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The effect of the mandibular lip bumper and maxillary bite plate on tooth movement, occlusion and space conditions in the lower dental arch.

The present study reports the effect of treatment with a mandibular lip bumper and maxillary biteplate on tooth movements, occlusion and space conditions in the lower dental arch. The maxillary biteplate was used to eliminate adverse forces of occlusion. The patients selected for the study could, on the basis of a morphological cephalometric analysis, be expected to be of the anterior rotation type.

The tooth movements and the changes observed in the facial skeleton were studied three-dimensionally on study casts and cephalograms. Metal implants were used as reference marks. After approximately 7 months of treatment labial tipping of the lower incisors and a distal tipping of the lower first molars were observed, and extrusion/eruption of the lower first molars took place—in two cases to an extent beyond the level dictated by the biteplate. The tooth movements resulted in changes in the perimeter of the lower dental arch and occlusion. On average the overbite and the overjet decreased, and the molar relationship changed in a distal direction.

The cephalometric analysis showed that the effect on the overbite could be ascribed to a treatment-induced posterior rotation of the lower jaw with the centre of rotation situated in the hinge axis area. This posterior rotation carried the lower incisors dorsally, thus reducing the effect of the simultaneously induced forward tipping of the lower incisors on the overjet. However, individual exceptions to this pattern were observed. The cephalometric values of mandibular inclination could be decreased or unchanged and mandibular prognathism could be increased or unchanged. These variations could be referred to individual differences in the magnitude of the treatment-induced posterior rotation and in the amount and direction of the growth of the facial skeleton, especially with regard to the mandibular condyles.