Introduction
Rapid palatal expansion (RPE) is a widely used orthopedic procedure for patients with maxillary deficiency, which can cause unilateral or bilateral posterior crossbites and dental crowding [1]. When expansion forces are applied to the teeth and alveolar processes, the periodontal ligament compresses, bending the alveolar processes and tilting the anchor teeth. If force exceeds the threshold for skeletal expansion, the midpalatal suture eventually separates [2,3].
Although midpalatal splitting via RPE is possible in adults, increased skeletal maturity leads to greater interdigitation of the palatal suture, limiting both expansion and stability. Additionally, RPE can cause adverse effects on periodontal and dental structures, including buccal tipping of anchor teeth [4,5]. To address these limitations, surgically assisted rapid palatal expansion (SARPE) was introduced as an alternative to tooth-borne RPE. Although SARPE has lower morbidity compared with orthognathic surgery, it still carries surgical risks, including hemorrhage, infection, trauma to central incisors, hospitalization, and high costs [6,7].
Interest has grown in the use of microimplants or miniscrew-assisted rapid palatal expansion (MARPE). MARPE can involve tooth-bone-borne or bone-borne expansion, using four miniscrews to transfer expansion forces directly to the palate. This approach maximizes skeletal effects while minimizing dentoalveolar side effects, achieving results comparable to SARPE [8,9]. Although several studies have demonstrated MARPE’s efficacy in late adolescents and adults [8-10], to the best of our knowledge, few have examined its use in younger patients.
In this report, we present three cases of MARPE treatment in patients at different dentition stages: early mixed, late mixed, and permanent dentition. These cases highlight MARPE’s effectiveness in younger patients and provide insights into its clinical application.
Case reports
The publication of these case reports and any supplemental photographs was approved by the patients’ legal guardians, with informed consent provided.
1. Case 1
A 7-year-old girl with early mixed dentition visited Seoul National University Dental Hospital presenting with anterior crossbite as her chief complaint. Intraoral examination revealed Class III molar and canine relationships, with bilateral maxillary first and second premolars restored with stainless steel crowns (Fig. 1). She had a concave facial profile, and extraoral radiographs indicated skeletal Class III malocclusion with maxillary retrusion and mandibular protrusion (- 0.95° of A point-Nasion-B point) (Fig. 2). Her cervical vertebral maturation (CVM) stage was at CS 2. Given her chief complaint, maxillary arch length discrepancy, and midfacial deficiency, orthopedic treatment with facemask and maxillary expansion was recommended. However, as all primary molars were restored with stainless steel crowns, concerns arose regarding anchor loss with tooth-borne RPE. To enhance anchorage and optimize facemask treatment, MARPE was chosen as a faster, more reliable treatment option.
A maxillary skeletal expander (MSE) type 1 (Biomaterial Korea Inc., Seoul, Korea) with a 10.0 mm expansion jackscrew was used, supported by 4 palatal miniscrews (1.5 mm diameter and 9.0 mm length) from the same manufacturer. The patient was required to activate the screw by 0.2 mm daily. Two weeks after MARPE activation, she was instructed to wear a facemask for at least 12 hours per day. Extraoral force was applied at approximately 20° anteroinferiorly to the occlusal plane. After 5 weeks of activation, a positive overjet was established, however, the right posterior miniscrew loosened, and inflammation with pain developed on the left posterior arm due to tight palatal mucosa contact (Fig. 3B). The loosened screw and arm were removed, and screw activation was discontinued while facemask use continued.
At 4 months, with increased arch width and an over-corrected overjet, all appliances were removed. The patient achieved a convex facial profile, and the anteroposterior skeletal discrepancy was resolved (Fig. 3D - 3F). Changes in cephalometric measurements before and after treatment are listed in Table 1. Overexpansion was performed to prevent relapse, and the changes in arch dimensions of both the maxilla and mandible are summarized in Table 2. Retention with PreOrtho (Biomaterial Korea Inc.) type 3 began immediately. Intraoral and extraoral photos taken 9 months after appliance removal confirmed a stable positive anterior overjet and convex facial profile (Fig. 4).
2. Case 2
A 9-year-old girl with late mixed dentition presented with concerns that a removable expansion plate used at a local clinic had failed to correct her maxillomandibular discrepancy. She sought immediate orthodontic treatment. Intraoral and panoramic radiographs revealed a congenitally missing right maxillary lateral incisor and exfoliation of the primary lateral incisor, primary canine, and primary first molar of the maxilla. She was diagnosed with dental Class III malocclusion with anterior and bilateral posterior crossbite (Fig. 5).
Cephalometric analysis indicated skeletal Class III malocclusion with maxillary and mandibular protrusion. The patient exhibited mandibular hypergrowth and a straight facial profile (Fig. 6). Given her previous treatment duration, immediate arch expansion with maxillary protraction was preferred. Owing to multiple exfoliating primary teeth and her CVM stage at CS 4, anchorage reinforcement was crucial. To optimize facemask efficacy, modified MARPE with guiding arms was selected as the treatment.
An MSE type 1 (Biomaterial Korea Inc.) with a 10.0 mm expansion jackscrew was used, supported by 4 palatal miniscrews (1.5 mm diameter and 9.0 mm length) (Fig. 7A). The patient activated the jackscrew 0.2 mm daily for 4 weeks while wearing a facemask for at least 12 hours per day. Extraoral force was applied approximately 20° anteroinferiorly to the occlusal plane. After 3 months, with posterior bite raising, a positive anterior overjet was achieved (Fig. 7B, 7C). Facemask therapy continued, and screw activation was adjusted to every other day for an additional 8 weeks. At 7 months, her facial profile appeared convex, and the anterior guiding arms were removed (Fig. 7D, 7E). She continued turning the screw every other day for another 10 weeks to overcorrect the posterior crossbite. By 10 months, positive anterior and posterior overjet were well established, and the device was fully removed (Fig. 8A). No adverse periodontal effects were observed. One month later, braces were bonded with a transpalatal arch to maintain maxillary intermolar width (Fig. 8B). Eleven months after MARPE removal, the congenitally missing right maxillary lateral incisor and peg-shaped left maxillary lateral incisor were restored with composite resin (Fig. 8C - 8E). After transi-tioning to fixed appliances, extraoral photos and lateral cephalogram confirmed that her facial profile remained stable (Fig. 9, Table 3).
3. Case 3
An 11-year-old boy with permanent dentition visited for orthodontic treatment. Intraoral examination revealed severe maxillary anterior crowding and anterior crossbite of both lateral incisors (Fig. 10). Based on orthodontic examination, the patient was diagnosed with skeletal Class I malocclusion with mandibular protrusion and dental Class II malocclusion with a narrow maxillary arch (Fig. 11).
Severe maxillary arch length discrepancy often necessitates premolar extractions. However, considering his straight facial profile and parental reluctance toward extractions, maxillary expansion was proposed as the treatment option. As his CVM stage was at CS 4, making tooth-borne expansion less effective than at earlier stages, enhanced anchorage was prioritized for maximal expansion. Ultimately, MARPE was proposed as the treatment option.
The expander and miniscrews used were identical to those in the previous cases. The patient activated the jackscrew by 0.2 mm per day for 4 weeks, followed by 3 months of retention. After 4 months, the MARPE anterior arms were removed, and braces were boned with a 0.014 copper nitinol wire insertion (Fig. 12B, 12C). At 5 months, MARPE was removed, and sufficient space had been created for the remaining crowding, allowing continued treatment with fixed appliances (Fig. 12D, 12F).
Discussion
Maxillary deficiency presents with various clinical manifestations, most notably posterior and anterior crossbites. Studies suggest that a constricted maxillary arch is associated with functional issues, including temporomandibular disorders and sleep-disordered breathing [11-13]. Severe maxillary deficiency can also negatively affect a child’s psychosocial development, making early RPE intervention crucial for optimizing skeletal growth [14].
The debate over whether tooth-borne RPE causes more periodontal damage relative to MARPE remains unresolved. Traditional hyrax expanders apply expansion forces indirectly through the molars and premolars to the midpalatal suture, often causing buccal tipping of anchor teeth and reducing buccal bone thickness, potentially leading to alveolar dehiscence [15-17]. Tooth-borne RPE generates greater expansion at the crown level and increases alveolar inclination in the first molar region, however, studies have shown no significant difference in absolute dental tipping values between expander types. Skeletal and dental changes are similar with both expander types, with dental effects exceeding skeletal changes [3,10,18,19]. Additionally, overexpansion with tooth-borne RPE can result in uprighting of the molars over time, minimizing long-term buccal flaring [20]. Maxillary arch width remains stable after RPE removal, without clinically significant buccal gingival attachment loss.
Nevertheless, MARPE is widely acknowledged to induce greater skeletal expansion while minimizing dentoalveolar side effects [10,21]. MARPE’s rigid structure promotes more parallel maxillary expansion rather than the triangular pattern observed with tooth-borne expanders. A study on late adolescent patients found that while skeletal changes were less pronounced than dental changes, MARPE achieved greater sutural expansion compared with tooth-borne RPE [21]. Moreover, RPE exhibited significantly greater buccal tipping of anchor teeth and alveolar bending. As shown in Cases 2 and 3, MARPE helped preserve alveolar integrity while achieving skeletal expansion, even in the absence of supporting teeth.
Skeletal maturity strongly influences maxillary expansion outcomes. As palatal suture density increases with age, resistance to expansion forces rises, limiting RPE’s skeletal effects [8,22]. Studies using Hass expanders have demonstrated that patients at earlier skeletal maturation stages (CS 1 - 3) exhibit significantly greater maxillary width increases compared with those at later stages (CS 4 - 6), where expansion primarily affects dentoalveolar structures [15]. To better assess midpalatal suture maturation, Angelieri et al. [23] proposed a classification system (Stages A to E) using CBCT. Stages A and B, observed in younger patients up to 13 years, correspond to earlier skeletal maturation stages (CS 1 - 2) and are more favorable for RPE. In contrast, Stages D and E, characterized by suture fusion, are less responsive to RPE and may require surgical intervention [24]. With MARPE, skeletal expansion in older patients with rigid maxillary interdig-itation has become feasible. This was evident in our third case, where maxillary alignment was achieved without extractions. Similarly, a case report involving a 14-yearold girl with permanent dentition and suture maturation Stage C, where sutural fusion begins, showed that successful expansion was achieved with daily activation [25].
Midpalatal suture closure occurs during the juvenile period, progressing faster in the posterior region. For a more linear opening, the RPE structure must be rigid and positioned posteriorly [26]. In our cases, high palatal vaults and the absence of erupted second molars made miniscrew placement between the first and second molars impractical. Therefore, miniscrews were inserted between the first molars and premolars or primary molars, with additional arms extending to the gingival tissue or teeth to enhance anchorage.
A key factor in MARPE success is the stability of temporary anchorage devices (TADs). Unlike dental implants, which achieve osseointegration, TADs rely on mechanical interlocking with bone shortly after insertion. Premature force application enhances mechanical retention against displacement, ensuring sufficient primary stability for orthodontic loading. However, screws remain vulnerable to failure during early healing owing to immature interfacial bone [27,28]. A minimum healing period of 2 weeks is associated with a high success rate, but delaying loading for at least 3 weeks further improves primary stability, with optimal bone healing occurring at around 6 weeks [28-30]. Although premature loading remains possible, avoiding it during the first 3 weeks improves TAD stability and bone formation. Other TAD failure risk factors include excessive placement torque (> 10 N cm), inflammation, and short screw length [31]. Furthermore, the thickness of the palatal bone increases with age, with younger children exhibiting thinner bone [32,33]. Hence, achieving appropriate screw retention in younger children is challenging. In our cases, the screws used were shorter than those used in prior studies [27], and screw loosening occurred in the first case. In Case 1, given the patient’s skeletal immaturity (CS 2), immediate application of expansion force may have compromised initial stability. To enhance stability, reinforcement strategies should be considered. A resin ball was added to all four screws to prevent loosening in subsequent cases. Additionally, supplementary arms on dental tissues may be necessary for children with an immature maxilla. Furthermore, skeletal maturity assessment in our cases was limited to CVM staging, resulting in an incomplete evaluation of maxillary bone development. CBCT evaluation may be crucial for assessing midpalatal suture maturation and palatal bone thickness in children to determine MARPE suitability. Despite these concerns, the extent of expansion and the effectiveness of screws as anchorage for facemask therapy demonstrated success.
Several reported cases have also successfully used MARPE in patients with insufficient anchorage. Luzzi et al. [34] reported successful cases of TAD-assisted treatment in an 8 - year - old child with ectodermal dysplasia and a 9 - year - old child with dentinogenesis imperfecta. Due to agenesis and the inherent weakness of their teeth, obtaining adequate dental anchorage was impossible. Consequently, a modified form of MARPE was adopted to achieve sufficient palatal expansion, demonstrating that TADs can serve as a reliable anchorage for facemask therapy. Similarly, in a report on an 8 - year - old patient who exhibited unilateral tooth loss and maxillary constriction following the removal of a tumor, treatment with an RPE supplemented with miniscrews and a facemask resulted in significant maxillary protraction and improvement in facial profile [35]. Along with these cases, our cases demonstrate the potential use of MARPE in children.
Facemask therapy is widely used to address midfacial deficiency in Class III malocclusion. TAD-anchored maxillary protraction has proven effective for patients with late mixed dentition and maxillary deficiency, as it minimizes dentoalveolar compensations [36]. With toothborne RPE, facemask therapy applies forward and downward forces on the maxilla while inducing backward mandibular rotation, affecting the soft tissue profile [37]. Moreover, direct skeletal anchorage facilitates significant midfacial development, optimizing orthopedic effects. Inserting miniscrews near the maxillary center of re-sistance transfers orthopedic forces more efficiently to sutural sites, optimizing facemask traction forces [38]. A finite element study demonstrated that positioning the anchorage in the palatal bone rather than the buccal bone provides more stable support, particularly maximizing the forward movement of the maxilla by facemask [39]. This was prominent in Case 1, with significant improvement in facial convexity (Table 1). Furthermore, clockwise mandibular rotation improves the flat facial profile and helps correct Class III malocclusion [37,40,41]. In our Case 1, the Sella-Nasion-B point angle decreased by 1.99°, the mandibular plane angle increased by 2.13°, and the facial axis angle decreased by 1.5°. In Case 2, the mandibular plane angle increased by 1.27°, and the facial axis angle decreased by 1.83°. These improvements contributed to high patient satisfaction. Nevertheless, longterm follow-up is needed to assess the stability of skeletal and soft tissue changes over time.
Facemask therapy combined with tooth-borne appliances often results in labial inclination of the maxillary incisors [42], and direct anchorage from bony structures has been suggested to mitigate this effect [40]. In Case 1, maxillary central incisor inclination (U1 to NA) increased from 24.75° to 29.87° post-treatment, whereas in Case 2, no notable change was observed (24.89° to 24.51°). These variations may be attributed to the fixed orthodontic appliances in Case 2, which likely contributed to enhanced torque control.
Despite strategies such as delayed force application and reinforced anchorage that improve miniscrew retention, patient comfort and acceptance remain key considerations. Miniscrews are generally considered a nonsurgical approach, with no objective evidence supporting higher pain levels relative to those associated with conventional RPE [18,43]. However, in pediatric patients, the use of screws often raises concerns among the children and their guardians. Therefore, careful consideration and parental consent are essential. To foster cooperation in younger patients, sedative agents may be considered. In Cases 1 and 2, mild sedation with nitrous oxide gas improved patient compliance and facilitated successful treatment.
Maxillary expansion has been reported to increase the volume of the upper airway. By separating the midpalatal suture, the narrow palate is transformed into a wider and shallower shape, facilitating the anterior and superior displacement of the tongue, opening the oropharyngeal airway between the tongue and soft palate, and reducing nasal airway resistance. MARPE allows for greater expansion of the basal bone with fewer dentoalveolar effects, producing increased airway improvement compared to RPE [44,45]. In addition, facemask therapy is known to significantly increase upper airway volume [46], leading to a more pronounced maxillary displacement and reduced mandibular rotation when combined with MARPE [47]. In our Cases 1 and 2, upper airway volume was measured using the method proposed by Moon et al. [48] (Table 1, 3). A significant increase in upper airway volume was observed in Case 2, whereas a reduction in volume was noted in Case 1. This may be attributed to the more pronounced posterior and downward rotation of the mandible induced by facemask therapy in Case 1 compared to Case 2. However, lateral cephalograms have limitations in assessing the transverse dimension of airway volume. Therefore, CT imaging would be more suitable for achieving a more precise analysis. Given the patient’s age and potential for further growth, long-term monitoring of airway changes is necessary.
Summary
This report demonstrated the application of MARPE in patients with mixed and permanent dentition. Using palatal bone for anchorage, MARPE enhances skeletal expansion while minimizing dentoalveolar side effects. Moreover, its combination with facemask therapy effectively addresses maxillary deficiency and improves facial profiles in growing patients.
Although MARPE is a viable option for younger patients, their lower bone density and thickness increase the risk of screw loosening, necessitating careful pretreatment assessment. Additionally, miniscrew placement in the palate may be perceived as invasive, requiring informed consent and patient cooperation. Mild sedation can further improve compliance and treatment outcomes in pediatric cases. Despite these considerations, MARPE remains a reliable and effective approach for maxillary expansion and protraction in growing patients, providing favorable skeletal and dental outcomes.
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