This research concerns the reasons for having the mother located beside the dental chair and the influence on the dental staff by the patient's mother. The subjects were a total of 390 persons, of which 100 children, 100 mothers, 100 doctors and 90 assistants. A total of 20 items consisting of 10 items from the psychological test and 10 items from the dental charts. Discriminant analysis was carried out according to the second class of Hayashi's quantifying theory concerning the entrance into the dental office or non-entrance chosen as an external criterion. The mothers answered questions on the psychological test about the psychological distance between the mother and the child. They also answered the questionnaires about their psychological process. The doctors and assistants answered concerning to "manifest anxiety scale" and questionnaires about their psychological process. The results are summarized as follows: 1. The ratio of the distinctive efficiency of external criteria to the entrance or non-entrance was found to have a high correlative coefficient, 0.70. When the factors mentioned above are ranked according to the external criteria the order is as follows: "treatment experience of the child", "adaptation degree to the treatment of the child", "birth order of the child", "clinical experience of the doctor", "the child's age". 2. The psychological distance of "the mother waiting out of the dental office" is longer than the distance of "the mother in the dental office". 3. The mother's presence in the dental office had some psychological influence on the doctor and the assistant.