Analysis of surface roughness and free energy of orthodontic materials

Introduction: The purpose of this study was to analyze the differences in surface characteristics of various orthodontic materials, which may provide valuable information on bacterial adhesion to orthodontic materials. Methods: Surface 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 metal, 1 monocrystalline sapphire, 1 polycrystalline alumina and 1 plastic) and bovine incisor (BI) were investigated using confocal laser scanning microscopy and sessile drop method. Results: This study showed that that there were significant differences in SR and SFE characteristics among orthodontic materials. BI showed the roughest surface, while monocrystalline sapphire showed the smoothest surface. However, there were only small variations in SR (less than 0.3 ƒÝm) among materials except BI. 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. In particular, resin-modified glass ionomer cements had the highest SFE, dispersive component and polarity, which is more favorable for bacterial adhesion. Conclusions: This study suggests that SFE characteristics may influence bacterial adhesion to orthodontic materials more than SR and bracket materials may have less favorable SFE characteristics for bacterial adhesion than orthodontic adhesives.