Age-related efficacy of parathyroid hormone on osseointegration in the rat

Aging is a physiological determinant that can distinguish the outcome of a pharmaceutical therapy to improve osseointegration of titanium implants. Here we examined the possible interaction of intermittent parathyroid hormone (PTH) and the age of the recipient on the parameters of osseointegration in a rat tibia implantation model.

Twenty female Wistar rats aged 8 months and 20 female rats aged 2 months received PTH at 60 microg/kg body weight or a vehicle by a subcutaneous injection three times a week. After 4 weeks, histomorphometric analysis of the peri-implant area was performed. The possible interaction of the two factors on 'bone volume per tissue volume' (BV/TV) and 'bone-to-implant contact' (BIC) was tested by two-way analysis of variance.

Based on data from the medullary compartment, two-way analysis of variance revealed that the effect of 'intermittent PTH' depends on the 'age of the recipient' when BV/TV is considered the dependent variable (P=0.04). Post hoc tests indicated that PTH leads to an increase of BV/TV of adult and young rats. However, when BIC was considered the dependent variable, no interaction was observed (P=0.14). PTH but not aging has a significant impact on BIC. In the cortical compartment, no effects of PTH on osseointegration were observed.

The findings indicate that treatment with PTH is more effective on the peri-implant bone regeneration in adult than in young animals, supporting the importance to consider the influences of age on the development of pharmaceutical therapies to increase the process of osseointegration.