Efficacy of Skeletally Anchored Modified Leaf Expander Versus Modified Conventional Hyrax in Maxillary Molar Distalization: A Randomized Clinical Trial

Study setting and populations:

This prospective study included 30 patients consecutively enrolled and treated at the dental clinics, Orthodontic Department, Faculty of Dentistry, Tanta University, Egypt. Patients were aged between 15 and 18 years. All patients underwent maxillary molar distalization using one of two appliances.

Groups' randomization The patients involved in the study groups were randomly distributed through a simple online-generated randomization plan using online software found at the website http://www.graphpad.com/quickcalcs/index. cfm. The allocation ratio is 1:1.

• Group 1: Patients treated with the modified skeletally supported self-activated Leaf expander as a distalization appliance (7 males, 8 females).
• Group 2: Patients treated with the modified skeletally supported conventional HYREX expander as a distalization appliance (6 males, 9 females).

Inclusion Criteria

• Class II molar relation.
• Patients aged between 15 and 18 years.
• Overjet less than 6 mm
• ANB angle between 5° and 7°.
• Non-extraction treatment plan with molar distalization.
• Horizontal or normal growth pattern with symmetrical, balanced facial appearance.
• Minimal crowding in the mandibular arch. Exclusion Criteria
• Congenitally missing teeth
• Congenital anomalies
• Systemic diseases
• Previous orthodontic treatment Ethical Considerations All patients were informed about the nature, purpose, risks, and benefits of the study prior to enrollment. Written informed consent was obtained from each participant. Patient confidentiality was maintained, and participants retained the right to withdraw at any time without affecting their treatment. Approval for this research was obtained from the Research Ethics Committee, Faculty of Dentistry, Tanta University, Egypt. Under the No. #R-ORTH-08-25-3220.

The Self-Activated Leaf Expander The Leaf Expander (Leaf Expander®, Leone SpA, Sesto Fiorentino, Florence, Italy) resembles a rapid palatal expander but incorporates Nickel Titanium MEMORIA leaf springs that provide continuous force. It consists of two body parts connected by rods over which the leaf springs slide. The springs are held compressed by staples on each side of the body parts. The superelastic nickel-titanium leaf springs deliver a controlled, continuous force once the staples are removed. Two types of Leaf Expanders are available, delivering either 450 or 900 grams of force; the 450-gram/ 6 mm in length version was used in this study.

Intervention Elastic separators were placed mesial and distal to the maxillary first molars bilaterally for 3 days to create space for band placement (19). Appropriate bands were selected and fitted to the molars. An alginate impression was taken with the bands in place, then the bands were removed and repositioned in the impression. The impression was poured in stone to fabricate the working model.

Fabrication of the Modified Palatally Anchored Expander Appliance

The positions of the screws for skeletal anchorage were determined on the model within a safe square on the anterior palatal area. Four lines were drawn (9):

• The first line, 8 mm distal to the incisive papilla, marked the anterior boundary.
• The second line, parallel to the first, passed through the distal surfaces of the second premolars to mark the posterior boundary.
• Two additional lines, each 8 mm lateral to the median palatal raphe, were drawn perpendicular to the first two lines.

The four-point support expander was modified by rotating the line of action 90° to align anteroposteriorly for distalization (9). The distalizer was centered on the palate. The two anterior legs were bent forward and welded to metal sleeves (3 mm diameter) placed 2 mm from the midpalatal raphe. The posterior legs were bent to be welded to the bands on the upper first molars bilaterally. The distalizer was soldered to the bands, finished, polished, and prepared for intraoral insertion

Study outcomes:

The primary outcomes of the current study were: Arch length in millimetres , Inter-canine width in millimetres, Inter-first premolar width in millimetres , Inter-second premolar width in millimetres and Inter-first molar width in millimetres.

While the secondary outcomes were skeletal and dental cephalometric measurements; SNA in degree , SNB in degree , and ANB angles in degree, FH-MP angle in degree, overjet in millimetres , U1/PP (upper incisor to palatal plane) in degree, L1/MP (lower incisor to mandibular plane) in degree, and interincisal angles in degree.

Statistical Analysis

Data were analyzed using Microsoft Excel 2010 and SPSS version 20 (SPSS Inc., Chicago, IL, USA). Numerical data are presented as means ± standard deviations (SD). The Shapiro-Wilk test confirmed normal data distribution. Parametric tests were used for analysis:

• Paired sample t-tests compared pre- and post-distalization measurements within each group.
• Statistical significance was set at ( p < 0.05 ).
• Intraobserver reliability was assessed using the Intra-Class Correlation Coefficient (ICC).

To account for multiple comparisons, a Bonferroni correction was applied. With 11 primary comparisons, the adjusted significance threshold was α = 0.0045. P-values ≤ 0.0045 were considered statistically significant. Effect sizes (Cohen's d) were reported to indicate clinical relevance, even when p-values exceeded the corrected threshold. Clinical relevance (effect sizes) was emphasized alongside strict statistical significance.