INTRODUCTION

In daily orthodontic practice, root resorption continues to be a complex, significant challenge.¹ Over the years, a good deal of research has been devoted to this topic^2–4 of critical medical and legal importance in orthodontics. Nevertheless, still no consensus exists on the optimal diagnostic method for this pathology or on the most effective approach to measure its severity.⁵

In the orthodontic literature, various methods of assessing root resorption have been explored, ranging from traditional diagnostic radiography to three-dimensional (3D) methods using cone-beam computed tomography (CBCT).⁶ Nevertheless, lateral, panoramic, and periapical radiographs are still the types most commonly used for orthodontic diagnostics in everyday clinical practice.^7,8

In a historical review of the literature, a variety of measurement methodologies have been used to diagnose and assess the severity of root resorption, ranging from elementary techniques⁹ to more sophisticated methods involving complicated mathematical formulas,¹⁰ or even software analysis.¹¹ Other methods^12,13 provide a nuanced classification of the severity of external apical root resorption (EARR) based on a perceptual assessment of the apex by an observer. These measurement methods are important in determining and classifying the extent of EARR in the individual patient, as they elucidate the specific risk factors for as well as those that protect against the occurrence, severity, and development of EARR.

Several patient-related factors, such as age,⁶ malocclusion,¹⁴ and genetic predisposition,¹⁵ have been associated with EARR, with some degree of conflicting results. Treatment duration has been identified in several meta-analyses as a significant treatment-related predisposing factor associated with EARR occurrence and severity.^6,16 However, substantial variability exists among studies regarding its impact, likely due to differences in methodology, measurement techniques, and sample characteristics.¹⁷

The complexities of diagnosing and measuring EARR present a significant challenge in making sense of the best scientific evidence currently available in orthodontics. The uncertainty regarding the influence of EARR diagnostic processes on associated risk-factor predictors highlights critical knowledge gaps. The aim of this paper was to conduct and provide a comprehensive scoping review of EARR diagnoses made using panoramic and periapical radiographs, the two methods most commonly used in clinical practice. Secondary aims included enhancing understanding and informing clinical practice by critically evaluating the measurement methods used, the severity spectrum, and the influence of different approaches on the association with treatment duration.

MATERIALS AND METHODS

Data Extraction

Data extraction was conducted by one reviewer (P.I.D.) and verified by a second reviewer (A.O.P.). Data were divided into two categories: panoramic versus periapical radiographs, further subdivided by measurement method and whether EARR results were reported in percentages or millimeters. The variables recorded are described in Tables 1 and 2.^{3,4,8,9,11,13,21–56}

Table 1.Characteristics of Included Studies That Used Panoramic Radiography for the Diagnosis of External Apical Root Resorption (EARR)^a

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Table 2.Characteristics of Included Studies That Used Panoramic Radiography for the Diagnosis of External Apical Root Resorption (EARR)

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RESULTS

Search Results

The search strategy yielded 704 studies, of which 3 were duplicates. Following the PCC criteria, screening by title and abstract yielded 389 articles for full-text review, and 40 studies were finally included in this review.^{3,4,8,9,11,13,21–54} The PRISMA flowchart in Figure 1 illustrates the process. Reasons for exclusion are summarized and described in Appendix 2.

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EARR (Definition and Threshold Values, Type of Results, and Severity)

A bewildering array of techniques and perspectives exists for diagnosing and estimating EARR. While some researchers set the threshold for defining EARR at 2 mm⁴² of apical root loss, others⁵² considered even minimal losses of 1.20 mm as significant. Surprisingly, some even suggested the onset of EARR as early as 0.1 mm.^41,49 The adoption by some investigators of severity scales of Malmgrem et al.¹² or Sharpe et al.¹³ introduced further complexity into the assessment of EARR.

The EARR results compiled in Figure 2 provide interesting data and insights into the diagnosis of EARR. The findings are mostly presented in millimeters or percentages and vary from study to study. More particularly, Chen et al.²⁴ and Qin et al.⁴ reported minimal mean EARR values (0.32 ± 0.14 mm), which contrasted with Lee et al.,¹¹ who reported notably higher measurements (2.9 ± 2.4 mm). In terms of percentage measurements, Picanço et al.³¹ reported the lowest EARR (0.17% ± 0.09), whereas Zahedani et al.³⁸ reported the highest (16.87%).

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DISCUSSION

After reviewing the results of this study, it was clear from the literature that no common criteria existed for the diagnosis of EARR. Some authors²⁵ used periapical radiographs for diagnosis, whereas others⁵⁴ used panoramic radiography. Different methods for EARR measurement were reported, some using the incisal edge as a correction factor (CF)²⁵ and others⁵⁴ using the modified Linge and Linge³ method by Brezniak et al.¹⁰ The assessment method also varied, with some expressing results in millimeters and others reporting EARR in percentages. With all of the differences in diagnostic techniques, measurement methods, and units, it could be concluded that the discrepancies in the scientific literature came from many different sources.

It should be noted that the study designs of the included studies did not differ, but notable differences existed in sample size among the studies and a wide range of teeth examined in each study; this could compromise the representativeness of the results. To mitigate these differences and strive for consistency, in this study, we only included studies that focused on maxillary incisors, which are not only the teeth most commonly used in studies focusing on EARR but are also more prone to EARR.¹⁴ Additionally, treatment duration has been extensively discussed in the literature as a factor influencing EARR, and considerable variability existed in the findings. Due to this, in the current review, only studies that reported full treatment duration from initiation to completion were included to ensure consistency and avoid biases from partial treatment evaluations.^6,16,17

The use of CBCT is currently not a feasible alternative to routine panoramic views, mainly for economic and ethical reasons, particularly in young patients.^8,58 Consequently, panoramic and periapical radiographs are still the preferred imaging modalities for diagnostic purposes and for routine assessment of root resorption.⁸ Nevertheless, some concerns have been raised regarding the potential overestimation of root loss by panoramic radiographs compared with intraoral radiographs, with authors of some studies suggesting an overestimation of 20% or more.³⁴ In the present study, panoramic radiographs showed an average EARR of 1.49 mm compared with 1.22 mm in periapical radiographs. It should be noted, however, that this difference could be attributed to possible overestimation by panoramic radiographs or to inherent variability in the results of the studies themselves. This could be attributed, in part, to proclination of the upper incisors, which was not verified by measuring proclination on cephalometric radiographs. Hence, it would be of great interest to include incisor proclination as a factor in the formula for calculating resorption when using panoramic radiographs to diagnose EARR.⁵⁹

The use of different measurement methods in different studies is a significant source of bias when interpreting the results. Katona (2007)⁶⁰ demonstrated that compensatory algorithms for EARR assessment, including assumed parallel x-ray beams, resulted in inaccuracies when the source was at a finite distance. As these methods remain widely used, their limitations must also be acknowledged when analyzing contributing factors. However, it should be noted that the cementoenamel junction (CEJ) can be used as a reliable landmark for correction, and some authors³⁴ concluded that its identification is often challenging in radiographs. Despite this, authors of a surprising 62% of the studies analyzed in this review used it to diagnose EARR. Some authors²⁵ used a metal ball cemented to the tooth, whereas others⁴¹ used the mesiodistal size of the molar.

The lack of consistency in the current literature highlights the urgent need for consensus on EARR diagnostic methods, measurement techniques, and interpretation criteria. Variability across studies leads to discrepancies in prevalence rates and treatment outcomes, hindering the creation of standardized clinical protocols. Collaborative efforts among researchers, clinicians, and professional organizations are essential to develop universally accepted guidelines for imaging modalities, measurement standardization, and clear criteria for EARR severity. Establishing these standardized protocols will enhance research comparability, improve diagnostic accuracy, and facilitate better monitoring and management. Given the discrepancies in imaging modalities and measurement techniques, prioritizing periapical radiographs and incorporating cephalometric analysis to account for incisor proclination could improve diagnostic reliability. A unified approach will strengthen clinical decision-making and lead to more effective prevention and management strategies in orthodontic practice.

The findings revealed a notable lack of consensus among the authors of the studies reviewed regarding the diagnosis and methods of measurement of root resorption (EARR). In addition, the variability of the measurement techniques suggests that no single method consistently provides comparable results. This inconsistency poses a major challenge to the accurate assessment and management of root resorption in clinical practice. Resolving this issue is critical to improving diagnostic accuracy, treatment planning, and ultimately, patient outcomes in orthodontic care. Future researchers should focus on standardizing diagnostic protocols and refining measurement techniques to establish a more uniform approach for assessing root resorption using two-dimensional (2D) radiography.

CONCLUSIONS

• In the orthodontic literature, a wide range of assessment methods for EARR has been described, from traditional 2D and 3D radiographic techniques to innovative approaches such as biomarker-based detection or aided by artificial intelligence.

• Considerable variability exists in the methods used to measure EARR across studies, with some using CFs and others relying on perceptual assessment to classify severity.

• Patient- and treatment-related factors such as treatment duration are inconsistently associated with the development of EARR.

• Standardization of diagnostic criteria, measurement methods, and severity classification is essential to increase reliability and comparability between studies and to improve clinical management of EARR.

SUPPLEMENTAL DATA

Appendices 1 through 3 are available online.