CBCT in orthodontics: assessment of treatment outcomes and indications for its use

Abstract

Since its introduction into dentistry in 1998, CBCT has become increasingly utilized for orthodontic diagnosis, treatment planning and research. The utilization of CBCT for these purposes has been facilitated by the relative advantages of three-dimensional (3D) over two-dimensional radiography. Despite many suggested indications of CBCT, scientific evidence that its utilization improves diagnosis and treatment plans or outcomes has only recently begun to emerge for some of these applications. This article provides a comprehensive and current review of key studies on the applications of CBCT in orthodontic therapy and for research to decipher treatment outcomes and 3D craniofacial anatomy. The current diagnostic and treatment planning indications for CBCT include impacted teeth, cleft lip and palate and skeletal discrepancies requiring surgical intervention. The use of CBCT in these and other situations such as root resorption, supernumerary teeth, temporomandibular joint (TMJ) pathology, asymmetries and alveolar boundary conditions should be justified on the basis of the merits relative to risks of imaging. CBCT has also been used to assess 3D craniofacial anatomy in health and disease and of treatment outcomes including that of root morphology and angulation; alveolar boundary conditions; maxillary transverse dimensions and maxillary expansion; airway morphology, vertical malocclusion and obstructive sleep apnoea; TMJ morphology and pathology contributing to malocclusion; and temporary anchorage devices. Finally, this article utilizes findings of these studies and current voids in knowledge to provide ideas for future research that could be beneficial for further optimizing the use of CBCT in research and the clinical practice of orthodontics.

Keywords: CBCT; cone beam computed tomography; evidence-based diagnosis; orthodontics; three-dimensional imaging; treatment planning and treatment outcomes.

Figure 1

Distinctions between iterative closest point (ICP) and shape correspondence in determining growth and treatment changes in craniofacial structures. Diagrammatic representation of ICP (a) and shape correspondence (b) used to compute surface distances to quantify longitudinal changes for example shown here for condylar displacement. The closest points are linear distances (shown as lines), while the shape correspondence measurements are vectors (shown as lines with direction represented by arrows). Note that the closest surface points fail to quantify the displacement when large translational changes occur. Reproduced from Hajati et al, Copyright © 2014, John Wiley and Sons.

Figure 2

Depiction of post-surgical three-dimensional changes in the mandible using cranial base superimposition and either iterative closest point or shape correspondence for the same patient to demonstrate how these methods result in different visual representation of treatment outcomes. (a) Semi-transparency superimposition provides a visual assessment of treatment outcomes, but the changes cannot be quantified. (b) Colour-coded map of the closest point method where blue represents inward and red outward changes with the magnitude of change shown in the accompanying colour scale. (c) Outcomes assessment with shape correspondence method depicts a colour-coded map and vectors that provide the direction and magnitude of the displacement. (d) A zoomed-in image of the chin to demonstrate the vectors from (c) in greater detail. Reproduced from Kim et al, Copyright © 2014, John Wiley and Sons. For colour images see online: www.birpublications.org/doi/pdf/10.1259/dmfr.20140282.

Figure 3

Clinical scenarios in which the use of CBCT may be indicated on the basis of research evidence or case- or clinical judgment-based determination of the need for imaging. All three levels of indicators require a careful consideration of the benefit-to-risk analyses prior to undertaking CBCT. Reproduced from Kapila, Copyright © 2014, John Wiley and Sons. dx, diagnosis; TAD, temporary anchorage device; TMJ, temporomandibular joint; tx, treatment.

Figure 4

Pre-treatment images derived from CBCT of a patient with retained mandibular primary second molars and impacted second premolars. (a) Reconstructed panoramic radiograph shows a distally impacted mandibular right second premolar and mesially impacted mandibular left second premolar. The precise spatial positions of the mandibular second premolars and their relationships to neighbouring structures can be determined from axial (b, c), sagittal (d, e) and three-dimensional volumetric (f) reconstructions to develop a virtual treatment and biomechanical plan. Reproduced from Kapila and Nervina, Copyright © 2014, John Wiley and Sons.

Figure 5

Utility of CBCT in diagnosis of localization of impacted teeth and identification of associated root resorption. Two-dimensional images are prone to superimposition and other limitations, which may be overcome with CBCT that can be useful in identifying the precise location of the impacted tooth, its relationship with other structures and any associated root resorption. In this case, pre-treatment panoramic (a) and periapical (b) radiographs are not adequate for precise location of the impacted tooth or discerning if root resorption truly is present. Approximately a year into treatment and failure of tooth to erupt, a CBCT scan was taken revealing the proximity of the impacted tooth to the lateral incisor and substantial root resorption on the lateral incisor as seen here in sagittal (c), axial (d), coronal (e) and lateral (f) volumetric representations. Given the lack of pre-treatment CBCT, it is not possible to determine the extent of pre-treatment root resorption or the contributions of treatment to the current root damage. However, because of the position of the bond on the tooth cingulum and despite desirable force vectors, it is likely that the cusp tip has continued to move along the root of the lateral incisor contributing to root resorption and difficulty in retrieval. Reproduced from Kapila and Nervina, Copyright © 2014, John Wiley and Sons.

Figure 6

CBCT offers important information and finer details in treatment planning of supernumerary teeth. (a) The panoramic view extracted from the CBCT scan shows the presence of a supernumerary tooth in the upper right lateral incisor area with delayed eruption of the maxillary right central incisor. It is difficult to discern from the panoramic view (or even from periapical radiographs, not shown) which of the two teeth, marked with an asterisk and arrowhead would be optimal morphologically to serve as the lateral incisor. Since the contralateral lateral incisor has not erupted yet, it cannot be examined clinically for size and form for comparison. (b–d) Various three-dimensional views from CBCT scans allow the comparison of the two teeth on the right lateral incisor area with the unerupted left lateral incisor. An analysis of the mesiodistal measurements of these unerupted teeth revealed that the tooth marked with an asterisk most closely matches the contralateral lateral incisor morphologically and dimensionally, while the tooth marked with an arrowhead is almost 1 mm larger mesiodistally than the contralateral lateral incisor. Reproduced from Kapila et al.

Figure 7

CBCT images of incisors with thin alveolar boundary condition biotype before (a–e) and after (f–j) non-extraction orthodontic treatment involving anterior expansion and flaring of the incisors. Sagittal sections along the long axis of the mandibular left lateral (a, f), left central (b, g), right central (c, h) and right lateral (d, i) incisors show considerable loss of alveolar buccal bone following treatment. Pre- and post-treatment axial slices (e, j) demonstrate protrusion of mandibular incisors at the end of orthodontic treatment. To make valid comparisons, the sections in post-treatment images were taken as close as possible to those in pre-treatment images. Reproduced from Kapila and Nervina, Copyright © 2014, John Wiley and Sons.

Figure 8

Pre-treatment CBCT images of a patient with bilateral complete transpositions of the maxillary canines and first premolars demonstrate the possible restrictions placed by boundary conditions on treatment options. Three-dimensional volumetric reconstructions of the buccal aspect of the right (a) and left (b) sides showing the complete transpositions of the canines and first premolars and detailing the spatial positions of the transposed teeth and their relationships to each other and neighbouring structures. (c) Coronal section demonstrating the proximity of the roots of the translocated teeth to each other and to alveolar boundaries. Lines d, e and f in this panel represent locations at which axial cross-sections of the images, depicted in d, e and f, respectively, were reconstructed to visualize the relationships of the crowns and roots of the transposed teeth to each other. Axial section at mid-crown (d), cemento-enamel junction (e) and mid-root (f) of the transposed teeth demonstrate details of tooth–tooth and tooth–bone relationships. These images can be used to establish the treatment decisions on extractions if needed, and in non-extraction cases, whether to retain the transposed teeth closest to the current locations or move them into their correct locations in the arch. The images are also useful for biomechanics planning in any of the latter two treatment options that may include proactively moving tooth roots out of the path to be used to relocate the transposed tooth or root, determining if the boundary conditions will permit such movements, planning the force systems, and vector(s) of movements. These considerations taken together can help define the prognosis of moving transposed teeth or roots past each other to arrive at the optimal treatment choice. Reproduced from Kapila and Nervina, Copyright © 2014, John Wiley and Sons.

Figure 9

Volume rendering of CBCT scans of an individual with a unilateral cleft lip and palate (a) before and (b) after alveolar bone grafting. With CBCT imaging, assessing the morphology, locating the position and determining the developmental stage of the unerupted maxillary left canine (arrow) permit the orthodontist and surgeon to time the placement of the alveolar graft ahead of canine eruption. Sufficient lead time allows the graft to mature and gives the orthodontist sufficient time for arch development to better support the canine as it erupts into the arch. Reproduced from Oberoi et al, Copyright © 2014, John Wiley and Sons.

Figure 10

Statistical significance maps of correlations between local morphological differences in condylar shape and pain intensity. Significance maps show statistically significant correlations between pain intensity and morphologic differences in the superior surface of the condyle (a) and the lateral and posterior surfaces of the condyle (b). The colour scale at the bottom represents correlation p-values between pain and morphological variance in the condyle relative to an average condyle. Reproduced from Majati et al, Copyright © 2014, John Wiley and Sons. For colour image please online: www.birpublications.org/doi/abs/10.1259/dmfr/20140282.

Figure 11

Three-dimensional (3D) airway visualization in the lateral (a), three-quarter (b) and frontal (c) views. Both qualitative and quantitative assessments of the airway can be made by thresholding-specific tissue density either through features built into the software program as performed here, or by customized selection of a window of density to obtain refined and accurate 3D volumetric, cross-sectional area and linear measurements of the airway. Reproduced from Kapila, Copyright © 2014, John Wiley and Sons.