Material and methods

Sample size estimation was based on the standard deviations of a similar study by Kartalian et al, who found a statistically significant increase of 5.42 ± 3.02 mm in external molar widths. Assuming an increase of 25% in this previous finding, with an α error of 0.05 and a power of 80%, we calculated that our sample size should be 30 patients per group.

The CBCT records of 30 patients with unilateral skeletal crossbite (13 boys: mean age, 14.2 ± 1.3 years; range, 12.5-16 years; and 17 girls: mean age, 13.8 ± 1.3 years; range, 12.3-15.4 years) who underwent treatment with ARME were selected from the archives of the Department of Orthodontics of Selcuk University, Konya, Turkey. Ninety-six patients with unilateral posterior crossbites were admitted to our orthodontic department from 2010 to 2013, and 39 of them had unilateral skeletal crossbites. Thirty patients who met the inclusion criteria were selected for this study. All patients were in the permanent dentition and had unilateral posterior crossbites of the nonfunctional type with coincident midlines. In 14 patients, the crossbite was on the left side; in 16, it was on the right side. Any relationship of the unilateral posterior crossbite and the mandibular shift was evaluated clinically. The patients had no craniofacial abnormalities or previous surgical or extraction treatment. The same orthodontist (Z.I.) treated all patients. Ethical approval for this study was obtained from the regional ethical committee on research of Selcuk University.

The ARME appliance used was built by adding an occlusal locking mechanism to a modified acrylic bonded RME appliance. The modified acrylic bonded RME appliance was a splint-type tooth and tissue-borne appliance ( Fig 1 ). The acrylic part of the appliance extended over the occlusal and middle thirds of the vestibular surfaces of all teeth. A hyrax screw (Dentaurum, Pforzheim, Germany) was placed in the acrylic plate parallel to the second premolars and as near to the palate as possible. Holes were drilled on the cusps of the maxillary teeth on the ARME appliance to allow escape of the luting cement. On the noncrossbite side, an acrylic extension was formed that extended vertically from the palatal part of the maxillary posterior teeth to the lingual part of the mandibular posterior teeth. The acrylic part of the appliance extended to the middle third of the vestibular surfaces of the mandibular posterior teeth after forming the occlusal tracks of these teeth. The occlusal locking mechanism was formed by covering the lingual and vestibular aspects of the mandibular posterior teeth with acrylic.

ARME appliance.

The appliance was activated with a quarter turn twice per day in the first week to overcome the resistance of the sutures and once per day after the sutures were mobilized. Expansion was stopped when the holes on the palatal cusps of the maxillary posterior teeth occluded with the buccal cusps of the mandibular posterior teeth (average time, 4-6 weeks). The expander was used for retention for the first 3 months and then replaced with a transpalatal arch.

All CBCT images were obtained with a Kodak unit (model CS 9300; Carestream Health, Rochester, NY) set as follows: exposures were made at 8.0 mA and 70 kV for 6.15 seconds with an axial slice thickness of 0.18 mm. The patients were asked to put their heads in the Frankfort horizontal position for the CBCT scans. The DICOM images were imported, and cross-sectional slices were obtained using Mimics software (version 14.01; Materialise, Leuven, Belgium). To establish the standard orientation of the craniofacial structures, 3-dimensional reference planes were set. The Frankfort horizontal plane was defined as the plane that passed through bilateral porion and right orbitale. The midsagittal plane was defined as the plane perpendicular to the horizontal plane passing through nasion and the midporion point. The frontal plane was constructed from nasion and perpendicular to the horizontal and midsagittal planes. Each 3-dimensional rendered image was then reoriented using the Frankfort horizontal, midsagittal, and horizontal planes. All transverse linear and angular measurements were recorded for each scan before ARME treatment (T1) and after a 3-month retention period (T2). One investigator (M.A.) took all measurements.

In this study, 40 linear and 6 angular measurements of the maxilla were taken ( Fig 2 ). Kartalian et al described the linear and angular measurements for the maxilla and the maxillary teeth. The nasal floor was assessed relative to the midsagittal plane, parallel to the lower border of the hard palate and tangent to the nasal floor at its most superior level. The palatal floor was also assessed relative to the midsagittal plane, parallel to the lower border of the hard palate and tangent to the hard palate. The external maxillary linear measurements were taken relative to the midsagittal plane at the buccal alveolar crest, the most prominent point of the crown at the buccal aspect, the buccal cusp tip, the apex of the buccal root levels of the maxillary first and second premolars, and the maxillary first molars on the crossbite and noncrossbite sides. The internal maxillary linear measurements were taken relative to the midsagittal plane at the apex of the palatal root and the palatal alveolar crest levels of each included tooth on the crossbite and noncrossbite sides. The angular measurements of maxillary teeth were taken relative to a horizontal reference line parallel to the palatal plane. The angle between the long axis of the maxillary teeth and the reference line was measured for the crossbite and the noncrossbite sides.

Maxillary linear and angular measurements on the crossbite and noncrossbite sides of the maxilla: A, nasal and palatal floor measurements, and external maxillary widths measured relative to the midsagittal plane at 4 levels: the buccal apex, buccal alveolar crest, most prominent point of the crown, and buccal cusp tip; B, internal maxillary widths measured relative to the midsagittal plane at 2 levels: the palatal apex and palatal alveolar crest; C, the angle between the long axis of the palatal root and a horizontal reference line parallel to the palatal plane.

Forty linear and 8 angular measurements were taken of the mandible ( Fig 3 ). Baysal et al described the linear and angular measurements for the mandible and the mandibular teeth. The external mandibular linear measurements were taken relative to the midsagittal plane at the buccal alveolar crest, the most prominent point of the crown at the buccal aspect, the buccal cusp tip levels of the mandibular canines, the mandibular first and second premolars, and the mandibular first molars on the crossbite and noncrossbite sides. The internal mandibular linear measurements were taken relative to the midsagittal plane at the most prominent point of the crown at the lingual aspect and the lingual alveolar crest levels of each included tooth on the crossbite and noncrossbite sides. The angular measurements of the mandibular teeth were taken by considering a horizontal reference line passing through the lower borders of the mandible. The angle between the long axis of the mandibular teeth and the reference line was measured for the crossbite and noncrossbite sides.

Mandibular linear and angular measurements on the crossbite and noncrossbite sides of the mandible: A, external mandibular widths measured relative to the midsagittal plane at 3 levels: the buccal alveolar crest, most prominent point of the crown, and buccal cusp tip; B, internal mandibular widths measured relative to the midsagittal plane at 2 levels: the most prominent point of the crown and the lingual alveolar crest; C, the angle between the long axis of the mesial root and a horizontal reference line passing through the lower borders of the mandible.

Results

The descriptive statistics and intragroup comparisons of the crossbite and noncrossbite sides are shown in Table I for the maxillary linear measurements. All maxillary linear and angular measurements increased after treatment with ARME. T1 to T2 comparisons showed that these increases were statistically significant on the crossbite side of the maxilla ( P <0.05). Comparison of changes in the maxillary linear measurements between the 2 sides showed statistically significant differences ( Table II ; P <0.05). The descriptive statistics and intragroup comparisons of the crossbite and noncrossbite sides are shown in Table III for the maxillary angular measurements. Comparisons of the changes in maxillary angular measurements between the 2 sides showed statistically significant differences ( Table IV ; P <0.001).

Table II

Comparison of changes in maxillary and mandibular linear measurements (mm) between the crossbite and noncrossbite sides

	n	Crossbite side		Noncrossbite side		Significance
		Mean	SD	Mean	SD
Maxillary linear measurements
Nasal floor	30	1.93	0.93	0.27	0.29	†
Palatal floor	30	2.85	0.87	0.61	0.54	‡
External
Apex
First premolar-Y	30	3.49	1.13	0.43	0.39	‡
Second premolar-Y	30	2.93	0.89	0.42	0.32	‡
First molar-Y	30	2.35	0.94	0.53	0.37	†
Alveolar crest
First premolar-Y	30	3.64	1.21	0.68	0.48	‡
Second premolar-Y	30	2.96	1.17	0.40	0.43	‡
First molar-Y	30	2.79	1.05	0.69	0.31	‡
Buccal
First premolar-Y	30	3.27	1.24	0.77	0.53	‡
Second premolar-Y	30	3.11	1.02	0.64	0.41	‡
First molar-Y	30	2.93	0.93	0.89	0.56	†
Occlusal
First premolar-Y	30	3.58	0.87	0.81	0.43	‡
Second premolar-Y	30	2.86	0.94	0.52	0.31	†
First molar-Y	30	2.15	0.79	0.60	0.48	∗
Internal
Palatal apex
First premolar-Y	30	3.63	1.19	0.48	0.32	‡
Second premolar-Y	30	3.15	1.08	0.51	0.46	‡
First molar-Y	30	2.59	1.02	0.34	0.32	‡
Palatal alveolar crest
First premolar-Y	30	2.93	0.93	0.51	0.37	‡
Second premolar-Y	30	3.15	0.98	0.48	0.41	‡
First molar-Y	30	2.29	0.84	0.47	0.29	†
Mandibular linear measurements
External
Occlusal
Canine-Y	30	0.24	0.54	1.62	0.62	†
First premolar-Y	30	0.13	0.48	1.82	0.73	†
Second premolar-Y	30	0.28	0.38	2.08	0.70	†
First molar-Y	30	1.12	0.92	2.20	0.73	∗
Buccal
Canine-Y	30	0.50	0.39	1.68	0.53	∗
First premolar-Y	30	0.53	0.42	1.98	0.78	†
Second premolar-Y	30	0.84	0.67	1.88	0.88	∗
First molar-Y	30	1.18	1.02	1.86	0.94	∗
Alveolar crest
Canine-Y	30	0.61	0.74	0.94	0.77	NS
First premolar-Y	30	0.68	0.59	2.18	0.69	†
Second premolar-Y	30	1.51	1.07	1.73	1.09	NS
First molar-Y	30	1.65	1.12	2.68	0.97	∗
Internal
Lingual
Canine-Y	30	0.38	0.62	1.17	0.88	∗
First premolar-Y	30	0.54	0.58	1.39	0.67	∗
Second premolar-Y	30	0.68	0.61	1.68	0.78	∗
First molar-Y	30	1.41	0.99	2.28	0.84	NS
Alveolar crest
Canine-Y	30	0.38	0.62	1.69	0.82	∗
First premolar-Y	30	0.41	0.32	2.44	0.59	†
Second premolar-Y	30	1.29	0.51	2.67	0.79	∗
First molar-Y	30	1.11	0.78	3.31	0.96	†

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