OPTEC- Bonding Flashcards
What are dental adhesives used for?
(Resins )provide a high bond strength to tooth tissue by penetrating the primed dentine to form the hybrid layer.
What tooth substance is easier to bond to and why?
Enamel as it has long enamel prisms filled with hydroxyapaptite crystals.
How does the acid etch technique work?
This uses acid to roughen the enamel. This allows resin to flow into the roughness and mechanical bonding to occur..
It also increases the enamel surface energy.
What is the enamel wettability?
The ability of another material to flow on enamel.
Why does the enamel need to be dry before we add a restoration?
To allow flow of resin into the etched surface. Moisture would prevent this flow preventing the bond.
What is the critical surface energy?
The surface tension of a liquid that will spread on the surface of a solid. (for a liquid to flow it must have a lower surface energy than the surface it is placed on to)
Why do we use bonding agents?
To increase the critical surface energy of the wet dentine in order to allow composite to stick
What is molecular entanglement?
Where the mineral is removed from hydroxyapatite and replaced with resin. This interlocks producing the bond.
What does total etch contain?
Acid primer and resin.
What is the function of the acid in etching?
It removes the smear layer and opens the dentinal tubules causing exposition of the collagen network.
What is the function of the primer in etching?
It penetrates the demineralised dentine making the surface high energy and hydrophobic.
What can happen if you over etch?
You can cause the collagen fibres to collapse. This prevents the resin from penetrating.
What happens if the dentine surface is too dry?
The dentine surface collapses, This reduces the porosity of dentine preventing primer penetration therefore weakening bonds.
When etching what would happen if the dentine surface is too wet?
The primer is diluted so is weaker.
How do self etching primers work?
They infiltrate and incorporate the smear layer into the hybrid rather than removing it (so do not have the phosphoric acid first)
