Comparison of Linear Measurements of Detailed Crown Structures in the Maxil lary First and Second Premolars

Abstract

The detailed three-dimensional（3D）surface structures in the maxillary first premolar （P¹）and second premolar（P²）obtained by calculating the distances between landmarks were analyzed to clarify the differences among maxillary premolars, especially structures related to distinguishing between the right and left sides. The study population included 27 boys at the elementary and junior high schools from Chiba Prefecture, Japan. Plaster casts were collected, and the 3D coordinates were recorded. Linear measurements between 9 landmarks were calculated using the 3D coordinates. The absolute and relative sizes of the outer and inner slopes of the buccal cusp were larger in P¹ than in P². The absolute sizes of the lingual cusp were similar between P¹ and P², but the relative size of the lingual cusp in P² was larger. In P¹, the curvature features were often opposite, with the buccal most prominent point located mesially. Most of P² exhibited no curvature features, and the most buccal prominent point was situated centrally. The buccal cusp tip was located more distally in P¹ than in P². Since the cusp tips in the crown structures are formed the earliest ontogenetically, P¹ may be adopt a pattern in which the mesiodistal positional relationship of the cusp differs from those of other teeth in the early developmental stages. The developmental process may produce P¹ with unique characteristics in the fully developed crown not found in other teeth.