Biomechanics Optimum Design And Selection Of Dental Implant In Posterior Maxilla

With the outstanding advantages of the implant denture, the implant denture has been regarded as"the third teeth of human beings". At the beginning of the contemporary dental implant era, the patients with better bone quality and quantity have been listed as the indication. The anterior mandible was primary implant site because it demonstrated remarkably good results in long-term follow-up studies. Patients with poorer bone quality and less quantity of bone, especially in the posterior region of maxilla, have been excluded from implant treatment for a long time. Because implant treatment of the edentulous posterior maxilla occasionally meet with problems due to the lack of bone volume beneath the maxillary sinus cavity. Resorption of the alveolar process after loss of posterior teeth support can proceed either from the oral side or by expansion of the sinus cavity into the alveolar process. The stability of the implant can be reduced and if implant break through the mucosa, which can result to the failure of the implant. Different bone grafting techniques have been developed and orthognathic surgical procedures adapted to the special demands of implant surgery have meant that most bone problems can now be solved.The success of the dental implant should represent osseointegration with the bone. The implant should behavior better biomechanics compatibility except biocompatibility for better distribution of the stress in jaw bones. Excessive load on the interface of implant and bone caused by stress centralizing can induce the absorption of the bone around implant even result the failure of the implant. Lots of researches have demonstrated that the factors influencing implant biomechanics transmission of occlusal forces include implant material, macrostructure, surface treatment, prosthetic restoration design, connection design, and biomechanics characteristic of jaw bone et.al.Many of the studies about biomechanics characteristic of implant in posterior maxilla region were univariate, discrete and independent. And these findings were insufficient and inaccurate. The main aim of the present study, through the 3DSS structure light scanning techniques, Pro/E and Ansys Workbench DesignXplorer mechanical engineering optimum technology, to analysis the implant optimum selection in different situations systematically. And provided us the theoretical references for the clinical design and selection of dental implant in the sinus region.Experiment 1A maxillary segment in the sinus region with an implant and a superstructure was modeled using Pro/E, Ansys Workbench and Three Dimensional Sensing System (3DSS). The implant-bone complexes were assembled based on implant parameters by self-adapting assembled programme of Pro/E. Then the models were imported to Ansys Workbench software by bidirectional parameters transmitting of the two softwares. Self-adapting assembled 3D finite element analysis models of dental implant-bone complexes were rebuild and the accuracy of the models was also evaluated. The self-adapting assembled models provide the technical platform for further implant optimum design and analysis. Experiment 2Implant-bone complex models in experiment 1 were applied in this experiment. The vertical height of bone in sinus region was set as 12.00 mm. Implant diameter (D) and implant length (L) were set as input variables. D ranged from 3.00 mm to 5.00 mm, and L ranged from 6.00 mm to 16.00 mm. The Max EQV stresses in jaw bone and Max displacements in implant-abutment complex were set as evaluation targets. The results showed that larger implant diameter can improve the buccal-lingual stress distribution while larger implant length can improve the vertical stress distribution. Implant diameter exceeding 4.20 mm and implant length exceeding 9.50 mm are optimal selection for a cylinder implant in clinic, given that there is sufficient bone quality. Implant diameter is more important than implant length in implant selection and design.Experiment 3In this experiment, vertical height of bone in sinus region (P) was set as input variable. P ranged from 6.00 mm to 12.00 mm. Evaluation targets setting was as same as experiment 2. The results showed that P was apt to affect the cortical bone stress and implant stability under AX load. P should exceed 10.00 mm in the sinus region.Experiment 4In this experiment, implant length (L) was set as input variable. L ranged from 8.00 mm to 12.00 mm. Evaluation targets setting was as same as experiment 2. The results showed that L plays an important part in cancellous bone stress under AX load and have little effect on cortical bone stress and implant stability under BL load. Implant should just penetrate sinus floor by biomechanical and clinical consideration.Experiment 5In this experiment, implant diameter (D) was set as input variable. D ranged from 3.00 mm to 6.00 mm. Evaluation targets setting was as same as experiment 2. The results showed that D favored cancellous bone stress under AX load, as well as cortical bone stress and implant stability under BL load. When there is insufficient bone height, implant diameter should exceed 4.50 mm by biomechanical consideration.Experiment 6In this experiment, implant thread height (H) and thread width (W) were set as input variables. H ranged from 0.20 mm to 0.60 mm, and W ranged from 0.10 mm to 0.40 mm. The results showed that with the increasing of H and W, better stress distribution under AX load could be achieved, while there were little changes in the implant stability under both AX and BL loads. Thread height exceeding 0.40 mm and thread width exceeding 0.26 mm are optimal selection for a screwed implant by biomechanical consideration. Thread height is more important than thread width in implant selection and design.Experiment 7In this experiment, 3D finite model including maxilla, grafted bone and implant-abutment complex was created based on the modes in experiment 1. This model provides the technical platform for the optimum design and analysis of bone grafting in the sinus region.Experiment 8In this experiment, grafted bone height (T) and width (R) were set as input variables. T ranged from 1.00 mm to 6.00 mm, and W ranged from 5.00 mm to 10.00 mm. The results showed that with the increasing of T and R, better stress distribution under AX load could be achieved in the bone grafting in the sinus region. T exceeding 3.00 mm and R exceeding 8.50 mm are optimal selection by biomechanical consideration. R is more important than T in bone grafting in the sinus region.To sum up, when there is sufficient bone quality, implant diameter should exceed 4.20 mm and implant length should exceed 9.50 mm. Meanwhile, implant with diameter exceeding 4.50 mm is more suitable to the region with insufficient bone quality. In this condition, implant tip should just penetrate sinus floor. Implant thread height should exceed 0.40 mm and implant thread width should exceed 0.25 mm. In bone grafting, grafted bone height should exceed 3.00 mm and bone width should exceed 8.50 mm.