Abstract
The reference standard value of tooth germ development and tooth eruption have been reported by Nolla, Schour and Massler, Moorrees, etc, and are used in daily clinical practice.Recently, we have the impression that we encounter cases where the beginning of calcification in mandibular premolar germs is slower than the reference standard value. It is important to know whether the reference standard value for the diagnostic criteria reflects the real condition or not, because the congenital absence of premolars affects the treatment plan for the deciduous predecessors.In this research, we investigated whether a time discrepancy exists between the degree of actual calcification of the first and the second premolar germs and their standard time of calcification using dental x-ray films taken in the Pony Dental Clinic located at Edogawa area in Tokyo.The study examined 296 dental X-ray films taken from child patients (male : 143, female : 153) for the diagnosis of caries on their first and second deciduous molars. Calcification stage of successive premolar germs was evaluated using the classification by Nolla.Calcification of both the first and the second premolar germs tended to occur later than the standard. The time differences between the first and the second premolars was also bigger than the standard.Although it is true that the mandibular second premolar is the most frequently congenitally missing tooth, these results indicate careful and sufficient observation is required for the diagnosis of a congenitally missing tooth. In addition, further nationwide investigation of calcification of premolar germs is necessary in Japan.
