The effect of laser-activated bleaching with 810 nm and 980 nm diode lasers on enamel micro-hardness; an in vitro study

Abstract

The aim of this study was to assess the micro-hardness of treated enamel with 810 nm and 980 nm diode lasers and to compare it with a conventional bleaching process. A sample of 45 caries-free human premolar teeth were selected. The enamel surfaces were completely polished. The crown portion of each tooth was then sectioned with a diamond disk, at dimensions of 3  ×  3  ×  3 mm. These sections were embedded in acrylic resin. The initial micro-hardness was determined by Vickers hardness apparatus at a vertical load of 200 g for 15 s. The samples were then randomly assigned to three groups of 15 samples. – Study group 1 (SG1): bleaching with Heydent JW gel and an 810 nm diode. – Study group 2 (SG2): bleaching with Heydent JW gel and a 980 nm diode. – Control group (CG): bleaching with Opalescense Boost. After bleaching, the Vickers micro-hardness was again evaluated. An analysis of covariance (ANCOVA) was used to compare the micro-hardness between the groups after bleaching, considering the initial micro-hardness as a covariate. A paired samples t-test was also used to compare micro-hardness before and after bleaching in each group and between groups. There was a significant difference in micro-hardness after bleaching with a laser and without a laser. After bleaching, the Vickers micro-hardness in the CG was significantly higher than in SG1 and SG2. There was no significant difference between SG1 and SG2 after bleaching (p value  >  0.05). According to this study, laser irradiation with 810 nm and 980 nm diode lasers during tooth bleaching could cause a significant decrease in enamel micro-hardness.