隐形矫治治疗中与各种正畸牙齿移动相关的牙根外吸收的量化：一项回顾性临床研究 机翻

ARTICLE | Article in Press Scientific Reportshttps://doi.org/10.1038/s41598-026-77321-y Scientific Reports This Article in Press is shared early to give you faster access to new research. It is citable and carries a permanent DOI. The final edited version will replace it automatically. Quantifying external root resorption associated with various orthodontic tooth movements in clear aligner treatment: a retrospective clinical study Safa Kurnaz · Muhammed Hilmi Buyukcavus Received: 20 May 2026 / Accepted: 19 October 2026 © The Author(s) 2026 Abstract This study investigated associations between tooth movements and external root resorption (ERR) during clear aligner (CA) orthodontic treatment (OT). Forty-eight patients who underwent non-extraction OT using ClearCorrect aligners were included. Maxillary and mandibular incisors and canines were assessed, comprising 576 teeth. Pre- and post-OT digital models were superimposed to quantify intrusion, extrusion, crown tipping, crown torque, rotation, buccolingual translation, and mesiodistal translation. Root length, projected root surface area (PRSA), and ERR were measured on pre- and post-OT panoramic radiographs. Associations between tooth movements and root length, PRSA, and ERR were evaluated using correlation and multivariable linear regression analyses, with correction for multiple comparisons where appropriate. Significant movement-specific associations were observed in the maxillary lateral incisors and canines, with crown torque associated with root length and ERR changes and crown tipping associated with ERR in the lateral incisors, while extrusion was associated with PRSA changes in the canines. No significant movement–resorption associations were observed in the mandibular teeth. The magnitude of the observed resorptive changes was generally limited. Overall, the findings suggest that root responses during CA treatment may vary according to both the type of tooth movement and tooth group; however, the observed movement-specific associations should be interpreted cautiously. Keywords Clear aligner · Endodontics · External root resorption · Orthodontics · Tooth movement Abbreviations ERR External root resorption OT Orthodontic treatment CA Clear aligner ABO American Board of Orthodontics SD Standard deviation CEJ Cementoenamel junction CBCT Cone-beam computed tomography PRSA Projected root surface area FDR False discovery rate

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y Introduction Orthodontic treatment (OT) can lead to a common side effect known as external root resorption (ERR), resulting in irreversible loss of apical root tissue 1 . While OT often results in improved aesthetics and function, with clinically insignificant ERR in most cases, severe cases can compromise tooth structure and potentially lead to tooth loss 2,3 . Several factors can influence the risk of ERR during OT. These include genetics, age, sex, and systemic health conditions, as well as treatment-related factors, such as the severity of malocclusion, root morphology, and the duration and intensity of orthodontic forces. Treatment methods, including tooth extraction, appliance type, and movement magnitude, can also influence ERR 4,5 . Although ERR can occur during the OT of any tooth, the risk is generally higher for maxillary and mandibular incisors 6 . While various factors have been implicated in ERR, the precise mechanisms by which they contribute to this process are not fully understood 7 . Fixed appliance treatments have long been the standard for OT. However, clear aligners (CAs) have gained popularity due to improved comfort, aesthetics, and reduced treatment time 8,9 . Although evidence remains heterogeneous, recent systematic reviews and meta-analyses suggest that the incidence and severity of ERR are generally lower with CAs than with fixed appliances 10–14 . Factors such as intermittent force application, lighter forces, and shorter treatment times may contribute to this reduced risk 15,16 . OT applies multidirectional forces to achieve tooth movement, potentially disrupting the balance between bone resorption and formation at the root apex. Excessive or prolonged forces can exceed the adaptive capacity of periodontal tissues, leading to the progressive loss of root structure 17,18 . Both the magnitude and direction of orthodontic forces can influence the risk of ERR 19,20 . Intrusive forces are more likely to induce ERR than extrusive forces 21 . In addition, an animal study reported that tipping tooth movements were associated with greater ERR compared to bodily tooth movements 22 . Furthermore, human studies also show that increased root torque, tipping, and rotation are associated with higher ERR 23–25 . However, it is difficult to isolate the specific tooth movements that contribute to ERR. This is because orthodontic appliances typically produce a combination of complex movements, including extrusion, intrusion, translation, tipping, torque, and rotation 20 . Many clinicians perceive ERR as a potentially preventable complication during OT and often hold orthodontists responsible for its occurrence. However, detailed information regarding the overall relationships between endodontics and orthodontics in treatment decisions remains limited 26 . Therefore, further research on factors contributing to ERR is essential to improve treatment outcomes and minimize adverse effects. A thorough investigation could determine how the amount of ERR is influenced by the different types and magnitudes of orthodontic tooth movements and displacements 27 . Recent systematic reviews and meta-analyses have primarily focused on comparing the incidence and severity of ERR between CAs and fixed appliances, generally suggesting a lower risk of ERR with CA treatment 12–14 . However, these reviews have also emphasized the heterogeneity of the available evidence, methodological limitations, and the need for further high-quality clinical studies 28 . Importantly, previous studies have largely evaluated ERR as an overall treatment outcome rather than investigating the specific contribution of individual orthodontic tooth movements to ERR during CA treatment. To the best of our knowledge, no previous clinical study has comprehensively evaluated the association between different orthodontic tooth movements, including intrusion, extrusion, translation, crown tipping, crown torque, and rotation, and the magnitude of ERR across different tooth groups in patients treated exclusively with CAs. Therefore, the present study aimed to investigate the association between different orthodontic tooth movements and ERR and to quantify the magnitude of ERR associated with each movement type across different tooth groups following CA treatment, thereby providing clinically relevant evidence on movement-specific resorption patterns. The null hypothesis (H0) of this study posits the following: There is no difference in the amount of ERR in different tooth groups resulting from different orthodontic tooth movements.

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y Methods This retrospective clinical study was approved by the local university ethics committee (reference number: 2024/07-36). All participants provided informed consent. For participants under the age of 18, consent was obtained from their legal guardians. A sensitivity power analysis was performed for the multivariable linear regression analyses with seven predictors. With a sample size of 48, an α level of 0.05, and 80% power, the analysis indicated a minimum detectable overall effect size of f 2 = 0.35. The radiographs of patients treated at our clinic between July 2022 and December 2024 were retrospectively analyzed. Patients were selected based on predefined inclusion and exclusion criteria. The inclusion criteria were established to obtain a clinically homogeneous study population and to minimize potential confounding factors that could influence ERR. Accordingly, only patients with high-quality standardized panoramic radiographs suitable for accurate landmark identification, complete permanent dentition without missing teeth (excluding third molars), and who underwent OT with CAs were included. Patients were also required to have skeletal Class I malocclusion, moderate crowding, and treatment plans that did not involve tooth extraction. In addition, only patients without parafunctional habits (e.g., bruxism or clenching), treated with the same CA system, and with a similar planned degree of tooth movement were included 10,11,29–31 . The exclusion criteria were applied to minimize biological and treatment-related factors that could influence ERR. Patients were excluded if they had tooth or root anomalies, including unerupted teeth, regardless of the affected tooth. Patients with a history of dental trauma, previous OT, missing records, or tooth extractions were also excluded. Additional exclusion criteria included systemic diseases, craniofacial anomalies, temporomandibular disorders, poor oral health (caries or periodontal disease), root-filled teeth, open apices, and pre-existing root resorption 10,11,29–31 . To further minimize variability related to case complexity, the American Board of Orthodontics (ABO) discrepancy index was used to assess the difficulty of each case. Patients with high complexity scores were excluded to maintain a more homogeneous study population 30,32 . Treatment protocol After applying inclusion and exclusion criteria to 235 patients, 48 patients (26 females, 22 males) treated with CAs were included. The mean age of the participants was 19.22 ± 2.08 years. Each patient’s maxillary and mandibular central, lateral, and canine teeth were evaluated individually. This resulted in an analysis of 96 teeth per tooth group, totaling 576 teeth. The treatment group consisted of patients who had undergone OT using ClearCorrect CAs (ClearCorrect ® , ClearCorrect LLC, Round Rock, TX, USA). A virtual treatment plan was created using ClearCorrect’s Clear- Pilot™ software (ClearCorrect’s Treatment Planning Tool, version 5) to guide the treatment process. The plan outlined a sequence of treatment steps, including interproximal reduction, attachment placement, and the use of intermaxillary elastics. Patients were instructed to change their aligners every 15 days and wear them for approximately 22 h daily. Measurement of tooth movement All digital model measurements were performed using a standardized workflow to ensure measurement consistency and reproducibility. The same reference landmarks, regions of interest, registration procedure, and measurement tools were used for all pre- and post-treatment models. Digital impressions were captured using a 3Shape TRIOS 3 (3Shape TRIOS A/S, Copenhagen, Denmark) intraoral scanner and uploaded to the ClearPilot platform for treatment design. STL files of the resulting models were saved using 3D Slicer 5.0. Model superimposition was performed according to the palatal rugae-based method described by Garib et al. 33 , using stable palatal reference areas for registration. Landmarks were placed on the incisive papilla’s posterior

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y border, the medial edges of the second and third palatal rugae, and 10 mm distally from the third rugae’s medial edge. Regions of interest were defined around these landmarks. Regions of interest for the incisive papilla and third rugae projections had a 5-vertex radius; second and third rugae regions of interest had a 30 radius, ensuring regions of interest remained distant from the teeth. Using Slicer’s “CMF registration” tool, the post-treatment maxilla was superimposed onto the pre-treatment maxilla via region of interest matching. Mandibular models were then aligned in occlusion with the superimposed maxilla. The maxillary superimposition matrix was applied to the mandibular models, aligning them with the maxilla. Finally, predefined landmarks were placed on all models to quantify the magnitude of orthodontic tooth movement achieved during treatment (Fig. 1). Landmarks were placed on maxillary and mandibular models to measure: (1) horizontal/vertical linear displacements (canine buccal cusp tips and incisor mesial incisal edges), (2) mesiodistal rotations (most mesial/distal points from an occlusal view), and (3) buccolingual tipping (incisor incisal center and deepest cervical point). Using 3D Slicer’s Fiducial Registration Wizard, x, y, and z coordinates for linear displacement landmarks were recorded for pre/post-treatment and initial/final predicted models. Coordinate differences quantified the achieved and predicted changes. Q3DC measured the angles between mesial/distal landmarks (mesiodistal rotations) and incisal/cervical landmarks (buccolingual tipping) for each model pair. For each of the 12 teeth evaluated (maxillary centrals, laterals and canines, and mandibular centrals, laterals and canines), the total intrusion, extrusion, buccolingual translation, mesiodistal translation, crown tip, crown torque, and rotation amounts that occurred in the relevant teeth from the beginning to the end of the OT (including refinement aligners) were taken from the system in degrees and/or millimeters. Measurement methodology for external root resorption To minimize measurement bias, all radiographic measurements were performed using a standardized measurement protocol under identical imaging and measurement conditions. The extent of ERR was assessed for all teeth using digital panoramic radiographs obtained before and immediately after OT. All radiographs were taken in natural head position to ensure consistency. This was achieved by instructing patients to look straight ahead into the unit’s built-in mirror, allowing self-alignment. The Castellini X-ray unit (Castellini X Radius Compact, Imola, Italy) was used to acquire the images and to assist with head stabilization through its integrated positioning system. Crown and root length measurements were performed using the measurement software of the Castellini X-ray unit according to a previously validated methodology described in earlier studies 11,29,31,34 . Measurements were obtained from standardized pre- and post-treatment panoramic radiographs using identical anatomical reference points for all teeth. The reference points and procedures used for linear and PRSA measurements are illustrated in Fig. 2. Fig. 1 Superimposition of pre- and post-treatment models using the palatal rugae method.

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y The crown and root length measurements were performed in several steps. First, the cementoenamel junction (CEJ) was identified by drawing a straight line between the mesial and distal CEJ points. The crown length was then measured on both the initial and final radiographs. This measurement was defined as the longest distance from the incisal edge to the CEJ. A similar method was applied for root length measurements in all teeth, where the distance from the CEJ to the root apex was recorded 11,29,31,34 . ERR was calculated as follows: ERR (mm) = (pre-OT root length − post-OT root length) × (pre-OT crown length/post-OT crown length). The crown-length ratio was used as a proportional correction factor to compensate for differences in radiographic magnification between the pre- and post-OT panoramic images 11,29,31,34 . Accordingly, ERR was expressed in millimeters. To complement linear measurements, projected root surface area (PRSA) was analyzed from panoramic radiographs (Fig. 2). Before PRSA measurements, each panoramic image was calibrated in SketchAndCalc by defining a known linear distance on the radiographic image and entering its corresponding length in millimeters, thereby establishing the pixel-to-millimeter scale. Root surface measurements were then performed using SketchAnd- Calc software (Axiom Welldone, https://www.sketchandcalc.com/). The entire root surface was carefully traced, starting at the CEJ and extending to the radiographic apex, following both the mesial and distal outlines of the root. To ensure measurement precision, digital points were manually placed at one-pixel intervals along the traced root boundary. An average of 25 (± 5) points per root was used, depending on the root length and curvature. The software then automatically computed the enclosed area in square millimeters, representing the PRSA 11,31 . The same calibration and tracing procedure was applied to the pre- and post-OT radiographs. Statistical analysis Data normality was assessed using the Shapiro–Wilk test. As the data were normally distributed, parametric statistical analyses were performed. Measurement reliability was assessed before the main analyses. All measurements were performed by a single calibrated investigator. Prior to the main study, reliability and reproducibility were evaluated using panoramic radiographs from 16 randomly selected patients. The same investigator repeated the measurements after a two-week interval, and a second investigator independently repeated the same process. Fig. 2 Reference points and measurement procedures for crown length, root length, and PRSA on panoramic radiographs.

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y The intraclass correlation coefficients for intra- and inter-examiner agreement were 0.953 (95% CI 0.925–0.981) and 0.929 (95% CI 0.902–0.956), respectively, indicating excellent measurement reproducibility. Descriptive statistics were expressed as mean ± standard deviation (SD), frequencies (n), and percentages (%). Pearson correlation analyses were performed to evaluate the associations between the seven orthodontic toothmovement variables (intrusion, extrusion, buccolingual translation, mesiodistal translation, crown tip, crown torque, and rotation) and changes in root length, PRSA, and ERR according to tooth position. To account for multiple testing, correlation p values were adjusted using the Benjamini–Hochberg false discovery rate (FDR) procedure, with FDR-adjusted p values < 0.05 considered statistically significant. Follow-up multivariable linear regression analyses were performed for tooth-group/outcome combinations with at least one association remaining significant after FDR correction. All seven tooth-movement variables were entered simultaneously, with adjustment for side and patient-clustered robust standard errors to account for within-patient dependence. Each regression model included 96 teeth from 48 patients, and results are reported as unstandardized coefficients (B), patient-clustered robust standard errors, standardized coefficients (β), 95% confidence intervals, t statistics, p values, R 2 , adjusted R 2 , and the joint F statistic for the seven tooth-movement predictors. These follow-up regression analyses were considered exploratory. All statistical analyses were performed using IBM SPSS Statistics for Windows, version 26 (IBM Corp., Armonk, NY, USA). Results Table 1 presents descriptive statistics of the study participants, including age, gender, number of aligners, treatment duration, and treatment complexity scores based on ABO criteria. The extent of tooth movement in the patients’ anterior teeth resulting from the CA treatment is shown in Table 2. Figure 3 provides a graphical overview of the distribution of root resorption parameters across the different orthodontic tooth movements. Changes in root length, PRSA, and ERR following OT are presented in Table 3. The results of the correlation analyses between root resorption parameters and the extent of tooth movements are presented in Table 4 for maxillary teeth and Table 5 for mandibular teeth. After Benjamini–Hochberg FDR correction, statistically significant correlations remained only in the maxillary teeth. The results of the multivariable linear regression analyses are presented in Table 6. For the maxillary lateral incisors, crown torque was negatively correlated with root length change (r = − 0.504, BH-p = 0.016) and positively correlated with ERR (r = 0.527, BH-p = 0.010), while crown tip was positively correlated with ERR (r = 0.555, BH-p = 0.006) after FDR correction. In the multivariable regression analyses, each 1-degree increase in crown torque was associated with an approximately 0.07-mm greater reduction in root length (B = − 0.070, 95% CI −0.136 to − 0.003, p = 0.041) and approximately 0.09-mm greater ERR (B = 0.093, 95% CI 0.025 to 0.160, p = 0.008). Rotation was also associated with root length change (B = 0.032, 95% CI 0.006 to 0.058, p = 0.018) and ERR (B = − 0.030, 95% CI −0.060 to − 0.001, p = 0.044) after adjustment for the other tooth-movement variables and side. Characteristics Number (n) GenderFemale26 Male22 CharacteristicsMean ± SD Chronological age (years)19.22 ± 2.08 ABO discrepancy index12.06 ± 1.91 Number of total aligners32 ± 12 Number of refinements1.81 ± 0.75 Treatment duration (years)1.31 ± 0.47 Table 1 Descriptive statistics of the study participants. ABO, American board of orthodontics; n, Number; SD, Standard deviation.

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y For the maxillary canines, extrusion was negatively correlated with PRSA change (r = − 0.552, BH-p = 0.006) after FDR correction. In the multivariable regression analysis, each 1-mm increase in extrusion was associated with an approximately 6.29-mm 2 greater reduction in PRSA (B = − 6.292, 95% CI −9.385 to − 3.198, p < 0.001). Discussion Despite the increasing use of CAs, their impact on ERR remains understudied 7 . Previous studies have consistently shown that ERR is less prevalent in patients treated with CAs than in those treated with fixed appliances 10,11,30,35 . Recent systematic reviews and umbrella reviews have reached similar conclusions while also highlighting the heterogeneity of the available evidence, methodological limitations, and the need for cautious interpretation 13,14 . However, these studies primarily compared the overall incidence or severity of ERR between appliance systems rather than evaluating the influence of specific orthodontic tooth movements on ERR in different tooth groups. Table 2 Descriptive statistics of orthodontic tooth movements in anterior teeth. Tooth movementIntrusion (mean ± SD, Min–Max, mm) Extrusion (mean ± SD, Min–Max, mm) Translation (buccolingual) (mean ± SD, Min– Max, mm) Translation (mesiodistal) (mean ± SD, Min– Max, mm) Crown tip (mesiodistal) (mean ± SD, Min–Max, °) Crown torque (buccolingual) (mean ± SD, Min–Max, °) Rotation (mean ± SD, Min–Max, °) Tooth number Maxilla110.20 ± 0.34 (0.0–1.3) 0.19 ± 0.39 (0.0–1.6) 0.80 ± 0.65 (0.0–2.1) 0.55 ± 0.47 (0.0–1.8) 1.85 ± 1.78 (0.0–6.2) 4.36 ± 3.58 (0.0–13.2) 9.15 ± 7.88 (0.0–30.1) 120.28 ± 0.49 (0.0–1.6) 0.37 ± 0.52 (0.0–1.9) 0.82 ± 0.59 (0.0–2.3) 0.64 ± 0.58 (0.0–2.1) 2.95 ± 4.14 (0.0–10.7) 3.34 ± 3.11 (0.0–10.1) 8.29 ± 9.59 (0.0–34.4) 130.29 ± 0.45 (0.0–1.4) 0.13 ± 0.27 (0.0–1.1) 0.70 ± 0.70 (0.0–2.5) 0.54 ± 0.74 (0.0–2.9) 2.23 ± 3.21 (0.0–11.3) 3.69 ± 3.91 (0.0–17.1) 6.90 ± 8.13 (0.0–30.2) 210.21 ± 0.31 (0.0–0.9) 0.25 ± 0.38 (0.0–1.4) 0.90 ± 0.50 (0.2–2.2) 0.60 ± 0.64 (0.0–2.7) 2.91 ± 3.32 (0.0–11.1) 4.38 ± 5.18 (0.0–19.1) 7.12 ± 4.64 (0.0–16.1) 220.21 ± 0.38 (0.0–1.4) 0.42 ± 0.52 (0.0–1.5) 0.60 ± 0.56 (0.0–2.6) 0.42 ± 0.44 (0.0–1.6) 1.65 ± 2.69 (0.0–12.2) 3.89 ± 3.65 (0.0–10.3) 9.68 ± 8.93 (0.0–34.5) 230.14 ± 0.24 (0.0–0.9) 0.22 ± 0.36 (0.0–1.3) 0.62 ± 0.55 (0.0–1.8) 0.57 ± 0.64 (0.0–3.1) 1.26 ± 2.10 (0.0–8.1) 2.09 ± 2.47 (0.0–8.3) 9.21 ± 6.58 (0.0–25.1) Mandible310.55 ± 0.64 (0.0–1.7) 0.07 ± 0.14 (0.0–0.6) 0.99 ± 0.64 (0.0–2.4) 0.68 ± 0.54 (0.0–1.8) 2.52 ± 2.14 (0.0–8.1) 4.64 ± 5.02 (0.0–18.1) 9.45 ± 7.77 (0.0–28.1) 320.64 ± 0.60 (0.0–1.8) 0.03 ± 0.08 (0.0–0.3) 0.92 ± 0.74 (0.0–2.6) 0.88 ± 0.76 (0.0–2.8) 3.85 ± 3.27 (0.0–9.1) 2.69 ± 3.24 (0.0–12.1) 8.88 ± 8.64 (0.0–34.5) 330.49 ± 0.49 (0.0–2.2) 0.05 ± 0.16 (0.0–0.6) 0.74 ± 0.73 (0.0–2.9) 0.81 ± 0.67 (0.0–2.3) 2.46 ± 3.25 (0.0–10.3) 2.70 ± 2.32 (0.0–7.5) 9.07 ± 6.88 (0.0–26.3) 410.59 ± 0.65 (0.0–2.6) 0.07 ± 0.18 (0.0–0.7) 0.89 ± 0.67 (0.0–2.3) 0.87 ± 0.83 (0.0–3.3) 2.52 ± 2.53 (0.0–8.1) 4.70 ± 5.50 (0.0–20.1) 7.45 ± 6.14 (0.0–27.2) 420.68 ± 0.74 (0.0–3.2) 0.08 ± 0.21 (0.0–0.7) 1.03 ± 0.85 (0.0–2.9) 0.72 ± 0.63 (0.0–2.4) 2.16 ± 2.57 (0.0–9.2) 3.97 ± 4.30 (0.0–13.4) 6.77 ± 5.64 (0.0–17.2) 430.49 ± 0.44 (0.0–1.7) 0.04 ± 0.13 (0.0–0.5) 0.82 ± 0.85 (0.0–2.9) 0.62 ± 0.47 (0.0–1.7) 1.98 ± 2.96 (0.0–8.5) 2.35 ± 2.89 (0.0–9.1) 8.69 ± 5.15 (0.0–16.5) SD, standard deviation; Min–Max, minimum–maximum; mm, millimeter; °, degree. Fig. 3 Graphical representation of point distribution for root resorption parameters across various tooth movements.

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y Consequently, this study aimed to investigate the associations between specific orthodontic tooth movements and root resorption parameters across different tooth groups and to quantify the resorptive changes associated with these movements in patients undergoing CA treatment. The present findings demonstrated movement- and toothspecific associations with root resorption parameters, predominantly in the maxillary anterior teeth. Significant associations were observed particularly for crown torque in the maxillary lateral incisors and extrusion in the maxillary canines, with related patterns also observed in the exploratory multivariable analyses. The magnitude, duration, and continuity of orthodontic forces are critical determinants of ERR 36,37 . Heavier and continuous forces correlate with an increased prevalence and severity of ERR 4,38 . Conversely, intermittent forces may mitigate resorption by facilitating cementogenic repair 37,39 . The magnitude and direction of forces exerted by CAs differ from those generated by brackets and archwires. CAs are believed to deliver lighter, intermittent forces, potentially contributing to a reduced incidence of ERR compared to fixed appliances 40,41 . This interpretation is supported by recent reviews suggesting that the intermittent force pattern of CAs may allow periods of periodontal and cemental repair, although the clinical evidence remains heterogeneous 14,28 . Few studies have assessed the extent of ERR associated with orthodontic tooth movement, and substantial methodological disparities limit direct comparisons. This study is the first to explore this phenomenon specifically in the context of CA treatment. While Phillips 42 observed no correlation between ERR and angular or sagittal apical movements of the maxillary central incisor, DeShields 43 identified significant associations between these parameters. Mirabella and Årtun 44 posited that both anterior and posterior root movements can contribute to ERR. Parker and Harris 20 consistently observed predictive relationships between ERR and vertical apical movement, vertical incisal movement, and incisor proclination changes. Currell et al. 45 reported an association between intrusive movements and ERR, while Tieu et al. 46 demonstrated an association with anteroposterior apical root displacement and retraction mechanics. Moreover, the distribution and localization of ERR appear to vary according to the type and direction of orthodontic tooth movement. Areas exposed to compressive forces have been reported to be more susceptible to root resorption than those subjected to tensile forces 38 . For example, buccal tipping movements were primarily associated with resorption on the buccocervical and linguoapical root surfaces 47,48 . Buccal root torque resulted in resorption predominantly on the bucco-apical and palato-cervical regions 23 . Rotational movements around the long axis of the tooth demonstrated a predilection for resorption at the interfaces between the buccal and distal surfaces, as well as between the lingual and mesial surfaces 24 . Distal root tipping showed increased resorption on distal aspects in the apical and middle thirds, with additional resorption on mesial aspects in the cervical third 25 . Extrusion movements were Table 3 Changes in root length, projected root surface area, and external root resorption in anterior teeth. Root lengthProjected root surface areaExternal root resorption (mean ± SD, mm) Pre- (mean ± SD, mm) Post- (mean ± SD, mm) Difference (mean ± SD, mm) Pre- (mean ± SD, mm 2 ) Post- (mean ± SD, mm 2 ) Difference (mean ± SD, mm 2 ) Tooth number Maxilla1113.47 ± 2.4512.88 ± 2.26− 0.59 ± 1.3661.02 ± 18.2049.07 ± 14.46− 11.95 ± 9.500.92 ± 0.69 1212.51 ± 2.1011.51 ± 2.11− 1.00 ± 0.9442.24 ± 11.3733.63 ± 8.97− 8.61 ± 6.821.10 ± 0.99 1313.14 ± 2.0011.80 ± 2.00− 1.34 ± 1.1244.47 ± 14.2238.69 ± 13.09− 5.77 ± 4.761.24 ± 1.16 2113.53 ± 2.4212.54 ± 2.44− 0.99 ± 0.7857.29 ± 19.8845.99 ± 11.70− 11.31 ± 12.931.05 ± 0.83 2212.63 ± 1.7711.55 ± 2.14− 1.08 ± 0.9339.96 ± 11.9534.07 ± 10.64− 5.89 ± 6.721.10 ± 0.98 2313.30 ± 1.6312.11 ± 1.36− 1.19 ± 0.9244.29 ± 8.8337.56 ± 7.55− 6.73 ± 4.931.27 ± 1.00 Mandible3111.77 ± 1.8210.59 ± 1.85− 1.18 ± 1.4032.30 ± 11.3125.97 ± 8.82− 6.33 ± 6.601.27 ± 1.57 3212.41 ± 1.9611.42 ± 2.00− 0.99 ± 1.5735.12 ± 10.8329.88 ± 8.48− 5.24 ± 6.261.24 ± 1.94 3313.42 ± 2.1812.73 ± 1.96− 0.69 ± 0.9244.09 ± 12.1339.35 ± 10.61− 4.74 ± 6.560.72 ± 0.99 4111.70 ± 1.7810.50 ± 1.84− 1.20 ± 1.1632.32 ± 9.8125.75 ± 7.24− 6.57 ± 5.801.30 ± 1.41 4212.39 ± 2.5211.07 ± 1.92− 1.32 ± 1.1635.38 ± 12.4628.83 ± 8.83− 6.55 ± 6.711.49 ± 1.41 4313.79 ± 2.0912.72 ± 2.15− 1.07 ± 0.9247.71 ± 12.4840.79 ± 9.62− 6.92 ± 7.391.11 ± 0.94 mm, millimeter, mm 2 , square millimeter; SD, standard deviation.

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y ∆Root length ∆Projected root sur - face area External root resorption ∆Root length ∆Projected root surface area External root resorption Tooth number Tooth movement Tooth number Tooth movement Maxillary central teeth 11 Intrusion r − 0.091 0.051 0.008 21 Intrusion r 0.025 0.119 − 0.050 p 0.537 0.731 0.956 p 0.867 0.419 0.735 Extrusion r 0.051 − 0.381 − 0.326 Extrusion r 0.060 − 0.084 − 0.064 p 0.733 0.008(BH− p = 0.131) 0.024(BH− p = 0.269) p 0.683 0.571 0.665 Translation BL r − 0.149 − 0.135 0.199 Translation BL r 0.095 0.267 − 0.092 p 0.314 0.361 0.176 p 0.521 0.067 0.534 Translation MD r − 0.261 0.014 0.284 Translation MD r − 0.030 − 0.208 0.059 p 0.073 0.924 0.050 p 0.842 0.156 0.691 Crown Tip MD r 0.054 − 0.423 0.254 Crown Tip MD r − 0.224 − 0.245 0.209 p 0.716 0.003(BH− p = 0.084) 0.081 p 0.126 0.094 0.153 Crown Torque BL r − 0.059 − 0.351 0.234 Crown Torque BL r − 0.225 − 0.353 0.214 p 0.690 0.014(BH− p = 0.201) 0.109 p 0.124 0.014(BH− p = 0.201) 0.144 Rotation r 0.161 − 0.071 − 0.059 Rotation r − 0.080 − 0.273 0.067 p 0.274 0.631 0.692 p 0.589 0.060 0.653 Maxillary lateral teeth 12 Intrusion r − 0.202 0.141 0.136 22 Intrusion r − 0.155 0.277 0.205 p 0.168 0.340 0.355 p 0.293 0.057 0.162 Extrusion r 0.123 − 0.161 − 0.033 Extrusion r 0.207 − 0.429 − 0.292 p 0.404 0.275 0.825 p 0.157 0.002 0.044 Translation BL r − 0.115 − 0.100 0.090 Translation BL r 0.300 0.190 − 0.274 p 0.436 0.501 0.543 p 0.038 0.196 0.060 Translation MD r − 0.180 0.167 0.180 Translation MD r 0.020 0.008 − 0.001 p 0.222 0.257 0.221 p 0.894 0.956 0.996 Crown Tip MD r 0.088 − 0.035 − 0.087 Crown Tip MD r − 0.456 − 0.176 0.555 p 0.551 0.811 0.558 p 0.001 0.231 < 0.001(BH− p = 0.006) Crown Torque BL r − 0.504 − 0.284 0.527 Crown Torque BL r − 0.036 0.075 0.127 p < 0.001(BH− p = 0.016) 0.051 < 0.001(BH− p = 0.010) p 0.807 0.611 0.391 Rotation r 0.215 − 0.277 − 0.191 Rotation r 0.040 0.109 0.030 p 0.143 0.057 0.193 p 0.790 0.459 0.842 Table 4 Correlation analysis between resorption parameters and tooth movement amounts for maxillary teeth.

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y ∆Root length ∆Projected root sur - face area External root resorption ∆Root length ∆Projected root surface area External root resorption Maxillary canine teeth 13 Intrusion r 0.155 0.090 − 0.244 23 Intrusion r − 0.029 − 0.126 0.019 p 0.294 0.544 0.095 p 0.847 0.395 0.896 Extrusion r − 0.212 − 0.552 0.161 Extrusion r − 0.134 − 0.283 0.128 p 0.148 < 0.001(BH− p = 0.006) 0.273 p 0.362 0.052 0.388 Translation BL r − 0.089 − 0.379 0.123 Translation BL r − 0.015 − 0.027 0.008 p 0.548 0.008(BH− p = 0.131) 0.404 p 0.919 0.855 0.957 Translation MD r 0.146 0.108 − 0.177 Translation MD r − 0.164 − 0.153 0.165 p 0.321 0.464 0.229 p 0.265 0.298 0.261 Crown tip MD r 0.063 − 0.094 − 0.074 Crown tip MD r − 0.049 0.083 0.102 p 0.669 0.526 0.616 p 0.739 0.575 0.489 Crown torque BL r − 0.020 − 0.195 0.025 Crown torque BL r − 0.299 0.154 0.320 p 0.894 0.185 0.867 p 0.039(BH− p = 0.298) 0.296 0.027(BH− p = 0.269) Rotation r 0.220 0.014 − 0.200 Rotation r − 0.156 − 0.185 0.161 p 0.132 0.923 0.173 p 0.291 0.208 0.275 Δ, Difference; BL, Buccolingual; MD, Mesiodistal; r, Pearson correlation coefficient; p, unadjusted p value; BH-p, Benjamini–Hochberg false discovery rate−adjusted p value. BH-p values are reported for correlations with unadjusted p < 0.05. Table 4 (continued)

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y ∆Root length ∆Projected root surface area External root resorption ∆Root length ∆Projected root surface area External root resorption Tooth number Tooth movement Tooth number Tooth movement Man - dibular Central Teeth 31 Intrusion r − 0.293 0.101 0.301 41 Intrusion r − 0.138 − 0.055 0.229 p 0.043(BH− p = 0.300) 0.496 0.038(BH− p = 0.298) p 0.350 0.712 0.117 Extrusion r − 0.059 − 0.368 0.042 Extrusion r − 0.044 0.085 0.016 p 0.690 0.010(BH− p = 0.157) 0.775 p 0.765 0.564 0.915 Translation BL r − 0.401 − 0.334 0.395 Translation BL r − 0.213 − 0.432 0.315 p 0.005(BH− p = 0.112) 0.020(BH− p = 0.254) 0.005(BH− p = 0.113) p 0.146 0.002(BH− p = 0.084) 0.029(BH− p = 0.274) Translation MD r − 0.071 − 0.009 0.002 Translation MD r 0.292 0.081 − 0.289 p 0.631 0.954 0.990 p 0.044(BH− p = 0.300) 0.585 0.046(BH− p = 0.308) Crown Tip MD r − 0.303 − 0.222 0.230 Crown Tip MD r 0.124 0.104 − 0.129 p 0.037(BH− p = 0.298) 0.129 0.116 p 0.399 0.484 0.383 Crown Torque BL r − 0.004 − 0.039 0.002 Crown Torque BL r 0.103 − 0.146 − 0.016 p 0.979 0.790 0.987 p 0.488 0.324 0.911 Rotation r − 0.143 − 0.209 0.185 Rotation r 0.165 − 0.262 − 0.149 p 0.332 0.153 0.208 p 0.263 0.072 0.312 Man - dibular lateral teeth 32 Intrusion r − 0.272 − 0.118 0.280 42 Intrusion r 0.192 0.139 − 0.154 p 0.062 0.423 0.054 p 0.192 0.347 0.296 Extrusion r 0.175 0.248 − 0.143 Extrusion r − 0.108 − 0.145 0.103 p 0.235 0.090 0.332 p 0.465 0.324 0.487 Translation BL r 0.073 − 0.214 0.062 Translation BL r − 0.090 − 0.037 0.031 p 0.621 0.145 0.675 p 0.542 0.800 0.836 Translation MD r 0.160 0.090 − 0.102 Translation MD r − 0.175 − 0.326 0.072 p 0.276 0.544 0.490 p 0.234 0.024(BH- p = 0.269) 0.625 Crown Tip MD r − 0.091 − 0.125 0.212 Crown Tip MD r − 0.054 − 0.386 0.046 p 0.537 0.396 0.148 p 0.716 0.007 (BH− p = 0.130) 0.759 Crown Torque BL r 0.265 0.160 − 0.140 Crown Torque BL r − 0.152 − 0.156 0.072 p 0.069 0.278 0.343 p 0.303 0.290 0.626 Rotation r 0.080 0.071 − 0.046 Rotation r 0.139 0.017 − 0.098 p 0.590 0.632 0.758 p 0.348 0.907 0.506 Table 5 Correlation analysis between resorption parameters and tooth movement amounts for mandibular teeth.

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y ∆Root length ∆Projected root surface area External root resorption ∆Root length ∆Projected root surface area External root resorption Tooth number Tooth movement Tooth number Tooth movement Man - dibular canine teeth 33 Intrusion r 0.339 0.139 − 0.321 43 Intrusion r 0.038 0.161 − 0.032 p 0.019(BH− p = 0.247) 0.347 0.026(BH− p = 0.269) p 0.798 0.275 0.828 Extrusion r − 0.176 0.064 0.158 Extrusion r − 0.002 0.078 − 0.045 p 0.232 0.668 0.282 p 0.990 0.597 0.761 Translation BL r 0.304 0.302 − 0.296 Translation BL r 0.062 − 0.144 − 0.046 p 0.036(BH− p = 0.298) 0.037(BH− p = 0.298) 0.041(BH− p = 0.300) p 0.675 0.329 0.757 Translation MD r 0.323 − 0.011 − 0.318 Translation MD r − 0.053 − 0.063 0.066 p 0.025(BH− p = 0.269) 0.942 0.028(BH− p = 0.269) p 0.718 0.668 0.657 Crown Tip MD r 0.098 0.144 − 0.113 Crown Tip MD r 0.199 − 0.061 − 0.249 p 0.509 0.330 0.445 p 0.175 0.678 0.088 Crown Torque BL r 0.004 0.094 − 0.012 Crown Torque BL r − 0.037 − 0.400 0.042 p 0.980 0.524 0.937 p 0.805 0.005(BH− p = 0.112) 0.778 Rotation r 0.016 − 0.102 − 0.013 Rotation r 0.089 − 0.420 − 0.098 p 0.916 0.491 0.930 p 0.548 0.003(BH− p = 0.084) 0.509 Δ, Difference; BL, Buccolingual; MD, Mesiodistal; r, Pearson correlation coefficient; p, unadjusted p value; BH-p, Benjamini–Hochberg false discovery rate-adjusted p value. BH-p values are reported for correlations with unadjusted p < 0.05. Table 5 (continued)

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y primarily associated with increased resorption on the distal root surfaces 49 . Regarding intrusion movements, the findings were not entirely consistent. One study reported increased resorption on the mesial and distal root surfaces 50 , particularly in the apical thirds. Conversely, another study observed greater resorption on the buccocervical root surfaces and in the apical thirds of the roots 51 . In the present study, movement-specific associations with root resorption parameters were observed predominantly in the maxillary anterior teeth. Despite these findings, the magnitude of the observed resorptive changes was generally limited. Therefore, the observed associations should be interpreted in the context of the relatively small magnitude of these changes and should not necessarily be considered indicative of clinically relevant root damage. This may partly reflect the intentional inclusion of non-extraction cases with moderate crowding to maintain relatively standardized treatment conditions. While these criteria reduced clinical heterogeneity, they may also limit the generalizability of the findings to patients requiring more extensive or complex orthodontic movements. In the maxillary lateral incisors, crown torque emerged as the most consistent movement-specific factor, showing associations with both root length change and ERR. In the multivariable analyses, each 1-degree increase in crown torque was associated with an approximately 0.07-mm greater reduction in root length and 0.09-mm greater ERR. Crown tipping was also positively correlated with ERR; however, this association was attenuated in the multivariable model, suggesting that its relationship with ERR may partly overlap with the effects of Table 6 Multivariable linear regression analyses of the associations between orthodontic tooth movements and root resorption parameters. Tooth group/movementBStandard errorβ p t95% CI lowerUpper Maxillary lateral teeth—Δ root length (mm) Intrusion− 0.1150.315− 0.0530.717− 0.364− 0.7470.518 Extrusion0.2450.1690.1330.1541.448− 0.0950.585 Translation BL0.2970.1550.1820.0621.915− 0.0150.609 Translation MD0.0500.1710.0270.7730.290− 0.2950.394 Crown Tip MD− 0.0490.029− 0.1850.094− 1.711− 0.1080.009 Crown Torque BL− 0.0700.033− 0.2490.041*− 2.105− 0.136− 0.003 Rotation0.0320.0130.3130.018*2.4570.0060.058 Model SummaryR 2 = 0.171Adjusted R 2 = 0.095F(7,47) = 5.625 p < 0.001 Maxillary lateral teeth—external root resorption (mm) Intrusion− 0.0430.287− 0.0190.881− 0.150− 0.6200.534 Extrusion− 0.2760.173− 0.1430.117− 1.596− 0.6240.072 Translation BL− 0.3110.155− 0.1810.051− 2.003− 0.6230.001 Translation MD− 0.0110.175− 0.0060.950− 0.063− 0.3640.342 Crown Tip MD0.0600.0310.2140.0571.951− 0.0020.122 Crown Torque BL0.0930.0340.3150.008*2.7610.0250.160 Rotation− 0.0300.015− 0.2800.044*− 2.072− 0.060− 0.001 Model summaryR 2 = 0.190Adjusted R 2 = 0.115F(7,47) = 8.105 p < 0.001 Maxillary canine teeth—Δ projected root surface area (mm 2 ) Intrusion− 2.0201.602− 0.1510.214− 1.260− 5.2431.204 Extrusion− 6.2921.538− 0.415< 0.001*− 4.091− 9.385− 3.198 Translation BL− 1.0521.058− 0.1350.325− 0.994− 3.1811.077 Translation MD0.7020.8520.0990.4140.824− 1.0122.417 Crown Tip MD− 0.0650.104− 0.0360.535− 0.625− 0.2740.144 Crown Torque BL0.0460.1300.0320.7240.356− 0.2150.308 Rotation− 0.0200.082− 0.0310.804− 0.250− 0.1850.144 Model summaryR 2 = 0.198Adjusted R 2 = 0.124F(7,47) = 3.096 p = 0.009 B, Unstandardized regression coefficient; SE, patient-clustered robust standard error; β, standardized regression coefficient; BL, buccolingual; MD, mesiodistal; R 2 , coefficient of determination; t, t statistic. Each regression model included 96 teeth from 48 patients. All models were adjusted for side. Patient-clustered robust standard errors were used to account for dependence between bilateral teeth from the same patient. The F statistic represents the joint test of the seven tooth-movement predictors after adjustment for side. *p < 0.05.

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y concomitant tooth movements. In contrast, rotation remained associated with both root length change and ERR in the multivariable analyses after adjustment for the other tooth-movement variables and side; however, these findings should be interpreted cautiously. In cases of moderate crowding, maxillary lateral incisors may be positioned palatally because of space limitations, and their buccal repositioning during OT may require substantial root and crown torque movements 52 . Torque movements are associated with increased stress concentration at the root surface due to their force–moment characteristics, which may contribute to the observed association with ERR. However, the association between torque and root length change should also be interpreted in light of the limitations of panoramic radiography. Buccolingual changes in root orientation may alter the two-dimensional projection of the root and thereby contribute to apparent changes in measured root length. Accordingly, the torque-related findings may reflect both biological responses to orthodontic loading and projection-related effects inherent to two-dimensional imaging. In the multivariable regression analysis, greater extrusion was associated with a decrease in PRSA in the maxillary canines, with an estimated reduction of approximately 6.29 mm² per 1-mm increase in extrusion. ERR is influenced by factors such as the surface area subjected to force and the magnitude of the applied force 6,53 . Although extrusion generally produces a less compressive periodontal environment than intrusion, the association observed in the present study suggests that extrusive movement may still be relevant to root resorption under specific biomechanical conditions. This finding may also reflect the relatively greater extrusion requirements of maxillary canines, potentially related to their frequent supraocclusion. This often results from early loss of primary canines, leading to space loss and subsequent impaction or supraeruption of permanent canines 54 . Taken together, these findings suggest that the observed association may reflect not only the characteristics of the extrusion movement itself but also the specific biomechanical demands and initial positional characteristics of maxillary canines. Orthodontically induced ERR has no definitive treatment; management primarily involves early radiographic detection and minimizing further progression by adjusting force levels or shortening treatment duration when necessary 55 . In the present study, all radiographic evaluations were performed immediately after the completion of OT. Thus, the observed ERR reflects an early-phase status. As demonstrated by Asscherickx et al. 56 , root defects caused by orthodontic mini-implant insertion exhibited substantial repair through cementum deposition. This suggests that some resorptive changes may have the potential to repair biologically, depending on individual patient conditions. Therefore, post-treatment resorptive findings should be interpreted with caution. Endodontic intervention should be guided by a thorough clinical assessment that considers patient symptoms, functional concerns, and serial radiographic evaluations, rather than relying solely on post-treatment images. In cases of suspected advanced resorption, collaboration between orthodontists and endodontists can help support appropriate treatment decisions and improve long-term outcomes. From a clinical perspective, in cases requiring extensive tooth movement—particularly in teeth considered more susceptible to ERR—clinicians may consider increasing the number of aligners to reduce the magnitude of movement per aligner. This approach may help minimize the risk of ERR by reducing excessive or abrupt forces. However, increasing the number of aligners may also prolong overall treatment duration, which itself has been associated with increased root resorption. Therefore, clinicians should carefully balance force magnitude and treatment duration when planning aligner protocols in patients at higher risk of ERR. In such susceptible teeth, regular radiographic monitoring throughout OT may help detect early signs of ERR and allow timely modification of force application. Beyond these clinical implications, the present findings also contribute to the understanding that the biological response to orthodontic treatment may vary according to both tooth type and the specific biomechanics of the planned tooth movement. Several limitations should be considered when interpreting the findings of the present study. One important limitation is the inherent difficulty of isolating the individual contributions of specific tooth movements to ERR, because multiple movements occur simultaneously during routine clinical OT. Nevertheless, the present study provides clinically relevant insights under conditions that closely reflect routine orthodontic practice. Assessing the isolated effects of specific tooth movements on resorption typically requires finite element models or in

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y vitro simulations. While previous animal studies and finite element analyses have explored the resorptive effects of different tooth movements, the present study complements this evidence by examining movement-specific associations within the clinical context of CA treatment, a widely utilized orthodontic procedure. Furthermore, the multivariable analyses showed movement-specific associations with root resorption parameters in the maxillary lateral incisors and canines, providing evidence that may inform future investigations of the biomechanical determinants of ERR during CA treatment. Additionally, as the mandible does not provide a validated stable anatomical reference for superimposition in non-CBCT datasets, mandibular models were oriented relative to the superimposed maxilla, consistent with previously published digital model analyses. Although strict inclusion criteria minimized substantial occlusal or skeletal changes, minor effects of occlusal settling on mandibular measurements cannot be excluded. In addition, all patients in this study were treated with the ClearCorrect system using a single aligner material. As material properties may influence force transmission, outcomes may vary across different systems. Another limitation is the use of panoramic radiographs, although ERR is a three-dimensional process. While cone-beam computed tomography (CBCT) offers more accurate volumetric measurements of these changes 7 , its higher radiation dose limits routine use 57 . Conversely, two-dimensional imaging methods such as panoramic radiographs may overestimate ERR, as shown by Gandhi et al. 58 , who reported a 0.2 mm higher mean resorption value with 2D techniques compared to CBCT. Although periapical radiographs and CBCT are more sensitive, they are not routinely used during OT 59 . In this study, panoramic radiographs were used for both pre- and post- OT evaluations, reflecting standard orthodontic practice and supporting retrospective analysis. Prior ERR studies have similarly utilized panoramic radiographs 11,29,31,60 . Stramotas et al. 61 reported that linear measurements on serial panoramic radiographs may be sufficiently accurate when the angulation of the occlusal plane is kept similar between serial images and the occlusal plane is not tilted by more than approximately 10°. To minimize measurement errors, all radiographs were obtained by a trained assistant using the same panoramic unit with standardized positioning. Nevertheless, minor differences in head and occlusal-plane positioning between serial examinations cannot be completely excluded and may have contributed to variation in linear measurements. Although panoramic imaging is prone to dimensional distortion 62 , the consistent imaging protocol and equipment use throughout the study were intended to minimize measurement variability and improve the comparability of pre- and post-OT measurements. The proportionally greater reductions in PRSA compared with root length should be interpreted in light of the different dimensional and anatomical characteristics of these measurements. Root length is a one-dimensional measure primarily reflecting apicocoronal shortening, whereas PRSA represents the two-dimensional projected area enclosed by the entire root contour; therefore, equivalent proportional changes are not expected. Moreover, changes predominantly affecting the apical region may be more apparent in root length, whereas alterations involving the mesial and distal root contours may produce a greater change in PRSA with comparatively limited apicocoronal shortening. Accordingly, the greater proportional reductions in PRSA do not necessarily indicate a discrepancy with the corresponding changes in root length but rather reflect the complementary aspects of root morphology captured by these two measurements. However, the inherent limitations of two-dimensional imaging must be acknowledged. In particular, buccolingual torque movements may influence the radiographic projection of the root, potentially leading to apparent reductions in measured root length. Therefore, torque-related associations involving linear root measurements should be interpreted with caution when inferring true morphological root resorption. Similarly, PRSA measurements may also be influenced by changes in tooth orientation, including torque and axial rotation, because the projected area of a three-dimensional structure on a two-dimensional image may vary with its orientation. Therefore, PRSA should not be interpreted as a direct three-dimensional measure of morphological root loss. Unlike previous studies, this investigation quantified ERR not only at the root apex but also along the mesial and distal surfaces, using a digital area calculation program to assess changes in projected root surface area 11,31 . Moreover, the analysis was limited to incisors and canines—teeth most susceptible to ERR—although future studies involving other tooth types are needed to generalize the findings.

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y This study has several key strengths. First, the study applied strict inclusion and exclusion criteria to enhance the consistency and comparability of the study population. Second, the analysis incorporated both linear and projected root surface measurements, allowing root changes to be evaluated using complementary two-dimensional metrics. Third, this study evaluated a broad range of orthodontic tooth movements across different anterior tooth groups and examined their associations with multiple root resorption parameters within the clinical context of CA treatment. This comprehensive approach provides clinically relevant exploratory data for understanding movement-specific patterns of root change during CA therapy. Conclusions Within the limitations of the present study, the associations between specific orthodontic tooth movements and ERR-related changes during CA treatment varied according to both movement type and tooth group. Crown torque in the maxillary lateral incisors and extrusion in the maxillary canines showed the most consistent movement-specific associations with root resorption parameters. These findings should be interpreted with caution and warrant confirmation in future prospective studies using three-dimensional imaging and larger cohorts. Author contributions S.K.: Conceptualization, methodology, supervision, data acquisition and interpretation, writingoriginal draft preparation. M.H.B.: Conceptualization, methodology, data acquisition and interpretation, analysis, critically revised the manuscript. All authors gave final approval and agreed to be accountable for all aspects of the work. Funding The authors received no financial support for the research, authorship, and/or publication of this article. Data availability The datasets for the current study are available from the corresponding author on reasonable request. Declarations Ethics approval and consent to participate This study was performed in line with the principles of the Declaration of Helsinki. Informed consent was obtained from all the participants including both patients and the legal guardians of children involved in the present study. Approval was granted by the Clinical Research Ethics Committee of Kutahya Health Sciences University, Kutahya, Türkiye (no: 2024/07-36). Competing interests The authors declare no competing interests. Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit h t t p : / / c r e a t i v e c o m m o n s . o r g / l i c e n s e s / b y - n c - n d / 4 . 0 / . References 1. Topkara, A., Karaman, A. I. & Kau, C. H. Apical root resorption caused by orthodontic forces: A brief review and a longterm observation. Eur. J. Dent. 6, 445–453 (2012). 2. Harris, E. F., Kineret, S. E. & Tolley, E. A. A heritable component for external apical root resorption in patients treated orthodontically. Am. J. Orthod. Dentofac. Orthop. 111, 301–309 (1997). 3. Pinheiro, L. H. M. et al. Genetic variation involved in the risk to external apical root resorption in orthodontic patients: A systematic review. Clin. Oral Investig. 25, 5613–5627 (2021).

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y 4. Weltman, B., Vig, K. W., Fields, H. W., Shanker, S. & Kaizar, E. E. Root resorption associated with orthodontic tooth movement: a systematic review. Am. J. Orthod. Dentofac. Orthop. 137, 462–476 (2010). 5. Årtun, J., Van’t Hullenaar, R., Doppel, D. & Kuijpers-Jagtman, A. M. Identification of orthodontic patients at risk of severe apical root resorption. Am. J. Orthod. Dentofac. Orthop. 135, 448–455 (2009). 6. Sameshima, G. T. & Sinclair, P. M. Predicting and preventing root resorption: Part I. Diagnostic factors. Am. J. Orthod. Dentofac. Orthop. 119, 505–510 (2001). 7. Butsabul, P., Kanpittaya, P. & Nantanee, R. Root resorption in clear aligner treatment detected by CBCT: a systematic review and meta-analysis. Int. Dent. J. 74, 1326–1336 (2024). 8. Fujiyama, K., Honjo, T., Suzuki, M., Matsuoka, S. & Deguchi, T. Analysis of pain level in cases treated with Invisalign aligner: comparison with fixed edgewise appliance therapy. Prog. Orthod. 15, 1–7 (2014). 9. Buschang, P. H., Shaw, S. G., Ross, M., Crosby, D. & Campbell, P. M. Comparative time efficiency of aligner therapy and conventional edgewise braces. Angle Orthod. 84, 391–396 (2014). 10. Li, Y. et al. Prevalence and severity of apical root resorption during orthodontic treatment with clear aligners and fixed appliances: a cone beam computed tomography study. Prog. Orthod. 21, 1–8 (2020). 11. Kurnaz, S. & Buyukcavus, M. H. Panoramic evaluation of external root resorption in mandibular molars during orthodontic treatment: a comparison between root-filled and vital teeth treated with fixed appliances or clear aligners. BMC Oral Health. 24, 1152 (2024). 12. Singh, S., Jain, R. K. & Balasubramaniam, A. CoComparative assessment of external apical rootresorption between subjects treated with clear aligners and fixed orthodontic appliances: Asystematic review and meta-analysis.. J. Dent. Res. Dent. Clin. Dent. Prospects. 18, 85–94 (2024). 13. Darvizeh, A. et al. External apical root resorption following orthodontic treatment with clearaligners versus fixed appliances: A systematic review and meta-analysis. Dent. J. 13, 580 (2025). 14. Selvaraj, M., Nivethitha, B. & Madhan, B. Orthodontically induced external apical rootresorption with clear aligners compared to fixed appliance treatment: An umbrella review. J.Oral Biol. Craniofac. Res.. 15, 938–947 (2025). 15. Kumasako-Haga, T., Konoo, T., Yamaguchi, K. & Hayashi, H. Effect of 8-hour intermittent orthodontic force on osteoclasts and root resorption. Am. J. Orthod. Dentofac. Orthop. 135, 278e1–278e9 (2009). 16. Elhaddaoui, R., Qoraich, H. S., Bahije, L. & Zaoui, F. Orthodontic aligners and root resorption: A systematic review. Int. Orthod. 15, 1–12 (2017). 17. Brezniak, N. & Wasserstein, A. Orthodontically induced inflammatory root resorption. Part I: the basic science aspects. Angle Orthod. 72, 175–179 (2002). 18. Feller, L., Khammissa, R. A., Thomadakis, G., Fourie, J. & Lemmer, J. Apical external root resorption and repair in orthodontic tooth movement: biological events. Biomed. Res. Int. 2016, 4864195 (2016). 19. Segal, G., Schiffman, P. & Tuncay, O. Meta analysis of the treatment-related factors of external apical root resorption. Orthod. Craniofac. Res. 7, 71–78 (2004). 20. Parker, R. J. & Harris, E. F. Directions of orthodontic tooth movements associated with external apical root resorption of the maxillary central incisor. Am. J. Orthod. Dentofac. Orthop. 114, 677–683 (1998). 21. Han, G., Huang, S., Von den Hoff, J. W., Zeng, X. & Kuijpers-Jagtman, A. M. Root resorption after orthodontic intrusion and extrusion: an intraindividual study. Angle Orthod. 75, 912–918 (2005). 22. Nakano, T. et al. Effects of different types of tooth movement and force magnitudes on the amount of tooth movement and root resorption in rats. Angle Orthod. 84, 1079–1085 (2014). 23. Bartley, N. et al. Physical properties of root cementum: Part 17. Root resorption after the application of 2.5 and 15 of buccal root torque for 4 weeks: A microcomputed tomography study. Am. J. Orthod. Dentofac. Orthop. 139, e353–e360 (2011). 24. Wu, A. T. et al. Physical properties of root cementum: Part 18. The extent of root resorption after the application of light and heavy controlled rotational orthodontic forces for 4 weeks: A microcomputed tomography study. Am. J. Orthod. Dentofac. Orthop. 139, e495–e503 (2011). 25. King, A. D. et al. Physical properties of root cementum: Part 21. Extent of root resorption after the application of 2.5 and 15 tips for 4 weeks: A microcomputed tomography study. Am. J. Orthod. Dentofac. Orthop. 140, e299–e305 (2011). 26. Hamilton, R. & Gutmann, J. Endodontic-orthodontic relationships: a review of integrated treatment planning challenges. Int. Endod. J. 32, 343–360 (1999). 27. Flatten, J., Gedrange, T., Bourauel, C., Keilig, L. & Konermann, A. The role of bone and root resorption on the biomechanical behavior of mandibular anterior teeth subjected to orthodontic forces: A finite element approach. Biomedicines 12, 1959 (2024). 28. Zhang, M., Zhang, P., Koh, J.-T., Oh, M.-H. & Cho, J.-H. Evaluation of aligners and rootresorption: An overview of systematic reviews. J. Clin. Med. 13, 1950 (2024). 29. Lee, Y. J. & Lee, T. Y. External root resorption during orthodontic treatment in root-filled teeth and contralateral teeth with vital pulp: A clinical study of contributing factors. Am. J. Orthod. Dentofac. Orthop. 149, 84–91 (2016). 30. Almagrami, I. M. et al. A quantitative three-dimensional comparative study of alveolar bone changes and apical root resorption between clear aligners and fixed orthodontic appliances. Prog. Orthod. 24, 6 (2023).

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y 31. Kurnaz, S. & Buyukcavus, M. H. External root resorption in root-filled and vital teeth after extraction and non-extraction orthodontic treatments: A split-mouth retrospective study. Acta Odontol. Scand. 79, 282–288 (2021). 32. Cangialosi, T. J. et al. The ABO discrepancy index: a measure of case complexity. Am. J. Orthod. Dentofac. Orthop. 125, 270–278 (2004). 33. Garib, D. et al. Superimposition of maxillary digital models using the palatal rugae: does ageing affect the reliability? Orthod. Craniofac. Res. 22, 183–193 (2019). 34. Linge, L. & Linge, B. O. Patient characteristics and treatment variables associated with apical root resorption during orthodontic treatment. Am. J. Orthod. Dentofac. Orthop. 99, 35–43 (1991). 35. Papageorgiou, S. N., Koletsi, D., Iliadi, A., Peltomaki, T. & Eliades, T. Treatment outcome with orthodontic aligners and fixed appliances: A systematic review with meta-analyses. Eur. J. Orthod. 42, 331–343 (2020). 36. Liou, E. J. & Chang, P. M. Apical root resorption in orthodontic patients with en-masse maxillary anterior retraction and intrusion with miniscrews. Am. J. Orthod. Dentofac. Orthop. 137, 207–212 (2010). 37. Acar, A., Canyürek, Ü., Kocaaga, M. & Erverdi, N. Continuous vs. discontinuous force application and root resorption. Angle Orthod. 69, 159–163 (1999). 38. Roscoe, M. G., Meira, J. B. & Cattaneo, P. M. Association of orthodontic force system and root resorption: A systematic review. Am. J. Orthod. Dentofac. Orthop. 147, 610–626 (2015). 39. Ballard, D. J., Jones, A. S., Petocz, P. & Darendeliler, M. A. Physical properties of root cementum: Part 11. Continuous vs intermittent controlled orthodontic forces on root resorption. A microcomputed-tomography study. Am. J. Orthod. Dentofac. Orthop. 136, 8e1–8e8 (2009). 40. Yi, J., Xiao, J., Li, Y., Li, X. & Zhao, Z. External apical root resorption in non-extraction cases after clear aligner therapy or fixed orthodontic treatment. J. Dent. Sci. 13, 48–53 (2018). 41. Guan, W., Lu, Y., Yu-feng, Z., San-lian, L. & Ji-wei, Z. A retrospective study on incisor root resorption in patients treated with bracketless invisible appliance and straight wire appliance. Shanghai Kou Qiang Yi Xue. 26, 121–124 (2017). 42. Phillips, J. R. Apical root resorption under orthodontic therapy. Angle Orthod. 25, 1–22 (1955). 43. DeShields, R. W. A study of root resorption in treated Class II, Division I malocclusions. Angle Orthod. 39, 231–245 (1969). 44. Mirabella, A. D. & Årtun, J. Risk factors for apical root resorption of maxillary anterior teeth in adult orthodontic patients. Am. J. Orthod. Dentofac. Orthop. 108, 48–55 (1995). 45. Currell, S. D., Liaw, A., Grant, P. D. B., Esterman, A. & Nimmo, A. Orthodontic mechanotherapies and their influence on external root resorption: A systematic review. Am. J. Orthod. Dentofac. Orthop. 155, 313–329 (2019). 46. Tieu, L. D., Saltaji, H., Normando, D. & Flores-Mir, C. Radiologically determined orthodontically induced external apical root resorption in incisors after non-surgical orthodontic treatment of class II division 1 malocclusion: A systematic review. Prog. Orthod. 15, 1–13 (2014). 47. Chan, E. & Darendeliler, M. A. Physical properties of root cementum: Part 5. Volumetric analysis of root resorption craters after application of light and heavy orthodontic forces. Am. J. Orthod. Dentofac. Orthop. 127, 186–195 (2005). 48. Barbagallo, L. J., Jones, A. S., Petocz, P. & Darendeliler, M. A. Physical properties of root cementum: Part 10. Comparison of the effects of invisible removable thermoplastic appliances with light and heavy orthodontic forces on premolar cementum. A microcomputed-tomography study. Am. J. Orthod. Dentofac. Orthop. 133, 218–227 (2008). 49. Montenegro, V. C. J., Jones, A., Petocz, P., Gonzales, C. & Darendeliler, M. A. Physical properties of root cementum: Part 22. Root resorption after the application of light and heavy extrusive orthodontic forces: a microcomputed tomography study. Am. J. Orthod. Dentofac. Orthop. 141, e1–e9 (2012). 50. Harris, D. A., Jones, A. S. & Darendeliler, M. A. Physical properties of root cementum: Part 8. Volumetric analysis of root resorption craters after application of controlled intrusive light and heavy orthodontic forces: a microcomputed tomography scan study. Am. J. Orthod. Dentofac. Orthop. 130, 639–647 (2006). 51. Harry, M. & Sims, M. Root resorption in bicuspid intrusion: A scanning electron microscope study. Angle Orthod. 52, 235–258 (1982). 52. Nanda, R. S. & Tosun, Y. S. Biomechanics in Orthodontics. Principles and Practice (Quintessence Publishing Co., 2010). 53. Sameshima, G. T. & Sinclair, P. M. Predicting and preventing root resorption: Part II. Treatment factors. Am. J. Orthod. Dentofac. Orthop. 119, 511–515 (2001). 54. Proffit, W. R., Fields, H. W. & Sarver, D. M. Contemporary Orthodontics, 4th edn (Mosby Elsevier, 2007). 55. Kim, S., Hwang, S. J. & Seo, M. S. Effect of orthodontic treatment on the periapical radiolucency of endodontically treated teeth: A CBCT analysis. BMC Oral Health. 23, 289 (2023). 56. Asscherickx, K., Vannet, B. V., Wehrbein, H. & Sabzevar, M. M. Root repair after injury from mini-screw. Clin. Oral Implants Res. 16, 575–578 (2005). 57. Patel, S., Dawood, A., Wilson, R., Horner, K. & Mannocci, F. The detection and management of root resorption lesions using intraoral radiography and cone beam computed tomography—an in vivo investigation. Int. Endod.J. 42, 831–838 (2009).

Article in Press Scientific Reports https://doi.org/10.1038/s41598-026-77321-y 58. Gandhi, V. et al. Comparison of external apical root resorption with clear aligners and pre-adjusted edgewise appliances in non-extraction cases: A systematic review and meta-analysis. Eur. J. Orthod. 43, 15–24 (2021). 59. Yi, J. et al. Cone-beam computed tomography versus periapical radiograph for diagnosing external root resorption: A systematic review and meta-analysis. Angle Orthod. 87, 328–337 (2017). 60. Llamas-Carreras, J. et al. Study of external root resorption during orthodontic treatment in root-filled teeth compared with their contralateral teeth with vital pulps. Int. Endod. J. 43, 654–662 (2010). 61. Stramotas, S., Geenty, J. P., Petocz, P. & Darendeliler, M. A. Accuracy of linear and angular measurements on panoramic radiographs taken at various positions in vitro. Eur. J. Orthod. 24, 43–52 (2002). 62. Lien, L. C. & Soh, G. Accuracy of the orthopantomogram in assessment of tooth length in orthodontic patients. Singap. Dent. J. 23, 68–71 (2000). Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Authors and Affiliations Safa Kurnaz 1  · Muhammed Hilmi Buyukcavus 2 Safa Kurnaz safa.kurnaz@ksbu.edu.tr 1 Department of Endodontics, Faculty of Dentistry, Kutahya Health Sciences University, 43270 Kutahya, Turkey 2 Department of Orthodontics, Faculty of Dentistry, Antalya Bilim University, Antalya, Turkey