To evaluate the effects of experimental light-activated bleaching procedures, which demonstrated a potential of improving the bleaching process, on surface microstructure and microhardness of human enamel and dentine.
Method:
Forty human third molars were randomly divided into four groups and dissected in half. One half of molar was used for enamel and other half for dentine microhardness assessment. In each group (n=20), except the control, bleaching of both surfaces was induced by different light source – LED405, OLED or femtosecond laser, for 2×15 minutes. Effects of these experimental light sources on surface microhardness were tested for applications of three bleaching agents – ZOOM2 (Discus Dental, USA), Opalesence BOOST (Ultradent, USA) and 30% VivaStyle (Ivoclar, Liechtenstein). Vickers microhardness was measured at the baseline, after the light-activated bleaching treatment and after 2 weeks storage in either artificial saliva with amorphous calcium phosphate (ACP) gel treatment or in deionized water. Surface microstructure was evaluated using SEM.
Result:
The bleaching activation with LED405, OLED and femtosecond laser did not promote additional microhardness reduction or micromorphology changes compared to the bleaching without light activation (control). However, bleaching procedure induced significant reduction in surface microhardness for all bleaching agents applied (p<0.001). Application of ZOOM2, which had the lowest pH value, showed larger decrease in microhardness (p=0.005) compared to BOOST and VivaStyle. After the bleaching procedure surface microstructure showed mild alterations with no loss of superficial structure. Post-treatment with artificial saliva and ACP significantly increased the surface microhardness (p<0.001).
Conclusion:
Application of light sources like LED405, OLED and femtosecond laser does not induce greater damage of the surface microhardness and micromorphology of enamel and dentine than bleaching without light activation. Post-bleaching treatment with ACP increased surface microhardness and roughness, and enhanced the remineralization of the hard dental tissues.
This study was supported by the MSES and CSF.