Canine Traction in Orthodontics: A Comprehensive Systematic Review and Meta-Analysis of Biomechanical Principles, Clinical Outcomes, and Emerging Innovations

BackgroundCanine impaction represents one of the most challenging clinical scenarios in orthodontic practice, with maxillary canines being the second most commonly impacted teeth after third molars. The management of impacted canines through orthodontic traction requires an advanced understanding of biomechanical principles, surgical techniques, and patient-specific factors. The decision to attempt traction must be informed by accurate differentiation between mechanical impaction and primary failure of eruption (PFE), as applying orthodontic force to PFE teeth results in failure and iatrogenic ankylosis. Recent systematic synthesis of eruption disorders further underscores the need to differentiate mechanical impaction from genetically mediated eruption failure prior to orthodontic traction [59]. In a companion systematic review, we have synthesized the evidence on genetic etiology and diagnostic accuracy for PFE. The present review focuses specifically on the management of confirmed mechanical impaction requiring orthodontic traction, providing a complete evidence-based framework for clinicians. ObjectiveTo provide the most comprehensive quantitative synthesis to date of orthodontic traction for impacted canines, encompassing biomechanical principles, comparative outcomes of open versus closed surgical exposure techniques, radiographic predictors of traction duration, complications, innovations, and evidence-based clinical recommendations with a practical decision algorithm. MethodsA systematic search of PubMed/MEDLINE and the Cochrane Library was conducted for studies published between January 2000 and February 2026, supplemented by citation tracking in Google Scholar. The PRISMA 2020 guidelines were followed. The protocol was prospectively registered on the Open Science Framework (DOI: 10.17605/OSF.IO/3UDH6). Eligible studies included randomized controlled trials, prospective cohort studies, retrospective cohort studies with at least 20 patients, case-control studies, systematic reviews, and meta-analyses. Risk of bias was assessed using ROBINS-I, RoB 2.0, and ROBIS tools. Meta-analyses employed random-effects models with Hartung-Knapp adjustment. Heterogeneity was assessed using I-squared and tau-squared statistics. Prediction intervals were calculated for meta-analyses with substantial heterogeneity. The GRADE framework evaluated evidence quality. Given the predominance of observational studies, pooled estimates should be interpreted as associations rather than causal effects. ResultsFrom 3,587 records, 94 studies (9,156 patients) met inclusion criteria. Optimal force magnitudes range from 50-150g, with force direction determined by the center of resistance located halfway along the root length. Meta-analyses demonstrated comparable success rates between open (91%, 95% CI: 88-94%) and closed (93%, 95% CI: 89-95%) surgical exposure techniques (9 studies; 3 RCTs, 6 observational; tau-squared = 0.00). Open exposure was associated with reduced traction duration (mean difference -4.7 months, 95% CI: -7.3 to -2.1; I-squared = 87%, tau-squared = 5.82; prediction interval -9.8 to 0.4 months) and lower ankylosis risk (OR 0.15, 95% CI: 0.03-0.83; I-squared = 0%, tau-squared = 0.00). Closed exposure was associated with reduced postoperative pain (mean difference -1.9 VAS, 95% CI: -2.6 to -1.2; I-squared = 0%, tau-squared = 0.00). Radiographic predictors include alpha-angle (beta = 0.16 months/degree), d-distance (beta = 1.20 months/mm), and sector location. Three-dimensional analysis demonstrates that cusp tip displacement explains approximately 55.4% of variance in traction duration. Complications include root resorption (23-48% of adjacent incisors; pooled MD 0.69 mm, 95% CI: 0.58-0.80 mm), alveolar bone loss (pooled MD 0.51 mm, 95% CI: 0.31-0.72 mm), and ankylosis (3.5-14.5%). GRADE evidence quality ranged from high (postoperative pain) to very low (acceleration modalities). Innovations: temporary anchorage devices (moderate-high, established); digital workflows (moderate, emerging); clear aligner-based traction (low, experimental); low-level laser therapy (low-moderate, adjunct only); vibration devices (high-quality negative evidence, not recommended). ConclusionsThis most comprehensive quantitative synthesis demonstrates that both open and closed surgical exposure techniques yield excellent success rates. Open exposure offers advantages in reduced traction duration and lower ankylosis risk, while closed exposure provides superior patient comfort. Radiographic predictors enable accurate pretreatment estimation of treatment duration. The findings of this review, combined with our companion analysis of the genetic and diagnostic basis of PFE [59], support a paradigm shift toward a genetically informed and mechanistically driven approach to all forms of failed tooth eruption. A practical clinical decision algorithm is provided to guide evidence-based management.