F09. Explain how it is possible to have a certain dentin bond strength and at the same time also some degree of microleakage.

(Courtesy of T. Jacobsen, 1993)

This SEM picture shows cavitation formation within the dentin-bonding agent. The picture was taken of a resin-dentin interfacial region. The bonding resin system had been bonded to an obliquely cut surface (facial cusp had been removed). After the resin had been placed in contact with the dentin, it was covered by a Mylar strip and light-cured. As the resin shrunk, it pulled away from the primed dentin surface, leaving shrinkage cavities behind at the primer-bonding resin interface.

Cavitation that occurs in the above manner explains why a bonded restoration can remain bonded, but also be associated with marginal staining and/or microleakage.