Kakizawa Yoshiko, Meenakarn Wanpen
Department of Anatomy, Nihon University School of Dentistry, Tokyo 101-8310, Japan.
J Oral Sci. 2003 Dec;45(4):213-21. doi: 10.2334/josnusd.45.213.
Juveniles of the Mekong giant catfish, Pangasianodon gigas (Teleostei), have 3 sorts of tooth-upper and lower jaw teeth, palatal teeth, and pharyngeal teeth--but adults are toothless. To investigate the histogenesis and disappearance of the teeth, we made serial sections of the mouth and teeth of juvenile fish at 10 developmental stages (from ca. 8.5 to ca. 30 cm in total length) and examined them under scanning electron microscope and light microscope. Observations of teeth and surrounding tissues in the serial sections revealed the process of tooth resorption by active odontoclast-like cells. Numbers of jaw and palatal teeth decreased with age. When the fish reached ca. 14 cm in total length, the numbers of functional upper jaw teeth and successional tooth germs decreased rapidly, and the developmental rate of successional tooth germs slowed. When the fish reached ca. 24 cm, no teeth existed in the upper jaw. It is clear that tooth disappearance results from the shedding of functional teeth and the lack of replacement tooth germs.
湄公河巨鲶（Pangasianodon gigas，硬骨鱼纲）幼鱼有三种牙齿——上下颌齿、腭齿和咽齿——但成鱼无齿。为了研究牙齿的组织发生和消失过程，我们对处于10个发育阶段（全长约8.5至约30厘米）的幼鱼的口腔和牙齿制作了连续切片，并在扫描电子显微镜和光学显微镜下进行观察。连续切片中牙齿及周围组织的观察揭示了活跃的破骨样细胞进行牙齿吸收的过程。颌齿和腭齿的数量随年龄增长而减少。当鱼全长达到约14厘米时，功能性上颌齿和继承性牙胚的数量迅速减少，继承性牙胚的发育速度减慢。当鱼全长达到约24厘米时，上颌中已无牙齿。显然，牙齿消失是功能性牙齿脱落以及缺乏替换牙胚所致。
