| Background & ObjectiveLight-cured composite resins are commonly used in the treatment of caries or pulpitis. The tensile bond strength (TBS) and the adaptation take very important roles in composite resin restorations. At present, 35%～37% phosphoric acid solution is the routine method to condition enamel surface, but there is no reliable method for the dentine conditioning. Though the etching technique greatly improved the bond strength of resin to enamel, there were still some deficiencies. Firstly, phosphoric acid might stimulate pulp tissue and gingival tissue in the etching process. Secondly, in the class Ⅵ restoration of incisors, the bond strength was not enough to chew the hard food and the microleakage might cause the secondary caries around the fillings, which lead the treatments to failing. Thirdly, the etching technique would not make well bond strength and adaptation when it was used to condition the dentine surface in the restoration of the cervix wedge-shaped defect and the root caries. Recently the lasers, especially pulse Nd:YAG laser, have been widely used in the oral disease treatments, such as soft tissue cutting, pit and fissure sealant, dental desensitization, root canal treatment, superficial caries treatment. It has been reported that the laser irradiation can rough the surface of dental hard tissue. The irregular honeycomb or crater were observed in the lased area under scanning electronic microscopy (SEM). The smear layer was removed and the orifices of dentinal tubules were sealed or partly sealed. The roughness by the laser might offer more space for the penetration of the acrytic monome and contribute the formation of resin process. However, whether it could obtain high bond strength and well adaptation need further studying.In this study, the suitable combination of pulse Nd:YAG laser parameters for enamel or dentin conditioning were selected first and the comparison between laser irradiation and other conditioning methods was made on TBS, the adaptation and the SEM surface morphology, to evaluate the effect of pulse Nd:YAG laser on bonding and the feasibility as a conditioning method of enamel or dentine.Material & method Seventy freshly extracted caries-free human premolars were selected. The teeth were from the patients(Age: 10-20 years old) who underwent orthodontic treatments. They wererandomly divided into ten groups, five enamel groups and five dentine groups, seven specimens each group. The buccal surfaces were prepared and the enamel or dentine surfaces were respectively conditioned by pulse Nd:YAG laser with five parameter combinations. Then the Single Bond primer was brushed onto the surface and the Restorative Z100 resin was applied. After 24 h under 37℃, TBS was determined.Another 81 human premolars were used in this step and the requirements were the same as mentioned above. The teeth were divided into nine groups with nine teeth each group. There were five enamel groups and four dentine groups. The enamel surface was conditioned respectively with 37% phosphoric acid gel, pulse Nd:YAG laser(ink added), laser(ink added) + acid gel, acid gel + laser(ink added), no treatment. The dentine was conditioned respectively with 37% phosphoric acid gel, pulse Nd:YAG laser, 10-3 solution, no treatment. Of each group, seven specimens were used for TBS test and two for interface SEM examination. After TBS test, the debonded fracture patterns were observed macroscopically and examined under SEM.60 human premolars were selected as mentioned above. One class Ⅴ cavity was prepared in buccal surface of each tooth. Half of gingival margins were finished approximately 1 mm below cemento-enamel junction(CEJ) with cavity 4 mm long, 4 mm wide and 2 mm deep, and half approximately 1 mm above CEJ(4 mm × 2 mm ×2 mm). The sepecimens were divided into six groups (ten specimens each group) and each group was subdivied into two groups, for occlusal margin and gingival margin of each cavity were examined respectively. The occlusal margins were conditioned with six differe... |
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