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We developed a noninvasive method to evaluate bone structural integrity. It is based on the measurement of the dynamic characteristics of the bone using sweeping sound excitation in the range of acoustic frequencies. The Quality Factor (a measure of material damping) has been used as an indicator of the tendency of the bone to fracture. Results of animal studies have supported this hypothesis since linear correlations were observed between bone density, quality factor, and impact strength. A vibration excitation in the form of an acoustic sweep signal is applied to a bone to measure the quality factor. Rat bones were tested, obtained from animals with osteoporosis age-dependent (tested in vitro) or ovariectomy-induced (tested in vivo), and compared with bones of healthy (control) rats. The change in damping was, on average, equal or greater to the change in density. Moreover, excellent correlation of the quality factor was obtained with bone fracture energy measured with an impact test. During a vibration cycle, the changing strain results in temperature changes due to the reciprocity of temperature and strain. Nonreversible conduction of heat due to the unequal temperature change results in entropy production that is enhanced due to the stress concentration about the voids associated with bone porosity. Damping is a measure of the production of entropy. Its measure, the quality factor, represents a potentially useful tool for monitoring bone integrity, which is deteriorating in diseases characterized by disruption of the trabecular architecture, such as osteoporosis. A computational model yielded results that are in good correlation with the experimental results.

After menopause, women lose postcranial and oral bone. Hormone/estrogen replacement therapy (HRT/ERT) reverses these losses. Whether alveolar crest height (ACH) change attributable to HRT/ERT occurs at specific sites within the alveolar processes or is generalized throughout the processes is unknown. The objective was to determine the pattern of ACH changes in women treated with HRT/ERT. The sample consisted of 49 healthy postmenopausal women, who received HRT/ERT for 3 years. Full-mouth vertical bitewing radiographs were taken of each patient. Measurements of ACH were made from the cemento-enamel junction to the alveolar crest on the digital images of dental radiographs. Postcranial bone mineral density (BMD) measurements of the femur and spine were made with dual energy x-ray absorptiometry. Measurements were made from baseline and year-three images. A mean ACH change was calculated for each patient. In addition, for each patient, the sites with the greatest, 2nd and 3rd greatest changes were determined. Measurements of ACH change were tested for correlations (r) with the BMD measurements. Over the 3-year study, the mean change in ACH had an average correlation of -0.24 with postcranial BMD change. The site of maximum ACH change had a correlation of -0.23 with BMD change, but the correlations dropped off rapidly for the sites with the 2nd and 3rd greatest changes (-0.14 and -0.12). The correlations for the site-specific changes were substantively weaker than were the correlations for generalized change. The results suggest that ACH change attributable to HRT/ERT is generalized and not site specific. In studies, of the effect of HRT/ERT on ACH, multiple ACH measurements should be made to minimize errors associated with site-specific measurements. The study was supported USPHS grant DE09861, with additional support from Wyeth-Ayerst Laboratories and Smith-Kline Beecham.