Effects of Low-Dose Long-Term Sodium Fluoride Preventive Treatment on Rat Bone Mass and Biomechanical Properties

Abstract

Effects of fluoride on bone strength and cortical bone mass remain controversial. We compared 9-month, low-dose sodium fluoride (NaF) treatment with estrogen replacement therapy. Female Wistar rats 4.5 months old were divided into baseline, sham-operated (sham), sham-treated with NaF at 0.5 mg NaF/kg/day in drinking water, and ovariectomy (OVX), OVX treated with NaF and with estrogen. Bone mass was measured by dual X-ray absorptiometry (DXA) in vitro. Dimensions of the first lumbar vertebral body (L1) were determined by radiogrammetry. The right femur was processed undecalcified to obtain a midshaft cross-section to determine cross-sectional moments of inertia (CSMIs). L1 compressive test and left femoral torsional test were performed. OVX induced significant bone loss in L1 and femoral midshaft. Bone mass was increased to a greater extent in NaF-treated rats than in rats receiving estrogen replacement therapy. Femoral CSMIs in OVX rats, both L1 sizes and femoral CSMIs in NaF-treated rats, were significantly increased. Estrogen treatment had the least dimension expansion. OVX significantly decreased L1 compressive variables. There was no statistical difference in compressive parameters between NaF-treated groups and controls. OVX significantly increased femoral torsional strength but NaF treatment did not. Bone fluoride content was significantly increased after treatment with NaF. No significant difference in bone mineralization degree (ash and calcium) was found between treated and control rats. The discrepancy that an increase in bone mass and geometric properties in both trabecular and cortical bones by low-dose, long-term NaF treatment did not increase vertebral strength nor proportionally improve femoral strength indicated that the bone intrinsic biomechanical properties could be changed by NaF treatment.

Improved Bone Biomechanical Properties in Rats after Oral Xylitol Administration

“…These indicate a beneficial effect of xylitol on the mechanical properties of both the cortical and trabecular part of the bone, and negate the possibility that dietary xylitol, in spite of the increased bone mineral content, could cause such qualitative changes in bone that might compromise the mechanical properties of bone. In this respect the present results with xylitol differ from the results of recent rat model studies with fluoride [12,30] where the increased bone mass and geometric properties did not unambiquously lead to increased bone strength.…”

“…In fact, an increased mass does not always lead to better mechanical properties [11,12]. Therapeutic interventions monitoring increases in bone mass without regard to alteration in cancellous bone architecture have only limited ability to document antifracture efficacy of therapy [13].…”

Effects of Denosumab, Alendronate, or Denosumab Following Alendronate on Bone Turnover, Calcium Homeostasis, Bone Mass and Bone Strength in Ovariectomized Cynomolgus Monkeys

“…The magnitude of vertebral strength increments in the three DMAb groups appeared to exceed that which may have been expected from the modest gains in lumbar vertebral aBMD and L2 trabecular BV/TV, which may suggest some improvement in bone quality. Relationships between structural strength and bone mass were also examined as a test of bone quality, based on prior evidence that sodium fluoride therapy created a biomechanically unfavorable disconnect between these variables . In normal healthy animals, bone mass and bone strength typically exhibit a strong and linear correlation, which provides a benchmark for normal bone quality.…”

Long-Term Changes in Bone Mineral and Biomechanical Properties of Vertebrae and Femur in Aging, Dietary Calcium Restricted, and/or Estrogen-Deprived/-Replaced Rats

“…This test is appropriate for whole bone structures because the site of fracture is not predetermined by the testing procedure. Since the fractures all occur at the femoral shaft,( 24 ) where no trabecular bone is present, torsional strength is due to the cortical bone. It is a realistic loading mode producing a failure similar to clinical high impact fractures.…”