Dental Composites; Aesthetic Restorative Materials

Question 1

Give 4 uses of composite restorative materials.

Answer 1

1. Restoration of anterior and posterior teeth
2. Pit and fissure sealants
3. Cementation of fixed prostheses
4. Bonding of ceramic veneers

Question 2

Give 3 contraindications for dental composites.

Answer 2

1. Large posterior restorations
2. Bruxism
3. Poor isolation

Question 3

Give 4 positives of dental composites.

Answer 3

1. They can withstand the environment in the oral cavity
2. Be easily shaped to the anatomy of the cavity
3. Match the natural tooth colour
4. Bond directly to the tooth tissue.

Question 4

What types of resin composites should be used for class 1 and 2 restorations?

Answer 4

1. Multipurpose
2. Nanocomposites
3. Highly filled composites for posterior restorations.
4. Ceram X
5. G-aenial

Question 5

What types of resin composites should be used for class 3 and 4 restorations?

Answer 5

1. Multipurpose
2. Nanocomposites
3. Hybrid (microfilled)

Question 6

What types of resin composites should be used for cervical restorations?

Answer 6

Flowable composites

Question 7

What the 2 major consituents of dental composites?

Answer 7

1. High molecular weight monomers (matrix phase aka resin)
2. Fillers (discontinuous phase)

Question 8

What the 3 minor consituents of dental composites?

Answer 8

1. Diluents or viscosity modifiers (dimethacrylate monomers with low molecular weight and viscosity)
2. Inhibitors, stabilisers
3. Silane coupling agents (filler is treated with the coupling agent)

Question 9

Give examples of 2 resin monomers used in composites.

Answer 9

Bis GMA
UDMA

Question 10

What does increasing the amount of filler in a composite do to its mehcnaical qualities?

Answer 10

1. Lowers thermal diffusivity so heat has less impact on the pulp etc.
2. Reduces polymerisation shrinkage as filler particles are inert.
3. Improves surface hardness.
4. Improves aesthetics as its refractive index is similar to resin, giving a translucent appearance.
5. Decreases water sorption as filler absorbs less water.

Question 11

Why are composites composed of different sizes of filler and what is this called?

Answer 11

1. This improves efficiency of filler loading.
2. Hybrid composites.

Question 11

Give 2 examples of diluents.

Answer 11

1. TEGDMA
2. EDMA

Question 12

What is the role of diluents in composite and why is this important?

Answer 12

1. Reduces viscosity
2. This enables easy manipulation of blending of filler particles with the monomer.

Question 13

On polymerisation how do diluents increase the strength of composites?

Answer 13

1. On polymerisation, dimethacrylate monomers form cross linked networks form.
2. This increases strength of the composite because water uptake is minimised as a result of the cross linking.

Question 14

What is the role of inhibitors in composites?

Answer 14

They are compounds that:

1. Prevent premature polymerisation during storage, handling and placement.

Question 15

Give 3 examples of inhibitors in composite.

Answer 15

1. Hydroquinone
2. PMP
3. BHT

Question 16

What is the role of silane coupling agents?

Answer 16

It improves the adhesion between filler and polymer matrix.

Question 17

How do silane coupling agents aid the adhesion between cements and ceramics?

Answer 17

A silane coupling agent has a polymerisable group along with a hydrophilic end which may have the ability to condense with hydroxyl groups present on the surface of the ceramic.

Question 18

What is the most common photoinitiator used in composites and what is its appearance?

Answer 18

Camphorquinone.

Canary yellow

Question 19

How do photoinitiators work in composites?

Answer 19

1. Absorb blue light, 400-500nm range.
2. Initiator reacts with amine activator.
3. Forms free radicals
4. Initiates addition polymerisation.

Question 20

What undergoes free radical polymerisation in composites?

Answer 20

Methacrylates

Question 21

What are the 2 ways free radical polymerisation occurs in composites?

Answer 21

Free radical are either generated by a:

1. Chemical reaction

Two paste systems, initators such as benzoyl peroxide: BPO+Amine → Free radicals.

OR

1. Photointiated

One paste system, photoinitiators sycg as camphorquinone: Camphorquinone+amine activator → free radicals.

Question 22

What is the weakest phase in dental composites and why?

Answer 22

Matrix - where methacrylate monomers polymerise.

As it can absorb fluids and is responsible for shinkage .

Question 23

What is a negative of chemical activation curing in composites?

Answer 23

Limited working time mixing may incorporate air bubbles- oxygen inhibits polymerisation.

Question 24

Give 2 positives of light activation curing in composites.

Answer 24

1. No mixing. 2. Command set.

Question 25

What are 3 negatives of light activation curing in composites?

Answer 25

1. Light attenuation 2. Limited depth of cure. 3. Incremental curing required.

Question 26

What are the steps in photopolymerisation?

Answer 26

1. The photopolymerisation process of dimethacrylate-based dental resins is triggered by free radicals. 2. The free radicals are generated on irradiation of a light-sensitive initiator (initiation) 3. The free radical attacks the double bond of the methacrylate groups, creating monomer free radicals leadint to the generation of a chain (propagation)

Question 27

What is meant by the degree of cure or conversion (DC) and what does it vary between?

Answer 27

1. The extent of polymerisation from the ratio of uncured monomer or the remaining double bonds to the amount initally present. 2. 40-78%

Question 28

What properties of composite can vary with the ratio of resin to filler content?

Answer 28

1. Hardness 2. Roughness 3. Abrasion resistanct 4. Water sorption 5. Thermal properties 6. Colour and appearance 7. Adhesion

Question 29

What does a low viscosity diluent such as TEGDMA do to the DC of composite?

Answer 29

1. Greater rate of conversion 2. Higher shrinkage 3. Inferior mechanical properties.

Question 30

- With increasing DC what happens to the mechanical properties of composite and why?

Answer 30

1. They usually improve. 2. As high molecule weight polymers can give rise to superior mechanical properties.

Question 31

What can undercuring of composite lead to and why is this bad?

Answer 31

1. Higher residual monomer. 2. Leads to plasticization of matrix- this is due to monomers intruding between polymer chains therefore lowering the DC. 3. Ingress of oral fluids- can result in discolouration and also bacterial ingress and eventually failure.

Question 32

What components in composite can cross link the network?

Answer 32

Viscosity modifiers and diluents are low molecular weight dimethacrylate monomers which csan crosslink the network.

Question 33

What can an increase in crosslinking in composite do to the physical properties?

Answer 33

1. Decrease fluid sorption and reduce interaction with surrounding environment or solvents. 2. An increase in the glass transition temperature. 3. Reduce in interaction with surrounding fluids so there is less bacterial infiltration.

Question 34

What can polymerisation shrinkage lead to?

Answer 34

Gap formation which then leads to: 1. Secondary caries formation 2. Marginal leakage 3. Post-operative sensitivity

Question 35

How can polymerisation shrinkage be counteracted?

Answer 35

1. Lower shrinkage composites (bis GMA) 2. Incremental placement.

Question 36

What 3 things does curing depth depend on?

Answer 36

1. Light type 2. Irradiance (do not touch the tooth as it can form bacterial film over tooth)- but be as close as possible to enable proper curing. 3. Time

Question 37

what is water sorption

Answer 37

Water sorption in dental restorations refers to the process by which water molecules are absorbed or taken up by the dental material over time.

Question 38

How does water sorption affect on the long term performance of a restoration?

Answer 38

Causes the loss of ionic species from the fillers. Therefore fluid uptake affects the fatigue life of polymers.

Question 39

How is water sorption counteracted when placing restorations?

Answer 39

Use of rubber dams.

Question 40

For deep cavities what composite in terms of polymerisation exotherm should be used?

Answer 40

One with a lower polymerisation exotherm.

Question 41

What are compomers in relation to composites?

Answer 41

Poly acid modified composites.

Question 42

Give 7 advantages of compomers.

Answer 42

1. Ease of placement 2. No mixing 3. Easy to polish 4. Good aesthetics 5. Excellent handling 6. Less susceptible to dehydration 7. Radiopaque.

Question 43

Give 7 disadvantages of compomers.

Answer 43

1. Limited clinical experience 2. Require a bonding agent like composites. 3. More marginal staining and chipping 4. Wears more than composites 5. Variation of products makes longevity difficult to predict 6. Weaker physical properties than composites that decrease over time 7. Clinical significance of fluoride release undetermined

Question 44

What are nanocomposites in relation to composites?

Answer 44

They are composites that are less than 100nm in size.

Question 45

Give 8 advantages of nanocomposites.

Answer 45

1. Easy handling 2. Good aesthetics 3. High flexural strength 4. Low abrasion 5. Low polymerisation shrinkage 6. Increased polish retention due to less spacing between particles 7. Reduction of interstitial spacing between filler particles 8. Increase filler loading so less shrinkage

Question 46

After brushing nanocomposites remain very smooth in comparison to composite, why is this better?

Answer 46

As it is smooth, this means it won’t retain stains and will therefore have better aesthetics.

Question 47

Give 7 benefits of high polish retention.

Answer 47

1. Long lasting perfect aesthetics 2. Reduced plaque adhesion 3. Reduced risk of secondary decay 4. Reduced risk of gingival inflammation in class V restorations 5. No external discolouration 6. Reduced antagonistic wear 7. High oral comfort

Question 48

How can flowable composites lead to post op pain, marginal discolouration, recurrent caries and loss of restoration?

Answer 48

They have high contraction stresses during polymerisation of composites, which are transferred to the tooth.

Question 49

In terms of composition what is the difference between flowable composite and composite?

Answer 49

Flowable composites have 20-25% lower filler content.

Question 50

Give 2 drawbacks to flowable composite.

Answer 50

1. Higher shrinkage as they have more resin content. 2. Lower rigidity.

Question 51

What are the indications for flowable composite and why is this?

Answer 51

1. Liners, fissure sealants and small restorations. 2. This because they have a 20-30% lower modulus of elasticity and low viscosity. 3. This means they are easier to place and manipulate into smaller spaces.

Question 52

Why do some people pre-warm composites and how does it work?

Answer 52

1. Pre-heating composites lead to lower viscosity during placement. 2. Seen as an alternative to flowable composite. 3. This works as temperature changes strongly influence the flowability of composite resins as viscosity decreases due to thermal vibration of the monomers/oligomers resulting in increased entropy.