Effects of Repeated Application of a 2.8% Hydrogen Peroxide Gel on Tooth Lightness: An In Vitro Study

Objective: This in vitro study aimed to observe changes in tooth lightness following repeated application of a gel-type tooth whitening product containing 2.8% hydrogen peroxide.Methods: Thirty enamel specimens were prepared from extracted bovine incisors and artificially stained using black tea.A gel-type whitening agent containing 2.8% hydrogen peroxide was applied to the enamel surfaces once daily for 18 consecutive days using a polisher.Tooth color was measured at baseline and after each application using a dental spectrophotometer (VITA Easyshade Advance V).Color changes were evaluated using the VITA classical A1-D4 and VITA SYSTEM 3D-MASTER shade systems.Changes in lightness values were analyzed using descriptive statistics and paired t-tests.Results: Progressive decreases in lightness values were observed with repeated application in both shade systems.No statistically significant differences were found after the first and second applications compared with baseline (p0.05).From the third application onward, statistically significant differences were observed in both the VITA classical A1-D4 and VITA SYSTEM 3D-MASTER systems (p0.0001).After 18 applications, mean lightness values were markedly reduced compared with baseline measurements. Conclusion:Under the conditions of this in vitro study, repeated application of a low-concentration hydrogen peroxide whitening gel was associated with progressive changes in tooth lightness.These findings provide preliminary data on patterns of tooth color change following repeated application.However, because this study was conducted in vitro without control groups, the results should be interpreted with caution.Further in vivo studies are required to clarify the clinical relevance of these findings.