Evaluation of Spiro Orthocarbonate Monomers Capable of Polymerization with Expansion as Ingredients in Dental Composite Materials

Abstract

The free radical polymerization of unsaturated spiro orthocarbonate monomers has been shown to occur by a double ring-opening process which is notably characterized by an expansion in volume. While potential applications for these unique monomers are quite extensive, the topic of dental restorative resins is one area of polymeric biomaterials, in which the need for materials with reduced polymerization shrinkage is well established. An efficient synthesis of unsymmetrically substituted spiro orthocarbonate monomers has been devised and their ring-opening polymerization with a 2–3% expansion in volume was investigated. Various techniques for incorporating the spiro monomers into conventional dental composite resins were related to polymerization shrinkage and physical properties observed for these cured experimental systems. Depending on the formulation method, the addition of spiro orthocarbonates to conventional dental monomers yielded materials with significantly reduced polymerization contraction and dramatically improved adhesion. A strong correlation between the degree of polymerization shrinkage and the adhesive strength of the dental composite was apparent.