Evaluation of the effects of different remineralizing agents on the microhardness and mineral content of bleached enamel along different storage times

This study evaluated the effects of various remineralizing agents on Vickers microhardness (HV) and mineral weight percentages (wt%) of bleached enamel during 30 days of storage in artificial saliva. For HV testing, a total of 154 human specimens were used, including 14 specimens that were assigned to two control groups: a positive (sound unbleached enamel, n = 7) and a negative control (bleached using a 32% hydrogen peroxide, n = 7). The remaining 140 specimens were bleached and randomly divided into 20 experimental groups (n = 7), based on two factors: remineralizing agents; four agents (potassium nitrate with fluoride, casein-phosphopeptide-amorphous calcium phosphate with fluoride, hydroxyapatite with fluoride, and PAMAM), and storage times; five times (24 h, 3 days, 7 days, 15 days, and 30 days). For mineral wt%, 110 human enamel specimens were used, including 10 specimens for positive (n = 5) and negative control (n = 5), and 100 bleached enamel specimens divided into 20 experimental groups (n = 5/group), based on two factors, same as for HV testing. Data were analyzed using two-way ANOVA followed by Tukey’s HSD post hoc tests (α = 0.05). Remineralizing agents and storage time significantly affected HV of bleached enamel (p < 0.001). PAMAM showed the highest HV at 7, 15, and 30 days (p < 0.05). Calcium (Ca) wt% was unaffected by either remineralizing agents (p = 0.848) or storage time (p = 0.141). Phosphorus (P) wt% was significantly influenced by both factors (p < 0.001 and p = 0.023, respectively). Fluoride (F) wt% was significantly affected only by the remineralizing agents (p = 0.001). Bleaching significantly decreased enamel HV and F wt%, whereas remineralizing agents effectively restored both. The use of different remineralizing agents may help counteract the detrimental effects of bleaching on enamel.