Clinical composites

Question 1

when would you apply direct filling materials?

4

Answer 1

• primary dental caries
• failed restorations / secondary caries
• abrasion / erosion
• trauma

Question 2

what are the ideal properties of direct filling materials?

10

Answer 2

• mechanical - strength, rigidity, hardness
• bonding to tooth
• thermal properties
• aesthetics
• handling/viscosity
• smooth surface finish / polishable
• low setting shrinkage
• radiopaque
• anticariogenic
• biocompatible

Question 3

what makes up composite resin?

5

Answer 3

1. filler particles - glass
2. resin
3. camphorquinone
4. low weight dimethylacrylates
5. silane coupling agent

Question 4

what are the filler particles that make up composite resin?

Answer 4

• microfine silica
• quartz
• borosilicate glass
• lithium aluminium silicate
• borium aluminium silicate etc.

Question 5

what monomers are in the resin? what are the key characteristics?

2,2

Answer 5

BIS-GMA and urethane dimethacrylates
* difunctional molecule
* undergoes free radical addition polymerisation

Question 6

what is camphorquinone?

3

Answer 6

• activated by blue light
• produces radical molecules which initiate free radical addition polymerisation of BIS-GMA
• leads to changes in resin properties -stronger, more viscous

Question 7

why are low weight dimethylacrylates added to composite resin?

Answer 7

adjusts the viscosity and reactivity, easier to manipulate

Question 8

what is silane coupling agent added to composite resin?

Answer 8

bonds filler particles and resin

Question 9

when would you use composite rather than other materials?

7

Answer 9

• where aesthetics are important
• class 3, 4, 5 permanent restorations
• class 2 - limited occlusal wear
• labial veneers
• inlays, onlays - indirect technique
• cores
• modified forms as luting cements

Question 10

what are good handling characteristics of composite resin?

3

Answer 10

• condensable - greater porosity
• syringeable - good adaption, lesser porosity, easy to apply
• flowable - lower filler content, more shrinkage, difficult to apply

Question 11

describe the size of hybrid filler particles

Answer 11

hybrid composites have filler particles of different sizes

Question 12

what is the effect of adding filler particles to composite resin?

6

Answer 12

• improved mechanical properties - strength, rigidity, hardness, abrasion resistance
• lower thermal expansion
• lower polymerisation shrinkage
• less heat of polymerisation
• improved aesthetics
• some are radiopaque

Question 13

how do different types of curing development for composite resins?

5

Answer 13

• self curing - two pastes
• UV activation - one paste
• light curing - blue light, one paste
• direct curing - in mouth
• indirect curing / post curing - in lab

Question 14

how do self curing composites set?

Answer 14

benzoyl peroxide + aromatic tertiary amine = polymerisation

Question 15

how do light curing composites set?

Answer 15

camphorquinone + blue light (430-490nm)

Question 16

what are the two light sources for curing composite resin? which is better and why?

Answer 16

halogen and LED
* difference in optical spectral range
* LED is better as it absorbs the same wavelengths as camphorquinone, especially at optical excitation

Question 17

what are the advantages of light curing systems?

6

Answer 17

• extended working time - command set
• less finishing
• immediate finishing
• less waste
• higher filler levels (not mixing 2 pastes)
• less porosity (not mixing 2 pastes)

Question 18

where on composite is light absoprbed most?

Answer 18

close to the surface
* composite resin nearest the surface sets teh most readily and becomes hard

Question 19

describe the depth of cure ISO 4049

Answer 19

• column of composite is light cured
• soft composite is removed from bottom of column
• hard composite is reached and no longer can be scraped
• distance of hard composite is measured
• distance is divided by 2
• remaining distance is considered the depth of cure

Question 20

what does the depth of cure show?

Answer 20

the depth to which the composite resin polymerises sufficiently
* indicated increment thickness to use when restoring

Question 21

how deep can hybrid composites be cured? what happens when more composite is used?

Answer 21

2mm
* using >2mm increments results in under-polymerised base and poor bonding to tooth = early failure

Question 22

what is depth of cure defined as?

Answer 22

depth at which material hardness is about 80% of the cured surface

Question 23

describe this depth of cure profile

Answer 23

• around 80% of material hardness of cured surface is around 12
• if you read a hardness of 12 on the graph, the depth equivalent is around 1.5mm
• so the depth of cure is <1.5mm

Question 24

what are the potential problems of light curing

5

Answer 24

• light / material mis-match
• premature polymerisation from dental lights
• optimistic depth of cure values (too high)
• recommended setting times too short
• polymerisation shrinkage

Question 25

what are the differences between conventional, microfine and hybrid composites?

Answer 25

* conventional = strong but problems with finishing and staining due to soft resins and hard glass filler particles * microfine = smaller particles so smoother surface for better aesthetics fro longer period but inferior mechanical properties * hybrid = compromise between conventional and microfine - improved filler loading and coupling agents have led to improvements in mechanical properties

Question 26

what is abrasion?

Answer 26

* removal of surface layers when two surfaces make frictional contact * tooth grinds/slides along the opposing tooth surface or restorative material and the surface is roughened

Question 27

what does surface roughness affect? | 3

Answer 27

* appearance * plaque retention * sensation when in contact with tongue

Question 28

what happens when composite wears? what does the roughness depend on?

Answer 28

* surface layer is removed so uneven surface and filler particle protrudes * roughness depends on size of filler particle in composite resin

Question 29

what material factors affect the wear of composite? | 5

Answer 29

* filler material * particle size distribution * filler loading * resin formulation * coupling agent

Question 30

what clinical factors affect the wear of composite? | 6

Answer 30

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

Question 31

what is the bond strength of composite resin to enamel and dentine?

Answer 31

40MPa

Question 32

what does a good bond to the tooth give rise to? what does a poor bond do? | 2, 1

Answer 32

* reduced microleakage and counteracts polymerisation shrinkage * transfers stress to tooth and alveolar bone * poor bond concentrates stress at different interfaces so more likely to fail

Question 33

what is the compressive strength, tensile strength, elastic modulus and hardness of amalgam and hybrid composite compared to dentine and enamel?

Answer 33

* amalgam and composite have a higher compressive strength than enamel and dentine * amalgam and composite have a higher tensile strength than enamel and sometimes dentine * amalgam and comosite have a lower elastic modulus than enamel but higher than dentine but composite is similar to dentine * amalgam and composite are harder than dentine but less hard than enamel

Question 34

describe the ideal thermal conductivity of cmposite resins

Answer 34

should be low to avoid pulpal damage from hot and cold foods and drinks

Question 35

what is thermal diffusivity and what is ideal for composite resins?

Answer 35

* how readily a material transmits heat when exposed to a short/transient stimulus * should be low and similar to dentine

Question 36

what is the ideal thermal expansion of composite resins? what are the thermal expansion values for enamel, dentine and other restorative materials?

Answer 36

should be equal to the tooth to reduce microleakage but it is high = poor

Question 37

why are composite resins good for aesthetics? | 5

Answer 37

* shade range * translucency * maintenance of properties over time * resistance to staining * surface finish

Question 38

how is the handling/viscosity of composite resins? | 4

Answer 38

* light curing - on demand setting * mixing, working time - depends on the material * viscosity - some flow and some need to be packed * user friendly

Question 39

when would you use resin modified glass ionomer clinically? | 3

Answer 39

* high caries risk * frequent attenders * anticariogenic - releases fluoride

Question 40

when would you use compomers clinically? | 3

Answer 40

* medium caries risk * caries under comtrol * regular attenders

Question 41

when would you use composite resins?

Answer 41

patients with low caries risk