An analysis of permanent mesiodistal crown size.

Abstract This article refers to the mesiodistal size of the permanent teeth and presents an effective way of locating and analyzing crown-size discrepancies. The analysis proposed contributes to a more complete study of intraoral etiologic factors and a more precise diagnosis and prognosis of the dental problem. It has been illustrated that crown-size patterns differ greatly, even among good occlusions (Figs. 1 and 2). Common to both subjects are the small premolars and molars. Favorable crown-size discrepancies (Fig. 2) usually involve smaller teeth, particularly posterior teeth, which allow flexibility for the self-correction of minor anterior space deficiencies. In contrast, the remaining figures illustrate various crown-size discrepancies and the resulting malocclusions. Irregularities associated with the size disharmonies include (1) crowding of the mandibular incisors, (2) labial displacement of canines, (3) end-to-end premolar relationships, and (4) marked labial inclination of the anterior teeth. The effects on interdigitation of discrepant teeth must be differentiated from the effects of rotations and tipping of the teeth. Fig. 5 shows Class I molar and first premolar relationships; however, there is a tendency toward an end-to-end second premolar relationship because of mesial inclination of the maxillary second premolar. The complexity of interdigitation in orthodontic treatment is emphasized by the theoretical existence of more than 22,000 billion possible combinations of crown-size discrepancies (excluding the third molars).