EFFECT OF OVARIECTOMY ON THE LOCAL RESIDUAL RIDGE REMODELING

Statement of problem. Osteoporosis and edentulism are two disease proc esses that affect a large group of elderly people in the United States (24 and 25 million, respectively). These two diseases are independent of each other; however, they have several pathologic symptoms in comm on, such as reduction in bone mass. Purpose. The purpose of this study was to determine whether estrogen deficiency or its replacement thera py have any effect on the phenomenon of residual ridge remodeling. Mat erial and methods. Three animal groups were formed that consisted of s ix female Sprague-Dawley rats each. The two groups had ovariectomy and received either a vehicle solution or a daily dose (1.5 mu g/day) of 17 beta-estradiol delivered through osmotic pumps. The control group u nderwent sham surgery and received a vehicle solution. Animals were pa ir fed throughout the experiment. Unilateral molar extraction was perf ormed in the maxilla, which produced a suitable site for examination o f histologic characteristics and molecular biologic analyses. At the 4 -week postextraction period the bone remodeling activity was noted at the surface of the residual ridge in the control group. Results. The o variectomized group showed increased bone resorption activity, whereas ;the surface of the residual ridge alveolar bone of the ovariectomized and estrogen-treated group was covered by a layer of hyaline tissue. Poly(A)+ ribonucleic acid samples were isolated from the remodeling re sidual ridge tissues. Expression of alpha 2(I), alpha 1(II), alpha 1(I X), and alpha 1(X) collagens were examined by ribonucleic acid transfe r dot blots. Compared with the control group, ovariectomized animals s howed a reduction in bone formation with decreased expressions of type I and II collagens. In contrast, the estrogen-treatment group showed decreased formation oft)rpe I collagen with a much increased expressio n of type II collagen. Further examination of type II collagen formati on on the ovariectomized and estrogen-treated group by means of in sit u hybridization revealed the notable labeling by the type IIA collagen probe, which was associated with the surface tissue of the residual r idge alveolar bone. Conclusion. These findings suggest that estrogen d eficiency and its replacement therapy seem to affect the activity of r esidual ridge bone remodeling at the molecular level.