Development of an oxirane/acrylate interpenetrating polymer network (IPN) resin system.

ABSTRACT

OBJECTIVE: Develop a hydrophobic, degradation-resistant dental restorative based on an Oxirane-Acrylate IPN System (OASys) with low shrinkage-stress to substantially extend clinical lifetime. METHODS: Unfilled OASys blends were prepared using dipenta-erythritol-hexaacrylate (DPHA) and p-cycloaliphatic-diepoxide (EP5000). Varying proportions of camphorquinone/iodonium photoinitiator, with a co-reactant oligomeric-diol, served as the experimental curing system. The effects of oxirane-acrylate ratio on the degree-of-cure (Durometer-D hardness), hydrophobicity (contact angle), mechanical properties (3-point bending), near-infrared FTIR degree-of-conversion (DoC), polymerization shrinkage, and shrinkage stress were determined. 7030 BisGMATEGDMA resin served as control. RESULTS: Oxirane tended to decrease hardness and increase hydrophobicity. 0100, 2575, 5050 EP5000DPHA are harder after 24h than control. 7525 and 1000 EP5000DPHA increased in hardness over 24h, but were softer than control. All groups increased in contact angle over 24h. After 24h, 5050, 7525 and 0100 EP5000DPHA were more hydrophobic (∼75-84°) than the control (∼65°). Acrylate DoC was ∼60% across all experimental groups. Initial oxirane conversion varied from ∼42% in 1000 EP5000DPHA to ∼82% 7525 EP5000DPHA. However, oxirane DoC increased for 1000 EP5000DPHA to ∼73° over 24h, demonstrating dark cure. Moduli and ultimate transverse strengths of OASys groups were higher than for 0100 EP5000DPHA, with 5050 EP5000DPHA having higher modulus than other experimental groups. However, the control had higher modulus and UTS than all experimental groups. Volumetric shrinkage averaged 7% for experimental groups, but stress decreased dramatically with increasing oxirane content. SIGNIFICANCE: Hydrophobic, low shrinkage-stress OASys resins are promising for development of composites that improve longevity and reduce the cost of dental care.