Shear Bond Strength of Ceramic Brackets on Enamel Conditioned With CO2 Laser

Objective This study evaluated the shear bond strength of ceramic brackets on enamel conditioned using three methods: CO₂ laser, 37% phosphoric acid, and a combination of both, and analyzed the adhesive remnant index (ARI) to determine the amount of residual adhesive after bracket removal. Material and methods A total of 120 human premolars were stored in 0.2% thymol (Wt/vol) and divided into four groups (n=30/group): Group I was enamel conditioned with 37% phosphoric acid; Group II was irradiated with a CO₂ laser at 0.5W power; Groups III and IV, 37% phosphoric acid; and CO₂ laser was combined at powers of 0.5W and 3W, respectively. Brackets were bonded using Transbond Plus CC resin. Samples were light-cured for 15 seconds and stored (37°C, 24 h). ARI assessment: The amount of adhesive remaining on the enamel surface was determined using a scale of 0 to 3. The analysis of shear bond strength and ARI was performed using the Kruskal-Wallis Test. Results Statistical analysis revealed significant differences between some groups. Group III, which combined acid etching and CO₂ laser conditioning, showed lower bond strength than the control group, although not significantly. On the other hand, Group II (CO₂ laser only) showed the lowest bond strength and significant differences compared to the different groups, indicating that the exclusive use of laser is ineffective for conditioning. Significant differences were also observed between Groups III and IV, with Group IV exhibiting higher bond strength. However, the average value (GIII: 10.59±5.66 and GIV: 18.01±8.95 MPa) exceeded the recommended range (5.9 - 7.8 MPa). Regarding the ARI, Group II showed the lowest value, with significant differences compared to the other groups. Although Group IV had a higher ARI value than Group III, this difference was not statistically significant. Conclusions The combined use of phosphoric acid and CO₂ laser provides adequate bond strength for ceramic brackets, with a lower amount of residual adhesive, which facilitates their removal and reduces the risk of damage to the enamel. Although laser irradiation alone does not provide sufficient bond strength, its use in combination with 37% phosphoric acid optimizes retention and minimizes the negative effects associated with conventional acid etching.