In vitro Caries Model Suitable for Testing MFP Dentifrices

Objectives: Sodium monofluorophosphate (MFP) based dentifrices have been widely used to fight caries, and the clinical efficacy of MFP is well documented and accepted. Laboratory in vitro testing of the effect of MFP based dentifrices has been challenging, because fluoride in the MFP form does not become bioavailable until hydrolysis of the MFP occurs by salivary phosphatase enzymes. The objective was to develop an in vitro caries model to demonstrate the dose response effects of clinically tested fluoride dentifrices with NaF or MFP.
Methods: The in vitro model adopted a biology based approach to simulate the caries process. Enamel blocks were treated with dentifrice slurries (made by mixing dentifrice with water at 1:2 ratio) followed by incubation in a saliva sucrose culture. The dentifrice treatment – saliva sucrose incubation cycle was repeated for a total of 4 times a day for 5 days. Surface microhardness measurements of enamel blocks were taken before and after the 5 day treatment period using a Buehler Microhardness Tester.
Results: This in vitro model has been designed to assess the benefits of different actives when formulated within a common base. The model demonstrated fluoride dose responses similar to that shown in conventional caries studies. For MFP dentifrices, monographed level (1500 ppm) F was directionally better than middle level (750 ppm) F and both were significantly better than no fluoride. For NaF, monographed level (1100 ppm) F was significantly better than middle level (550 ppm) F and both were significantly better than no fluoride.
Conclusions: This in vitro caries model illustrates the anti-caries benefits of fluoride dentifrices including those containing MFP and provides a suitable screening method for assessing the anti-caries potential of formulations prior to completing in situ or human caries clinical studies.