Tribological behavior of restorative dental microcomposites after exposure to mouth acids

In this work, the effect of the exposure to acids that are usually present in the mouth environment on the tribological behavior of restorative dental microcomposites is evaluated. A commercial microcomposite widely used in dentistry (Filtek Z250) and a strong and a week acid that are part of the mouth environment (hydrochloric and lactic acid, respectively) were chosen for the study. Samples of the microcomposite were exposed to each acid for two different periods: 1 day and 7 days, respectively. It was observed that the exposure to both acids lead to an increase of the surface roughness, especially in the samples that contacted for the shorter period with hydrochloric acid, and the same trend was observed in what concerns the coefficient of friction. Concomitantly, the resins’ microhardness suffered a small decreased after exposure to both acids. However, it was observed that the wear resistance of the microcomposite is only affected in a statistically significant manner after the exposition to the hydrochloric acid solution. Atomic force microscopy observation of the worn regions enables to attribute the decrease of the wear resistance of the material after the exposure to the strong acid to the detachment of the resin’s filler microparticles of silica and zirconia caused by the corrosive action of the strong acid. The results strongly suggest that the exposure to acids affects the dental resins’ tribomechanical performance which may compromise the restorations’ lifetime, especially in the case of exposure to the strong acids, such as hydrochloric.