Development of a Screening Method to Establish if pH of Oral Care Products Affects Hard Tissues

Objectives: To develop a transferable, simple screening method to evaluate the effect of pH of oral care products on oral hard tissues.

Methods: The method reported here is based on the assessment of oral hard surface changes produced by oral care products measured via Vickers Surface Microhardness (SMH). Two variations of this screening test method were developed, one including the use of salivary pellicle and human teeth and a second using bovine substrates with artificial saliva. The test method using bovine substrates and artificial saliva was replicated in a second laboratory in Beijing, China to verify reproducibility and transferability of the technique.

Results: Both approaches confirmed changes on surface hardness with 1% citric acid. All tested marketed products, including those formulated at pH < 5.5, showed no significant %SMH difference from the positive control (water), and demonstrated a significant difference from the negative control (1% citric acid). The two laboratories produced similar results (pH effects, standard deviation, and statistical rank-ordering of treatments).

Conclusions: This simple screening method accurately assesses the influence of positive and negative controls, regardless of the source of hard tissue (human vs. bovine) and saliva (human vs. artificial). It correctly shows that marketed products with pH below 5.5 that demonstrate favorable in vivo safety profiles do not contribute to detrimental hard tissue changes. The method is easily transferable and shows potential as a tool for the safety profile assessment of oral care products.