Time programme of the early tooth development in the domestic sheep (Ovis aries, ruminantia)

Abstract

The knowledge of a generally valid pattern of odontogenesis is a prerequisite for the identification of diseases and developmental anomalies in the oral cavity of domestic animals and man. The sheep is a very interesting model species for the investigation of tooth development, as it shows specialisation processes of the mammalian dentition, such as reduction, complication, transformation and translocation, in one object. In this paper, an attempt at an explanation of the time programme of early odontogenesis in the sheep is made to provide a basis for further studies of this object. Heads of 19 staged embryos and fetuses were decalcified, embedded in paraffin and serial transversal sections were made. Stained series were examined by light microscopy. The dental lamina was formed at DO33 (days of ontogenesis). Later dental buds and dental caps for the deciduous dentition developed. The tooth primordia of the permanent dentition did not appear until DO53. Rudimental primordia of upper incisors and canines, which disappeared after DO55, were also observed. An enamel knot-like structure could be distinguished within these rudiments. The time programme of tooth development in the sheep is comparable with the odontogenesis in other terrestial mammals.