[Effects of bond strength evaluation on different durations of adult permanent teeth and youth permanent teeth by using universal adhesives to dentin]

To compare the dentin bonding strength evaluation between adult permanent teeth and youth permanent teeth after treatment for different durations by universal adhesives.Ten adult permanent teeth and ten youth permanent teeth were selected for this study. The occlusal enamel layer was removed, and each tooth was cut into three pieces along the long axis. In total, 30 pieces of adult and youth teeth were prepared. The adult and youth teeth pieces were randomly divided into three groups and treated by universal adhesives for 10, 20, and 30 s. In this study, Scotchbond Universal (SBU) was selected as the universal adhesive. Slabs were treated by dual-cure resin cements. The specimens were tested by microshear strength test through a universal testing machine. Fracture modes were observed by a stereomicroscope. Other adult teeth and youth teeth were selected, two for each type, and treated and grouped in the same manner. Fluorescein (0.1% Rhodamine B) was dissolved in SBU adhesive, and the specimens were treated by the adhesives for 10, 20, and 30 s. Micromorphology of the resin protrusions on the adhesive surface was observed by laser confocal microscopy (CLSM).For the adult teeth, the highest micro-shear bonding strength was observed in the 20 and 30 s groups, and the values were higher than that of the 10 s group (P0.05). For the youth teeth, the highest micro-shear bonding strength was observed in the 10 and 20 s groups, and the values were higher than that of the 30 s group (P0.05). The micro-shear bonding strength in the 10 s youth teeth group was higher than that of the 10 s adult teeth (P0.05) and was same as the adult teeth treated for 20 s (recommendation time of material instructions) (P0.05). The main break patterns in different groups comprised adhesive failure fractures and several mixed failure fractures. No resin fracture mode was observed. CLSM revealed very few short resin protrusions in 10 s adult teeth group, whereas the number and length of resin protrusions significantly increased in the 20 s adult teeth group. The resin protrusions of the 30 s group were shorter than those of the 20 s adult teeth group. In different durations, the bonding interface in different youth teeth groups presented the same trend of change as the adult teeth. However, the number and length of resin protrusions in the 10 s group of youth teeth were all higher than those of the 10 s adult teeth group.In clinical practice, the bonding agent treatment duration shall be shortened appropriately for youth permanent teeth, and that for adult permanent teeth shall not be shortened to less than 20 s. On the whole, the bond strength of youth permanent teeth can achieve no significant difference with the adult permanent teeth.目的 应用通用型粘接剂Scotchbond Universal（SBU），比较在不同处理时间下对成熟恒牙与年轻恒牙牙本质粘接的粘接强度，探讨其应用于年轻恒牙的效果。方法 收集成熟恒牙与年轻恒牙各10颗，去除面釉质层，平行于牙体长轴将牙齿切为3块，获得成熟恒牙30块，年轻恒牙30块，各随机分为3组，自凝树脂包埋，分别采用通用型粘接剂SBU处理10、20、30 s，粘接后采用万能试验机检测其微剪切粘接强度，并在体视显微镜下观察粘接断面，确定断裂模式。另取成熟恒牙与年轻恒牙各2颗，同样方法分组，荧光素0.1% Rhodamine B溶解于SBU粘接剂中，分别处理10、20、30 s，粘接后采用激光共聚焦显微镜（CLSM）观察各组粘接面树脂突的微观形态。结果 成熟恒牙：20 s组及30 s组微剪切强度最大，二者间差异无统计学意义（P0.05），但均显著高于10 s组（P0.05）。年轻恒牙：10 s组及20 s组微剪切强度最大，显著高于30 s组（P0.05）。年轻恒牙10 s组微剪切强度高于成熟恒牙10 s组（P0.05），与成熟恒牙20 s组（材料说明书推荐时间）间的差异无统计学意义（P0.05）。成熟恒牙20 s组与年轻恒牙20 s组间差异无统计学意义（P0.05），而成熟恒牙30 s组粘接强度显著高于年轻恒牙30 s组（P0.05）。各组主要的断裂模式均为粘接材料断裂，极少数为混合断裂，未观察到树脂断裂模式。CLSM观察可见，成熟恒牙处理10 s后，牙本质表层处形成极少极短的树脂突；处理20 s，树脂突数量及长度显著增加；处理30 s，树脂突长度相对20 s有所减短。年轻恒牙在不同处理时间下，3组牙本质表层树脂突变化情况与成熟恒牙大致相同，但年轻恒牙处理10 s组较成熟恒牙处理10 s组树脂突数量及长度均有增加。结论 临床使用SBU时，年轻恒牙可适当缩短粘接剂处理时间，而成熟恒牙的处理时间不低于20 s。.