Analysis of surface roughness and surface free energy characteristics of various orthodontic materials

IntroductionThe purpose of this study was to analyze the differences in surface characteristics of various orthodontic materials; this might provide valuable information on bacterial adhesion to orthodontic materials.MethodsSurface roughness (SR) and surface free energy (SFE) characteristics of 5 orthodontic adhesives (2 composites resins, 2 resin-modified glass ionomer cements, and 1 compomer), 5 bracket materials (2 stainless steel, 1 monocrystalline sapphire, 1 polycrystalline alumina, and 1 plastic) and bovine incisors were investigated by using confocal laser scanning microscopy and the sessile drop method.ResultsThere were significant differences in SR and SFE characteristics among orthodontic materials. Bovine incisors showed the roughest surface, and monocrystalline sapphire showed the smoothest surface. However, there were only small variations in SR (less than 0.3 μm) among the materials, except for bovine incisors. In contrast to SR, there were big differences in SFE characteristics among materials. Generally, bracket materials showed lower SFE—specifically, dispersive and polar components on their surfaces—than orthodontic adhesives. Resin-modified glass ionomer cements had the highest SFE, dispersive component, and polarity; these conditions are more favorable for bacterial adhesion.ConclusionsThis study suggests that SFE characteristics can influence bacterial adhesion to orthodontic materials more than SR, and bracket materials might have less favorable SFE characteristics for bacterial adhesion than orthodontic adhesives.