Characterization of Water Inhibition in Light-Cured Dental Resins

Abstract

The conversion of medical resins in vivo occurs with increasing regularity, both in clinical practice and from a research perspective. In adhesive bonding for medical applications, most of these curing resin systems use a free radical polymerization mechanism to advance the chemical reaction and solidify the resin (1). Chemical conversion is usually accomplished by either a light activation system, which triggers the decomposition of an activator in the resin, or by direct chemical reaction, through mixing of components in a two-part system. Inhibition of the free radical polymerization by oxygen has been reported in the literature (1). Given that bony tissues, including dentin and other soft tissues, contain a substantial amount of water, the presence of water is ultimately an unavoidable circumstance in a large number of medical applications involving adhesives. Water is a key component of mineralized tissues, and cannot be readily removed without destruction of the tissue. Under ordinary circumstances, clean, dry surfaces are necessary for successful bonding. For longterm bonding in vivo, adhesives must successfully compete with water at the bond interface (2). How conversion has been affected by the presence of water has not been adequately characterized, but it has generally been considered a problem. Efforts have been undertaken to reduce the overall impact of water by drying the environment in which the resin application is performed (3).