| Since the long-term successful rate of traditional delayed loading of dental implant were rather high, the focus has changed into shortening the treatment period and enhancing certain esthetics factors and function during the transition period from raising the successful rate. The literature suggested that there is a critical threshold of micromotion between the bone-implant interface above which fibrous encapsulation prevails over osseointegation, thus the primary stability of immediately loading implants is thought to be the essential factor on osseointegation.At present, most biomechanical research focus on stress/strain in implant-bone interface after osseointegation, the results showed that, implant macro structure could affect the biomechanical transmission of implant-bone interface, but seldom about the primary stability of immediately loading implants, and how the implant shape affect the stability is unknown yet.The main aim of this present study, through the Pro/E and ABAQUS, was to analyze implant macrostructure (such as shape of implant in cancellous bone, shape of implant neck and taper) through finite element method by biomechanical consideration. And this study was also to make us a better understanding about the effect of implant macrostructure on the primary stability. At the same time, present study was to provide us the theoretical references for the clinical selection and design of immediately loading dental implant.In experiment 1, 3-D models of screw-type dental implants, superstructure and a segment of mandibular bone were generated by Pro/E software. Then using ABAQUS software, the implant-bone complex was meshed. The interfacial contact of bone and implant was defined to be a frictional contact. Using different size of unit to mesh interface for evaluating the accuracy of result, this provide the meshing standard and platform for further finite element analysis.In experiment 2, the micromotions of the finite element models with different implant shape in cancellous bone was computed using ABAQUS software. The results showed that, under vertical load, the displacement in neck region of step implant was the minimum(2.582μm), and that of taper implant was the maximum(4.813μm). In root apical region, the displacement of cylinder implant was the minimum(1.969μm), and that of taper implant was the maximum(2.636μm). Under horizontal loading, the displacement in neck region of cylinder implant was the minimum(11.961μm), and that of taper implant was the maximum(13.587μm); in root apical region, that of taper implant was the minimum(2.815μm), and wedge implant was the maximum(3.839μm). The results implied that implants with parallel profile had better primary stability.In experiment 3, the micromotions of the finite element models with different implant neck design were computed. The results showed that, the micromotions of neck 4 were the minimum, and those of neck 1 were the maximum under vertical loading and horizontal loading. The results implied that the existence of threads in cortical bone could raise the primary stability. Nevertheless, it raised the stress of cortical bone at the same time. Its effect on long-term stability of implant-bone interface needs further research.In experiment 4, the micromotions of the finite element models with different taper were computed. The results showed that, the micromotions were the minimum in 0°implant, and maximum in 6°implant regardless of loading directions. The results implied that the primary stability decreased with implant taper increasing.To conclude, horizontal load should be decreased in immediately loading implants and implants with parallel profile and threads in cortical bone should be selected.
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