Enamel composition
~96 wt% mineral
hydroxyapatite crystals surrounded by firmly bound water
~4 wt% organic and water
primarily Type I collagen
Instrumentation of enamel exposes prisms in several planes. How does this impact dentistry?
- perpendicular exposure of prisms vs. parallel exposure may result in ~50% loss of bond strength
How did Buonocore contribute to esthetic dentistry?
- The idea of using phosphoric acid on dental surfaces was first introduced by Buonocore (1955), who observed that adhesion to metal surfaces by paints improved when acids were used.
Effect of phosph acid on enamel
- it creates microporosities either w/in the center of enamel prisms or between them on the periphery
Which of the following is the most impacted when enamel is exposed to acid? The interprismatic structure The prismatic structure The water content The collagen content
Prismatic structure (i think)
How demineralization occurs as a result of etching (3)
i) selective because of morphologic arrangement of prisms
ii) prism angulations lead to varying demineralization at the head or periphery
iii) results in micro-morphologic difference
The results of demineralization by etching (4)
i) it removes ~10 μm of surface
ii) If remineralization occurs, it will occur in the 5 μm to 50 μm porous layer
iii) surface free energy of tooth structure increased ~2x
iv) capillary attraction facilitates resin penetration
Bonding agents used in bonding enamel are _________ in nature. Why?
- Hydrophobic
because enamel, although there is always that monolayer of water, is relatively hydrophobic.
What makes bonding to dentin different?
- a lot more significant problem in that there is a lot more fluid in dentin
What is the composition of Optibond Solo Plus?
- a combination of a hydrophilic primer and a more hydrophobic adhesive
List 3 examples of hydrophilic primers
HEMA – hydroxyethyl methacrylate
BPDM – bis-phenyl dimethacrylate
4-META – 4-methacryloxyethyl trimellitate anhydride
