Mandibular Response After Rapid Maxillary Expansion in Class II Growing Patients: a Pilot Randomized Controlled Trial

Class II malocclusions are commonly observed in orthodontic patients. 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.

it has been showed 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 (ie, maxillary constriction) can be observed clinically. 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. 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.

As reported by several authors, 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. The mandibular arch acts as a ''foot'' that moves forward after the ''shoe'' is widened.

However, the effectiveness of RME on the sagittal dental or skeletal parameters is still controversial because very little has been written regarding the behavior of antero-posterior 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, ie, skeletal growth or the use of additional appliances during transition from mixed to permanent dentition. Moreover, the majority of the studies show some limits: they are not randomized, 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 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 antero-posterior mandibular position induced by bonded or banded RMEs compared with an untreated Class II control group.