Effects of laser debonding treatment on the optical and mechanical properties of all-ceramic restorations

The objective of this study was to evaluate how erbium-doped yttrium aluminium garnet (Er:YAG) laser debonding treatment affects the optical and mechanical properties of dental ceramics. In total, 120 rectangular (22*5*1.2 mm) IPS E.max Press specimens were fabricated and divided into 4 groups: the control group, 3 W laser group, 4 W laser group, and 5 W laser group. For each group, 10 specimens were used for the colour test (colour difference (△E) and transparency parameter (TP)), 10 specimens were used for the flexural strength test, and 10 were used for the Vickers hardness test. One random sample from each colour test specimens was observed by scanning electron microscopy (SEM). The L*, a*, b*, △E, TP, flexural strength, and Vickers hardness values were measured and calculated. According to the Kruskal-Wallis test, the L*, a*, and b* values showed no significant variations (P > 0.05), except for the b* value in the 5 W laser group (P < 0.05). The △E, TP, flexural strength, and Vickers hardness values were analysed by one-way analysis of variance (ANOVA). The 5 W laser group exhibited a higher △E value, which exceeded the perceptible threshold and significantly lower TP values than the other groups (P < 0.05). The mean flexural strength and Vickers hardness values after Er:YAG laser debonding revealed no significant changes (P > 0.05). Microcracks were detected during the SEM analysis of the 5 W laser group. Er:YAG laser debonding treatment did not affect the mechanical properties, but changed the optical properties of dental ceramics.