Effect of Er: YAG laser on the bond strength of glass ceramic to bleached enamel and mechanism investigation
TL;DR
Reduced H2O2 levels, increased resin polymerization, and modification of the enamel surface may contribute to the improved bonding performance observed after Er: YAG laser treatment of bleached enamel.
Abstract
This study aimed to evaluate the efficacy of Er: YAG laser treatment for glass-ceramic bonding to bleached enamel and to further investigate the potential mechanisms. This in vitro study included 132 molars, with each molar used to prepare a single specimen. A total of 48 enamel slices, 48 enamel blocks, and 36 embedded whole-tooth specimens were prepared. The specimens were randomly allocated to four groups: the Control group, hydrogen peroxide (HP) group, HP combined with sodium ascorbate (HP-SA) group, and HP combined with Er: YAG laser (HP-Er: YAG) group. They were subsequently evaluated for enamel surface morphology, residual hydrogen peroxide (H2O2) concentration, resin degree of conversion (DC), resin penetration, shear bond strength (SBS), and failure mode. SEM showed that the HP-Er: YAG group exhibited rough and irregular enamel surfaces, while the HP and HP-SA groups showed no obvious morphological changes. Compared with the HP group (109.60 ± 10.38 µmol/L), H2O2 concentrations were significantly lower in the HP-SA (51.05 ± 20.06 µmol/L) and HP-Er: YAG (29.96 ± 13.01 µmol/L) groups (P < 0.0001). The HP-Er: YAG group showed a lower concentration than the HP-SA group (P < 0.05).The DC of the HP-Er: YAG group (51.10 ± 7.02%) was comparable to that of the Control (59.84 ± 5.36%) and HP-SA (41.82 ± 7.28%) groups (P > 0.05). The Control and HP-Er: YAG groups exhibited extensive resin penetration at the enamel-adhesive interface. SBS was significantly higher in the Control (21.92 ± 4.33 MPa) and HP-Er: YAG (22.62 ± 4.06 MPa) groups than in the HP (13.46 ± 3.62 MPa) and HP-SA (17.76 ± 2.56 MPa) groups (P < 0.01). For ARI scores, the Control and HP-Er: YAG groups did not differ significantly (P > 0.05), whereas all other pairwise comparisons were statistically significant (P < 0.05). Reduced H2O2 levels, increased resin polymerization, and modification of the enamel surface may contribute to the improved bonding performance observed after Er: YAG laser treatment of bleached enamel. Compared with 10% SA treatment for 10 min, Er: YAG laser was more effective in restoring bond strength, suggesting its potential for immediate glass‑ceramic bonding to bleached enamel.