The Evolution of a Polyurethane Dental Adhesive System

Screening of common adhesives showed that polyurethanes, as a class, to be most suitable for adhering to wet tooth tissue. The isocyanate groups in the adhesive may react with the tooth mineral; this view is supported by a number of approaches, including measuring γ_c at several humidities, which may be interpreted as showing tooth tissue surfaces to be rich in hydroxyl groups. The bonding of polyurethanes to enamel could be improved by pre-treatments (including acid etching and acetone drying) and by proper choice of polyol, fillers, and coupling agents. From scanning electron micrographs the etching is interpreted to debride a weak boundary layer. The preferred formulation was a TiO₂-filled polyurethane formed from equal weights of castor oil and polymethylene polyphenyl isocyanate catalyzed by from 1 ½ to 10% of tin octoate. Joints of teeth bonded with polyurethanes withstood long-term exposures to water and synthetic saliva and dental restorations in rabbits appeared to adapt well.