Changes in Molar Teeth and Their Supporting Structures of Rats Following Extraction of the Upper Right First and Second Molars *

Data have been presented indicating that changes occur in the dental structures of growing albino rats fed diets adequate except for extreme restriction of inorganic salts (Arnim et al.2). Marked rarefaction of the alveolar bone and the formation of irregular dentine containing few tubules, many spaces, and occasional cells were observed. This unusual dentine was most prominent in the cusps of the molars, where it was deposited in the parts formerly occupied by the pulp horns, forming an irregular core. No evidence was seen of the resorption of dentine or enamel that might be related to the consumption of the low-salt ration. Fractures occurred in cusps which had been shortened by wear exposing irregular dentine on the occlusal surface. Lesions involving the dentine, enamel, and pulp, called cusp caries, were observed at the sites of fracture. In order to study the effect of wear on the incidence of the "cusp lesion" associated with the fracture of the irregular dentine, the upper right first and second molars of young rats were extracted. The present paper deals with those changes attributable to the lowsalt ration and to the operative procedure.