The commissure line of the mouth for orienting the occlusal plane.

This study investigated the positional relation of the commissure line of the mouth to the maxillary first molars. Thirty-five volunteers, 20 to 40 years old, with normal natural dentitions were recruited. Maxillary casts with marks locating the commissure were digitally scanned to measure the vertical distance from the tip to the base of the mesiofacial cusp (CO) and from the tip to the mark (CM). There was no significant difference (t test; P > .05) between the CO (1.61 ± 0.41 mm) and CM (1.14 ± 0.68 mm). The mean distance of the commissure mark from the occlusal plane was 0.78 mm.