The current status of cone beam computed tomography imaging in orthodontics

Abstract

Cone beam CT (CBCT) has become an increasingly important source of three dimensional (3D) volumetric data in clinical orthodontics since its introduction into dentistry in 1998. The purpose of this manuscript is to highlight the current understanding of, and evidence for, the clinical use of CBCT in orthodontics, and to review the findings to answer clinically relevant questions. Currently available information from studies using CBCT can be organized into five broad categories: 1, the assessment of CBCT technology; 2, its use in craniofacial morphometric analyses; 3, incidental and missed findings; 4, analysis of treatment outcomes; and 5, efficacy of CBCT in diagnosis and treatment planning. The findings in these topical areas are summarized, followed by current indications and protocols for the use of CBCT in specific cases. Despite the increasing popularity of CBCT in orthodontics, and its advantages over routine radiography in specific cases, the effects of information derived from these images in altering diagnosis and treatment decisions has not been demonstrated in several types of cases. It has therefore been recommended that CBCT be used in select cases in which conventional radiography cannot supply satisfactory diagnostic information; these include cleft palate patients, assessment of unerupted tooth position, supernumerary teeth, identification of root resorption and for planning orthognathic surgery. The need to image other types of cases should be made on a case-by-case basis following an assessment of benefits vs risks of scanning in these situations.

Figure 1

Rendered images from cone beam CT (CBCT) scans provide details in three dimensions for precise location of impacted canines and identifying associated root resorption as well as optimal planning for retrieving impacted teeth. (a) A panoramic radiograph provides limited information on the exact location of the canines and their relationship to the roots of the incisors. In contrast, (b) the occlusal, (c) frontal and (d) superior CBCT images of bilateral impacted canines show the presence of root resorption on both lateral incisors. These images also provide important information to the clinician on the best surgical approach, appropriate placement of the bonded attachments and planning of biomechanics. In this case the direction of movement of the canines should, initially, be distally away from the lateral incisor roots before moving these teeth into the arch. The left canine was more rotated and may require a different location for attachment placement compared with the right canine

Figure 2

Use of cone beam (CBCT) in diagnosis and treatment planning of transposed teeth. A case demonstrating transposed roots of the maxillary canines and first premolars in which CBCT reveals that the canine root is buccal to the premolar root. Evaluation of these (a) CBCT derived three-dimensional and (b,c) two-dimensional cross-sectional images may help the clinician to optimize treatment planning. This includes proactively moving tooth roots out of the path to be used and to relocate the transposed tooth or root, determining if the boundary conditions will permit such movement, planning the biomechanics (including the force systems, types and direction of movements), which together define the prognosis of moving transposed teeth or roots past each other

Figure 3

Cone beam (CBCT) images offer important information for the finer details in treatment planning of supernumerary teeth. (a) The panoramic view shows the presence of a supernumerary tooth in the maxillary right lateral incisor area with delayed eruption of the maxillary right central incisor. It is difficult to discern from the panoramic view (or from periapical radiographs, not shown) which of the two teeth, marked with an asterisk and arrow head, would be morphologically optimal to serve as the lateral incisor. Since the contralateral lateral incisor has not yet erupted, it cannot be examined clinically for size and form for comparison. Various three-dimensional views from CBCT scans (b,c,d) allow the comparison of the two teeth in the maxillary right lateral incisor area with the unerupted upper 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 morphology and dimensions of contralateral lateral incisor while the tooth marked with an arrowhead is almost 1 mm larger mesiodistally than the contralateral lateral incisor

Figure 4

The use of cone beam CT (CBCT) in the diagnosis of root morphology and boundary conditions. (a) Panoramic view of a patient with bimaxillary protrusion, which owing to its two-dimensional perspective, does not provide information on any potential buccolingual boundary limitations and suggests a near normal length of the roots of the maxillary anterior teeth (crown:root ratio of approximately 1:2). In contrast, the sagittal cross-sections along the long axis of the central incisors (b,d) as well as the three-dimensional reconstruction (c) show that the roots of the incisors are short (crown:root ratio of 1:1). Also, the boundary conditions particularly in the mandible where the labio-lingual width of the roots of the anterior teeth approximate the width of the cortical bone housing, would likely limit the clinician's ability to retract teeth. Despite orthodontic indications for extraction of four first premolars and high anchorage to retract maximally the incisors, the limits imposed by the short roots and boundary conditions resulted in a different treatment approach involving non-extraction treatment and a possible genioplasty at a later date

Figure 5

CBCT provides novel information on boundary conditions that are not discernable from routine radiographs or during clinical examination, which may impact on treatment options. (a) Pre-treatment coronal view showing the lingual inclination (arrows) of maxillary premolars and proximity of their buccal roots of the to the cortical bone margin (arrowheads). (b) Post-treatment coronal view demonstrating that the limitations offered by the boundary conditions bone-root relationships have been addressed through lingual torquing of the roots such that the torque of these teeth more closely matches the inclination of the cortical and alveolar process of the maxilla. (c) Sagittal and (d) occlusal views from CBCT scans of an individual with severe limitations in boundary conditions where the cortical bone margins are incapable of sustaining orthodontic movements in any plane of space. Orthodontic treatment would be contraindicated in this case

Figure 6

Cone beam CT provides concurrent assessment of temporomandibular joint (TMJ) morphological changes and related discrepancies in craniofacial morphology as well as maxillomandibular and interarch dental relationships. (a) A patient with chronic degenerative TMJ disease of the right TMJ as well as (c) left condylar hyperplasia presents with an asymmetric Class II relationship. The height differences between the right and left condyles seen on the two dimensional cross-sectional views can be better related to each other and to maxillomandibular relationships on the three dimensional rendered view (b), which also demonstrates the asymmetric mandible and compensatory inclinations of the posterior and anterior mandibular teeth. This information may be important to the oral surgeon and orthodontist in planning, preparing for and performing orthognathic surgery