| Objective: As a common systemic disease, osteoporosis often has a serious impact on the quality of the alveolar ridge bone in implanting areas, so how to improve peri-implant bone quality in patients with osteoporosis and enhance the early stability of the implant becomes the focus of the researchers. Studies mainly focus on medical administration and preparation of the implant site. Parathyroid hormone (PTH), as a strong anabolic agent, can significantly enhance the trabecular thickness and increase the bone mineral density. The osteotome technique, on the other hand, has been widely used for preparing the implant site and improve the local trabecular bone density. However, cortical bone is also an important factor in the implant osseointegration. But the effect of PTH and osteotome technique on the implant osseointegration in cortex is rarely reported, so the aim of this experiment is to study the impact of PTH (1-34) administration and osteotome technique on the implant osseointegration in cortical bone of osteoporosis animal models by bio-mechanics test and histological observations, providing references for the future research and clinical application.Methods: 24 Japanese white rabbits were randomly divided into three groups, two of them were ovariectomized to set up the osteoporosis model, the other group was sham-ovariectomized. Before and after three months of the ovariectomy, 5th lumbar vertebrae and bilateral femoral neck bone mineral density(BMD) were measured respectively by dual-energy X-ray to monitor the situation of osteoporosis. After the completion of osteoporosis models, implant operation was performed on the proximal end of tibia cortex and the implant site was prepared by different ways between the two sides. On the left, after preparing the hole with gun-shaped drill and 2.0mm twist drill, 2.0mm, a set of spreader with a diameter of 2.2mm and 2.4mm were orderly used to compress the implant site to its final size. Each spreader was left for 1 minute inside the hole before the next was used and then implant was knocked in. On the right: after preparing the hole with gun-shaped drill and 2.0mm twist drill, a 2.4mm formation drill was used to complete the preparation and then implant was knocked in. Implantation site was selected in the center of the proximal tibia inner surface with an implant depth of 6.0mm. After implanting, ovariectomized animals were randomly divided into two groups, one group as the experimental group and the other as the negative control group. Daily subcutaneous injections (3 days a week) of 60μg/kg of PTH(1–34) or vehicle (saline and 2% heat-inactivated rabbit serum) were then administered to the respective groups. The sham-ovariectomized group, as the blank control group, was also inject with vehicle. Half of the animals in each group were sacrificed after 4 or 8 weeks and bone specimens with the implant area were harvested. Then the peak force value during the pull out of implant was tested and recorded by INSTKON1121 electronic universal material testing machine. Following that, bone specimens were cut into a 2mm thick sheet by a diamond cutter, along the long axis and through the diameter of the implant hole. After conventional embedding, decalcification, sliced and HE stain, the prepared slice was observed by an optical microscope with OLYMPUS cameras.Results: The results of dual-energy X-ray measurement of the 5 lumbar vertebrae and bilateral femoral neck bone mineral density showed that the average bone mineral density BMD of 5 lumbar vertebrae after 3-month of ovariectomized surgery (0.10133±0.003512 g/cm2) was significantly lower than the average before the surgery (0.14333±0.002517 g/cm2) (P <0.05), but the two measurements showed the bilateral femoral neck BMD change was not statistically significant. In the pull-out force measurement, at week 4, the non-compressed side of experimental group (63.033N), and the compressed side (41.733N) were significantly higher than the other groups (P <0.05). In addition, in experimental group the force was significantly higher for non-compressed side (P <0.05), while the same tendency was found in the other two groups, but the difference is not significant. At week 8, the non-compressed side(154.750N) and the compressed side (119.650N) of experimental group remained significantly higher than other groups (P <0.05). In experimental group and negative control group the force was significantly higher for non-compressed side (P <0.05), Blank control group had the same tendency with no significant difference.Considering of the observation of slice, at week 4, the porosity of peri-implant cortical bone: the experimental group >negative control group > blank control group, bone-implant contact range: the experimental group>control group>negative control group. In the experimental group, the cortical bone around the implant became extremely porous, continued with new formed trabecular bone along the implant wall extending towards the root end. Compared with the non-compressed side of experimental group, the compressed side showed an irregular formed trabecular bone with a scattered arrangement, larger gap and less connection. In other groups, the bone near the implant surface seemed denser and extended towards the root end . At week 8, in the experimental group, porosity of cortical bone is significantly reduced comparing to week 4, but still more than other groups. The cortical bone-implant contact of experimental group was further extended, higher than other groups. The histological difference between the compressed side and non- compressed side in the same group was not obvious, yet the bone near the implant surface extended towards the root end.Conclusion: Either in osteoporosis state or healthy state the implant osseointegration in the cortical bone has no significant differences, but the intermittent subcutaneous PTH (1-34) can significantly increase the osteoporosis cortical bone and implant contact area, thereby greatly improves the implant osseointegration in the cortical bone. The use of osteotome technique which compresses the cortical bone shows an adverse effect in consider of implant osseointegration, especially when an anabolic agent like PTH (1-34) was applied. |
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