Glycosaminoglycans of predentin, peritubular dentin, and dentin: a biochemical and electron microscopic study

Localization of sulfated sialic acids in the dentinal tubules during tooth formation in mice

Lectin-like properties of the major enamel protein amelogenin suggest that it binds to glycoconjugates in dentinal tubules released at the dentin-enamel junction (DEJ) during enamel formation. Therefore, a detailed mapping of glycosylation in dentinal tubules during tooth formation was undertaken using histochemistry and lectin-binding assays. The tubular content exhibited sialidase-susceptible gamma-metachromasia with Toluidine Blue (pH 2.5) and staining with Alcian Blue (pH 1.0). The presence of sulfate groups was confirmed by benzidine reactions (Bracco-Curti's and tetrazonium assays). Alpha2,3-, alpha2,6- and alpha2,8-sialidases entirely abolished staining with the benzidine reactions. The presence of sialic acids in dentinal tubules was confirmed with the Bial's reaction and sialidase-susceptible binding of Limax flavus lectin suggesting that sialic acids are the major sulfated sugars in the glycoconjguates. Immunostaining with the monoclonal antibody 5-D-4 before and after treatment with chondroitin-4- and chondroitin-6-sulfatase confirmed the presence of keratan sulfate (KS), a sialylated proteoglycan, in dentinal tubules. We suggest that sulfated sialic acids are part of the KSs. The sulfated glycoconjugates are also found in dentin and the DEJ but not in predentin suggesting that amelogenin binds to the sialoconjugate during enamel formation.

Regional odontodysplasia: a bibliography

Regional odontodysplasia is a localized disorder of tissues of dental origin resulting in characteristically bizarre clinical and radiographic appearances. It most commonly affects the maxillary anterior teeth of both the permanent and primary dentitions. The authors present a worldwide bibliography of reported cases and discuss the suggested theories regarding the condition's etiology. Although the majority of cases of regional odontodysplasia must be regarded as idiopathic, various developmental anomalies may produce identical changes in the teeth in one or more quadrants. A number of previously reported cases are also reconsidered with regard to their diagnosis and guidelines are suggested for the treatment of patients affected by regional odontodysplasia.

Radioautographic analysis of [3H]-fucose utilization by mouse odontoblasts with emphasis on intracytoplasmic and plasma membrane glycoproteins

[3H]-fucose utilization by odontoblasts was studied by light and electron microscopic radioautography. At 10 min after injection, fucose label was concentrated in the Golgi area. By 20-30 min, there was a progressive decline in Golgi labelling with label present at the plasma membrane, terminal web, odontoblast process and predentine matrix. At 4 h, the predentine and the predentine-dentine junction were heavily labelled. At the ultrastructural level, Golgi labelling at 10 min was mostly localized to cisternal elements and at 20 and 30 min secretory granules and dense bodies were also labelled. Most of the silver grains observed in the terminal web were associated with microfilaments near the plasma membrane. In the predentine, the matrix itself accounted for 23.0 per cent of the label at 4 h and the plasma membrane of the odontoblast process accounted for 19 per cent. The results indicate that odontoblasts, in addition to secreting glycoproteins into the dentinal matrix, also continuously manufacture glycoproteins for incorporation into the cell surface, the lysosomal system and the terminal web.

Effects of vitamin A deficiency on rat incisor formation

Vitamin A deficiency (A-) is known to cause morphologic changes in tooth structures. However, its effects on glycosaminoglycan (GAG) distribution in dental pulp, and the role of retinoic acid (RA) in altering these effects are not clearly defined. Tissue changes induced by vitamin A deficiency and RA administration were evaluated histologically in incisors of rats fed on one of 3 different diets: a) vitamin A sufficient (A+); b) vitamin A deficient (A-); and c) vitamin A deficient supplemented with retinoic acid (A-/RA). Four weeks after the onset of vitamin A deficiency, all rats were killed and their 4 continuously erupting incisors evaluated histologically. A- rats had altered dentine and pulp with disrupted histodifferentiation of pulpal mesenchymal cells to normal odontoblasts. The frequency of these abnormalities in dentine and pulp was lower in A-/RA rats. The enamel organ was unremarkable in the 4-week deficient period. Using special stains, we noted that pulpal GAG accumulation in A- and A-/RA rats was limited to the lingual area, while in A+ rats, GAG were distributed throughout. These data suggest that vitamin A deficiency affects histodifferentiation of pulpal mesenchymal cells to odontoblasts, as well as GAG distribution in pulp. RA administration reduces the A- changes and therefore, appears to have some activity in dentinogenesis.

The distribution and morphologic variation of hyaline deposits in odontogenic lesions

The deposits of homogeneous hyaline substances present in epithelium-containing odontogenic lesions were evaluated in 201 tumors. The material was evaluated to establish the types of odontogenic lesions capable of producing the substance, its frequency of occurrence, its microscopic variation, and the different morphologic relationships of the substance to the odontogenic epithelium present in the lesions. The deposits were found in 40.3 percent of the 201 odontogenic tumors and frequently in several other nonneoplastic odontogenic lesions. It was most consistent in odontomas but was found to some extent in all types of epithelium-containing odontogenic tumors. It was present either in a basement membrane location or as a diffuse deposit in the connective tissue. In the latter location, the deposits commonly contained enclaved islands of odontogenic epithelium and had a distinct tendency to calcify. The study also suggests that since some odontogenic tumors may contain large amounts of the hyaline deposits, multiple sections through different parts of the tumor may be required to find the epithelial elements necessary for the correct diagnosis.

Ultrastructural, electron-probe, and microhardness studies of the controversial amorphous areas in the dentin of regional odontodysplasia

The amorphous areas, which are gray in sections stained with hematoxylin and eosin and which are a prominent feature in the coronal dentin of the more severely affected cases of regional odontodysplasia, were studied ultrastructurally and with an electron probe and a Vickers microhardnesss tester. The ultrastructural findings confirmed previous histochemical evidence that the amorphous material consists of glycosaminoglycans and represents collagen-free dentinal matrix, that is, ground substance. Phosphoproteins may also present. The ultrastructural examination of nondecalcified material and electron-probe and microhardness tests supported previous microradiographic evidence that the amorphous areas are more heavily mineralized than normal dentin. The boundaries of the amorphous areas were found on ultrastructural examination to be distinct but very irregular.

Glycosaminoglycans of EDTA soluble and insoluble dentin in dentinogenesis imperfecta type I

A study of glycoasminoglycans (GAGs) in dentinogenesis imperfecta Type I (DI I) revealed increased GAG in DI I EDTA soluble dentin as compared to controls. EDTA insoluble GAG contained less GAG than age-matched controls. The role of GAG in dentin pathosis is discussed.