Use of an incisor diagnostic triangle for evaluating incisor positions relative to the APo line.

Angular values of the upper and lower incisors to the APo line were measured in a sample of fifty subjects with clinically acceptable occlusions, ranging from 10 to 14 years of age. Correlations were high between both upper and lower incisor angulations to the APo line and the interincisal angle. The correlation was low between the upper incisor angulations to the APo line and the lower incisor angulations to the APo line. An incisor diagnostic triangle was introduced. This is made up of the interincisal angle and the intersection of the long axes of the upper and lower incisors to the APo line. Incisor diagnostic templates were introduced and their uses as diagnostic and visual aids were enumerated. These templates were constructed by using an idealized linear position of the tip of the lower incisors on the APo line, the upper incisor angulation to the APo line, and the interincisal angle. By relating both incisors to the APo line and to each other through the interincisal angle, the orthodontist is provided with a simple, specific diagnostic aid. The incisors are positioned in relation to a skeletal reference line (APo) which is more intimately associated with the patient's facial profile than more distant skeletal reference lines or planes, such as sella-nasion, Frankfort horizontal, or the mandibular plane.