Structural Characterization of the Mandibular Condyle in Human Fetuses: Light and Electron Microscopy Studies

Abstract

Mandibular condyles from 18- to 20-week-old human fetuses were examined in the light and electron microscope with particular attention to intratissue organization and extracellular matrix. In the human fetus the condyle has been divided into five layers: (1) the most superficial, articular layer, (2) chondroprogenitor cell layer, (3) condroblast cell layer, (4) nonmineralized hypertrophic cell layer, and (5) mineralized hypertrophic cell layer. The articular layer is rich in collagen fibers (mostly of the type I collagen), but the cells seldom divide. By contrast, in the chondroprogenitor cell layer and upper part of the chondroblastic cell layer mitosis gives rise to new cells. The matrix in the latter layer is composed of thick banded ‘lucent’ fibrils in a loose feltwork of granules representing cartilage proteoglycans. The daughter cells in the progenitor cell layer undergo differentiation which is apparently completed along the lower border of the mineralized hypertrophic cell layer – the ossification front. The matrix in the hypertrophic cell layer reveals distinct matrix vesicles that undergo mineralization and subsequently coalesce to form larger sheets of mineralized extracellular matrix. Mineralized cartilage serves as a backbone for new bone formation as marrow-derived osteoblasts and osteoclasts attach to remnants of mineralized cartilage, which enables the turning on of the remodeling cycles involved in new bone formation. It can be concluded that the process of endochondral ossification as has been reported in lower animals is recapitulated in the human fetus, thus the dynamics associated with condylar morphogenesis is maintained through phytogeny.

The Pediatric Mandible: I. A Primer on Growth and Development

“…During this time and subsequently throughout development, the condylar cartilage takes on a stratified organization with five principal layers: (1) articular cartilage, (2) chondroprogenitor cells, (3) chondroblasts, (4) nonmineralized hypertrophic chondrocytes, and (5) mineralized hypertrophic chondrocytes. 25 It is this particular cellular organization that allows the joint to function as both an articular surface and a site of bone deposition, with the first endochondral bone being deposited during the fourteenth week after conception. With increasing age, the articular portion of the condylar cartilage increases in thickness, while the sizes of the chondroprogenitor cells and chondroblasts remain relatively stable.…”

Ultrastructural Characterization of the Rabbit Mandibular Condyle following Experimental Induction of Anterior Disk Displacement

“…Several ultrastructural studies using normal human [Ben-Ami et al, 1992] and animal condylar cartilage [Silva, 1967;Appleton, 1975Appleton, , 1978Silbermann and Lewinson, 1978;Luder et al, 1988;Livne et al, 1990;Marchi et al, 1991] have shown that normal condylar cartilage is composed primarily of three layers, a perichondrium which is a fibroelastic connective tissue composed of fibroblasts, undifferentiated mesenchymal cells, type I collagen and elastic fibers [Wilson and Gardner, 1984;De Bont et al, 1984, 1985Mizuno et al, 1992;Missankov, 1995;Klinge, 1996], a hyaline cartilage composed of chondrocytes located in lacunae, two or more cells are enclosed in a capsule or a chondron. Chondrons are connected by pericellular channels [Broom and Myers, 1980;Broom and Poole 1982;Poole et al, 1982Poole et al, , 1984Poole et al, , 1991.…”

Architecture and mineralization of developing trabecular bone in the pig mandibular condyle

“…Extensive research has been performed on the fetal development of the mandibular condyle. However, these studies focused mainly on the cartilage part (Durkin and Irving, 1973; Hall, 1987; Copray et al, 1988; Ben‐Ami et al, 1992; Shibata et al, 1996). The underlying endochondrally developing trabecular bone has received little attention.…”