Densitometric evaluation of skull and jaw bones after administration of thyroid hormones in rats

An investigation was performed by use of optical densitometry to observe the effects of different doses of thyroid hormone on bone density of skull and jaw bones and to evaluate the relationship between T3, T4, thyroid stimulating hormone (TSH) serum levels and bone density.

40 Sprague-Dawley rats were randomly divided into four groups with 10 rats in each (a control group that received 10 ml kg(-1) i.p. per day normal saline and three levothyroxine groups that received 5, 10, or 20 microg kg(-1) i.p. per day levothyroxine, respectively). Radiographs were taken of their skulls on days 3 and 16. At the end of the experimental period blood was drawn by intracardiac puncture and serum was analysed for thyroid hormones (T3 and T4) and TSH level. After that, optical density measurements were made on the radiographs of four selected points on the skull and jaw with a digital densitometer. Density measurements were analysed using the student's t-test, one way analysis of variance, Spearman correlation analysis and regression analysis.

Levothyroxine administration reduced bone density (P < or = 0.05) and increasing the dose of thyroid hormone produced a significant decrease of bone density (P < or = 0.05). The mandible was more susceptible to density changes compared with hard palate, skull and alveolar bone (P < or = 0.05).

Radiographs of the mandible can be utilized to characterize loss of bone density elsewhere. In addition this investigation indicated that optical densitometry is an inexpensive and low risk method for studying bone density.