STAGES OF ODONTOGENESIS IN THE FIELD VOLE (MICROTUS-AGRESTIS, RODENTIA) - A PILOT-STUDY

The aim of this study was to obtain basic morphological data on prenat al development of this dentition and its timing using serial histologi cal sections and computer-assisted three dimensional 3D reconstruction s. Twenty nine embryos and fetuses were classified into nine Sterb's c omparable stages (SCS) and their ontogenetic age was estimated within 13th and 20th day of ontogenesis (DO). Dental lamina was formed on DO- 13. During the next stage, dental cap arose for the first incisor and the first molariform tooth. On DO-16, the dental caps deepened and the ir histodifferentiation was evident. Measuring of the thickness of the dental epithelium revealed transient rudimental tooth primordia in bo th the upper and lower jaw quadrant, apart from the functional teeth: one rudiment anterior to the incisor anlage and three rudiments in the the future diastema (margo interalveolaris). Later however, each of t hese vestiges disappeared. On DO-17, dental caps for the incisor and f irst molariform tooth transformed into bell-shaped enamel organs. A de ntal cap was formed for the second molariform tooth from the peg-shape d dental epithelium, which projected posteriorly from the enamel organ of the first molariform tooth into the mesenchyme. On DO-20, bell-sha ped enamel organs for the incisor and first molariform tooth, as well as the bell-shaped enamel organ for the second molariform tooth, were well differentiated. In 3D computer-assisted representations, the enam el organs for the molariform teeth exhibited a typical plicident struc ture. An epithelial peg-shaped expansion grew out of the posterior end of the second molariform tooth primordium. This expansion was predest ined to give rise to the third molariform tooth postnatally. Contrary to the second and third molariform tooth, which originated posteriorly from the subepithelial peg shaped protrusion of the dental epithelium , the incisor and first molariform tooth in the field vole developed o n the labial side of the dental lamina arising directly from the oral epithelium. The free terminal margin of the dental lamina projected li ngually from the base of the later tooth primordia.