| With the maturation of osseointegration theories and the improvement of implant materials, the success rate of implant rehabilitation has been improved, but implant failures were reported occasionally, including the fracture, loose, till the falling off. The one of main causes of implant failure is high load caused by stress centralizing, and the excessive loads on the interface of implant and bone, which induce the absorption of bone around implant. So, the success of dental implants needs the implants with better bio-mechanic compatibility except better biocompatibility, and stress on implants during mastication can be even, almost without concentration, and the maximum of stress and displacement is very low. Meanwhile, during the design of implants, the conduction and distribution of stress on tissue interface are important aspects should be regarded. With the loads on denture, whether the stress distribution on interface is reasonable or not will influence the formation and maintenance of osseointegration interface directly, then influence the success rate and long-term effect of implant-supported prostheses. Lots of research work has demonstrated that factors influencing stress distribution include implant itself of material, shape design and size, and out factors such as anatomy of bone, form of histology and quomodo of load. Therefore, when we are designing and choosing implants we should according to some bio-mechanic principle, which is the key to keep implant in bone safely and secularly. Now, there are so many kinds and shapes of implant systems that choosing which system is the question every implant clinical doctor will confront. In past papers, there are lots of research about implant shape, while, there are few profound and systemic research on bio-mechanics of implant thread. In this experiment, we used the Solidworks and Cosmos software, from bio-mechanic point, to study one aspect of implant shape—design of implant thread. With software we made up five different groups of models according to thread shape, angle, screw pitch and location of thread. Vertical and oblique concentrative forces of 30N and 300N were applied to the model, then we investigated stress distribution and displacement of implant with different designed thread under static load, to find out the characteristic of stress and displacement, the Von-Mises maximum stress values and maximum displacement values, to compare all the different designed models, to reveal the bio-mechanic influence of different designed thread of implant on interface of implant and bone, and to help clinical doctors choose implant systems and to help factories make implant better. In this research, the result was demonstrated by three-dimensional digital photographs and charts: three-dimensional digital photographs can reflect the characteristic of stress under different conditions, and the charts was used to indicate the Von-Mises maximum stress values and maximum displacement values of interface of implant and bone under all kinds of conditions. We looked into the section of three-dimensional digital photographs which across the center of implant to find out the data of maximum stress values and maximum displacement values, at the same time, we noted data of four points of implant (crest of cortical bone, junction of cortical and cancellous bone, midway between height 2 and apex of implant, and apex), and drew the charts of stress values, to compare the characteristic of stress of different models. According to the data and charts, we drew such conclusions as followed: In the models of symmetric thread, the thread with 60。angle and screw pitch as 1.0mm was reasonable whose maximum stress value was low and stress distribution was more even than others; In the models of asymmetric thread, the thread with plano-slope shape and 45。 angle was more reasonable according to bio-mechanic request, and we can consider to choose in clinic;The one which thread located on inferior 1/3 of implant was more advisable...
|
PDF Full Text Request