radiopaque
• anticariogenic
• biocompatible

Question 2

what is composite resin composed of?

Answer 2

• filler particles
• resin
• camphorquinone
• low weight dimethacrylates
• silane coupling agent

Question 3

what part of composite resin is hard?

Answer 3

the filler particles (glass)

Question 4

what is the photo-initiator in composite called?

Answer 4

camphorquinone

Question 5

what is the purpose of low weight dimethacrylates in composite resin?

Answer 5

allow varied mechanical properties

Question 6

what is the purpose of silane coupling agent in composite resin?

Answer 6

allows intimate contact between filler and resin

Question 7

what resin monomers are commonly used?

Answer 7

• BIS-GMA

* urethane dimethacrylates

Question 8

what are the key characteristics of monomers?

Answer 8

• difunctional molecule (C=C bonds facilitate cross linking)

- undergoes free radical addition polymerisation

Question 9

how is camphorquinone activated?

Answer 9

by blue light

Question 10

what occurs when camphorquinone is activated?

Answer 10

• radical molecules produced
• these initiate free radical addition polymerisation of BIS-GMA
• leads to changes in resin properties

Question 11

how can filler types in composite be classified?

Answer 11

• conventional
• microfilled
• hybrid

Question 12

what are the handling characteristics of composite?

Answer 12

• condensable
• syringeable
• flowable

Question 13

how can you make composite stronger?

Answer 13

adding more filler molecules

Question 14

what occurs when more filler particles are added to composite?

Answer 14

• improved mechanical properties
• lower thermal expansion
• lower polymerisation shrinkage
• less heat of polymerisation
• improved aesthetics

Question 15

what wavelength of light must be used when curing composite?

Answer 15

430nm-490nm

Question 16

what are the advantages of light curing systems?

Answer 16

• extended working times
• less finishing
• immediate finishing
• less waste
• higher filler levels and less porosity

Question 17

what is meant by depth of cure?

Answer 17

• the depth to which the composite resin polymerises sufficiently

Question 18

what is the typical depth of cure for composite?

Answer 18

2mm

Question 19

what can occur if you use increments larger than 2mm?

Answer 19

• underpolymerised base

* poor bonding to tooth

Question 20

what problems can arise from light curing?

Answer 20

• recommended setting times too short

- polymerisation shrinkage

Question 21

why is polymerisation shrinkage bad?

Answer 21

• affects bond to tooth

* potential for cuspal fracture & microleakage

Question 22

how can polymerisation shrinkage be avoided?

Answer 22

use small increments

Question 23

what type of composites are used most frequently now?

Answer 23

hybrids

Question 24

what is meant by abrasion?

Answer 24

removal of surface layers when two surfaces make frictional contact

Question 25

how can abrasion occur inside the mouth?

Answer 25

tooth grinds/slides along the opposing tooth surface

Question 26

what acid is involved in the acid etch technique & how long must it sit on the tooth?

Answer 26

30% phosphoric acid & 20 secs

Question 27

what is the thermal conductivity of composite?

Answer 27

low - which is good !

Question 28

what is the thermal diffusivity of composite?

Answer 28

low - similar to dentine

Question 29

what is the thermal expansion coefficient of composite?

Answer 29

high - which is bad !

Question 30

what is meant by thermal diffusivity?

Answer 30

how readily a material transmits hear when exposed to a short/transient stimulus