Estrogen deficiency increases variability of tissue mineral density of alveolar bone surrounding teeth
Introduction
Estrogen deficiency leads to disproportionate bone remodeling by increasing bone resorption more than bone formation.1, 2 This altered bone turnover activity can result in net bone loss and reduction of bone quality that characterizes post-menopausal osteoporosis.3, 4, 5 While the effects of osteoporosis on decreased bone quality and increased fracture risk of long bones and vertebra are well established, the effects on jaw bone are less understood. Oral health status has a dramatic impact on the quality of life.6 If post-menopausal osteoporosis has significant oral consequences, then it is possible that quality of life can be compromised beyond the commonly associated skeletal fractures. Many studies have found osteoporotic effects on the onset and progression of periodontal disease and subsequent tooth loss7, 8, 9, 10, 11, 12 and in delayed alveolar wound healing.13, 14 Also, orthodontic tooth movement has been found to be more rapid, and subsequently more unstable, in the absence of estrogen.15, 16 These findings suggest that estrogen deficiency has a substantial effect on oral bone properties.
As tooth-bearing bones, the maxilla and mandible are arguably more complex than other bones. The functional demands of mastication on alveolar bone surrounding teeth increase the complexity of both structural makeup and subsequent mechanical properties. Significant regional variation in oral bone quality has been observed as the alveolar bone demonstrates higher rates of remodeling and subsequent decreased mineral density and mechanical property compared to bone more distant from teeth.17, 18 However, the specific effects of estrogen deficiency on the regional variation of oral bone quality have not been clearly elucidated.
Bone tissue mineral density (TMD) distribution has been shown to change significantly in the presence of disease states or clinical treatments that affect bone metabolism.19 Bone tissue is composed of individual cortical osteons and trabecular bone packets that are produced at different points in time. These heterogeneous compartments of bone matrix reflect bone turnover activity, mineralization kinetics and average bone matrix age.19, 20, 21 With untreated, disease-free bone as a reference, bone with high turnover activity has a higher proportion of less mineralized tissue and subsequent increased variability of TMD. Recently, radiographic imaging technology based studies have been able to describe the local variation in TMD using a histogram of gray level frequency distribution.22, 23, 24
The objective of this study was to investigate the effect of estrogen deficiency on TMD distribution of alveolar bone. We hypothesized that estrogen deficiency would amplify the regional variation of TMD distribution in mandibular bone. This hypothesis was tested by examining (1) intra-specimen regional variation for TMD distribution parameters and (2) inter-group differences of the TMD parameters between normal and estrogen deficiency groups. The TMD of mandibular bone was assessed using three-dimensional micro-computed tomography (3D micro-CT) images of sham surgery and ovariectomized rat models.
Section snippets
Materials and methods
Twenty 6-month-old Sprague–Dawley female rats were utilized for the following experimental protocol approved by the Institutional Animal Care and Use Committee of The Ohio State University. Ten rats were bilaterally ovariectomized (OVX) and 10 rats were subjected to a sham surgery (Sham) at Harlan Laboratories (Harlan Laboratories Inc., Indianapolis, IN, USA). The rats received an intraperitoneal calcein (25 mg/kg) injection 3 days prior to euthanization. At 2 months post-surgery, the rats were
Results
Calcein labels confirmed the presence of newly formed bone tissue and demonstrated remodeling in the alveolar bone region (AB). The total volume of the mandibles, after digitally removing the teeth, was significantly smaller for the OVX group (47.312 ± 3.109 mm3) than for the Sham group (51.235 ± 3.829 mm3) (p < 0.022). The AB and CB were successfully isolated using the 3D micro-CT image of each specimen (Fig. 1) and these volumes were not significantly different from each other (p = 0.469).
The heuristic
Discussion
We found that the alveolar bone region (AB) had significantly lower TMD values (Mean, Low5 and High5) but more variability (SD and COV) of TMD than the control bone region (CB), independent of estrogen deficiency. A state of estrogen deficiency amplified these regional differences for the variability measures and for the TMD of the less mineralized portion (Low5) while maintaining the TMD of the mean and highly mineralized portion (Mean and High5). These findings indicate that bone remodeling
Conflict of interest statement
No conflict of interests for all authors.
Ethical approval
This study followed the experimental protocol approved by the Institutional Animal Care and Use Committee of The Ohio State University (Protocol #: 2008A0145).
Contact point: OSU research foundation (1-614-292-4494, [email protected]).
Acknowledgements
The project described was, in part, supported by Grant Number AG033714 from National Institute on Aging (Kim, D.-G.). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the National Institute on Aging. We thank Ms. Michelle Carlton who scanned the specimens and Dr. Ramiro Toribio and Dr. Michael Knopp who gave us access to the micro-CT scanner.
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