Resin-Composite

Question 1

Benefits of Acrylics over Silicates x5

Answer 1

1. Less prone to erosion
2. Less soluble over a wide pH range
3. Less acidic
4. Less brittle
5. Better thermal insulators –> Lower value of thermal diffusivity

Question 2

Define resin composite

Answer 2

A combination of 2 chemically different materials with a distinct interface separating the components and having properties that cannot be achieved by any of the components acting alone

Question 3

3 major components of the resin-composite

Answer 3

1. Organic resin matrix
2. Inorganic filler
3. Coupling agent

Question 4

Which is the most chemically active component of the resin composite?

Answer 4

Organic resin matrix

Question 5

What reaction does the fluid monomer undergo to become a rigid polymer?

Answer 5

Radical addition reaction

Question 6

What is the benefit conferred from the fluid monomer –> rigid polymer reaction?

Answer 6

The ability to convert from a plastic mass into a rigid solid allows the material to be used for the restoration of dentition

Question 7

Name 2 examples of monomers of the resin matrix

Answer 7

1. BisGMA

2. Urethane dimethacrylate

Question 8

Are the monomers of the resin matrix of high or low viscosity?

Answer 8

High (because of high molecular weight) ==> Addition of even a small amount of filler would produce a composite with a stiffness that is excessive for clinical use

Question 9

Give an example of a monomer added to help control viscosity. Is this monomer of high or low viscosity?

Answer 9

TEGMA; low viscosity

Question 10

Why is TEGMA added to the resin matrix?

Answer 10

To help control viscosity, facilitating manufacturers filler addition and clinical handling

Question 11

Which compound is added to ensure a long shelf life for the composite?

Answer 11

An inhibitor is included, usually hydroquinone in amounts of 0.1% or less

Question 12

What type of compound is hydroquinone?

Answer 12

Inhibitor - it prevents premature polymerisation so as to ensure a long shelf life for the composite

Question 13

Name the 4 factors of the filler that can control properties

Answer 13

1. Type of filler
2. Concentration of filler
3. Particle size
4. Particle size distribution

Question 14

Examples of fillers x5

Answer 14

1. Quartz
2. Silica
3. Glasses (Aluminsilicates)
4. Borosilicates
5. Barium oxide

Question 15

Benefits of inclusion of fillers x5

Answer 15

1. By incorporating a large amount of glass filler, the shrinkage is reduced as the amount of resin used is reduced and the filler does not take part in the polymerisation process
2. Addition of ceramic fillers reduce the coefficient of thermal expansion, bringing it closer to that of tooth tissues
3. Fillers can improve mechanical properties such as hardness and compressive strength
4. The use of heavy metals e.g. barium and strontium incorporated in the glass provides radio-opacity
5. Fillers provide the ideal means of controlling various aesthetic features e.g. colour, translucency and fluorescence

Question 16

Effect of addition of filler on composite shrinkage

Answer 16

Addition of filler reduces the amount of shrinkage as the amount of resin used is reduced and the filler does not take part in the polymerisation process

Question 17

Effect of addition of filler on coefficient of thermal diffusivity

Answer 17

Addition of filler lowers the coefficient of thermal diffusivity, as methacrylate monomers have a high coefficient of thermal expansion (~80ppm/deg).

Question 18

Effect of addition of fillers on mechanical properties e.g. surface hardness

Answer 18

Higher the filler content, higher the value of surface hardness (VHN)

Question 19

Function of the coupling agent

Answer 19

The coupling agent transfers the stresses generated under loading from the rigid and brittle filler to the more flexible and ductile polymer matrix.

Question 20

Most commonly used coupling agent

Answer 20

y-methacryloxypropyltriethoxysilane (y-MTPS)

Question 21

What will a lack of bonding between the resin and glass filler particle create?

Answer 21

Crack initiation sites

Question 22

What is a fundamental problem of resins? What is the solution to this problem?

Answer 22

Resins are hydrophobic, whereas silica-based glasses are hydrophilc due to a surface layer of hydroxyl groups bound to the silica. Hence, the resin does not have a natural affinity to bond to the glass surface.
The solution lies in the use of a suitable coupling agent - e.g. the silane coupling agent

Question 23

Types of classification of resin-composite (x4)

Answer 23

1. Method of activation - light vs chemical
2. Filler particle size and distribution
3. Handling characteristics - packable vs flowable
4. Intended clinical application - type I vs type 2

Question 24

What is Type I resin-composite used for under ISO4049?

Answer 24

Restoration of cavities involving the occlusal surfaces

Question 25

What is Type 2 resin-composite used for under ISO4049?

Answer 25

All other polymer based filling and restorative materials

Question 26

Name the 3 chemical wear mechanisms of resin composites

Answer 26

1. Abrasive
2. Erosive
3. Fatigue

Question 27

Describe the abrasive wear mechanism of resin-composite

Answer 27

Hard asperities penetrate the polymer matrix removing materials by shearing and cutting

Question 28

Describe the erosive wear mechanism of resin-composite

Answer 28

Impact of asperities produces damage of the polymer matrix

Question 29

Describe the fatigue wear mechanism of resin-composite

Answer 29

Localised deformations of the polymer are subjected to repeated stresses, resulting in its failure

Question 30

Name the 3 stages of wear as visualised by Ag staining

Answer 30

1. Little wear + No subsurface damage
2. Higher wear + considerable damage
3. Catastrophic wear as a result of extensive subsurface damage