Research progress on the application of the transpalatal arch in orthodontic clinics and its mechanical mechanism

The transpalatal arch (TPA) is widely used in clinical orthodontics for various purposes. This article reviews the versatile clinical uses and mechanics of TPAs for clinical reference. Traditionally, TPA is conceived as an anchorage reinforcement device. However, the literature does not support the sole use of TPA for anchorage control. TPA, combined with other conventional anchorage means, can only provide sufficient anchorage in certain cases. As an adjunct to fixed appliance treatment, TPA can be applied for arch width maintenance, tooth alignment and habit braking to improve treatment efficiency and reduce side effects. Meanwhile, TPA can be used to provide active orthodontic forces for maxillary molars to move or rotate bilaterally and unilaterally in all three planes of space, especially on occasions where molar rotation and transverse discrepancy exist. A two-couple system is formed with a TPA connecting bilateral maxillary first molars, the mechanical analysis of which can improve the understanding of treatment mechanics and make tooth movement more predictable. In recent years, TPA has also been used in combination with temporary anchorage devices for maxillary molar intrusion and full arch mesialization or distalization. The combined use of TPA with TADs and maxillary skeletal expanders could be further investigated in the future.