Materials and methods

This retrospective study assessed the CBCT records of 30 adult patients (19 females and 11 males) who underwent SARME. The inclusion criteria were patients with a maxillary transverse deficiency of 5 mm or greater, the presence of a posterior crossbite, and SARME performed with osteotomies of the maxillary lateral walls, midpalatal suture, and separation of the pterygomaxillary suture. The exclusion criteria comprised patients with previous orthodontic treatment, cleft lip and palate, or congenital craniofacial syndromes. Surgeries were performed by two surgeons (group 1 by V.A.P.-F. and group 2 by E.S.G.) in a hospital environment under general anaesthesia, between the years of 2010 and 2012. This study was performed with ethics committee approval.

The sample was divided into two groups according to the lateral osteotomy design: group 1 included 16 patients with a mean age of 30.4 years (range 18.7–39.7 years), who underwent SARME with pterygomaxillary disjunction, midpalatal suture osteotomy, and lateral osteotomy performed in a horizontal straight fashion ( Fig. 1 a ). Patients in this group were treated with a Hyrax type appliance and at an activation rate of one-quarter turn (0.2 mm) three times a day until the crossbite was corrected. Group 2 included 14 patients with mean age of 24.2 years (range 19.3–33.2 years), who underwent SARME with pterygomaxillary disjunction, midpalatal suture osteotomy, and lateral osteotomy performed in parallel to the occlusal plane with a step at the zygomatic buttress ( Fig. 1 b). In this group, patients were treated with Hyrax ( n = 8) or Hass ( n = 6) appliances. An initial activation of 1 mm was carried out, followed by a one-quarter turn twice a day for the first week, and after this, a one-quarter turn every day until the crossbite was corrected. In both groups, appliance activation was initiated 7 days postoperatively. After expansion, appliances were blocked and left in place for 4 months. After this period, appliances were replaced with a transpalatal arch.

Volumetric rendering from CBCT scans of patients who underwent SARME. (a) Straight osteotomy from piriform rim to pterygomaxillary suture; (b) osteotomy performed in parallel to the occlusal plane with a step at the zygomatic buttress.

CBCT scans were acquired before surgery (T1), immediately after expansion (T2), and at 6 months after expansion (T3) for each patient, using an i-CAT scanner (Imaging Sciences International, Hatfield, PA, USA) with settings of 120 kVp, 36 mA, 0.3-mm voxels, and a field of view (FOV) of 17 cm × 23 cm. CBCT images were evaluated randomly by a calibrated examiner using Dolphin 3D software (Dolphin Imaging, Chatsworth, CA, USA). The orientation of each dataset was standardized according to three reference planes using volume rendering and multiplanar views ( Fig. 2 ). Linear and angular measurements were performed on the coronal slices at the level of the upper first molars and upper premolars to determine nasal floor width, maxillary width, distance between the palatal root apices, and distance between the buccal cusps and tooth tipping ( Figs 3 and 4 ).

Orientation and reference planes: axial plane (blue) defined by right and left orbitale and right porion landmarks; coronal plane (green) defined by right and left porions, perpendicular to the axial plane; sagittal plane (red) defined as the plane orthogonal to axial and coronal planes passing through the nasion landmark. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Distances measured at the level of the upper first molars. (1) Nasal floor width: measured at the most inferior level of the nasal floor. (2) Maxillary width: distance between maxillary lateral walls at the level of the nasal floor. (3) Interradicular width: distance between the apex of the palatal roots of the right and left molars. (4) Intermolar width: the distance between the mesiobuccal cusps of the right and left molars. (5) Intermolar angle: angle between the lines passing through mesiobuccal cusp and palatal root apex of the right and left molars.

Distances measured at the level of the first premolars. (1) Nasal floor width: measured at the most inferior level of the nasal floor. (2) Maxillary width: distance between maxillary lateral walls at the level of the nasal floor. (3) Interradicular width: distance between the apex of the palatal roots of the right and left premolars. (4) Interpremolar width: distance between the buccal cusps of the right and left premolars. (5) Interpremolar angle: angle between the lines passing through the buccal cusp and root apex of the right and left premolars.

Eighteen CBCT images were chosen at random and assessed twice by the same calibrated examiner, with an interval of at least 30 days. Reliability was confirmed by the intra-class correlation coefficient (ICC), which ranged from 0.984 to 0.998. The Shapiro-Wilk and Levene tests were used to investigate assumptions of normality and equality of variances between groups. Once these assumptions were confirmed, the Student’s t -test was used to compare the amount of expansion between groups 1 and 2, the differences in expander appliances used in group 2, and differences between the anterior and posterior maxillary regions. The non-parametric Mann–Whitney test was used for the data that did not fit normality.

Longitudinal changes between time points for both groups were evaluated using a mixed analysis of variance (ANOVA) for repeated measures, with Greenhouse–Geisser adjustment for violation of sphericity. In the case of statistically significant results, the Bonferroni multiple comparison test was used to assess differences between groups and time points. The association between expander opening and dentoskeletal changes was investigated using the Pearson correlation coefficient. The data analysis was performed using SPSS version 16.0 software (SPSS Inc., Chicago, IL, USA) with a significance level of 5% ( α = 0.05).

Results

The average expansion in group 1 was 8.00 mm (standard deviation (SD) 1.64 mm) and in group 2 was 8.16 mm (SD 1.24 mm), with no significant difference between them ( P = 0.764). No statistically significant differences were found between time points with the Hass and Hyrax appliances used in group 2 ( Table 1 ), thus the entire group 2 ( n = 14) was used as a single sample for the analyses.

Mixed-design ANOVA revealed no significant interaction effects between groups over time points for any dental or skeletal measurements in this study ( P > 0.05). There were no differences between groups regarding the expansion of dental and skeletal measurements ( P > 0.05). However, changes over time points were significant for all measures ( P < 0.001), as shown in Table 2 .

The lack of interaction effects indicated comparable patterns of change for the two groups. Thus, both groups were pooled for pairwise comparisons, which revealed a significant increase in all measures assessed post-expansion (T2–T1, P < 0.001). Significant differences between time points T2 and T3 were found for the distance between the palatal root apices in molars, intermolar angle, nasal floor width at the level of premolars, and interpremolar angle ( Table 3 ).

Table 3

Results of Bonferroni multiple comparison tests applied between time points (pooled groups).

	Time point comparison	Mean difference	SE	P -value	95% CI
					Lower	Upper
First molar
Nasal floor width (mm)	T2–T1	1.36	0.25	<0.001 a	0.73	1.99
	T3–T2	–0.07	0.08	1.000	–0.27	0.13
	T3–T1	1.29	0.22	<0.001 a	0.74	1.84
Maxillary width (mm)	T2–T1	0.97	0.15	<0.001 a	0.59	1.35
	T3–T2	–0.19	0.11	0.271	–0.48	0.09
	T3–T1	0.78	0.14	<0.001 a	0.42	1.13
Interradicular width (mm)	T2–T1	3.50	0.30	<0.001 a	2.73	4.28
	T3–T2	1.28	0.20	<0.001 a	0.77	1.79
	T3–T1	4.79	0.32	<0.001 a	3.97	5.60
Intermolar width (mm)	T2–T1	7.47	0.38	<0.001 a	6.51	8.43
	T3–T2	−0.42	0.27	0.409	−1.12	0.28
	T3–T1	7.05	0.37	<0.001 a	6.10	7.99
Intermolar angle (°)	T2–T1	11.42	1.13	<0.001 a	8.51	14.32
	T3–T2	–4.44	0.91	<0.001 a	–6.75	–2.13
	T3–T1	6.98	0.97	<0.001 a	4.48	9.47
First premolar
Nasal floor width (mm)	T2–T1	1.95	0.27	<0.001 a	1.25	2.65
	T3–T2	–0.29	0.10	0.017 a	–0.54	–0.04
	T3–T1	1.66	0.25	<0.001 a	1.02	2.30
Maxillary width (mm)	T2–T1	2.87	0.34	<0.001 a	2.01	3.73
	T3–T2	–0.28	0.17	0.368	–0.72	0.17
	T3–T1	2.60	0.35	<0.001 a	1.70	3.50
Interradicular width (mm)	T2–T1	4.03	0.43	<0.001 a	2.91	5.14
	T3–T2	0.21	0.20	0.969	–0.32	0.73
	T3–T1	4.23	0.43	<0.001 a	3.15	5.31
Interpremolar width (mm)	T2–T1	7.71	0.37	<0.001 a	6.76	8.66
	T3–T2	–0.37	0.22	0.302	–0.92	0.18
	T3–T1	7.34	0.34	<0.001 a	6.47	8.22
Interpremolar angle (°)	T2–T1	10.44	1.05	<0.001 a	7.75	13.14
	T3–T2	–2.66	1.01	0.042 a	–5.23	–0.08
	T3–T1	7.89	0.96	<0.001 a	5.33	10.24

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