Therapeutic changes in the occlusal plane inclination using intermaxillary elastics

The goal of the study was the evaluation of opposing intermaxillary elastics concerning potential change in the occlusal plane inclination relative to relevant vertical structures.

Thirty-two late adolescent, skeletally homogeneous patients (basal-sagittal relationship: neutral; basal-vertical: neutral; no transverse discrepancies) were treated either with Class II (group A; n=16) or Class III elastics (group B; n=16) for unimaxillary space closure. Mean wearing times were 26 (A) and 24 months (B). Cephalograms at the start and end of treatment were analyzed. Changes in the inclination of the occlusal plane (BOP according to Downs) relative to three reference planes (NL, ML, NSL), as well as changes in the reference planes toward each other underwent statistical testing with a two-tailed Student t-test.

The occlusal plane shift differed significantly when opposing elastics were applied (p<0.001). The induced shift with Class II elastics (A) was clockwise, while Class III elastics were counterclockwise (A: NL-BOP: +0.9°, ML-BOP: -2.1°; B: NL-BOP: -3.1°, ML-BOP: +3°). Reference planes NL and ML underwent insignificant change towards one another (A: -1.2°; B: -0.1°). The maxillo-mandibular complex itself rotated counterclockwise toward the anterior cranial base (NSL) (A: NL-NSL: -0.8°, ML-NSL: -2°; B: NL-NSL: -0.6°, ML-NSL: -0.7°). Thus, almost no change in BOP (+0.1°, n.s.) relative to NSL was detected when Class II elastics were applied, whereas the use of Class III elastics led to a significant counterclockwise rotation (-3.7°, p<0.001)

Class III elastics enhance the physiologic inclination of the maxillo-mandibular complex at the level of the occlusal plane, whereas Class II elastics oppose or even eliminate the process.