Oral medicine practice includes the diagnosis and nonsurgical treatment of oral and orofacial diseases and oral manifestations of systemic conditions. Oral medicine specialists in medical and dental settings often require imaging in assessment and treatment of these conditions. This article reviews imaging that may be used in practice, particularly as relevant for facial pain, bone conditions, and salivary gland disease. It reviews imaging that may be considered in a hospital setting for assessment of admitted patients, patient evaluation before surgical procedures, and provision of dentistry in a hospital setting for patients who cannot submit to treatment in an outpatient setting.
A wide variety of basic and advanced imaging modalities in dentistry and medicine are employed in oral medicine practice regardless of setting.
Several oral medicine conditions, in particular facial pain, require imaging for appropriate diagnosis and treatment, and may require a variety of imaging modalities in their assessment.
Salivary gland disease also presents a diagnostic conundrum, and imaging in diagnosis and treatment may be prescribed according to findings and suspected etiologies.
Before hospital procedures and during hospital admissions, plain radiography and occasionally advanced imaging are essential to reach diagnosis and treat patients.
Many patients undergoing surgical procedures are referred for dental evaluation and determination of teeth that require intervention, commonly assessed using plain radiography.
Indications and general guidelines
Oral medicine is the eleventh dental specialty recognized by the American Dental Association (ADA). The scope of oral medicine practice is wide and includes management of patients with a variety of orofacial concerns and local manifestations of systemic conditions.
Most of the plain images obtained in a dental practice are digital, captured via either solid state (charge-coupled device/complementary metal–oxide–semiconductor) or storage phosphor–based (photostimulable phosphor sensors) using intraoral x-ray machines. Digital panoramic radiographs commonly are obtained as a first-line radiographic examination if patients are unable to open their mouth or otherwise cannot tolerate intraoral imaging. The resolution of panoramic radiographs is 4 line pairs per millimeter (lppm) to 5 lppm, far less than intraoral digital radiographs (7–24 lppm).
Digital skull views (extraoral) also can be obtained in any practice setting provided there is a dedicated cephalostat unit attached to the x-ray machine. The extraoral unit can be either a panoramic x-ray machine or a cone beam computed tomography (CBCT) machine with a cephalostat arm extension. Lateral oblique views are obtained at the hospital to view the body of the mandible and the condyles bilaterally if a panoramic radiograph machine is not available, although, in general, they are considered obsolete.
CBCT machines are an integral part of dental practice. In oral medicine practice, CBCT is used for evaluation of craniofacial anomalies; pathology extending beyond the teeth; soft tissue calcifications of head and neck; and anatomic structures, including the TMJs, external auditory meati, foramina and fossae, inferior alveolar nerve canals, incisive foramen and nasopalatine canals, paranasal sinuses, nasal fossa, and ostiomeatal complex, to name a few. CBCT can be obtained for a focused area (small field of view [FOV]), single jaw (medium FOV) or the entire skull (large FOV) based on the area being investigated. Interpretation can be performed either in house or by sending to an oral and maxillofacial radiologist for formal interpretation and reporting. CBCTs obtained at the dental office can be coded using the ADA code on dental procedures and nomenclature. There are 3 medical codes (Current Procedural Terminology) available for CBCT-related image capture, interpretation, and 3-dimensional (3-D) rendering.
Imaging for facial pain
After a thorough history and physical examination, the oral medicine specialist examining a patient with facial pain may use several imaging techniques to identify the source. These include digital radiographs of the teeth and jaws, cervical spine series, selected FOV CBCT, magnetic resonance imaging (MRI) with and without contrast, and magnetic resonance angiography. A brain MRI can be acquired to identify any definitive vascular, neural, or bony pathology that would give rise to the facial pain. Magnetic resonance neurography is emerging as a useful diagnostic test for detection of abnormalities of craniospinal nerves below the skull base.
Imaging for Trigeminal Neuralgia and Atypical Facial Pain
Trigeminal neuralgia, also known as tic douloureux, is a chronic pain condition affecting the trigeminal nerve (fifth cranial nerve). MRI is the diagnostic test of choice to rule out a tumor, multiple sclerosis, or an impinging blood vessel. In some cases, imaging is not possible for reasons including presence of cardiac pacemakers or metal implants, and, in such cases, recording of trigeminal reflexes to assess trigeminal nerve function is an established alternative assessment method.
Atypical facial pain, also known as persistent idiopathic facial pain and atypical odontalgia, is a nonspecific pain where no organic cause can be identified. The pain does not follow the anatomic pathways of cranial or peripheral nerves. Patients must be investigated thoroughly before a diagnosis of atypical facial pain is reached. Investigations may include intraoral periapical radiographs, panoramic radiography, CBCT, CT head with and without contrast, and brain MRI. The choice of imaging is selected by the oral medicine practitioner, depending on the clinical findings and characterization of facial pain.
Imaging for Temporomandibular Joint Disorders
Temporomandibular disorders (TMDs) may affect the joint, joint-associated structures, or muscles of mastication and can manifest as impaired jaw function, pain, or joint sounds. The oral medicine specialist has primary responsibility for several TMDs and should be familiar with the radiographic appearance of the temporomandibular joint (TMJ) and TMJ-related disorders. A thorough clinical examination of the TMJ and orofacial region is essential prior to determining the need for diagnostic TMJ imaging. A necessary first step in evaluating possible TMDs is to rule out any odontogenic or orofacial source that could be causing a patient’s complaint. Indications for TMJ imaging vary with each patient. The following imaging modalities frequently are used in assessing the TMJ: panoramic radiography, MRI, computed tomography (CT), CBCT, ultrasound (US), and scintigraphy.
Panoramic radiography is a readily available modality used to evaluate the joints bilaterally and assess the jaws and orofacial structures for any abnormalities that would necessitate further diagnostic imaging ( Fig. 1 ). Indications for panoramic imaging of the TMJ can include assessment of suspected joint tumors, condylar hypoplasia/hyperplasia, or degenerative bone disease. The oral medicine specialist should be cautious in interpreting condylar morphology using only a panoramic image because the beam orientation allows examination of only the central and lateral parts of the condyle. , The superimposition of structures of the skull and zygomatic arch also limits the diagnostic value in assessing the glenoid fossa and articular eminence. This is supported by the American Academy of Oral and Maxillofacial Radiology position statement on imaging of the TMJ, which states that panoramic imaging is an ideal modality for TMD patients only in assessing the teeth and jaw structures to rule out any gross osseous or odontogenic sources of the patient’s complaint.
Magnetic resonance imaging
MRI is the recommended imaging modality to assess the TMJ, including the articular disk, due to its ability to visualize both bone and soft tissues. On a T1-weighted image, the bone marrow and posterior attachment have a high signal due to fat content whereas the disk and bone display a low signal. A T2-weighted image again reveals a low signal of the disk and bone with an occasional high signal seen in the intermediate zone of the disk. Fluid-attenuated inversion recovery (FLAIR) sequence from T2-weighted images has been investigated for join effusions and found to have a strong correlation with decreased signal intensity, suggesting variable protein content in effusions. FLAIR signal intensity was found to be higher in painful joints compared with joints without pain, which may be due to increased protein. It also has been suggested that FLAIR is useful in detecting bone marrow changes of the condyle, such as edema, in painful joints of patients with TMD. Joint effusion is represented radiographically by a high signal area in a T2-weighted MRI image and there is evidence of an increased frequency of joint effusion in disks that are displaced. An MRI study found patients with disk displacements (both with and without reduction) frequently presented with joint pain and joint effusion, although the causal relationship is not clear.
There are cases where imaging the TMJ with MRI is not possible, including when cost is prohibitive, claustrophobic patients, or in patients with cardiac pacemakers. Ultrasound (US) represents an acceptable, cost-effective, and noninvasive alternative method for assessing the TMJ in such cases. Joint effusions and disk displacements in the closed mouth and opened mouth positions can be detected by US of the TMJ. Sonography is less sensitive and less specific than an MRI or helical CT in the detection of TMJ internal derangements but may still provide useful information.
Multidetector computed tomography/cone beam computed tomography
CBCT is superior to panoramic radiography in evaluating the TMJ because it allows assessment of bone structures in 3 planes and reconstructs the image utilizing the long axis of the mandibular condyle; this allows visualization of the condylar position relative to the fossa. CBCT also is superior to CT for imaging the TMJs due to its significantly lower radiation exposure to the patient and higher spatial resolution of the image. CBCTs perform equally to multidetector CT (MDCT) in detecting osseous and morphologic changes of the TMJ , , , and are superior to MRI and panoramic radiographs in diagnosing arthritic changes of the TMJ. The same findings and indications for a CT apply to CBCT. The following conditions can be evaluated with MDCT/CBCT.
Osteoarthritis is the most common degenerative joint disease (DJD) that affects the TMJs. Although disk position and shape cannot be assessed by a CT or CBCT, a more posteriorly positioned mandibular condylar head in the glenoid fossa can be a sign of disk displacement and internal derangement. An MRI confirms the diagnosis of internal derangement as the disk is best visualized there.
MDCT or CBCT findings that indicate TMJ osteoarthritis include osteophytes, surface erosions, generalized sclerosis, and subcortical/subchondral cysts. The oral medicine specialist should be cautious in evaluating DJD. Narrowing of the TM joint space is not considered a reliable indicator of DJD because it also can occur in otherwise healthy joints or in joints exhibiting disk displacements only. Likewise, flattening of the condylar head, glenoid fossa, or articular eminence is indicative of DJD only when associated with osteophyte formation because it otherwise could indicate remodeling of the condylar head that occurs with aging or a displaced disk. In addition, osteophytes have been noted as an anatomic variation, and cortical surface irregularities have been found in asymptomatic individuals. Barring significant changes and evidence of bone destruction, it is prudent to consider subtle findings as normal anatomic variations, especially in asymptomatic patients. A promising future direction for CBCTs in assessing osteoarthritis includes utilizing 3-D virtual surface models in assessing condylar morphology, because condylar resorption in TMJ osteoarthritis has been correlated with pain.
Inflammatory arthritis represents a group of conditions causing inflammation of the joints’ synovial membrane. Discussion of all inflammatory arthritides is beyond the scope of this article, and only the most common condition likely encountered in the oral medicine clinic, rheumatoid arthritis (RA), is discussed.
RA is the most common inflammatory arthritis. Early osseous changes may be detected on CBCT. The classic CT radiographic finding of RA is cortical erosion without bone proliferation, which can be coupled with osteoarthritic changes, such as flattening of the articular surfaces, subchondral sclerosis, and osteophyte formation. These radiographic findings, however, are nonspecific and may be present in other inflammatory arthritides as well. Correlation with clinical signs and symptoms and serology may be required to assess the patient accurately. Findings of a normal disk position on an MRI with evidence of bone destruction should lead the clinician to suspect trauma or the presence of a rheumatic disease because the articular disk frequently is found in a normal position in inflammatory arthritic cases. In a systematic review conducted by Mupparapu and coworkers, 2-dimensional radiographs, CBCT, MDCT, and MRI were found to be the most common methods employed in the detection of RA. PET-CT was found to be useful for quantifying TMJ involvement in active RA.
Imaging for bone lesions
Imaging for Osteomyelitis
Osteomyelitis is defined as inflammation of the bone marrow spaces and the vessels that leads to either bone loss or necrosis. This process may be acute, subacute, or chronic. Outcomes depend on the severity of the inflammation and blood supply to the area affected. When a necrotic part of the bone becomes isolated, they are termed a sequestrum . Sequestra typically are more radiopaque (radiodense) than surrounding bone on plain films due to accelerated deposition of calcium and phosphates. Demonstration of a sequestrum on a radiograph is the hallmark of osteomyelitis. In addition, infected bone gives the classic radiographic moth-eaten appearance ( Figs. 2 and 3 ). Intraoral radiographs may not demonstrate these features. A panoramic radiograph may demonstrate some features but due to the 2-dimensional nature of the modality, does not show all the affected areas. MDCT is the best modality to show the osteomyelitic area. MDCT is ideal for this purpose due to its better inherent contrast (higher kilovoltage peak and radiation dose). A CBCT also may be acceptable if an MDCT is not available. Several studies show the utilization of additional advanced imaging modalities for early detection of osteomyelitis. This includes single-photon CT (SPECT) and PET-CT, both of which may be able to visualize early changes before they become apparent on a radiograph, due to the higher sensitivity and specificity of these techniques. This is attributed to the higher sensitivity and specificity of these techniques. SPECT is best utilized in initial diagnosis, and fluorodeoxyglucose F 18 18 F-FDG-PET can be used adjunctively and during follow-up in cases of chronic osteomyelitis.
Imaging for Osteoradionecrosis of the Jaw and Medication-Related Osteonecrosis of the Jaw
Osteonecrosis of the jaw is bone death due to lack of blood circulation. When infected, the area becomes clinically detectable through mucosal ulceration and bone exposure. Medication-related osteonecrosis of the jaw (MRONJ) is the term for when this condition occurs secondary to use of a medication that interferes with normal physiologic bone turnover (bone resorption and/or bone deposition). The best radiographic modality for visualizing these changes is a high-resolution CBCT (less than 100-μm pixel resolution). Radiographic and histologic appearance of bone necrosis is identical regardless of etiology. Unexplained bone loss and or separation (sequestrum) may be suspected on intraoral or panoramic radiographs and can be confirmed via MDCT or CBCT ( Fig. 4 ). MRI is advantageous for evaluation of the nerves.
Imaging is an integral part of the investigation for oral cancer, whether a primary malignancy or a metastatic lesion. Occasionally, malignant changes can be recognized in intraoral radiographs, but they generally are more evident when evaluated on extraoral imaging and coupled with clinical presentation. For example, oral squamous cell carcinoma can extend into alveolar bone. Although CBCT shows bone invasion and destruction, due to limitations in contrast, MDCT is preferred. An MRI is indicated when the suspected lesion is of soft tissue origin or if occult or inaccessible for oral examination. More advanced imaging like technetium Tc 99m, SPECT, or PET-CT is preferred when the cancer is suspected to be widespread. These tests generally are done in conjunction with an oncologist. Biopsy and staging are mandatory in all suspected and confirmed cases of cancer.
Imaging for salivary gland disease
Several pathologies can affect the salivary glands, including inflammatory and infectious diseases, obstructions, neoplasms, and autoimmune disorders. Signs of salivary gland disease include diffuse enlargement or limited enlargement with or without pain. These clinical findings often are nonspecific and require further diagnostic evaluations for a more definitive diagnosis. Several imaging modalities are available for salivary gland diagnosis and management. ,
Given the availability of advanced imaging modalities, there is little clinical value in plain radiography of the salivary glands.
US is a noninvasive, safe, and readily available modality that is useful in initially assessing the salivary glands. US performance is comparable to CT and MRI in detecting superficial salivary gland tumors that are hypoechoic compared with normal salivary glandular tissue. US is the modality of choice in evaluating superficial parotid masses that are palpable. It also has proved successful in confirming clinically suspicious masses and differentiating benign from malignant neoplasms. High-grade malignant neoplasms may appear as nonhomogenous hypoechoic regions with irregular ill-defined borders. In addition, lesions can be biopsied with an US-guided core needle. , US drawbacks include overlap of adjacent structures, which impairs its ability to detect deeper lesions.
US can successfully detect sialoliths of the salivary glands, where they appear as echogenic foci. The high sensitivity of US in diagnosing sialoliths makes it an acceptable alternative to sialography and the imaging modality of choice in assessing sialoliths due to the lack of radiation exposure and availability.
Sialoliths and microbial organisms often are the cause of acute inflammatory conditions of the salivary glands. US can detect edema and inflammation of the gland and rule out sialoliths or abscesses within the glandular parenchyma that may be causing the acute sialadenitis.
In addition, US is a commonly used modality to assess the extent of salivary gland involvement in Sjögren syndrome. Involvement of the glands is evident via atrophy, fibrosis, and sialectasis. Sialectasis appears as hypoechoic and anechoic regions. A meta-analysis concluded that US of Sjögren syndrome patients may be an acceptable alternative to other imaging modalities in evaluating the salivary glands.
Sialography ( Fig. 5 ) involves injection of a contrast medium into the glands, allowing visualization of ductal anatomy and parenchyma. Indications include suspected strictures and sialoliths.