Indications for CBCT Use

The ability to capture three-dimensional (3D) dental and skeletal relationships is a tremendous benefit in the specialty of orthodontics, and cone-beam computed tomography (CBCT) provides this advantage at a relatively low cost. The diagnostic capabilities of CBCT are far more advanced than traditional two-dimensional (2D), or traditional, radiography. As dental hygienists are leaders in patient education, it is important they understand how CBCT is used in orthodontic treatment. This article will discuss specific indications for CBCT in orthodontics.

DEVELOPMENTAL ANOMALIES IN DENTAL POSITION

CBCT imaging has indications for the assessment and diagnosis of a number of specific conditions in orthodontic patients.^1–4 Developmental anomalies of tooth structure can lead to disturbances in maxillary and mandibular dental arch lengths, occlusal arch discrepancies resulting in crowding and poor esthetics, and inter-arch differences producing malocclusions. These anomalies may have local or more generalized effects, producing regional or more widespread disturbances. Developmental anomalies include variations in tooth morphology (eg, fusion, gemination, microdontia, or peg-shaped maxillary and mandibular lateral incisors, macrodontia, dilacerated tooth, and transposed roots); number (eg, oligodontia, hypodontia, or congenitally missing maxillary lateral incisors, mandibular incisors and canines, and maxillary and mandibular premolars, and hyperdontia, or supernumerary teeth, as seen in Figure 1); and structure (eg, internal root resorption or congenital conditions affecting the entire dentition, such as amelogenesis imperfecta).

Imaging can play a role in the evaluation of impacted teeth, commonly the mandibular third molars or maxillary canines (Figure 2); the presence of unerupted and impacted supernumerary teeth, like the mesiodens seen in Figure 1; anomalies in dental eruption sequence; and ectopic eruption, including teeth associated with jaw clefts. Visualization of these conditions can assist in decisions, such as whether to remove the tooth, and on surgical approaches and techniques. Important information includes determining the size of the crown of the tooth; localizing the position of the tooth, such as inclination of the long axis of the tooth; relative buccal and palatal positions; the amount of bone covering the tooth; determining the effect on adjacent teeth, such as resorption of the roots of adjacent teeth and the condition of adjacent teeth; identifying local anatomic surgical considerations, such as location of the nasopalatine canal, mental foramen, or inferior alveolar canal; determining the overall stage of dental development; and the assessment of associated pathology.

DENTO-ALVEOLAR MORPHOLOGY

The width of the alveolus of the jaws defines anatomic facio-palatal/lingual boundaries for orthodontic torque movement of teeth, or retraction, arch expansion, or labial movement of incisors (Figure 3). Evaluation of fenestrations and dehiscence on the buccal and lingual surfaces can be an important consideration in certain patients, such as those with bimaxillary protrusion, compromised periodontal status, and/or clefts of the alveolus. In addition, determination of dento-alveolar volume is important for patients who are potential candidates for dental implants, bone grafts, or temporary anchorage devices.^2,5,6

DENTOFACIAL DEFORMITIES AND CRANIOFACIAL ANOMALIES

Three-dimensional volumetric imaging is a particularly useful tool in the analysis of severe skeletal discrepancies producing facial or mandibular asymmetry (Figure 4), and anteroposterior, vertical, and transverse deficiencies, as well as an assessment of their dental effects.^7–13 Appreciation of the complexity of these abnormalities demands visualization of the inter-relationships of the dental, skeletal, and soft tissue elements. CBCT data can be exported to specific software programs that can be used for virtual treatment simulations to plan orthopedic corrections, such as orthognathic surgery or distraction osteogenesis.

MALOCCLUSIONS AND SKELETAL DISCREPANCIES

Identification of Class II and Class III skeletal malocclusions (Figure 5)^8,14–16 and increased or decreased vertical facial height and asymmetry,¹⁷ either alone or in combination, involves an appreciation of the contribution of maxillary and mandibular anterior-posterior, vertical, and transverse discrepancies that are well-visualized with CBCT images. These anomalies may present clinically as the following: chin or mandibular deviation; dental midline deviation; occlusal cant (tilt) discrepancies; anterior open bite; deep overbite; skeletal lingual or buccal crossbites; or excessive dental compensation of the bucco-lingual inclination of posterior teeth.

TEMPOROMANDIBULAR JOINT

Visualizing the morphology of the temporomandibular joint (TMJ) articulation can be necessary if orthopedic treatment is anticipated that may affect structural development during growth—such as head gear, functional appliances, or if the patient has a history of previous condylar trauma (Figure 6). TMJ pathologies that result in alterations in the size, form, quality, and spatial relationships of the osseous joint components may lead to skeletal and dental discrepancies, such as progressive bite changes, including bite opening and limitation; deviation upon opening or closing; and changes in tooth position, occlusion, and the TMJ of the unaffected side. Such TMJ instabilities can lead to unpredictable orthodontic outcomes.

Affected joints are particularly important to image in patients with diminishing quality of life issues, such as persistent pain or limited opening. TMJ conditions include developmental disorders such as condylar hyperplasia, hypoplasia, or aplasia, and patients with moderate to severe arthritic degeneration. In these situations, CBCT imaging provides additional diagnostic information, such as the size, shape, and position of mandibular condyle heads in established positions and the presence of active disease that may influence management.

POST-THERAPY AND AIRWAY ASSESSMENT

CBCT may be useful in assessing the treatment outcomes of orthognathic surgery, grafting procedures, and the use of nonsurgical devices to affect vertical or transverse discrepancies (Figure 7).^2,5

CBCT imaging also can be used to assess the airway—particularly for patients with obstructive sleep apnea (OSA)/hypopnea syndrome—but measurements should be interpreted with caution (Figure 8). For these individuals, CBCT images of the airway are most often acquired in the standing or seated position, whereas imaging should ideally be made with patients in the supine position. Although a number of studies have measured airways and changes in airways over time (particularly with regard to OSA), the reliability and validity of such measurements present a number of challenges. The boundaries of the nasopharynx with the maxillary/paranasal sinuses and the boundaries of the oropharynx with the oral cavity are not consistent among subjects and image acquisitions, and airway shapes and volumes vary markedly with dynamic processes, such as breathing and head postures.^18–20

PATHOLOGY

CBCT imaging demonstrates the location, size, shape, extent, and full involvement of pathology of the jaws. Various conditions which may be encountered—most commonly infections (Figure 9), benign cysts, and tumors of the jaws—may require surgical intervention prior to orthodontic therapy.

SUMMARY

CBCT is a valuable supplemental imaging modality to 2D radiography for the assessment and diagnosis of many specific conditions in the orthodontic patient. While evidence does not currently support CBCT imaging as a replacement for extraoral (lateral cephalometric and panoramic) radiography in orthodontics, it serves a valuable purpose in the diagnosis, treatment, and post-therapy stages of orthodontic treatment. CBCT imaging in orthodontics, however, should be used prudently, as it emits more radiation than traditional radiography. Its use among children should be very conservative, as their radiation risk is three to five times greater than that of adults for the same exposure.^21–23

ACKNOWLEDGMENT

Some of this information was provided with permission from the American College of Radiology (ACR) and taken from the ACR Appropriateness Criteria^®. The ACR is not responsible for any deviations from the original ACR Appropriateness Criteria content.

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From Dimensions of Dental Hygiene. September 2014;12(9):71–74.