In Vitro Study Of Re-bonding Time Of Feldspathic Ceramic Restoration After Abscission

Objective:Bonding is an important step in restorations of dental defects, it is essential to the quality and long-term effects of the restorations. However, due to the complexity of the oral physiological environment and dental tissue structure,the adhesive has been subjected to all kinds of physical and chemical components,at the same time,the restorations have been subjected to the force in all directions in the exercise of function,all of the above could lead to the failure of the restorations.Once the restorations fall off,various physical and chemical compositions of the oral cavity directly acted on the exposed dentin surface,whether these components could effect the re-bonding strength of the restorations,has not been reported in the literature.In this experiment, we choose adhesive Multilink N and feldspathic porcelain Vita Mark II,to study the microtensile bond strength of Multilink N and the effect of saliva immersion time on the re-bonding strength after the restorations fell off through microtensile bond strength test,the purpose of this work was to evaluate the tensile bond strength of feldspathic porcelain restorations and to provide reference for the re-bonding time of clinical restorations.Methods:Collect 15 caries-free、defect-free third molars which were extracted between 1~6 months, embed the molars to CEJ level with self-curing plastic,remove the tooth tissue until 2mm above the CEJ,to make sure the exposed dentin surface is not less than 6×6mm2,prepare the consistent standard dentin surface under water polishing;Vita Mark II were sectioned into6 × 6 × 4mm3 cubes under the running water, prepare the consistent standard feldspathic porcelain surface under water polishing;Define the bonding area using double-sided tape with a 6×6mm2square hole in the middle,the bonding process is carried out in strict accordance with the instructions of adhesive Multilink N. Devide the 15 molars into 5 groups according to the different saliva immersion time randomly,3molars in each group. A:control group;B:immediatly re-bonding group;C:saliva immerse 1 d;D:saliva immerse 4 d;E:saliva immerse 7 d.Specimens in group B~E were tested by microtensile bond strength test, and the values were recorded, then re-bonding those specimens in accordance with the expecimental procedure of each group. The bonding specimens in group A and re-bonding specimens in group B~E were made into micro tensile specimens with cross-sectional area of about 1×1mm2,in order to carry out the micro tensile bond strength test,the fracture mode is counted,the structure of the bonding interface is observed,and both the thickness of the hybrid layer and the length of the resin tags were measured by SEM.Analysis theresults of each group using ANOVA with SPSS 17.0 statistical software.Results:In tensile bond strength test of the specimens in group B~E,there occorded only one mixed fracture,the rest all occored interfacial fracture;The value of the tensile bond strength was 23.24±1.62MPa;The microtensile bond strength decreased from group A to group E,cmpared with the control group, microtensile bond strength of the specimens in immediatly re- bonding group、saliva immerse 1d group and saliva immerse 4d group, the difference was not statistically significant; There were significant differences in microtensile bond strength of the specimens between saliva immerse 7d group and the control group. The proportion of interfacial fructure from group A to group E raised:A:62.5%,B:64.7%,C:71.4%,D:78.9%,E:86.4%. The formation of the hybrid layer and resin tag between dentin and feldspathic porcelain could be observed in all groups by SEM,the thickness of the hybrid layer and the length of the resin tags in each group has no sinificant difference.Conclusions:The tensile bond strength of Multilink N is at the requred level of the clinical dentin bond strength. The main fracture mode was interfacial fracture when bonding the feldspathic porcelain restorations using adhesive Multilink N,the integrity of the restorations was almost not affected. The feldspathic porcelain restorations bonding to the dentin usingMultilink N adhesive systems, could be cleaned and then re-bonded within 4 days after abscission,although the bond strength decreased,the difference was not significant;If the abscission occored 7 days, the bond strength decreased significantly,a new restoration was proposed to make.