Estrogen Deficiency-Associated Bone Loss in the Maxilla: A Methodology to Quantify the Changes in the Maxillary Intra-radicular Alveolar Bone in an Ovariectomized Rat Osteoporosis Model

Abstract

The effects of estrogen deficiency on bone characteristics are site-dependent, with the most commonly studied sites being appendicular long bones (proximal femur and tibia) and axial bones (vertebra). The effect on the maxillary and mandibular bones is still inconsistent and requires further investigation. This study was designed to evaluate bone quality in the posterior maxilla of ovariectomized rats to validate this site as an appropriate model to study the effect of osteoporotic changes. Forty-eight 3-month-old female Sprague-Dawley rats were randomly divided into two groups: an ovariectomized (OVX) group (n=24) and Sham-operated (SHAM) group (n=24). Six rats were randomly sacrificed from both groups at time points 8, 12, 16, and 20 weeks. The samples from tibia and maxilla were collected for micro computed tomography (μCT) and histological analysis. For the maxilla, the volume of interest area focused on the furcation areas of the first and second molar. Trabecular bone volume fraction (BV/TV, %), trabecular thickness (Tb.Th.), trabecular number (Tb.N.), trabecular separation (Tb.Sp.), and connectivity density (Conn.Dens) were analyzed after Micro CT scanning. At 8 weeks the indices BV/TV, Tb.Sp., Tb.N., and Conn.Dens showed significant differences (p<0.05) between the OVX and SHAM groups in the tibia. Compared with the tibia, the maxilla developed osteoporosis at a later stage, with significant changes in maxillary bone density only occurring after 12 weeks. Compared with the SHAM group, both the first and second molars of the OVX group showed significantly decreased BV/TV values from 12 weeks, and these changes were sustained through 16 and 20 weeks. For Tb.Sp., there were significant increases in bone values for the OVX group compared with the SHAM group at 12, 16, and 20 weeks. Histological changes were highly consistent with Micro CT results. This study established a method to quantify the changes of intra-radicular alveolar bone in the posterior maxilla in an accepted rat osteoporosis model. The degree of the osteoporotic changes to trabecular bone architecture is site-dependent and at least 3 months are required for the osteoporotic effects to be apparent in the posterior maxilla following rat OVX.

The effects of implant topography on osseointegration under estrogen deficiency induced osteoporotic conditions: Histomorphometric, transcriptional and ultrastructural analysis

“…The animals were subsequently allowed to develop osteoporosis over three months prior to implant placement. This period of time has been shown to be sufficient to develop osteoporotic conditions in this model [22].…”

“…After acclimatization for 2 weeks, the rats were randomly divided into two groups, sham-operated (SHAM, n=32) and ovariectomised (OVX, n=32). Ovariectomy was performed according to our previously established methods [15,22] where both histological and micro-CT analyses demonstrated successful induction of osteoporosis. SHAM group rats were also subjected to the same surgical procedure with an equivalent amount of fat tissue removed instead of the ovaries.…”

“…For SEM analysis of osteocytes, polished resin embedded samples were first acid etched with 37% phosphoric acid for 10 seconds then immersed in 5% sodium hypochlorite for 5 min and air-dried overnight [22,37]. The sections were subsequently coated with gold prior to SEM observation.…”

“…As there are significant differences in the embryological origin, ossification process and the response to osteoporotic conditions between long bones and craniofacial bones [20,21], the relevance of results obtained in a long bone model to the oral environment is questionable. We have shown that the bone quality in the posterior rat maxilla is negatively affected by estrogen deficiency induced osteoporotic conditions [22], and that the first molar site in the posterior maxilla is a suitable model for dental implant research [23].…”

Effect of icariin on fracture healing in an ovariectomized rat model of osteoporosis

“…The most common type of osteoporosis is the post-menopausal bone loss associated with ovarian hormone deficiency (36). Several previous studies report that estrogen is the most important hormone in maintaining bone mass and that a deficiency of this hormone is a major cause of bone loss associated with age in both genders (37)(38)(39). Notably, when the circulating estrogen level decreases, calcium in the bones rapidly decreases, and calcium loss occurs via an increase in its urinary excretion (40).…”