Trial design and any changes after trial commencement

This single-center study was a randomized clinical trial with 2-parallel arms. This randomized clinical trial followed the Consolidated Standards of Reporting Trials’ statement and guidelines, and no changes in methods after trial commencement were required.

Participants, eligibility criteria, and settings

This study was ethically analyzed before trial commencement by the Research Institutional Board of the Bauru Dental School, University of São Paulo, and was approved under protocol number 1.292.365. Additionally, the protocol of this study was registered in the ClinicalTrials.gov with the identifier NCT02810353 .

Recruitment of patients occurred in the Clinic of Orthodontics, Bauru Dental School, University of São Paulo from May to November 2015. Eligibility criteria included patients of both sexes in the mixed dentition, with ages ranging from 7 to 11 years diagnosed with maxillary constriction and Class I or Class II sagittal relationships. Exclusion criteria were the presence of cleft lip and palate, craniofacial syndromes, carious lesions, and history of previous orthodontic treatment.

Interventions

Patients who met the eligibility criteria during recruitment were invited to participate in the study. Written consent terms were obtained from the patients and legal guardians. At this time, 1 researcher opened an envelope that contained a card with the name of 1 of the 2 types of expanders. Therefore, patients were randomly allocated into 1 of the 2 study groups. The treatment of the patients from both groups was performed by the same operator (ACMA).

The experimental group comprised patients treated with the EDO ( Fig 1 , A – C ). The EDO was composed of 2 11-mm prefabricated screws, 1 posteriorly positioned on the palate at the level of the first permanent molars and the other anteriorly positioned at the level of the first deciduous molars (Great Lakes Orthodontics, Tonawanda, NY). Orthodontic bands were preferentially adapted on the maxillary first permanent molars, and clasps were bonded on the maxillary deciduous canines. When the maxillary first permanent molars were partially erupted, or the distal aspect of the crown was covered by gingiva, the maxillary second deciduous molars were banded, and a wire extension was soldered on the palatal aspect of the first permanent molars. Both expander screws were concurrently activated for 6 days, with an activation protocol of half a turn in the morning and half a turn in the evening. Afterward, only the anterior screw was activated for an extra 4-day time with the same protocol. After the active expansion period, the expander was kept in the mouth as a retainer for 6 months. At the end of the retention phase, the expanders were removed, and a removable retention plate was installed.

Expander with differential opening ( A-C ) and conventional Hyrax expander ( D-F ).

The comparison group comprised patients who underwent RME using the conventional Hyrax expander ( Fig 1 , D – F ). The Hyrax expander was composed of a 11-mm screw centrally positioned on the palate. Similar to the experimental group, either maxillary first permanent molars or maxillary second deciduous molars were banded, and circumferential clasps were bonded on the maxillary deciduous canines. The screw was activated half a turn in the morning and half a turn in the evening for 6 days. After the active expansion period, 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.

Maxillary occlusal radiographs were obtained at the end of the expansion active phase (T2). The radiographic images were taken according to the biosecurity and radioprotection requirements, using the Insight occlusal radiographic film (Kodak Company, Rochester, NY) and a dental x-ray machine of 10 mA and 70 kV. The radiographic films were manually processed in a darkroom, using the temperature or time technique. Standardized frontal intraoral photographs were taken orthostatically for each patient immediately pre-expansion (T1) and at the end of the active expansion phase (T2); for example, 6 or 10 days after the appliance’s installation. The photographs were taken at a distance of 30 cm from the patients using a Canon T1i digital camera (Canon EOS Digital Rebel Inc, Tokyo, Japan), 100-mm macro lens, circular flash, f 11, shutter speed 1/125, and ISO 200. Standardized conventional dental models were obtained for each patient immediately pre-expansion (T1) and 6 months after expansion (T3). The maxillary dental arch models were digitized using a 3Shape R700 3D scanner (3Shape A/S, Copenhagen, Denmark), and the obtained 3-dimensional images were saved in an .stl file format.

Outcomes (primary and secondary) and any changes after trial commencement

The primary outcomes of this study were the dimension of anterior midpalatal suture opening ( Pr-Pr ‘); the changes in the interincisal diastema, maxillary dental arch widths ( c-c , d-d , e-e, and 6-6 ), arch perimeter and length, palatal depth and inclination of posterior teeth ( Ic , Ie, and I6 ), dental arch shape, and the amount of differential expansion in the anterior region compared with the posterior region of the maxillary dental arch. No outcome changes occurred after trial commencement.

The dimension of the anterior midpalatal suture opening was digitally measured on the maxillary occlusal radiographs using Dolphin Imaging software, version 11.0 (Dolphin Imaging and Management Solutions, Chatsworth, Calif), as shown in Figure 2 .

Dimension of midpalatal suture opening was analyzed measuring the distance between prosthion landmarks ( Pr-Pr’ ) on the maxillary occlusal radiographs, obtained at the end of the expansion active phase.

The width of the interincisal diastema was measured using a modification of a method proposed in a previous study. Initially, the mesiodistal width of the clinical crown of the maxillary right central incisor of each patient was manually measured on the pre-expansion conventional dental models using a caliper. Using a digital millimetric ruler, the photograph was resized in Microsoft PowerPoint 2013 (Microsoft Corporation, Redmond, Wash) according to the actual size of the measured tooth. The interincisal diastema was measured using Dolphin Imaging software, as shown in Figure 3 .

The interincisal diastema width was analyzed measuring the distance between the points located at the confluence of the mesial aspect of the maxillary central incisors with the gingival papilla on the intraoral frontal photographs obtained before ( A ) and after ( B ) the active phase of rapid maxillary expansion. Interincisal diastema change was considered the difference between the values obtained at T2 and T1.

The measurements of maxillary dental arch widths, arch perimeter and length, palatal depth, and inclination of posterior teeth were performed on the pre- and postexpansion digital dental models using the OrthoAnalyzer 3D software (3Shape A/S), as shown in Figures 4-6 .

Maxillary arch widths ( A ) comprised the distances c-c (deciduous intercanine distance at the level of the palatal gingival margin midpoint), d-d (inter–first deciduous molars distance at the level of the palatal gingival margin midpoint), e-e (inter–second deciduous molars distance at the level of the palatal gingival margin midpoint), and 6-6 (inter–first permanent molar distance at the level of the palatal gingival margin midpoint). Arch perimeter ( B ) was the sum of P6-c (linear distance between the mesial aspect of the right first permanent molar to the mesial aspect of the right deciduous canine), Pc-1 (linear distance between the mesial aspect of the right deciduous canine to the most prominent point of the mesial aspect of the left permanent central incisor), P1-c ‘ (linear distance between the most prominent point of the mesial aspect of the left permanent central incisor to the mesial aspect of the left deciduous canine), and Pc ‘ -6 ‘ (linear distance between the mesial aspect of the left deciduous canine to the mesial aspect of the left first permanent molar).

Arch length ( A ) was measured perpendicularly in the horizontal plane from a line connecting the mesial aspects of the first permanent molars to the point between the maxillary central incisors at the level of the gingival papilla. Palatal depth ( B ) was measured from a line passing through the mesial gingival papilla of the first permanent molars to the deepest point on the palate surface, perpendicularly to the arch length.

Tooth inclination was measured using as reference the occlusal plane passing through the mesiobuccal cusp tips of the maxillary first permanent molars, bilaterally, and through a mesioincisal point on the left central incisor. The tooth long axis was represented as an arrow in the virtual setup of the OrthoAnalyzer software. On the buccal view of each tooth ( A and C ), this arrow was mesiodistally manipulated to represent tooth angulation according to Andrews’ facial axis point. On the distal view of each tooth ( B and D ), the arrow was buccolingually manipulated to represent the crown tip, according to Andrews. The angle between the arrow and the occlusal plane was automatically calculated by the software. After expansion, increasing values of the angle meant tooth buccal inclinations of the teeth, and decreasing values meant lingual tooth inclination.

The dental arch shape was evaluated using the Geomagic Wrap 2015 software (Raindrop Geomagic Inc, Morrisville, NC) and the Microsoft Excel 2013 (Microsoft Corporation). In the Geomagic Wrap 2015 software, Andrews’ facial axis points were set on the maxillary teeth. These points were decomposed in 3 cardinal directions generating values on the x-, y-, and z-axis. Considering the y-axis values referred to the depth dimension (cervico-oclusal plane), only the x-axis values (transversal plane) and the z-axis values (sagittal plane) were tabulated. Microsoft Excel 2013 was used to graphically determine the mean maxillary dental arch shape for both study groups at T1 and T2, using the interpolar function.

Sample size calculation

A minimum difference of 2 mm in the intercanine distance, a standard deviation of 1.65, an alpha error of 5%, and a test power of 80% were considered for sample size calculation. Twenty participants were required in each group.

Interim analyses and stopping guidelines

Not applicable.

Randomization (random number generation, allocation concealment, implementation)

A simple electronically generated randomization was performed before trial commencement using the Random Allocation Software program. Randomization ensured patients’ allocation in both groups with a 1:1 ratio. Allocation concealment involved numbered, sealed, and opaque envelopes prepared before trial commencement. One envelope was sequentially opened for each participant during recruitment. Each envelope contained a card with the name of 1 expander. The initials of the name of the participant, the type of expander, and the date of allocation were identified in the external surface of the envelope. One operator was responsible for the randomization process, allocation concealment, and implementation.

Blinding

Double-blinding was not possible because the operator and patients were aware of the type of expander that was being installed. However, blinding was accomplished during outcome assessment once the maxillary occlusal radiographs, the photographs, and the digital dental models were unidentified during analysis.

Error study

One operator (ACMA) performed all the measurements and repeated them in 30% of the sample at least 1 month later. The intraexaminer error was assessed using the intraclass correlation coefficient.

Statistical analysis (primary and secondary outcomes, subgroup analyses)

Kolmogorov-Smirnov tests were used to verify normal distribution of variables. Considering that the variables showed normal distribution, parametric tests were used. Intergroup comparisons for initial age were performed with t tests. A chi-square test was used for intergroup comparison regarding sex ratio. Intergroup comparisons of T1-T2 changes were performed using multiple linear regression analysis. The independent variables were both treatment and the starting forms to adjust the comparisons to possible differences at T1. Results were regarded significant at P < 0.05. Bonferroni correction for multiple tests (tests performed on a set of 12 measurements) was applied. Differential expansion assessment was performed, comparing the difference between c-c and 6-6 width change in both groups using t tests. Associated 95% confidence intervals were calculated. All statistical tests were conducted with SPSS Statistics for Windows, version 25.0 (IBM, Armonk, NY).

Baseline data

Baseline characteristics were similar in both groups ( Tables I and II ).

Table I

Intergroup comparisons for age and sex ratio ( t and chi-square tests)

Variable	Experimental group (n = 22)			Comparison group (n = 24)			P
	Mean	SD	CI 95%	Mean	SD	CI 95%
Initial age (y)	8.46	1.40	1.08-2.00	8.92	1.21	0.94-1.70	0.238 ∗
Sex
Male	10			6			0.458 †
Female	12			18

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