Comparison of lithium disilicate-reinforced glass ceramic surface treatment with hydrofluoric acid, Nd:YAG, and CO2 lasers on shear bond strength of metal brackets.

Abstract

To evaluate and compare the effects of different surface conditioning methods of lithium disilicate-reinforced ceramic on shear bond strength (SBS) of metallic brackets. Thirty-six lithium disilicate ceramic blocks mounted in acrylic resin blocks were assigned to 3 groups (n = 12): 9.6% hydrofluoric acid (HF); neodymium-doped yttrium aluminium garnet (Nd:YAG) laser; and carbon dioxide (CO2) laser. The glass ceramic surfaces were primed with a silane, and the brackets were bonded using a light-cured composite resin. SBS test was carried out in a universal testing machine at 0.5 mm/min crosshead speed until the brackets were debonded. The remaining adhesive was evaluated under a stereomicroscope in terms of the adhesive remnant index (ARI). The surface hardness was determined with a 100-gr force using a microhardness tester. Glass ceramic surface changes were evaluated using the scanning electron microscope. One-way ANOVA and post hoc Tamhane tests were used to compare microhardness values, and Kruskal-Wallis and Mann-Whitney U tests were used to analyze SBS values and ARI. The median and interquartile range of SBS values in 3 groups were 6.48 (1.56-15.18), 1.26 (0.83-1.67), and 0.99 MPa (0.70-2.10), respectively. Microhardness analysis revealed significant differences between the CO2 laser and intact porcelain groups (P = 0.003), without significant differences between the other groups. Group 1 exhibited the highest ARI. Neither CO2 nor Nd:YAG lasers resulted in adequate surface changes for bonding of brackets on ceramics compared with the samples conditioned with HF. CO2 laser decreased the microhardness of ceramics. Surface conditioning with HF resulted in clinically acceptable SBS values.