Physical, histological and roentgenographic characteristics of the grey lethal mouse

A project was undertaken to investigate the development of dental and osseous abnormalities in the grey lethal mouse. In this study particular attention was focused on the nature of these anomalies and the exact time of onset. Twenty‐five grey lethal mice, with siblings serving as controls, were sacrificed at two day intervals from the eighth to the twentieth day. Color photographs and lateral full body radiographs were taken at each developmental stage studied. Microscopic sections of the jaws and femurs of each animal were prepared and stained with hema‐toxylin and eosin. Abnormalities in the incisor region of the grey lethal mouse were demonstrated radiographically at the eighth day. Interference with Hertwig's sheath of the developing first molar tooth was observed histologically at the eighth day. Establishment of molar root bifurcation was not observed in the grey lethal mice. Bone resorption was retarded in both jaws and femurs. Differences between experimental and control animals became more apparent with increasing age. It was thought that apical root development and osseous apposition in the area of bifurcation of developing molars, as well as resorption of bone occlusal to the crowns of the teeth are constituents in axial movement of developing teeth. Evidence tending to support this concept is presented, since all three functions were shown to be altered in the noneruption dentition of the grey lethal mouse.