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

Prospective Randomized Controlled Study Comparing Dentoalveolar, Skeletal, Periodontal and Nasal/Airway Effects of a Two-miniscrew Bone-borne Expander, a Four-miniscrew Bone-borne Expander, and a Conventional Tooth-borne Hyrax Expander in Adolescents.

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.

Inclusion Criteria:

• Age 10 to 15 years (under 16 at enrollment).
• Late mixed or permanent dentition.
• Maxillary transverse deficiency ≥ 8 mm (unilateral or bilateral).
• Parent/guardian able to provide written informed consent; participant assent where applicable.

Exclusion Criteria:

• Poor oral hygiene.
• Prior orthodontic treatment.
• Craniofacial syndromes.
• Cleft lip and/or palate.
• Genetic or congenital diseases likely to affect craniofacial growth or bone quality.
• Inability/unwillingness to attend scheduled follow-up visits.