ADA specification testing for resin composite materials calls for specimen fabrication at the ambient temperature and humidity of the laboratory. However, under clinical conditions, composite resin is polymerized within the oral environment at a higher temperature and humidity. The difference in environmental conditions may adversely affect polymerization and resultant flexural properties. Objectives: The objective of this investigation was to compare the flexural properties of 3 resin composite materials polymerized under ambient laboratory conditions and conditions modeling the oral environment humidity and temperature. Methods: Protocol for specimen fabrication followed ANSI/ADA specification 27 for resin-based filling materials, except that specimens were fabricated and polymerized at ambient laboratory conditions or in an environmental chamber at 90% humidity and 37°C. Ten specimens were made of each material at each condition. After aging specimens in 10 ml of sterile, deionized water, 37°C for 24 h, flexural properties were measured using a 3-point bend test. Results: A 2-way ANOVA (α= .05) indicated there were significant main effects of material and condition on flexural modulus and strength, with Z250=TPH>Prodigy and environmental chamber>ambient. Statistical comparisons of the flexural properties within each material as a function of fabrication conditions indicated there was a significant increase in the flexural modulus of Z250 and TPH at 90% humidity and 37°C (overall α= .05; pairwise comparisons α= .017, Bonferonni adjustment). In contrast, within each material, flexural strength was not significantly affected by fabrication conditions (p³ .017). Conclusions: The evidence indicates that environmental fabrication conditions with increased humidity and temperature do not adversely affect resin composite flexural properties. Thus, although modeling intraoral conditions is valuable in laboratory investigations, humidity and temperature do not appear to be significant in vitro factors for resin composite polymerization.

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