Comparing Ligation Methods During Canine Retraction Stage Using Conventional Brackets

This Randomized Controlled Trial (RCT) aims to provide objective, quantifiable data on the effectiveness of different ligation methods during the canine retraction stage. Canine retraction is a crucial phase in fixed appliance orthodontic therapy, particularly in cases involving crowding and protrusion of maxillary anterior teeth. While numerous mechanics and materials have been developed over the years for tooth movement, the choice of ligature in conventional brackets remains a subject of debate due to observed differences in tooth movement rate, biofilm formation, friction, and force application.

A significant research gap exists in the literature regarding studies that specifically investigate the effect of different ligation methods on conventional brackets concerning anchorage loss and three-dimensional positional changes of canines. Although self-ligating brackets have gained popularity, conventional brackets remain widely used and do not always show significant improvements over conventional brackets in key treatment outcomes. Furthermore, prior studies have rarely investigated canine extrusion as a parameter during retraction with various ligation methods, which this study addresses. The study seeks to provide practitioners with objective evidence to inform their choice of ligation method, potentially improving treatment efficiency by identifying methods that facilitate optimal space closure within a given timeframe and minimize unwanted tooth movements. The use of 3D intraoral scanners and digital superimposition is prioritized for its safety, simplicity, accuracy, and patient comfort in assessing tooth movement.

• Research Aim: To evaluate and compare the effectiveness of different ligation methods during the canine retraction using conventional orthodontic brackets in terms of amount of canine retraction, three-dimensional position change of maxillary canines and anchorage loss of maxillary first molars.

• Objectives: i. General Objective: To identify the most effective ligation method during the canine retraction stage of orthodontic treatment using conventional brackets.

ii. Specific Objectives

• To compare the amount of maxillary canine retraction during the retraction phase using different ligation methods.
• To evaluate three-dimensional positional change of maxillary canines (rotation, tipping and extrusion) using different ligation methods.
• To assess anchorage loss of maxillary first molars during canine retraction using different ligation methods.

• Research Questions:

• What is the effect of different ligation methods on the amount of maxillary canine retraction using conventional brackets?
• How do various ligation methods influence the three-dimensional positional changes-specifically rotation, tipping, and extrusion-of maxillary canines during retraction?
• What is the effect of different ligation methods on the amount of anchorage loss in the maxillary first molars during canine retraction using conventional brackets?

• Study Design This will be a single-centre, three-arm parallel prospective randomised controlled trial. The allocation ratio will be set at 1:1:1 for the three intervention groups. Reporting will be done based on the CONSORT 2010 Guidelines

• Study Groups This study will consist of three-arm parallel groups as described in Table 1. The three interventions will be randomly allocated to quadrants on the upper arch of subjects.

i. Group A - Elastomeric power chain on all bracket wings. ii. Group B - Stainless steel ligatures with elastomeric power chain placed over all bracket wings.

iii. Group C - Elastomeric modules on mesial wings and power chain on distal wings.

• Study Population Participants will consist of patients receiving fixed appliance orthodontic treatment in IIUM, Kuantan who meet the inclusion and exclusion criteria.

i. Inclusion Criteria I. Patients aged 16 years and above. II. Patients who require extraction of one or both maxillary first premolars as part of their orthodontic treatment.

III. Patient who are planned for maximum anchorage using Nance appliance. IV. Patients who require at least 4mm of maxillary canine retraction as part of their orthodontic treatment.

V. Patients with good oral hygiene.

ii. Exclusion Criteria I. Patients with craniofacial anomalies. II. Patients with systemic or bone diseases that could affect tooth movement (e.g., osteopetrosis, osteogenesis imperfecta, Paget's disease).

III. Patients on medications that may affect tooth movement. IV. Patients with hypodontia. V. Patients with poor dental health where orthodontic treatment is not feasible.

Patients who do not fulfil all the inclusion criteria or has any one of the exclusion criteria will be excluded from the study.

• Intervention and Treatment Protocol:

i. Pre-treatment Phase: After screening and consent, a comprehensive orthodontic examination will be performed, including intraoral and extraoral photographs, alginate impressions for stone models, and panoramic and lateral cephalometric radiographs. Molar bands and a Nance button will be fabricated and cemented before dental extractions of maxillary first premolars.

ii. Bond-Up Stage: Two weeks post-extraction, preadjusted edgewise stainless-steel brackets with MBT prescription will be bonded. Initial 0.012-inch nickel titanium alloy archwires (NiTi) will be placed and ligated with A-1 Elastomeric modules.

iii. Alignment and Levelling Phase: Patients will progress through alignment using progressively larger archwires at 4-week intervals: 0.012-inch (round) NiTi, 0.016-inch (round) NiTi, 0.018 x 0.025-inch (rectangular) NiTi, and finally 0.019 x 0.025-inch (rectangular) stainless steel (SS). The final SS archwire will remain for at least 4 weeks to ensure complete alignment and levelling.

iv. Canine Retraction Stage (Baseline T0 and Follow-ups):

• At baseline (T0), the archwire will be removed for intraoral 3D scanning. After the scan, the working archwire will be re-placed. All brackets will be ligated with elastomeric modules, except for the study canine(s).
• Canine retraction will utilize elastomeric power chains stretched to approximately twice their resting length and changed at each subsequent visit. A standardized force level of 150g will be used, measured with a calibrated force gauge.
• The study employs a two-step retraction mechanics, where the maxillary canine is retracted in isolation into the extraction space using the elastomeric power chains. This approach is preferred given that a Nance button, used for anchorage standardization, would typically become embedded during en-masse retraction.

v. Follow-up appointments (T1, T2, T3) will occur at 4-week intervals for repeated 3D intraoral scans and power chain replacement.

• Data Collection and Measurement: Digital intraoral scans will be performed using a calibrated Alliedstar AS 200E intraoral scanner, with images exported in Standard Triangle Language (STL) file format.

Superimposition: Scans will be superimposed using Materialise 3-matics software (Version 13.0) by a single operator (SR). The 3D surface-to-surface matching (best-fit) method will be utilized, employing specific palatal landmarks: definite points (posterior limit of the incisive papilla, right/left lateral edges of the third palatal rugae) and a vertical line along the median palatal raphe. Elective points include medial edges of the second and third palatal rugae, which may be omitted if obstructed by the Nance button. Color-coded superimposition will be used to enhance accuracy. Superimposition will be done incrementally (T1 on T0, T2 on T1, T3 on T2) to record interval changes.

• Randomization and Blinding: Randomization: After consent, eligible patients' quadrants will be listed in Microsoft Excel and stratified by gender. A reputable online tool (Sealed Envelope Ltd. 2019) will generate separate block randomization sequences for each gender, utilizing a fixed block size of six (two assignments for each group per block).

Allocation Concealment: Group assignments will be printed on individual sheets, folded, and sealed in opaque, sequentially numbered envelopes. An independent individual not involved in recruitment or treatment will prepare and store these envelopes. Envelopes will only be opened prior to the space closure appointment (T0).

Blinding: Due to the visible nature of the interventions, patient and clinician blinding is not possible. However, assessor blinding will be ensured by using anonymized 3D scan files, which will be renamed and recoded by an independent individual before measurements and statistical analysis by the principal investigator. Group identities will remain concealed until after statistical analysis is complete.

• Calibration and Standardization: To ensure consistency and validity, comprehensive calibration and standardization protocols will be implemented.

Investigators: All post-graduate orthodontic residents involved in treating study patients will receive training from the Principal Investigator (SR) on ligation techniques, power chain placement, intraoral scanning, force gauge usage for standardized 150g force, two-step canine retraction mechanics, archwire sequence, and Nance button design and care. This training will be supervised by Co-Supervisor Dr. Kumeran Mohan.

Measurement Calibration: The Principal Investigator (SR) will be calibrated to a gold standard (Co-Supervisor KM) on identifying specific landmarks on 3D intraoral digital scans for measurements and superimposition. Inter-rater and intra-rater reliability will be assessed using Interclass Correlation Coefficient (ICC) on ten random 3D scans.

Equipment Calibration: The force gauge and intraoral scanner will be calibrated according to manufacturer instructions by qualified technicians prior to and routinely throughout the study.

• Data Management and Statistical Analysis: The Principal Investigator (SR) will manage all data, which will be stored in encrypted, password-locked files to maintain confidentiality.

Statistical Analysis:

Descriptive statistics will summarize outcomes. One-way ANOVA or Kruskal-Wallis test will be used for intergroup analysis (comparing the three ligation methods).

Repeated measures ANOVA will compare changes over time within groups (T0 to T1, T1 to T2, etc.).

Paired t-tests or Wilcoxon Signed Rank test will compare outcomes between right and left quadrants.

Pearson's or Spearman's correlation may be performed to assess relationships between numerical outcomes.

If ANOVA results are significant (p<0.05), a post-hoc test such as Tukey HSD will be performed.

Intention-to-Treat (ITT) analysis will be performed to account for patient dropouts or withdrawals, utilizing the last observation carried forward (LOCF) method for missing data.

Inclusion criteria

• Patients aged 16 years and above.
• Patients who require extraction of one or both maxillary first premolars as part of their orthodontic treatment.
• Patient who are planned for maximum anchorage using Nance appliance.
• Patients who require at least 4mm of maxillary canine retraction as part of their orthodontic treatment.
• Patients with good oral hygiene.

Exclusion criteria

• Patients with craniofacial anomalies.
• Patients with systemic or bone diseases that could affect tooth movement (e.g., osteopetrosis, osteogenesis imperfecta, Paget's disease).
• Patients on medications that may affect tooth movement.
• Patients with hypodontia.
• Patients with poor dental health where orthodontic treatment is not feasible.