Biomechanical Research About The Effects Of Bone Quality And Quantity On Stress Of Immediate Implant Placement And Loading

With the development of implantology, osseointegrated implants are accepted as one of the major treatment concepts for restoring partially edentulism in clinical protocols. In order to get favorable bone-implant osseointegration ,traditional implantation need 4 to 6 months without loading. However, it is difficult to suffice patients for the long time of teeth missing. In 1979, Ledermann put forward theory of immediate loading. The practice of immediate implant placement and simultaneous immediate loading is gaining momentum in clinical practice and can be a very rewarding way to deliver implant therapy to our patients. So this technique has been the hotspot in implant dentistry.According to current opinions,the primary stability of the immediately implant placement and loading is thought to be the most important determining factor on immediate implant placement and loading. The literature suggested that there is a critical threshold of micromotion of the bone-implant interface above which fibrous encapsulation prevails over osseointegration. And, the tolerated micromotion threshold was found to lie somewhere between 100μm to 150μm. Data from the available literature suggest that several methods may improve the stability of the immediate implant placement and loading, such as choosing high quality bone type,placing implants with press-fit technique,choosing the screw type implants and splinting implants. Nonetheless, data from these studies are based mainly on clinical experience and limited human research. There is in defect of basic researches on how the outcome of the immediate implant placement and loading was influenced by the factors mentioned above. There is no impersonal standard for applying of immediate implant placement and loading in bone defect. So the three-dimensional finite element(FEM) approach was used in this research. This study adopted a 3D finite element(FE)approach which built the models of immediate implant placement and loading in maxilla with Hyperworks8.0 software, and used compositive analysis software ABQUS to calculate and analyze the stress of the implant and surrounding bone, in order to expatiate the relation between bone quality\quantity and the technique of immediate implant placement and loading. This study will provide theoretical instruction for clinical work.An adult human maxilla edentulous distal was selected as the partially dentate model in this study. A cylinder screw implant(φ:4.3mm;L:13mm)at the position of 1 in maxilla, covered by a restoration. This study contains two parts:Part 1: Supposed that the bone around implant was absorbed by different degree(1/4,1/3,1/2 of the length of implant ),Built 3 models. Part 2: Supposed that the bone quality around implant was different, type II(the depth of cortex was 1.6 mm)and III bone quality(the depth of cortex was 0.8mm).The alveolar bone, prosthesis attachment, and implant material properties were considered as homogeneous, isotropic and linearly elastic in the analyses. After the model had been meshed, A static load of 100N was applied, to calculate the stress(von Mises,p1,p3) values in implant and the bone surrounding the implant, to observe the distribution and variety of stress values.When loading vertically, the stress concentrated at the area of inner alveolar plates contacted to implant, and Von-mises stress also major distributed in this area. The stress in central section and apical part of root was comparatively equal.With the absorption of the alveolar bone around implant, the stress in implant and bone around implant (Von-mises, press-tress, draw- stress) increased correspondingly, the Von-mises in 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 t implant were larger than that in type II bone quality models.According to the results above, we can get conclusion as follow:1. The models built by CT scanning and Hyperworks software were precise, experimental results were reliable.2. The stress values of the implant and their surrounding bone increased when their surrounding bone decreased by bone absorption when used immediate implant placement and loading. The stress increased more obviously around implants. So we should evaluate the condition of surrounding bone around the extracting teeth 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.