Abstract
Since the low level of available evidence and the limited number of studies do not clarify whether clear aligners are a good option for extrusion, finite element (FE) analyses were performed to obtain more accurate biomechanical data about open-bite treatment in the upper arch. The aim of this study is to answer three questions: Are aligners efficient in performing upper incisor extrusion? Does the number, position, and shape of attachments influence the force system? Is posterior anchorage preserved during incisor extrusion? Six different simulations were performed with different attachment patterns. The results of this study were consistent with the biomechanical information obtained from clinical trials, and highlighted the need of better knowing undesired forces during teeth movement with clear aligners. Some attachment configuration seems to lead to a better force system. The presence of rectangular horizontal attachments on the buccal or palatal surface of upper incisors in combination with rectangular vertical attachments on posterior teeth was found to produce the most efficient force system with minimal aligner deformation.
Highlights
Since the beginning of the aligner orthodontics era, the possibility of vertical movement control with these appliances has been a strongly debated topic
Is posterior anchorage preserved during incisor extrusion?
The finite element (FE) simulations of incisor extrusion are emblematic of this concept—planning a pure bodily extrusion of the four incisors, without any other movement that could generate undesired forces and displacements, will result in retroclination of anterior teeth, as well as buccal inclination and intrusion of the posterior ones, independently of the adopted attachments configuration
Summary
Since the beginning of the aligner orthodontics era, the possibility of vertical movement control with these appliances has been a strongly debated topic. From the 2014 review by Rossini et al, the accuracy for vertical movements performed with clear aligners was reported to range between 30% and 41% of the planned movement [1]. In the past few months, four clinical studies analyzing outcomes of vertical movements with aligners [2,3,4,5] were published. Focusing on open-bite treatment, three cephalometric studies from Garnett et al [4], Moshiri et al [3], and Harris et al [5] reported the results of correction with clear aligners. The study of Moshiri et al retrospectively analyzed 30 adult patients, measuring preand post-treatment cephalograms. The authors reported significant changes for several cephalometric values, stating that bite closure was mainly achieved by a combination of counterclockwise rotation of the mandibular plane, lower molar intrusion, and lower incisor extrusion [3]
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