Factors Influencing the Duration of Orthodontic Traction of Impacted Maxillary Canines: A Systematic Review and Meta-Analysis

Abstract

Background: The maxillary canine is the second-most frequently impacted tooth, affecting 1–3% of the population. It plays a crucial role in occlusion, facial esthetics, and arch development, making orthodontic traction the preferred approach over extraction or clinical monitoring without intervention. This systematic review aimed to identify the factors associated with the duration of orthodontic traction for impacted maxillary canines and to evaluate their influence. Methods: A systematic search was conducted in MEDLINE, Cochrane Library, Embase, Web of Science, and grey literature following PRISMA guidelines. Traction duration was defined as follows: (A) time from traction initiation to alignment; (B) time to cusp emergence; and (C) time to appliance removal. Risk of bias was assessed using RoB 2 and ROBINS-I v2. Results: Out of 1156 initial studies, 43 were included in qualitative analysis and 24 in quantitative analysis. The pooled mean treatment duration was 43.13 months (95% CI: 32.50–53.77; I² = 99.6%) for definition A, 44.81 months (95% CI: 23.28–66.34; I² = 99.8%) for definition B, and 87.48 months (95% CI: 69.80–106.07) for definition C. Alpha angle, vertical height, and sector were the most frequently reported factors, potentially influencing traction duration. Meta-regression showed a significant association between mean patient age and treatment duration for definition B (β = −8.168, 95% CI: −15.299 to −1.037; p = 0.025), whereas no significant associations were observed for definition A. Heterogeneity across studies was high, and most non-randomized studies showed moderate to serious risk of bias, while randomized trials presented some concerns. Conclusions: Patient- and treatment-related factors, including higher alpha angle, greater vertical height, and more midline positioning, appear to influence traction duration. Despite variability across studies, these findings provide valuable insights for clinical practice.

1. Introduction

Maxillary canine impaction is a common orthodontic challenge, with a prevalence ranging from 1 to 3% of the population [1,2,3]. It is defined as a tooth that remains infraosseous after its expected eruption period [2,3]. The maxillary canine is the second-most frequently impacted tooth after third molars [4]. This condition is more prevalent in females, with palatal displacement reported in more than half the cases [1,2,3,4,5,6], and occurs bilaterally in approximately 17–45% of individuals with impacted maxillary canines [7].

Due to its key functional and esthetic role in the stomatognathic system, influencing facial appearance, dental arch development, and occlusion, orthodontic traction has been the most commonly used treatment approach [1,2,4]. This approach is particularly indicated in cases with a favourable prognosis, such as growing patients and those without severe arch space deficiencies [2]. Various techniques and biomechanics can be employed to apply traction to impacted canines [3].

Orthodontic treatment involving an impacted canine generally requires a longer duration than comparable malocclusion in which all the teeth erupted normally [8]. It is important to distinguish between “traction duration”, which refers specifically to the time required for guided eruption of the impacted canine, and “total treatment time”, which encompasses the entire course of orthodontic therapy. The literature identifies several factors that can influence the duration of orthodontic traction, including those related to the severity of canine impaction, such as location (unilateral/bilateral), position (buccal, palatal, or midalveolar), sector of impaction (based on Ericson and Kurol’s diagnostic approach), height (distance to occlusal plane) and alpha angulation (angle between the canine’s axis and midline). Patient-related factors, such as age and sex, may also affect the overall duration of treatment [2,9].

Prior investigations have reported inconsistent associations between these factors and traction duration, which may be explained by methodological heterogeneity across studies, including differences in study design, sample sizes, outcome definitions, and clinical protocols. Consequently, clinicians often rely on clinical experience to estimate the expected duration of orthodontic traction, as heterogeneous evidence limits the development of clear guidelines and accurate treatment predictions [10]. Accurate prediction of traction duration is essential not only for clinical scheduling and resource allocation but also for optimizing patient adherence, satisfaction, and overall treatment outcomes [9,10].

Despite the increasing number of studies investigating factors associated with maxillary canine traction, the available evidence remains fragmented and has not yet been comprehensively synthesized. In this context, the present systematic review and meta-analysis aim to synthesize available evidence on determinants of maxillary canine traction duration, address inconsistencies in the literature, and apply meta-regression to elucidate factors exerting significant influence. A comprehensive understanding of these determinants may enhance the predictability of orthodontic treatment planning and support evidence-based clinical decision-making.

2. Materials and Methods

2.1. Protocol Registration and Research Question

This systematic review was registered in the International Prospective Register of Systematic Reviews (PROSPERO) database under the ID number: CRD420251250073. The review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [11]. The PEO (population, exposure and outcome) question is presented in

Table 1. PEO (population, exposure and outcome) question.

Population	patients undergoing orthodontic traction of impacted maxillary canines
Exposure	patient-related factors and treatment-related factors
Outcome	duration needed to successfully traction the canine

.

2.2. Eligibility Criteria

The inclusion criteria regarding study design encompassed case reports, case series, observational studies (cross-sectional, cohort and case–control studies) and randomized and non-randomized controlled trials that evaluated factors influencing the duration of impacted maxillary canine traction. Editorials, academic books, reports, review articles and studies that did not evaluate the factors that influence the duration of impacted maxillary canine traction were excluded.

2.3. Information Sources and Search

The research was carried out by searching several databases, namely Medline (through PubMed), Cochrane Library, Web of Science (all databases) and Embase. A search was also conducted in the grey literature on the following websites: OpenGrey Europe (https://opengrey.eu) and ProQuest (https://www.proquest.com). The last search was conducted on 1 May 2025. No filters, language restrictions, or date limits were applied in the search strategy. The search strategy for each database is in

Table A1. Search Formulas for each database.

Database	Search Key
PubMed (Medline)	(“unerupted canine*” OR “impacted canine*” OR “impacted maxill* canine*” OR “ectopic canine*” OR “retained canine*” OR “displaced canine*” OR “canine* impact*” OR “canine* displac*”) AND (“maxilla”[Mesh] OR maxill* OR upper OR “Palate”[Mesh] OR palat*) AND (traction OR “orthodontics”[Mesh] OR orthodont* OR “tooth movement technique”[Mesh] OR “tooth movement technique*” OR “movement technique*, tooth” OR “technique*, tooth movement” OR “Orthodontic Extrusion”[Mesh] OR “forced eruption*” OR “eruption*, forced” OR “forced tooth eruption” OR “tooth extrusion*” OR “extrusion*, tooth” OR exposure) AND (“Duration of Therapy”[Mesh] OR duration OR time OR period OR term OR length) Filter: exclude preprints
Embase	(‘unerupted canine*’ OR ‘impacted canine*’ OR ‘impacted maxill* canine*’ OR ‘ectopic canine*’ OR ‘retained canine*’ OR ‘canine*, impact*’ OR ‘displaced canine*’ OR ‘canine*, displac*’) AND (‘maxilla’/exp OR ‘maxill*’ OR ‘upper’ OR ‘palate’/exp OR ‘palat*’) AND (‘traction’ OR ‘orthodontics’/exp OR ‘orthodont*’ OR ‘orthodontic tooth movement’/exp OR ‘tooth movement technique*’ OR ‘movement technique*, tooth’ OR ‘technique*, tooth movement’ OR ‘orthodontic extrusion’/exp OR ‘forced tooth eruption’ OR ‘forced eruption*’ OR ‘eruption*, forced’ OR ‘tooth extrusion*’ OR ‘extrusion*, tooth’ OR ‘exposure’) AND (‘treatment duration’/exp OR ‘duration’ OR ‘time’ OR ‘period’ OR ‘term’ OR ‘length’) AND ([article]/lim OR [article in press]/lim OR [data papers]/lim OR [letter]/lim OR [short survey]/lim OR [clinical trial]/lim)
Cochrane	#1 (unerupted NEXT canine*) #2 (impacted NEXT canine*) #3 (impacted NEXT maxill* NEXT canine*) #4 (ectopic NEXT canine*) #5 (retained NEXT canine*) #6 (displaced NEXT canine*) #7 (canine* NEXT impact*) #8 (canine* NEXT displac*) #9 MeSH descriptor: [Maxilla] explode all trees #10 maxill* #11 upper #12 MeSH descriptor: [Palate] explode all trees #13 palat* #14 traction #15 MeSH descriptor: [Orthodontics] explode all trees #16 orthodont* #17 MeSH descriptor: [Tooth Movement Techniques] explode all trees #18 (movement technique* NEXT tooth) #19 (technique* NEXT tooth movement) #20 (tooth movement NEXT technique*) #21 (movement technique* NEXT tooth) #22 MeSH descriptor: [Orthodontic Extrusion] explode all trees #23 (tooth NEXT extrusion*) #24 (forced NEXT eruption*) #25 “forced tooth eruption” #26 (Eruption* NEXT forced) #27 (extrusion* NEXT tooth) #28 exposure #29 MeSH descriptor: [Duration of Therapy] explode all trees #30 duration #31 time #32 period #33 term #34 length #35 #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7 OR #8 #36 #9 OR #10 OR #11 OR #12 OR #13 #37 #14 OR #15 OR #16 OR #17 OR #18 #19 OR #20 OR #21 OR #22 OR #23 OR #24 OR #25 OR #26 OR #27 OR #28 #38 #29 OR #30 OR #31 OR #32 OR #33 OR #34 #39 #35 AND #36 AND #37 AND #38
Web of Science	(“unerupted canine*” OR “impacted canine*” OR “impacted maxill* canine*” OR “ectopic canine*” OR “retained canine*” OR “displaced canine*” OR “canine* impact*” OR “canine* displac*”) AND (maxill* OR upper OR palat*) AND (traction OR orthodont* OR “tooth movement technique*” OR “movement technique*, tooth” OR “technique*, tooth movement” OR “forced eruption*” OR “eruption*, forced” OR “forced tooth eruption” OR “tooth extrusion*” OR “extrusion*, tooth” OR exposure) AND (duration OR time OR period OR term OR length)

from Appendix A. Moreover, a manual search of the reference list of the included studies was performed to identify potentially eligible studies.

2.4. Selection of Sources of Evidence

After removing duplicates, two independent reviewers (D.B and R.T.) screened the remaining studies and selected only those that met the predefined eligibility criteria. Initially, studies were selected based on their title and abstract. Those that fulfilled the inclusion criteria were evaluated through full-text reading. Any disagreements during either stage were resolved through mediation with a third reviewer (I.F.).

2.5. Data Charting Process and Data Items

The information extracted from each source included the following: author; year of publication; study design; sample characterization (size, sex and age); factors influencing the duration of orthodontic traction (including patient-related and treatment-related factors); location and position of the impacted canine, orthodontic traction method, evaluation method, results, and conclusion. Data extraction was performed by two authors independently (D.B and R.T.). Any differences in the collection of information between reviewers were resolved through consultation with a third reviewer (I.F.). When required data were missing or unclear, attempts were made to contact the corresponding authors for clarification.

2.6. Risk-of-Bias Assessment

The quality of studies included was assessed by two reviewers (D.B. and R.T.) using two scales. In the case of disagreement, a third reviewer (I.F.) was consulted. The Risk of Bias in Non-randomized Studies—of Interventions Version 2 (ROBINS-I V2) [12] was adopted for assess non-randomized studies, while the revised Cochrane risk-of-bias tool for randomized trials (ROB 2) [13] was used to evaluate the randomized studies. The overall risk of bias of each study was assessed using the ROBINS-I V2 tool and categorized as low, moderate (corresponding to “some concerns”), serious, or critical. In ROB 2, each study may vary its overall classification regarding bias risk as low, high or some concerns.

The figures summarizing the analysis were created using the Robvis tool [14].

2.7. Synthesis of Results

Because the included studies used three distinct definitions of traction duration (A, B, and C) representing different clinical endpoints, all meta-analyses were stratified by definition type. Studies from different definitional strata were not pooled together at any stage of the analysis. Several meta-analyses have been conducted to synthesize the results of multiple studies. Only studies reporting sufficient quantitative data to estimate the effect size (mean traction duration and a corresponding measure of variability, such as standard deviation or confidence intervals) were included in the meta-analysis. All analyses were carried out using the “Metafor” package in R (v. 4.1.2). A random-effects model was adopted for each meta-analysis, taking into account the potential heterogeneity between the results. Stratification by traction duration definition (A, B, and C) was implemented prior to pooling, as these definitions represent distinct clinical endpoints that are not directly comparable. This stratification constitutes the primary analytical response to definitional heterogeneity. Within each stratum, a random-effects model was adopted to account for residual clinical and methodological heterogeneity, accepting wider confidence intervals as the appropriate conservative choice. Confidence intervals are presented in the forest plots to convey the uncertainty. The average treatment time was adopted as a measure of effect and evaluated according to three different definitions: (1) Definition A: time elapsed from the initiation of orthodontic traction until the canine was aligned; (2) Definition B: time from the initiation of orthodontic traction to the emergence of the canine cusp in the oral cavity; (3) Definition C: time from orthodontic traction to the removal of fixed appliances.

Additionally, univariate meta-regressions were conducted to explore clinical variables reported in at least five studies, aiming to identify potential sources of heterogeneity. A sensitivity analysis excluding studies at high risk of bias was considered. However, for several definitions, doing so would leave an insufficient number of studies to conduct a reliable meta-regression. Heterogeneity between studies was assessed using Cochran’s Q test and the I² index. The Q test evaluates the presence of heterogeneity, while I² estimates the proportion of total variability attributable to heterogeneity across studies. In the meta-regressions, the R² was calculated to determine the proportion of heterogeneity explained by each covariate. Results were visually presented using forest plots, which display effect sizes and confidence intervals for individual studies as well as the overall summary effect. Potential publication bias was assessed through funnel plots and, when applicable, Egger’s test. Relationships examined in the meta-regressions were illustrated using bubble plots, reporting regression coefficients, 95% confidence intervals and statistical significance. Multivariate meta-regression was considered but could not be implemented due to the sparse and inconsistent reporting of predictor variables across included studies. Very few studies reported multiple candidate predictors simultaneously, making joint modelling statistically underdetermined. The univariate results presented therefore represent the maximum achievable level of synthesis given the available data.

3. Results

3.1. Selection of Sources of Evidence

The process of identification, screening and inclusion is described in Figure 1. The initial search yielded 1156 studies. After removing duplicates, 576 records remained for title and abstract screening, resulting in 93 potentially relevant studies. Full-text review led to the inclusion of 43 studies that met the eligibility criteria for this systematic review. Among these, 24 were included in quantitative analysis.

3.2. Characteristics and Results of Sources of Evidence

This systematic review and meta-analysis included 43 clinical studies that evaluated factors influencing the duration of maxillary canine traction. Studies addressing treatment-related factors are summarized in

Table 2. Summary of included studies addressing treatment-related factors.

Author, Year	Factors Influencing the Duration of Orthodontic Traction: Patient Factors and Treatment Factors	Sample Characterization (Size, Sex and Age)	Position and Location of the Impacted Canine	Results/Conclusions
Zogakis, I. et al., 2025 [16]	Treatment factors Type of active unit (ballista spring vs. cantilever) and type of bonded attachment (eyelet vs. bracket).	29 patients (20 F/9 M) 34 ICs Ballista: n = 22; Cantilever: n = 12; Bracket: n = 10; Eyelet: n = 24 Median age: (all) = 16 y; (ballista) = 16 y; (cantilever) = 17 y; (eyelet) = 16 y; (bracket) = 17 y.	PIC	No significant difference between ballista and cantilever in alignment duration. However, the use of bracket significantly increased TD compared to eyelets. - Median TD: - Ballista: 18 months - Cantilever: 17.5 months - Bracket: 32.5 months - Eyelet: 16.5 months
Fekonja, A., 2024 [20]	Treatment factors Traction using double-wire composed of 0.013 CuNiTi wire connected to the basal 0.019 × 0.025 Niti wire (EG) and traction using a 0.012-inch stainless-steel ligature to the 0.019 × 0.025 Niti wire (CG).	54 ICs CG: 20 patients (14 F/6 M); 26 ICs; mean age: 13.88 ± 1.58 y EG: 21 patients (14 F/7 M); 28 ICs; mean age: 14.02 ± 1.61 y	NR	TD was significantly shorter with the double-wire technique (EG). Active Traction (Mean ± SD): - EG: 31 ± 4.2 weeks - CG: 37 ± 6.3 weeks
Verma, S. et al., 2023 [26]	Treatment factors Traction applied using K9 Spring (Group 1) and Ballista Spring (Group 2).	30 patients (19 F/11 M) 30 ICs Mean Age: Group 1 = 16.8 ± 2.6 y; Group 2 = 17.1 ± 2.4 y; All = 16.97 ± 2.47 y.	PIC	Although the TD was shorter for Group 1 (296.13 ± 96.45 days) compared to Group 2 (311.93 ± 94.34 days), no statistically significant differences were found between the two groups for TD.
			UIC
Mousa, M. et al., 2023 [27]	Treatment factors Traditional method with eyelet and twisted ligature wire (CG) and same method as the CG combined with corticotomy in the cortical bone (EG).	46 patients (13 M/33 F) 46 ICs CG: 23 patients; mean age: 20.26 ± 2.17 y EG: 23 patients; mean age: 20.39 ± 2.27 y	PIC: 19 in CG and 20 in EG;	There was a statistically significant difference concerning the mean TD: - CG: 9.68 ± 3.24 months - EG: 6.13 ± 1.81 months When using corticotomy for the treatment, TD dropped 36% and TT decreased 29%.
			MA: 4 in CG and 3 in EG;
			UIC
Migliorati, M. et al., 2022 [28]	Treatment factors Anchorage method: indirect anchorage with mTPA (EG) and direct anchorage with miniscrews (CG).	27 patients 35 ICs EG: 14 patients (7 M/7 F); 15 IC CG: 13 patients (7 M/6 F); 20 IC Mean age (all patients): 14.4 ± 1.2 y	PIC	There was a slightly faster movement in the CG (median timespan of 85.50 days, while the EG had a median timespan of 130.00 days), but there was no statistically significant difference in total TT.
Björksved, M. et al., 2021 [25]	Treatment factors Open and closed surgical techniques.	117 patients (73 F/44 M) 117 ICs (open technique group: 58; closed technique group: 59) Mean age: (all) = 13.4 ± 1.48 y; Open technique: M = 13.5 ± 1.0 y, F = 13.2 ± 1.5 y; closed technique: M = 14.0 ± 1.4 y, F = 13.3 ± 1.6 y	PIC	Open technique had faster initial eruption (3 months faster). However, the alignment phase (TD) took longer in the open group, balancing out total TT. So, TT was almost identical between the groups. TT between groups was equal, with a mean difference of 0.1 months: - Open technique: 26.4 ± 7.0 months - Closed technique: 26.3 ± 9.4 months
			UIC: 87
			BLIC: 30
			(the most severe IC was considered for the study in BLIC cases)
			IC-R: 52
			IC-L: 65
Migliorati, M. et al., 2021 [30]	Treatment factors Anchorage method: TPA (CG) and TAD (EG).	16 patients (12 F/10 M) 16 ICs Mean age: 13.4 y	PIC: 9	No significant differences were found between groups in apex or tip displacement or timespan. No correlations were found between the ICs’ movement and patient age.
			BIC: 7
Ferguson, D. et al., 2019 [44]	Treatment factors Traction without osteotomy–decortication technique (CG) and traction with ostectomy–corticotomy technique (EG).	118 patients 151 ICs CG: 61 patients; 79 IC EG: 57 patients; 72 IC Mean age: CG = 14.5 ± 2.8 y; EG = 15.3 ± 2.3 y	PIC	A markedly longer TD was observed in the CG compared to the EG (21 months vs. 6.6 months, respectively). Within the CG, the TD did not vary based on the initial palatal position of the IC. However, in the EG, TD increased significantly when the IC had a larger pretreatment ‘a angle’, was positioned closer to the midline horizontally, and was located further vertically from the OP.
			UIC: 85
			BLIC: 66 (both ICs were considered for 33 patients)
			IC-R: 47 CG + 44 EG = 91
			IC-L: 32 CG + 28 EG = 60
Naoumova, J. et al., 2018 [36]	Treatment factors Glass-ionomer open exposure (GOPEX) and closed exposure.	60 patients 60 ICs Open exposure (GOPEX): 30 patients (18 F/12 M), 30 ICs Closed technique: 30 patients (20 F/10 M), 30 ICs Mean Age: open exposure = 14.0 ± 1.6 y; closed technique = 13.9 ± 1.6 y	PIC	Although traction of the IC was initiated earlier in the closed exposure cases, the TD was shorter in the open exposure cases. The overall TT did not differ: - Open technique: 28.0 ± 9.7 months - Closed technique: 27.1 ± 8.4 months
			UIC
			IC-R: 14 (A) + 18 (B) = 32
			IC-L: 16 (A) +12 (B) = 28
Yussif, N. et al., 2018 [32]	Treatment factors Conventional traction (CG) and traction supported by both orthodontic treatment and intraepidermal vitamin C injections (EG).	12 patients (9 F/3 M) 12 ICs CG: 6 patients, 6 ICs EG:6 patients, 6 ICs Age:16–34 y	PIC	A significantly higher mean area percentage of tooth movement rate in the EG, with a mean of 2.25 ± 0.274%, compared to 1.08 ± 0.376% in CG.
			UIC
			IC-R: 6
			IC-L: 6
Bertl, M. et al., 2016 [47]	Treatment factors Closed and open exposure techniques.	55 patients (20 M/35 F) 79 ICs Mean age: 19.1 ± 7.8 y	PIC: 41	Out of 55 patients, seven required repeat surgery, with two needing a third procedure. Additional surgeries were significantly more common after the closed exposure technique compared to the open technique. In cases requiring repeat surgery, TT did not significantly exceed that of patients with a single intervention. The duration of stage 1 was significantly longer, stage 2 was significantly shorter, and stages 3 and 4 showed no significant differences. TT was not significantly related to sex, age, location of IC, or the surgical technique, although TT was significantly prolonged for patients with BLIC.
			BIC: 8
			MA: 6
			UIC: 31
			BLIC: 48 (both ICs were considered for the 24 patients)
Fleming, P. et al., 2009 [6]	Treatment factors Open and closed exposure techniques.	45 patients (36 F/9 M) 54 ICs Mean age: 14.81 ± 2.83 y	PIC	The horizontal position was the only variable significantly correlated with TD. No significant correlation was found between TD and factors such as age, angulation, vertical height, root apex location, or the type of surgical exposure.
			UIC: 36
			BLIC: 18
Fischer, T. 2007 [29]	Treatment factors Open surgical exposure (CG) and open surgical exposure with corticotomy (EG).	6 patients (4 F/2 M) 12 ICs Age: 11.1–12.9 y	PIC	The TD was shorter for ICs treated with corticotomy assistance compared to their contralateral counterparts exposed using the conventional method.
			BLIC: 6 (each patient as their own control)
			IC-R: 6
			IC-L: 6
Baccetti, T. et al., 2007 [31]	Patient factors ‘a angle’, vertical height, sector, age, sex, location, position and side of IC.	168 patients (40 M/128 F) 168 ICs Mean age: 17.2 ± 6.0 y	PIC: 118	For every 5° increase in the ‘a angle’, approximately one additional week of active traction was required. Similarly, each 1 mm increase in vertical height corresponded to roughly one more week of traction. ICs in sector 1 required approximately six more weeks of traction compared to those in sector 3. Other pretreatment variables, such as sex, age, location, position and side of IC, showed no significant association with TD.
			BIC: 50
			UIC: 125
			BLIC: 43 (one was chosen per patient)
			IC-R: 90
			IC-L: 78
Jeong, S. et al., 2007 [33]	Patient factors Initial crowding of maxillary arch, maxillary anterior dental width, mandibular anterior dental width, angulation to the midline, canine angulation to the midline grade, position of the IC root apex horizontally, height of the IC crown vertically, height of the IC crown vertical grade, IC overlap to the adjacent Mx2 root grade, root closure state of IC grade and root curvature of IC from tooth axis.	36 patients (8 M/28 F) 36 ICs Mean age: 13.7 ± 2.5 y 2 groups, based on the mean TT of 21 months: - short treatment: 5 M/13 F, mean age: 13.3 ± 5.4 y - long treatment: 3 M/15 F, mean age: 13.2 ± 5.3 y	PIC	A significant difference was observed in the extent of IC crown overlap with the root of neighbour Mx2. However, no significant differences were noted in the other parameters. Compared to the long-term treatment group, the short-term group exhibited lower values for angulation to the midline, vertical height of the crown, overlap to the adjacent MX2 root grade and root curvature from tooth axis, but higher values for position of the root apex horizontal and root closure state of de IC.
			UIC
			UIC-R: 18
			UIC-L: 18
Grande, T. et al., 2006 [51]	Patient factors IC distance and angulation to the OP. IC tip position relative to Mx2 and Mx1 adjacent roots. Frequency of MD root deviations.	47 patients (28 F/19 M) 59 ICs Mean age: 15.5 ± 4.6 y	PIC: 52	No correlation was observed between TT and vertical height, the angle of inclination to the OP, position of the crown tip or root deviation.
			BIC: 7
			UIC: 35 (15 M + 20 F)
			BLIC: 24 (4 M + 8 F)
			IC-R: 34
			IC-L: 25
Zhang, J. et al., 2006 [19]	Patient factors Age: adolescent (CG) and adult (EG).	34 patients (EG: 6 M/11 F; CG: 8 M/9 F) 42 ICs Mean age: CG = 13.7 y; EG = 28.8 y	PIC: 28	TD differed significantly between adults and adolescents. Mean TD: - CG: 8.4 ± 3.1 months - EG: 15.1 ± 5.4 months
			BIC: 14
			In each group: - UIC: 13 - BLIC: 8
Zuccati, G. et al., 2006 [22]	Patient factors Age, ‘a angle’, beta and eta angles, vertical height, MD position, omega angle and d2.	87 patients 87 ICs Mean age: 16.7 ± 7.6 y	UIC: 66	The variable “number of visits” had a strong correlation with age, vertical height and the MD position. On the other hand, a weaker inverse correlation was found with the beta angle.
			BLIC: 21 (only one was included, the one that took the longest)
			IC-R: 43
			IC-L: 44
Becker, A. et al., 2003 [8]	Patient factors Age: younger (CG) and adult (EG).	38 patients (CG:8 F/12 M; EG: 7 F/12 M) 46 ICs Mean age: CG = 13.7 ± 1.3 y; EG = 28.8 ± 8. 6 y	PIC	There were no significant differences in the overall TT and appointments between the adults and young patients, but adults took over twice as long (12.1 vs. 5.5 months) and needed more visits (15.3 vs. 6.9) to resolve IC. In adults, impaction treatment made up half the total time, compared to one-third in controls. Mean TT: - CG: 5.5 ± 3.4 months - EG: 12.1 ± 10.3 months
			In each group: - UIC: 15 - BLIC: 8
Stewart, J. et al., 2001 [10]	Patient factors Sex, location of the IC, vertical height, ‘a angle’, MD position, Angle’s classification of occlusion, the amount of maxillary and mandibular crowding, the overjet, and overbite.	47 patients (30 F/17 M) 65 ICs Mean age: 14.4 ± 2.2 y	PIC	Age and mandibular crowding significantly predicted TT, explaining 30% of its variance. Younger age correlated with longer treatment. Greater vertical height was linked to increased ‘a angle’, closer proximity to the MSP, and longer TT. The TT average for UIC was 25.8 months, while the BLIC average was 32.3 months.
			UIC: 29
			BLIC: 36
			IC-R: 33
			IC-L: 32
Iramaneerat, S. et al., 1998 [17]	Patient factors Age, incisor relationship, vertical height; horizontal distance from the IC tip and angular relationship of the IC to the perpendicular line passing through the A point in lateral cephalometric radiograph. Treatment factors Open exposure with a ribbon gauze pack soaked in Whitehead’s varnish sutured in position for 10 ± 14 days and close exposure with flap replaced.	50 patients (34 F/16 M) 50 ICs Mean age: - open exposure: 13.9 y - close exposure with flap replaced: 13.5 y	PIC	Both groups showed wide variability in time to debond, 16.5–44.5 months for the open exposure group and 16.0–62.0 months for the flap-replaced group. A similar pattern was observed for TD: 8.3–34.3 months and 7.5–46.8 months, respectively.
			UIC
Pearson, M. et al., 1997 [18]	Treatment factors Surgical and orthodontic traction: open exposure with spring traction on molar bands joined by a TPA (Centre A) and exposure with immediate bracketing, flap replacement, and elastic traction to a fish-tail appliance (Centre B).	104 patients 134 ICs Centre A: 64 (20 M/32 F) Centre B: 70 (32 M/20 F) Mean age: - centre A: 13.9 y - centre B: 14.5 y	PIC	Centre A extended management by 6 months. Mean TT: - centre A: 25.7 months - centre B: 21.8 months
			73 UIC
			30% BLIC = Approximately, 31 patients
Galloway, I. et al., 1989 [15]	Patient factors Age and location of IC.	86 patients	PIC	TT was similar for UIC and BLIC with comparable appliance complexity. Age at diagnosis did not significantly affect TT, which was more influenced by ectopic tooth position.

‘a angle’: angle between the long axis of the impacted canine and the midline/midsagittal plane; Beta angle: angle between the long axis of the canine and the long axis of the lateral incisor; BIC: buccal impacted canines; BLIC: bilateral impacted canines; CG: control group; CuNiTi: copper–nickel–titanium archwire; d2: perpendicular distance from the canine tip to the occlusal plane; EG: experimental group; Eta angle: angle between the long axis of the canine and the first premolar axis; F: female; IC: impacted canine; IC-L: left impacted canine; IC-R: right impacted canine; ICs: impacted canines; M: male; MA: midalveolar impacted canines; MD: mesiodistal; MSP: midsagittal plane/midline; mTPA: miniscrew (temporary anchorage device) with transpalatal arch; Mx1: maxillary central incisor; Mx2: maxillary lateral incisor; NiTi: nickel–titanium archwire; NR: not reported; omega angle: angle between the canine and the occlusal plane, in the lateral cephalogram; OP: occlusal plane; PIC: palatal impacted canines; sector: impacted canines are classified as sector 1 to 5, based on the location of their cusp tip in relation to adjacent incisors (definition by Ericson and Kurol); TAD: temporary anchorage device; TD: traction duration; TPA: transpalatal arch; TT: full orthodontic treatment time; UIC: unilateral impacted canines; UIC-L: unilateral left-side canine; UIC-R: unilateral right-side canine; y: years old.

, while studies examining patient-related factors are presented in

Table 3. Summary of included studies addressing patient-related factors.

Author, Year	Factors Influencing the Duration of Orthodontic Traction: Patient Factors and Treatment Factors	Sample Characterization (Size, Sex, and Age)	Position and Location of the Impacted Canine	Results/Conclusions
Vasović, D. et al., 2025 [39]	Patient factors Sex, age, side of impaction, angle classification, vertical position, horizontal position, ’a angle’, vertical height, contact with Mx2, localization of the crown, localization of the apex, bucco-palatal position of the crown tip, inclination, root resorption.	64 patients (18 M/46 F) 68 ICs Mean age: 15.17 ± 3.69 y	PIC: 54	Significant associations found between the following: - Crown tip position (BIC vs. PIC): IC with buccal-placed crowns emerged significantly faster than PIC or ML-located ones. - Horizontal position: IC near Mx2s had shorter TTs compared to those near Mx1s. - Angulation to midline: Greater angulation (>30° to midline) increased TT. - Vertical position, age, sex and side of impaction had no significant impact.
			BIC: 17
			MA: 12
			UIC: 45 (UIC-R: 22; UIC-L: 23)
			BLIC: 19
Perrotta, S. et al., 2024 [40]	Patient factors Age, sector, ‘a angle’, location and position.	103 patients (60 F/43 M) 125 ICs Mean age: 18.2 ± 5.7 y Median age: 16 y	PIC: 87	No statistically significant difference in TD based on age, sector, or position of the IC. However, a statistically significant association was found between a reduced ‘a angle’ and shorter TD.
			BIC: 39
			IC-R: 54.2%
			IC-L: 41.2%
Goh, P. et al., 2024 [5]	Patient factors Vertical and horizontal displacement, angulation, apical curvature, buccolingual inclination and crown rotation.	37 patients (21 F/16 M) 37 ICs Mean age: 15.1 ± 1.5 y	PIC: 23	No significant TT difference based on location, position or impaction side. However, crown rotation significantly affected TT: for every degree of mesiopalatal rotation, TT increased by 0.32 weeks. Increased rotation, apical hook curvature, and severe displacement were associated with prolonged TT. Age and sex, in combination, also influenced TT (older F had shorter TT than younger M).
			BIC/MA: 14
			UIC: 30
			BLIC: 7—only 1 of each was selected, based on sector, height above the OP and ‘a angle’
			IC-R: 15
			IC-L: 22
Güllü, Y. et al., 2024 [21]	Patient factors Age, sector, ‘a angle’, vertical height, vertical height relative to the adjacent Mx2, apex position.	121 patients (34 M/87 F) 134 ICs Mean age: Overall = 16.2 y; F = 16.2 y; M = 16.21 y	PIC: 99	For every 1 mm increase in vertical height, the TD increased by 8.4 days. This included the sector as a dummy variable in the model that showed that TD was 73 days longer in sector 4 and 99.5 days longer in sector 5. Additionally, as age increased, TD declined by 0.2 days.
			BIC: 35
			UIC: 108
			BLIC: 26
			IC-R: 73
			IC-L: 61
Yang, J. et al., 2022 [7]	Patient factors Sector, vertical height, ‘a angle’, horizontal height, angle with the OP, impaction location (BIC or PIC).	74 patients (32 M/42 F) 47 ICs Mean Age: 10.9 ± 2.4 y	PIC: 22	The correlation between the TD and the measurements in OPGs showed that all measurements were statistically significant, except the angle with the OP. No significant difference in TD between BIC and PIC, across any sector. Vertical height had the strongest correlation with TD.
			BIC: 65
			UIC: 61
			BLIC: 26
			IC-R: 45
			IC-L: 42
Han, J. et al., 2022 [34]	Patient factors Sex, age, type of impaction, mesiodistal location, bucco-palatal location, vertical height, angulation to OP, root developmental stage, root dilaceration.	73 patients (31 M/42 F) 93 ICs Mean age: 11.66 ± 1.93 y	PIC: 12	No significant differences in TD by age, sex or position. There was a statistically significant difference in TD regarding location, which BLIC had shorter TD. ICs closer to the Mx2 or Mx3 region had shorter TD. No significant difference was found with root development stage or angulation to OP.
			MA: 28
			BIC: 53
			UIC: 52
			BLIC: 41
Amuk, M. et al., 2021 [41]	Patient factors Sex, relationship of root and cortex borders of the NC and/or maxillary sinus. MD position. ‘a angle’, vertical height, location (BIC or PIC). Root shape as normal, blunt, or apically bent, CL.	38 patients (22 F/16 M) 38 ICs Mean age: F = 15.36 ± 1.67 y; M = 15.18 ± 1.22 y	PIC: 24	PIC took approximately 2 months longer to treat than BIC, although not statistically significant. Apically bent roots significantly increased TD. Greater (positive) root–cortex relationship was associated with prolonged TD.
			BIC: 14
			UIC
Grisar, K. et al., 2021 [42]	Patient factors Sector, vertical height, angulation, age, and position.	132 patients (47 M/106 F) 153 ICs Median age: 14 ± 4.6 y	PIC: 87	TT increased with age and was significantly longer for PICs. BLICs and greater impaction severity, based on sector, angulation, and vertical height, were also significantly associated with prolonged TT. A significant relationship was found between older age, TT and the need for reintervention.
			MA: 31
			BIC: 35
			UIC: 111
			BLIC: 42
			In patients with BLIC, separate treatment durations were considered.
Sosars, P. et al., 2020 [43]	Patient factors Angulation of the long axis of the canine to the OP, ‘a angle’, vertical and horizontal heights, and MD position category of the IC cusp tip.	88 patients (27 M/61 F) 106 ICs Mean age: 16.8 ± 6.1 y	PIC	Moderate correlations were found between TD and ‘a angle’ on OPG; the position category and ‘a angle’ assessed on the CBCT’s frontal plane. In the multivariate analysis, only the angulation on CBCT (frontal plane) remained statistically significant, explaining 36% of the variation in TD.
			UIC-L: 33
			UIC-R: 35
			BLIC: 38
Arriola Guillén, L. et al., 2019 [9]	Patient factors Location, sector, side, position, height, alpha and beta angles, CL, IC root area. Sex, age, malocclusion, premolar extractions, previous incisor root resorption, ANB, APDI, and SNA angles, and ANS-PNS distance.	30 patients (11 M/19 F) 45 ICs Mean age: 18.16 ± 7.32 y	PIC: 20	Sex significantly affected TD, with F patients requiring approximately 2.049 months longer than M. Cases involving BLIC showed an average increase of 2.74 months compared to UIC. Additionally, for every 1° increase in the beta angle, TD extended by about 0.055 months. Bicortically ICs added roughly 2.85 months to the TD, and those located in sectors 4 or 5, closer to the MSP, took around 2.35 months longer to treat than those in sectors 1 to 3.
			BIC: 18
			MA: 7
			UIC: 15
			BLIC: 30
			IC-R: 25
			IC-L: 20
Ferguson, D. et al., 2019 [44]	Patient factors ‘a angle’, horizontal and vertical positions.	118 patients 151 ICs CG: 61 patients; 79 IC EG: 57 patients; 72 IC Mean age: CG = 14.5 ± 2.8 y; EG = 15.3 ± 2.3 y	PIC	A markedly longer TD was observed in the CG compared to the EG (21 months vs. 6.6 months, respectively). Within the CG, the TD did not vary based on the initial palatal position of the IC. However, in the EG, TD increased significantly when the IC had a larger pretreatment ‘a angle’, was positioned closer to the midline horizontally, and was located further vertically from the OP.
			UIC: 85
			BLIC: 66 (both ICs were considered for 33 patients)
			IC-R: 47 CG + 44 EG = 91
			IC-L: 32 CG + 28 EG = 60
Kocyigit, S. et al., 2019 [45]	Patient factors Age and sex, classification of occlusion, secondary surgery due to the button breakage, ‘a angle’, the distance from the IC tip to its target point on the OP, the rate of root formation, the MD position of the IC tip in relationship to the adjacent Mx2.	50 patients (12 M/38 F) 50 ICs Mean age: all = 20.0 ± 6.3 y; adult group = 24.61 ± 6 y; adolescent group: 15.91 ± 1.7 y	PIC	Adult group: 23.88 ± 5.96 months Adolescent group: 25.86 ± 6.75 months No significant correlation was identified between patient age, IC angulation, MD position of the IC tip in relationship to the adjacent Mx2 and the rate of root formation and overall TT. The only radiographic factor found to have a mild association with TT was vertical height.
			UIC: 38
			BLIC: 12
			IC-R: 21
			IC-L: 29
Shin, H. et al., 2019 [46]	Patient factors Presence, size and volume of dental follicles, bone density, CL, age, ‘a angle’, horizontal height, distance from the IC cusp tip to the XY plane, distance from the IC cusp tip to the XZ plane, angle between the long axis of the IC and the XY plane, angle between the long axis of the IC and the XZ plane, angle between the long axis of the IC and the long axis of the Mx2 of the IC. Interdental distance.	27 patients (6 M/23 F) 29 ICs Mean age: 12.5 ± 2.9 y	BIC	The only factor significantly associated with TD was the ‘a angle’. No significant associations were found between TD and follicle size and volume, bone density, CL or age.
			UIC: 25
			BLIC: 4
			IC-R: 14
			IC-L:15
Tepedino, M. et al., 2018 [38]	Patient factors FMA; MP-MxP; MP-OP; MxP-OP.	26 patients Mean age: 15.8 ± 0.9 y	PIC	No relation was found between facial divergence and extrusion time.
Lin, Y. et al., 2018 [37]	Patient factors Age, sector, vertical height, ‘a angle’.	60 patients (23 M/37 F) 60 ICs Mean age: 12.3 ± 3.2 y	PIC: 17	Angle, line spacing and location were significantly associated with TD. PICs required longer TD compared to those positioned BICs. The greater the vertical height and angle of the IC, the longer the TD. Conversely, the closer the IC is to the first premolar, the shorter the required TD.
			BIC: 43
			UIC
			IC-R: 31
			IC-L: 29
Schubert, M. et al., 2018 [23]	Patient factors Age, sex, side of impaction, predicted eruption path length (in the three methods: OPG, CBCT (simplified and trigonometric analysis)).	30 patients (18 F/12 M) 30 ICs Mean age: 13.8 ± 1.7 years	PIC	No significant sex-specific differences were found in the TD or in the overall TT. However, the TD showed a strong and statistically significant correlation with the eruption path length.
			UIC
			IC-R: 15
			IC-L: 15
Potrubacz, M. et al., 2018 [35]	Patient factors ‘a angle’, height of the IC crown in respect to the CEJ of the Mx2, overlap over the Mx2, position of the IC crown in sectors 1 to 5, age and sex.	22 patients (12 F/10 M) 30 ICs Mean age: F = 15.0 ± 3.9 y; M = 15.4 ± 4.8 y	PIC	TT was strongly influenced by the patient’s age, with the shortest TT observed in patients aged 11 to 12 years. A statistically significant interaction was found between age and the TD, as well as between sex and both the vertical position of the IC crown and TD. However, the severity of impaction, defined by the position of the IC, did not have a statistically significant effect on TD.
			UIC: 14
			BLIC: 16 (both ICs were considered for the 8 patients)
			IC-R: 13
			IC-L: 17
Bertl, M. et al., 2016 [47]	Patient factors Sex, age, location and position of the IC.	55 patients (20 M/35 F) 79 ICs Mean age: 19.1 ± 7.8 y	PIC: 41	Out of 55 patients, seven required repeat surgery, with two needing a third procedure. Additional surgeries were significantly more common after the closed exposure technique compared to the open technique. In cases requiring repeat surgery, TT did not significantly exceed that of patients with a single intervention. The duration of stage 1 was significantly longer, stage 2 was significantly shorter, and stages 3 and 4 showed no significant differences. TT was not significantly related to sex, age, location of IC, or the surgical technique, although TT was significantly prolonged for patients with BLIC.
			BIC: 8
			MA: 6
			UIC: 31
			BLIC: 48 (both ICs were considered for the 24 patients)
Kim, M. et al., 2013 [48]	Patient factors Age, CL, vertical height, angulation of IC related to the OP, ‘a angle’, angulation of IC to coronal plane (plane perpendicular to the MSP, aligned with the Mx1’s incisal edges).	17 patients (7 M/10 F) 18 ICs Mean age: 13.8 ± 2.43 y	UIC: 16	A significant positive correlation between age and TT. Similarly, greater vertical height was associated with longer TT. In contrast, longer CL correlated with shorter TT. Additionally, angulation between the ‘a angle’ was positively correlated with TT, whereas an angle between the canine axis and the OP showed a negative correlation.
			BLIC: 2
Bazargani, F. et al., 2013 [24]	Patient factors Vertical height, ‘a angle’, sector, sex, age, location and side of impaction.	66 patients (23 M/43 F) 66 ICs Mean age: 14.9 ± 1.7 y	PIC	TT remained significantly longer (by an average of 7.6 months) for ICs located in zones 4 and 5 compared to those in zones 1 and 2. TT increased with greater vertical height, with an average increase of 1.7 months per millimetre without adjustment, and 1.2 months per millimetre after adjustment. Each degree increase in the ‘a angle’ corresponded to an average increase in TT of 0.30 months unadjusted, and 0.19 months adjusted, statistically significant difference.
			UIC: 51
			BLIC: 15 (only 1 considered)
			IC-R: 39
			IC-L: 27
Nieri, M. et al., 2010 [50]	Patient factors Sex, age, location, side, position, vertical height, ‘a angle’ and sector.	168 patients (40 M/128 F) 168 ICs Mean age: 17.2 ± 6.0 y	PIC: 118	An increase in the vertical height was associated with a longer TD and, consequently, an extended overall TT. The greater ‘a angle’, the greater vertical height, the higher the prevalence for sectors 1 and 2, the longer TD. Impactions located in sectors 1 and 2 were associated with prolonged TD. BLIC determines a longer TD.
			BIC: 50
			UIC: 125
			BLIC: 43 (one was chosen per patient)
			IC-R: 90
			ICL: 78
Fleming, P. et al., 2009 [6]	Patient factors ‘a angle’, vertical height, MD position of IC cusp, position of canine root apex anteroposterior and incisor relationship.	45 patients (36 F/9 M) 54 ICs Mean age: 14.81 ± 2.83 y	PIC	The horizontal position was the only variable significantly correlated with TD. No significant correlation was found between TD and factors such as age, angulation, vertical height, root apex location, or the type of surgical exposure.
			UIC: 36
			BLIC: 18
Schubert, M. et al., 2009 [49]	Patient factors Age, alpha and beta angles, vertical height, distance to the target point in the OP, MD position.	57 patients 57 ICs Mean age: - UIC: 13.3 ± 1.6 y - BLIC: 12.4 ± 0.8 y	PIC	The ‘a angle’, the distance from the canine cusp tip to its target on the OP, the TD and overall TT were all significantly correlated with the position of the ICs across zones 1 to 5. ICs in zone 2 showed significantly shorter overall TT and TD compared to those located in zones 3 to 5. The ‘a angle’ and both distance measurements were significant predictors when TD was used as the dependent variable. Mean TD: UIC: 18.0 ± 5.3 months BLIC: 23.5 ± 5.5 months
			UIC: 41 (29F/12M)
			BLIC: 16 (12F/4M) (the IC in the worst position was selected)
			IC-R: 23
			IC-L: 34
Baccetti, T. et al., 2007 [31]	Patient factors ‘a angle’, vertical height, sector, age, sex, location, position and side of IC.	168 patients (40 M/128 F) 168 ICs Mean age: 17.2 ± 6.0 y	PIC: 118	For every 5° increase in the ‘a angle’, approximately one additional week of active traction was required. Similarly, each 1 mm increase in vertical height corresponded to roughly one more week of traction. ICs in sector 1 required approximately six more weeks of traction compared to those in sector 3. Other pretreatment variables, such as sex, age, location, position and side of IC, showed no significant association with TD.
			BIC: 50
			UIC: 125
			BLIC: 43 (one was chosen per patient)
			IC-R: 90
			IC-L: 78
Jeong, S. et al., 2007 [33]	Patient factors Initial crowding of maxillary arch, maxillary anterior dental width, mandibular anterior dental width, angulation to the midline, canine angulation to the midline grade, position of the IC root apex horizontally, height of the IC crown vertically, height of the IC crown vertical grade, IC overlap to the adjacent Mx2 root grade, root closure state of IC grade and root curvature of IC from tooth axis.	36 patients (8 M/28 F) 36 ICs Mean age: 13.7 ± 2.5 y two groups, based on the mean TT of 21 months: - short treatment: 5 M/13 F, mean age: 13.3 ± 5.4 y - long treatment: 3 M/15 F, mean age: 13.2 ± 5.3 y	PIC	A significant difference was observed in the extent of IC crown overlap with the root of neighbour Mx2. However, no significant differences were noted in the other parameters. Compared to the long-term treatment group, the short-term group exhibited lower values for angulation to the midline, vertical height of the crown, overlap to the adjacent MX2 root grade and root curvature from tooth axis, but higher values for position of the root apex horizontal and root closure state of de IC.
			UIC
			UIC-R: 18
			UIC-L: 18
Grande, T. et al., 2006 [51]	Patient factors IC distance and angulation to the OP. IC tip position relative to Mx2 and Mx1 adjacent roots. Frequency of MD root deviations.	47 patients (28 F/19 M) 59 ICs Mean age: 15.5 ± 4.6 y	PIC: 52	No correlation was observed between TT and vertical height, the angle of inclination to the OP, position of the crown tip or root deviation.
			BIC: 7
			UIC: 35 (15 M + 20 F)
			BLIC: 24 (4 M + 8 F)
			IC-R: 34
			IC-L: 25
Zhang, J. et al., 2006 [19]	Patient factors Age: adolescent (CG) and adult (EG).	34 patients (EG: 6 M/11 F; CG: 8 M/9 F) 42 ICs Mean age: CG = 13.7 y; EG = 28.8 y	PIC: 28	TD differed significantly between adults and adolescents. Mean TD: - CG: 8.4 ± 3.1 months - EG: 15.1 ± 5.4 months
			BIC: 14
			In each group: - UIC: 13 - BLIC: 8
Zuccati, G. et al., 2006 [22]	Patient factors Age, ‘a angle’, beta and eta angles, vertical height, MD position, omega angle and d2.	87 patients 87 ICs Mean age: 16.7 ± 7.6 y	UIC: 66	The variable “number of visits” had a strong correlation with age, vertical height and the MD position. On the other hand, a weaker inverse correlation was found with the beta angle.
			BLIC: 21 (only 1 was included, the one that took the longest)
			IC-R: 43
			IC-L: 44
Becker, A. et al., 2003 [8]	Patient factors Age: younger (CG) and adult (EG).	38 patients (CG: 8 F/12 M; EG: 7 F/12 M) 46 ICs Mean age: CG = 13.7 ± 1.3 y; EG = 28.8 ± 8.6 y	PIC	There were no significant differences in the overall TT and appointments between the adults and young patients, but adults took over twice as long (12.1 vs. 5.5 months) and needed more visits (15.3 vs. 6.9) to resolve IC. In adults, impaction treatment made up half the total time, compared to one-third in controls. Mean TT: CG: 5.5 ± 3.4 months; EG: 12.1 ± 10.3 months.
			In each group: - UIC: 15 - BLIC: 8
Stewart, J. et al., 2001 [10]	Patient factors Sex, location of the IC, vertical height, ‘a angle’, MD position, Angle’s classification of occlusion, the amount of maxillary and mandibular crowding, the overjet, and overbite.	47 patients (30 F/17 M) 65 ICs Mean age: 14.4 ± 2.2 y	PIC	Age and mandibular crowding significantly predicted TT, explaining 30% of its variance. Younger age correlated with longer treatment. Greater vertical height was linked to increased ‘a angle’, closer proximity to the MSP, and longer TT. The TT average for UIC was 25.8 months, while the BLIC average was 32.3 months.
			UIC: 29
			BLIC: 36
			IC-R: 33
			IC-L: 32
Iramaneerat, S. et al., 1998 [17]	Patient factors Age, incisor relationship, vertical height; horizontal distance from the IC tip and angular relationship of the IC to the perpendicular line passing through the A point in lateral cephalometric radiograph.	50 patients (34 F/16 M) 50 ICs Mean age: - open exposure: 13.9 y - close exposure with flap replaced: 13.5 y	PIC UIC	Both groups showed wide variability in time to debond, 16.5–44.5 months for the open exposure group and 16.0–62.0 months for the flap-replaced group. A similar pattern was observed for TD: 8.3–34.3 months and 7.5–46.8 months, respectively.
Galloway, I. et al., 1989 [15]	Patient factors Age and location of IC.	86 patients	PIC	TT was similar for UIC and BLIC with comparable appliance complexity. Age at diagnosis did not significantly affect TT, which was more influenced by ectopic tooth position.

‘a angle’: angle between the long axis of the impacted canine and the midline/midsagittal plane; ANB angle: angle formed by subspinale, nasion, and submental points; ANS-PNS: anterior nasal spine–posterior nasal spine plane or maxillary plane; APDI angle: anteroposterior dysplasia indicator; the arithmetic sum of three angles: Frankfort horizontal plane to facial plane, A–B plane to facial plane, and to Frankfort plane; Beta angle: angle between the long axis of the canine and the long axis of the lateral incisor; BIC: buccal impacted canines; BLIC: bilateral impacted canines; CBCT: cone-beam computed tomography; CG: control group; CL: canine root length; d2: perpendicular distance from the canine tip to the occlusal plane; EG: experimental group; Eta angle: angle between the long axis of the canine and the first premolar axis; F: female; FMA: angle between the Frankfurt horizontal and mandibular planes; horizontal height: horizontal distance from the canine cusp tip to the midline; IC: impacted canine; IC-L: left impacted canine; IC-R: right impacted canine; ICs: impacted canines; M: male; MA: midalveolar impacted canines; MD: mesiodistal; MP-MxP: angle between the mandibular plane and the maxillary plane; MP-OP: angle between the mandibular and occlusal planes; MSP: midsagittal plane/midline; Mx1: maxillary central incisor; Mx2: maxillary lateral incisor; MxP-OP: angle between the maxillary and occlusal planes; NC: nasal cavity; Omega angle: angle between the canine and the occlusal plane, in the lateral cephalogram; OP: occlusal plane; OPG: panoramic radiograph; PIC: palatal impacted canines; sector: impacted canines are classified as sector 1 to 5, based on the location of their cusp tip in relation to adjacent incisors (definition by Ericson and Kurol); SNA angle: angle formed by sella, nasion, and subspinale points; TD: traction duration; TT: full orthodontic treatment time; UBIC: unilateral buccal impacted canine; UIC: unilateral impacted canines; UIC-L: unilateral left-side canine; UIC-R: unilateral right-side canine; vertical height: vertical distance from the canine cusp tip to the occlusal plane; XZ plane: plane passing through the superior foramina of the nasopalatine canal, normal to the XY plane and midline (axial plane); XY plane: plane passing through the superior foramina of the nasopalatine canal, normal to the inferior border of the nasal floor (coronal plane); y: years old.

. Additional detailed information is available in a

Table A2. Additional details of the included studies.

Author, Year	Study Design	Position and Location of the Impacted Canine	Orthodontic Treatment: Surgical Exposure and Orthodontic Mechanic	Method for Assessing Impacted Canine Characteristics
Zogakis, I. et al., 2025 [16]	Retrospective observational	PIC	Surgical exposure not specified.	NR
Vasović, D. et al., 2025 [39]	Retrospective	PIC: 54	Closed eruption technique and stainless-steel archwire.	OPG
		BIC: 17
		MA: 12
				CBCT
		UIC: 45 (UIC-R: 22; UIC-L: 23)
		BLIC: 19
Perrotta, S. et al., 2024 [40]	Retrospective	PIC: 87	“Canine-first technique”. Type of surgical exposure (open, closed, or apically repositioned flap) selected according to individual case characteristics. TADs were used in 78,63% of the cases.	OPG
		BIC: 39
		IC-R: 54.2%
		IC-L: 41.2%
Goh, P. et al., 2024 [5]	Retrospective case–control	PIC: 23	Open exposure technique and mechanics were individualized. TPAs were generally used for PICs. Fixed orthodontic appliances were placed prior to surgical exposure.	CBCT
		BIC/MA: 14
		UIC: 30
		BLIC: 7—only one of each was selected, based on sector, height above the OP and ‘a angle’
		IC-R: 15
		IC-L: 22
Fekonja, A., 2024 [20]	Retrospective case–control	NR	Open exposure technique	OPG
Güllü, Y. et al., 2024 [21]	Retrospective cross-sectional	PIC: 99	Closed exposure technique and traction were applied with a stainless-steel wire. A chain was connected to the tooth, and when the vertical position was adequate, the IC was aligned with a Kilroy Spring.	OPG
		BIC: 35
		UIC: 108
		BLIC: 26
		IC-R: 73
		IC-L: 61
Verma, S. et al., 2023 [26]	Randomized clinical trial	PIC UIC	Open technique and TPA for anchorage. Traction applied using either K9 Spring or Ballista Spring.	CBCT
Mousa, M. et al., 2023 [27]	Randomized controlled clinical trial	PIC: 19 in CG and 20 in EG;	Closed exposure technique. Eyelet and twisted ligature. Corticotomy in the EG.	CBCT
		MA: 4 in CG and 3 in EG;
		UIC
Yang, J. et al., 2022 [7]	Retrospective Cross-sectional	PIC: 22	Closed eruption technique. A small attachment with ligature wire was bonded to the IC.	CBCT
		BIC: 65
		UIC: 61
		BLIC: 26		OPG
		IC-R: 45
		IC-L: 42
Migliorati, M. et al., 2022 [28]	Prospective controlled clinical trial	PIC	Open technique was used for superficial impaction and closed eruption technique was used for deep impactions. A button and chain were bonded to the IC. Miniscrews and TPA for anchorage and titanium–molybdenum alloy cantilevers in both groups.	CBCT
Han, J. et al., 2022 [34]	Retrospective	PIC: 12	Surgical exposure not specified. Miniscrews, miniplates and multibrackets.	CBCT
		MA: 28
		BIC: 53
				OPG
		UIC: 52
		BLIC: 41
Björksved, M. et al., 2021 [25]	Randomized controlled trial	PIC	Closed and open surgical techniques. Elastomeric thread was used for traction. TPA and GG with soldered springs were used in some cases. All patients received fixed orthodontic appliances.	CBCT
		UIC: 87
		BLIC: 30
		(the most severe IC was considered for the study in BLIC cases)
				OPG
		IC-R: 52
		IC-L: 65
Amuk, M. et al., 2021 [41]	Retrospective longitudinal	PIC: 24	Surgical exposure not specified. Traction performed in all cases with fixed appliances. Gold chain or button bonded during surgery. Modified TPAs were used in some cases.	CBCT
		BIC: 14
				OPG
		UIC
Grisar, K. et al., 2021 [42]	Retrospective	PIC: 87	Open or closed exposure technique was used, depending on case. Various attachments: gold chains, ligature wires, extrusion plates. Fixed appliances used.	OPG
		MA: 31
		BIC: 35
		UIC: 111
		BLIC: 42
		In patients with BLIC, separate treatment durations were considered.
Migliorati, M. et al., 2021 [30]	Prospective Randomized Controlled trial	PIC: 9	“Canine first” Closed exposure technique. Both groups used beta-titanium cantilevers.	CBCT
		BIC: 7
Sosars, P. et al., 2020 [43]	Retrospective	PIC	Open exposure technique was used. Pre-adjusted edgewise system was used to align the teeth and create space.	CBCT
		UIC-L: 33
		UIC-R: 35		OPG
		BLIC: 38
Arriola–Guillén, L. et al., 2019 [9]	Retrospective	PIC: 20	Closed exposure technique. A single rigid TAD was attached to the first permanent molars using stainless-steel bands. Traction was applied using nickel–titanium closed-coil springs.	OPG
		BIC: 18
		MA: 7
		UIC: 15		Lateral head films
		BLIC: 30		CBCT
		IC-R: 25
		IC-L: 20
Ferguson, D. et al., 2019 [44]	Retrospective cohort	PIC	CG: both closed and open exposure methods were applied. After surgery, a bracket and power chain were attached to the crown. EG: the ostectomy–corticotomy technique and exposure enabled ideal placement of the bracket.	OPG
		UIC: 85
		BLIC: 66 (both ICs were considered for 33 patients)
		IC-R: 47 CG + 44 EG = 91
		IC-L: 32 CG + 28 EG = 60
Kocyigit, S. et al., 2019 [45]	Retrospective	PIC	Closed technique Brackets from the pre-adjusted system. A button, along with an attached chain or wire, was bonded to the crown. Traction using either a ballista spring or elastic chains.	Lateral cephalometric radiographs
		UIC: 38
		BLIC: 12
		IC-R: 21		OPG
		IC-L: 29
Shin, H. et al., 2019 [46]	Retrospective	BIC	Closed exposure technique. Orthodontic bracket bonded for traction.	CBCT
		UIC: 25
		BLIC: 4
				OPG
		IC-R: 14
		IC-L:15
Tepedino, M. et al., 2018 [38]	Retrospective	PIC	The appliance consisted of a TPA featuring a distal loop, which was welded to bands on the maxillary first molars. A cantilever was attached to the TPA.	Cephalograms
Naoumova, J. et al., 2018 [36]	Retrospective	PIC	Closed and glass-ionomer open exposure techniques. Fixed appliance and/or anchorage methods as extraoral traction, GG, TPA, lingual arch, mTPA. Gold chains were often bonded to exposed teeth.	Intraoral radiographs
		UIC		OPG
		IC-R: 14 (A) + 18 (B) = 32		CBCT
		IC-L: 16 (A) +12 (B) = 28
Lin, Y. et al., 2018 [37]	Retrospective	PIC: 17	NR	OPG
		BIC: 43
		UIC
		IC-R: 31
		IC-L: 29
Schubert, M. et al., 2018 [23]	Retrospective observational cohort	PIC	Closed exposure technique was employed alongside the EWC system, which uses a passive closed-coil spring, following surgical exposure and attachment bonding.	OPG
		UIC
		IC-R: 15		CBCT
		IC-L: 15
Yussif, N. et al., 2018 [32]	Prospective randomized controlled trial	PIC	Closed exposure technique. Orthodontic traction with an active power chain tied on the main sain steel arch wire. In EG, traction was carried out with orthodontic treatment and intraepidermic vitamin C injection.	OPG
		UIC
				occlusal radiography
				CBCT
		IC-R: 6
		IC-L: 6
Potrubacz, M. et al., 2018 [35]	Retrospective cohort	PIC	Opercolectomy technique. An orthodontic button or bracket was bonded to the exposed IC and open traction was initiated. The appliance was anchored using a fixed TPA with a distal loop.	OPG
		UIC: 14
		BLIC: 16 (both ICs were considered for the eight patients)		cephalograms
				intra and extraoral photographs
		IC-R: 13
		IC-L: 17
Bertl, M. et al., 2016 [47]	Retrospective cohort	PIC: 41	Closed and open exposure techniques. Fixed appliances.	CBCT
		BIC: 8
		MA: 6
		UIC: 31
		BLIC: 48 (both ICs were considered for the 24 patients)
Kim, M. et al., 2013 [48]	Retrospective	UIC: 16	Surgical exposure not specified.	CBCT
		BLIC: 2
Bazargani, F. et al., 2013 [24]	Retrospective observational	PIC	12 patients underwent traction using elastics attached to fixed appliances, while 54 were treated with a TPA featuring a spring arm.	OPG
		UIC: 51
		BLIC: 15 (only 1 considered)
		IC-R: 39
		IC-L: 27
Nieri, M. et al., 2010 [50]	Retrospective	PIC: 118	Closed exposure technique. Traction was applied via an elastic connected to a round archwire, while anchorage was provided by a rectangular archwire. Tunnel technique used when the crown of the IC was close to the deciduous IC (n = 24).	OPG
		BIC: 50
		UIC: 125
		BLIC: 43 (one was chosen per patient)
		IC-R: 90
		ICL: 78
Fleming, P. et al., 2009 [6]	Retrospective	PIC	Closed and open techniques. Use of pre-adjusted edgewise appliances, with elastomeric traction applied using a stainless-steel archwire.	OPG
		UIC: 36
		BLIC: 18
Schubert, M. et al., 2009 [49]	Retrospective	PIC	Closed exposure technique. EWC system, in which an attachment was adhesively fixed to the IC.	OPG
		UIC: 41 (29 F/12 M)
		BLIC: 16 (12 F/4 M) (the IC in the worst position was selected)
				lateral cephalograms
		IC-R: 23
		IC-L: 34
Fischer, T. 2007 [29]	Preliminary	PIC	Open exposure technique (CG) and corticotomy procedure (EG). An orthodontic attachment was placed on the IC, and orthodontic traction was not specified.	Periapical radiographs
		BLIC: 6 (each patient as their own control)
		IC-R: 6
		IC-L: 6
Baccetti, T. et al., 2007 [31]	Prospective longitudinal	PIC: 118	Closed surgical exposure. Traction using a chain connected to the bonded attachment and to an elastic element (through a round archwire). A rectangular archwire was employed for stabilization and anchorage.	OPG
		BIC: 50
		UIC: 125
		BLIC: 43 (one was chosen per patient)
		IC-R: 90
		IC-L: 78
Jeong, S. et al., 2007 [33]	Retrospective	PIC	Closed exposure technique was used. Orthodontic traction by attaching an elastic rubber band to the ligature.	OPG
		UIC
		UIC-R: 18
		UIC-L: 18
Grande, T. et al., 2006 [51]	Retrospective	PIC: 52	Surgical exposure not specified. Multi-band/multi-bracket appliance.	OPG
		BIC: 7
		UIC: 35 (15 M + 20 F)
		BLIC: 24 (4 M + 8 F)
		IC-R: 34
		IC-L: 25
Zhang, J. et al., 2006 [19]	Retrospective case–control	PIC: 28	Surgical exposure (closed technique more use on PICs, while open technique was used mainly for BICs). The ligature wire on the traction device ties to the maxillary auxiliary stainless-steel arch wire, secured by a spiral push spring.	CBCT
		BIC: 14
		In each group: - UIC: 13 - BLIC: 8		OPG
Zuccati, G. et al., 2006 [22]	Retrospective observational	UIC: 66	Open exposure technique was used whenever feasible, while the closed exposure technique was mainly used for deeply ICs. Fixed appliances.	OPG
		BLIC: 21 (only one was included, the one that took the longest)
		IC-R: 43
		IC-L: 44
Becker, A. et al., 2003 [8]	Retrospective	PIC	Closed eruption technique. Orthodontic traction was not specified.	OPG
				cephalometric radiographs
		In each group: - UIC: 15 - BLIC: 8		periapical radiograph
Stewart, J. et al., 2001 [10]	Retrospective observational	PIC	Surgical exposure and orthodontic traction were not specified.	OPG
		UIC: 29
		BLIC: 36		cephalometric radiographs
		IC-R: 33
		IC-L: 32
Iramaneerat, S. et al., 1998 [17]	Retrospective	PIC	Open exposure or close exposure with flap replaced. Bonded attachments with gold chains were used.	Lateral cephalometric radiographs
		UIC
Pearson, M. et al., 1997 [18]	Retrospective	PIC	Centre A: open exposure with spring traction on molar bands joined by a TPA. Centre B: exposure with immediate bracketing, flap replacement, and elastic traction to a fish-tail appliance.	NR
		73 UIC
		30% BLIC = Approximately, 31 patients
Galloway, I. et al., 1989 [15]	Retrospective	PIC	56 cases with exposure and traction with fixed and removable appliance combination. 30 cases with exposure and traction with fixed appliance.	NR

‘a angle’: angle between the long axis of the impacted canine and the midline/midsagittal plane; BIC: buccal impacted canines; BLIC: bilateral impacted canines; CBCT: cone-beam computed tomography; CG: control group; EG: experimental group; GG: Goshgarian arch; IC: impacted canine; IC-L: left impacted canine; IC-R: right impacted canine; ICs: impacted canines; MA: midalveolar impacted canines; mTPA: miniscrew (temporary anchorage device) with transpalatal arch; NR: not reported; OP: occlusal plane; OPG: panoramic radiograph; PIC: palatal impacted canines; sector: impacted canines are classified as sector 1 to 5, based on the location of their cusp tip in relation to adjacent incisors (definition by Ericson and Kurol); TAD: temporary anchorage device; TPA: transpalatal arch; UIC: unilateral impacted canines; UIC-L: unilateral left-side canine; UIC-R: unilateral right-side canine.

in Appendix A.2. The publication years of the included studies ranged from 1989 [15] to 2025 [16], with only five published before 2006 [8,10,15,17,18]. The study designs included three case–control [5,19,20], two cross-sectional [7,21], five observational [10,16,22,23,24], five randomized clinical trials [25,26,27,28,29] and one pilot [30]. In terms of timeline, eight studies were prospective [25,26,27,28,29,30,31,32] and 35 were retrospective [5,6,7,8,9,10,15,16,17,18,19,20,21,22,23,24,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51].

3.3. Synthesis of Results

The factors identified as associated with the duration of orthodontic traction of the impacted maxillary canine are listed in

Table 4. Factors evaluated associated with the duration of orthodontic traction of the impacted maxillary canine.

Factor			Number of Articles
Patient-related factor	Patient characteristics	Age	19
		Sex	7
	Severity of displacement	Position	12
		Location	8
		Vertical height (distances from the impacted canine cusp tip to the occlusal plane and to the cementoenamel junction of the lateral incisor)	20
		Distance to canine’s final position in dental arch	2
		Horizontal height (canine cusp tip to midline)	4
		Alpha angle (long axis of canine and midline)	21
		Beta angle (long axis of canine and lateral incisor)	3
		Angle between long axis of canine and occlusal plane	4
		Sector/Zone (by Ericson and Kurol)	14
		Mesiodistal position	5
		Incisor Overlap	1
Treatment-related factor	Surgical exposure	Closed and open techniques	7
		Surgical exposure with corticotomy technique	3
	Orthodontic treatment mechanics	Type of spring (Ballista, Kilroy and K9)	2
		Anchorage system (transpalatal arch and miniscrew)	3
		Bonded attachment (eyelet and bracket)	1

.

These factors may be associated with both the patient and the treatment. A total of 28 studies focused on patient-related factors [5,7,8,9,10,15,19,21,22,23,24,31,35,37,38,39,40,41,42,43,45,46,48,49,50,51], 11 examined only treatment-related factors [16,18,20,25,26,27,28,29,30,32,36] and four considered both [6,17,44,47]. The most studied patient-related factor was the severity of displacement, specifically alpha angle, vertical height and age. Among the factors related to treatment, the surgical exposure technique was the most frequently evaluated [6,19,25,36,42,44,47].

The sample size of the included studies comprised 2362 patients and 2543 impacted maxillary canines. Of these, approximately 1877 were in a palatal position, 434 in a buccal position and 91 in a midalveolar position. In terms of location, there were 1645 unilateral and 666 bilateral impactions. Regarding the impaction side, 13 studies reported more right-sided than left-sided canines [7,9,10,21,24,31,36,37,40,43,44,50,51], while eight found the opposite [5,22,25,35,39,45,46,49]. Four studies reported equal distribution on both sides [23,29,32,33] and 18 did not specify the side [6,8,15,16,17,18,19,20,26,27,28,30,34,38,41,42,47,48]. The mean age of participants ranged from 10.9 ± 2.4 years [7] to 29.8 ± 8.6 years [8], with most studies having adolescents samples, in which the mean age was between 13 and 16 years old [5,6,8,10,16,17,18,19,20,23,24,25,28,30,33,35,36,38,39,40,41,42,44,45,48,49,51]. Nearly all studies included a higher proportion of female participants [5,6,7,9,10,16,17,19,20,21,23,24,25,26,27,29,30,31,32,33,34,35,36,37,39,40,41,42,43,45,46,47,48,50,51].

Orthodontic treatment of impacted maxillary canines involved surgical exposure and orthodontic mechanics. Three studies employed corticotomy [27,29,44], whereas ten did not specify the surgical technique used [10,15,16,19,24,34,38,41,48,51]. A total of 16 studies used the closed eruption technique [7,8,9,21,23,27,30,31,32,33,36,39,45,46,49,50], six used open exposure [5,20,26,29,35,43] and 11 employed both techniques depending on the position of the canine [6,17,18,19,22,25,28,40,42,44,47].

Orthodontic mechanics varied with respect to the type of spring, anchorage system, and bonded attachments. Kilroy [21] and K9 springs [26] were each used in one study, ballista springs were reported in three studies [16,26,45] and cantilever systems in four [16,28,30,38]. Anchorage methods included goshgarian arches (n = 2) [25,36], transpalatal arches (n = 10) [5,18,24,25,26,28,30,36,38,41] and temporary anchorage devices (n = 6) [9,28,30,34,36,40]. The type of attachment was not specified in most cases. However, two studies used eyelets [16,27], five used bonded brackets [16,18,35,44,46] and four used bonded buttons [28,35,41,45].

Orthopantomography (n = 18) [6,8,10,20,21,22,24,31,33,35,37,40,42,44,45,49,50,51] and CBCT (n = 7) [5,26,27,28,30,47,48] were the most used methods to assess impacted maxillary canines. In some cases, both methods were employed (n = 12) [7,9,19,23,25,32,34,36,39,41,43,46]. Lateral cephalograms (n = 8) [8,9,10,17,23,35,38,45], occlusal X-ray (n = 1) [32] and periapical radiographs (n = 3) were less commonly used [8,29,36]. Three studies did not report the imaging method applied [15,16,18].

3.4. Quantitative Analysis of Results

Meta-analyses were performed using 24 studies to identify and quantify the influence of clinical variables on the treatment duration of impacted maxillary canines [6,7,8,9,19,20,21,22,23,25,27,29,31,35,36,38,39,41,42,43,44,46,49,50]. The substantial difference in pooled estimates across definitions (approximately 43, 45, and 87 months for Definitions A, B, and C, respectively) is itself clinically informative: it reflects the cumulative treatment burden added at each stage, and underscores that future studies should adopt and report a consistent definition to allow meaningful cross-study comparisons.

Among studies that defined traction duration as the time until the canine was positioned in its proper location within the dental arch (definition A; n = 19), three studies were low risk, five had some concerns, and 11 were high risk. The pooled effect size was 43.13 [32.50, 53.77] (effect size [95% CI]) (Figure 2). The heterogeneity between studies is high (I² = 99.6%). Egger’s test showed evidence of publication bias (test Egger, p < 0.001).

In studies that defined treatment duration as the interval from initiation of the traction device to the clinical emergence of the cusp tip in the oral cavity (definition B, n = 7), five were rated low risk, one had some concerns, and one was rated high risk. The effect size was 44.81 [23.28, 66.34] (effect size [95% CI]) (Figure 3). The heterogeneity between studies is high (I² = 99.8%). Egger’s test showed no evidence of publication bias (p = 0.231).

For studies defining treatment duration as the entire period from the onset of active traction to the removal of fixed appliances (definition C, n = 4), one was rated as having some concerns and three were rated high risk. The pooled effect size was 87.48 [69.80,106.07] (effect size [95% CI] (Figure 4). Egger’s test showed no evidence of publication bias (p = 0.524).

3.4.1. Definition A for Treatment Duration

Univariable meta-regressions did not demonstrate a statistically significant association between treatment duration and either mean age (β = 0.168, 95% CI: [−3.038, 3.374], p = 0.918) or mean vertical height (β = 2.518, 95% CI: [-16.340, 21.375], p = 0.794). In both cases, the models explained 0.0% heterogeneity between studies (R² = 0.0%) and the residual heterogeneity remained high (QE = 1483.5 and 105.3; I² = 99.7% and 98.9%, respectively; p < 0.001). Figure 5 and Figure 6 show the relationships between treatment duration and mean age and mean vertical height, respectively. Each circle represents a study, with size proportional to its weight in the meta-regression. The solid line represents the estimated regression line, and the shaded area indicates the 95% confidence interval.

3.4.2. Definition B for Treatment Duration

Univariable meta-regression showed a statistically significant association between mean age and treatment duration (β = −8.168, IC 95% [−15.299, −1.037], p = 0.025) (Figure 7). The model explains 40.0% of heterogeneity between studies (R² = 40.0%). Residual heterogeneity remained high (QE = 536.2, p < 0.001, residual I² = 99.7%). The coefficient for mean age (β = −8.168) indicates that, on average, each additional year of mean patient age in a study cohort was associated with approximately eight fewer months of traction duration. This association, while statistically significant, should be interpreted with caution: it reflects a study-level (ecological) association and may be confounded by differences in diagnostic timing, impaction severity, or treatment protocol across age groups.

The relationship between the mean vertical height and treatment duration (Figure 8) revealed no statistically significant association (β = −2.651, IC 95% [−8.034, 2.732], p = 0.334). The model explained 0.0% of heterogeneity between studies (R² = 0.0%), and residual heterogeneity remained high (QE = 580.9, p < 0.001, residual I² = 99.9%).

Overall, the examined predictors showed variable levels of evidence depending on the definition of traction duration. Mean age demonstrated a statistically significant association when treatment duration was defined as the time from traction initiation to cusp emergence (definition B), suggesting a potential influence of patient age during the early phase of canine eruption. No significant association was observed when duration was defined as the time from traction initiation to alignment (definition A). Mean vertical height was not significantly associated with treatment duration in the present analyses, and its predictive role requires further investigation.

3.5. Risk of Bias

The risk-of-bias assessment for non-RCTs is presented in Figure 9. Overall, nine studies were judged as having some concerns, while 24 studies were classified as having a high risk of bias. These judgements were primarily driven by bias due to confounding, which was rated as presenting some concerns or a high risk of bias in most studies. In contrast, bias due to selection of participants, bias due to missing data, and bias in measurement of outcomes were consistently assessed as having a low risk of bias across all included studies.

The quality assessment of the included RCTs is presented in Figure 10. Three studies were classified as having a low overall risk of bias. The remaining two studies were judged as having some concerns regarding the overall risk of bias, primarily due to randomization process.

A summary of the overall risk-of-bias classification for both non-randomized studies and randomized controlled trials is presented in

Table 5. Summary of risk-of-bias distribution across included studies.

Study Type	Number of Studies	Low Risk	Some Concerns	High Risk	Main Observations
Non-randomized studies	38	5	9	24	Confounding was the main reason for high risk; other domains generally presented lower risk
Randomized controlled trials	5	3	2	0	Some concerns mainly related to the randomization process

.

4. Discussion

Accurately predicting treatment duration and the number of appointments can improve practice efficiency and patient satisfaction [9,10]. However, this remains a significant challenge due to the variability in impaction characteristics of maxillary canines. This systematic review and meta-analysis aimed to identify patient- and treatment-related factors that influence the duration of orthodontic traction for impacted maxillary canines and determine their influence. The breadth of clinical variation across included studies—encompassing different surgical exposure techniques, orthodontic mechanics, anchorage systems, and patient demographics—is a defining feature of the current evidence base and is explicitly reflected in the high heterogeneity values observed. The random-effects framework adopted in the meta-analyses was selected precisely because it accommodates, rather than ignores, this variability. Readers should therefore interpret the pooled estimates as characterizing the central tendency of a genuinely diverse population of clinical scenarios, rather than as a single predicted outcome for a homogeneous patient profile. Therefore, the predictors identified in this review should be interpreted as factors that may assist clinicians in estimating treatment duration rather than providing precise or definitive predictions for individual patients.

Regarding patient-related factors, findings on age are inconsistent. The study by Stewart et al. reported that younger patients required longer treatment times [10], while Güllü et al. observed a reduction of 0.2 days in treatment duration for each additional year of age [21]. Conversely, other studies linked increasing age with longer treatment durations [8,19,22,35,42,48]. Jeong et al. further noted that dentition stage plays a role, with shorter durations observed prior to the full eruption of permanent dentition [33]. Therefore, age should be considered in the context of developmental variables, rather than as a standalone determinant. The statistical analysis of this review showed no significant effect of age when treatment duration was measured, until alignment, however, showed a statistically significant association when it was measured until the emergence of the cusp in the oral cavity. Overall, patient-related factors such as age and sex demonstrated variable and sometimes contradictory findings across studies, suggesting that their predictive value for traction duration remains uncertain.

Most studies do not assess the influence of sex on traction duration due to the predominance of female participants in the samples, which could introduce bias in the results; nevertheless, among the studies that conducted this analysis, most did not find significant differences between sexes, with the exception of two, which reported longer traction times in female patients [9,15,23,31,34,35,47]. According to Arriola–Guillén et al., this finding may be attributed to the inherent characteristics of the sample [9], whereas Potrubacz et al. suggest that the difference in skeletal maturation timing between sexes may explain the observed discrepancy [9,35].

The severity of impaction was the most frequently evaluated factor in the included studies, primarily assessed through position [5,7,31,34,35,37,39,40,41,42,47,50], location [5,9,15,31,34,42,49,50], vertical height [6,7,9,10,17,21,22,24,31,33,34,37,39,42,43,44,48,49,50,51], alpha angle [6,7,9,10,21,22,24,31,33,35,37,39,40,42,43,44,45,46,48,49,50] and sector [7,9,10,21,22,24,25,31,37,39,40,42,49,50]. While many studies found no correlation between position and traction duration, some reported that palatal impactions required longer treatment [37,39,41,42,50].

Han et al. reported shorter treatment times in cases of bilateral impactions [34]. However, other authors [9,42,49] suggest the opposite, associating bilateral impactions with greater clinical complexity and extended treatment durations. Additionally, some studies found no significant differences based on location [5,15,31]. It should be noted that several studies evaluated only the more severely impacted canine in bilateral cases, which may interfere with the reported results [5,22,24,25,31,49,50]. Among the evaluated predictors, radiographic parameters describing the severity and spatial position of the impacted canine—such as alpha angle, vertical height, sector, and mesiodistal position—showed the most consistent associations with traction duration across studies.

The angular measurements evaluated were essentially three: alpha angle [6,7,9,21,22,24,31,33,35,37,39,40,42,43,44,45,46,48,49,50], beta angle [9,22,49] and the angle with the occlusal plane [7,34,48,51]. Most studies demonstrated a positive correlation between the alpha angle and traction duration [7,10,21,24,31,37,39,40,42,43,44,46,48,49,50], while others found no statistically significant relationship [6,9,22,33,35,45]. Since the lateral incisor can influence the canine’s eruption path, a few studies considered the beta angle [9,22,49]. Schubert et al. and Arriola–Guillén et al. reported positive correlations [9,22], whereas Zuccati et al. reported an inverse, albeit weak relationship, in which each 4.55° decrease was associated with an additional visit [49]. Of the four studies that analyzed the angle with the occlusal plane and its relationship on traction duration [7,34,48,51], only Kim et al. found a correlation, which was negative, indicating that a greater angle was associated with shorter treatment duration [48].

Considering linear measurements, the vertical height was the second-most frequently studied factor, following the alpha angle. Some studies reported a positive correlation [7,10,21,22,24,31,33,34,37,42,44,48,49,50], while others reported no association [6,9,17,39,43,51]. Additionally, the meta-analysis conducted in this review confirmed that vertical height did not significantly influence traction duration. Other measurements, such as the eruption path length, appear to be more consistent predictors and should be considered in conjunction with vertical position [45,49]. The horizontal distance from the canine cusp tip to the midline also showed a negative correlation with traction duration, suggesting that canines positioned closer to the midline tend to require longer traction [7,39,44]. It is important to note that angular measurements generally demonstrate greater reliability and reproducibility compared to linear measurements, particularly when using two-dimensional imaging modalities such as panoramic radiographs. This is partly due to the fact that angular parameters are less affected by radiographic magnification and geometric distortion, which are inherent limitations of such imaging techniques. Furthermore, while linear measurements require precise calibration to ensure dimensional accuracy, a step that is not consistently implemented in clinical settings, angular measurements are independent of this process. Angular values are also less influenced by variations in head positioning during image acquisition, whereas minor deviations in patient orientation can significantly compromise the accuracy of linear measurements [52]. From a clinical perspective, angular measurements are not only more accessible using conventional imaging software but also demonstrate greater reliability and a stronger correlation with orthodontic traction duration. In the absence of three-dimensional imaging, they may offer a more practical and consistent method for assessing impaction severity and estimating treatment time. Given that panoramic radiographs are two-dimensional images with known limitations [46,51], particularly in the anterior maxilla, where focal trough narrowing often results in blurred or distorted apices and associated structures, linear measurements can be inaccurate or misleading [6]. In contrast, CBCT imaging provides orthogonal beam projection, minimizing distortion and eliminating magnification effects [46]. As a result, some studies have opted to assess canine position relative to adjacent teeth, rather than relying on potentially unreliable linear measurements [6,53].

The sector-based assessment is made in relation to the other teeth and most studies adopted the original Ericson and Kurol sector classification [7,9,10,21,22,24,25,37,39,40,42,49]. In three of these, no correlation was found between sector and traction duration [7,25,40]. In contrast, other studies reported shorter treatment durations when the canine was located closer to the premolars, likely due to a more favourable eruption path [9,10,21,22,24,37,39,42,49]. Modified classifications, such as those proposed by Baccetti et al. and the Bayesian analysis proposed by Nieri et al., have also showed that canines closer to the midline are associated with longer traction durations [31,50]. Similar findings have been reported in studies using mesiodistal position instead of sector-based classifications [6,34,43]. This increase in traction duration may be attributed to the retrograde movement that is often required before vertical extrusion force when the canine is near the central incisor [34]. Similarly, Jeong et al. reported that greater overlap of the maxillary incisors correlated with longer traction [33]. However, the other studies that evaluated the relationship between the cusp of the impacted canine and the root of the adjacent maxillary lateral incisors found no association [20,32,35].

Concerning the treatment-related factors, the surgical technique was the most reported. It was noted that open exposure technique was generally preferred for superficially impacted canines, and the closed technique was more commonly employed for deeper impactions [22,28,36]. Some studies have found no significant differences in traction duration between these approaches [6,19,25,42], whereas others observed shorter durations with the open exposure technique [36,47]. Bertl et al. attributed these results to the reduced need for surgical reinterventions [47]. Naoumova al. highlighted an earlier treatment completion when a biocompatible glass-ionomer cement was used [36]. Combining surgical exposure with osteotomy yielded faster results, although this effect was influenced by the severity of the canine position [44].

The influence of orthodontic mechanics on traction duration has been evaluated in a limited number of studies. Zogakis et al. and Verma et al. compared ballista springs with cantilevers and K9 springs, respectively, and found no differences in treatment duration [16,26]. Fekonja found that a double-wire system may reduce treatment time when compared to the traditional stainless-steel ligature on the principal arch [20]. The results of Migliorati et al. also suggested that miniscrews, whether used for direct or indirect anchorage, may provide an advantage in reducing traction duration [28,30].

This systematic review and meta-analysis presents several limitations: (1) heterogeneity in patient-related factors (e.g., age, sex, canine position and severity of displacement); (2) differences in treatment protocols and surgical techniques; (3) inconsistencies in the definitions of canine-related variables; and (4) varied definitions of traction duration, with some authors reporting orthodontic traction duration and others reporting total orthodontic treatment time, which complicates direct comparisons and may contribute to discrepancies between reported outcomes. When evaluating the results, it is necessary to take account that most non-RCTs were scored as some concerns are high to the domain of bias due to confounding. More randomized clinical trials with standardized protocols are needed to reduce confounding factors as missed appointments or repeated procedures, which are often not controlled in retrospective studies. Despite these limitations, this systematic review and meta-analysis provides valuable insights into factors influencing traction duration, aiding in the decision-making process for treatment planning and patient communication. A formal subgroup analysis by impaction position (palatal vs. buccal) was considered but not performed due to the pronounced asymmetry in the available data (approximately 1877 palatal vs. 434 buccal cases), which would have rendered such analysis underpowered. The predominance of retrospective designs (35/43 studies) introduces the potential for selection bias and precludes standardized data collection. In many included studies, important clinical confounders—including patient compliance, number of missed appointments, malocclusion severity, whether the case was extraction or non-extraction, and the individual orthodontist’s experience—were neither reported nor controlled for. These variables may exert effects on traction duration comparable to or exceeding those of the anatomical parameters studied. Future research should prioritize prospective collection of these variables.

Several important confounding factors—including arch space availability, patient compliance, missed appointments, malocclusion severity, and orthodontist experience—were not consistently reported or controlled for in the included studies. These factors may independently influence traction duration and their absence from the pooled analyses limits causal inference. Radiographic measurement variability represents a further source of heterogeneity: the majority of studies used orthopantomography (OPG; n = 18), which has known limitations for three-dimensional angular and positional assessments compared to CBCT (n = 7). Future prospective studies should standardize both imaging modality and reporting of confounders to enable more robust synthesis.

The sources of high heterogeneity are multiple and partially irreducible given the current evidence base: they include variability in patient demographics (age range, sex distribution), impaction severity and position, surgical approach, orthodontic mechanics, imaging modality, and—most fundamentally—the definition of traction duration itself. The stratification by definitional type (A, B, C) was designed to address the last of these, but within-stratum heterogeneity remained high, reflecting genuine clinical diversity across studies conducted in different institutional and cultural settings. Although high-risk studies could not be excluded in sensitivity analyses due to the limited remaining studies, the potential influence of risk of bias on the findings was qualitatively considered. Overall, the available evidence suggests that radiographic indicators of impaction severity show the most consistent associations with traction duration, whereas patient-related variables demonstrate more variable findings. Although these parameters cannot provide precise predictions of treatment duration, their systematic assessment may support more informed clinical decision-making and facilitate realistic treatment planning and patient communication.

5. Conclusions

Patient- and treatment-related factors may influence the duration of orthodontic traction for impacted maxillary canines, but the certainty of evidence is low to moderate due to high risk of bias and study heterogeneity. Severe impaction, characterized by a greater alpha angle, increased vertical height, and a sector closer to the central incisor, tends to be associated with longer treatment duration. Evidence for other variables, including patient age, beta angle, occlusal plane angulation, and surgical technique, remains limited and inconclusive. To improve clinical decision-making and provide more accurate treatment planning, further research using standardized diagnostic criteria and prospective study designs is warranted to clarify the role and predictive value of these factors.