Study of Congenitally Missing Second Premolars and Space Factors in the Arches

Abstract

The theory that human dentition is passing through a transitional stage leading to a decrease in the number of teeth is supported by most odontologists. Recently, Dahlberg (2) discussed this tendency and referred to the general trend toward a reduction in size, form, and number of teeth in human beings. The causal factors associated with this deficiency in the dental arches is difficult to identify. Several theories which have been presented, such as those by Montagu (3), Schultz (5), and others, seem to fit special cases but do not account for the congenital absence of teeth located in the premolar region of the arches. Mere chance alone does not explain the failure of some types of teeth to develop. In an earlier publication (1), the authors called attention to a definite pattern or regularity with which certain teeth failed to develop in 184 persons. They reported that the teeth most frequently congenitally missing were the upper second incisors, second premolars, and third molars. Any other tooth may on occasion be congenitally absent, but except for the lower first incisors the frequency is very low. Since that report, 232 new cases of congenitally missing teeth have been collected and studied. In tabulating the new data we find that the pattern of the congenital absence of teeth remains the same. The upper second incisors, second premolars, and third molars which are most often absent have also been found to be the most variable in pattern and size (6). It seems justifiable, therefore, to assume that some factor or factors control the variation in the development of these tooth buds. The authors of this report have suggested in a previous publication (1) that arch size and congenital absence of teeth seem to be separate entities. This contention is also borne out by our study of missing second premolars which is reported in the present paper. All interpretations are based upon examinations of the patients with a study of dental models made from impressions of the arches and complete oral radiographs of those persons.