Differences in permeability of microperoxidase and horseradish peroxidase into the alveolar bone of developing rats

Microperoxidase (small m.wt tracer) and horseradish peroxidase (large m.wt tracer) were used to investigate the existence of extracellular (between blood vessels and bone cells) and intracellular transport pathways in the alveolar bone cells of five-day-old rats. HRP directly penetrated the cytoplasm and nucleus of the osteocytes and osteoblasts, but MP did not. These findings suggest that HRP at high dosages is more toxic to bone cells than is MP, since the direct penetration of HRP probably results from alteration of plasma membrane permeability. If so, MP seems to be a more suitable tracer than HRP. The findings from MP tracing suggest that a main transport pathway of bone fluid exists between the external part of the unmineralized zone, which is located in the lacunar and canalicular spaces around bone cells, and the innermost edge of the mineralized matrix, which constitutes the lacunar and canalicular walls; in addition, minor pathways as accessory routes might diverge from the main pathway to go around the bone cells.     

Dental development, dental age and tooth counts

Emergence data on the 20 deciduous teeth and the first 29 permanent teeth were collected from 212 randomly selected urban Swedish children who were followed from birth to 18 years of age. The sex difference in the emergence of the deciduous teeth is less than one month, which is not statistically significant. Boys are consistently ahead of girls until the 17th deciduous tooth. From the 17th deciduous tooth on through most of the permanent dentition, girls are consistently ahead of boys. In the permanent dentition the sex difference ranges from 3 MO to 11 MO; these differences are statistically significant except for the 29th tooth. Reference data on dental age based on counts of 1-19 deciduous and 1-27 permanent teeth are tabulated and tooth emergence curves constructed. The tooth emergence curves can be used to express individual dental development in terms of standard deviation scores. Validity of dental age assessed by counts of permanent teeth is evaluated by a cross-sectional comparison with another sample of Swedish boys and girls. The mean difference between estimated age and chronological age is about one month in either sex. Precision of an individual estimate of dental development in terms of 95% confidence level (approximately equal to +/- 2 S.D.) varies from about +/- 4 months in the deciduous dentition to +/- 3 years in the permanent dentition. Assessment of dental development and dental age by means of tooth counts is a convenient and simple method, although it can only be applied at ages when emergence can be expected. It is especially useful in cross-sectional evaluations, as no serial data are required. In populations with a low incidence of caries the impact of such disturbing factors on emergence is correspondingly low, further increasing the validity of assessments of dental development based on tooth emergence.     

Management of the primary dentition in vitamin D-resistant rickets

Vitamin D-resistant rickets (familial hypophosphatemia) is a systemic disease secondary to defective renal-tubular reabsorption of phosphate. The major oral manifestations are spontaneous abscesses in a caries-free dentition. Pulpotomies or extractions were frequently described in the dental literature as the therapies of choice. This article presents a new prophylactic approach utilizing zinc oxide--eugenol pulpectomies and full crown coverage in an attempt to retain the primary dentition and prevent abscess formation.     

Effects of synthetic muramyl dipeptide on bone metabolism in the fetal rat

Synthetic N-acetyl-muramyl-L-alanyl-D-isoglutamine (MDP) stimulated the release of 45Ca from fetal rat long bones in culture for 48 h and also increased the number of osteoclasts per bone and the number of nuclei per osteoclast. It also increased calcium uptake in enriched populations of osteoclasts obtained by sequential collagenase digestions of newborn rat calvaria. This effect was observed after a 120 min incubation with 10(-6) M MDP. Effects of MDP on calcium uptake in osteoblasts were not consistently observed. No effects on cyclic AMP were noted in either osteoclast or osteoblast populations treated with MDP for periods from 1-120 min at 37 degrees C.     

The role of intracellular lysosomal enzymes in the autocellular-surveillance of unhydroxylated collagens in dermal and gingival fibroblasts

The turnover of unhydroxylated collagen was investigated in dermal and gingival fibroblasts derived from C57Bl/6J mice. Unhydroxylated collagen molecules were fostered by the inhibition of prolyl- and lysyl-hydroxylase by the addition of alpha, alpha' dipyridyl. Turnover of collagens was determined by single isotope continuous labeling, double-isotopic labeling, the use of lysosomal pH modulators, and proteinase inhibitors. These studies reveal that the turnover of unhydroxylated collagen is an extracellular event, in spite of the susceptibility of these abnormal structural and conformational proteins to proteolysis; the synthesizing cell does not utilize intracellular lysosomal enzymes as a means of modulating the quantities of non-helical unhydroxylated collagen as an intolerable post-translational error of protein processing.