| Objective: Many researches have confirmed that mechanical stimuli can promote the osseointegration,and it is of great significance in the formation and reconstruction of peri-implant bone.At present,most of studies are conducted to investigate the effect of stress on bone around dental implant by using the external loading device.The objective of this paper is to design two groups of implants with different profile,including full-thread and delete-thread,and to set up the different stress states and analyze their effects on surrounding bone.The paper is divided into two parts: the first part is an animal experiment that two groups of implants are inserted into the proximal tibial metaphysis of rabbits and then evaluate the bone formation around implant.The second part is a finite element analysis,which simulates the whole implantation process and analyses the von Mises stress distribution at implant-bone interface.Materials and methods: Part one: The thirty-two self-designed and machined implants made of Titanium were fabricated and then implant surface treatment technology of SLA was performed.The implants were divided into two groups:full-thread and delete-thread implant,according whether the fourth screw thread was remove,and then they were placed in bilateral proximal tibial metaphysis of rabbits under general and local anesthesia.The animals were sacrificed at 7 days,15 days,30 days and 60 days after surgery.Tibia blocks with implant were extracted and fixed,Micro-CT was used to evaluate bone around implants.The undecalcified tissue was immersed in fluid methyl methacrylate resin.Resin-embedded specimens including implants were sectioned along the long axis of the implant and the sections were ground and polished to make its surface appear like a mirror.Before SEM analysis,a novel acid etching methodology was introduced in this study in order to remove mineralized tissue and visualize the osteocyte.SEM analyses was performed for the evaluation of morphology and density of osteocyte in specific areas.Then,acquired data were analyzed by paired t-test and an ?-level of 0.05 was considered to indicate statistical significance.Part two: Two types of implants models were constructed in computer-aided design software.Meanwhile,the tibia segment was selected to be scanned by CBCT and the acquired image data was used to generate the bone model.Subsequently,the bone and implants model were assembled into finite element processing software.The material properties of bone used in this study were obtained based on the results of mechanical testing.The displacement load that allow implant rotate and move downwards into bone cavity was applied.Finally,the von Mises stress in peri-implant bone were recorded and analyzed.Results: Part one: In the animal experiment,Micro-CT results showed that there were significant differences in peri-implant bone between two groups of implants at 7 days,15 days and 30 days;SEM images indicated that differences of the density and morphological of osteocyte between two groups of implants at 7 days and 15 days were significantly observed.But the differences disappears in the other time groups.Part two: The surrounding bone within 0.75 mm from surface of implant in full-thread implant group exhibits higher von Mises stress than delete-thread implant.The bone volume fraction associated with different stress ranges in two groups of implants were varied.Conclusion: 1.Stress stimulation promotes bone formation around implants,the biological activity of osteocyte is closely related to the stress state,and it may responds well to the mechanical stimuli in the early stage of osseointegration,manifested in the changes of number and morphology of osteocyte.2.The two groups of implants have different stress stimuli on the peri-implant bone.This confirms that the removal of thread is an effective method to study the effect of stress on surrounding bone. |
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