Effect of degree of conversion of different resin composite monomers (methacrylate and silorane) on two caries-associated bacteria: “An in Vitro study”

Background and Objectives: The biological response of oral bacteria to dental restorative polymer composites is mediated by the release of unpolymerized residual monomers. The aims of the present study were first, evaluating the effect of composite elutes from methacrylate composite resins and silorane-based composites on two cariogenic bacterial pathogens: Streptococcus mutans and Lactobacillus acidophilus and second, determination of degree of conversion (DC) of standardized discs made from the low-shrinkage silorane-based composite (FiltekTM P90) resin and methacrylate-based composite resin (FiltekTM Z350XT nanocomposite, FiltekTM Z350 Flow) using Fourier transform infrared spectroscopy (FTIR). Materials and Methods: Thirty-six composite specimens were prepared for the agar diffusion test and dissolved in a solvent (dimethyl sulfoxide) to attain a suspension, which was used to assess the effect of the residual monomers from methacrylate composite resins and silorane-based composites on the growth of S. mutans and L. acidophilus. To avoid more dilutions of the specimens, the colonies of bacteria were counted by the naked eye. Thirty composite specimens of 2 mm × 6 mm were polymerized for DC test, and the DC was measured using FTIR, also for unpolymerized composite resin. Results: The growth of S. mutans bacteria was inhibited when cultured with Filtek Z350 Flow composite resin, while the growth of L. acidophilus bacteria was stimulated by the Filtek Silorane p90 and Filtek Z350 Flow composite resin. The DC test with the Filtek Silorane composite resin showed highest DC (58%), then the Filtek Z350XT (Nanocomposite) (42%) followed by the Filtek Z350 Flow (Flowable) showed lowest (35%). Conclusions: Our results demonstrate that composite filling materials have a versatile nature of effect on oral pathogenic bacteria, which could modulate their pathogenesis. Dentists may thus select the appropriate type of composite filling according to the caries susceptibility of patients.