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Dental material science > Composite > Flashcards

Composite Flashcards

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1
Q

What are the ideal properties of direct filling materials

A

mechanical – strength, rigidity, hardness

bonding to tooth / compatible with bonding systems

thermal properties

aesthetics

handling / viscosity

smooth surface finish/ polishable

low setting shrinkage​

radiopaque

anticariogenic

biocompatible

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2
Q

What types of glass filler particles are in composite resin

A

microfine silica​

quartz​

borosilicate glass​

lithium aluminium silicate​

barium aluminium silicate

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3
Q

What is BIS-GMA a reaction product of

A

bisphenol-A and glycidyl methacrylate​

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4
Q

What are the key characteristics needed to be monomers in resin

A
  • difunctional molecule ​
    (C=C bonds – facilitate crosslinking)

undergoes free radical addition polymerisation

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5
Q

How is composite resin able to be cured by light

A

Camphorquinone

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6
Q

What process occurs under blue light to cause the composite to cure

A

Camphorquinone – ​
-activated by blue light ​
-produces radical molecules
-these initiate free radical addition polymerisation of BIS-GMA
-leading to changes in resin properties (ie increased molecular weight, so increased viscosity, and strength)

causes degree of conversion of resin:
35-80%

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7
Q

Why do composite resins contain low weight dimethacrylates (eg TEGDMA)

A

added to adjust viscosity & reactivity

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8
Q

Why does composite contain silane coupling agent

A

good bond between filler particle and resin is essential

normally water will adhere to glass filler particles, preventing resin from bonding to the glass surface

a coupling agent is used to preferentially bond to glass and also bond to resin

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9
Q

How does a coupling agent act with the fillers and resin

A

Surrounds the glass fillers allowing better bonding between them and the resin

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10
Q

What handling characteristics are desirable

A

condensable - “amalgam feeling” - greater porosity ​

syringeable - good adaptation, less porosities, easy to apply​

flowable - lower filler content, more shrinkage, difficult to apply, place for them -with fibre ribbons

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11
Q

What effect does adding filler particles have on composite resins

A

improved mechanical properties​
-strength, rigidity, hardness, abrasion resistance etc​

lower thermal expansion (still not perfect)​

lower polymerisation shrinkage (still a problem)​

less heat of polymerisation (BUT not negligible)​

improved aesthetics​

some radiopaque

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12
Q

What types of composite curing are there

A

self curing (two pastes)​

UV activation (obsolete, one paste)​

Light curing ​
-blue light 440nm​(one paste)

direct curing (in mouth)​

indirect curing / post curing​(in laboratory)

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13
Q

How does a composite self cure

A

Free radicals from the reaction break the resin c=c bonds
polymerisation (formation of chain)

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14
Q

What reactants are present in self cure composite

A

benzoyl peroxide + aromatic tertiary amine

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15
Q

What are the advantages of light curing systems

A

extended working time​
-on-demand set, triggered when light activated​

less finishing​

immediate finishing​

less waste​

higher filler levels (not mixing two pastes)​

less porosity (not mixing two pastes)

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16
Q

What part of composite sets quickest

A

Most of blue light absorbed close to surface which sets readily and becomes hard

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17
Q

How is depth of cure value calculated according to ISO 4049

A

Column of composite light cured, soft comp scraped off, measured distance of hard comp is then divided by 2 giving the depth of cure

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18
Q

How is depth of cure defined

A

DoC is defined as depth at which material HARDNESS is about 80% that of the cured surface​

the depth to which the composite resin polymerises sufficiently

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19
Q

At what depth does the composite resin usually polymerise sufficiently

A

typically 2mm

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20
Q

What composite increment thickness is best to use in restorations

A

2mm as greater than this wikk result in under-polymerised bases
-soggy bottom and poor bonding to tooth

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21
Q

What is an example of a bulk fill comp

A

Tetric evoceram

22
Q

How is a bulk fill composite different to hybrid composites

A

Lucerin initiator as well as camphorquinone​

​

Has different optical absorption spectrum ​

hence UV and blue light ​

needed to polymerise (cure) material fully ​
23
Q

What are some potential problems of light curing

A

light / material mismatch - overexpose

premature polymerisation from dental lights - avoid exposure

optimistic “depth of cure” values​
-product, shade, light exposure & intensity​
-use small increments - 2 mm max

recommended setting times too short​
-product, light used, light/ material distance, ​
-contamination or damage to light guide, ​
-timer accuracy, ​
-variations in light output (eg over repeated use, between different units)​
use > 30 s​

polymerisation shrinkage ​
-affects bond to tooth, ​
-potential for cuspal fracture, microleakage ​
- use small increments - light from different angles

24
Q

What dangers occur with light curing

A

Exothermic reaction so adjacent enamel and dentine can conduct heat up to 16 degree rise

Divergent light beam - unless optical rod is ALWAYS close to the composite resin surface ​
SOME blue light MAY illuminate patient’s soft tissues and may cause thermal trauma ​

two clinical incidents in 2017​

25
Q

What temperature can cause potentially irreversible trauma to dental pulp

A

5.5 degrees

26
Q

How is occular damage prevented when curing

A

Safety sheilds or safety glasses

27
Q

Why is hybrid composite preffered

A

Various glass filler sizes to maximise percentage of composite resin made up of particles which improve mechanicalproperties

28
Q

In a large posterior cavity what clinical requirements are there of the composite

A

High strength, high YM, high abrasion resistance

29
Q

What does hardness refer to

A

​

material surface​

resistance to scratching​

indentation resistance

30
Q

What is abrasion (wear)

A

removal of surface layers when two surfaces make frictional contact​

31
Q

What are the affects of surface roughness

A

appearance​

plaque retention​

sensation when in contact with tongue​

32
Q

What are the surface roughness depths of conventional and microfine

A

Conventional 80um
Microfine 10um

33
Q

What material factors affect wear

A

filler material​

particle size distribution​

filler loading​

resin formulation​

coupling agent

34
Q

How can clinical factors affect wear

A

cavity size & design​

tooth position​

occlusion​

placement technique​

cure efficiency​

finishing methods

35
Q

How is composite bonded to tooth

A

enamel - acid etch technique

dentine - dentine / universal bonding systems

36
Q

What percent phosphoric acid is in etch

A

30%

37
Q

What is the typical bond strength of composite to enamel and dentine

A

40MPa

38
Q

What does bond strength depend on

A

Surface prep, composite brand and method

39
Q

What is the value of shear bond strength

A

40MPa

40
Q

Why is an uneven cavity floor with ridges undesirable

A

Concentrates stress at the interface increasing liklihood of failure

41
Q

What material has a greater
Compressive strength (MPa), Tensile strength (MPa), Elastic modulus (GPa) and Hardness
Amalgam or composite

A

Amalgam

42
Q

What is the thermal conductivity of composites

A

should be low to avoid pulpal damage from hot & cold foods/fluids - it is low​

43
Q

What is thermal diffusivity

A

How readily a material transmits heat when exposed to a short/transient stimulus

44
Q

What is the thermal diffusivity of composite (hybrid)

A

Low - similar to dentine

45
Q

What is the ideal thermal expansion of composite

A

should be equal to tooth, to reduce microleakage - BUT it’s high - which is poor​

46
Q

What material has the lowest thermal expansion coefficient

A

Ceramic

47
Q

What is the thermal expansion coefficient of compostie compared to glass ionomer

A

Comp 25-68ppm (highest of materials)
GI 10-11ppm

48
Q

What factors are important for aesthetics

A

shade range​

translucency​

maintenance of properties over lifetime​

resistance to staining​

surface finish

49
Q

What are the potential problems of light curing

A

Must ensure blue light is delivered correctly (intensity, exposure time, proximity of optical rod to tooth/material) to ensure increment is fully curedand proper bond made

50
Q

What is the most common failing material in posterior composites

A

Micro-filled composites ahead of fine hybrid composites

51
Q

What are the choices of material for high, medium and low risk caries patients

A

Resin Modified GI - high caries risk​
- frequent attenders

Compomer - medium caries risk​
- caries under control​
- regular attenders​

Composite resin - low caries risk patients

Dental material science (5 decks)

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