| With the development of implantology, osseointegrated implants are accepted as one of the major treatment concepts for restoring partially edentulism in clinical protocols. However, anatomical limitations of space for implants or failure of implants to osseointegrate with bone may create a situation in which it would be desirable to connect implants to natural teeth in a FPD. The dissimilar mobility between osseointegrated implants and teeth formed the biomechanical dilemma in the tooth/implant-supported FPD. Many investigations about this restoration had been done, and the results showed that the design was doable. Many experts indicated that: some safeguard should be taken in design to protect the implants.There is no impersonal standard for applying of tooth/implant-supported restoration connected by precision attachment. so the three-dimensional finite element (FEM) approach was used in the research. This study adopted a 3D finite element (FE) approach which built the models of tooth/implant-supported restoration connected by precision attachment in type II (alveolar bone quantity changed)and III bone quality mandible with Solidworks2003 software, used compositive analysis software Cosmos/works2004 to calculate and analyse the stress of nature tooth, implant and surrounding bone, in order to expatiate the relation between bone quality and tooth/implant-supported restoration connected by precision attachment. This study will provide theoretical instruction for clinical work.An adult human mandible edentulous distal to the second premolar was selected as the partially dentate model in this study, and the second premolar hadn't been damaged. Implant a BLB implant(φ:4.0mm;L:13mm) at the position of 7 in mandible, built bridge which splinted the implant and 5 , non-rigid keyway attachment and implant system were designed at the mesial side, connected 5 and pontic by McCollum precision attachment(Nickel - Chromium alloy). This study contains two parts:Part 1: Supposed that the bone around implant was up to snuff, the bone around 5 was absorbed by different degree (0,1/4,1/3,1/2 of the length of 5 ), Built 4 models.Part 2: Supposed that the bone around implant and 5 was up to snuff, the quality of alveolar bone was different, type II (the depth of cortex was 1.6 mm) and III bone quality (the depth of cortex was 0.8 mm ).The dental tissue, PDL, alveolar bone, prosthesis attachment, and implant material properties were considered as homogeneous, isotropic and linearly elastic in the analyses, implant 100% osseointegrated to bone. After the model had been meshed, A static load of 100N (vertical; 30°inclined to buccal side or lingual side) was applied at the occlusal surface of 5 pontic, implant, to calculate the stress (maximal von Mises, the first principle stress) values in natural tooth, implant and the bone surrounding natural tooth and implant, to observe the distribution and variety of stress values.The results showed that: When loading vertically, the stress concentrated at the area of cortical bone contacted to natural tooth root, pressing stress major distributed in distal area of tooth and mesial area of implant, draw stress major distributed in mesial area of tooth and distal area of implant, and Von-mises stress also major distributed in this area. The stress in central section and apical part of root was comparatively equal.When loading 30°inclined to buccal side, pressing stress major distributed in lingual side of the tooth and implant, Von-mises stress also major distributed in this area. The draw stress major distributed in buccal mesial area of tooth and in buccal distal area of implant. The stress in central section and apical part of root was comparatively equal. Contrarily, when loading 30°inclined to lingual side, pressing and draw stress switched in the area of buccal and lingual side.With the absorption of the alveolar bone around tooth, the stress in root, lamina dura, implant, bone around implant (Von-mises, press sressing, draw stress) increased correspondingly, the Von-mises in the tip of tooth and implant increased more obviously than in the middle. The stress distribution of stress in type III bone quality models was similar to type II bone quality models. But the stress values at apical section of tooth and implant were larger than that in type II bone quality models. In addition, the stress concentrated obviously at the floor of precision attachment model that under vertical loading and the wall of precision attachment model that under sideling loading.According to the results above, we can get conclusion as follow:1. The models built by CT scanning and solidworks software were precise, experimental results were reliable.2. The stress values of the tooth, implant and their surrounding bone increased when their surrounding bone decreased by bone absorption when used tooth/implant-supported restoration connected by precision attachment. The stress increased more obviously around implants. So we should evaluate the condition of tooth carefully to ensure effect of this restoration in long time.3. We should take tought of the stress variety because of bone quality changed in edentulous patients who need implant restoration, measures to enhanced the density of bone would be useful for restoration. Some experiments for drug that can improve alveolar bone quality should be done to enhance the capability of endure loading for alveolar bone.
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