Surface characteristics of orthodontic adhesives and effects on streptococcal adhesion

In this study, we analyzed the surface roughness (SR) and surface free energy (SFE) characteristics of various orthodontic adhesives and their effects on the adhesion of mutans streptococci (MS).

Three nonfluoride-releasing composites, 1 fluoride-releasing composite, 1 polyacid-modified composite (compomer), and 2 resin-modified glass ionomers (RMGIs) were analyzed with confocal laser scanning microscopy and the sessile drop method. Each material was incubated with whole saliva or phosphate-buffered saline solution. Adhesion assays were then performed by incubating each material with tritium-labeled cariogenic streptococci.

We found that SFE and its components were significantly different among the adhesives, despite relatively uniform SR. RMGIs showed significantly higher SFE-particularly, dispersive, polar, and acidic characteristics-than did the composites. The compomer had intermediate characteristics between the composites and RMGIs. MS adhered to RMGIs significantly more than to the composites and the compomer, but there was no significant difference among the composites. The longer incubation time increased MS adhesion, whereas saliva coating did not significantly influence MS adhesion. There was a correlation between SFE and MS adhesion. SFE and its dispersive, polar, and acid components significantly influenced MS adhesion irrespective of saliva coating.

This study suggests that initial MS adhesion is significantly influenced by SFE characteristics of adhesives rather than SR or saliva coating.