ABSTRACT
Objective:To study the prosthodontic design for the treatment of maxillary first molar mesio-lingual cusp defect with subfis-sue.Methods:A finite element model of maxillary first model,including mesio-lingual cusp defect with subfissue,periodontal support-ing tissue and a section of the maxilla was established by cone beam CT.Different prosthodontic designs for respective restoration and simulating different bite force were adopted,the Von Mises stress,maximum compressive stress and the crack distribution,J integral and the root displacement were analysed.Results:In the metal pile restoration model,the stress,JINT value and the equivalent stress and displacement of root were the smallest.With the increase of crack depth of the vertical and oblique fissue,the equivalent levels of stress (equivalent stress of J integral),the stress experienced by the dentin along with the peak of the maximum principal,increased signifi-cantly.Under 4 kinds of force direction and 3 repair methods,the equivalent stress peak value,J integral dentin stress,maximum prin-cipal stress peak value and dentin stress peak value of the cracks was 200 N,90°>200 N,45°>600 N,0°>200 N.Conclusion:High elastic modulus and all ceramic crown may lead to minimal equivalent stress,J integral,dentin equivalent stress and maximum principal stress.When subfissure is repaired,teeth fracture remains possible and any possible propagation may exist.The effect of later-al force on the crack and the dentin is greater than that of vertical force for crack expansion and tooth fracture.
ABSTRACT
The purpose of this study was to evaluate the effect of immediate or delayed composite resin filling on dentinal microtensile bond strength (microTBS) after applied the adhesive. The coronal dentin of human third molars was exposed. Single-Bond or One-Step was applied on the dentin surfaces, and composite resin were constructed immediately (group 1) or 5 min., 10 min., 15 min., 20 min. and 30 min. (groups 2-6) after an adhesive was applied. The specimens were sectioned and made bar-shaped. Each surface area of them was about 1mm2. The microTBS test was performed by EZ test. The results were analysed by One-way ANOVA and Tukey's test at 95% significance level. The results suggested that the microTBS of Single-Bond to dentin was decreased when the composite resin was constructed 20 min. and 30 min. after Single-Bond was applied. But the microTBS of One-Step was not affected by delayed composite resin filling.