Summary
Objective
The aim of this study was to evaluate and compare the amount of external apical root resorption (EARR) observed during the orthodontic treatment with pre-adjusted edgewise appliance (PEA) or clear aligner therapy (CAT) and with 2D or 3D radiographic methods of measuring the root resorption.
Search strategy and selection criteria
A search of PubMed MEDLINE, Scopus, Cochrane Central Register of Controlled Trials, LILACS, Web of Science, Dissertations & Theses Global, ClinicalTrials.gov registry, and the ISRCTN Registry was performed. Studies that have evaluated the amount of root resorption in non-extraction cases using CAT or PEA were selected for the systematic review. A meta-analysis was performed for the amount of root resorption of permanent maxillary incisors using PEA or CAT treatment modalities by either 2D or cone-beam computed tomography radiographic examination.
Data collection and analysis
Database research, elimination of duplicate studies, data extraction, and risk of bias were performed by authors independently and in duplication. A random-effect meta-analysis followed by subgroup comparisons were performed to evaluate EARR.
Results
A total of 16 studies (4 were prospective and 12 were retrospective) were identified for inclusion in the systematic review. The mean root resorption for the permanent maxillary incisors was in the range from 0.25 to 1.13 mm (overall: 0.49 mm; 95% confidence interval [CI] = 0.24 to 0.75 mm). The mean root resorption difference between CAT and PEA was statistically significant (P < 0.05) for 12 but not for 21, 11, or 22.
Limitations
One of the drawbacks is a lack of good quality prospective studies, specifically randomized clinical trials in the literature.
Conclusions and implications
Neither PEA or CAT technique leads to clinically significant root resorption (1 mm) of the maxillary incisors. The amount of EARR of maxillary incisors is not significant in comparing two treatment modalities (PEA and CAT), except for 12, where the PEA group has significantly more EARR when compared to CAT.
Registration
The protocol for this systematic review was based on the Cochrane Handbook for Systematic Reviews of Interventions 5.1.0 and was registered at PROSPERO database (https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42018113051). This systematic review is reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement.
Introduction
Root resorption is an unwanted and unavoidable sequela of orthodontic tooth movement. In addition to genetic factors and trauma, orthodontic treatment has been proposed as one of the factors that may lead to resorption of the apical part of the root,1,2 termed as external apical root resorption (EARR). Age, gender, nutrition, genetics, the type of appliance, the amount of force used during treatment, extraction or non-extraction, duration of treatment, and the distance the tooth/teeth move are some of the factors that have contributing effects on root resorption.3 The incidence of root resorption seems to be higher in the maxillary and mandibular incisors due to extensive tooth movement.4,5 It is important for clinicians to identify root resorption changes during orthodontic treatment as most of these changes are irreversible and may affect the longevity of the teeth.3,6 Thus, the outcome assessment of root resorption in patients undergoing orthodontic treatment is paramount.
In order to measure the extent of EARR, radiographic examination is necessary. Several studies have used panoramic or periapical radiographs to measure EARR7–9; however, there are inherent limitations in measuring EARR due to magnification and distortion of 2D radiography.6 To overcome these limitations, studies had used the ratio of the crown length to the root length rather than absolute measurements.7 Cone-beam computed tomography (CBCT) is a 3D volumetric technique that has a significant advantage over 2D radiography in the accurate detection and quantification of root resorption without image magnification/distortion as a limiting factor.10–12 However, 2D radiographs are routinely taken for orthodontic treatment and have been reported as a method for assessing root resorption in recent studies.13,14 Thus, it is important to analyze whether 2D radiographs are reliable and accurate in measuring EARR when compared with 3D radiographs.
The fixed-appliance treatment has become an integral part of contemporary orthodontics and has been a major focus point of orthodontic research.15 The introduction of the pre-adjusted edgewise appliance (PEA) had changed the course of orthodontic specialty and is the most commonly used appliance worldwide for orthodontic treatment. As a higher number of adults are opting for orthodontic treatment, there is an increased demand for esthetic options with orthodontic therapy. Clear aligner therapy (CAT) has emerged as an alternation esthetic option for patients seeking orthodontic treatment. Several studies have examined the effects of CAT or PEA on EARR, but there is some disagreement on the amount of EARR with either technique. Studies have reported that aligners cause a decreased amount of root resorption when compared with fixed orthodontic appliances.16 However, other studies have shown that aligner therapy may lead to increased EARR when compared to fixed orthodontic appliances.10 Thus, the literature shows conflicting results on the outcome of EARR with PEA and CAT.
Objectives
Thus, this systematic review cum meta-analysis was undertaken with the aim to evaluate and compare the amount of EARR observed during the orthodontic treatment with PEA and CAT. Another objective of this systematic review and meta-analysis was to compare the 2D and 3D radiographic methods of evaluating the root resorption during orthodontic treatment with PEA and CAT.
Materials and methods
Protocol and registration
Institutional review board submission and approval was not required for this study. This systematic review protocol was registered with PROSPERO (registration number of CRD42018113051; www.crd.york.ac.uk/prospero). The present systematic review is conducted according to the guidelines of the Cochrane Handbook for Systematic Reviews of Interventions version 5.1.017 and is reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement.18
Eligibility criteria
The criteria for considering studies for this review (PICOS) were the following: 1. participants: patients with the malocclusion requiring non-extraction orthodontic therapy; 2. intervention: orthodontic treatment with either PEA or CAT; 3. comparison: pre-treatment and post-treatment root lengths; 4. outcome: amount of EARR measured based on the CBCT or 2D radiographic images; 5. study design: randomized clinical trials (RCTs) and prospective or retrospective radiometric studies.
Information sources and search strategy
The health sciences librarian used sentinel articles to harvest and test search terms; the following search strategy was developed for PubMed/MEDLINE in order to retrieve all records using natural language and controlled vocabulary (when available) relating to the concepts of root resorption and either clear aligners or conventional brackets: (‘Root Resorption’[Mesh] OR ‘root resorption’[tw]) AND (‘Orthodontic Appliances’[Mesh] OR ‘Tooth Movement Techniques’[Mesh] OR ‘orthodontic appliance’[tw] OR align*[tw] OR removable[tw] OR fixed[tw] OR bracket*[tw] OR ‘orthodontic treatment’[tw] OR edgewise[tw]).
This strategy was translated and adapted for the other databases. The following databases were searched from the date of inception through 31 December 2019: PubMed MEDLINE (including Pre-MEDLINE and non-MEDLINE; 1945 to December 2019), Scopus (Elsevier; 1966 to December 2019), Cochrane Central Register of Controlled Trials (Wiley; through December 2019), LILACS (VHL Regional Portal; 1936 to December 2019), Web of Science (BIOSIS, MEDLINE, Zoological Record; Clarivate Analytics; 1900 to December 2019), and Dissertations & Theses Global (ProQuest; 1637 to December 2019). The ClinicalTrials.gov registry and the ISRCTN Registry were searched on 13 December 2019 as well. No filters were used for language, publication date, or methodology. Additional records were found by compiling forward citations and references of all full-text records that were selected for study inclusion. ProQuest RefWorks (Legacy version) was used to de-duplicate and manage all citations.
Study selection
Inclusion criteria were randomized or non-randomized clinical trials; prospective or retrospective cohort studies; and before and after radiometric studies. We included studies that investigated the amount of root resorption during non-extraction orthodontic therapy using PEA or CAT treatment modalities by either CBCT or 2D radiographic examination. We also included studies that have investigated the root resorption considering multiple parameters using PEA or CAT; however, they must have reported the amount of root resorption specific to non-extraction cases independently.
Exclusion criteria were meta-analysis or systematic reviews; animal studies; review articles; abstracts; letters from editor; opinion articles; case reports; case series; histological evaluation of root resorption; studies evaluating teeth with some sort of anomalies in root form, shape, or structure; and studies evaluating traumatized, transplanted or re-implanted teeth. We also included studies with combined samples of extraction and non-extraction cases; however, the amount of root resorption must be reported independently for non-extraction treatment cases in the study to be part of our systematic review.
Data items and collection form
A customized data collection form was created and used to gather information from the selected studies. This information included authors, year of publication, type of studies, details of the interventions, characteristics of participants, duration of treatment, and outcome measures. The data extraction was performed by authors (GV/MS) independently and in duplication. An attempt to contact the authors was made for any missing information. In the case of a disagreement, a third reviewer (YS) was contacted to provide an independent decision on the conflict.
Risk of bias and quality assessment of individual studies
After imposing exclusion and inclusion criteria, no randomized controlled trial addressing our PICO question was found. To ascertain the validity of eligible non-randomized studies, pairs of reviewers (GV/MS) worked independently and with adequate reliability to determine the accuracy of the objectives, adequacy of concealment of allocation, blinding of patients, data collectors, outcome assessment, extent of loss to follow-up (i.e. proportion of patients in whom the investigators were not able to ascertain outcomes), and prospective calculation of the study size. The methodological index for non-randomized studies (MINORS) was utilized to assess the risk of bias of non-randomized studies.19 We chose to include eight events in the risk of bias assessment and a higher event rate allows us to give a more precise estimate of the influence of studied determinants. The items were scored 0 if not reported; 1 when reported but inadequate; and 2 when reported and adequate. The global ideal score was 16 for non-comparative studies. If only abstracts were available, they were automatically judged to be at high risk of bias. Consensus was reached by the two reviewers (GV/MS) when there was difference in opinion on an item. If no consensus was reached, the independent opinion of a third reviewer was decisive (YS). The quality assessments of the studies included in this systematic review and meta-analysis are given in Figure 1.
Figure 1.
Risk of bias assessment using ‘methodological index for non-randomized studies (MINORS)’. Items 1–8 represent: 1, a clearly stated aim; 2, inclusion of consecutive patients; 3, prospective collection of data; 4, endpoints appropriate to the aim of the study; 5, unbiased assessment of the study endpoint; 6, follow-up period appropriate to the aim of the study; and 7, loss to follow-up less than 5%; 8, prospective calculation of the study size. An item scoring 0 means that it was not mentioned (red), 1 means reported but inadequate (yellow), and 2 means reported and adequate (blue). The total score was 16 for self-controlled studies.
Summary measures, approach to synthesis, and planned methods of analysis
EARR following the non-extraction orthodontic therapy was the primary measure of the treatment effect. The data were grouped and classified according to the type of intervention into two broad categories: root resorption with PEA and root resorption with CAT. The majority of the studies evaluated ‘EARR’ of four permanent maxillary incisors and were selected for the meta-analysis. The meta-analyses to estimate the mean EARR were performed for individual and four permanent maxillary incisors combined (permanent upper left central incisor: 21, permanent upper right central incisor: 11, permanent upper left lateral incisor: 22, and permanent upper right lateral incisor: 12), where the mean EARR was averaged across the four incisors and the associated standard deviation (SD) was calculated using incisor-specific SDs and correlations between incisors estimated by the mean EARRs from the included studies. Additionally, comparisons were made between PEA versus CAT and 3D versus 2D imaging.
The heterogeneity among studies in each subgroup was evaluated by I2 and Q statistic and the between-group comparison was conducted in a mixed-effects meta-regression model assuming a random study effect and fixed effects of intervention type (PEA or CAT) or imaging type (3D or 2D), with and without adjustment for treatment duration. We used the R package metafor to make forest plots and to fit mixed-effects meta-regression models. A P-value smaller than 0.05 was deemed to be statistically significant. All the statistical analyses were performed in R version 3.5.1.
Risk of bias across studies
We evaluated the publication bias for individual permanent upper incisors. The funnel plots with standard error versus residual after adjusting for intervention type (CAT versus PEA), CBCT dimension, and treatment did not show any asymmetric patterns, with no evidence suggesting publication bias (Supplementary Figure 1).
Results
Study selection
The search strategy leads to a total of 5613 results. The search strategy and the exclusion of the studies are mentioned in Figure 2. A total of 16 studies were identified for inclusion in the systematic review (Table 1). The type of orthodontic treatment, either PEA or CAT, was the chief determinant for which group the study fell into. Five studies assessed the EARR with the CAT7,8,13,20,21 and nine studies used PEA for the orthodontic treatment and observed EARR.5,9,14,22–27 Two of the selected studies utilized both (CAT and PEA) of the orthodontic treatment modalities and evaluated EARR.16,28 Nine studies (two CAT,20,21 six PEA,9,14,23-26 and one both28) from the final 16 studies included in the review had quantitatively described EARR of permanent maxillary central and lateral incisors. These data were collected for meta-analysis to evaluate the root resorption with the type of orthodontic treatment (PEA versus CAT) and the method of radiographic assessment (2D versus CBCT; Table 1). Six studies used panoramic7,8,13,16,22,27 radiographs, three studies evaluated periapical9,23,25 radiographs, six studies used CBCT imaging,5,20,21,24,26,28 and one study used both CBCT and periapical radiographs14 as the method to measure root resorption with CAT and PEA. In three studies using panoramic radiographs,7,8,27 the relative changes in the root-crown ratios (rRCR) were measured to assess root resorption. Studies that used periapical radiographs measured the root length from the cementoenamel junction to the root apex9 and from the incisal edge to the root apex.14 From the studies that used CBCT for measuring root resorption, the total length of the tooth was measured in from crown tip to root apex in two studies,24,26 whereas the two studies used a Cartesian co-ordinate system to measure the length of the tooth to assess root resorption.20,21 The detailed description of the method for measuring root resorption is given in Supplementary Table 1.
Figure 2.
Preferred Reporting Items for Systematic Reviews and Meta-Analyses flow diagram of information through the different phases of a systematic review.
Table 1.
Study characteristics: participants (sample size, demographic information), intervention and comparison (type of appliance), secondary comparison (radiographic method), study design, and outcome (amount of root resorption in permanent upper incisors). CAT, clear aligner therapy; CBCT, cone-beam computed tomography; PEA, pre-adjusted edgewise appliance
| Sr. no. | Study | Participants (sample size) | Participants (demographic information) | Intervention and comparison (type of appliance) | Secondary comparison (radiographic method) | Study design | Outcome Root resorption in permanent upper incisors |
|---|---|---|---|---|---|---|---|
| 1 | Krieger et al.7 | 100 subjects (n = 1600; upper and lower anteriors and first molars) | Mean age: 37.7 (17–75) years (37 male and 63 female) | CAT (Invisalign) | Panoramic radiographs | Retrospective radiometric study | — |
| 2 | Gay et al.8 | 71 subjects (n = 1083; upper and lower anteriors and upper first premolars and molars) | Mean age: 32.8 ± 12.7 years (25 male and 46 female) | CAT (Invisalign) | Panoramic radiographs | Prospective radiometric study | — |
| 3 | Yi et al.13 | 40 subjects (n = 640; upper and lower incisors) | Mean age: 21.80 ± 5.11 years (9 male and 31 female) | CAT | Panoramic radiographs | Retrospective radiometric study | — |
| 4 | Eissa et al.20 | 11 subjects (upper incisors) | Mean age: 18.35 ± 2.83 years (5 male and 6 female) | CAT (Smart Track) | CBCT | Cohort study | 12: 0.36 ± 0.32 mm, 11: 0.51 ± 0.43 mm, 21: 0.46 ± 0.36 mm, 22: 0.44 ± 0.3 mm |
| 5 | Farouk et al.21 | 15 subjects (upper incisors) | Mean age: 26 ± 11 years | CAT (Smart Track) | CBCT | Retrospective radiometric study | 12: 0.36 ± 0.32 mm, 11: 0.51 ± 0.43 mm, 21: 0.45 ± 0.36 mm, 22: 0.44 ± 0.3 mm. |
| 6 | Fowler et al.16 | 45 subjects-only CAT45 subjects-only PEA | CAT: mean age: 38.24 ± 12.59 years (only female) PEA: mean age: 15.82 ± 7.287 years (only female) | CAT and PEA | Panoramic radiographs | Retrospective radiometric study | — |
| 7 | Metcalf 28 | 30 subjects-only CAT30 subjects-only PEA | CAT: mean age: 22.2 ± 11.5 years (12 males, 18 females)PEA: mean age: 19 ± 10.7 years (11 males, 19 females) | CAT and PEA | CBCT | Retrospective radiometric study | CAT: 11: 0.33 ± 0.70 mm, 12: 0.36 ± 0.54 mm, 21: 0.58 ± 0.73 mm, 22: 0.51 ± 0.74 mm PEA: 11: 1.18 ± 1.09 mm, 12: 0.88 ± 0.89 mm, 21: 1.30 ± 1.12 mm, 22: 1.17 ± 0.84 mm |
| 8 | Agarwal et al.22 | 27 subjects (n = 540; upper and lower canines through first molar; n = 29 Roth, n = 31 MBT) | (30 males and 30 females in total) | PEA (Roth and MBT) | Panoramic radiographs | Retrospective radiometric study | — |
| 9 | Castro et al.5 | 30 subjects (n = 1256 roots; upper right second molar to upper left) | Mean age: 13 (11–16) years (11 male and 19 female) | PEA (Roth) | CBCT | Prospective study | — |
| 10 | Kocadereli et al.23 | 20 subjects (n = 80; upper incisors) | Mean age: 14.9 ± 2.8 years (6 males and 14 females) | PEA (Roth) | Periapical radiographs | Prospective randomized study | 11: 0.7 ± 0.62 mm, 12: 0.98 ± 0.74 mm, 21: 0.73 ± 0.4 mm, 22: 0.6 ± 0.39 mm |
| 11 | Leite et al.24 | 8 subjects (n = 64; upper and lower incisors) | Mean age: 20.6 years (11–30 years; 2 males and 6 females) | PEA | CBCT | Prospective randomized study | U1: 0.33 mm, U2: 0.44 mm, L1: 0.31 mm, L2: 0.40 mm |
| 12 | Nassif et al.25 | 20 subjects (n = 80; upper incisors) | Mean age: 23.43 years (8 males and 12 females) | PEA (Roth) | Periapical radiographs | Retrospective radiometric study | 11: 0.66 ± 0.65 mm, 12: 0.77 ± 0.62 mm, 21: 0.85 ± 0.60 mm, 22: 0.83 ± 0.82 mm |
| 13 | Patel et al.26 | 14 subjects (upper and lower incisors) | Mean age: 12.76 ± 1.59 (9 males and 5 females) | PEA | CBCT | Retrospective radiometric study | 11: 0.37 ± 0.53 mm, 21: 0.52 ± 0.74 mm, 12: 0.85 ± 0.76 mm, 22: 0.57 ± 0.80 mm |
| 14 | Lago et al.14 | 25 subjects (upper and lower incisors) | Mean age: 18.02 ± 6.06 (12 males and 13 females) | PEA | CBCT and periapical radiographs | Retrospective radiometric study | Periapical 11 = 0.85 mm, 21 = 1.03 mm, 12 = 0.97 mm, 22 = 0.98 mm CBCT: 11 = 0.28 mm, 21 = 0.22 mm, 12 = 0.30 mm, 22 = 0.21 mm |
| 15 | Wong et al.9 | 37 subjects (upper and lower anterior teeth) | Mean age: 13.93 ± 3.49 years | PEA | Periapical radiographs | Retrospective radiometric study | 11: 0.64 ± 0.77 mm, 21: 0.76 ± 0.75 mm, 12: 1.08 ± 0.84 mm, 22: 0.96 ± 1.17 mm |
| 16 | Pamukcu et al.27 | 30 subjects (n = 360; upper and lower anterior teeth) | Mean age: 26.14 ± 9.16 years (9 males and 21 females) | PEA | Panoramic radiographs | Retrospective radiometric study | — |
Study characteristics
Out of 16 studies, 4 were prospective and 12 were retrospective studies. The details about the type of appliance used in the study, the study design, the radiographic method used to measure root resorption, the number of participants, demographic information, and outcomes (root resorption in permanent upper incisors) are provided in Table 1. The aims of the study, treatment duration, methods of assessment, and specific outcomes of the individual studies are described in detail in Supplementary Table 1. The risk of bias assessment was done using MINORS index.19 All the studies scored more than 10 on a 16-point scale. Most common missing aspects in the studies were missing information about the inclusion of consecutive patients, unbiased assessment of the study end point, and missing prospective calculation of the study size. The details about the risk of bias assessment are described in Figure 1.
The type of orthodontic treatment used for the patient was the determinant used to divide the studies into two groups. Subjects in the PEA group all had labial orthodontic prescription. Of all the studies that used PEA, four studies used MBT prescription,16,22,24,26 four studies using Roth,5,22,23,25 and three studies did not mention the bracket prescription9,14,27 for the orthodontic treatment. The subjects treated with clear aligner therapy group were treated with Invisalign in two studies,7,8 with smart-track aligner in two studies,20,21 and one study did not report the type of aligner.13
The mean age for the patients in the CAT group was 28.12 years and, for the PEA group, was 16.82 years. The studies were quite similar with respect to the gender distribution: 66% of the patients in the CAT group were females, whereas 56% of the patients in the PEA group were females. The gender of the sample population was not mentioned in two studies.8,19 The measurements done at either post-treatment or at a fixed time interval after the beginning of orthodontic treatment were compared with the pre-treatment values to assess the root resorption. The mean observation period for the CAT group was 17.91 months and for PEA group was 15.94 months. The observation period for the root resorption in all the studies was less than 24 months except for one study in which the observation period of which was 31.08 months.9 The summary of the results of the studies is described in Supplementary Table 1.
The mean root resorption for the permanent maxillary central incisors (21, 11) and permanent maxillary lateral incisors (22, 12) was in the range from 0.25 to 1.13 mm, specifically 0.60 mm (95% CI = 0.42 to 0.77 mm) for 21, 0.53 mm (95% CI = 0.38 to 0.67 mm) for 11, 0.59 mm (95% CI = 0.42 to 0.77 mm) for 22, 0.61 mm (95% CI = 0.43 to 0.80 mm) for 12, and 0.49 mm (95% CI = 0.24 to 0.75 mm) for the four permanent incisors combined (Table 2; Figures 3 and 4).
Table 2.
Comparison of the studies with the clear aligner therapy (CAT; n = 3) versus pre-adjusted edgewise appliance (PEA; n = 7) appliance showing apical root resorption during the orthodontic treatment
| 95% Confidence interval | 95% Confidence interval | |||||
|---|---|---|---|---|---|---|
| Tooth | CAT | PEA | Unadjusted mean difference | Unadjusted P-value | Adjusted mean difference | Adjusted P-value |
| 21 | 0.48 (0.36, 0.61) | 0.65 (0.40, 0.91) | −0.15 (−0.54, 0.24) | 0.452 | −0.20 (−0.55, 0.16) | 0.275 |
| 11 | 0.45 (0.31, 0.59) | 0.57 (0.36, 0.79) | −0.12 (−0.46, 0.23) | 0.504 | −0.15 (−0.49, 0.20) | 0.398 |
| 22 | 0.45 (0.34, 0.57) | 0.66 (0.41, 0.91) | −0.19 (−0.57, 0.20) | 0.337 | −0.25 (−0.53, 0.03) | 0.077 |
| 12 | 0.36 (0.26, 0.47) | 0.74 (0.51, 0.97) | −0.37 (−0.71, −0.02) | 0.037 | −0.41 (−0.67, −0.15) | 0.002 |
| Overall | 0.44 (−0.00, 0.89) | 0.52 (0.20, 0.83) | −0.07 (−0.62, 0.47) | 0.792 | −0.19 (−0.77, 0.39) | 0.524 |
Statistical calculations are based on the unadjusted and adjusted mean differences in reference to the treatment duration.
Figure 3.
Forest plots showing the comparison of clear aligner therapy and pre-adjusted edgewise appliance for the EARR of permanent upper incisors.
Figure 4.
Forest plots showing the comparison of clear aligner therapy and pre-adjusted edgewise appliance for the overall external apical root resorption of permanent upper incisors.
Root resorption with PEA and CAT
The mean root resorption for the permanent maxillary central incisors (21, 11) and permanent maxillary lateral incisors (22, 12) was less than 1 mm. The mean root resorption difference between CAT and PEA was statistically significant (P < 0.05) for 12 (CAT: 0.36 mm, 95% CI = 0.26 to 0.47 mm; and PEA: 0.74 mm, 95% CI= 0.51 to 0.97 mm) but not for 21, 11, or 22. Furthermore, no statistically significant difference was found in the overall amount of EARR for permanent upper incisors with either CAT (EARR: 0.44 mm; 95% CI = 0.00 to 0.89 mm) or PEA (EARR: 0.52 mm; 95% CI = 0.20 to 0.83 mm) techniques (Table 2; Figures 3 and 4).
Root resorption with 3D and 2D
In the comparison between CBCT volume and 2D, it was found that the amount of root resorption for all permanent maxillary incisors was less when measured with CBCT than with 2D panoramic radiograph, particularly, for 12 (P = 0.04, adjusted for treatment duration, CBCT—EARR: 0.58 mm; 95% CI= 0.29 mm to 0.87 mm and 2D—EARR: 0.94 mm; 95% CI= 0.75 mm to 1.13 mm). The estimate for mean EARR in a subgroup or mean difference of EARR between groups and the corresponding 95% confidence intervals are presented in forest plots of Figures 5 and 6 and in Table 3.
Figure 5.
Forest plots showing the comparison of 2D and CBCT radiographic methods for measurement of the external apical root resorption involving permanent upper incisors.
Figure 6.
Forest plots showing the comparison clear aligner therapy and pre-adjusted edgewise appliance for the external apical root resorption (EARR) of permanent upper incisors (involving studies with CBCT imaging for the measurement of EARR).
Table 3.
Comparison of the studies with the 3D versus 2D radiometric measurements to quantify apical root resorption during the orthodontic treatment
| 95% Confidence interval | 95% Confidence interval | |||||
|---|---|---|---|---|---|---|
| Tooth | 3D | 2D | Unadjusted mean difference | Unadjusted P-value | Adjusted mean difference | Adjusted P-value |
| 21 | 0.57 (0.11, 1.03) | 0.77 (0.64, 0.89) | −0.23 (−0.74, 0.28) | 0.379 | −0.16 (−0.68, 0.36) | 0.548 |
| 11 | 0.51 (0.13, 0.89) | 0.69 (0.54, 0.84) | −0.21 (−0.64, 0.22) | 0.348 | −0.15 (−0.62, 0.32) | 0.539 |
| 22 | 0.58 (0.17, 0.99) | 0.75 (0.52, 0.97) | −0.20 (−0.73, 0.33) | 0.451 | −0.12 (−0.53, 0.28) | 0.551 |
| 12 | 0.58 (0.29, 0.87) | 0.94 (0.75, 1.13) | −0.37 (−0.76, 0.01) | 0.055 | −0.30 (−0.59, −0.01) | 0.04 |
Statistical calculations are based on the unadjusted and adjusted mean differences in reference to the treatment duration.
Risk of bias within studies
According to the MINOR scale used to evaluate the risk of bias, one study received a score of 10, the lowest score, and three studies received 15 each, the highest score in our systematic review. Eleven studies did not provide sufficient information about recruiting consecutive patients. Nine studies did not include prospective sample size calculations before initiating the study. Five studies did not provide sufficient information about blinding or performed single blinding for subjective data, and nine studies did not provide any information about blinding in their methodology (Figure 1). Thus, the risk of bias of the individual studies should be taken into consideration while extrapolating the results obtained from this meta-analysis.
The heterogeneity analysis results were quite sensitive to the sample size, that is, the number of studies. Subgroups with few studies tended to suggest insignificant heterogeneity. By the rule of thumb, a Q value >25 or I2 >75% implies considerable heterogeneity. The heterogeneity among studies was modelled by a random study effect in the mixed-effects meta-regression model (Supplementary Table 2).
Discussion
The aim of this meta-analysis was to evaluate if there is a difference in the amount of EARR with orthodontic treatment between PEA or CAT. The search strategy used was comprehensive with multiple database searches. No filters were used for language or publication date in order to generate maximum results and minimize bias. The risk of bias assessment of the studies involved in the meta-analysis was done according to the MINORS scale for judging the quality of the studies.19 The included studies used either 2D radiographs or CBCT volumes to evaluate the amount of root resorption in the patients undergoing orthodontic treatment.
Risk of bias within studies
All the studies scored 2 points for the appropriate follow-up period to the aim of the study except Kocadereli et al.,23 in which the observation period was 9 months, and Leite et al.24 and Lago et al.,14 in which the observation period was 6 months. Only a few studies8,13,18,20,24 reported inclusion of consecutive patients. As the other studies did not report consecutive patient enrolment, they were not scored the maximum of two marks. The details about the risk of bias assessment are described in Figure 1. All the studies scored more than 10 on a 16-point scale, indicating the moderately high quality of the studies, and seven studies ranged from 13 to 15,8,13,20,21,24–26 indicating the high quality of these studies.
Root resorption with PEA and CAT
Delivering the orthodontic treatment to the best aesthetic results in minimal time is desired both by the clinician and the patients. A clinical complication that hampers this outcome is EARR. Thus, when choosing between two types of orthodontic appliance either PEA or CAT, it becomes important to understand its effects on the root resorption. Varying degree, severity, and amount of root resorption with orthodontic treatment have been reported in the literature and are possibly due to small sample size, poor qualities of the published studies, and the difference in methodology to assess EARR. This meta-analysis provides evidence that minimal root resorption occurs in the maxillary permanent incisors in patients undergoing orthodontic treatment with either PEA or CAT. The amount of EARR in CAT and PEA group with 95% CI, as well as the mean difference, both unadjusted and adjusted based on treatment duration, is reported in Table 2. The comparative analysis between PEA and CAT for the EARR of 21, 11, and 22 teeth showed a statistically non-significant difference (P > 0.05). However, only in 12, PEA group (EARR: 0.74 mm; 95% CI = 0.51 to 0.97 mm) had significantly more root resorption as compared to CAT group (EARR: 0.36 mm; 95% CI = 0.26 to 0.47 mm; P = 0.002; Figure 3; Table 2). Non-significant EARR of upper permanent incisors (overall) was observed with either PEA or CAT orthodontic treatment modalities (Figure 4; Table 2). Also, the root resorption with CAT for the maxillary permanent incisors was less than PEA but it was not statistically significant, except for 12 (Figures 3 and 4). This effect may result from the decreased magnitude of force delivered by CAT compared to PEA or due to intermittent force application with CAT compared to PEA.20,29,30 Furthermore, non-extraction treatment plan, shorter treatment duration, and the limited amount of root movement during the orthodontic treatment could be the possible reason for non-significant EARR with either CAT or PEA.13,31
The method of detection of root resorption involves either 2D radiographs, such as periapical radiographs, and panoramic radiographs, or CBCT. CBCT has been found to be very accurate in measuring root resorption.25,26 In order to avoid bias associated with the method of measuring the root resorption, we analyzed the studies that involved CBCT for measuring root resorption separately as a subgroup (Figure 6; Table 4).
Table 4.
Comparison of the studies with the clear aligner therapy (CAT; n = 3) versus pre-adjusted edgewise appliance (PEA; n = 4) appliance showing apical root resorption measured using only 3D radiographic method
| 95% Confidence interval | 95% Confidence interval | |||||
|---|---|---|---|---|---|---|
| Tooth | CAT | PEA | Unadjusted mean difference | Unadjusted P-value | Adjusted mean difference | Adjusted P-value |
| 21 | 0.48 (0.36, 0.61) | 0.57 (0.11, 1.03) | −0.05 (−0.57, 0.46) | 0.835 | −0.21 (−0.49, 0.07) | 0.136 |
| 11 | 0.45 (0.31, 0.59) | 0.51 (0.13, 0.89) | −0.04 (−0.47, 0.39) | 0.855 | −0.16 (−0.58, 0.26) | 0.462 |
| 22 | 0.45 (0.34, 0.57) | 0.58 (0.17, 0.99) | −0.11 (−0.58, 0.37) | 0.654 | −0.26 (−0.57, 0.05) | 0.107 |
| 12 | 0.36 (0.26, 0.47) | 0.58 (0.29, 0.87) | −0.19 (−0.50, 0.12) | 0.223 | −0.30 (−0.55, -0.05) | 0.019 |
Statistical calculations are based on the unadjusted and adjusted mean differences in reference to the treatment duration.
The difference in the amount of root resorption with CAT and PEA was not statistically significant. Additionally, the amount of root resorption was less with CAT than with PEA, which was consistent in the 3D subgroup and overall. Thus, we conclude that CAT causes clinically non-significant reduced root resorption than PEA.
Our meta-analysis showed that the mean amount of EARR found with 2D methods was about 0.2 mm higher than with 3D methods. This could be due to the difficulty in identifying the incisor tip and the incisor root apex on the 2D radiographs because of overlying structures or due to magnification errors compared with the CBCT volume. Thus, the 2D methods may overestimate the amount of root resorption. However, the difference between the 2D and 3D methods was not statistically significant except for 12 (P = 0.04; Table 3). Furthermore, we considered 2D methods like periapical or panoramic radiographs used to measure EARR and evaluated them together. Almost all studies included in meta-analysis, except for Wong et al.9, considered either rRCR or calibration to control magnification error between two time points for their measurement to eliminate the potential bias. However, inconsistency between these 2D methods should be considered before interpreting results.
Limitations
One drawback is a lack of good-quality prospective studies, specifically RCTs in the literature. Most studies on EARR are retrospective in nature. Further research encompassing extraction cases, as well as assessing other parameters like skeletal or dental malocclusion are needed to better evaluate the incidence and severity of root resorption following the use of CAT and PEA. However, there are no studies evaluating EARR in extraction cases with CAT. Another limitation of this study would be the accuracy of the measurements of the tooth length on 2D radiographs or CBCT images. We tried to overcome this limitation by analyzing the 2D and CBCT studies separately and comparing them with each other.
In the absence of randomized controlled trials, a meta-analysis from good quality prospective and retrospective studies will be the highest form of evidence to definitively answer the question of the amount of EARR with PEA and CAT. However, the results from this meta-analysis should be used in conjunction with sound clinical judgement.
Conclusions
On the basis of this systematic review and meta-analysis, we concluded:
Neither PEA nor CAT technique lead to clinically significant root resorption (up to 1 mm) of the permanent maxillary incisors.
The amount of EARR of permanent maxillary incisors is non-significant on comparing two treatment modalities (PEA and CAT), except for 12 where the PEA group has significantly more EARR as compared to CAT.
CBCT shows a decreased magnitude of EARR than 2D radiographs, and that is why 2D radiographs may overestimate the amount of EARR with orthodontic treatment.
Supplementary Material
Supplementary material
Supplementary materials are available at European Journal of Orthodontics online.
1. Supplemental Figure 1. Funnel plots for the evaluation of the publication bias.
2. Supplemental Table 1. Summary of included studies: aim of study, mean treatment duration, method of measurement, and outcomes.
3. Supplemental Table 2. Results showing the heterogeneity among studies in each subgroup.
4. Supplemental File: List of studies included in the systematic review
Funding
This study was supported by National Institutes of Health (KO8DEO25914 to S.Y.).
Conflicts of interest
None to declare.
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