Effect Of Estrogen Replacement Therapy On Osseointegration Of Titanium Implants In Osteoporotic Rats

Objective: To investigate the effect of estrogen replacement therapy on osseointegration of titanium implants in ovariectomized rats.Methods: Thirty six 32-week-old female SD rats were randomly divided into three groups, an ovariectomized group, a sham-operated group and an estrogen-replacement-therapy group. Pure screw titanium implants were placed in the proximal metaphyses of the tibiae at 12 weeks after ovariectomy surgery , and the rats in estrogen group were prescribed benzyl estradiol one day after implant surgery. Undecalcified sections with implants were examined histologically and bone histomorphometric parameters were measured to quantify the changes of new bone around implants at intervals of 4 and 12 weeks after implant surgery. Scanning electron microscope was also used to observe the formation of new bone around titanium implants .Results: 1. At 4 and 12 weeks after implant surgery, the weight of rats increased significantly in ovariectomized group compared with sham-operated group (p<0.01 ), while the level of serum estradiol significantly decreased( p<0.01 ) . Compared with ovariectomized group, the weight of rats in estrogen group decreased significantly(p<0.01) , while the level of serum estradiol significantly increased (p<0.01) . There were no significant changes of above two parameters between estrogen group and sham-operated group (P>0.05). 2. The results by light microscope showed as follows: At 4 weeks after implant surgery, the estrogen group and sham-operated group showed similar histological changes. In cortical bone area, the new bone was mainly formed by woven bone which was in direct contact with implants. In cancellous bone area , the thickness of interface bone lamella , the density of trabecular bone , and contact of new bone with implants were all greater in estrogen group and sham-operated group than those in ovariectomized group. At 12 weeks after implant surgery, the woven bone was substituted by lamellalike new bone in cortical bone area in all of three groups. In cancellous bone area, the interface bone lamella was thin, the density of trabecular bone and contact of new bone with implants were less in ovariectomized group compared with other two groups. 3. The results by fluorescence microscope showed as follows: At 4 weeks after implant surgery, the fluorescent intensity and the distance between two tetrocycline-labelled lines were both greater in estrogen group and sham-operated group than those in ovariectomized group. At 12 weeks after implant surgery, the fluorescentintensity in sham-operated group decreased dramatically, while the estrogen group and sham-operated group showed similar changes and only slight decrease occured in the two groups. 4. The results by scanning electron microscope showed as follows: Larger calcified crystals at interface in cortical bone area and thinner uncalcified bone collagen at interface in cancellous bone area were observed in estrogen group and sham-operated group compared with ovariectomized group. Other changes were similar to those observed by light microscope. 5 . The results of bone histomorphometry were as follows: At 4 and 12 weeks after implant surgery, all the bone histomorphometric parameters decreased significantly in ovariectomized group compared with sham-operated group (P<0.05 or P<0.01). All the bone histomorphometric parameters except cortical implant-bone contact rate and bone mineralization rate at 12 weeks were significantly increased in estrogen group compared with ovariectomized group (P<0.05 or P<0.01). While compared with sham-operated group, all above parameters except cancellous bone volume and bone mineralization rate at 4 weeks , which were significantly decreased (p<0.01), did not show any apparent changes in the estrogen group (p>0.05).Conclusion: 1. Experimental osteoporosis canblock bone osseointegration of titanium implants by decreasing the thickness of interface bone lamella, the implant-bone contact rate and cancellous bone volume .2. Estrogen replacement therapy can...