Methods: Polymethyl methacrylate (PMMA) (Rapid Simplified, Vertex®) was employed to prepare 15 mm x 15 mm square with 2 mm in thickness samples. These heated cure acrylic samples were separated into two groups. Group I (well-polished) included the samples with surface roughness less than 0.2 mm (Ra< 0.2 mm), whereas Group II (poor-polished) were the ones with surface more than 0.2 mm (Ra>0.2 mm). Both S. epidermidis DMST and another clinical strain were tested. The acrylic samples were placed in 24-well tissue-culture plates containing 2 ml of bacterial suspension (106CFU/ml) and incubated at 37°C with constant agitation for 2 h (initial adhesion). Then the samples were transferred to new fresh medium for biofilm formation for 24, 48 and 72 h with identical incubation procedure. The biofilm mass at certain time was analyzed by staining with 1% crystal violet solution and measured the optical density at 600 nm.
Results: Different degrees of biofilm mass formed on these two groups of acrylic samples were observed. Relatively less bacterial biofilm was formed on the well-polished group, compared to the poor polished one at any periods of time. Slightly different of biofilm mass was observed from the reference strain and the clinical strain.
Conclusions: Surface roughness of the heated cure PMMA clearly influenced on S. epidermidis biofilm formation. The greater the roughness appeared (Ra>0.2micron), the more massive the bacterial biofilm formed.