Evaluation of the Effect of Phosphoric Acid or Er: YAG Laser on the Shear Bond Strength of Orthodontic Brackets to Enamel Surfaces Followed by 980-Laser Assisted Bleaching: An In Vitro Study

The residual oxygen remained on tooth surface after bleaching may interfere with adhesion of brackets to enamel surface. This study aimed to evaluate the influence of phosphoric acid and Er: YAG laser as an etching technique on the shear bond strength (SBS) of orthodontic brackets to enamel surfaces after 980-laser-assisted bleaching.

A total of 84 human premolars were recruited in the present study. Samples were divided into 6 groups including conventional bleaching with conventional etching, conventional bleaching with Er: YAG laser etching, laser-assisted bleaching with conventional etching, and Laser-assisted bleaching with Er: YAG laser etching, without bleaching with traditional etching, and without bleaching + Er: YAG laser etching. Following thermocycling, the debonding of brackets was conducted using a universal testing machine. Scanning electron microscope (SEM) microscope evaluation and adhesive remnant index (ARI) scores were assessed. The comparison of SBS values between groups was carried out by means of a one-way analysis of variance, followed by post-hoc tests.

The non-bleaching with conventional etching group showed the highest SBS mean value (23.45 ± 5.16 MPa), whereas the conventional bleaching with conventional etching group represented the lowest SBS mean value (8.8 ± 3.83 MPa). In all groups, the most common type of failure was classified as either score 1 or score 2. No significant difference was observed in terms of SBS mean between the groups (P = 0.165); however, the average SBS of bleached teeth was significantly lower, compared to the non-bleached group (P = 0.000). Honeycomb structure and porosity were observed following Er: YAG laser etching on the tooth surface.

Increased bond strength of brackets was observed in bleached teeth following Er: YAG laser etching. Therefore, if necessary, bond the brackets on the same day of bleaching will be done, the application of Er:YAG laser as etching technique will can be recommended.