Dentoskeletal comparison of miniscrew-anchored maxillary protraction with hybrid and conventional hyrax expanders: A randomized clinical trial

Abstract

This randomized clinical trial aimed to compare the skeletal and dental effects of miniscrew-anchored maxillary protraction (MAMP) using hybrid hyrax (HH) and conventional hyrax (CH) expanders in growing patients with Class III malocclusion. This was a randomized, parallel, controlled trial. Forty growing patients with Class III malocclusion and maxillary deficiency (Wits appraisal of less than -1mm) were randomized into 2 groups. Patients were recruited at the Orthodontic Clinic of Bauru Dental School, University of São Paulo, Brazil. The HH group was composed of patients with Class III malocclusions in the late mixed or early permanent dentition treated with a HH expander with 2 miniscrews in the maxilla and 2 miniscrews in the anterior region of the mandible. Class III elastics were used from the maxillary first molars to the mandibular miniscrews placed between permanent canines and first premolars. The CH group was composed of patients treated with a similar protocol except for the use of a CH expander in the maxilla. The primary outcomes included the frequency of overjet correction and sagittal skeletal effects produced with treatment. Allocation was performed with a simple randomization process. Blinding was performed only during assessments. Data were analyzed blindly on an intention-to-treat basis. Intergroup comparison was performed using analysis of covariance. Mean differences (MD) and 95% confidence interval (CI) were obtained for all variables. The final sample for the HH group was 20 subjects (8 female, 12 male; initial age of 10.7years), whereas the final sample for the CH group was 15 subjects (6 female, 9 male; initial age of 11.5years). The frequency of overjet correction observed in the HH and CH groups was 94.4% and 71.4% (risk ratio, 1.32; 95% CI, 0.93-1.88), respectively. Both groups presented similar skeletal sagittal and vertical outcomes after maxillary protraction. The maxillary length (CoA) showed a similar increase in both groups (MD, 1.12mm; 95% CI, -0.03 to 2.27). The CH group demonstrated a greater mesial displacement of maxillary first molars after treatment than the HH group (MD, 1.22mm; 95% CI, 0.33-2.11). HH and CH groups produced 2.88 and 1.97 overjet corrections (MD, 0.53mm; 95% CI, -0.52 to 1.59), respectively. MAMP using HH and CH expanders produced a frequency of overjet correction of 94.4% and 71.4%, respectively. Similar skeletal effects were observed between MAMP using HH and CH expanders. Greater control of the mesial displacement of maxillary first molar during maxillary protraction using hybrid expanders was observed. The trial was registered at http://ClinicalTrials.gov, under the identifier NCT03712007. This trial protocol was not published. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brasil (CAPES) - Finance Code 001, and by the São Paulo Research Foundation (FAPESP) - Grants nos. 2017/04141-9, 2017/24115-2, and 2019/03175-2.