Immunohistochemical and ultrastructural evaluation of matrix components in mandibular condylar cartilage in comparison with growth plate cartilage in cartilage calcification insufficient rats.

Matrix components of growth plate cartilage and mandibular condylar cartilage were immunohistochemically analyzed in cartilage calcification insufficient (CCI) rats, a model for dwarf rats. Reduction in total tibial length, elongation of growth plate, and appearance of noncartilaginous regions in the growth plate were observed in CCI rats. Immunoreactivity for type I collagen and hyaluronic acid (HA) staining were observed in the noncartilaginous region. However, weak immunoreactivity was observed for aggrecan, collagen types II and X, and decorin in this region. Transmission electron microscopy indicated that the noncartilaginous region showed a loose network of thin collagen fibrils, indicating that HA is predominantly involved in capturing space of the noncartilaginous region in the growth plate. Meanwhile, the mandibular condylar cartilage in CCI rats also showed elongation of the cartilaginous region and had a noncartilaginous region, predominantly comprising thick collagen fibrils. The structural difference between the two types of cartilages in CCI rats may be due to the presence of the fibrous cell zone and the fibrocartilaginous nature of the normal condylar cartilage. Additionally, the reduction in mandibular length was relatively less than the reduction in tibial length. The outline of the condylar process showed only slight abnormality. These results suggest that the condylar cartilage compensated its growth by supplying the characteristic noncartilaginous region effectively and may adapt to severe structural changes observed in CCI rats.

Distributions of magnesium and sulphur in defect layers of incisor dentine in magnesium-deficient rats.

This study examined the mechanism governing the occurrence of defect layers of incisor dentine in Mg-deficient rats by X-ray microanalysis. Young (5 weeks of age) Wistar male rats were pair-fed semi-synthetic diets containing either control (0.05% Mg) (N = 8) or Mg-deficient (0.001% Mg) (N = 8) ingredients for 17 days. All animals were time marked with a combination of 0.1 mol nitrilotriacetato lead and 0.1 mol nitrilotriacetato zinc (2mg Pb/kg body weight) on days 0, 7 and 14 into incisor dentine. Blood samples were obtained on days 10 and 17 in order to measure Ca, Mg, P and alkaline phosphatase activity levels in serum; moreover, hypomagnesaemia and hypercalcaemia were confirmed. After the 17th day, rats were sacrificed humanely under anaesthesia and mandibular incisors were removed. Dentine formation of right mandibular incisors was assessed (time marking lines); furthermore, Ca, P, Mg and sulphur (S) concentrations as well as Ca/P molar ratio were determined in left mandibular incisors based on contiguous measurement points at 2 microm intervals from dentine pulp to dentine of the lingual aspect via X-ray analysis. Additionally, proteoglycan distribution was observed in other Mg-deficient rat dentine. These findings demonstrated decreases in body weight, incisor formation and incisor length in Mg-deficient rats. Mg and S levels increased in the defect layers, whereas proteoglycan decreased. This phenomenon was possibly attributable to condensation of Mg and S contents consequent to decreased dentine formation during Mg-deficiency and a transient increase in Mg due to transport of Mg as a result of inhibition of cell proliferation in soft tissues.

[The specificity of bone resorption process in the maxilla and the mandible].

The jaws comprise the maxilla and the mandible which is a tooth-bearing bone. The part of them which supports and protects the teeth is well known as an alveolar bone. In an experimental model of alveolar bone resorption, bone resorption was obvious in the cancellous bone during the early period of the experiment and then the cortical bone was seen to resorb. However, the contour of mandible, the alveolar bone proper and thin layer of bone which surrounds the mandibular canal still remained. These results suggest that the process of alveolar bone resorption is related to the mechanical forces induced by the occlusal function of the tooth.

Elderly women with oral exostoses had higher bone mineral density.

We examined the relationship between two opposite phenomena in elderly bone, bone loss (osteoporosis) and excessive bone formation (oral exostosis). We recruited, randomly, 44 female subjects without any conditions known to affect bone metabolism. The subjects were examined for exostosis, and bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry. The Z score of the BMD was calculated; this is the deviation from the weight-adjusted average BMD of each age. Subjects with palatal tori ( n = 15) had a higher femoral BMD than controls ( n = 14) (0.580 +/- 0.213 vs -0.271 +/- 0.182; P = 0.0054). The subjects with palatal tori ( n = 12) also had a higher BMD than controls ( n = 12) at the radius (0.417 +/- 0.235 vs -0.533 +/- 0.294; P = 0.0194). In addition, subjects with mandibular tori ( n = 13) had a higher femoral BMD than controls ( n = 14) (0.569 +/- 0.242 vs -0.271 +/- 0.182; P = 0.0097). These results suggest that some common mechanisms are involved in the elevation of skeletal BMD and the occurrence of oral exostoses.