Acid Etching Before Chemical And Laser Bleaching: Effects On Enamel Microhardness

Aims: The aim of this study was to compare the microhardness of enamel bleached with two different bleaching solutions (chemical and laser activated), preceded or not with acid etching.Materials and methods: Thirty bovine teeth were prepared and haphazardly assigned into two groups (n=15) depending on the bleaching technique. Each group was subdivided into three subgroups (n=5) consistent with acid etching by 37% phosphoric acid. A digital Vickers microhardness tester (VHN) was used to measure enamel microhardness. Three read-outs were conducted to each sample to quantify microhardness. The samples were held in artificial saliva for five days. The microhardness was measured immediately and five days after bleaching. Paired samples t-test and independent samples t-test were employed for statistical analysis.Results: The results of the paired sample t-tests used to evaluate enamel microhardness of the conventional and laser-assisted bleached groups before and immediately after bleaching revealed a significant decrease in both methods in all groups. However, the microhardness after five days increased significantly in all groups when it was compared to that immediately after bleaching. The results of the independent samples t-test employed to assess enamel microhardness between conventional and laser bleaching of the same group type showed no significant differences between any of the groups, with the exception of C2-L2 groups at immediately after bleaching.Conclusion: Acid etching of enamel followed by chemical or laser assisted bleaching resulted in significant microhardness reduction with no effect of etching time (5 or 10 sec.). Storage of samples in artificial saliva for 5 days after bleaching increased the microhardness but wasn't able to restore them to the levels before acid etching and bleaching. As a clinical implication, and for cases requiring enamel etching before bleaching, five seconds etching time may be preferred over ten seconds.