# Efficacy of skeletally anchored modified leaf expander versus modified conventional Hyrax in maxillary molar distalization: a randomized clinical trial

## TL;DR

This study compares two orthodontic devices for moving maxillary molars backward, finding that one achieves the result faster than the other.

## Contribution

The study introduces a randomized clinical trial comparing two skeletally anchored distalizers for maxillary molar distalization.

## Key findings

- Both appliances achieved significant distalization of maxillary first molars with minimal angular changes.
- The Hyrax Expander achieved distalization faster than the Leaf Expander with a significantly shorter treatment duration.
- Skeletal and dental parameters showed no significant differences after Bonferroni correction.

## Abstract

Distalization in orthodontics is one of conservative treatment modalities that result in gaining space especially in dental orthodontic cases of class ΙΙ molar relationship.

A prospective parallel double group randomized clinical trial aimed to compare the distalization effects of the skeletally anchored modified Leaf Expander versus the skeletally anchored modified conventional Hyrax Expander. Skeletally anchored distalizers for orthodontic treatment are better than dentally anchored distalizers (Superiority).

Thirty patients (15–18 years) who were requiring maxillary molar distalization, were randomly allocated into two groups (n = 15 each). Group 1 received the modified skeletally anchored self-activated Leaf Expander, and Group 2 received the modified skeletally anchored conventional Hyrax Expander. Pre- and post-distalization lateral cephalometric radiographs and digital dental models were analyzed for skeletal, dental, and arch dimensional changes. The primary outcomes of the current study were: Arch length, Inter-canine width, Inter-first premolar width, Inter-second premolar width and Inter-first molar width, all these parameters were assessed after completion of distalization and result in class 1 molar relationship. Treatment duration and adverse events were also recorded. Statistical analysis included paired t-tests and independent t-tests, with Bonferroni correction (α = 0.0045) applied for multiple comparisons. Effect sizes (Cohen’s d) were calculated to assess clinical relevance.

Both appliances achieved significant distalization of maxillary first molars as assessed on lateral cephalometric analysis (Leaf: −7.65 ± 0.74 mm(95% CI: −8.06 – −7.24); Hyrax: −6.95 ± 0.82 mm(95% CI: −7.41 – −6.49) with effect size (d) 0.87) with minimal angular changes. Treatment duration was significantly shorter for the Hyrax group (6.52 ± 1.52 months (95% CI: 6.02–7.54)) compared to the Leaf group (10.43 ± 1.52 months (95% CI: 9.94–11.46); p < 0.001, effect size (d) = 2.35). Skeletal parameters (SNA, SNB, ANB, FH-MP), incisor inclinations (U1/PP, L1/MP), overjet, and arch dimensions showed no statistically significant differences after Bonferroni correction, though some differences were clinically relevant. Mild gingival enlargement occurred in three patients, managed conservatively.

Both appliances effectively achieved significant distalization of maxillary molars; however, the modified skeletally anchored conventional Hyrax Expander achieved distalization faster than the modified skeletally anchored Leaf Expander.

ClinicalTrials.gov Identifier: NCT06308640. Retrospectively registered on 29 February 2024. (first enrolment).

The online version contains supplementary material available at 10.1186/s12903-026-07836-3.