OPTEC- Composite Flashcards
Includes: DMS- composite resin OPTEC- clinical composite lecture
What is shown in this image?
This is an Enamel fracture and is characterised by the white line around the edge of the restoration. This shows that the restoration is doomed for failure.
What dentine is used in the creation of the hybrid layer and why?
Primary dentine is used as it has open tubules.
Tertiary dentine is unfavourable due to its irregular structure.
What is the configuration factor?
This is the ratio of surfaces bonded to the tooth and surfaces not bonded to the tooth.
High configuration factor= more surfaces bonded = increased polymerisation contraction stress.
Low configuration factor= less surfaces bonded = lower polymerisation contraction stress.
What is polymerisation contraction shrinkage?
when the material shrinks and tries to pull away from the tooth surface as the restoration polymerises (hardens)
How do we compensate for the composite shrinking?
By putting in more composite than is needed in order to keep the contacts.
Describe the procedure of placing a composite restoration:
- Check the dentine quality
- Etch the tooth- 10s enamel and 10s enamel + Dentine
- Prime the dentine surfaces
- Add composite (first to the floor and then in increments)
- Cure the composite
- Polish the tooth
- Surface seal.
Discuss the placement theory for composite restorations
Use a lower viscosity composite (flowable) to the floor of the cavity to act as a stress reducer.
The composite is added in increments touching as few walls as possible.
Do not join the enamel margins for the final increments.
What is composite made of?
- Filler particles
- Resin
- Camphorquinone
- Low weight dimethacrylates
- Silane coupling agent
What is the function of filler particles in composite?
These make the material harder.
What is the function of Camphorquinone in composite?
This is the photo initiator that is activated by blue light.
This causes free radical production for polymerisation to make the material stronger.
What is the function of the silane coupling agent?
The silane coupling agent is used to create a good bond between filler and resin by bonding to them.
How does the filler type affect composite?
The more filler particles the harder, stronger and more rigid the restoration. It also lowers polymeristion shrinkage.
The filler is commonly a hybrid- a mixture of large conventional particles and small microfine particles. This is to try and pack the full area.
Compare the light cure mechanism to the self cure mechanism
Light cure is made out of 1 paste (Camphorquinone) and blue light.
Self cure is made of 2 pastes (Benzoyl peroxide and aromatic tertiary amine).
These react to give free radicals.
What is the depth of cure?
Where the hardness of the material is half of that at the surface.
This is 2mm.
Why is the depth of cure important?
If we use greater than 2mm incremments of composite, they will not adequately polymerise. This results in a soggy bottom.
Why do we need to be careful when light curing?
Light curing is an exothermic reaction from the resin. This heat is conducted by adjacent enamel and dentine.
So you need to keep the optical rod close to the composite resin surface in order to prevent thermal trauma to the patient’s soft tissues.
Why is the hardness of composite important?
If composite resin isn’t hard enough it will experience wear. The abrasion will remove surface layers.
What is young’s modulus?
This is used to describe the rigidity of the material.
YM= stress/ strain
A high young’s modulus = more rigid.
What is the elastic limit?
This is the stress beyond which a material will change shape.
A high elastic limit means you can put a lot of stress on the material before it deforms.
Compare Conventional microfine and hybrid fillers
Conventional fillers are strong. But the soft resin and hard particles make finishing and staining difficult.
Microfine fillers- The smaller particles allow for a smoother surface but they have inferior mechanical properties
Hybrid- Improved mechanical properties.
Discuss surface roughness
Surface roughness is due to the composite resin surface being removed.
This allows resin particles to cause the roughness which results in plaque retention and sesnation when in contact with the tounge.
Discuss the thermal conducitivity of composite?
The thermal conductivity is low which means that heat is transferred poorly. This avoids pulpal damage from hot &cold food and drink.
Discuss the thermal expansion of composite?
The thermal expansion is high.
This means Composite does not exapnd at the same rate as enamel or dentine. So microleakage occurs causing gaps between the bonds.
So there is more stress = it is more likely to fracture.
How do we achieve bonding to enamel?
By the acid etch technique.
Explain why a good bond helps the restoration last longer?
If you have a good bond, the forces are spread uniformly between the tooth tissue. So the tooth can survive larger stresses.
Explain why a poor bond means the restoration doesn’t last as long?
The gaps in composite resin (poor bond) prevent the force being spread evenly.
This causes stress focusing in certain regions and makes the restoration more likely to fracture.
What is Compomer?
A material that is a hybrid of composite and resin modified glass Ionomer.
