In-vitro evaluation of the effects of power bleaching on enamel microhardness and tooth colour

This in-vitro study aimed to evaluate the surface microhardness of human enamel subjected to bleaching with Zoom AdvancedPower and Opalescence Boost; an in-office vital bleaching agent; andafter bleaching procedure to evaluate the re-hardening effects of sodiumascorbate, APF gel and Relief gel.One hundred recently extracted and intact human impactedthird molar teeth were used. The specimens were randomly assigned to 5groups. G1: Placebo gel and Zoom AP light, G2: Zoom 2 25% hydrogenperoxide in-office bleaching gel, G3: Zoom 2 25% hydrogen peroxide inofficebleaching gel and Zoom AP light, G4: Opalescence Boost 38%hydrogen peroxide in-office bleaching gel, G5: Control (no light no gel).Each group specimens were subjected to the treatment agents for threesequences of 15 minutes. After the bleaching procedure 90 of thespecimens were treated with APF sodium ascorbat or Relief gel. Enamelmicrohardness was measured via Vicker?s Microhardness Tester. Colourchanges were measured by two examiners using a Vita Shade Guide. Thedata were evaluated via one-way ANOVA, Dunnet, Kruskal-Wallis andpost-hoc test and t tests.Statistical analyses revealed no significant microhardnessdifference among initial enamel groups (p>0,05); however significantdifferences occurred between initial and after treatment group value for G3(p<0,05). After re-hardening of the specimens only sodium ascorbategroup showed a statistically significant increase in microhardness levels.(p<0,05). Except the control group (G5) each group showed a statisticallysignificant improvement in tooth colour after bleaching. (p<0, 05)Bleaching treatment conducted with light had no adverseeffect on enamel microhardness and it improves the colour of the teethmostly. Sodium ascorbate can be used after bleaching to alter adverseeffects of bleaching on enamel.Keywords: Bleaching, enamel, microhardness, toothcolour, re-hardening