| Dental defect and dentition deficiency are frequently-occurring diseases for human beings. These diseases impair not only chewing, phonation, maxillofacial region development, periodontal tissue,but also human health and appearance. In dentistry, since ceramic Gingival Prosthesis has desirable characteristics of beauty, biocompatibility, wear resistance, lustre stability, good function, it is well known as a ideal permanent repair material for dental defect and dentition deficiency, and has been widely used for restoration of destroyed or missing teeth. In recent years, with the increasing number of adult orthodontic patients, ceramic prosthesis is commonly found in the adult patient mouth, thus, it is urgent to find a method of firmly bonding orthodontic brackets to ceramic restorations. Objectives: This study aims to evaluate the influence of integrated treatment of Nd:YAG laser irradiation and hydrofluoric acid (HF) etching on bond strength of brackets to porcelain using in vitro experiment.Methods: 102 metal ceramic Prostheses were divided into 6 treatments (17 samples per treatment) according to the different surface treatment methods: (1) A was untreated control, (2) B was etched by 9.6%HF for 2 minutes, (3) C was deglazed by grinding and then etched by 9.6%HF for 2 minutes, (4) D was treated with Nd:YAG laser irradiation (l5 Hz, 50 mJ, 0.75 w) and HF etching, (5) E, Nd:YAG laser irradiation (15 Hz, 70 mJ, 1.05 w) and HF etching, (6) F, Nd:YAG laser irradiation (15 Hz , 90 mJ, 1.05 w) and HF etching. Randomly choose one sample out of each sub-group for surface observation, and the other samples were bonded to the brackets. Divide every treatment into two sub-groups in term of their bonding mode. 3M Unitek TM bonding adhesive agent was used in sub-groups, A1, B1, C1, D1, E1 and F1; silane coupling agents and 3M Unitek TM bonding adhesive agent were used in sub-groups A2, B2, C2, D2, E2 and F2. Soak all samples in artificial saliva for 24 hours, take the temperature cycling test for 1200 times under 0℃and 55℃, measure the shear bond strength (the SBS) and tensile bond strength (the TBS), and then calculate the porcelain fracture rate. Statistical analyses were performed using SPSS. Results: Surface topography: a lot of inerratic cracks with the shapes of rhombuses and grid, and crater with a shape of circle were observed on the ceramic surface after treatment with energy parameters of 15 Hz, 70 mJ, 1.05w Nd:YAG laser irradiation and 9.6% hydrofluoric acid etching through SEM of 100 or 200 magnification, and there were also some small holes in these crack and crater. Further 500 or 1000 magnification showed a lot of concaves on the inner wall of the cracks. A 5000 magnification showed the concaves with diameter of 5-10μm can be observed on the inner wall of the holes, which had a diameter of 15μm.Non-silanated sub-groups: there was a significant enhancement of bonding strength after surface treatment (P<0.01). The SBS of brackets bonded to the B1 sub-group was significantly higher than those to the E1 and F1 sub-groups (P<0.05). Compared with the B1 sub-group, the D1, E1 and F1 sub-groups showed significant difference for TBS (P<0.05). Compared with the C1 sub-group, the E1 and F1 sub-groups showed significant difference for TBS (P<0.05). The mean SBS and TBS Nd:YAG laser irradiation and hydrofluoric acid etching were 7.5688±0.83325Mpa and 11.2075±0.99685MPa, respectively. Shear bond strength showed positive correlation with tensile bond strength.Silanated sub-groups: compared with the non-silanated sub-groups, silanated sub-groups showed significant increase in bond strength. There was a significant enhancement of bonding strength after surface treatment (P<0.01). The result showed there were higher TBS in E2 and F2 sub-groups than in B2 sub-group (P<0.01). The SBS of brackets bonded to the C2 sub-group was significantly higher than that bonded to the E2 and F2 sub-groups (P<0.05). Compared with the B2 sub-group, the E2 and F2 sub-groups showed significant difference for TBS (P<0.05). The mean SBS and TBS Nd:YAG laser irradiation and hydrofluoric acid etching were 10.4525±0.92502Mpa and 17.9150±1.10231MPa, respectively. Shear bond strength showed positive correlation with tensile bond strength.Porcelain fracture rate: bond failure used shear strength, the result showed there were higher porcelain fracture rate in C1 and F1 sub-groups than those in the other sub-groups (P<0.05). Porcelain fracture rates of C2 and F2 sub-groups were significant higher than those of the other sub-groups (P<0.05). Porcelain fracture rates of silanated sub-groups were significant higher than those of non-silanated sub-groups (P<0.01). Compared with the TBS sub-group, SBS sub-group showed significant difference for porcelain fracture rate. Porcelain fracture rate of non-silanated sub-group was 2.1%.Conclusion: .1. The use of Nd: YAG laser irradiation with the energy parameters of 15 Hz, 70 mJ, 1.05 w and the hydrofluoric acid with a concentration of 9.6%, which can evenly coarsen the porcelain surface, is an effective surface treatment method. A lot of inerratic cracks with the shapes of rhombuses and grid, and crater with a shape of circle were observed on the ceramic surface. Concaves with diameter of 5-10μm can be observed on the inner wall of the cracks and holes.2. Surface treatment could increase bond strength of metal brackets to porcelain. The appropriate energy parameter pulsed Nd:YAG laser and hydrofluoric acid could increase bonding with formation of composite resin. Shear bond strength showed positive correlation with tensile bond strength.3. Silane coupling agent could increase bond strength of metal brackets to porcelain. But only use silane coupling agent could not produce the effective bonding strength. A sequential use of silane coupling agent and surface treatment could provide adequate bonding strength. Appropriate energy parameters of Nd:YAG laser irradiation and hydrofluoric acid etching showed the highest value of shear bond strength (10.45±0.925MPa).4. Silane coupling agent could increase porcelain fracture rates, using energy parameters of 15 Hz, 70 mJ, 1.05 w Nd:YAG laser irradiation and hydrofluoric acid etching, without silane coupling agent could to provide adequate bonding strength, and tensile force was recommended to debond brackets in clinic.
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