Objectives: Visible light cure oxirane/polyol resins of Cyracure(TM) UVR-6105 with pTHF-250 has been previously shown useful for development of dental composites. This oxirane/polyol (4016) in combination with other oxiranes were formulated into composites (4016E, 4016G and 4016GB) containing 72.9-74.9% quartz filler. The main objective of the study was to evaluate some of the physical properties and the biocompatibility of the composites. Results: PhotoDSC analysis of composites demonstrated twice the enthalphy values of Z100 (31 J/g). Composites 4016E and 4016G showed compressive strengths similar to Z100 (337+/-35 Mpa), P > 0.05. Discs of composite 4016E, containing Epon(TM) 825 oxirane (E), and composite 4016G containing Araldite(TM) GY 281 oxirane (G) were non-cytotoxic (-) while the composite 4016GB, containing G and Ebecryl(TM) 1830 (13), was mildly (+) cytotoxic to L929 cells in the agar diffusion assay. Seven day extracts of 4016GB composite were cytotoxic while extracts of 4016E and 4016G were less cytotoxic to L929 cells in the MTT assay. Extracts were obtained from 7 day incubations of composite (3 cm 2 surface area/ml) in acetone or ethanol/saline (1:20) at 37degreesC. All composite extracts were non-mutagenic to Ames strains TA100, TA98, TA97a and TA1535. The overall results with composite 4016GB suggest that leachable components were cytotoxic but non-mutagenic. With the exception of oxirane components, G and E, the oxirane Cyracure(TM) LTVR-6105 and other components were non-mutagenic. From cytotoxicity studies, the photoinitiator, Sarcat(TM) CD 1012, was the most cytotoxic (TC50 = 14 muM) component. Components G (TC50 = 17 muM), E (TC50 = 50 muM) and B (TC50 = 151 muM) were significantly (p < 0.05) more cytotoxic than Cyracure(TM) UVR-6105 (1488 muM) and the polyol, pTHF-250 (TC50 = 6072 muM). Significance: Favorable results obtained with composites 4016G and 4016E indicates that suitable oxirane/polyol formulations can be designed and optimized for development of dental composites with acceptable mechanical properties and biocompatibility. However, leachable analysis of extracts obtained from longer incubation periods is needed before final conclusions could be drawn about the leachability of oxirane components. (C) 2002 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved.