Symmetric and asymmetric expansion of molars using a Burstone-type transpalatal arch. Biomechanical and clinical analysis.

Abstract

A transpalatal arch (TPA) directly connecting the maxillary first molars can be used in passive (for stabilization) and active (for molar or segment movement) modes. Activation may be symmetric or asymmetric. This study was performed to analyze the effectiveness of TPAs for transverse expansion treatment by measuring both the force systems they deliver and the clinical tooth movements thus achieved. Ten patients (six with symmetric and four with asymmetric transverse discrepancies) were treated using a TPA made of titanium-molybdenum alloy (TMA) and fitted with 0.032" × 0.032" Burstone lingual brackets. The force systems exerted by these TPAs and the resultant tooth movements were first simulated and measured inside the orthodontic measurement and simulation system (OMSS). All TPAs, whether used in the symmetric or asymmetric activation mode, were adjusted to an expansive force of 4 N. After a treatment of 12 weeks, their effectiveness was analyzed by comparing the clinical tooth movements to the movements simulated in the OMSS. Clinically, the symmetric treatments resulted in a mean correction of 4.5 ± 1.0 mm and a mean of buccal crown tipping of 10.1°, compared to 9.6° for the movements simulated in the OMSS. The four cases of unilateral crossbite were treated with an asymmetrically activated TPA (including a force on one side and a combination of force and negative torque on the other side). The intended unilateral expansion was achieved in all four cases. Vertical side effects were acceptably small in both the symmetric and the asymmetric treatment cases. The tooth movements could be implemented as planned in all 10 patients, whereby in 5 patients complete correction of the occlusal width discrepancy was achieved by the end of the 12-week treatment. Given this combination of good efficacy and minor side effects, the TMA/TPA appliance may be recommended as a suitable approach to correct transverse discrepancies. Recommendations expressed in previous studies for the use of Burstone-type TMA/TPA in these situations is confirmed by our study.