Apical root resorption is an undesirable effect, common in orthodontic treatment, that leads to permanent loss of dental structure. The clinical diagnosis of this condition is predominantly based on routine radiographic procedures such as periapical or panoramic radiographs. However, these methods are limited because they produce bidimensional images of a tridimensional structure, leading to labiolingual superimposition of the whole root structure. This limitation can jeopardize the diagnosis of root resorption because radiographic images might underestimate the extent of the apical root resorption lesion.

The advent of tridimensional images brought about the perspective of a precise quantitative evaluation that permits differentiating the levels of root resorption in various root surfaces.

Cone-beam computed tomography (CBCT) is an efficient technique to obtain data of dental structures. This method provides images in slices of the dental roots that eliminate superimposition of structures and show different levels of resorption on the labial and lingual surfaces, demonstrating it to be a precise tool in the diagnosis of root resorption lesions. In addition, it has the advantage of a much lower radiation burden to the patient when compared with conventional computed tomography.

In 1982, Malmgren et al created a quantitative evaluation index of apical root resorption made up of the following scores: irregular apical contour, apical root resorption less than 2 mm (minor resorption), apical root resorption from 2 mm to a third of the original root length (severe resorption), and apical root resorption exceeding a third of the original root length (extreme resorption). However, qualitative or quantitative classifications applicable to sagittal radiographic images of apical root resorption lesions could not be found in the literature.

Since the visualized images on periapical radiographs reflect the superimposition of the whole root structure, underestimating the extent of the resorption lesion, in this study, we aimed to determine, in sagittal images of CBCT, the lengths of the labial and lingual surfaces of the incisors with a diagnosis of apical root resorption by comparing them with the longest root length, and to create a qualitative visual scale for the classification of the images of apical root resorption.

Material and methods

The sample comprised 82 incisors with apical root resorption from 25 patients (14 female, 11 male; age range, 13-41 years; mean age, 20.4 years) having orthodontic treatment with fixed edgewise appliances and selected based on the diagnosis of apical root resorption in at least 1 maxillary incisor by means of follow-up periapical radiographs. In the pretreatment records, these patients did not have maxillary incisors with apical root resorption, root morphologic alterations, or history of trauma. This study was approved by the Human Research Ethics Committee of Juiz de Fora Federal University in Brazil.

The images were obtained with CBCT (i-CAT; Imaging Sciences International, Hatfield, Pa), operated at 120 kVp and 3-8 mA, voxel size of 0.4 mm, and a field of view of 160 × 100 mm, and analyzed with the software i-CAT Vision (Imaging Sciences International) with 0.5-mm-thick slices on the multiplanar reconstruction visualization mode.

The sagittal image selected for the analysis of each incisor was the one obtained from the sagittal cut of the mesiodistal center of the root and perpendicular to the incisal border ( Fig 1 ). Three points of reference were determined: L, the most apical point of the labial surface of the root from which apical root resorption begins; Li, the most apical point of the lingual surface of the root from which apical root resorption begins; and A, the most apical point of the tooth root. A horizontal line (line CE) was drawn passing through the median point of the labial and lingual cementoenamel junctions and perpendicular to the long axis of the tooth root. The lengths of the labial and lingual surfaces were determined, respectively, by the distance between points L and Li and their orthogonal projections on line CE. In the same way, the longest root length was determined by the distance between point A and its orthogonal projection on line CE ( Fig 2 ). The shortest root length was determined by the dimension of the shortest of either the labial or the lingual root surface.

Multiplanar reconstruction visualization mode screen on sagittal cut.

Sagittal cut of the maxillary incisor showing line CE, points L, Li, and A, and their respective orthogonal projections on line CE.

All root measurements of 15 randomly selected incisors were evaluated at 2 times in a 3-week interval and compared for determination of the average errors.

We created a qualitative visual scale for classifying the sagittal appearance of the apical root resorption lesions ( Fig 3 ), and its reproducibility was then determined. Sagittal cut images of the 82 incisor were selected, and the apical root resorption lesions were classified by 5 orthodontists according to a visual scale at 2 times, with an average interval of 30.6 days between them. The observers received no additional information or previous training and did not participate in the construction of the visual scale and the measurement of the incisors. During the second evaluation, the order of the radiographs was randomly changed in relation to the first one.

Visual scale representing the classifications of apical root resorption of the incisors in sagittal cuts: type 1, flat apical root resorption; type 2, flat apical root resorption associated with superficial resorption on the lingual surface; type 3, flat apical root resorption associated with superficial resorption on the labial surface; type 4, apical root resorption associated with superficial resorption on the labial and lingual surfaces; type 5, diagonal apical root resorption in the labiolingual direction; type 6, diagonal apical root resorption in the lingual-labial direction.