Materials and methods

After clinical evaluation and analysis of the initial orthodontic records, 24 adult patients (18 females and six males) were recruited consecutively into the study. The patients ranged in age from 18.3 to 31.8 years (mean 24.29 ± 3.48 years). The study inclusion criteria were as follows: transverse maxillary skeletal deficiency (>5 mm); skeletal maturity; presence of maxillary first premolars and maxillary first or second molars on both sides, with good structural and periodontal conditions to allow cementation and activation of the fixed expansion appliance; favourable physiological conditions of the cardiovascular system; no pre-existing medical contraindication to surgical procedures. Patients with severe asymmetry, limited periodontal health, and/or with congenital craniofacial deformities were excluded. This study was approved by the necessary institutional review board; written informed consent was obtained from all of the patients.

The patients were divided into two groups. Group 1 comprised 14 individuals who underwent SARME with midpalatal split (10 female, four male; mean age 24.44 ± 3.22 years). Group 2 comprised 10 individuals who underwent SARME without midpalatal separation (eight female, two male; mean age 24.08 ± 3.81 years). The Hyrax expander appliances (Hyrax II; Dentaurum, Ispringen, Germany) were cemented to the maxillary first molars and the first premolars. The appliances were scheduled for insertion as close as possible to the date of the surgical procedure. Two experienced senior oral and maxillofacial surgeons performed the surgeries. The surgeries were performed under local anaesthesia, as reported previously in the literature. The patients were not sedated because one of the objectives was to perform an intraoperative subjective assessment of the patient’s symptomatology.

In group 1, the SARME was performed through the technique described by Bell, in which a partial bilateral maxillary osteotomy from the piriform aperture to the pterygomaxillary fissure is done. The pterygomaxillary sutures were kept intact. The midpalatal disjunction was made using a surgical hammer and a thin straight chisel positioned between the central incisors and directed towards the palatine direction. During surgery, the screws of the appliance were activated 2 mm (eight turns). After a 2-day latency period, the patients were instructed to activate the screw two turns (0.5 mm) twice a day, completing 1 mm of activation each day.

In group 2, the technique proposed by Glassman et al. was used. A bilateral maxillary osteotomy was performed from the piriform rim to the zygomatic-maxillary buttress, ending just anterior to the pterygoid fissure, to break the resistance of the maxillary tuberosity and the contact between the maxilla and the zygomatic bones. The pterygomaxillary sutures were kept intact. The midpalatal suture was not separated during the procedure. During surgery, the screws were activated 1 mm (four turns). After a postoperative latency period of 2 days, the patients were instructed to activate the screw one turn (0.25 mm) twice a day, completing 0.5 mm activation each day.

The degree of expansion was calculated for each patient; expansion was continued until an overexpansion of 2–3 mm was observed. After expansion, the screws were fixed using ligature wire to avoid mobility of the expansion screw. The difference in relation to activation was due to the surgical technical protocol recommendations followed.

The patients in both groups received exactly the same postoperative medication and instructions. After the active treatment phase, the appliance was used as a passive retainer for 120 days. There were no dropouts or appliance failures during this study.

The efficacy of the technique was assessed in relation to the presence of a diastema between the upper incisors and radiographic evidence of separation of the maxillary bones in the midpalatal suture. To ensure that the midpalatal suture opened, a clinical evaluation was performed and an occlusal radiograph was taken immediately after the surgical procedure and at 14 days postoperative. Clinically, the suture opening was evaluated by the presence of a diastema between the maxillary central incisors. A senior oral and maxillofacial surgeon, who was not involved in the surgical procedure and who was blinded to the type of treatment, performed the clinical evaluation. For the radiographic evaluation, the midpalatal suture was considered open when a radiolucent area was observed in the suture region. A radiologist who was not involved in the surgical procedure and who was blinded to the type of treatment that had been performed conducted these evaluations. Failure was considered to have occurred if there was no evidence of a diastema between the maxillary central incisors and if an occlusal radiograph of the maxilla showed radiopacity at the alveolar crest between the maxillary incisors. In these cases, a new surgical procedure was performed after 14 days of postoperative follow-up, with midpalatal split.

The patient’s symptomatology was assessed using a questionnaire containing four questions: (1) How would you rate the discomfort of your surgery? (2) How would you rate the discomfort during appliance activation? (3) How would you rate your postoperative pain? (4) How would you rate your postoperative oedema? The first question was asked immediately after the surgical procedure and was repeated at 14 days postoperative. The other questions were asked only at postoperative follow-up (14 days postoperative) and addressed the degree of discomfort during the postoperative period.

The discomfort felt during and after the surgical procedure was measured using a pain and discomfort numerical visual analogue scale. The scores were assigned according to the answers to the questions relating to postoperative symptomatology and ranged from 0 to 10. Scores of 0 to 2.5 indicated a comfortable procedure, without pain or oedema; scores of 2.6 to 5.0 indicated a tolerable procedure, with pain or a little oedema; scores of 5.1 to 7.5 indicated an uncomfortable procedure that was painful or with moderate oedema; and scores of 7.6 to 10 indicated an intolerable procedure with severe pain or severe oedema.

A power analysis using G*Power software version 3.1.3 (Heinrich-Heine-Universität, Düsseldorf, Germany) showed that the sample size (10 per group) provided more than 95.3% power to detect a significant difference in efficacy between the groups at a significance level of 0.05.

The mean, median, and standard deviation values for each variable were calculated for both groups. Fisher’s exact test was used to evaluate the compatibility of the groups in relation to the sex distribution. The independent t -test was used to evaluate the compatibility of the two groups in relation to patient age. The Kolmogorov–Smirnov test was applied to determine the normality of the distribution of data. The treatment efficacy was compared between the groups using Fisher’s exact test. To evaluate the subjective assessment of symptomatology between the groups, the Mann–Whitney test was used. The Wilcoxon test was applied to compare the answers for discomfort of the surgical procedure (question 1) immediately after surgery and at 14 days postoperative. For question 1, the Pearson correlation test was applied to compare the answers given immediately after surgery and at the 14-day postoperative assessment. The level of significance was set at 5%. The statistical analyses were performed using Statistica version 5.1 software (StatSoft Inc., Tulsa, OK, USA).

Results

The groups were comparable with regard to sex distribution ( P = 1.00) and initial patient age ( P = 0.81).