Biomaterials/Adhesives Review Flashcards
What part of the tooth has predictable bonding?
Enamel
_______% phosphoric acid is most effective for enamel retention
30-40%
What does etching enamel remove?
10 um enamel
How long should etch be placed on enamel for?
15 sec prior to rinsing
What does etching create?
Porous layer 5-50 microns deep
Why should you rinse after etching?
For 10 sec to remove acid and leave enamel surface clean for bonding
Etching _______ the surface free energy to _______ the surface tension of bonding material
raises; exceed
What is the function of the spaces that etch produces?
spaces where resin can penetrate to form
resin tags
Where is mechanical interlocking formed in etch?
Between polymerized resin and porosities in etched enamel
What do you apply after etching?
Bond agent resin (low viscosity)
Where does bond agent resin flow into after being applied?
Microporosities
What does bond agent polymerize into?
Micromechanical bond
Describe the bond strength of the incisal and middle third of enamel
Predictable and strong
Describe the bond strength of the cervical enamel
- Less strong
- Shorter and fewer enamel tags
- Due to presence of prismless enamel
What is the bond strength of perpendicular enamel (enamel rods)?
25 MPa
What is the bond strength of parallel enamel (sides of rods)?
7-10 MPa
Why is dentin challenging to bond?
Bond strengths vary
Where in dentin has higher bond strength?
Superficial dentin more than deeper (close to pulp)
Why does superficial dentin have higher bond strength than pulpal?
The deeper dentin has more and larger dentinal tubules. This increases the amount of water and reduces the amount of collagen the adhesive is able to interact with and create micromechanical retention.
What does dentin bonding require intertubular dentin to do?
create hybrid layer in collagenous matrix
What are the types of bond systems?
Etch and rinse (total etch)
Self-etch
How does etch and rinse system work?
Etch is separate from bond agent
Primer and bond can be separate (3 step - etchant, primer, bond agent) or together (2 step - etchant, primer and bond agent combined)
What are the advantages of the etch and rinse system?
- More predictable, stronger bond
- Enamel adequately prepared
What are the disadvantages of the etch and rinse system?
- Collagen collapse is possible (user error due to overdrying)
- Etched zone is often deeper than hybrid layer
- Exposed demineralized, collagen fibrils
- Post operative sensitivity
What is the self-etch system?
No phosphoric acid etch step
Acid part of the primer or primer/bond agent
What is the 2 step self etch?
- Acidic primer
- Bonding agents
- Acidic primer partially dissolves smear
layer, allows penetration of bond resin
What is the 1 step- all in one?
Most variable/least predictable
* Acidic primer and bond resin, one silution
* Many require mixing
What are advantages of self-etch?
- No separate etch: overdried demineralized collagen not a problem
- Etched zone and hybrid layer comparable width; however, some exposed collagen
- Low post operative sensitivity
- Time efficient
What are disadvantages of self-etch?
- Not compatible with self-cure, dual cure composite
- Acidic monomers, low pH, kills the basic
amine activator - Will not etch unprepared enamel
How is the bond strength of self etch primer systems?
Long term bond strength is questionable
How is the bond strength of self etch adhesives?
- Lower bond strength
- Long term breakdown
- Collagen degradation over time
What is selective etch?
only etch the enamel, NOT dentin
What is complete etch?
Eetch enamel and dentin
Where can universal adhesives be used?
In total etch, self etch, or selective etch
What is the game changer for universal adhesives?
10-MDP
