Comparison of Two Miniscrew Bone-borne Expanders (2 vs 4 Screws) Versus Conventional Hyrax Expander in Adolescents

Overview

Rapid maxillary expansion (RME) is used to correct transverse deficiencies of the maxilla. This randomized controlled trial compares three RME devices in adolescents (age 10-15) with at least 8 mm maxillary transverse deficiency: (1) bone-borne expander supported by two palatal miniscrews, (2) bone-borne expander supported by four palatal miniscrews, and (3) conventional tooth-borne Hyrax expander. Devices were placed using static computer-guided miniscrew insertion (where applicable). All participants received the same activation protocol to reach 8 mm expansion. Cone-beam CT scans were obtained pre-treatment (T0) and at 6 months post-treatment (T1). The trial assesses skeletal, dentoalveolar, periodontal, and nasal/airway outcomes. Enrollment: 36 subjects. Study sites: Sapienza University of Rome.

This is a prospective, randomized, parallel-group clinical trial performed at the Department of Oral and Maxillofacial Sciences, Sapienza University of Rome (Nov 2021 - Sep 2024). Inclusion criteria included age under 16 years, late mixed or permanent dentition, and maxillary transverse deficiency ≥ 8 mm. Exclusion: poor oral hygiene; previous orthodontic treatment; craniofacial syndromes; cleft lip/palate; genetic/congenital diseases. After consent, eligible participants (N=36) were randomized (1:1:1) to: Group A - two-miniscrew bone-borne expander (paramedian screws near 1st-2nd premolar region); Group B - four-miniscrew bone-borne expander (two paramedian + two parapalatine); Group C - Hyrax tooth-borne expander banded to upper first molars. Miniscrews (Benefit system; PSM Medical Solutions) were placed using a CAD-CAM surgical guide planned from CBCT and digital models (Easy Driver). Activation: Hyrax click 10 mm screw; four quarter-turns at insertion then three quarter-turns/day for 12 days (0.20 mm/turn; \~0.6 mm/day) until 8 mm achieved. CBCT scan acquisition: Scanora 3Dx (Soredex). Measurements performed on Simplant v17 on defined landmarks (MaxBas, MaxAlv, MaxAlvPre, Ns, ZigMax, IntermCo, IntermoAp, molar angles, periodontal bone thickness measures, nasopalatine foramen width). Primary outcome: change in maxillary basal width (MaxBas) T0 to T1 measured on CBCT.