L14 Resin Composites 1

Question 1

Direct chairside indications of resin based composites

Answer 1

Filling material, fissure sealant, cementation

Question 2

Indirect lab clinical indications

Answer 2

Composite inlay, CAD/CAM crowns, fibre-reinforced bridge, 3D printing

Question 3

What is dental resin composite made up from?

Answer 3

Organic resin matrix - 20-30 mass% for high viscosity paste
Inorganic glass filler (treated*) - 70-80 mass% for high viscosity paste
*coupling agent - amphiphillic molecule to provide chemical affinity

Question 4

How are dental resin composites adjusted by the manufacturer?

Answer 4

Viscosity to make flowable composites
High viscosity composites for larger cavities etc

Question 5

Why is PMMA a bad direct restorative?

Answer 5

It suffers from excess shrinkage and poor wear resistance

Question 6

What is bisphenol-A the building block for?

Answer 6

Building block for many polymers, e.g., polyesters, polycarbonates, and epoxy

Question 7

How and why is the structure of bisphenol A useful?

Answer 7

Steric hindrance (H-bonding) and no rotation about benzene
BPA polymer chain rigidity&raquo_space; MA
Improves mechanical properties

Question 8

What is the controversy around bisphenol-A?

Answer 8

Potential hormonal effects with the release of BPA if consumed in the human body. Part of plastics. Biocompatibility concerns.
But very small amounts of release with no evidence for harmful effect of it in the mouth.

Question 9

What is Bowen’s resin?

Answer 9

BisGMA - Bisphenol A glycol dimethacrylate

Question 10

Why is BisGMA a good restorative material (brief)?

Answer 10

It has multiple functional groups to create polymers and high density of cross-links for rigidity needed for a restorative material.

Question 11

What is a thermoplastic?

Answer 11

More basic, linear, not as many cross-links, held together by entanglement and secondary bonds

Question 12

What is thermoset?

Answer 12

Increase of cross-link density network

Question 13

Structure of MMA

Answer 13

Linear structure
Entanglement
No cross links

Question 14

Structure of BisGMA

Answer 14

Cross-linked
Entangle
Bulky monomer
Reduced polarity
Difunctional
Non-toxic
Cheap

Question 15

Why can’t BisGMA be used by itself?

Answer 15

Because it is very viscous and hard to handle by itself. Must be admixed.

Question 16

What is BisGMA add mixed with?

Answer 16

Add mixed - diluents

Question 17

What are diluents?

Answer 17

Resins that will reduce the viscosity of the BisGMA and provide extra cross-links

Question 18

Compare BisGMA with TEGDMA

Answer 18

BisGMA has high molecular weight, high viscosity, H-bonding and limited filler load
TEGDMA has low molecular weight, diluent (non-volatile), little steric hindrance

Question 19

What other dental methacrylates are there?

Answer 19

HEMA, UDMA, 10-MDP
(do I need to know these?, gauge in lecture)

Question 20

What do the other monomers have and vary in?

Answer 20

All have an MA group, vary in molecular weight and viscosity and hydrobicity

Question 21

Resin matrix monomers

Answer 21

Usually BigGMA, UDMA or derivatives

Question 22

Resin matrix diluent crosslinkers

Answer 22

TEGDMA

Question 23

What does an inhibitor do in resin matrix?

Answer 23

Radical scavengers - help to stop any radicals formed from creating polymers before we want them to

Question 24

Examples of inhibitors

Answer 24

Hydroquinone

Question 25

Relevance of polymerisation chemistry in resin matrix

Answer 25

Polymerisation chemistry. Additives that allow the generation of radicals. Base/catalyst, photosensitiser.

Question 26

How was resin matrix cured before light curing technology?

Answer 26

Chemical cure - 2 large composites (base and catalyst)

Question 27

Why was mixing an issue for chemical cure of resin matrix?

Answer 27

Mixing is an issue because quantities and ratios have to be correct and it might trap air in the process.

Question 28

Is UV light dangerous?

Answer 28

Ionising and damaging for DNA

Question 29

What light do we use to cure?

Answer 29

High intensity blue light, around 470nm, not UV

Question 30

What else must be used with the light?

Answer 30

Co-initiator is needed which acts as a hydrogen donor enabling efficient activation and generation of radicals

Question 31

How has the light source developed?

Answer 31

Halogen Specific (single) diode emitting a much narrower wave-band of light - efficient Hand-held battery-operated lights - less degradation than in the past Multiple diodes

Question 32

Advantages of visible light during

Answer 32

No mixing - eliminates operator induced variability, reducing porosity Increased working time Improved colour stability Improved mechanical properties Command set

Question 33

Why is an interface needed to connect the filler and resin?

Answer 33

Interface needs to be connected between the filler and resin to create a strong interface.

Question 34

Why is a strong interface needed?

Answer 34

Inorganic component is the hard component compared to soft resin. So need to increase mechanical properties to slow down crack propagation within the material, improving fracture toughness. Without a strong interface means the crack occurs around the surface.

Question 35

What is silane?

Answer 35

An amphiphillic molecule

Question 36

What might silane do?

Answer 36

Accelerate water uptake in this region Lead to interfacial degradation and bulk fracture

Question 37

What does the inhibitor in resin matrix do?

Answer 37

Helps improve shelf life and ambient light stability (e.g., HQ)

Question 38

Are resin based composites hydrophilic or hydrophobic?

Answer 38

Hydrophobic

Question 39

Is hydrophobic or hydrophilic better for placing a material?

Answer 39

Hydrophobic is not good for when placing as if means you need moisture control. Hydrophilic will uptake and absorb the water.