| Objective There're scores years since the dental implant were applied to restore the missing teeth. As the biocoMpatibility of the implant was overcome by the use of titanium, many studies have focused on the connection between the bone tissue and implant success. The aim of this study, to begin with is to construct four mandibular FEMs (finite element models) with four different commercial screw-typed implant and standard mandibular teeth, to lay the foundations of further mechanics analysis. And then analyze in the different mandible under same loading, the stress distribution in mandible and implant, simulated the implant in the osteoporotic mandible.Materials and methods This study use HAUSER (made in Swiss projection to acquire the precise size of commercial screw-typed implants, apply the engineering program Pro/ENGENEER 2001 to build 3-demensioanal solid models, then transformed them to ANSYS format via IGES format; use ROLAND(made in Japanese) contact scanner to acquire the data of standard Chinese mandibular teeth, transformed it to ANSYS format via IGES format too; Open the 3-demensional model of mandible in ANSYS, which is constructed by helical CT previously. Combine the implants, the teeth and the mandible together in ANSYS, and then we can get mandibular FEMs, which contain four different implant and standard mandibular teeth, the implant in different osteoporotic mandible FEMs. According to the principle of St. Venant, the local loading methods can only influence stress distribution of local area and a small part adjacent it, and it can't influence the stress distribution far away from it. So we only choose the pivotal area of mandible, i.e. the area adjacent the implant, to process the finite element. According to the study of PHo, who use ultrasonic wave and strain micrometer to acquired the the cancellous's elastic module, the elastic modulus is 9500 Mpa in 1st grade cancellousbones, and 5500 Mpa in 2nd grade, 1600 Mpa in 3rdgrade, 690Mpa in 4lh grade. Then restrict the margin of mandible and apply loading respectively, coMpare the stress distribution and displacement variance in different bone.Results We constructed the mandibular FEMs, which contain the standard Chinese mandibular teeth and four different shape commercial screw-shaped implant, the units and the nodes were 1039,26585 in teeth ,324549,81202 in type A implant ,544089,885500 in type 6,1130845,20357 in type C and 569123, 105759 respectively in type D. and we also construct the mandibular FEMs which osteoporosis arranged from grade 1st to 4th ; simulated the stress distribution and deformation between implant and mandible in osteoporotic mandible. The result shows no matter what bones grade, the maximum strain in cancellous is local the neck of cancellous and surround the implant. The rule of strain distribution: peri-implant>middle of cancellous>margin of cancellous. The stress in implant is increasing from grade 1 to grade 4 bone. The maximum stress located the center of implant. The rule of stress distribution in implant surface is :neck>middle>root. The maximum stress (omax) in cancellous bone is 3.075lO-4Mpa,less than the intensity utmost ( OH ) of long bones.The stress of implant is 10.06x 10Mpa, under the yield utmost (o) of titanium evidencely. Conclution It's feasibility to establish the 3-demensinal FEMs of the mandible, which based on the data acquired from the projection of the screw-thread implant, scan the tooth by tridimensional scanner and mandibular data acquired by helical CT. The strains in cancellous is concentrating as the bone density is descending, but from the biomechanical opinion, the osteoporosis is foreign to the success of implant.
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