BACKGROUND:Biomechanical compatibility is the necessary condition to ensure the stable osseointegration with implants that then can function over a long period; therefore, it is especialy important to get knowledge about distribution of stress and strain between the maxilary central incisor and its surrounding bone tissue. OBJECTIVE: Based on five different anatomical types of natural teeth, to study the regularity of stress distribution between the maxilary central incisor root and implant.METHODS: According to the five different anatomical types of natural maxilary central incisors, UGNX and ANSYS were used to set up three-dimensional finite element models (B1, B2, M1, M2, P1) for the implant and surrounding structures, which were under 100 N static load at angles of 0o, 30o, 45o, 60o, 90o with the long axis of teeth. Then, the stress distribution between the five kinds of maxilary central incisor roots and implants was analyzed. RESULTS AND CONCLUSION:Among the five different anatomical types, the equivalent stress for both the natural central incisor and implant were increased with the increasing of angles, and the implant had a higher raising trend. The equivalent stress for the natural tooth concentrated upon B1 for the maximum value and M1 for the minimum value; while the equivalent stress for the implant focused on the maximum value at M1 and the minimum value at M2. There was a gap of 2%-31% between the equivalent stresses for the natural tooth roots and a gap of 4%-21% for the implants. The stress distribution range for the implant was just smaler than that for the natural tooth roots. It implies that the bit force of implant and natural tooth is in positive proportion to the bite angles, and the bite force that implant can burden is smaler than that the central incisor can.

Objective: Objective To explore the role of the Er: YAG laser in periodontal surgery. Methods : Twenty patients with chronic periodontitis in two quadrants were selected for this study. One quadrant was subjected to pure periodontal flap surgery, whereas the other was subjected to flap surgery with an adjunctive Er: YAG laser. The preoperative and 3- and 6-month postoperative clinical parameters, including the probing depth, clinical attachment level, gingival recession, plaque index, gingival index and tooth mobility, were recorded. Results: Significant differences were not observed between the open flap surgery + Er: YAG laser-assisted treatment group and the open flap surgery group except for the gingival index after 3 months (0.36 ± 0.26 vs. 0.58 ± 0.29, t=3.831, P < 0.001) and 6 months (0.60 ± 0.23 vs. 0.83 ± 0.22, t=4.013, P < 0.001). Conclusion Er:YAG as an auxiliary treatment for periodontal flaps, does not significantly reduce the depth of periodontal pockets, nor could it improve the clinical adhesion level and the gingival recession, but it can improve the recovery of gingival inflammation and accelerate the healing of tissue.