Example of a maxillary alveolar arch, where a and a′ are the root center points of central incisors. The aa′ line is the line that links the a and a′ points. b and b′ are the root center points of the canines. The line that links the b and b′ points (bb′ line) is the intercanine width. c and c′ are the root center points of the first premolars. The line between the c and c′ points (cc′ line) is the interpremolar width. am is the midpoint of the aa′ line. The bm point is the endpoint of the perpendicular line originating from am and extending to the bb′ line. The ambm line is the intercanine depth. The cm point is the endpoint of the perpendicular line originating from am to the cc′ line. The amcm line is the interpremolar depth.