The influence of light-curing time on the bacterial colonization of resin composite surfaces

Objectives: Bacterial colonization of composite surfaces represents the main factor in the etiology of secondary caries around adhesive restorations. The authors' aim was to evaluate the influence of light-curing time on mutans streptococci colonization (MS) of a resin composite material. Methods: Specimens obtained from a dental resin composite were divided into 12 groups and light-cured with the same light source respectively for 10, 20, 30, 40, 60 or 80 s using two different curing-power levels: 400 and 800 mW/cm2. A wild strain of MS was isolated and a 24-h-monospecific biofilm, adherent to the surfaces of the samples, was obtained. A colorimetric technique (MTT assay), based on the reduction of a yellow tetrazolium salt to a purple formazan, was used to evaluate the biomass adherent to the specimen surfaces. ANOVA and Scheffé's tests were used to statistically analyze the results. Results: Two-way ANOVA demonstrated there was no interaction between curing-time factor and curing-power factor (p = 0.970); one-way ANOVA was used to analyze separately the data obtained from each curing-power level. Both levels showed highly significant differences (p < 0.0001) among the different curing time groups. The non-parametric test for trend showed in both levels the existence of a highly significant trend (p < 0.0001) for bacterial colonization reduction as curing time increases. Significance: A reduced curing time seems to be responsible for increased in vitro colonization of composite surfaces by MS; this phenomenon is likely to be related to the presence of unpolymerized monomers on the material surface. © 2009 Academy of Dental Materials.