The effect of long-term use of tooth bleaching products on the human enamel surface

The aim of this in vitro study was to evaluate the long-term effect of bleaching on human enamel. Four groups of enamel specimens were prepared (n = 20): group 1: bleaching with Opalescence Boost [40% hydrogen peroxide (H₂O₂), 3 × 20 min/week]; group 2: control group (the specimens were stored in human saliva); group 3: beaching with Vivastyle Paint on Plus (6% H₂O₂, 2 × 10 min/day), and group 4: bleaching with Opalescence PF 16% [16% carbamide peroxide (CP), 6 h/day]. After each bleaching session the specimens were stored in human saliva. Knoop microhardness and surface roughness were measured: before bleaching, after 2-week and after 8-week bleaching. After 2-week treatment, surface roughness was significantly increased in all experimental groups (p < 0.05), while among them no significant difference was found (p > 0.05). The roughness changes exerted after 8-week bleaching were not significantly higher than the ones after 2 weeks (p > 0.05). After 8-week treatment, the increase in roughness caused by 16% CP was significantly higher (p < 0.05) than the one caused by 40% H₂O₂. Microhardness increased in all groups including control; however, only 40% H₂O₂ increased the microhardness significantly (p < 0.05). The effect of bleaching on enamel was not shown to be dependent on the method or the H₂O₂ concentration. Bleaching with CP 16% resulted in higher roughness than bleaching with H₂O₂, while 40% H₂O₂ caused the higher microhardness increase. The present study showed that in-office bleaching with 40% H₂O₂ seems to be at least as safe as home bleaching as far as their effects on human enamel are concerned.