"Sliding Jigs vs Retraction Hooks for Maxillary Dentition Distalization Using IZC Miniscrews"

Background and Rationale In non-extraction orthodontic treatment of Class II malocclusion or maxillary dentoalveolar protrusion, whole maxillary dentition distalization is a key treatment modality. The advent of temporary anchorage devices (TADs), specifically infrazygomatic crest (IZC) miniscrews, has revolutionized this approach by enabling predictable posterior translation of the entire maxillary arch without significant anchorage loss or reliance on patient compliance.

However, the biomechanical method for transferring force from the miniscrew to the dentition-whether through a sliding jig (continuous force via a rigid attachment) or separate retraction hooks (segmented force applied to individual teeth or groups)-may lead to clinically significant differences in movement type, efficiency, stability, and patient experience. No randomized clinical trial to date has directly compared these two popular clinical approaches.

This study will provide evidence-based recommendations for optimizing clinical mechanics in whole arch distalization protocols.

Objectives Primary Objective To compare the rate of maxillary first molar distalization (in mm/month) achieved using the sliding jig technique versus retraction hooks anchored by IZC miniscrews.

Secondary Objectives To assess the amount and type of tooth movement (tipping vs. translation) of the maxillary first molars and central incisors.

To evaluate anchorage stability by measuring 3D positional changes of the IZC miniscrews and any unintended distal movement of the maxillary dentition.

To compare changes in occlusal plane inclination and vertical dentoalveolar effects.

To record and compare patient-reported outcomes, including pain/discomfort levels, oral hygiene difficulty, and appliance interference.

To document clinical side effects, such as miniscrew stability, soft tissue irritation, and root proximity.

Study Design Design: Prospective, parallel-group, randomized controlled clinical trial (RCT).

Allocation Ratio: 1:1. Blinding: Single-blind (Outcome assessor will be blinded to group assignment. Patients and treating clinicians cannot be blinded due to the nature of the intervention). Methodology Participant Selection Source: Patients seeking orthodontic treatment at [Sana'a university]. Sample Size: [To be calculated based on power analysis; e.g., n=20 per group, total N=40].

Randomization \& Intervention After consent and initial records, participants will be randomly assigned to Group A (Sliding Jig) or Group B (Retraction Hooks) using computer-generated random numbers in sealed opaque envelopes.

Preintervention records were taken as T0, which include intraoral and extraoral photographs, lateral cephalometric and panoramic radiographs, and study models.

The IZCMI (infra-zygomatic mini-implant) will be 2 × 12 mm in diameter and length, respectively, will be placed in infrazygomatic crest area bilaterally.

The IZCMI will be placed distal to the maxillary first molar at 11-12 mm above the cemento-enamel junction at an angle of 50-70° from the occlusal plane.

Retraction hooks were modeled using 0.036-inch crimpable hook stainless steel (soldered 23-gauge stainless steel wire (0.574 mm) for making the hook) and located bilaterally between the lateral incisors and canines. Crimpable hook height of 8 mm will place on the arch wire between the lateral incisors and canines after levelling aligning in one side, and on the other side, A 0.7-mm round SS wire was used to construct the distalization jig. Regarding the design, the distal extension of the jig will be fitted before the molar band or tube. The mesial extension had a helix that surrounded the main archwire, and the jig in the distal section had a lever arm distal to the canine. The lever arm will be set at height according to the mini screw and center of resistance height.

For en-masse anterior retraction, according to Wu et al. a force of 300 g will be given from the IZC screws to the crimpable hooks placed in the region between lateral incisors and canines, and to the lever arm of sliding jig distal to the canine through nickel-titanium (NiTi) closed coil springs/E chains, which activated every 4 weeks. The amount of force was measured using a dontrix gauge.

All patients will be treated using a pre-adjusted edgewise appliance system using a Roth prescription, a slot size of 0.022 × 0.028 inch, and metal brackets with conventional ligation. After leveling and aligning the dentition, stainless steel wire (0.019 x 0.025 inch) was used as the working archwire for the maxillary dentition distalization and ended when an acceptable overjet will be achieved, and on reaching Class I relationship molar and canine.

For all patient, miniscrews will be checked for stability, every 4 weeks intra-oral scanning will be taken. Use digital scans to create 3D models of the dental arch and measure maxillary dentation movement with precision. The 3D model images will be assessed using Orth Analyzer software (3Shape, Copenhagen, Denmark). Furthermore, scanned 3D models will be superimposed over the subsequent model to measure the average monthly distalization. Anchorage loss of the first maxillary molars will be also measured on the digitally scanned models. Furthermore, molar rotation will be measured.

Outcome Measures \& Data Collection Primary Outcome: Rate of Molar Distalization. Measured on digital models (from intraoral scans) by comparing the 3D position of the maxillary first molar (mesial contact point) relative to the stable palatal rugae at T0 (pre-distalization) and T1 (after 4mm distalization achieved or 6 months).

Secondary Outcomes:

Tooth Movement Type: Angular changes (tipping) of molars and incisors on lateral cephalograms.

Anchorage Loss: 3D movement of miniscrews and mandibular molar position (digital models analysis).

Occlusal Plane Change: Cephalometric analysis. Patient-Reported Outcomes: Visual Analog Scale (VAS) for pain/discomfort at 24h, 3d, 7d; questionnaire on oral hygiene and function.

Clinical Side Effects: Miniscrew mobility, inflammation, mucosal coverage (clinical exam).

Reliability Analysis To determine inter-examiner reliability, two examiners will evaluate the images independently. Calibration of the examiners will be undertaken until intra-examiner reliability and reproducibility will be achieved. Kappa statistics will be used for assessing the agreement between observers using the statistical software.

Statistical Analysis:

Data will be evaluated using statistical package SPSS software system, (SPSS Inc, Chicago, Illinois, United States), and descriptive statistical analysis (mean, standard deviation) will be used to obtain the mean and standard deviation for continuous data. Paired t-test will be performed to analyze the changes in pre- and post-distalization. For any of the used tests, results will be considered as statistically significant if p value≤ 0.050.

. Ethical Approval:

• The study protocol will be submitted to the Ethical Committee of the College of Dentistry University of Sana'a, for review and approval.
• Written informed consent will be obtained from the patients of all participants prior to enrollment in the study.
• The study will adhere to the guidelines outlined in the World Medical Association Declaration of Helsinki, ensuring that the research complies with ethical standards for studies involving human subjects.

Expected Significance and Impact This study will provide high-level evidence (Level 2, RCT) to guide clinical decision-making in biomechanics for total arch distalization. Findings will help clinicians choose the most efficient, predictable, and patient-friendly method, ultimately improving treatment quality and efficiency. The results will be disseminated through peer-reviewed publication and conference presentations.