Sasaki T, Kim T W, Debari K, Nagamine H
Department of Anatomy, School of Dentistry and Medicine, Showa University, Tokyo, Japan.
J Electron Microsc (Tokyo). 1996 Jun;45(3):213-22. doi: 10.1093/oxfordjournals.jmicro.a023435.
The cellular mechanisms of cartilage-bone replacement in endochondral bone formation, in mandibular condylar heads, are poorly understood. In particular, there is no definitive evidence indicating whether cartilage is resorbed by so-called chondroclasts. Using 3-week-old male beagle dogs, we examined the cartilage-bone replacement processes in mandibular condylar heads by means of light and electron microscopy. Calcification of the cartilage matrix occurred in the central area of the longitudinal septa but not in thin transverse septa. Chondrocytic lacunae were opened by the removal of transverse septa by perivascular rough-surfaced endoplasmic reticulum (RER)-rich mononuclear cells. These cells also phagocytosed calcified cartilage fragments in the surface layer of longitudinal septa. Shortly thereafter, a thin bone layer was deposited on the remaining longitudinal septa by invading osteoblasts. Preosteoclastic multinucleated cells in lacunar canals developed neither ruffled borders nor clear zones in the cartilage matrix, but once the bone layer had been deposited on the remaining cartilage, these structures formed. Our results suggest that the cartilage-bone replacement in mandibular condylar heads involves four sequential processes: 1) degradation of the transverse septal cartilage by RER-rich mononuclear cells, 2) phagocytosis of calcified cartilage fragments in the longitudinal septa by these cells, 3) bone deposition of the remaining longitudinal septa, and 4) degradation of both bone and calcified cartilage by differentiated osteoclasts.
关于下颌髁突软骨内成骨过程中软骨-骨替代的细胞机制，目前了解甚少。特别是，尚无确凿证据表明软骨是否被所谓的破软骨细胞吸收。我们使用3周龄雄性比格犬，通过光学显微镜和电子显微镜检查了下颌髁突软骨-骨替代过程。软骨基质钙化发生在纵向隔的中央区域，而薄的横向隔中未发生钙化。富含血管周围粗面内质网（RER）的单核细胞通过去除横向隔打开软骨细胞腔隙。这些细胞还吞噬纵向隔表层的钙化软骨碎片。此后不久，侵入的成骨细胞在剩余的纵向隔上沉积了一层薄骨。腔隙管中的前破骨细胞多核细胞在软骨基质中既不形成皱褶缘也不形成透明区，但一旦在剩余软骨上沉积了骨层，这些结构就会形成。我们的结果表明，下颌髁突软骨-骨替代涉及四个连续过程：1）富含RER的单核细胞降解横向隔软骨；2）这些细胞吞噬纵向隔中的钙化软骨碎片；3）剩余纵向隔的骨沉积；4）分化的破骨细胞降解骨和钙化软骨。
