Synergistic effects of bioactive silica and fluoride in enamel protection and repair: an in vitro study

Erosive tooth wear (ETW) compromises enamel integrity. This study investigated the synergistic effects of bioactive silica and fluoride, as well as the independent performance of bioactive silica, in protecting sound enamel and repairing previously eroded enamel under erosive-abrasive challenges. An in vitro laboratory design was adopted using two models: (1) a protective model with sound enamel and (2) a remineralizing model with pre-eroded enamel. Ninety-six bovine enamel blocks were randomly allocated to four dentifrice groups (n=12/group) within two experimental models: RGS/NaF (bioactive silica + 1100 ppm NaF), RGS (bioactive silica without fluoride), NaF (1100 ppm NaF), and NC (fluoride/silica-free). Specimens were exposed to erosive cycling with 0.1% citric acid and simulated toothbrushing treatment for seven days (protective model) or five days (remineralizing model). Surface microhardness, quantitative light-induced fluorescence (QLF), 3D profilometry, and roughness were evaluated. Data were analyzed with ANOVA and Tukey's post hoc test (p < 0.05). In the protective model, all groups showed microhardness loss, but RGS/NaF maintained the highest hardness values (p < 0.05). In the remineralizing model, all groups demonstrated partial recovery, with RGS/NaF significantly outperforming the others. Bioactive silica alone performed similarly to NaF in several parameters, showing reduced roughness and less structural loss compared with the negative control. The combination of bioactive silica and fluoride provided superior protective and remineralizing effects against erosive-abrasive enamel loss. Bioactive silica alone also exhibited relevant benefits, reinforcing its potential as a viable fluoride-free alternative.