The permanent maxillary central incisor is the widest tooth mesiodistally in comparison to any other anterior Adult tooth numbers. A cusp is an elevation on an occlusal surface of posterior teeth and canines. It is formed by the union of the distal cusp ridge of the mesiolingual cusp and the triangular ridge of the distobuccal cusp. The second primary molar in the upper jaw on the right is assigned the letter A, and the numbering continues in the alphabetical order, with the second primary Adult tooth numbers on the left in the upper jaw being assigned the letter J. Please leave this field blank: Importance of Washing Your Hands.