Development of mandibular cartilages in the rat

Abstract

Background: The mammalian mandible develops around Meckel's cartilage and other secondary cartilages, including the dentary. There have already been many studies of the development of the rat mandible that have employed histological serial sections. However, no previous investigators have captured the three-dimensional features of the developmental process.Methods: In this study, the technique of double staining with alizarin red S and alcian blue was employed directly on whole body specimens to investigate the three-dimensional development of the rat mandible.Results The mandible is the largest and strongest bone of the face, and it is essential for the function of mastication. In mammals, the mandible consists mainly of a dentary bone, but Meckel's cartilage appears transiently during the early stages of development, a period of great interest to anatomists.Following the critical description of Meckel's cartilage (Meckel, 1820), some researchers claimed that it did not ossify or play any role in the development of the mandible (Brock, 1876). Low (1909) reported that Meckel's cartilage ossified partly but did not contribute to mandibular development or growth, whereas Bhaskar et al. (1953) and Frommer and Margolies (1971) stated that the cartilage ossified enchondrally and contributed to the growth of the mandible. The problem of the role of Meckel's cartilage now seems to have been solved for the rat and mouse because it appears to ossify and also plays a part in the development of the mandible.A few studies have been reported on the development of the dentary or second cartilages in the rat (Bhaskar, 1953;Youssef, 1969), but they were based on crosssectional examination of the tissues and the construction of models based on serial sections. These models were not exact or detailed. Because it takes considerable time and effort to make models, it is not possible to observe many specimens or stages. To date, no study has captured the three-dimensional features of the developmental process of the rat mandible.Thus, the aim of this paper was to describe the development of the dentary and second cartilages and of Meckel's cartilage in the rat mandible by using a technique of direct double-staining of whole body specimens. A second goal was to clarify the role of the cartilages in the developmental process. MATERIALS AND METHODSThis study was based on direct observation of doublestained whole body specimens from 2 male and 12 female Wistar rats. The rats were maintained at Kyushu Dental College under the care of the Animal Research Center. All animals were housed singly in a 12-hr light-dark cycle and were given laboratory chow and water. The male rats and the female rats, which were older than 8 weeks and were already sexually mature, were kept together for 12 hr overnight. The next morning, we observed vaginal smears. The day on which sperm was found in the vagina was considered to be day 0. The pregnant rats were anesthetized with ether and then killed by cervical dislocation. The embryos were removed by...

Prenatal development of the human mandible

“…Three stages of Streeter's development appeared particularly important during the mandibular development: stage 16 (appearance of Meckel cartilage), stage 20 (beginning of membranous ossification), and stage 23 (end of the human embryonic period, week 8) (Orliaguet et al, 1993a). Many authors presumed that the Meckel cartilage, the first branchial arch cartilage, had no relationship to the processes of mandibular ossification (Merida-Velasco et al, 1993;Orliaguet et al, 1993bOrliaguet et al, , 1994Rodriguez-Vazquez et al, 1997a,b;Tomo et al, 1997). Unlike the long bones, Meckel cartilage entirely regressed during the later fetal period (Ellis and Carlson, 1986).…”

“…We found that the intramembranous ossification as well as the condensed cellular mesenchyme of the condylar blastema was closely associated with a portion of perichondral fibrous tissue of the Meckel cartilage. Because the primary intramembranous ossification of the mandible greatly affects the following histomorphogenetic processes of the whole mandible (Bareggi et al, 1995;Berraquero et al, 1995;Orliaguet et al, 1993bOrliaguet et al, , 1994Rodriguez-Vazquez et al, 1997b;Tomo et al, 1997), we accentuate the primary intramembranous ossification and named it as the mandibular primary growth center (MdPGC). The MdPGC was approximated to the middle portion but lateral in position of the Meckel cartilage in the early embryonal period.…”

The growth and morphogenesis of the early mouse mandible: a quantitative analysis

“…It is not therefore surprising that BrdU incorporation rates are particularly high (> 35%) at the distal and proximal ends where the jaw is extending. More interesting, however, is the behaviour of the mandible at its superior and inferior edges: here the two edges of the bone deepen and extend medially to enclose Meckel's cartilage and the inferior alveolar nerve and, in the central region, to surround the molar tooth primordia (Tomo et al 1997).…”

Autophagy Prior to Chondrocyte Cell Death During the Degeneration of Meckel's Cartilage

“…Meckel's cartilage is present transiently in the developing mandible and usually disappears at early postnatal stages (Bhaskar et al, 1953). Meckel's cartilage provides mechanical strength and contributes to the normal development of the mandible (Tomo et al, 1997). At the distal portion of mouse Meckel's cartilage, cartilaginous bars of both sides fuse and undergo endochondral ossification for integration into mandibular symphysis, whereas the proximal portion forms anlages of malleus and incus (RodriguezVazquez et al, 1997;Shimo et al, 2004).…”