Surface Properties Modification Induced by Sterilization of Dental Resin Composites

Objective: There has been increased in vitro testing for possible degradation of resin composites and composite/dental tissue interfaces after bacterial challenge. Sample sterilization/disinfection is usually performed by immersion in ethanol or mild irradiation, with the unverified assumption that other methods would degrade the composite. We have systematically characterized surface modification of a composite sterilized with a number of methods, to test that immersion in ethanol is the only method that does not notably induce composite surface degradation.

Methods: Light-cured Filtek^TMLS (3M^-ESPE) discs were sterilized by autoclaving (44min, 122.7^oC, 22.6psi), X-Ray (90min, 120kV), O₂-, Ar cold-plasma (45min), or 70%-ethanol (1min). Samples with or without sterilization were incubated in media for 3 days. Negative controls were run by adding thymol (0.25%). The absence of colony growth on blood-agar plates assessed sterilization effectiveness. Samples were characterized by visual inspection (optical and SEM), wettability (water contact angle), microhardness, and chemical analysis (Diffusive-Reflectance FT-IR and EDS). Statistical differences were calculated using ANOVA-Tables with appropriate post-hoc tests. Positive controls were samples sterilized by different methods, incubated with dental plaque samples, in a biofilm reactor.

Results: Microhardness was significantly increased in all samples, including negative controls. Wettability was significantly modified by all sterilization methods except for immersion in ethanol. Cold plasma was the method that induced most dramatic surface modifications, i.e. notable wettability increase, surface roughening, and increasing of –CH groups. Material properties of the negative controls were not altered by thymol. No sterilization method altered the species composition of biofilms grown from plaque.

Conclusions: Disinfection with 70%-ethanol was the only method studied here that did not affect surface properties. Moreover, any residual bacterial remaining after ethanol treatment were overwhelmed when disks were incubated with dental plaque. This suggests that ethanol may be the best method for disinfecting composites before bacterial degradation experiments.

Supported by NIH-RO1DE021366.