Composite resins

Question 1

direct filling materials - ideal properties

Answer 1

mechanical properties;
- strength, rigidity, hardness
bonds to tooth/compatible with bonding systems
good aesthetics
suitable handling and viscosity
good thermal properties
smooth surface finish/polishable
radiopaque
anticariogenic
biocompatible

Question 2

composite r
esin constituents

Answer 2

filler particles
resin
camphorquinone
low weight dimethacrylates
silane coupling agent

Question 3

direct filling materials; applications

Answer 3

new dental caries
abrasion/erosion
failed restorations/secondary caries
trauma

Question 4

types of composite resin filler particles

Answer 4

microfine silica
quartz
borosilicate glass
lithium aluminium silicate
barium aluminium silicate

Question 5

monomers used in the resin of composite

Answer 5

BIS-GMA
urethane dimethacrylates

Question 6

key characteristics of the monomer in composite resin

Answer 6

C=C bonds
- facilitate cross linking
undergoes free radical addition polymerisation

Question 7

Camphorquinone - features and purpose in composite resin

Answer 7

activated by blue light
produces radical molecules
- these initiate free radical addition polymerisation of BIS-GMA
- leads to changes in resin properties

Question 8

low weight dimethacrylates - why are these added to composite?

Answer 8

to adjust viscosity and reactivity

Question 9

function of a silane coupling agent in composite resin?

Answer 9

normally water will adhere to glass filler particles, preventing resin from bonding
- a coupling agent is used to preferentially bond goo glass and also bond to resin

Question 10

uses of composite resin

Answer 10

where aesthetics important
inlays, inlays
cores
modified forms as luting cements
- some dual cured

Question 11

classifications of compose resin

Answer 11

filler type
curing method
- light cured
- self cured
- dual cured
area of use
handling characteristics
- condensable - greater porosity
- syringe able - good adaptation - less porosities
- flowable - lower filler content, more shrinkage

Question 12

effects of adding filer particles to composite

Answer 12

improved mechanical properties
- strength, rigidity, hardness etc
lower thermal expansion
lower polymerisation shrinkage
less heat of polymerisation
improved aesthetics
some radiopaque

Question 13

advantages of light curing system

Answer 13

extended working time
- on demand set
less finishing
immediate finishing
less waste
higher filler levels
less porosity
- not mixing 2 pastes

Question 14

define ‘depth of cure’

Answer 14

the depth to which the composite resin polymerises sufficiently
- hardness is about 80% of the cured surface
typically 2mm
6mm for bulk fill
indicates increment thickness to use when building a restoration

Question 15

consequences of using increments larger than 2mm

Answer 15

under-polymerised base
- ‘soggy bottom’
- poor bonding to tooth = early failure

Question 16

potential problems with light curing

Answer 16

premature polymerisation from dental lights
- avoid exposure
optimistic ‘depth of cure’ values
- dependent on product, shade and light intensity
polymerisation shrinkage
- affects bond to tooth
- potential for cuspal fracture and microleakage

Question 17

light curing - safety

Answer 17

use safety shields or safety glasses

Question 18

material factors affecting wear of composite

Answer 18

filler material
particle size distribution
resin formulation
filler loading
coupling agent

Question 19

clinical factors affecting wear of composite

Answer 19

cavity size and design
tooth position
occlusion
placement technique
cure efficiency
finishing methods

Question 20

Acid etch technique for composite

Answer 20

30% phosphoric acid for 20 seconds

Question 21

bonding to tooth surface - benefits

Answer 21

reduce micro leakage
counteract polymerisation shrinkage
- good bond reduces likelihood of gap between restoration and tooth
minimise cavity design
- no need for retention undercuts as bond holds restoration in place
stress transfer
- restoration does not have to withstand full stress - transferred to tooth and bone

Question 22

composite resin thermal properties

Answer 22

low thermal conductivity - good
low thermal diffusivity - similar to dentine
high thermal expansion coefficient = poor

Question 23

composite resin biocompatibility

Answer 23

generally considered ok
- increasing concern about resins in general - not all monomer polymerised