Attrition-corrosion wear of dental enamel

Abstract

Attrition-corrosion of human dental enamel is an enamel-on-enamel wear process in an acidic environment. Though the risk of attrition-corrosion is increasing nowadays, associated research is limited and the underlying wear mechanism remains unclear and hence is the subject of this study. Enamel-on-enamel attrition-corrosion wear tests were performed in vitro using a tribometer in a configuration of an enamel cusp reciprocating on an enamel flat surface sample for 30 mins with lubricants at 37℃. Wear tests with lubricants of citric and acetic acid at pH 3.2 and 5.5, respectively, and distilled water were performed to investigate the wear mechanism of attrition-corrosion and the effects of the acidity of lubricants on it. To study the effects of contact load, attrition-corrosion wear tests were also performed under loads of 7 – 13 N with lubricants of acetic acid (at pH 3.2 and 5.5) and distilled water. Following the attrition-corrosion wear tests, the substance loss from the enamel samples was measured to evaluate the wear severity. The wear scar and its subsurface were analyzed using focused ion beam (FIB) sectioning and scanning/transmission electron microscopy (SEM/TEM) to elucidate the wear process and underlying mechanisms. The mechanism of enamel-on-enamel attrition-corrosion wear is abrasion due to shaving of the softened layer formed on the flat surface enamel sample by the reciprocating enamel cusp, while the mechanism of enamel-on-enamel wear with distilled water was delamination resulting from subsurface crack formation/propagation and caused peeling off wear particles. The corrosion potential of the lubricant used was found to affect the substance loss following attrition-corrosion. There is a range for acid corrosion potential for which enamel wear is low. If a lubricant’s corrosion potential is below/above this range, the enamel wear loss will increase rapidly. In terms of the variation of wear loss with load, it was linear for lower loads, but exponential for higher loads with acetic acid at pH 5.5, which was attributed to the failure of the protective layer formed due to softening of enamel by the acids at a higher load. The wear losses with acetic acid at pH 3.2 and distilled water increased linearly with rising load.