Effects of ovariectomy on turnover of alveolar bone in the healed extraction socket in rat edentulous mandible.

OBJECTIVE: The number of patients with postmenopausal osteoporosis receiving dental implants because of edentulism is increasing. Since osseointegration around implants requires formation and maintenance of new bone, knowledge of how ovariectomy (OVX) affects turnover of mandibular and maxillary bone is required. In the present study, we investigated the effects of OVX on turnover of alveolar bone in the healed extraction socket of the rat left mandibular incisor. METHODS: The molars and the incisor on left side in 6-month-old Sprague-Dawley female rats (n=38) were extracted and left to heal for 4 months. Animals were then ovariectomized and killed at the time of OVX (baseline) (n=4), 6 weeks (n=10), 6 months (n=12) and 9 months (n=12) post-OVX. Changes in bone mass and bone turnover were assessed using static and dynamic histomorphometric parameters. RESULTS: Bone turnover was increased by ovariectomy (OVX) as reflected by increased static parameters of bone formation and resorption. The changes in dynamic parameters were not statistically significant. Cancellous bone volume/total volume (%) in the post-OVX group decreased more than that in the control group. CONCLUSIONS: Our results suggest that OVX increases the turnover of alveolar bone in the healed extraction socket of rat mandibular incisor, resulting in a decrease of cancellous bone volume with time.

Effects of lactation on alveolar bone loss in experimental periodontitis.

BACKGROUND: The development and progression of periodontitis are accelerated by various systemic conditions. The present study was designed to determine whether lactation affects alveolar bone loss in rat models of experimental periodontitis. METHODS: Sixty-two female Wistar rats were bred with male rats and divided into three groups that were fed diets containing 0.9%, 0.3%, and 0.02% calcium. They were divided further into two subgroups of lactating and non-lactating animals. An elastic ring was placed around the neck of the right mandibular first molar to induce periodontitis (experimental side) on day 32 after mating. The left first molar was not fitted with an elastic ring (control side). After the lactation period, bone mineral density (BMD) was determined, and a histologic examination of the interdental alveolar bone was performed. RESULTS: On the experimental and control sides, BMD decreased significantly according to the amount of calcium in the diet; however, the magnitude of this decrease was much greater in the lactating group. Histologic examination revealed that in lactating and non-lactating rats, the decrease in BMD was accompanied by a decrease in alveolar bone height on the experimental side, whereas similar results were not seen on the control side. CONCLUSIONS: Lactation could be a risk factor for alveolar bone loss, especially under conditions of calcium insufficiency. Increased systemic demand for calcium and an insufficient supply of calcium might enhance the development of alveolar bone loss in periodontitis.

[Effects of pregnancy, lactation and dietary calcium on alveolar bone loss].

Periodontitis is a local inflammatory disease mainly induced by periodontopathic bacteria including Porphyromonas gingivalis. This disease is characterized by the destruction of periodontal tissues including alveolar bone, which is accelerated by various local and systemic factors. In recent years, many investigators focused on the relationships between periodontitis and systemic diseases such as diabetes and osteoporosis. We are currently studying the effects of pregnancy, lactation and dietary calcium on the bone mineral density of rat alveolus. The results obtained so far showed that pregnancy and subsequent lactation decreased the bone mineral density, and could be the risk factors for alveolar bone loss, especially under the condition of Ca insufficiency or deficiency. Further studies are required to define the relationships between periodontitis and systemic diseases affecting bone metabolism.