Radiographic imaging is an integral part of the diagnostic process in clinical dentistry. This article provides the fundamentals of radiographic interpretation beginning with evidence-based guidelines on dental radiographic selection criteria and cone beam computed tomography use. The goal is to present to the reader with a systematic approach to radiographic interpretation such that no significant features are overlooked and an optimal differential diagnosis can be achieved. In addition, medicolegal considerations of radiographic acquisition, interpretation, and storage are discussed.
Key points
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Dental radiographs are an integral part of the diagnostic process in clinical dentistry.
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Radiographs aid in the diagnosis and characterization of the type and extent of disease, but care must be taken to minimize the radiation exposure to the patient.
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Selection guidelines help the practitioner choose the appropriate radiographs as an adjunct to their professional judgment.
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Two-dimensional or plain radiography is the first choice of imaging in many clinical scenarios; cone beam computed tomography should be used when 2-dimensional imaging cannot answer the clinical question.
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It is best to use a systematic method of reading and interpreting radiographs each time so that no significant features are overlooked. Knowledge of normal radiographic anatomy is paramount.
Introduction
The diagnostic process consists of a patient interview, clinical examination, and the ordering of tests to help the practitioner make a sound diagnosis. In dentistry, the most common test ordered in a preliminary examination is radiographic imaging ( Fig. 1 ). The patient is interviewed to determine the patient’s chief complaint, the history of the present illness, and the patient’s medical history. A systematic clinical examination of the patient is then performed and, based on the information collected, the practitioner will order diagnostic imaging. After reviewing the images, the dentist may perform further clinical examinations and order further testing to assist in formulating a differential diagnosis. Dental radiographs are an integral part of the diagnostic process in clinical dentistry. Appropriate radiographic selection and interpretation along with clinical information and other tests are essential for the formulation of a strong differential diagnosis.
Evidence-based selection criteria
After a history and clinical examination are performed, a decision must be made about whether or not to order radiographs to aid in the diagnosis. Radiographs aid in the diagnosis and characterization of the type and extent of disease, but care must be taken to minimize the radiation exposure to the patient using the as low as diagnostically acceptable principle. The Canadian Dental Association’s position paper concluded that the frequency of radiographic examinations is a matter of clinical judgment. The Food and Drug Administration and the American Dental Association as well as the US Department of Health and Human Services have issued guidelines to help the practitioner choose the appropriate radiographs as an adjunct to their professional judgment. The efficacy of these guidelines has been demonstrated by White and colleagues. Among 500 new adult patients, the guidelines resulted in a 43% decrease in the number of radiographs ordered and only 3.3% of carious lesions were missed. The guidelines have also been shown to be effective in the diagnosis of periodontal disease and defective restorations.
Recommended Radiographic Selection Criteria
New patient
Primary dentition
If the proximal surfaces cannot be probed, then select periapicals, occlusal, and/or bitewing radiographs should be taken. If there is no evidence of disease, no radiographs are recommended.
Transitional dentition
Either bitewing radiographs and a panoramic radiograph or bitewing and select periapical radiographs should be taken.
Permanent dentition
If there is no clinical evidence of disease or extensive dental treatment, individual radiographic examinations are recommended. Such examinations would include either bitewing and panoramic radiographs or bitewings and select periapical radiographs. If there is evidence of dental disease or extensive dental treatment, a full mouth series of radiographs should be taken.
Edentulous
In an edentulous patient, an individual radiographic examination based on clinical signs and symptoms is recommended.
Recall patient
Clinical caries or increased risk for caries
In a patient with clinical caries or an increased risk for caries, who has primary, transitional, or permanent dentition (before the eruption of third molars), and whose proximal surfaces cannot be probed, bitewing radiographs at 6- to 12-month intervals should be taken. In a patient with clinical caries or an increased risk for caries who has adult dentate or partially edentulous dentition, bitewing radiographs at 6- to 12-month intervals are recommended.
No clinical caries, not at increased risk for caries
In a patient with no clinical caries and who is not at increased risk for caries, and has primary, transitional, or permanent dentition (before the eruption of third molars), and the proximal surfaces cannot be probed, bitewing radiographs at 12- to 24-month intervals should be taken. For patients with no clinical caries and no increased risk for caries, with permanent dentition before the eruption of third molars, bitewing radiographs at 18- to 36-month intervals are recommended. Patients with no clinical caries and no increased risk for caries with adult dentate or partially edentulous dentition, should have bitewing radiographs exposed at 24 to 36-month intervals.
Periodontal disease
In a recall patient with clinical signs and symptoms of periodontal disease, the radiographic examination is based on clinical judgment to select the radiographs necessary to evaluate the presence and extent of periodontal disease. The recommendation is to take select vertical bitewing and periapical radiographs of the areas with periodontal disease.
Monitoring growth and development
To monitor growth and development in the primary dentition, choosing radiographs based on the practitioners’ clinical judgment of prior caries experience, oral hygiene, orthodontic treatment, and impending eruption of third molars should dictate the need for bitewing, periapical, and panoramic examinations. When evaluating implants, pathology, restorative/endodontic needs, periodontitis, and caries remineralization, clinical judgment of the need for radiographs needed is recommended. Practitioners should be mindful of the increased risks of radiation for growing children.
Evidence based cone beam computed tomography guidelines
Although two-dimensional (2D) or plain radiography is the first choice of imaging in many clinical cases, cone beam computed tomography (CBCT) can be used when 2D imaging alone cannot answer the clinical question. As with plain radiography, guidelines have been established to aid the dental practitioner using their best clinical judgment. In all cases, the smallest possible field of view, the smallest voxel size, the lowest mA setting, and the shortest exposure time in conjunction with the pulsed exposure mode should be used. In addition, the use of CBCT should be implemented only after the patient’s health history and imaging history have been carefully reviewed, a thorough clinical examination has been performed, and the diagnostic yield has been determined to improve the patient care, enhance patient safety, and significantly improve clinical outcomes.
Endodontics
In endodontic cases, the use of CBCT should be limited to the assessment and treatment of complex conditions.
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To identify potential accessory canals in teeth with suspected complex morphology as shown on plain radiography
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To identify root canal system anomalies and determine root curvatures
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To diagnose periapical pathoses:
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With contradictory or nonspecific clinical signs and symptoms
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With poorly localized symptoms associated with no evidence of pathosis by conventional imaging
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Where anatomic superimposition of roots or areas of the maxillofacial skeleton may interfere with adequate visualization of areas in question
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To diagnose periapical pathosis of a nonendodontic origin to determine the extent of a lesion and its effect on surrounding structures
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To assess intraoperative or postoperative endodontic treatment complications
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Overextended root canal obturation material
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Separated endodontic instruments
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Calcified canals
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Perforations
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To diagnose and manage dentoalveolar trauma
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Root fractures
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Luxation and/or displacement of teeth
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Alveolar fractures
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To localize and differentiate
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External from internal root resorption
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Invasive cervical resorption from other conditions
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For presurgical case planning
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To determine the exact location of root apex/apices
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To evaluate proximity to anatomic structures
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Implantology
In dental implant cases, panoramic radiography is the imaging modality of choice for the initial evaluation, and intraoral periapical radiography should supplement panoramic radiography. It is not recommended to use CBCT as the initial diagnostic examination. However, owing to inaccurate distance measurements and the lack of three-dimensional visualization, panoramic radiographs are extremely limited in usefulness in final implant planning.
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Preoperative site-specific imaging
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CBCT should be considered as the imaging modality of choice for preoperative cross-sectional imaging of potential implant sites
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CBCT should be considered if there is a clinical need for augmentation procedures or site development before implant placement
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Sinus augmentation
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Block of particulate bone grafting
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Ramus or symphysis grafting
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Assessment of impacted teeth in the field of interest
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Evaluation of previous traumatic injury
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CBCT should be considered if bone reconstruction and augmentation procedures have been performed to treat bone volume deficiencies before implant placement
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Postoperative imaging
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CBCT is recommended immediately postoperatively only if the patient presents with implant mobility or altered sensation, especially if in the posterior mandible
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Intraoral periapical and panoramic radiographs are recommended in the absence of signs or symptoms
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CBCT may be considered if implant retrieval is anticipated
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Periodontics
In periodontology, experts have addressed the use of CBCT in three specific areas: placement of implants, interdisciplinary dentofacial therapy involving orthodontic tooth movement in the management of malocclusion associated with risk to the supporting periodontal tissues, and the management of marginal periodontitis.
Placement of implants
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To evaluate root morphology and associated pathology for extractions and reconstruction
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To locate relevant anatomic structures and their relation to the planned implant
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For the preimplant evaluation of sinus grafting
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To evaluate the autogenous bone donor site
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To fabricate static surgical guides and dynamic navigation of implant placement
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For postbone augmentation implant planning
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To evaluate complications from previous implants
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Risk to supporting periodontal structures in tooth movement
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In a skeletally mature patient with malocclusion in need of fixed orthodontic appliance for decompensation
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When thin dentoalveolar phenotype and dentoalveolar bone deficiencies are suspected
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In patients with malocclusion requiring advanced tooth movement and there is an increased risk for positioning the roots outside the orthodontic boundary
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In a skeletally immature orthodontic patient requiring an interdisciplinary approach to treatment
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In an orthodontic patient with concomitant mucogingival deformities
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Other treatment considerations requiring global analysis, such as
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Temporomandibular disorders
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Dentofacial disharmonies requiring orthodontic-periodontal-orthognathic management
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Congenitally missing teeth
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Skeletal anchorage requirements
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Management of periodontitis
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Advanced furcation lesions with dental implants being considered as an alternative treatment option
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Advanced bone loss encroaching on anatomic structures such as sinus cavities or the inferior alveolar nerve
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Questionable root fracture, root resorption, or periodontal lesions confluent with apical inflammatory lesions that cannot be identified by 2D imaging and/or clinical evaluation
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Management and diagnosis of peri-implantitis when necessary
Cone Beam Computed Tomography Summary
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A 2D or plain radiograph is the first choice of imaging in many clinical scenarios, and CBCT should be used when 2D imaging alone cannot answer the clinical question.
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A comprehensive clinical examination must precede use of CBCT, and caution must be exercised to use dose-sparing techniques.
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Preimplant imaging using CBCT is more useful than postimplant imaging.
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The effective doses for dentoalveolar CBCT range from 11 to 674 μSv. The effective doses for craniofacial CBCT range from 30 to 1073 μSv.
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CBCT is indicated in situations where a tooth is impacted, infected, or missing, and 2D radiography did not reveal pathosis. Preimplant planning, preoperative evaluation, postsurgical evaluation in a variety of oral surgical, periodontal, endodontic, restorative, and prosthodontic conditions can be performed using CBCT.
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Interpretation
Quality of the Image
Initially, the radiograph must be of diagnostic quality. It should have the correct contrast and density where the region of interest or lesion is clearly visible. The surrounding normal tissue should be approximately 2 to 3 mm, and there should be no geometric distortion. Based on the initial radiographs, a clinical determination is made as to the necessity of additional radiographs or different projections, such as periapical, bitewing, occlusal, and panoramic radiographs. The clinician may also try to obtain prior radiographs for comparison even if they are not of highest quality ( Fig. 2 ). When deciding to expose the patient to additional radiation, the expected diagnostic yield from the radiographs should be taken into consideration.
