Numerical Simulation Of Damage And Failure In Peri-Implant Alveolar Bone Under Impact Load

Implant denture is one kind of prosthesis which is supported by the implant when the osseointegration between implant and alveolar bone is formed. Implant denture can improve masticatory function significantly without uncomfortableness. So it has gradually become the major restoration to the dentition defect and edentulous. Osseointegration is the key to the success of implant denture, which can maintain the stability of implant and support the bite force. If the osseointegration and peri-implant bone were damaged, the implant would be loose or even fall-off. In the process of mastication, occlusal force is loaded on the implant in a quasi-static way and is transformed to the surrounding alveolar bone. The stimulation of the bite force is the important factor to maintain the stability and remodeling of alveolar bone around the implant.Implant denture may sometimes suffer from impact as in sports and physical training. Impact load is the strength that occur suddenly increases at first and then quickly disappear when the object collisions. The characteristics of the impact force is not only in short time action, but the load amplitude is higher than the quasi-static load. The damage to human tissue under the impact load is closely related with the reaction time and the impact force. When the pulse width of impact load is in the microsecond magnitude, load transmits in the form of stress wave in implant and alveolar bone, and the wave spreads and reflects along the composite structure of implant, implant-bone interface and bone tissue. When the alveolar bone tissue can’t change its structure to absorb the impact impulse, the interface will be separated and destroyed. Microstructure of the surrounding bone will also be damaged. The presented researches on implant biomechanics were focused on the analysis of stress on implant and bone in static load. But the report of dynamic load on implant haven’t been reported, especially the damage and destruction of the peri-implant alveolar bone under impact load.In this study, the finite element model of the trabecular bone microstructure was established based on the experimental animal. Load-time history curve from animal experiment was set in Abaqus software to simulated the impact load. The n the dynamic changes of the stress distribution in peri-implant bone under different load direction and load impulse were analyzed. The results of simulated analysis were compared with the changes of peri-implant bone structure of animal experiments in Micro-CT and histological VG staining study. Then the damage characteristics and failure mechanism of prei-implant bone under the impact load were analyzed, in order to provide theoretical guidance for clinical. All the study can be divided into four parts: 1. The finite element model of impact injury was established.The implants were inserted into the lateral femoral of rabbits, and the impact load was analyzed after a good osseointegration formed. Then the animal model of impact damage was built, and morphology changes of the peri-implant bone were observed. The finite element model(FEM) including microstructure of trabecular bone was established using the data of animal model acquired by Micro-CT scan.The experimental results show that: the microstructure of the trabecular bone at the bottom of the implant changes after impact load, and the high stress area is founded in the bone tissue of the implant bone interface, which may cause the damage of the interface. The FEM can reflect the spreading of the stress wave and the stress distribution of the trabecular bone, which prepared a reasonable model for further research. 2. The damage characteristics of bone around the implant under impact load.The simulation results were compared with animal experiments to verify the reliability of numerical simulation, and to obtain a finite element model which can accurately describe the dynamic characteristics of the implant and surrounding bone. Use the FEM to analyze the spreading of the stress wave, the stress distribution of the trabecular bone and the deformation situation of the bone under different conditions which contain load direction and load duration.The experimental results show that after the impact load, the stress changed in the cortical bone connecting with the implant firstly, and the stress wave spread from the neck to the peri-implant. The location and degree of bone injury is related to the direction and impulse of the impact load. When the load direction was vertical to the implant, the stress distribution of the peri-implant reached to peak value. When loading time increases, the bone tissue maximum stress also increases, and propagation time of stress wave is longer. The simulation results are similar to the damage area from animal experiment. 3. The failure mechanism of bone around the implant under impact load.Damage of bone tissue and implant bone interface is analyzed by finite element model which is using the stress-strain curve and the yield stress from the experiment. These results reveal the failure mechanism of impact load combined with the data of bone mechanical properties.The experimental results suggested that: the high stress area of bone tissue is mainly distributed in the bone tissue at the bottom of implant; the stress wave transmission and reflection also lead to the stress concentration on the bone tissue of the implant bone interface. This local high stress area appears trabecular bone fracture and bone interface failure, and the results of simulation analysis are consistent with the site of bone tissue injury in animal experiment. 4. A finite element model of mandibular molar implant was established which is used for predicting the impact damage of peri-implant bone.The finite element model with implant and mandible is built through above method for analyzing the occurrence and characteristics of the impact damage of alveolar bone under impact load.The experimental results suggested that: the cortical bone of implant neck and the cancellous bone at the implant bottom have stress concentration under the impact load. With the change of load impulse and the load direction, the stress distribution and value of cancellous bone from implant bottom become higher, and the stress concentration areas may lead to bone fracture of cancellous bone. It suggests that we should do a comprehensive inspection and assessment during the clinical diagnosis and treatment on the impact injury patients. Conclusion:1. The higher stresses were mainly occurred in the bone at neck region and button of the implant, which would bring about the fracture of trabecular. The damage of bone are related to the direction and impulse of the impact.2. The failure of osseointegration was caused by the high stress along interface between the implant and bone where the stress wave were reflected. The area where high stress occurred would be fracture in the numerical simulation according the experimental test result.3. The results of numerical simulation consistent with the results of animal experiment. The stress distribution and damage characteristics of the prei-implant bone under impact load indicate the reliability of numerical simulation. The results can provide reliable guidance for prediction and protective in clinical practices...