In vitro evaluation of calcium and phosphorus concentrations in enamel submitted to an in-office bleaching gel treatment containing calcium.

The aim of this in vitro study was to evaluate the calcium and phosphorus concentrations in enamel surfaces before, during, and after treatment with in-office 35% hydrogen peroxide bleaching agents with 2% calcium gluconate (WCa) or without calcium gluconate (W). Twenty sound human third molars were divided into 2 groups of 10. The bleaching agents were applied to the tooth surfaces in accordance with the manufacturer's instructions: WCa, 40 minutes per day at 3 sessions with 7-day intervals; W, 3 × 15 minutes per day at 3 sessions with 7-day intervals. Enamel microbiopsies were performed prior to the bleaching treatment, immediately after each bleaching session (first, second, and third applications), and 7 and 14 days following the last bleaching treatment. The concentration levels of calcium and phosphorus in the microbiopsy specimens were recorded spectrophotometrically. There was a statistically significant decrease in the calcium concentration 7 days after the last bleaching treatment, but there was a recovery to baseline values at 14 days, regardless of the bleaching agent used (WCa and W). When W was used, there was no difference in the phosphorus concentration over time. The phosphorus concentration in the WCa group decreased after the third application, showing a significant difference from the W group at this time. However, an increase in the phosphorus concentration was observed in the posttreatment period, and no significant differences were observed between values at baseline and those at 14 days posttreatment. The in-office bleaching gel containing 2% calcium gluconate did not affect the calcium and phosphorus concentrations in enamel as compared to a calcium-free bleaching agent.