[The relationship between root form of the maxillary first premolar and periodontal involvement. II. Morphological study on the lateral groove of the root (author's transl)].

One hundred and six extracted upper first premolars with one root were examined for the incidence of the lateral grooves on each root surface, and their length and their form on the mesial surface.The results were as follows:1. The incidence of lateral grooves on both mesial and distal surfaces was 73.6%, on mesial was 17.9%, and on neither surface was 6.6%.2. As regard to the length of the groove, half of the grooves that originate from between the neck of the root and one-third of the root run across the one-half of the root.3. The form of the groove was divided into three categories by bucco-lingual ground sections of plastic tooth casts-flat type in 46.5%, shallow concaved in 39.4% and narrow V-shaped in 14.1%.