Laboratory screening evaluation of the safety of low pH oral care rinse products to dental enamel.

Purpose: To assess the hard tissue safety of a variety of low pH oral care rinses to dental enamel in a newly developed screening method.

Methods: Bovine enamel specimens were subjected to a cycling model that consisted of commercial mouthrinse product exposures and artificial saliva soaks based on a previously published screening method. The effect of test products on the surface of treated specimens was measured using surface microhardness (SMH). Results are presented as the change in SMH (between sound enamel baseline and cycling final). An assortment of rinse products were assessed relative to distilled water (positive control) and 1% citric acid (negative control). A priori, a product was considered safe if the change in measured SMH values over the course of six treatment cycles was both significantly greater than the negative control and was not significantly different from the positive control. A non-inferiority statistical test was applied to create a quantitative rule defining product safety.

Results: Products tested included two rinses with a pH in excess of 5.5, and eight with a pH less than 5.5. Four of the rinses included fluoride, while six did not. Analyses showed that all of the rinse products tested passed the non-inferiority acceptance criteria. One of the 10 marketed oral care rinses failed to meet the a priori criteria needed to be considered safe as the product was significantly better than the negative control but also significantly lower than the positive control treatment. This product had the lowest pH of all products tested and did not contain fluoride. Application of the non-inferiority statistical test showed the questionable product passing safety criteria. As a proposed method for a screening tool, further testing would be recommended based on these results.

Clinical Significance: An in vitro enamel safety screening method was applied as an assessment of the enamel demineralization safety to a number of oral care rinse products. Surface microhardness, coupled with a non-inferiority statistical evaluation, provided a reasonable approach for detecting potential product issues. Products failing this screening laboratory method may require additional testing to verify their safety on hard tissues.