In vitro simulations of in vivo bonding conditions.

Most in vitro bonding studies have been performed on extracted teeth of unknown age, stored in a wide variety of solutions, embedded in substances that encourage dehydration, and polished flat with abrasive paper. In vivo, teeth are vital and maintained moist by dentin fluid that exudes from pulpal blood vessels to dentin surfaces prepared with burs. In vivo conditions can be simulated in vitro by filling the pulp chamber of extracted teeth with physiologic solutions maintained under a positive pressure. Dentin bonding surfaces can be prepared flat using burs. More attention should be focused on the effects of dentin depth (superficial versus deep) and position (occlusal, proximal, etc.) on the bond strengths of materials during screening experiments. Alternatively, bonding of adhesives can be performed in vivo using various animals such as monkeys, goats and dogs. Although the bond strengths of adhesives are low in animals, this may represent species and tooth-type differences rather than unique in vivo conditions. The methods in these studies could be used in human teeth scheduled for extractions. Many of these models could be used before the introduction of new dentin bonding systems.