Joint Position
Statement of the American Association of Endodontists and the American Academy
of Oral and Maxillofacial Radiology
USE OF CONE-BEAM
COMPUTED TOMOGRAPHY IN ENDODONTICS
INTRODUCTION
The American Association of Endodontists (AAE) and the American
Academy of Oral and Maxillofacial Radiology (AAOMR) have jointly developed this
position statement. It is intended to provide scientifically based guidance to
clinicians regarding the use of cone beam computed tomography (CBCT) in endodontic
treatment as an adjunct to planar imaging. This document will be periodically
revised to reflect new evidence.
Endodontic disease adversely affects quality of life and can
produce significant morbidity in afflicted patients. Radiography is essential
for the successful diagnosis of odontogenic and non-odontogenic pathoses, treatment
of the pulp chamber and canals of a compromised tooth, biomechanical
instrumentation, evaluation of final canal obturation, and assessment of
healing.
Until recently, radiographic assessments in endodontic treatment
have been limited to intraoral and panoramic radiography. These radiographic
technologies provide two-dimensional representations of threedimensional tissues.
If any element of the geometric configuration is compromised, the image can demonstrate
errors1. In more complex cases, radiographic projections with
different beam angulations can allow parallax localization. However, complex
anatomy and surrounding structures can make interpretation of planar “shadows”
difficult.
CONE BEAM COMPUTED
TOMOGRAPHY
The advent of CBCT has made it possible to visualize the
dentition, the maxillofacial skeleton, and the relationship of anatomic
structures in three-dimensions2. Significantly increased use of CBCT
is evidenced by a recent Web-based survey of active AAE members in the U.S. and
Canada which found that 34.2% of 3,844 respondents indicated that they were
utilizing CBCT. The most frequent use of CBCT among the respondents was for
diagnosis of pathosis, preparation for endodontic treatment or endodontic
surgery, and for assistance in the diagnosis of trauma related injuries3.
CBCT, as with any technology, has known limitations.
There are also numerous CBCT equipment manufacturers and models available. In
general, CBCT can be categorized into large, medium, and limited volume units
based on the size of their “field of view.”
Volume Size (s)
The size of the “field of view” or FOV describes the scan volume
of CBCT machines and is dependent on the detector size and shape, beam
projection geometry and the ability to collimate the beam. Beam collimation limits
the x-radiation exposure to the region of interest and ensures that an optimal
FOV can be selected based on disease presentation. Smaller scan volumes
generally produce higher resolution images, and since endodontics relies on
detecting disruptions in the periodontal ligament space measuring approximately
200μm, optimal resolution is necessary4.
The principal limitation of large FOV cone beam
imaging is the size of the field irradiated. Unless the smallest voxel size is
selected in these larger FOV machines, there is also reduced resolution
compared to intraoral radiographs or limited-volume CBCT machines with inherent
small voxel sizes. The limited volume CBCT imaging in endodontics is
advantageous, but by irradiating
only one site or area, projections acquired may not contain the entire region
of interest. Reconstructed images may suffer from truncation artifacts5
when comparing medical CT with CBCT reconstructed images; medical CT scans
provide the most suitable images for tumor-derived alterations due to their
capacity for soft tissue visualization6.
For most endodontic applications, limited volume CBCT is preferred
over large volume CBCT for the following reasons:
1 *Increased spatial resolution to improve the accuracy of
endodontic-specific tasks such as the visualization of small features including
accessory canals, root fractures, apical deltas, calcifications, etc.
2 *Highest possible spatial resolution that provides a diagnostically
acceptable signal-to-noise ratio for the task at hand.
3 *Decreased radiation exposure to the patient.
*Time savings due to smaller volume to be interpreted.
Dose Considerations
Every effort should be made to reduce the effective radiation dose
to the patient for endodontic-specific tasks.
Using the smallest possible FOV, the smallest voxel size, the
lowest mA setting and the shortest exposure time in conjunction with a pulsed
exposure mode of acquisition is recommended. If extension of pathology beyond
the area surrounding the tooth apices or a multifocal lesion with possible
systemic etiology is suspected, and/or a non-endodontic cause for
devitalization of the tooth is established clinically, appropriate larger field
of view protocols may be employed on a case-by-case basis. Interpretation of
the entire acquired
volume will be essential to justify the use of task-specific
modification of acquisition protocol in such cases.
CBCT has a significant advantage over medical grade CT
as radiation doses from commonly used CBCT acquisition protocols are lower by
an order of magnitude.7 Selection of the most appropriate imaging
protocol for the diagnostic task at hand is paramount.
Patient Selection Criteria
CBCT must not be used routinely for endodontic diagnosis or for
screening purposes in the absence of clinical signs and symptoms. The patient’s
history and clinical examination must justify the use of CBCT by demonstrating
that the benefits to the patient outweigh the potential risks. Clinicians should
use CBCT only when the need for imaging cannot be answered adequately by lower
dose conventional dental radiography or alternate imaging modalities.
Patient Consent
Significant risks, benefits and alternatives of special importance
should be explained by disclosure and patient education and then documented in
patient’s record. The use of CBCT will expose the patient to ionizing radiation
that may pose elevated risks to some patients (e.g., cases of pregnancy,
previous treatment with ionizing radiation and younger patients). Patients
should be informed that CBCT volumes cannot be relied upon to show soft-tissue
lesions unless they have caused changes in hard tissues (teeth and bone), and some
of the images may contain artifacts that can make interpretation difficult.
A patient may understand the relevant facts and implications of
not following a recommended diagnostic or therapeutic action and still refuse
the proposed intervention. This is known as the medico-legal concept of “informed
refusal” and is recognized in certain state laws and court decisions.8
Should a patient be incapable of understanding or responding to an informed
consent presentation or be a minor, the informed consent or informed refusal
should be documented in the patient’s record and signed by an individual
legally responsible for the patient. If a legally responsible individual is not
available, a witness should acknowledge in writing that the informed consent or
refusal process took place.
Interpretation
Clinicians ordering a CBCT are responsible for interpreting the
entire image volume, just as they are for any other radiographic image. Any
radiograph may demonstrate findings that are significant to the health of the patient.
There is no informed consent process that allows the clinician to interpret
only a specific area of an image volume. Therefore, the clinician can be liable
for a missed diagnosis, even if it is outside his/her area of practice.9
Any questions by the practitioner regarding image data interpretation should
promptly be referred
to a specialist in oral and maxillofacial radiology.
Protection of Patients and Office Personnel
At this time, all CBCT equipment produce dose levels
and beam energies that are higher than conventional dental radiography,
requiring extra practical protection measures for office personnel. Appropriate
qualified experts should be consulted prior to and after installation to meet
state and federal requirements, and manufacturer’s recommended calibration
routines should be conducted at the recommended intervals.
RECOMMENDATIONS
The decision to order a CBCT scan must be based on the patient’s
history and clinical examination, and justified on an individual basis by
demonstrating that the benefits to the patient outweigh the potential risks of exposure
to X-rays, especially in the case of children or young adults. CBCT should only
be used when the question for which imaging is required cannot be answered
adequately by lower dose conventional dental radiography or alternate imaging
modalities. Initial studies regarding the use of CBCT for a variety of endodontic
related imaging tasks have demonstrated the effectiveness and comparability of
CBCT to
conventional radiography.10-15 In general, the use of
CBCT in endodontics should be limited to the assessment and treatment of
complex endodontic conditions such as:
· *Identification of potential
accessory canals in teeth with suspected complex morphology based on conventional
imaging.
· Identification of root canal
system anomalies and determination of root curvature.
· Diagnosis of dental
periapical pathosis in patients who present with contradictory or nonspecific clinical
signs and symptoms, who have poorly localized symptoms associated with an
untreated or previously 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.
· Diagnosis of non-endodontic
origin pathosis in order to determine the extent of the lesion and its effect
on surrounding structures.
· Intra or post-operative
assessment of endodontic treatment complications, such as overextended root canal
obturation material, separated endodontic instruments, calcified canal
identification, and localization of perforations.
· Diagnosis and management of
dento-alveolar trauma, especially root fractures, luxation and/or displacement
of teeth, and alveolar fractures.
· Localization and
differentiation of external from internal root resorption or invasive cervical resorption
from other conditions, and the determination of appropriate treatment and
prognosis.
· Pre-surgical case planning
to determine the exact location of root apex/apices and to evaluate the proximity
of adjacent anatomical structures.
· Dental implant case planning
when cross-sectional imaging is deemed essential based on the clinical evaluation
of the edentulous ridge.
SUMMARY
All radiographic examinations must be justified on an individual
needs basis whereby the benefits to the patient of each exposure must outweigh
the risks. In no case may the exposure of patients to X-rays be considered
“routine,” and certainly CBCT examinations should not be done without initially
obtaining a thorough medical history and clinical examination. CBCT should be
considered an adjunct to twodimensional imaging in dentistry. Limited field of
view CBCT systems can provide images of several teeth from approximately the
same radiation dose as two periapical radiographs, and they may provide a dose savings
over multiple traditional images in complex cases.
REFERENCES
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8. Goodman JM. Protect yourself! Make a plan to obtain informed
refusal. OBG Management. 2007; 3:45-50.
1. AAOMR executive opinion statement on performing and interpreting
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Copyright 2010: American Association of Endodontists and American Academy
of Oral and Maxillofacial Radiology
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