Effect of enamel surface pretreatment with different laser types and antioxidizing agents office-bleaching on the shear bond strength of orthodontic brackets

The aim of this study was to investigate orthodontics brackets shear bond strength (SBS) after pretreatment of bleached enamel surface with different laser types in comparison with antioxidants agent. A total of 150 sound human premolars were randomly assigned to into a control group which was experimental group (Group A) as bleached with 40 HP bleaching agent and not bleached (Group B). Then, both control and experimental groups were divided into five subgroups. Subgroup 1: no surface treatment Subgroup 2: treated by Nd:YAG laser (1 W, 100 mu s, 10 Hz) for 30 s. Subgroup 3: treated by Er: YAG laser (0.5 W, 230 mu s, 10 Hz, 5 mm distance) for 30 s. Subgroup 4: treated by CO2 laser (0.5 W, 10 Hz, pulse width of 1 ms) for 30 s. Subgroup 5: conditioned by 10 sodium ascorbate solution for 10 min. Then, the metal premolar brackets were bonded to conditioned enamel surface. All the specimens were debonded using the Universal Testing Machine. The data were analyzed by One-way analysis of variance and the Tukey's HSD. The SBS values of brackets bonded to bleached enamel in subgroup 1(no surface pretreatment) and 2(surface pretreatment with Nd:YAG laser) were significantly lower than subgroup 3(surface pretreatment with Er: YAG laser) and subgroup 4 (surface pretreatment with CO2 laser). The lowest SBS belonged to brackets bonded to bleached enamel in the subgroups 1 and 2, also the SBS values in subgroup 2 and subgroup 3 were significantly higher than subgroup 5. Pretreatment with Er: YAG and CO2 laser will improve SBS on bleached enamel surface more efficiently than surface pretreatment with Nd:YAG laser or antioxidant agent