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 coefficient of thermal expansion, 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 12

Give 2 examples of diluents.

Answer 12

1. TEGDMA
2. EDMA

Question 13

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

Answer 13

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

Question 14

On polymerisation how do diluents increase the strength of composites?

Answer 14

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 15

What is the role of inhibitors in composites?

Answer 15

They are compounds that:

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

Question 16

Give 3 examples of inhibitors in composite.

Answer 16

1. Hydroquinone
2. PMP
3. BHT

Question 17

What is the role of silane coupling agents?

Answer 17

It improves the adhesion between filler and polymer matrix.

Question 18

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

Answer 18

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 19

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

Answer 19

Camphorquinone.

Canary yellow

Question 20

How do photoinitiators work in composites?

Answer 20

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

Question 21

What undergoes free radical polymerisation in composites?

Answer 21

Methacrylates

Question 22

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

Answer 22

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 23

What is the weakest phase in dental composites and why?

Answer 23

Matrix - where methacrylate monomers polymerise.

As it can absorb fluids and is responsible for shinkage .

Question 24

What is a negative of chemical activation curing in composites?

Answer 24

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

Question 25

Give 2 positives of light activation curing in composites.

Answer 25

1. No mixing. 2. Command set.

Question 26

What are 3 negatives of light activation curing in composites?

Answer 26

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

Question 27

What are the steps in photopolymerisation?

Answer 27

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 28

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

Answer 28

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 29

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

Answer 29

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

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

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 33

What components in composite can cross link the network?

Answer 33

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

Question 34

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

Answer 34

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.