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Porous calcium polyphosphate (CPP) constructs of desired density were formed by sintering CPP powders. Articular cartilage was formed on these constructs in cell culture over an 8-week period with the resulting cartilage layer forming on the CPP surface and within the near surface pores thereby mechanically anchoring the cartilage to the CPP. The biphasic constructs so formed were implanted in sheep femoral condyle sites and left for short-term periods (3 to 4 months) or longer periods (9 months). Implant fixation within the condyle sites was achieved through bone ingrowth into the inferior CPP pores. The properties and characteristics of the as-in vitro-formed, short- and long-term implanted tissues were compared. The results indicated that such implants might be useful for repair of small subchondral defects. [ABSTRACT FROM AUTHOR]

B7-H3, a member of the B7 family of the Ig superfamily proteins, is expressed on the surface of the antigen-presenting cells and down-regulates T cell functions by engaging an unknown counter receptor on T cells. Although B7-H3 is ubiquitously expressed, its potential nonimmune functions have not been addressed. We found that B7-H3 is highly expressed in developing bones during embryogenesis and that its expression increases as osteob last precursor cells differentiate into mature osteoblasts. In vitro bone formation by osteoblastic cells was inhibited when B7-H3 function was interrupted by the soluble recombinant protein B7-H3-Fc. Analysis of calvarial cells derived from neonatal B7-H3 knockout (KO) mice revealed normal numbers of osteoblast precursor cells possessing a normal proliferative capacity. However, the B7-H3- deficient calvarial cells exhibited impaired osteogenic differentiation, resulting in decreased mineralized bone formation in vitro. These results suggest that B7-H3 is required for the later phase of osteoblast differentiation. Although B7-H3 KO mice had no gross skeletal abnormalities, they displayed a lower bone mineral density in cortical (but not trabecular) bones compared with WT controls. Consistent with the reduced bone mineral density, the femurs of B7-H3 KO mice were more susceptible to bone fracture compared with those of WT mice. Taken together, these results indicate that B7-H3 and its unknown counterreceptor play a positive regulatory role in bone formation. In addition, our findings identified B7-H3 as another molecule that has a dual role in the bone-immune interface. [ABSTRACT FROM AUTHOR]

Despite some studies correlating dental fluorosis (DF) and fluoride (F) concentration in dental enamel, no information is available about DF and dentin F concentration. Our objective was to determine the correlation between teeth F concentration and DF severity in unerupted human 3rd molars, and the correlation between dentin and enamel F concentrations in the same tooth. Ninety-nine 3rd molars were studied—53 from Fortaleza, Brazil (F water, 0.7 ppm), 22 from Toronto (1.0 ppm), and 24 from Montreal (0.2 ppm). DF severity was evaluated according to the Thylstrup-Fejerskov Index, while F concentration was analyzed by Instrumental Neutron Activation Analysis. DF severity varied between TF0 and TF4, while F concentration ranged between 39 and 550 ppm in enamel and 101 and 860 ppm in dentin. Our results showed correlation between dentin F concentration and DF (rS = 0.316, p = 0.001), but no correlation between enamel F concentration and DF (rS = 0.154, p = 0.133). No correlation was observed between dentin and enamel F concentrations in the same tooth (rS = 0.064, p = 0.536). [ABSTRACT FROM AUTHOR]

Objective: This study was designed to investigate the effects of estrogen alone or combined with two different progestins, norethindrone or norgestimate, on bone density and compressive mechanical properties in an aged rat model.Study Design: Twenty 11-month-old female Sprague-Dawley rats were sham operated (intact control) and 80 wee ovariectomized. Three groups of 20 ovariectomized rats were implanted with Silastic silicon rubber (Dow Corning, Midland, Mich.) capsules containing 5% estradiol (wt/wt) in cholesterol. All rats in the intact control (group 1) and the ovariectomized (group 2) and the first of the ovariectomized plus estrogen (group 3) groups were injected subcutaneously daily for 6 months with corn oil (vehicle). Two other groups of rats with estrogen capsules received daily injections of norethindrone (3 micrograms/rat/day) or norgestimate (1.5 micrograms/rat/day) in corn oil for 3 days out of every 6 days (interrupted progestin). The effects of these various treatments on bone mineral content and bone mineral density in the vertebrae were measured by dual energy x-ray absorptiometry. The L4 vertebral bodies were also tested to failure in compression.Results: The ovariectomized rats receiving corn oil alone had the lowest bone mineral density compared with intact controls. Estrogen treatment alone resulted in a lower bone mineral density than in the intact controls. In contrast, both interrupted progestin regimens resulted in vertebral bone mass index at the same level as the intact controls. Compression tests revealed that ovariectomized controls also had the lowest modulus of elasticity of all groups. However, unlike bone mineral density, estrogen alone resulted in mechanical properties similar to intact controls, whereas the vertebrae in both interrupted progestin groups had variable mechanical properties compared with the ovariectomized and intact control groups.Conclusions: We conclude that in this experimental model hormone replacement therapy with estrogen and an androgenic (norethindrone) or nonadrogenic (norgestimate) progestin result in similar bone mineral density and mechanical properties. In addition, both interrupted progestin regimens had a better effect than estrogen alone on vertebral bone density. [ABSTRACT FROM AUTHOR]

The effect of diet, age, and sex on the mineral content of primate bones was determined for free-ranging rhesus monkeys (Macaca mulatta) from the Caribbean Primate Research Center. Monkeys in this study were of known age and sex and had been provided with either a low protein (15%) or a high protein (25%) diet for most of their lives. Instrumental neutron activation analysis was used to assess bone mineral content. Results showed that diet had no significant effect on the bulk mineral composition of Ca, Mg, Br, and Cl in the bones. Of the minerals analyzed, only Na and Mn showed significant diet-related effects. The bone Ca content was found to be lower in females than in males when controlled for age. Finally, Ca content was found to be higher in young adults, lower at middle age, and higher in old age in both male and female monkeys. In conclusion, this study has shown that increasing protein content in the diet does not change the bulk mineral content of primate bones. The nondietary effect that Ca content of monkey bones is lower during middle age has not been previously reported. [ABSTRACT FROM AUTHOR]

The size of hydroxyapatite (HAP) crystals in calcified cartilage and cortical bone of the rat has been studied and compared with that of synthetic poorly crystalline hydroxyapatite (PCHA). Crystal size was determined by X-ray diffraction and selected-area dark field imaging, and their elemental compositions were determined by emission spectroscopy. The crystal size of cartilage, bone, and PCHA were found to be between 120 and 170 A in length by 50 A in width as determined by both X-ray diffraction and dark field imaging. Cartilage had a lower ash weight than bone but both have the same Ca/P ratio of 1.6. These findings, though in agreement with the X-ray diffraction literature, differ from observations made by conventional bright field electron microscopy. We conclude that mineral sites in cartilage and bone, which exist as platelike structures, are in fact aggregates of small 120-170 X 50 A HAP crystals. The consequences of these findings was discussed in view of crystal relationships with collagen and other macromolecules. [ABSTRACT FROM AUTHOR]

Formation of calcium pyrophosphate dihydrate (CPPD) crystals in native collagen gels represent an in vitro model system for the study of pathological cartilage calcification. The conditions under which CPPD forms in collagen gels have been determined. At low Ca X pyrophosphate product, CPPD forms directly. At high Ca X pyrophosphate product, CPPD forms via the amorphous intermediate calcium magnesium pyrophosphate (CMPP). Chondroitin sulfate (CS) inhibits formation of CPPD by both pathways, but apparently by different mechanisms. Direct CPPD formation is inhibited with low potency by CS, apparently by binding of Ca2+ ions. Indirect formation of CPPD is inhibited with high potency by CS, apparently by stabilization of the CMPP intermediate. Comparison of the inhibition of direct CPPD formation by the two glycosaminoglycan species occurring in cartilage proteoglycan showed that CS is a more potent inhibitor than keratan sulfate (KS), in agreement with the greater Ca2+-binding affinity of CS. The increase in KS/CS ration which occurs in human hyaline cartilage with aging may facilitate deposition of CPPD crystals by decreasing the exclusion of pyrophosphate anions. [ABSTRACT FROM AUTHOR]