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Friction of dental resin composite exposed to lactic acid

Introduction: Lactic acid concentration in the blood and saliva increases during physical exercise [1], leading to dental erosion and the degradation of restorative dental materials [2]. Our goal is to evaluate the effect of lactic acid exposure on the surface of a composite resin Materials and methods: 16 discs were made from Filtek ™ Z250. Every disc was divided into three distinct areas, resulting in a total of 48 samples that were randomly distributed into four groups (n = 12). Group A and B were placed in 5 mL of artificial saliva while group C and D were placed in 5 mL of lactic acid (pH =4.0). Intermittent exposure to the acidic solution (8 hours) alternated with artificial saliva (8 hours), till complete 1 day (group C) or 7 days (group D). All samples were submitted to nanotribological wear tests with a Nano-Tribometer (CSM Instruments SA, Peseux, Switzerland), using as counter-body a zirconia ball. Statistical analysis via one-way ANOVA with Tukey HSD Post Hoc test and independent samples t-tests were performed. Results: The highest friction coefficient (Table 1) was obtained with the acid lactic group at both timings (0.188 at 1 day and 0.144 at 7 days). Statistically significant differences between solutions were found with time: friction coefficient decreased in all groups when the exposition time increases from 1 to 7 days. (p < 0.05). Discussion and conclusions: The resin exposed in an intermittent way to lactic acid for 1 day presented the highest friction coefficient. The obtained results showed that lactic acid led to an increase of the friction coefficient, which was more significant for the lower exposure time. This may be attributed to the acid effect on the surface of the resin that wears the resin making it smoother, thus reducing friction.