## 1 Introduction  
Among the many factors contributing to malocclusion, anatomical factors can be broadly categorized as skeletal and dental. Skeletal elements include the relative anteroposterior, vertical, and transverse positioning of the maxilla and mandible. The diagnostic and treatment methods for defining and determining these elements have been the subject of much research and discussion. A constricted maxilla is one of the most frequent skeletal components of malocclusions. Narrow maxilla can cause arch length discrepancy resulting in crowding of the dentition and also can cause functional problems resulting from deficient posterior overjet or even posterior crossbite [1]. It is said that narrow maxilla is not only limited to transverse dimensional problem but is also related to the sagittal (i.e., Class II malocclusion) component of malocclusion [1]. Clinicians can resolve this skeletal malocclusion by applying a rapid palatal expander (RPE) in young patients and surgical options in adult patients. The treatment effect of a conventional RPE includes skeletal and dental expansion with more tendency of dental expansion [2]. To increase the skeletal expansion effect of the RPE, a combination of skeletal anchorage to the RPE has been proposed and is now widely accepted in clinical orthodontics [3].  
Skeletal anchorage-assisted RPE has two types: tooth-bone-borne and bone-borne. The tooth-bone-borne type RPE is not only assisted by skeletal anchorage but also supported by teeth [3]. Meanwhile, the bone-borne RPE type receives support solely from skeletal anchorage and is expected to exert only skeletal effects [4; 5]. Although results among studies and arguments among clinicians are conflicting, tooth-bone-borne expander treatment effects are mainly skeletal with some dental effects [3; 6; 7]. The tooth-bone-borne type is the addition of skeletal anchorage, mostly the miniscrew type, to the conventional RPE design and may be more familiar to clinicians who are used to it. Most types of tooth-bone-borne RPE use miniscrews for skeletal anchorage, which is called miniscrew-assisted RPE (MARPE).  
Reports on the treatment effect of MARPE have demonstrated its capability of more skeletal expansion of the maxilla than conventional RPE [8]. Furthermore, some reports have claimed that the mode of expansion is different from that of conventional RPE in that MARPE results in more parallel expansion between the palatal processes of the maxilla, whereas conventional RPE expands the maxilla more anteriorly than posteriorly [9]. Moreover, the age limitation has been extended using MARPE [10]. The age limitation of conventional RPE was considered 15 years after long-term clinical experience and anatomical studies; however, several reports have indicated that MARPE is capable of opening the palatal sutures in adults [11].  
Despite the increasing popularity of MARPE in clinical orthodontics and published studies, more data are needed to elucidate its therapeutic effects. However, no consensus on the activation mode of MARPE, its optimal design, assisted miniscrews, or retention protocols has been established. The reported treatment effects of MARPE differ between studies, which may be because of different MARPE designs, numbers, and sizes of miniscrews used as well as different modes of activation among clinicians. More data should be accumulated to establish the application method of MARPE and understand and predict the results of MARPE applications. Therefore, the purpose of this study was to investigate the skeletal and dental effects of miniscrew-assisted rapid palatal expansion (MARPE) in adolescents using cone-beam computed tomography (CBCT). Changes in zygomatic width and nasal bone deviation were also evaluated.