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

Objectives To evaluate and compare the effects of different surface conditioning methods of lithium disilicate-reinforced ceramic on shear bond strength (SBS) of metallic brackets. Materials and methods 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-WhitneyUtests were used to analyze SBS values and ARI. Results 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 CO(2)laser and intact porcelain groups (P= 0.003), without significant differences between the other groups. Group 1 exhibited the highest ARI. Conclusion Neither CO(2)nor Nd:YAG lasers resulted in adequate surface changes for bonding of brackets on ceramics compared with the samples conditioned with HF. CO(2)laser decreased the microhardness of ceramics.