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

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. 70:30 BisGMA:TEGDMA resin served as control. Results. Oxirane tended to decrease hardness and increase hydrophobicity. 0:100, 25:75, 50:50 EP5000:DPHA are harder after 24h than control. 75:25 and 100:0 EP5000:DPHA increased in hardness over 24h, but were softer than control. All groups increased in contact angle over 24 h. After 24 h, 50:50, 75:25 and 0:100 EP5000:DPHA were more hydrophobic (similar to 75-84 degrees) than the control (-65 degrees). Acrylate DoC was similar to 60% across all experimental groups. Initial oxirane conversion varied from similar to 42% in 100:0 EP5000:DPHA to similar to 82% 75:25 EP5000:DPHA. However, oxirane DoC increased for 100:0 EP5000:DPHA to similar to 73 over 24h, demonstrating dark cure. Moduli and ultimate transverse strengths of OASys groups were higher than for 0:100 EP5000:DPHA, with 50:50 EP5000:DPHA 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. (C) 2018 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.