Orthodontically induced external apical root resorption with clear aligners compared to fixed appliance treatment: An umbrella review

Abstract

Introduction

Orthodontically induced external apical root resorption (OIEARR) is an inevitable complication of orthodontic treatment. This study aimed to provide the existing highest level of evidence on OIEARR in patients undergoing orthodontic treatment with clear aligners compared to fixed orthodontics.

Materials and methods

A comprehensive electronic database search was conducted using predefined search terms without any restrictions on language and year of publication. Systematic reviews with or without meta-analysis comparing the OIEARR in fixed and clear aligner groups were only considered. The overlap of primary studies was assessed using the GROOVE tool, and two reviewers graded the quality assessment of included reviews independently using AMSTAR 2. A random effects meta-analysis was carried out for homogenous CBCT data.

Results

Out of 1181 articles, eight reviews were eligible; only four considered meta-analyses. A high overlap of 31 primary studies was reported, with 22 included in meta-analyses overlap. AMSTAR 2 tool outlined that the quality of the reviews was critically low in four, with two each being high and low quality. Meta-analysis between the aligner and fixed appliance groups revealed a significant mean difference of 0.62 mm in maxillary central incisors and 0.65 mm in maxillary lateral incisors. The heterogeneity of included primary studies ranged from moderate to high.

Conclusion

The incidence and severity of OIEARR are lower in clear aligners than in fixed appliance groups. The results need to be cautiously inferred due to the low to moderate quality of the evidence. Therefore, there is a future need for high-quality RCTs, considering the associated risk factors.

Highlights

• •OIEARR is an unpredictable and inevitable complication of orthodontic treatment.
• •Clear aligners are emerging alternatives to fixed appliances.
• •Evidence of OIEARR in clear aligners is inconclusive.
• •Umbrella review aims to provide the highest level of evidence on OIEARR.
• •Incidence and severity are less in clear aligners than in fixed appliances.

1. Introduction

Orthodontically induced external apical root resorption (OIEARR) is a significant and unpredictable complication of orthodontic treatment, resulting in irreversible root structure loss.¹ The root resorption prevalence in orthodontic patients ranges from 20 % to 100 %.² The severity of OIEARR resorption is linked to various patient-related factors like age, sex, genetic predisposition, habits, systemic diseases, type of malocclusion, trauma or endodontic treatment, root shape, and morphology. Significant treatment-related factors include the type, magnitude, duration of force, type of tooth movement, and extractions during treatment.^3,4

Histologically, during orthodontic treatment, excessive capillary pressure leads to sterile hyalinized necrotic regions, resulting in irreversible loss of root structure.⁵ Many studies have assessed the OIEARR in fixed orthodontic patients using subjective grading systems,⁶ histologically and radiographically,⁷ where 3D imaging is more reliable and accurate.³ From the evidence, more than one-third of patients undergoing fixed appliance treatment (FAT) present with 3 mm of root resorption, and maxillary incisors are more prone.⁵

Clear aligner therapy (CAT) is emerging as a promising addition to the orthodontist's treatment planning, offering a viable alternative to FAT. CAT's appeal among adults is due to its comfort and discreetness compared to FAT.⁸ However, it is important to note that CAT patients are also at risk of OIEARR, with some debate on the severity compared to FAT.⁹ Evidence suggests that FAT plays a role in OIEARR, with heavy orthodontic forces inducing greater resorption than lighter forces. Variations in bonding techniques and mechanical effects on teeth distinguish CAT and FAT, influencing expectations for root resorption. CAT uses resin polymers that are coupled to the morphology of teeth sequentially and work with intermittent forces that allow the root cementum to heal, potentially causing lower resorption.^10,11

Although studies have explored OIEARR in CAT, there is still debate about whether CAT offers any clear advantage over FAT in preventing root resorption, as the findings from different studies often conflict.10, 11, 12, 13, 14, 15 Root resorption during orthodontic treatment has been investigated through various study designs, including systematic reviews. Although systematic reviews (SRs) have also explored the relationship between OIEARR and various patient- or treatment-related factors, their findings remain inconclusive.^8,16, 17, 18 An important step forward is conducting an umbrella review to systematically evaluate root resorption associated with clear aligner therapy (CAT) versus fixed appliance therapy (FAT). By synthesizing and comparing findings from existing systematic reviews and meta-analyses, this study aims to offer the highest level of evidence on orthodontically induced external apical root resorption (OIEARR), supporting evidence-based clinical decisions.

2. Material and methods

2.1. Objective

This umbrella review aims to provide the highest level of evidence from the overview of current systematic review and meta-analysis on OIEARR in clear aligner therapy compared to fixed appliance treatment.

2.2. Protocol and registration

The study was designed to follow the Preferred Reporting Items for Reporting Overviews of Reviews (PRIOR) of healthcare interventions¹⁹ and the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA)²⁰ guidelines. Following an initial search, the protocol was registered apriori in the International Prospective Register of Systematic Reviews (PROSPERO) database; Registration no. CRD42024520453.

2.3. Eligibility criteria

The eligibility of the studies was determined according to Population(P); patients who underwent orthodontic treatment, Intervention(I); clear aligner therapy, Comparison(C); fixed appliance therapy, Outcome(O); external apical root resorption, Study design(S); systematic review with or without meta-analysis and recent Cochrane review based on OIEARR in CAT. Only comparative studies between CAT and FAT involving human participants with clearly described methodology were included. Case reports, case series, expert opinions, animal research and studies involving craniofacial syndromes and patients with cleft lip and palate were excluded.

2.4. Information sources and search strategy

One reviewer (M.S.) conducted the literature search across various databases on December 20, 2024 without any language and time restrictions. The search used the keywords; ‘root resorption’, ‘orthodontic treatment’, ‘clear aligner therapy’, and ‘fixed appliance therapy’ in PubMed, Embase, Web of Science, Scopus, EBSCO, and Cochrane Database (Supplementary Table 1.). The grey literature searches were done in OpenGrey, ClinicalTrials.Gov and the top 250 results of Google Scholar. In addition, the reference list of included articles was hand-searched to identify any other relevant articles.

2.5. Study selection

Articles from multiple databases were exported into the Rayyan QCRI software (http://rayyan.qcri.org/). Two reviewers (B.N. and M.S.) independently removed duplicates and screened the titles and abstracts of the identified studies. The same reviewers conducted a full-text review of articles that met the eligibility criteria. Any differences in opinion were resolved with the help of a third senior reviewer (B.M.) through consensus. This umbrella review included only systematic reviews with or without meta-analysis.

2.6. Data extraction

The following details were extracted from each study: study characteristics (authors, year of publication, country of origin and study design), journal source, studies involved in the review and meta-analysis, participants' characteristics, and quantitative and qualitative assessment of root resorption. Two reviewers (M.S. and B.N.) independently performed the data extraction.

2.7. Primary study overlap

Overlap of primary studies among systematic reviews and meta-analyses (SR and MA) is one of the main methodological challenges when conducting overviews. If not appropriately addressed, overlapping primary studies may significantly influence qualitative analyses or statistical weight and yield misleading results. Moreover, overlapping may represent the existence of duplicated efforts. Overlapped and non-overlapped primary studies were included in the SR and MA, and the corrected area and overall corrected covered area (CCA) were assessed using the Graphical Representation of Overlap for OVErviews (GROOVE) tool.²¹

2.8. Risk of bias and reporting bias assessment

Using a measurement tool to assess systematic reviews (AMSTAR-2), the quality of the included systematic reviews (SRs), including those with or without meta-analysis, was evaluated.²² The tool consists of 16 items within seven critical domains, evaluating the overall confidence in the review results and categorizing them as high, moderate, low, or critically low. Two reviewers (M.S. and B.N.) independently conducted the assessment. Any disagreements were resolved through discussion or by seeking the input of a third reviewer (M.B.). The evidence was subsequently rated on a scale from high to critically low.

2.9. Data synthesis result and summary measures

Data pooling was scheduled to quantitatively evaluate the impact of aligner treatment on root resorption, particularly in cases where clinical homogeneity was observed. Various study characteristics, like interventions, the methodologies applied for detecting and measuring OIEARR, and the study design, were considered to evaluate the homogeneity of the included reviews. The statistical analysis of the quantitative assessment was carried out with Review Manager 2020 (Review Manager 5 (RevMan 5) [Computer program]. Version 5.4.1 Copenhagen: The Cochrane Collaboration, 2020.). The meta-analysis compared the mean root resorption in mm in the CAT Vs FAT group. The random-effects model was used to calculate the mean difference (MD) with a 95 % confidence interval (CI). The Chi-Squared (χ 2) test assessed the heterogeneity of the studies, and a two-tailed Z test was used to examine the significance of the aggregated data, with the significance level set at p < 0.05.

3. Results

3.1. Study selection

The initial search of all databases yielded 1181 eligible studies. After removing duplicates, the title and abstract of 375 articles were screened, and 19 articles were selected for full-text review. Out of which, eleven articles were ineligible and excluded (Supplementary Table 2.). Those not comparing the OIEARR of CAT with FAT groups, narrative reviews and commentaries were excluded. The PRISMA flow diagram illustrating the literature screening and inclusion process is presented in Fig. 1. Finally, eight articles16, 17, 18^,23, 24, 25, 26, 27 that met the inclusion criteria were selected for comprehensive data collection, and only four^17,18,24,27 of these quantitatively analyzed the OIEARR between the CAT and FAT groups.

Fig. 1.

PRISMA flowchart depicting the screening and inclusion of the articles.

3.2. Study characteristics

The data synthesis of the included studies is represented in Table 1. These studies were published from 2016 to July 2024 in International Orthodontics,¹⁶ The Journal of Contemporary Dental Practice,²³ Orthodontic and Craniofacial Research,²⁴ Journal of Medical Sciences,²⁶ European Journal of Orthodontics,¹⁷ Applied Sciences,²⁵ Journal of Dental Research, Dental Clinics and Dental Prospects¹⁸ and Annals of Dental Specialty.²⁷ Two articles originated from Lithuania,^26,27 and others from the rest of the world. Five^{17,18,24,25,27} were registered apriori with PROSPERO, and only six^17,18,23, 24, 25^,27 had followed the PRISMA guidelines. The search limit of the included SR and MAs was July 2023, with most limiting it to English language^16,23,25, 26, 27 in the search restrictions. The quality assessment of the risk of bias tool was performed in all^17,18,23, 24, 25^,27 except in two^16,26 SR and MA.

Table 1.

Summary of data from included systematic reviews and meta-analysis.

Author/Year/Country	Number of primary studies	Primary studies in Meta-analysis	Guidelines/Protocol Registration	Quality assessment	Results and Heterogeneity among Studies	Results	Conclusion
Elhaddaoui et al.16 (2016) Morocco	3	NA	NR	NR	NA	-Two NRCTs and one RCT were included −54 % of teeth showed no signs of RR -The heavy force group presented nine times higher resorption, six times higher in the aligner group, and five times higher in the light force group.	The incidence and severity of root resorption are lower in thermoplastic aligners than in fixed appliances.
Aldeeri et al.23 (2018) Saudi Arabia	2	NA	PRISMA	Cochrane Collaboration Tool	NA	-One RCT (Low-RoB) and one retrospective cohort study (High-risk RoB). -RR assessed using CBCT was only included. -Aligner group had less RR and a statistically significant difference in heavy-force FAT	CAT is non-inferior to light-force and superior to heavy-force FAT OEARR risk.
Fang et al.24 (2019) China	11	3	PRISMA, Cochrane Handbook for Systematic Reviews of Interventions/PROSPERO	ROBINS-I	-Maxillary CI (MD = −0.61, 95 % Ci = −0.95, −0.27; p = 0.0004,χ2 = 0.06; I2 = 53 %), -Maxillary LI (MD = −0.61, 95 % Ci = −0.79, −0.44; p < 0.00001,χ2 = 0.16; I2 = 37 %), -Mandibular CI (MD = −0.53, 95 % Ci = −0.89, −0.18; p = 0.003,χ2 = 0.10; I2 = 62 %), and -Mandibular LI (MD = −1.06, 95 % Ci = −1.26, −0.86; p < 0.00001,χ2 = 0.69; I2 = 0 %)	-Four cohort studies and one case-control study compared CAT and FAT. -Six studies compared pre- and post-treatment RR in CAT. -Moderate to serious RoB among studies. -Meta-analysis of incisors showed a significant difference of decreased RR in CAT (MD = −0.65, 95 % Ci = -0.74, −0.55, P < 0.01) with a small publication bias. -Moderate to low level of heterogeneity. -Subgroup analysis of maxillary and mandibular central and lateral incisors showed significantly less RR in CAT.	CAT will not reduce RR, but incidence and severity are lower than FAT. There is a need for high-quality RCTs and consideration of confounding factors.
Sadauskiene et al.26 (2020) Lithuania	6	NA	NR	NR	NA	-Three studies compared CAT and FAT. -Patients treated by regular edgewise brackets have a higher RR than aligners. -The mean RR of maxillary and mandibular incisors in OPG was CAT (5.13 ± 2.81 %), significantly less than in FAT (6.97 ± 3.67 %).	RR during and after CAT is unavoidable. Incidence and severity were lesser in CAT.
Gandhi et al.17 (2021) United States	16	16	PRISMA, Cochrane Handbook for Systematic Reviews of Interventions/PROSPERO	MINORS	-Maxillary left CI (MD = 0.60, 95 % Ci = 0.42, 0.77; p < 0.001, I2 = 81 %), -Maxillary right CI (MD = 0.53, 95 % CI = 0.38,0.67; p = 0.001, I2 = 77.5 %), -Maxillary left LI (MD = 0.59, 95 % CI = 0.42,0.77; p < 0.001, I2 = 75 %), -Maxillary right LI (MD = 0.61; 95 % Ci = 0.43,0.80; p < 0.001, I2 = 83 %), and -Overall for incisors (MD = 0.49; 95 % Ci = 0.24,0.75)	-Only two retrospective radiometric studies compared RR in CAT and FAT. -Moderate level of RoB. -Mean RR of maxillary incisors was less than 1 mm. -Significant difference found in maxillary lateral incisors.	Lateral incisors in FAT had significantly more RR than CAT.CBCT shows a decreased magnitude of RR compared to 2D radiographs.
Inchingolo et al.25 (2024) Italy	9	NA	PRISMA/PROSPERO	RoB-2	NA	-One RCT and 8 NRCT. -Moderate to high RoB. -RR was lower in non-extraction patients treated with CAT than in FAT.	Lower prevalence and severity of RR in CAT. CBCT is a valuable tool that is highly accurate in diagnosing and quantifying RR.
Singh et al.18 (2024) India	10	6	PRISMA/PROSPERO	RoB-2 and ROBINS-I	-Maxillary CI (MD = −0.62, 95 % Ci = −0.88,-0.36, p < 0.00001,χ2 = 0.27; I2 = 22 %), -Maxillary LI (MD = −0.47, 95 % Ci = −0.85, −0.10, p = 0.01,χ2 = 0.02; I2 = 67 %), -Maxillary canine (MD = −0.79, 95 % Ci = −1.98, 0.39, p = 0.19,χ2 = 0.01; I2 = 83 %), -Mandibular CI (MD = −0.27, 95 % Ci = −0.52, −0.01, p = 0.04,χ2 = 0.32; I2 = 13 %), -Mandibular LI (MD = −0.33, 95 % Ci = −1.23, 0.58, p = 0.48,χ2 = 0.0001; I2 = 89 %), and -Mandibular canine (MD = −0.39, 95 % Ci = −1.51, 0.74, p = 0.50, χ2 = 0.0007; I2 = 91 %)	-One RCT (low RoB), one case-control, and eight retrospective studies (moderate to low RoB) were used. -Premolars and molars were not assessed in any studies. -Significant difference was seen in maxillary incisors and mandibular central incisors, favouring CAT. -Publication bias was reported due to the standard error and a small sample size.	Moderate quality of evidence with lower RR in CAT than FAT. Maxillary CI, LI, and mandibular CI had significantly less RR in CAT.
Varoneckaite et al.27 (2024) Lithuania	6	6	PRISMA/PROSPERO	RoB-2 and ROBINS-I	-Maxillary CI (MD = −0.40, 95 % Ci = −0.70, −0.10; p = 0.009,χ2 = 0.09; I2 = 45 %), -Maxillary LI (MD = −0.65, 95 % Ci = −0.98, −0.32; p = 0.0001,χ2 = 0.16; I2 = 39 %), -Mandibular CI (MD = −0.40, 95 % Ci = −0.65, −0.16; p = 0.001,χ2 = 0.41; I2 = 0 %), and -Mandibular LI (MD = −0.73, 95 % Ci = −1.51, −0.04; p = 0.06,χ2 = 0.0005; I2 = 87 %)	-Five retrospective cohort studies (moderate to low RoB) and one RCT (low RoB). -There was a significant difference in RR between CAT and FAT in maxillary and mandibular incisors.	RR in anterior teeth is less in CAT than in FAT. RCTs are needed for more conclusive results.

PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analysis; PROSPERO, International Prospective Register of Systematic Reviews; RoB-2, Risk of Bias-2; ROBINS-I, Risk Of Bias in Non-randomized Studies of Interventions-I; MINORS, Methodological Index for Non-randomized Studies; NRCT, Non-Randomized Clinical Trails; RCT, Randomized Clinical Trials; CAT, Clear Aligner Therapy; FAT, Fixed Appliance Therapy; RR, Root Resorption; MD, Mean Difference; CI, Central Incisors; LI, Lateral Incisors; Ci, Confidence Interval; OPG, Orthopantomogram; CBCT, Cone-Beam Computed Tomography; mm, millimetre; NR , Not reported; NA, Not applicable.

The OIEARR was diagnosed as dimensional changes in root length (mm) using 2D radiographs16, 17, 18^,24,26,27 (periapical radiographs and orthopantomogram) or three-dimensionally assessed with cone-beam computed tomography (CBCT)^{17,18,24,26,27} and microcomputed tomography.²³ Invisalign was the most preferred aligner group compared with the pre-adjusted edgewise appliance. Few studies compared self-ligating brackets (Damon) with aligners.^28,29 Most studies reported root resorption only in maxillary and mandibular anteriors.

3.3. Overlap of studies

Eight SR and MAs included 31 primary articles in qualitative analysis and 22 in four meta-analyses, with high overlap. Fig. 2. The overall results of primary studies included in the meta-analysis are presented in six node pairs of review. The covered area is 35.23 %, and the corrected covered area (CCA) is 13.64 % of primary studies. Therefore, a quantitative analysis was performed on the primary studies included in the meta-analysis.

Fig. 2.

The overlap of primary studies included in (a) Systematic reviews and (b) Meta-analysis, assessed using the GROOVE tool.

4. Results of individual studies

The results of the included reviews are described in Table 1. Studies have shown a lower incidence of root resorption in the anterior teeth with clear aligners.^16,24,26 Light forces during orthodontic treatment reduce the severity of OIEARR. Elhaddaoui et al. (2016)¹⁶ and Aldeeri et al. (2018)²³ reported a nine-fold increase in the incidence of root resorption in the high orthodontic forces group compared to the aligner and light force group. Similar results were reported by Barbagallo et al. assessed with microcomputed tomography, which noted a mean root resorption of premolars were 26.182 pixels with light force (25 g), 29.034 pixels with clear aligners and 46.447 pixels with heavy force (225 g).³⁰

Most of the quantitative analysis showed less than 1 mm of root resorption in the anterior teeth in the aligner group.^17,18,24,27 Sadauskiene et al. (2020) found the incidence of root resorption ranged between 46 % and 81 %, with severe resorption of more than 20 % ranging between 3.7 % and 6.3 % of teeth. However, clear aligners caused similar or significantly less RR compared to FAT.²⁶ Singh et al. (2024) concluded that the extent and severity of RR in upper and lower incisors were lower in clear aligners than in fixed appliances.¹⁸ Similar findings were reported by Varoneckaite et al. (2024) that clear aligners had statistically significantly lower RR in maxillary incisors and mandibular central incisors.²⁷

Fang et al. (2019) observed significantly less OIEARR in the CAT group's maxillary and mandibular central incisors. They attributed relatively higher resorption in the FAT group to the intermittent force with jiggling movement in the latter.²⁴ Gandhi et al. (2021). reported more root resorption in the lateral incisors in the fixed appliance group. However, there was no clinically significant difference in root resorption of the permanent maxillary incisors. In addition, CBCT was the preferred method to diagnose OIEARR, as 2D radiographs tend to overestimate it.¹⁷ Inchigolo et al. (2024) substantiated that CBCT helps better understand the factors influencing RR, such as alveolar bone thickness, height and root length in both clear aligner and fixed appliance groups.²⁵ The overall quality of the primary studies included in the SR and MA was low or moderate in evidence.

4.1. Quality of the evidence

The overall confidence of the included SR and MA assessed with the AMSTAR 2 tool revealed the quality to be critically low in four,^16,23,25,26 and two each in high^18,24 and low^17,27 quality. The assessment results of individual SR and MA are presented in Fig. 3. Meta-analysis was conducted only from four studies.^17,18,24,27 Most studies did not report critical domains such as justifications for study exclusion, risk of bias and publication bias in the results. In addition, six SRs and MAs mentioned the funding source^17,18,23, 24, 25^,27 and conflict of interest.16, 17, 18^,23,25,27 There was a unanimous consensus among the reviewers regarding the quality assessment.

Fig. 3.

AMSTAR 2 Quality assessment scoring of systematic review and Meta-analysis.

4.2. Meta-analysis

Among the twenty-two primary studies included in four^17,18,24,27 SR and MA, only five^{10,11,29,31,32} were eligible for homogeneous data synthesis and were pooled for statistical analysis. Primary studies that compared OIEARR in CAT and FAT groups using CBCT were only included, as it is a highly reliable and accurate diagnostic imaging method. A quantitative analysis of OIEARR in maxillary and mandibular anterior teeth was performed. Fig. 4. There was a significant difference in OIEARR between the CAT and FAT groups in maxillary incisors. The mean difference (MD) was 0.62mm in maxillary central incisors (95 % CI: −0.95, −0.29, I²: 60 %, p < 0.05) and 0.65 mm in maxillary lateral incisors (95 % CI: −1.22, −0.07, I²:85 %, p = 0.03). Similarly, there was a statistically significant mean difference of 0.31 mm in mandibular central incisors (95 % CI: −0.48, −0.15, I²:22 %, p < 0.05). The descriptive data of quantitative analysis is depicted in Supplementary Table 3. The heterogeneity of included studies ranged from low (22 %) to very high (93 %). The sensitivity analysis did not significantly improve the results after removing any study. However, given the very high to low level of heterogeneity and very few included studies, these results must be interpreted cautiously. In addition, since all included studies were non-randomized with high to moderate heterogeneity, the certainty of evidence was not assessed.

Fig. 4.

Forest plot using random effects models comparing the OIEARR in CBCT between the clear aligner and fixed appliance groups (a) Maxillary central incisors, (b) Maxillary lateral incisors, (c)Mandibular central incisors, (d) Mandibular lateral incisors, (e) Maxillary canine, and (f) Mandibular canine.

5. Discussion

The desire for inconspicuous orthodontic appliances has ushered the change in patient preference from fixed metal to lingual and ceramic brackets, with clear aligners being the latest. Along with the progressive technological advancements in three-dimensional scanning and imaging, clear aligner therapy has become more convenient, predictable and customized.^33,34 Due to minimal concealed attachments, fewer dietary restrictions, reduced orthodontic appointments with no metal wire change, and ease of oral hygiene maintenance, patients and orthodontists increasingly prefer clear aligners.^35,36

One of the major iatrogenic effects of orthodontic treatment is orthodontically-induced root resorption. Due to complex surface anatomy, force concentration, periodontal fibre direction and variable composition of cementum, particularly in the root apex region, could influence the resorption process.³⁷ Literature evidence has proven that 2–5 % of orthodontic patients are vulnerable to severe OIEARR up to 5 mm, which could affect the longevity of the tooth affected.³⁸ Radiometric Studies reported that more than 20 per cent root resorption was present in 6.3 %¹⁵ and 3.7 %¹⁴ patients undergoing CAT. However, the evidence of OIEARR, particularly in aligner treatment, lacks certainty due to studies with poor quality methodology, study design and small sample size. Zhang et al. in their overview of reviews, concluded similar findings. Unfortunately, only four systematic reviews were included, and no quantitative analysis was performed.³⁹ Therefore, this review provides more cogent evidence from collective data from systematic reviews and meta-analyses of OIEARR in patients undergoing aligner orthodontic treatment.

The patient-related risk factors are unavoidable, but the treatment prognosis could be determined early if the patient is more prone to OIEARR. The randomization of participants could reduce this; unfortunately, only two primary studies were randomized among the thirty-one.^30,40 Previous studies have concluded an inconsistent association of OIEARR based on age and gender.^41,42 This review had no supporting evidence due to the lack of available data.

The treatment-related risk factors depend solely on the biomechanics and prescription used. The study results concluded that OIEARR is inevitable in aligners and fixed treatments. However, the incidence and severity were lower than those of the heavy force and more than or comparable to those of the light forces used in FAT. The risk of OIEARR increases with continuous heavy or jiggling forces and round-tripping.²⁴ Removable aligners are light and intermittent; most are non-extraction orthodontic treatments that cause less root resorption. In addition, staged and planned movements with less torque control and unpredictable biomechanics are very limited in CAT.⁴³ Also, the intermittent wear of removable aligners helps heal and repair cementum following resorption.¹⁴

The amount of root resorption is diagnosed quantitatively using 2D orthopantomogram, periapical radiographs and 3D cone beam computed tomography and subjectively using scoring or grading scores. Few studies reported Sharpe and Reed's subjective grading of RR severity and found that aligners presented with less resorption in anterior teeth than FAT.^11,32 Since root resorption is a three-dimensional phenomenon, two-dimensional radiographs have limitations, and it was found that panoramic radiographs overestimated RR by 20 %.⁴⁴ Therefore, limited field of view CBCT is a reliable and accurate in measuring the amount of root resorption. Hence, the data synthesis of this review is a homogeneous quantitative analysis of root resorption in CBCT between CAT and FAT.

Any alteration in the tooth morphology, such as dilacerated, pipette-shaped roots and short crown-root ratio, are high-risk factors.³⁷ Additionally, orthodontic treatment takes a longer duration in cases of premolar extraction and retraction of anterior teeth, arch expansion, and apical intrusive and extrusive movements, such as deep bite correction.⁴⁵ Evidence suggests that, regardless of genetic or treatment-related factors, the maxillary incisor consistently averages more apical root resorption than any other tooth in premolar extraction cases. The anterior teeth are more subject to vertical and sagittal correction, and maxillary lateral incisors are prone due to anatomical dysmorphology.⁴⁶ To substantiate, most of the included studies in this review assessed the root resorption of maxillary and mandibular anteriors and supported it with statistical evidence.

The use of different bracket prescriptions also influences the OIEARR. Previous studies reported that the self-ligating brackets (SLB) had less and longer protective effects of OIEARR in maxillary incisors due to less frictional force.⁴⁷ In this review, a few studies compared SLB and pre-adjusted edgewise appliances with aligners. Similar results were reported that SLB had less root resorption than conventional appliances, but more than aligners.²⁸ The maxillary central incisors in the aligner group exhibited an average of 23.68 ± 4.82 mm³ root volume loss and less than 1.4 mm resorption, compared to 28.24 ± 6.07 mm³ and 2.3 mm in the SLB group.²⁹

The evidence related to the association of OIEARR in different malocclusions is still uncertain. Studies have reported that root resorption is invariably seen in all class I, II and III malocclusions.⁴⁸ Chen et al. concluded that root resorption was significantly less in the aligner group compared to FAT in Class II division 2 non-extraction patients.²⁹ The challenging severe teeth are crowding and proclination with first premolar extraction and retractions of anteriors with demanding biomechanics. The repercussions are felt on maxillary incisors, which are more susceptible to an average OIEARR of more than 1.5 mm.⁴⁹ Most aligner studies included mild to moderate teeth crowding with a non-extraction plan, and few combined extraction plans with no distinct facts. Therefore, the results of our study were also inconclusive based on the severity of crowding and malocclusion.

6. Limitations and future recommendations

Aligner treatment could be a promising treatment in future with improved efficiency. Therefore, its adverse effects, such as OIEARR, have been evaluated in this review. The study results should be cautiously inferred, as most primary studies were non-randomized studies with a smaller sample size. The quantitative analysis assessed only the primary studies included in the reviews. Hence, a few related studies that were not reported could have been obscured. The data evidence exhibited low to very high heterogeneity, and fewer than ten primary studies were included in the meta-analysis; hence, the assessment of publication bias was inconceivable. Inadequate data concerning patient-related and treatment-related risk factors were not defined in the included studies for subgroup and sensitivity analysis. Therefore, future studies should carefully consider these drawbacks, ensuring that any association between OIEARR and risk factors is provided, with a structured methodology and randomized design. Most of the included studies evaluated root resorption of the maxillary anteriors and were short-term findings; even though they are more susceptible, assessing the other teeth longitudinally is critical. Very few studies have reported volumetric resorption. The resorption occurs throughout the root surface, and very few studies have reported it. Therefore, future studies should contemplate overall three-dimensional volumetric resorption.

7. Conclusion

OIEARR is multifactorial and inevitable in any patient undergoing orthodontic treatment. Evidence suggests that the severity of root resorption were lesser in the CAT than in the FAT group. In aligner therapy, the root resorption was lesser by 0.62 mm and 0.65 mm in maxillary central and lateral incisors, respectively. However, there is a future need for high-quality RCTs, considering the associated risk factors of OIEARR for credible evidence.

Patient/guardian consent form

We declare that this is a review article titled (Orthodontically induced external apical root resorption with clear aligner compared to fixed appliance treatment: An umbrella review.) and does not involve any studies with human participants or animals performed by any of the authors.

Credit author contribution statement

Madhanraj Selvaraj: Conceptualization, Methodology, Investigation, Data curation, Writing-Original Draft, Writing-Review and Editing.

Bhaskar Nivethitha: Conceptualization, Methodology, Investigation, Data curation, Writing-Original Draft, Writing-Review and Editing.

Balasubramanian Madhan: Conceptualization, Methodology, Investigation, Data curation, Writing- Review and editing, Critical revision and supervision.

Data availability

Relevant data and supplementary files have been included in this study. Any other data related to study findings will be available upon request from the corresponding author.

Ethical clearance form

We declare that this is a review article titled (Orthodontically induced external apical root resorption with clear aligners compared to fixed appliance treatment: An umbrella review.) and does not involve any studies with human participants or animals performed by any of the authors. Therefore no institutional ethical clearance was required and PROSPERO registration was done prior to start of the study.

Source of funding form

Nil

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Appendix A. Supplementary data

The following are the Supplementary data to this article: