Abstract: Objective To investigate the promoting effect of parathyroid hormone on implant osseointegration in aged rats and its mechanism. Methods Forty-eight aged rats (22-month-old) were divided into the elderly group and the parathyroid hormone group accorded to the random number method, with 24 rats in each group. Twenty-four adult rats (12-month-old) were used as control group. Three groups of rats were implanted with titanium nails in the left tibia. Rats in the parathyroid hormone group were injected intraperitoneally with parathyroid hormone (20 μg/kg, qod), and rats in the control group and the elderly group were intraperitoneally injected with the same amount of normal saline for 8 weeks. The maxillary and tibia bone mineral densities were measured by dual-energy X-ray absorptiometry. Eight weeks after implantation, the bone-to-implant contact ration (BIC), trabercular area (TA), thickness of cortical bone (TCB), average trabecular width (TW) and combined bone width (CBLW) were measured. The alkaline phosphatase (ALP), osteopontin (OPN), osteocalcin (OCN) and interleukin-6 (IL-6) mRNA levels in bone tissues around the implant were detected by real-time quantitative polymerase chain reaction (qPCR). Results Before implantation, compared with the control group, the bone mineral densities of the maxilla and tibia were decreased in the elderly group and the parathyroid hormone group (P＜0.05). After 8-week implantation, compared with the elderly group, the bone densities of maxillary and tibia in the parathyroid hormone group were increased (P＜0.05), the values of BIC, TA, TCB, TW and CBLW were increased (P＜0.05), the levels of ALP,OPN and OCN mRNA in the bone tissue around the implant were increased (P＜0.05), and the IL-6 mRNA level was decreased (P＜0.05). In the control group and parathyroid hormone group, the implant bone was well combined. In the elderly group, the implant bone was poorly coupled. Conclusion The bone density of aged rats is reduced, which affects the osseointegration of implants. Parathyroid hormone can increase bone mineral density in old rats and promote bone remodeling.

Key words: dental implantation, endosseous, parathyroid hormone, bone density, rats, Sprague-Dawley, old age, implant titanium nail