Mandibular response after rapid maxillary expansion in class II growing patients: a pilot randomized controlled trial

Lione et al. Progress in Orthodontics (2017) 18:36 DOI 10.1186/s40510-017-0189-6 RESEARCH Open Access Mandibular response after rapid maxillary expansion in class II growing patients: a pilot randomized controlled trial Roberta Lione1,2* , Valerio Brunelli1,2, Lorenzo Franchi3,4, Chiara Pavoni1,2, Bernardo Quiroga Souki5 and Paola Cozza1,2 Abstract Background: The aim of this pilot randomized controlled trial (RCT) was to evaluate the sagittal mandibular response induced by rapid maxillary expansion (RME) therapy in mixed dentition patients with class II malocclusion, comparing the effects of bonded RME and banded RME with a matched untreated class II control group. Methods: This RCT was designed in parallel with an allocation ratio of 1:1:1. The sample consisted of 30 children with a mean age of 8.1 ± 0.6 years who were randomly assigned to three groups: group 1 treated with bonded RME, group 2 treated with banded RME, and group 3 the untreated control group. All patients met the following inclusion criteria: early mixed dentition, class II molar relationship, transverse discrepancy ≥ 4 mm, overjet ≥ 5 mm, and prepubertal skeletal maturity stage (CS1–CS2). The expansion screw was activated one quarter of a turn per day (0.25 mm) until overcorrection was reached. For each subject, lateral cephalograms and plaster casts were obtained before treatment (T1) and after 1 year (T2). A randomization list was created for the group assignment, with an allocation ratio of 1:1:1. The observer who performed all the measurements was blinded to group assignment. The study was single-blinded in regard to statistical analysis. Results: RME was effective in the correction of maxillary deficiency. Class II patients treated with both types of RME showed no significant improvement of the anteroposterior relationship of the maxilla and the mandible at both skeletal and occlusal levels. The acrylic splint RME had significant effects on reducing the skeletal vertical dimension and the gonial angle. Conclusions: The orthopedic expansion did not affect the sagittal relationship of class II patients treated in the early mixed dentition when compared with the untreated control group. Additional studies with a larger sample are warranted to elucidate individual variations in dento-skeletal mandibular response to the maxillary expansion protocol in class-II-growing patients. Trial registration: ClinicalTrials.gov NCT03159962. Keywords: Rapid maxillary expansion, Mandibular response, Class II malocclusion, Growing subjects * Correspondence: 1 Department of Clinical Sciences and Translational Medicine, University of Rome “Tor Vergata”, Viale Oxford, 81, 00133 Rome, Italy 2 Department of Dentistry UNSBC, Tirana, Albania Full list of author information is available at the end of the article © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Lione et al. Progress in Orthodontics (2017) 18:36 Background Class II malocclusions are commonly observed in orthodontic patients [1]. During treatment planning among the several dento-skeletal pattern combinations of class II malocclusion, it is important to consider the maxillary transverse deficiency, which is often overlooked [2]. Tollaro et al. [3] showed an underlying posterior interarch transverse discrepancy of 3 to 5 mm in subjects in early mixed dentition with class II malocclusions without posterior crossbites in centric occlusion. When these class II patients are asked to posture their lower jaw forward in a class I molar relationship, this transverse discrepancy (i.e., maxillary constriction) can be observed clinically [3]. It was postulated that in these subjects, the mandible is kept in a distal position relative to centric relation because the constricted maxilla is holding it back [4, 5]. The presence of a primitive transverse discrepancy between the dental arches induces a backward position of the mandible, as the occlusal goal is to obtain the highest number of functional contacts [5]. As reported by several authors [6–9], widening the maxilla with rapid maxillary expansion often leads to spontaneous forward posturing of the mandible during the retention period. The orthopedic expansion removes occlusal interferences, allowing the mandible to posture forward, thus improving the sagittal relationships [10, 11]. The mandibular arch acts as a “foot” that moves forward after the “shoe” is widened [4, 5]. Caprioglio et al. reported that patients with smaller mandibular length and more acute superior gonial angles are expected to show greater improvement in class II molar relationship [2]. However, the effectiveness of rapid maxillary expansion (RME) on the sagittal dental or skeletal parameters is still controversial because very little has been written regarding the behavior of anteroposterior mandibular changes in class-II-growing subjects who underwent RME as the phase 1 treatment intervention. The reported significant occlusal improvement could be attributed to other reasons, i.e., skeletal growth or the use of additional appliances during the transition from mixed to permanent dentition. Moreover, the majority of the studies [3, 6–9] show some limits: they are not randomized [12], they are not prospective, and they have no control group or they use patients from growth studies as a source for the control group. Considering that it was not possible to estimate from previous studies the standard deviation to be used for sample size calculation of the main trial with special regards to the type of intervention and observation intervals, the primary objective of the present investigation was to conduct a pilot randomized controlled trial (RCT) evaluating the changes in the anteroposterior mandibular position induced by bonded or banded RMEs compared with an untreated class II control group. Page 2 of 7 Methods The Consolidated Standards of Reporting Trials (CONSORT) checklist was used as a guideline for conducting and reporting this trial [13]. The present pilot RCT was designed as a prospective three-arm parallel group randomized clinical trial with a 1:1:1 allocation ratio. The study was approved by the Ethics Committee at the University of XXXX, (protocol number 130/14), and informed consent was obtained from the patients’ parents. The trial was registered on ClinicalTrials.gov (registration number: NCT03159962). A total of 30 subjects with a mean age of 8.1 ± 0.6 years (range 6.6–9.1 years) who sought for an orthodontic treatment, were enrolled in the Department of Orthodontics at the University of XXXX. All children met the following inclusion criteria: early mixe (...truncated)