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. Author manuscript; available in PMC: 2021 Sep 1.
Published in final edited form as: Clin Oral Investig. 2021 Feb 12;25(9):5247–5256. doi: 10.1007/s00784-021-03832-9

Maxillary dentoskeletal outcomes of the expander with differential opening and the fan-type expander: a randomized controlled trial

Camila Massaro 1, Daniela Garib 2, Lucia Cevidanes 3, Guilherme Janson 1, Marilia Yatabe 3, José Roberto Pereira Lauris 4, Antonio Carlos Ruellas 3,5
PMCID: PMC8357852  NIHMSID: NIHMS1688380  PMID: 33580351

Abstract

Objectives

The aim of this study was to compare the maxillary dentoskeletal outcomes of the expander with differential opening (EDO) and the fan-type expander (FE).

Material and methods

Forty-eight patients with maxillary arch constriction in the mixed dentition were randomly allocated into EDO and FE groups. Cone-beam computed tomography scans were acquired before and after expansion. Linear and angular three-dimensional changes were assessed after cranial base superimposition using the ITK-SNAP and the 3D Slicer software. T or Mann-Whitney U tests were used for intergroup comparisons (P<0.05).

Results

The EDO group comprised 24 patients treated with the EDO (13 female, 11 male; 7.6 years). The FE group comprised 24 patients treated with the FE (14 female, 10 male; 7.8 years). Skeletal lateral displacements were greater in the EDO group with greater expansion in the orbital, nasal cavity, zygomatic bone, and palate regions (mean intergroup differences of 0.4, 0.8, 0.9, and 1.1 mm, respectively). Intercanine expansion and canine buccal inclination were greater in the FE group, while intermolar distance changes and molar buccal inclination were greater in the EDO group. Similar changes were observed for vertical and anteroposterior displacements and palatal plane rotation.

Conclusions

The EDO produced greater transverse skeletal expansion compared to the FE, with similar vertical and anteroposterior effects. Dental changes were greater in the molar region for patients treated with the EDO and in the canine region for patients treated with the FE.

Clinical relevance

The EDO and the FE are capable of producing skeletal changes in the mixed dentition. The decision between both expanders will depend on the amount of expansion required in the molar region and in the nasomaxillary complex.

Trial registration

The trial was registered at ClinicalTrials.gov, under the identifier NCT03705871.

Keywords: Orthodontics, interceptive; Palatal expansion technique; Orthodontic appliances; Imaging, three-dimensional

Introduction

Rapid maxillary expansion (RME) is the orthopedic procedure of choice to treat maxillary constriction and posterior crossbite. Dental, skeletal, and periodontal effects of this procedure have been widely discussed in the orthodontic literature [1–13]. Correction of maxillary constrictions can be accomplished with different appliance designs [1, 14, 15]. Conventional expanders, including Haas and Hyrax type, promote similar increases of the maxillary intermolar and intercanine distances by means of parallel opening of the expander screw [1, 10, 12, 16]. When maxillary constriction is more evident in the anterior region of the arch, the fan-type expander (FE) or the expander with differential opening (EDO) can be indicated [14, 15]. The FE has a posterior hinge that concentrates the expansion effect in the intercanine region, with mild effects in the intermolar distance [8, 10, 14]. The EDO has two palatal screws and the differential activation protocol promotes different amounts of expansion for the anterior and posterior regions of the maxillary arch [12, 15]. Careful selection of the maxillary expander is important to correct the maxillary morphology avoiding negative side effects associated with undesired under or extreme overexpansion.

Previous comparisons of the immediate outcomes produced by Haas and Hyrax expanders showed similar orthopedic effects [9, 17]. When comparing Hyrax and FE using lateral headfilms and maxillary dental models, similar expansion in the intercanine distance was noticed, while the conventional opening group showed greater expansion in the nasal cavity, maxillary width, and intermolar distance [8, 10]. A recent randomized clinical trial comparing the Hyrax expander and the EDO using dental models and occlusal radiographs showed that the EDO promoted greater split of the anterior region of the midpalatal suture and greater increase of the intercanine distance [12]. Our previous comparison between the EDO and the FE using digital dental models showed distinct maxillary arch width and shape changes after RME. The EDO showed greater dentoalveolar expansion in the molar region, while the FE produced greater intercanine distance increase [13].

With the advent of cone-beam computed tomography (CBCT) in dentistry, studies were performed to assess the RME effects using this tool, contributing to a better understanding of the dentoalveolar and skeletal effects [9, 18–20]. We previously demonstrated dental arch changes of the EDO and FE expanders [13]. However, no previous study has compared the skeletal outcomes of the EDO and the FE by means of computed tomography. In order to help clinicians make a decision between these two types of expanders, some issues should be clarified. Are the anteroposterior, transverse, and vertical orthopedic effects different between treatment with the EDO and the FE? Are the zygomatic bone changes similar between the two types of expanders? Do both expanders produce similar tooth inclination in the canine and molar region?

Specific objectives or hypotheses

The aim of this study was to compare the maxillary dentoskeletal outcomes of the expander with differential opening (EDO) and the fan-type expander (FE) in the mixed dentition, by means of CBCT three-dimensional models superimposed on the cranial base. The null hypothesis is that both therapies show similar outcomes.

Material and methods

Trial design

This was a single-center randomized controlled trial (RCT) with two-parallel arms and a 1:1 allocation ratio. This RCT followed the Consolidated Standards of Reporting Trials (CONSORT) statement and guidelines [21] and was registered at Clinicaltrials.gov (NCT03705871). Ethical approval was obtained by the Research Ethics Committee of Bauru Dental School, University of São Paulo, Brazil (protocol number: 71648917.6.0000.5417) and informed consent was obtained from all patients and their parents or legal guardians.

Participants, eligibility criteria, and settings

Patients were recruited at the Orthodontic Clinic of Bauru Dental School, University of São Paulo, Brazil, from November 2017 to June 2018. The selection criteria were patients of both sexes from 7 to 11 years of age with maxillary constriction and posterior crossbites. The exclusion criteria were a Class III malocclusion, craniofacial syndromes, clinical absence of maxillary deciduous canines, and history of previous orthodontic treatment.

Interventions

The EDO group was treated with the expander with differential opening (n=24; Fig. 1), and the FE group was treated with the fan-type expander (n=24; Fig. 1). All patients from both groups were treated by the same orthodontist (CM). Orthodontic bands were adapted on the maxillary second deciduous molars, clasps were bonded on the maxillary deciduous canines, and a wire extension was soldered on the palatal aspect of the first permanent molars (Fig. 1).

Fig. 1.

Fig. 1

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Expander with differential opening (a–d) and fan-type expander (e–h)

The anterior and posterior screws of the EDO (Peclab Ltda., Belo Horizonte, MG, Brazil) were concurrently activated for 6 days, with an activation protocol of two 1/4 turns in the morning and two 1/4 turns in the evening. Afterwards, only the anterior screw was activated for 4 additional days following the same activation protocol. The amount of expansion was 8 mm and 4.8 mm in the anterior and posterior screws, respectively (Fig. 1c).

The screw of the FE (Morelli Ortodontia, Sorocaba, SP, Brazil) was activated two 1/4 turns in the morning and two 1/4 turns in the evening for 10 days, resulting in a screw expansion of 8 mm (Fig. 1g). In both groups, after a 10-day active phase, the expander was kept in the oral cavity as a retainer for 6 months. At the end of the retention phase, the expander was removed, and a removable retention plate was installed. No clinical data was generated after the delivery of the retention removable plate.

The 3D Accuitomo CBCT scanner (J. Morita Corp, Kyoto, Japan) was used to acquire CBCT scans at 2 time points for each patient. The first CBCT (T1) scan was obtained before treatment and the second scan (T2) after the rapid maxillary expansion (T2), from the first to the sixth month after active phase of the expansion (mean of 3 months after expansion). Images were saved in DICOM format. The image acquisition protocol was adjusted to reduce as much as possible the radiation dose [22], with 90Kvp, 7mA, FOV 17×12 cm, lower exposure time allowed of 17.5 s, and voxel size of 0.3mm.

Outcomes

The primary outcomes assessed in this study were maxillary dentoskeletal lateral displacements and changes in molars and canines buccolingual inclination. Anteroposterior and vertical displacements and maxillary rotation were considered secondary outcomes.

The 3D analysis was performed using the two open-source software ITK-SNAP, version 2.4.0 (www.itksnap.org) [23], and 3D Slicer, version 4.10.2 (www.slicer.org) [24]. The following previously validated steps [25–27] for image analysis were performed:

  1. Construction of the 3D volumetric label maps (segmentations) and 3D surface models (vtk files) of the T1 scans: ITK-SNAP and 3D Slicer software (Intensity Segmenter and Model Maker tools);

  2. Head orientation of the T1 model: 3D Slicer (Transforms tool). The 3D model from each patient at T1 was oriented to a standardized fixed coordinate system using as reference the Frankfurt plane (bilateral orbitale and porion) perpendicular to the midsagittal plane (glabella, crista galli, and basion) [25]. The matrix generated from this process was saved and applied to the T1 scans and segmentations;

  3. Approximation: 3D Slicer (Transforms tool). The T2 scan was moved to reach the best fit superimposition of the cranial base in relation to the oriented T1 scan [26];

  4. Construction of 3D volumetric label maps of the approximated T2 scans: ITK-SNAP and 3D Slicer (Intensity Segmenter and Model Maker tools);

  5. Voxel-based registrations of the cranial base: 3D Slicer (Growing Registration on the CMF Registration tool). The software automatically superimposes the approximated T2 scan over the oriented T1 scan, using the cranial base as reference [26];

  6. Pre-labelling: ITK-SNAP. The T1 oriented and T2 registered segmentations were cleaned, and the mandible was removed to facilitate placing of the landmarks by changing the color of the label without modifying the anatomy [27]. The following landmarks were placed: right and left orbitale (OrR and OrL), right and left zygomatic bone (ZygR and ZygL), right and left nasal cavity (NCR and NCL), right and left palatine foramen (PFR and PFL), right and left apex of the mesial root of the maxillary first permanent molars (M′R and M′L), right and left root apex of the maxillary deciduous canines (C′R and C′L,), right and left mesiobuccal cusp tip of the maxillary first permanent molars (MR and ML), right and left cusp tip of the maxillary deciduous canines (CR and CL), anterior nasal spine (ANS), and posterior nasal spine (PNS), as shown in Fig. 2;

  7. Generation of the T1 and T2 3D surface models with landmarks: 3D Slicer (Model Maker tool). 3D models were generated for the segmented skull and the pre-labelled landmarks for both T1 and T2 files of each patient;

  8. Quantitative assessments: 3D Slicer (Quantification of 3D Components, Q3DC, tool). Anterior, inferior, and lateral displacements as well as expansion, buccal inclination, and clockwise rotation were considered positive values.

Fig. 2.

Fig. 2

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Three-dimensional models illustrating the pre-labelled landmarks. Right and left orbitales (OrR and OrL), placed at the lowest point in the inferior margin of the right and left orbitals; right and left zygomatic bones (ZygR and ZygL), placed at the most inferior portion of the right and left zygomatic bones; right and left nasal cavity (NCR and NCL), placed at the most inferior and external point of the concavity of the right and left nasal cavity; right and left palatine foramen (PFR and PFL), placed at the middle and most inferior point of the right and left palatine foramen; right and left apex of the mesial root of the maxillary first permanent molars (M′R and M′L); right and left root apex of the maxillary deciduous canines (C′R and C′L); right and left cusp tip of the mesiobuccal cusp of the maxillary first permanent molars (MR and ML); right and left cusp tip of the maxillary deciduous canines (CR and CL); posterior nasal spine (PNS) and anterior nasal spine (ANS)

The maxillary lateral displacement comprised the changes in the distance between OrR and OrL, NCR and NCL, ZygR and ZygL, PFR and PFL, MR and ML, and CR and CL. For assessment of the maxillary anteroposterior and vertical displacements, midpoints were generated for the following bilateral landmarks: orbitale (OrM), nasal cavity (NCM), zygomatic bone (ZygM), palatine foramen (PFM), cusp tip of the maxillary first permanent molars (MM), and cusp tip of the maxillary deciduous canines (CM). Angular measurements were used to assess the maxillary rotation and the changes in the molar and canine buccolingual inclination. Vertical maxillary rotation was assessed through the pitch changes in the palatal plane (ANS-PNS). The lateral maxillary rotation was calculated considering the roll changes of the angle formed by the right and left orbitale–zygomatic lines (OrR-ZygR–OrL-ZygL). Changes in molar and canine buccolingual inclination were measured comparing the T1-T2 roll angle of the tooth long axis relative to the Or-Zyg line on right and left sides.

Sample size calculation

The sample size was calculated considering a significance level of 5% and a statistical power of 80%. For a standard deviation of 2.18 mm for the change in the intercanine distance [12] and to detect a minimal intergroup difference of 2.0 mm, a sample of 20 patients was required. Considering possible losses, 24 patients were selected in each group.

Randomization

A block randomization was performed using the Web site Randomization.com (http://www.randomization.com) [28]. The software generated a randomization list, ensuring equal distribution in both groups. Allocation concealment was achieved with sequentially numbered, opaque, sealed envelopes, containing the treatment allocation cards. In addition, opacity was implemented by inserting the card with the assignment into foil. The envelopes containing the name of the expander were prepared before trial commencement and were sequentially opened for each participant during recruitment. The initials of the participants’ names were written on the envelope before opening it. The randomization process, allocation concealment, and implementation were performed independently by different researchers.

Blinding

Blinding during treatment was not possible for the orthodontist and patient since both knew the type of maxillary expander that was installed. However, the study design was blinded during analysis since data was unidentified before assessment.

Statistical analysis

One orthodontist (CM) performed all the measurements and 30% of the sample was assessed twice after a 30-day interval. The intra-rater error was assessed using intraclass correlation coefficients (ICC).

Normal distribution of the variables was verified with Shapiro-Wilk tests. Intergroup comparisons regarding age and sex were performed with t and chi-squared tests, respectively. T tests or Mann-Whitney U tests with Holm-Bonferroni correction were used for intergroup comparisons. All statistical analyses were performed using IBM SPSS Statistics for Mac, version 24.0 (Armonk, NY: IBM Corp.). The level of significance considered was 5%.

Results

Participant flow

The flow chart was previously published [13]. From the 300 individuals assessed for eligibility, 240 were excluded because did not meet the inclusion criteria and 12 decline to participate. Forty-eight patients were enrolled, and all participants completed the study, 24 patients in the EDO group and 24 patients in the FE group.

Baseline data

Demographic characteristics of each group at baseline are presented in Table 1. Both groups were similar regarding sex, age, and interorbital, interzygomatic, intermolar, and intercanine distances at baseline (Table 1).

Table 1.

Intergroup comparisons for sex ratio, age, and maxillary widths at baseline

Variable EDO, n=24 FE, n=24 P
Mean (SD) Mean (SD)
Initial age (years) 7.62 (0.92) 7.83 (0.96) 0.448
Sex Female 13 14 0.771
Male 11 10
OrR-OrL 63.54 (4.91) 64.03 (3.67) 0.701
ZygR-ZygL 78.88 (4.20) 77.01 (3.22) 0.091
MR-ML 49.61 (2.70) 48.26 (2.55) 0.084
CR-CL 30.24 (2.91) 29.78 (2.36) 0.549
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Chi-squared test (sex); t test (age and maxillary widths); P < 0.05. EDO, expander with differential group; FE, fan-type expander; SD, standard deviation; Or, orbitale; Zyg, zygomatic; M, first permanent molars; C, deciduous canines; R, right; L, left

Number analyzed for each outcome

Rapid maxillary expansion was performed in 48 patients. The EDO group was composed by 24 patients treated with the EDO (13 female, 11 male; mean initial age of 7.6 years ± 0.9). The FE group comprised 24 patients treated with the FE (14 female, 10 male; mean initial age of 7.8 years ± 0.9).

Intra-rater reliability varied from very good to excellent, with an intraclass correlation coefficient ranging from 0.78 to 0.99 [29].

Intergroup comparison is shown in Table 2. The EDO promoted significantly greater expansion when compared to the FE at the level of orbitale (0.4 mm ± 0.1), nasal cavity (0.8 mm ± 0.2), zygomatic bone (0.9 mm ± 0.1), palatine foramen (1.1 ± 0.1), and permanent first molar cusp tips (2.5 mm ± 0.2). The intercanine distance expansion was significantly greater in the FE group (−0.7 mm ± 0.3). Molar (0.9° ± 0.3) and canine (−3.0° ± 0.8) buccal inclinations were significantly greater in the EDO and FE groups, respectively. The maxillary vertical and anteroposterior displacements were similar in both groups. Palatal plane rotation was similar for both groups (P=0.120) while the lateral maxillary rotation was significantly greater in the EDO group (P=0.009). Figures 3 and 4 show the cranial base superimposition for a patient from the EDO and FE groups, respectively.

Table 2.

Intergroup comparisons (t or Mann-Whitney U tests with Holm-Bonferroni correction method)

Variable EDO, n=24 FE, n=24 Difference (SD) 95%CI P
Mean (SD) Mean (SD) Upper, lower
Lateral displacements (mm) OrR-OrL 1.50 (0.47) 1.00 (0.50) 0.49 (0.14) 0.21; 0.78 0.001†*
NCR-NCL 3.09 (0.62) 2.28 (1.03) 0.80 (0.24) 0.31; 1.30 0.002†*
ZygR-ZygL 2.63 (0.46) 1.65 (0.52) 0.97 (0.14) 0.68; 1.26 <0.001†*
PFR-PFL 2.12 (0.50) 0.92 (0.30) 1.19 (0.12) 0.94; 1.44 <0.001†*
MR-ML 5.03 (1.09) 2.51 (0.75) 2.51 (0.27) 1.96; 3.05 <0.001†*
CR-CL 8.16 (1.03) 8.95 (1.36) −0.78 (0.34) −1.49; −0.08 0.011‡*
Sagittal displacements (mm) Orm 0.27 (0.19) 0.23 (0.17) 0.03 (0.05) −0.07; 0.14 0.386‡
NCm 0.80 (0.27) 0.82 (0.46) −0.02 (0.10) −0.24; 0.19 0.829†
Zygm −0.12 (0.22) −0.14 (0.28) 0.01 (0.07) −0.13; 0.16 0.810†
PFm 0.51 (0.26) 0.45 (0.39) 0.06 (0.09) −0.13; 0.26 0.140‡
Mm 0.18 (0.64) 0.11 (0.45) 0.07 (0.16) −0.24; 0.40 0.643†
Cm 1.34 (0.70) 1.58 (0.70) −0.23 (0.20) −0.64; 0.17 0.250†
ANS 0.75 (0.38) 0.74 (0.51) 0.00 (0.13) −0.26; 0.26 0.982†
Vertical displacements (mm) Orm 0.10 (0.18) 0.08 (0.13) 0.01 (0.04) −0.07; 0.11 0.570‡
NCm 0.58 (0.41) 0.47 (0.39) 0.10 (0.11) −0.12; 0.34 0.397‡
Zygm 0.04 (0.17) 0.10 (0.23) −0.05 (0.05) −0.17; 0.05 0.316†
PFm 1.03 (0.40) 0.88 (0.46) 0.15 (0.12) −0.09; 0.41 0.215†
Mm 0.35 (0.34) 0.56 (0.35) −0.21 (0.10) −0.41; 0.00 0.043†
Cm 0.47 (0.41) 0.27 (0.55) 0.19 (0.14) −0.08; 0.48 0.165†
ANS 1.09 (0.28) 0.93 (0.34) 0.16 (0.09) −0.01; 0.35 0.068†
Angular changes (°) ANS-PNS 0.46 (0.35) 0.64 (0.42) −0.17 (0.11) −0.40; 0.04 0.120†
OrR-ZygR/OrL-ZygL 3.43 (1.80) 2.21 (1.21) 1.22 (0.44) 0.32; 2.11 0.009†*
Or-Zyg/M′-M 2.19 (1.28) 1.27 (0.71) 0.92 (0.30) 0.31; 1.52 0.004†*
Or-Zyg/C′-C 5.01 (2.25) 8.09 (3.70) −3.08 (0.88) −4.86; −1.29 0.001†*
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†

t test;

‡

Mann-Whitney U test;

*

Statistically significant.

EDO, expander with differential group; FE, fan-type expander; SD, standard deviation; Or, orbitale; NC, nasal cavity; PF, palatine foramen; Zyg, zygomatic; M, first permanent molar cusp tip; C, deciduous canines cusp tip; M′, first permanent molars root apex; C′, deciduous canines root apex; m, midpoint; R, right; L, left

Fig. 3.

Fig. 3

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Cranial base superimposition of the pre- (white) and post- (red) expansion 3-dimensional surface models in an anterior, lateral, and inferior view of a patient treated with the expander with differential opening

Fig. 4.

Fig. 4

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Cranial base superimposition of the pre- (white) and post- (green) expansion 3-dimensional surface models in an anterior, lateral, and inferior view of a patient treated with the fan-type expander

Harms

No important harm was caused to the participants of this study. Pain or discomfort was reported by 62% and 45% of the patients treated with the EDO and the FE, respectively. In addition, a slight change in the nasal bridge region was observed by one patient of the FE group after the active phase of the expansion. It was a temporary effect that spontaneously disappeared in the retention phase. Two CBCT scans were acquired from the subjects in this study. The acquisition protocol was adjusted following radiology ALADA (As Low As Diagnostically Acceptable) principles to minimize the radiation dose to patient and surroundings to a level as low as reasonably achievable.

Discussion

Evaluation of maxillary constriction prior to treatment is required to determine whether the patient presents different severities of transverse deficiency at the level of the canine compared to the molar regions. The outcomes of expansion depending on the appliance design should be taken into account to guide treatment planning. The EDO and the FE caused differential expansions between the anterior and the posterior maxillary arch widths [8, 10, 12, 13, 15]. Previous studies showed that the EDO and the FE demonstrated greater intercanine expansion when compared with conventional expanders [8, 10, 12, 15]. We showed in a previous comparison of dental arch changes after differential and fan expansions using digital dental models a greater intermolar increase in patients treated with the EDO and a slightly greater intercanine increase in patients treated with the FE. [13]. The present study intended to elucidate the three-dimensional dentoskeletal differences between the two expanders.

To overcome the limitations of a two-dimensional assessment, CBCT scans were used. CBCT imaging allows assessment of skeletal changes in craniofacial imaging analysis, demonstrating high accuracy and reliability [30, 31]. CBCT scans have lower cost, lower radiation dose, and less metallic artifacts compared to helical CT [32, 33]. The use of CBCT scans in this study allowed assessment of maxillary 3D displacements relative to the cranial base after RME, which have not been previously described. A previous systematic review evaluating RME outcomes in growing patients showed that both CT and CBCT are useful tools to assess the three-dimensional expansion effects [20]. Among the advantages, quantification of the lateral changes in the zygomatic bone region, not possible in a bidimensional image, was successfully demonstrated in the present 3D assessment. Many previous studies used CBCT to evaluate conventional RME outcomes in growing patients [9, 18, 19]. However, the EDO and FE was not previously compared by means of CBCT images in non-cleft patients. In the present study, CBCT replaced the initial and postexpansion orthodontic records. Following the ALADAIP principles [22], the acquisition protocol was adjusted to decrease the radiation exposure as much as possible without compromising image assessment. Additionally, the good to excellent intra-rater reliability showed that the method was reliable.

The results of the intergroup comparison for initial age, sex ratio, and maxillary widths at baseline confirmed the sample homogeneity and ensured an effective randomization and allocation of the patients, minimizing the risk of bias in intergroup comparisons (Table 1) [34]. The activation amount in the anterior region was also standardized to ensure a viable intergroup comparison.

The present study outcomes confirm that the EDO and the FE are capable of producing orthopedic effects after RME procedure (Table 2 and Figs. 3 and 4). The EDO promoted a statistically significant greater increase in all transverse skeletal distances including the interzygomatic (Zyg-Zyg) and interorbital (Or-Or) distances. The greatest intergroup skeletal difference was observed for the interpalatine foramen distance (PF-PF) that increased on average 1.1 mm more in the EDO group. The skeletal expansion at the level of palatine foramen was approximately 26% of the anterior screw activation in the EDO group and 11% of the screw activation in the FE group. In addition, treatment with the EDO led to a slightly and significantly greater lateral rotation of the maxillary halves (OrR-ZygR–OrL-ZygL) than treatment with the FE. These intergroup differences are probably due to the posterior screw activation of the EDO. Previous studies with anteroposterior cephalometric radiographs showed greater maxillary and nasal cavity expansion for the Hyrax expander compared to the fan-type expander [8, 10]. No previous study using CBCT scans has assessed outcomes of the fan-type expander in non-cleft patients. A previous study using CBCT in a sample of individuals with cleft lip and palate also demonstrated that fan-type expanders produced slight less maxillary transverse expansion at the level of permanent first molars compared to Hyrax expanders [11]. A previous CBCT study in patients with cleft lip and palate demonstrated similar nasal cavity and maxillary width changes of EDO and Hyrax expanders [35]. Nasal cavity expansions of averages of 3.0 and 2.2 mm were observed in the EDO and FE groups, respectively. Nasal cavity increase might be beneficial to patients with oral breathing and sleep apnea [1–3, 6]. The nasal cavity expansion was slightly greater in the EDO group, and further studies should evaluate the functional impact of these changes in pediatric obstructive sleep apnea.

Intermolar expansion was twice greater in the EDO group (Table 2). This finding is in accordance with previous assessment performed in digital dental models [13]. This intergroup difference is explained by the expansion of the posterior screw in the EDO. Conversely to the intermolar distance, the intercanine distance had a significantly greater increase in the FE group than in the EDO group (mean difference of 0.7 mm). The greater canine buccal inclination found for the FE group in this study (mean difference of 3.0°) may explain the greater increase in the intercanine distance also observed in this group (Table 2).

No intergroup difference was observed for the maxillary sagittal and vertical effects relative to the cranial base (Table 2). The anteroposterior and superoinferior maxillary displacements were mild in both groups. Anterior displacement of the anterior nasal spine, nasal cavity, and palatine foramen showed that the nasomaxillary complex moved slightly forward in both groups (Table 2; Figs. 3 and 4). The inferior displacement of the maxillary skeletal landmarks showed a slight downward movement of the maxilla with a negligible clockwise rotation of the palatal plane (less than 1.0° in the EDO and FE). Facial growth might have had a limited influence on the sagittal and vertical displacements observed in this study considering the short T1-T2 interval. Additionally, previous studies assessing RME outcomes reported slight downward and forward maxillary displacements right after RME [1–6, 8, 19, 20]. With the midpalatal suture split, the wider maxilla is moved forward and downward [1–3]. Our results showed that independently of the geometry of the expansion, the maxilla was similarly displaced in the vertical and sagittal directions.

To assess pure dental buccolingual inclination regardless of the maxillary movements, an angle between the long axis of the molars and canines (M′-M and C′-C) and a maxillary line (Or-Zyg) was used on both sides. The average between right and left side changes was used for the intergroup comparison. Both permanent first molars and deciduous canines showed buccal inclination after the expansion in the EDO and the FE groups (Table 2). Previous studies reported buccal inclination in the anchorage teeth after expansion procedure with the EDO and the FE [11, 12]. Greater molar buccal inclination was observed in the EDO group and can be explained by the greater posterior activation in this expander. However, the slightly greater canine buccal inclination in the FE group is harder to explain since the anterior activation was the same in both study groups. A possible explanation is that the posterior hinge in the FE concentrates the activation force in the canine region during the complete active phase of the expansion. In a different manner, the activation of the anterior and posterior screws in the EDO group during the first 6 days of activation better distributes the expansion force between molars and canines, concentrating the stress on the canines only in the final period of activation. Future investigations using finite element analysis may compare the stress distribution between the EDO and FE to clarify this assumption.

A previous study assessing dental arch morphology in patients with maxillary constriction revealed that one third of the patients display greater constriction in the anterior region of the arch [36]. The EDO and the FE are alternative options when greater intercanine expansion is required. In a clinical point of view, in cases with need for intermolar expansion, the EDO or the conventional opening expander should be preferred instead of the fan-shape expander. The clinical indication of the EDO is cases with posterior crossbites including molars and canines associated with a greater constriction in the canine region and a significant maxillary incisor crowding. The FE should be clinically indicated when the posterior crossbite is restricted to the canine region not including molars. Both expander designs produced maxillary skeletal changes. However, a greater orthopedic expansion was observed in patients treated with the EDO compared to the patients treated with the FE. Further evaluation of the influence of the expander design on the changes of nasal air permeability and pediatric sleep apnea index might also contribute to expander-type selection in the mixed dentition.

Limitations

One limitation of the study is the absence of a conventional expander group to compare the outcomes, and a functional analysis. Further studies should compare the skeletal effects of the EDO and the FE with the conventional expander and evaluate the functional impact of the orthopedic differences observed after RME.

Generalizability

The results of this trial may be generalized to non-cleft patients treated in the mixed dentition with similar expander and activation protocol.

Conclusions

The null hypothesis was rejected. In the mixed dentition:

  • The expander with differential opening showed greater maxillary lateral displacement compared with the fan-type expander, at the level of the palate, nasal cavity, zygomatic bone, and orbital.

  • The intercanine distance increase and the canine buccal inclination were greater for the fan-type expander.

  • The intermolar distance increase and the molar buccal inclination were greater for the differential expander.

  • Maxillary vertical and anteroposterior displacements as well as palatal plane rotation were similar for both expander types.

Funding

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001, São Paulo Research Foundation (FAPESP) - Grant numbers 2017/12911–9, 2017/24115–2 and 2018/16154–3, and NIDCR R01 DE024450.

Footnotes

Ethics approval In this article, all procedures involving human participants were in accordance with the ethical standards of the Research Ethics Committee of Bauru Dental School, University of São Paulo, Brazil (protocol number: 71648917.6.0000.5417).

Informed consent Informed consent was obtained from all individual participants included in the study.

Conflict of interest Licensed patent of the expander with differential opening (PI 1101050–9) was registered by the second author (DG), São Paulo Research Foundation (FAPESP) and University of São Paulo at the National Institute of Industrial Property (INPIBrazil).

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