The lingual enamel morphology and bracket shear bond strength influenced by Nd:YAG laser and aluminum oxide sandblasting preconditioning.

Objectives: This study aimed to investigate the influence of Nd:YAG laser and aluminum oxide sandblasting on the shear bond strength (SBS) of lingual brackets and to optically analyze the behavior of the enamel morphology.
Materials and Methods: Thirty-five bovines' incisors teeth were divided into 5 groups (n = 7), according to the surface preconditioning: G1, control group; G2, Nd:YAG laser; G3, laser + aluminum oxide sandblasting (Al ₂ O ₃ ); G4, Al ₂ O ₃ ; and G5, Al ₂ O ₃ + laser. All groups had lingual brackets bonded and shear debonded after 72 h. SBS values were analyzed, and the enamel morphology was evaluated by optical coherence tomography (OCT) and scanning electron microscope (SEM), before and after preconditioning surface. The optical attenuation coefficient (α) analysis was obtained from OCT images. Data analysis used the ANOVA test, followed by post hoc Tukey, Kruskal Wallis, and post hoc Dunn tests (significance of 5%).
Results: The SBS values presented similarly among groups, but the value of α showed statistical difference (p-value = 0.0124) between G3 and G5 with the others. Optical analyses indicated a melting on the enamel that suffered laser irradiation for G2 and G5 and crystal surface disorganization for G4. Sandblasting partially removes the melting of the laser effect (G3).
Conclusion: The sandblasting is a dispensable step for bonding lingual brackets, and the melting of the enamel after laser irradiation does not compromise the bracket adhesive resistance.
Clinical Relevance: The Nd:YAG laser became an interesting tool to prevent caries and decrease prevalence of white spot lesions in orthodontic treatments, without systemic effects in patients with genetic high risks of caries.