Effects of Streptococcus mutans and their metabolites on the wear behavior of dental restorative materials.

The wear behavior of dental restorative materials is highly related to the biolubricating medium in the oral environment. Bacteria, along with their metabolic products, are essential substances in the oral cavity and have not been studied as a potential factor affecting lubrication performance during mastication. In this study, the effects of the Streptococcus mutans bacterial cells and their metabolites were investigated on the wear behavior of resin composites, polymer-infiltrated ceramic networks and zirconium-lithium silicate glass-ceramics. A reciprocating friction test and quantitative analysis of the wear morphology were utilized to determine the coefficient of friction (COF) and wear resistance of the test materials. The results showed that the bacterial metabolite medium significantly reduces the COF and wear rate of the three restorative materials and provide better protection against superficial abrasion. When tested under lactic acid medium, a key acid production in bacterial metabolites, similar wear reduction results were observed in the three materials, which confirmed that lactic acid should be accountable for the excellent lubricating property of bacterial metabolites. Furthermore, the resin composite with lower wettability exhibited a more significant wear reduction than the other two materials when lubricating with a bacterial metabolite medium. These findings provide novel insights into the biological basis of lubrication mechanisms in the oral cavity under high-loading and low-velocity conditions.