Journal of Interdisciplinary Dentistry

REVIEW ARTICLE
Year
: 2014  |  Volume : 4  |  Issue : 3  |  Page : 118--122

Add a third dimension to your patient care with cone beam computed tomography


Nandita Shenoy1, Junaid Ahmed1, Sanjay M Mallya2,  
1 Department of Oral Medicine and Radiology, Manipal College of Dental Sciences, Manipal University, Mangalore, Karnataka, India
2 Department of Oral and Maxillofacial Radiology, University of California, Los Angeles School of Dentistry Los Angeles, California, USA

Correspondence Address:
Junaid Ahmed
Department of Oral Medicine and Radiology, Manipal College of Dental Sciences, Manipal University, Mangalore, Karnataka, India

Abstract

Cone-beam computed tomography (CBCT) has been specifically designed to produce undistorted three-dimensional information of the maxillofacial skeleton, including the teeth and their surrounding tissues with a significantly lower effective radiation dose compared with conventional computed tomography. The revolutionary introduction of CBCT in all fields of dentistry is unprecedented as it has created a true paradigm shift from a conventional two-dimensional approach to a three-dimensional understanding. In doing so it has expanded the role of imaging from its traditional one in diagnosis to image guidance of operative and surgical procedures. Clinical Relevance To Interdisciplinary Dentistry
  • Detecting anatomical variants such as accessory neurovascular canals, bony undercuts, and local alterations in trabecular patterns, all of which influence implant treatment planning
  • Identification of root canal system anomalies and determination of root curvature for successful endodontic practice
  • Cone beam computed tomography, offers an opportunity to see inside the bone and pinpoint and measure densities in small localized areas such as a vertical periodontal defect or alveolar bone graft
  • Three-dimensional and cross-sectional evaluation of the implant patient and it allows virtual implant placement that can guide the implantologist in terms of density and thickness of the alveolar bone.



How to cite this article:
Shenoy N, Ahmed J, Mallya SM. Add a third dimension to your patient care with cone beam computed tomography.J Interdiscip Dentistry 2014;4:118-122


How to cite this URL:
Shenoy N, Ahmed J, Mallya SM. Add a third dimension to your patient care with cone beam computed tomography. J Interdiscip Dentistry [serial online] 2014 [cited 2019 Aug 22 ];4:118-122
Available from: http://www.jidonline.com/text.asp?2014/4/3/118/147328


Full Text

 INTRODUCTION



Radiographic imaging is essential in the diagnosis of a variety of dento-maxillofacial pathological conditions and provides valuable information for treatment planning and follow-up of a variety of dental and maxillofacial surgical procedures. The interpretation of a conventional two-dimensional image is usually confounded by a number of factors that include the regional anatomy and superimposition of adjacent structures. Intra oral periapical radiographs reveal a rather limited two-dimensional view of actual three-dimensional anatomy with a certain amount of geometric distortion being inherent. These problems can be overcome by utilizing cone-beam computed tomography (CBCT) imaging, which produces accurate three-dimensional images of the teeth and surrounding dentoalveolar structures. [1],[2],[3]

The revolutionary introduction of CBCT in all fields of dentistry is unprecedented as it has created a true paradigm shift from a conventional two-dimensional approach to a three-dimensional understanding. In doing so it has expanded the role of imaging from its traditional one in diagnosis to image guidance of operative and surgical procedures.

 Cone-Beam Computed Tomography Image Production



Imaging is accomplished by using a rotating gantry to which an X-ray source and detector are fixed. A divergent pyramidal-or cone-shaped source of ionizing radiation is directed through the center of the area of interest onto an area X-ray detector placed on the opposite side. [4] The X-ray source and detector rotate around a fulcrum fixed within the center of the region of interest. During the rotation, multiple sequential planar projection images of the field of view (FOV) are acquired in a complete or sometimes partial arc. This varies from a traditional medical computed tomography (CT), wherein a fan-shaped X-ray beam is used in a helical progression to acquire individual image slices of the FOV that are then stacked to obtain a three-dimensional representation [Figure 1], resulting in a prolonged and greater exposure. Current cone-beam machines scan patients in three possible positions: [5] (1) Seated, (2) standing, and (3) supine. Equipment that requires the patient to lie supine occupies a larger surface area and may not be feasible for patients with physical disabilities. Standing units may not be adjustable to a height that accommodates wheelchair-bound patients. Seated units are the most comfortable; however, fixed seats may not allow scanning of physically disabled or wheelchair-bound patients. The four components of CBCT image production are (1) acquisition configuration, (2) image detection, (3) image reconstruction, and (4) image display.{Figure 1}

 FIELD OF VIEW



Unlike medical CT, where we typically expose the patient for a full head scan even if the area of interest is a small portion of the jaw, in CBCT, a particular location can be selected and irradiated for diagnostics. Field size limitation, therefore, ensures that an optimal FOV can be selected for each patient based on disease presentation and the region designated to be imaged. The dimensions of the FOV or scan volume, are primarily dependent on the detector size and shape, beam projection geometry and the ability to collimate the beam. [3] Collimation of the primary X-ray beam limits X-radiation exposure to the region of interest. In general, the smaller the scan volume, the higher the resolution of the image and the lower the effective radiation dose to the patient.

 Advantages of Cone-Beam Computed Tomography In Dentistry



Cone beam computed tomography equipment is approximately one quarter to one fifth the cost of conventional CT.

Cone beam computed tomography provides images of highly contrasting structures and is, therefore, particularly well-suited for the imaging of osseous structures of the craniofacial area. The use of CBCT technology in clinical dental practice provides a number of advantages for maxillofacial imaging. [5]

 RAPID SCAN TIME



Because CBCT acquires all projection images in a single rotation, scan time is comparable to panoramic radiography, which is desirable because artifact due to subject movement is reduced.

 Beam limitation



Collimation of the CBCT primary X-ray beam enables limitation of the X-radiation to the area of interest. Therefore, an optimum FOV can be selected for each patient based on suspected disease presentation and region of interest.

 Three-Dimensional Volume Rendering



Volume rendering refers to techniques that allow the visualization of three-dimensional data through integration of large volumes of adjacent voxels and selective display. This view helps in surgical planning in orthognathic cases.

 APPLICATIONS IN DENTISTRY



Currently, CBCT is used most commonly in the assessment of bony and dental pathologic conditions, including fracture; structural maxillofacial deformity and fracture recognition; preoperative assessment of impacted teeth; temporomandibular joint imaging; and in the analysis of available bone for implant placement. In orthodontics, CBCT imaging is now being directed toward three-dimensional cephalometry. [2]

The availability of CBCT is also expanding the use of additional diagnostic and treatment software applications, all directed toward three-dimensional visualization, image-guided surgery. Diagnostic and planning software are available to assist in orthodontic assessment and analysis, implant planning, fabricate surgical models, facilitate virtual implant placement, computer-aided design and manufacture of implant prosthetics.

 Where can we use cone beam computed tomography in dental practice?



Dental implants

Assessing the need for augmentation of bone before implant placement in cases of increased bone resorptionLocating nerve canalsDetecting anatomical variants such as accessory neurovascular canals, bony undercuts, and local alterations in trabecular patterns, all of which influence implant treatment planning.

Oral and maxillofacial surgery

Impacted teethFractures of teeth and jawsDiagnosis of tumors and cysts of the jawExtent and spread of diseaseOrthognathic surgical proceduresPatients with cleft palate and other craniofacial developmental abnormalitiesProface scan.

Orthodontics

Displaced and impacted teethAnalysis of malaligned teeth and tooth position in the jawOrtho studio.

General dentistry

To get a three-dimensional picture of teeth and JawPeriodontal statusPatient consultationsRoot canal treatment failures and related complaints.

Ear, nose and throat application

Airway clearanceSinus related disorders.

Cone beam computed tomography in endodontics

For most endodontic applications, Small FOV CBCT is preferred for:

Identification of root canal system anomalies and determination of root curvatureDiagnosis of dental periapical pathosis in endodontically treated tooth with no evidence of pathosis identified by conventional imaging, and in cases where anatomic superimposition of roots or areas of the maxillofacial skeleton is required to perform task-specific procedures [Figure 2]Diagnosis of pathosis of nonendodontic origin in order to determine the extent of the lesion and its effect on surrounding structuresIntra- or post-operative assessment of endodontic treatment complications, such as overextended root canal obturation material, separated endodontic instruments, calcified the canal identification and localization of perforations [Figure 3]Diagnosis and management of dentoalveolar trauma, especially root fractures, luxation and/or displacement of teeth, and alveolar fracturesLocalization and differentiation of external from internal root resorption or invasive cervical resorption from other conditions, and the determination of appropriate treatment and prognosisPresurgical case planning to determine the exact location of root apex/apices and to evaluate the proximity of adjacent anatomical structures.Cone beam computed tomography for periodontal defect measurements
The extent of periodontal marginal bone loss is not always easy to determine and certainly not the extent with which furcation areas are involved. CBCT images provide better diagnostic and quantitative information on periodontal bone levels in three-dimensions than conventional radiography. CBCT is found to be as accurate as direct measurements using a periodontal probe and as reliable as radiographs for interproximal areas. Although two-dimensional radiography is of use for interproximal lesions, its limitation was anticipated during early investigations, determining its diagnostic value for periapical and periodontal disease. Hence, when buccal and lingual defects cannot be diagnosed with radiography, CBCT is a superior technique. [6],[7],[8],[9],[10]{Figure 2}{Figure 3}

Cone beam computed tomography precision in alveolar bone density measurement

Radiographic follow-up of bone healing after grafting is challenging because of the overlapping of gaining and losing areas within the graft. The new volumetric imaging method, CBCT, offers an opportunity to see inside the bone and pinpoint and measure densities in small localized areas such as a vertical periodontal defect or alveolar bone graft. This precision would make it possible to reproducibly quantify the bone remodeling after bone grafting. [11]

Cone beam computed tomography for diagnostic imaging for the implant patient

For the evaluation of implant placement, many radiographic projections are available, each with advantages and disadvantages. Radiography is an essential diagnostic tool for implant design and successful treatment of the implant patient. Selection of appropriate radiographic modality will provide the maximum diagnostic information, help avoid unwanted complications and maximize treatment outcomes while delivering "as low as reasonably achievable" radiation dose to the patient. [12]

Cone beam computed tomography scanning is the most successful and valuable imaging modality for three-dimensional and cross-sectional evaluation of the implant patient and it allows virtual implant placement that can guide the implantologist in terms of density and thickness of the alveolar bone. It helps in the selection of implants as it has an inbuilt implant library that allows placement of the specified implant.

 Limitations of Cone-Beam Computed Tomography Imaging



Cone-beam effect

The cone-beam effect is a potential source of artifacts, especially in the peripheral portions of the scan volume. Due to the divergence of the X-ray beam as it rotates around the patient in a horizontal plane, projection data are collected by each detector pixel. The total amount of information for peripheral structures is reduced because the outer row detector pixels record less attenuation, whereas more information is recorded for objects projected onto the more central detector pixels, which results in image distortion, streaking artifacts, and greater peripheral noise. [3]

X-ray beam artifacts

Computed tomography image artifacts arise from the inherent polychromatic nature of the projection X-ray beam that results in what is known as beam hardening (i.e. its mean energy increases because lower energy photons are absorbed in preference to higher energy photons). Because the CBCT X-ray beam is heterochromatic and has lower mean kilovolt (peak) energy compared with conventional CT, this artifact is more pronounced on CBCT images.

This beam hardening results in two types of artifact:

Distortion of metallic structures due to differential absorption, known as a cupping artifact,Streaks and dark bands that can appear between two dense objects.In clinical practice, it is advisable to reduce the FOV to avoid scanning regions susceptible to beam hardening that can be achieved by collimation, modification of patient positioning, or separation of the dental arches. Recent CBCT machines have introduced artifact reduction technique, and that helps to overcome this major problem in a small way.

 RADIATION DOSAGE



Cone-beam computed tomography machines use a cone-or pyramidal beam to scan the entire region of interest in a single semicircular or circular scan, as opposed to a medical CT that takes multiple axial slices in multiple full circle or helical scans. During the scan, each image is generated using a short X­ray pulse instead of continuous radiation. The total scanning time is 18 s for one volume, but the actual exposure time is only 3 s at the shortest. [13] Factors such as beam quality and filtration are unique to a specific machine, while other factors, such as FOV, can be operator controlled. In general, the smaller the FOV for a given system, the lower the radiation dose applied. [14]

 CONCLUSION



The development of CBCT technology dedicated for use in the maxillofacial region will undoubtedly increase general and specialist practitioner access to this imaging modality. CBCT is capable of providing accurate, submillimeter-resolution images in formats allowing three-dimensional visualization of the complexity of the maxillofacial region. The advantages of CBCT cannot be disputed as it is a valuable task-specific imaging modality, with minimal radiation dosage and providing maximal information to the clinician. CBCT with its high spatial resolution, affordability, smaller size, lower acquisition, and maintenance have made it a tailor-made technology for maxillofacial imaging.

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