[Three-dimensional finite element analysis of effect of root canal taper and post on tooth stress distribution].

OBJECTIVE: To evaluate the effect of root canal taper and post on tooth stress distribution. METHODS: Three-dimensional finite element models of human mandibular first molar with root canals prepared with 35# K file, ProTaper and Profile were established. The tooth were restored with fiber-resin, stainless steel and silver amalgam posts respectively. A vertical load on tooth occlusal surface was simulated. Marc software was used to analyze and calculate the stress distributions in the tooth restored with three kinds of different root canal posts, especially the in the cervical part and root. RESULTS: Different tapered root canals had no obvious influence on stress distribution in all three different posts. Stress distribution of stainless steel post located at the cervical and middle part of distal root, the highest Von-Mises stress was about 45 MPa. Stress distribution of silver amalgam post located at the orifice of root canal and pulp fundus, the highest Von-Mises stress was about 16 MPa. Stress distribution of fiber-resin post had no obvious stress concentration. CONCLUSIONS: Fiber-resin post is the most ideal root canal post. Stainless steel post causes remarkable stress concentration in the root, which may raise the possibility of root fracture.

[Clinical study of repair the defect of immediate implant by acellular dermal matrix].

OBJECTIVE: To evaluate the clinical effect of acellular dermal matrix allograft in repairing the oral mucosal defect of immediate implant. METHODS: 51 cases underwent immediate implant surgery for 67 implants right after the teeth or roots extracted. The mucosal defect of implant areas were repaired by acellular dermal matrix. The basal membrane side of acellular dermal matrix was exposed to oral cavity, and another side was attached to the implant and alveolar crest surface. It was intercalated between mucosal flap and alveolar and fixed by iodoform pack or base plate. To understand condition of wound healing the patients were followed up from 4 months to 6 months after operation. The acellular dermal matrix closed wound and histological changes were observed. The implant was followed up months to 4 years. RESULTS: The wounds were completely healed in 54 implant areas, partially healed in 11 implant areas, not healed 2 implant areas. histological examination wasn't differentiation between mucous epithelium and graft epithelium. None of 67 implants showed deterioration in the follow-up of one year. It was no obvious sign of immune rejection. CONCLUSION: The clinical result of acellular dermal matrix in repair the mucosal defect of immediate implant is good, the advantages are not to affect the integration bone with implant, less operation trauma, good esthetics results.