The Crown Odontoblasts of Rat Molars from Primary Dentinogenesis to Complete Eruption

Abstract

The involution of crown odontoblasts after primary dentinogenesis in teeth of limited eruption is discussed. The odontoblasts of rat first lower molars were analyzed morphometrically from the tenth day to the 40th day of age, i.e., from the late phase of primary dentinogenesis to complete eruption. All the organelles underwent atrophy, but at different rates. In particular, the membranes of the endoplasmic reticulum decreased progressively in surface area from day 10 to day 40, whereas those of the Golgi apparatus decreased significantly between day 10 and day 14, and then remained practically unchanged in size. The volume of the lysosome compartment never increased beyond that during primary dentinogenesis. The profile length of the endoplasmic reticulum in each observed cell section was taken as an estimate of secretory activity. At day 40, this organelle was smaller in approximately 95% of the cells than it had been in any cell at day 10. These results suggest that cell atrophy may occur without any increase in the degradation processes of the cytoplasmic components and that the organelles along the secretory pathway may have independent regulatory systems. In the odontoblasts, as in several types of secretory epithelial cells, only a small fraction of the cells is engaged in appreciable secretory activity. This occurs, however, when the overall activity of the same cell population is relatively low.

Expression of Dynamin II in Odontoblast During Mouse Tooth Development

“…It was reported that the area and ratio of the cytoplasm, rER and Golgi apparatus of the odontoblast were decreased gradually from the crown (PN10, 14,16) to erupted (PN40) stage in rat molar development. 23 In this study, the morphological characteristics of odontoblasts were similar to those of previous rat development (Figs. 3(a-c)).…”

Dentin basic structure and composition—an overview

“…It has been postulated that primary dentinogenesis ends when the crown is complete. This assumption is supported by the finding that cell organelles undergo atrophy at that point in rat molars (50). Primary dentinogenesis has also been timed to end when teeth becomes functional (12) and when root formation is complete (7,51).…”

Observation of the Internal Configuration of Rat Incisor Odontoblasts by Scanning Electron Microscopy Using the AODO Method

“…The granules containing fibrillar elements (the abacus-like vesicles) on the other hand, are morphologically similar to one type of cytoplasmic bodies closely related to the Golgi complex. Furthermore, these abacus-like vesicles stained positive for acid phosphate activity, and therefore have been elucidated to be the granules relating to the secretion and digestion of the procollagen in both the functioning and resting OBs by many previous studies (Tsuboi, 1968;Nagai, 1970a;Takuma and Nagai, 1971; Weinstock and Leblond, 1974;Leblond, 1989;Romagnoli et al , 1990;Linde and Goldberg, 1993). In the present SEM using the AODO method, we observed many empty vesicles (secretory-granule-like structures) near the nucleus and the cell membrane and some large membranous structures containing many small vesicles (multivesicular bodies; MVBs) in the functioning and resting OBs.…”

“…There have been many transmission electron microscopy (TEM) studies on the morphological changes and the fine structure related to secretion and absorption by odontoblasts (OBs) at different developmental stages (Reith, 1968;Tsuboi, 1968;Takuma and Nagai, 1971; Weinstock and Leblond, 1974;Gartner et al , 1979;Goldberg and Septier, 1985;Suzuki, 1985;Rule, 1986;Avery, 1987;Nagai, 1970a;Nagai, 1970b;Leblond, 1989;Romagnoli et al, 1990;Linde and Goldberg, 1993). The occurrence of various kinds of cytoplasmic bodies closely related to the Golgi complex and the smooth (agranular) endoplasmic reticulum (sER) has been reported during early and late dentinogenesis, respectively, in some of these studies (Tsuboi, 1968;Takuma and Nagai, 1971;Romagnoli et al, 1990), while others have suggested that the Golgi elements and some cytosomes (lysosomes) are organelles concerned with autodigestion and regulatory functions of the OBs at different developmental stages (Nagai, 1970a;Romagnoli et al, 1990).…”

“…The occurrence of various kinds of cytoplasmic bodies closely related to the Golgi complex and the smooth (agranular) endoplasmic reticulum (sER) has been reported during early and late dentinogenesis, respectively, in some of these studies (Tsuboi, 1968;Takuma and Nagai, 1971;Romagnoli et al, 1990), while others have suggested that the Golgi elements and some cytosomes (lysosomes) are organelles concerned with autodigestion and regulatory functions of the OBs at different developmental stages (Nagai, 1970a;Romagnoli et al, 1990). Additionally, the occurrence of coated vesicles at the cell membrane, the resorption of proteoglycans and fibrillar components and the formation of a lysosomal-vacuolar apparatus have been elucidated by TEM examination of freezefracture-replica images and ultrathin sections (Betti and Katchburian, 1982;Sasaki et al, 1982;Goldberg and Escaig, 1984;Sasaki et al, 1984;Koling, 1987;Goldberg and Septier, 1989).…”