Surface Properties and mutans streptococci Biofilm Formation on Dental Composites

Objectives: Surface properties and chemical composition of dental composite restorations deeply influence bacterial colonization of composites surfaces and interact with cariogenic microorganisms. The aim of this in vitro study was to investigate mutans streptococci (MS) colonization of four composites, differing in chemical composition and surface finishing, using a continuous culture system. Materials and methods: 168 standardized disks were prepared from four dental composites: a nanofilled methacrylate composite (3M Filtek Supreme XT®), a microfilled silorane composite (3M Filtek Silorane®), a nanohybride methacrylate composite (VOCO Grandio®), and an experimental nanohybride methacrylate composite (VOCO). Specimens were light cured (1500 mW/cm2) for 40 seconds to ensure a high degree of conversion. The disks were randomly divided into two groups and finished using two different surface finishing techniques (polymerization against Mylar® strip (MYL); polishing with 1000/4000-grit grinding paper (POL)). Surface roughness (SR) and surface free energy (SFE; OWRK approach) were determined on five randomly selected specimens. Composite surfaces were characterized using EDAX (Energy-dispersive X-ray spectroscopy). Monospecific MS biofilms growing on the disk surfaces were obtained using a Drip Flow Reactor; viable biomass was assessed after a 48- and 96-hour incubation using a colorimetric technique (MTT assay). Results: Statistical analysis (multi-way ANOVA; Α=.05) showed a similar pattern of MS colonization for both incubation times, with an increasing trend of adherent biomass. In most cases, POL samples were significantly less colonized than MYL samples. Grandio® and Filtek Supreme XT® POL groups showed a significantly lower MS colonization than the other groups. Polishing significantly reduced SFE but no significant influence of SR on MS colonization was found. EDAX showed higher silicium and lower carbon presence on the POL surfaces when confronted with the MYL ones. Conclusions: Finishing treatment and composite type have a significant influence on the biological behavior of the surface by modifying surface characteristics.