Untersuchungen über die Breitenrelation der Frontzähne und deren Missverhältnisse

Abstract

The goal of orthodontic treatment is an ideal occlusion, especially concerning the front teeth. It is important from both the functional as well as from the aesthetic point of view. The Bolton analysis has been used for over 50 years to detect tooth size discrepancy of the anterior teeth. The purpose of the present study was to test the validity of the Bolton analysis and to introduce a new method to diagnose tooth size discrepancy more reliable. The sample consisted out of 89 post-treatment plaster models with well shaped tooth arches. The lower front teeth were in contact with the palatal surface of the upper front teeth. Forty-five of these patients had a class-I-occlusion in the canine area, whereas the other 44 patients had a class-II-malocclusion. The arch length of the maxillary front teeth was measured in several vertical heights with a mechanical 3D-digitizer. The arch length of the mandibular front teeth was measured at the incisal edge. The measurement with the 3D-digitizer serves as the gold standard. It was used to test the validity of the Bolton analysis and the newly introduced method. In order to determine the Bolton ratio the mesio-distal tooth width was obtained by means of a digital caliper from the vestibular surface. In opposite to the Bolton ratio the maximum possible arch length of the upper front teeth was measured from the palatal surface for the new method. The measurement was taken in height of the contact points from the middle of the canines in each case. A tooth size discrepancy was diagnosed when the lower arch length was longer than the upper arch length. Statistically high significant differences were found between the upper arch length (p ≤ 0.003) and the Bolton ratio (p < 0.001) in class-I and class-II-patients. The differences in overbite (p = 0.110), overjet (p = 0.927) and the lower arch length (p = 0.673) can be neglected. There is a linear dependency between the different vertical measurements on the palatal surface of the maxillary front teeth and the length of the arch. The validity of the Bolton ratio was reviewed. The result pointed out that specificity (0.63 at 1 SD, 0.91 at 2 SD) and sensitivity (1 at 1 SD, 0.44 at 2 SD) were insufficient. The new method has a specificity of 0.95 and a sensitivity of 1. The area under the ROC curve is large (0.98). Therefore the new method can be considered valid. Because of that, the introduced method should be preferred for diagnosing a tooth size discrepancy of front teeth.