ELEMENTS OF LIGHT-CURED EPOXY-BASED DENTAL POLYMER SYSTEMS

The greatest problem with current dental composite systems is their po lymerization shrinkage. Extensive work is being done by many investiga tors to alleviate this problem. Our approach has been to examine epoxy -and spiro-orthocarbonate (SOC)-based resins. The hypothesis to be tes ted in this study was that the cure characteristics of experimental vi sible-light-cured epoxy resin systems are governed by the types and co ncentrations of co-reactants and activators. Resin samples containing onium salt initiators and a thiozanthone sensitizer were successfully cured by means of either an experimental visible-light irradiation sys tem or a commercially available dental lamp. Test resins consisted of di-epoxies alone or in combination, epoxy mixtures in combination with an SOC, or an epoxy in combination with a caprolactone-derived polyol . Significant findings were as follows: (a) Resins containing the SOC had longer cure times than their counterparts; (b) the optimum ratios of epoxy to polyol for most rapid cure were 50:50 or 60:40 under condi tions tested; (c) resins containing TONE 305 polyol generally were fas ter to cure than those containing no polyol, or TONES 201 or 310; and (d) a resin mixture was found that had a cure time of 1 to 3 min when irradiated with a commercial dental lamp. Based on this exploratory st udy, it should be possible for clinically relevant cure times to be ac hieved for visible-light-cured epoxy-based resins by careful manipulat ion and optimization of key elements.