Radioautographic study of the incorporation of (3H)-choline into the phospholipids of secretory ameloblasts and enamel of normal and essential-fatty-acid-deficient rats.

(3H)-choline, a precursor for phosphatidylcholine (PC) and sphingomyelin (SM), was injected into rats killed after 4, 24, 48, and 96 hrs. Radioautography carried out on malachite-green/aldehyde-fixed tissues demonstrated that labeled choline was incorporated into cells and further released into the extracellular matrix. In predentin, labeling decreased rapidly, whereas in dentin, silver grains formed a stable band. In contrast, labeling was still high at 48 and 96 hrs in secretory ameloblasts as well as in the forming enamel. This indicates that ameloblasts are actively involved in the synthesis of membranes. Membrane remnants of the ameloblasts could be released into the forming enamel. In rats fed with an essential fatty-acid-deficient (EFAD) diet for 42 days, (3H)-choline uptake was delayed and reduced in pulp cells and odontoblasts, and consequently the migration of labeled phospholipids into dentin. The influence of the EFAD diet on secretory ameloblasts was limited. No difference was detected between normally fed and EFAD-fed rats in the forming enamel.

Effects of essential fatty acid deficiency on rat molar pulp cells.

In rats fed an essential fatty acid deficient (EFAD) diet, either during pregnancy (DN) or for 4 wk postnatally (ND), the cell density in the central part of the pulp increased about two- and threefold, respectively, of that in rats who had received a conventional diet containing sunflower oil. Cells were especially numerous around capillaries. The cell density was also increased twofold in the subodontoblastic layer in the outer part of the pulp, cells being smaller in ND compared with DN. In contrast, the odontoblasts were reduced in height, and the Höhl cells formed a thin layer in EFAD rats. This emphasizes some aspects of pulp specificity which reacted differently from odontoblasts. We suggest that the function of killer cells which normally destroy cells at the periphery of the pulp may be impaired by the diet, leading to cell accumulation.

Lipids in predentine and dentine.

Using two histochemical methods, malachite green-aldehyde and iodoplatinate, phospholipids were visualized in the predentine of rat incisors in the spaces located between collagen fibers and in dentine as needle-like structures located along individual or groups of mineralizing collagen fibers. The same staining pattern was seen with phospholipase A2-gold. Autoradiographic investigation using 3H choline as labelled precursor, visualized the incorporation of membrane-associated and extracellular choline-containing phosphatidyl choline and sphingomyelin. The cell and membrane-associated labelling decreased gradually between 24 and 4 days, whereas incorporation of the labelled precursor as stable extracellular matrix component was seen in dentine. In addition to these investigations, pharmacologically induced (suramine) and genetically (Krabbe's disease) lysosomal storage pathology was investigated. Defects due to lipid metabolism alterations were seen in predentine and/or in dentine. The major differences visualized here between the non-mineralized and mineralized compartments and interactions between phospholipids and proteoglycans, support the view that phospholipids as matrix components play an important role in the mechanisms of dentine formation and mineralization.

Les Fractures mandibulaires : a propos de deux observations

Les Fractures mandibulaires representent 15 pour cent des fractures squelettiques; 70 pour cent des fractures de la face. Elles predominent chez l'adulte jeune (40 pour cent); notamment de sexe masculin (80 pour cent). Les circonstances de survenue sont; par ordre de frequence; les accidents de la voie publique; les rixes; le sport; les accidents de travail. Le traitement orthopedique consiste en une reduction puis une contention par blocage inter-maxillaire