[Numerical anomaly of teeth in mongrel juvenile dogs. Canis familiaris]

As this study subjects, upper and lower dentitions of 49 mongrel dogs were used. X-ray films of the upper and lower dentitions of the dogs were taken. These films were from the collection of the Department of Pedodontics, School of Dentistry, Aichi-Gakuin University. Although the data on the sex and age of the dogs were not available, the dental ages were judged to range from the deciduous dentition to the early mixed dentition. Molars were not dealt with in this study for two reasons: 1) the molars of many of the subjects had not yet been calcified, and 2) the upper second and/or lower third molars, if present, had frequently been sacrificed when the jaws were separated. Numerical anomalies were observed in 16 dogs (32.7%). And infranumerary teeth were observed in 14 dogs (26.8%). Incidences of infranumerary teeth were higher in the secondary dentitions than in the primary ones. Most of the infranumerary teeth were found in both the upper and lower premolars, but not in the upper incisors and the upper and lower canines. Infranumerary teeth often occurred symmetrically whereas supernumerary teeth occurred asymmetrically. This investigation suggests that tendency of the reduction of the upper third premolar was considered to be caused by the reduction of the maxilla through the process of domestication. These results are inconsistent with Fujita's terminal reduction theory.