Alveolar process anabolic activity in C3H/HeJ and C57BL/6J inbred mice.

BACKGROUND: The purpose of this study was to characterize bone activity of the alveolar process in C3H/HeJ (C3H) and C57BL/6J (B6) inbred mice. Based on observations in other animal species, we hypothesized that the bone-formation rate/bone surface (BFR/BS) is greater in the alveolar process compared to the body of the mandible and that the bone anabolic activity is greater in the alveolar process of the mandible than in the maxilla. We also examined the alveolar process of C3H and B6 mice for the presence of secondary osteons. METHODS: Jaws from 17-week-old C3H and B6 female mice (N = 15/group) were harvested. Histomorphometric parameters were evaluated in sections from the alveolar process, each of which included at least one molar root. RESULTS: In C3H and B6 mice, BFR/BS was not significantly different (P >0.05) between the alveolar process and the body of the mandible. In C3H mice, BFR/BS was significantly greater (P = 0.05) in the mandible compared to the maxilla. BFR/bone volume (BV) was not significantly different (P >0.05) between C3H mandible and maxilla. In the B6 inbred mouse, BFR/BS and BFR/bone volume (BV) were not significantly different (P >0.05) between jaws. After analyzing 165 bone sections, we identified 25 secondary osteons. CONCLUSIONS: The surface anabolic activity was not different between the body and the alveolar process of the mandible. The surface activity was greater in the C3H mandible than in the maxilla. Although secondary osteonal bone remodeling existed in the C3H and B6 alveolar bone, this process was not a consistent finding.

Adaptations in the mandible and appendicular skeleton of high and low bone density inbred mice.

The appendicular skeletons of high [C3H/HeJ (C3H)] and low [C57BL/6J (B6)] density inbred mice have been shown to differ in morphology, mechanical properties, and cellular activity. The focus of the current study was to (1) characterize the mandibular bone formation rate (BFR/BS), bone mass, indentation modulus (IM), and hardness of C3H and B6 mice and (2) investigate the relationship of the mechanical properties in three skeletal sites: mandible, femur, and tibia. Specimens from 17-week-old female C3H and B6 (n = 15/group) mice were obtained. Mandibular bone mass was estimated from the lateral-view area (LVA) and transverse cross sections. BFR/BS was measured in the mandibular section distal to the third molar. In addition, bone blocks from the distal surface of the third molar and the femoral and tibial midshaft were obtained for mechanical testing. BFR/BS, cortical area, and LVA were greater (P < 0.001) in C3H mandibles. IM was approximately 2 GPa higher in the C3H mandible (P > 0.05), femur (P < 0.001), and tibia (P < 0.01). Mandibular IM was lower (P < 0.05) than the femoral and tibial IM within each inbred mouse. IM was not significant between C3H and B6 mandibles. However, the magnitude of the difference ( approximately 12%) in the mandible was similar to the difference in the appendicular skeleton. This mandibular bone phenotype is similar to that observed in the appendicular skeleton of these distinct inbred mice.

The development of bone mass and bone strength in the mandible of the female rat.

The present study provides baseline data for a number of mandibular growth dimensions, specially on bone mass and bone strength, that were collected between the 21st and the 180th days of postnatal life, which are intended as a reference for researchers designing experimental studies, specially on mandibular catch-up growth, and as an aid for clinicians who must evaluate results from published animal studies for validity and potential extrapolation to the human clinical situation. Fifty weanling female Wistar (Hsd:Wi) rats were fed ad libitum a diet previously shown to allow normal, undeformed mandibular growth. Five of them were randomly selected at different times between 21 and 180 d of life. Mandibular growth was estimated directly on the right hemimandible by taking measurements between anatomical points; mandibular bone mass (calcium mass) was estimated from the mg of calcium, determined by atomic absorption spectrophotometry, present in the ashes of the left hemimandible; and mechanical properties of the right hemimandible were determined using three-point bending mechanical test. Dimensions, bone calcium mass and bone strength of the female rat mandible increased linearly from day 21 to approximately day 90. Bone growth, as expected, was more than twice when assessed from bone weight than when derived from mandibular area, length or height when the parameters were expressed as the relative increase from the mean infant condition. The growth rate of the posterior part of the mandible (behind the third molar) was almost five times greater than that of the anterior part. The rates of growth of the studied parameters showed a marked decline after day 90. ANOVA indicated that no statistical differences were found between day 90 and day 120 values. It could be concluded that the female rat mandible attains its adult size, peak bone calcium mass and bone structural mechanical properties at some point between 90 and 120 d of postnatal life. Because of the extremely high positive correlation between mandibular bone calcium mass and both mandibular area and mandibular weight, it was possible to calculate the mandibular peak bone mass from the relations 7.69 mgCa/cm2 and 0.19 mgCa/mg bone.

Effect of protein-energy malnutrition in early life on the dimensions and bone quality of the adult rat mandible.

Morphological and biomechanical features of the mandible are negatively affected by protein-energy malnutrition, whose effects are apparently dependent on the time of life of application. The aim here was to investigate, in neonatal rats nursed by dams put on a protein-free diet to depress milk production and thus create a state of protein-energy malnutrition in the offspring, subsequent growth and long-term effects by analyzing mandibular dimensions and bone quality in adulthood. Pregnant Wistar rats were fed a 20% protein diet (control) or a protein-free diet (malnourished) to obtain normal or subnormal milk production, respectively. After weaning, the offspring (males) were fed a 20% protein diet for 70 days. The dimensions of their excised mandibles were measured directly between anatomical points; the geometry and material quality of mandibular bone were assessed by peripheral quantitative computed tomography. Pups suckling from malnourished dams weighed 49.4% of those suckling from control dams at weaning; the actual difference between control and malnourished pups was 25.1g, which persisted until day 91 of age, indicating the absence of catch-up growth. As with body size, the mandibular base length, height and area (an index of mandibular size) were significantly smaller in malnourished than control rats at the end of the study. The mandibular cortical area, volumetric cortical bone mineral content and volumetric cortical bone mineral density assessed by peripheral quantitative computed tomography were similar in both groups of rats at the end of the observation period, but there was a significant reduction in the cortical axial moment of inertia in malnourished rats at this time of postnatal life. These findings suggest that catch-up growth was incomplete in rats malnourished during the suckling period and that the adaptation of mandibular bone architecture to body growth was apparently insufficient to attain normal values, thus not allowing complete compensation in mechanical competence at the end of the study because of an inadequate spatial distribution of resistive material through its cross-section rather than qualitative or quantitative impairment of cortical bone.