A Validated In-Vitro Model for Assessing EFU From Fluoride Varnishes

Objectives: Clinically validated laboratory methods for evaluating the cariostatic potential of fluoride varnishes have not been reported and do not accurately replicate what is observed clinically. The challenge is that intra-oral salivary flow in clinical in-situ models is extremely challenging to replicate accurately in-vitro. The methods used in other in-vitro models, such as immersion in water, saliva, or mineral solution with or without incrementally placing the specimens in fresh fluid over the length of the study, are insufficient in replicating what is observed clinically. The goal was to develop a clinically-validated laboratory method for determining the enamel fluoride uptake from fluoride varnish treatments.
Methods: 10 lesioned specimens inside an acrylic disc were treated with 1 of 3 dental varnishes which differed significantly in the rate of fluoride release in water over 24 hours. The release rates were 112, 3.1, and 2.1% for varnishes B, C, and D, respectively. A slow drip of deionized water (approximately 1mL/minute) was placed centrally over the disc. The water collecting on the surface eventually broke the tension holding it on the disc resulting in the water, now fluoridated, to run off into a separate collection chamber. After 24 hours, the varnishes were removed from the discs and the individual specimens were separated and analyzed for fluoride and calcium using the acid etching technique.
Results: Varnishes C and D were significantly more effective than the Varnish B (ANOVA, SNK, p<0.05). Varnish D was the only clinically-proven cariostatic varnish and served as the gold standard. Corresponding clinical studies were conducted at the research site which demonstrated that the calculated aqueous fluoride release rate of a varnish is not predictive of actual fluoride uptake into enamel.
Conclusions: This study replicates clinical data (presented at this meeting) and should be used as a valid laboratory model.