Fluoride-releasing Materials and their Anti-cariogenic Properties Tested in an in vitro Microbial Model

It is believed that fluoride-releasing restorative materials provide an additional protection against secondary caries. This protection has been widely demonstrated to happen in enamel, but only a few studies have demonstrated caries preventive effects from fluoride-releasing materials in dentin. Objective: The purpose of this investigation was to determine the caries preventive properties of four different restorative materials in human dentin specimens demineralized using an in vitro microbial caries model. Methods: One hundred and twelve dentin specimens (4x4x2.5 mm) were selected after a confocal microscopy screening of more than 200 specimens. Cavities (1.5 x 2 x 1.5 mm) were prepared using a standardized method. Specimens were divided in four groups of 28 and restored with either a conventional glass-ionomer cement (GI), a resin-modified glass-ionomer cement (RMGI), a polyacid-modified resin composite (PAMRC), or a resin composite (RC). Fifty-six specimens (14 per group) were initially demineralized for 3 days using an in vitro microbial caries model with Streptococcus mutans and Lactobacillus casei as the inoculum. Then, secondary caries around the restorations was analyzed using confocal laser scanning microscopy. The experiment was repeated with the remaining 56 remaining specimens. Results: No significant differences were found among the four groups for all the lesion parameters analyzed: wall lesion depth and area, outer lesion depth and area, total lesion depth and area, total and average fluorescence of wall, outer and total lesion. The results were similar in both studies. Conclusions: It was found that fluoride-releasing materials did not prevent demineralization of dentinal tissues when studied in this microbial caries model. Further research is needed in order to determine the amount of fluoride released from fluoride-releasing materials to prevent secondary caries from occurring in dentinal tissues, and the clinical relevance of this effect.