Influence of Sterilization on Composite Surface Properties and Biofilm Formation

Method: Disc-shaped specimens (n=39 total; D=10.0mm x 2mm thick) of an experimental composite (50:50 Bis-GMA/TEGDMA resin/72wt% filler=67%Sr-glass+5%OX50) were light cured (12J/cm²; Demi, Kerr). Specimens were polished (1000 grit SiC/5μm/1μm alumina) and divided into sterilization methods: 1) autoclave; 2) Ethylene oxide; 3) 50% Bleach; or 4) 50% Bleach followed by neutralization in 5% sodium thiosulphate(ST). Control specimens were not sterilized. Individual sterile culture plates were filled with 5 ml of BHI broth supplemented with 3% (wt/vol) sucrose. A test composite disk was added to each well and inoculated with 100 ul of an overnight culture of Streptococcus mutans (ATCC 27351). The plates were incubated (37°C; 5% CO₂) for 3, 7, and 10 days. Media was changed every other day. Gloss was measured with a glossmeter (Novo-Curve, Rhopoint Instrumentation), surface roughness with a profilometer (tracing length 2 mm; cutoff 0.8 mm; TR200, TIME Group), and Knoop hardness on a Duramin Hardness Tester (Struers) with a load of 100g and dwell time of 20s. Groups were compared with ANOVA/Tukey’s(α=0.05).

Result: S. mutans biofilms formed on all surfaces at all time periods. There were few differences in surface roughness vs. control (Bleach+ST>Control all times; ethylene oxide>Control at 10 days) and no differences in gloss among any of the groups(Table).  There were no differences in hardness at 3 days.  At 7 and 10 days, all of the treatment groups were equivalent and had reduced hardness compared to the Control (except ethylene oxide 10 days).

Conclusion: Sterilization method had minimal effect on the surface properties of composites, and did not appear to inhibit or disrupt biofilm formation. Surface softening during aging in bacteria was evident, but was equivalent for different sterilization treatments.