TMJ radiographs provide information on the morphological characteristics of osseus components of the joint and certain functional associations between the condyle, articular tubercle and fossa, but are inefficient for evaluating the soft tissues.1,14,16

Several anatomical and technical factors can prevent a clear and unobstructed radiographic image of the TMJ.16,17 When choosing TMJ radiography, one needs to consider the identification of boney structural details, the specific suspected clinical disorder, the amount of symptomatic information clinically available for the diagnosis, the cost of these examinations, and their radiation dose.3,14 The radiographic techniques most often used in the routine management of TMJD are panoramic radiography, planigraphy, and transcranial radiography1,3,13,15 (Fig. 1).

Figure 1.

Radiographic assessments of different TMDs. (a–c) Close-up in panoramic image showing mandibular condyle hypoplasia (a), horizontal impaction of the third molar (a, b) fracture line in the region of gonial angle (b) and elongated styloid process. The transcranial images (d–f) show the presence of osteophytes (d), preservation of joint spaces in maximum habitual intercuspation (MHI) (e) and the identification of condylar hyperexcursion (f). The planography techniques (g–j) demonstrate: mandibular neck fracture and ankylosis (g) elongated styloid process (h), advanced remodeling process, superior-anterior flattening, cortical irregularities, and osteophyte formation (i) in addition to mandibular head hyperexcursion, defining TMJ hypermobility (j).

(0.24MB).

As it provides a maxillary overview, it is useful in the differential diagnosis of odontogenic alterations whose symptoms overlap with TMJD.13,18 It can reveal advanced bone alterations in the condyle, such as asymmetries, erosions, osteophytes, fractures, changes in size and shape, degenerative and inflammatory processes, growth alterations, maxillary tumors, metastases, and ankylosis.1,13,15,16 However, it does not provide functional information on condylar excursion.14 Also, only gross alterations in the articular tubercle morphology can be seen because of the superimposition of images of the skull base and the zygomatic arch.3,14,16,18 This technique is useful as a screening tool, as it allows the initial diagnosis and assessment of TMJ alterations that are not so subtle.15 It is also indicated when the patient has reduced mouth opening and the differential diagnosis of fracture is considered.1,3

This method provides considerable accuracy and produces images without much overlap. It visualizes the articular boney detail and reveals any anatomical abnormalities in structures adjacent to the TMJ, such as the styloid process, mastoid process, and zygomatic arch.3,15 It can be obtained in the sagittal and coronal planes, documenting the relationship of the condyle with the articular fossa in maximum habitual intercuspation (MHI) and the excursion extension during maximal mouth opening (MMO). It provides a direct comparison of both sides regarding the hypo-, normo-, or hyperexcursion of the condyle, which is useful in confirming a clinical suspicion of hypermobility.1,3

In spite of the relative identification of the TMJ boney structures, it does exhibit some magnification that is inherent to the technique. However, it is useful for functional assessment of mouth opening, evaluation of morphological alteration and the joint spaces, analysis of dimension, fractures, and ankylosis.3

Similarly to the planigraphy, this evaluation provides good anatomical assessment of the condyle, fossa, and articular tubercle.1,14,17 In this technique, an X-ray beam is obliquely directed through the skull to the contralateral TMJ, producing a sagittal view.17 Thus, the central and medial portions of the condyle are projected inferiorly and only the lateral joint contour is displayed.17 It is useful to identify bone alterations and displaced fractures of the head and neck of the mandibular condyle, as well as to assess excursion and to determine radiographic joint spaces.3,14,17

This type of projection is limited by the fact that it produces an image with a large overlap of the skull bones; it also requires the use of a specific cephalostat for standardization, usually requiring complex positioning.1,13,14,17

Arthrography is a variant of the radiographic technique for TMJ, which aims to assess the TMJ soft tissues. In the 1970s and 1980s, arthrography was the method of choice for the identification of disc displacement.14,15,19 Disc morphology, positioning, and function were indirectly identified by contrast injection into the superior and/or inferior joint spaces.14 After the injection, dynamic images were obtained, recording mandibular movements.20

Even though it is useful for disc position identification, arthrography is not currently recommended as it is an invasive procedure and carries a risk of iatrogenic disc perforation and facial nerve damage.14 There are also the risks of radiation to radiosensitive structures (crystalline and thyroid), pain and limitation of movement after the injections, infections, allergies to the injected dye, and it is an examination that is considered difficult to perform.1,14,15,20

Due to the two-dimensional radiographic visualization of the TMJ, the combined use of different techniques is necessary to provide an accurate diagnosis and location of the alterations. The evaluation of the structures in different planes illuminates fracture extension, degenerative joint disease, postoperative status, ankylosis, and neoplasms.3 Additionally, the anatomic relations of areas adjacent to the lesion can be studied with greater diagnostic accuracy, providing more efficient surgical and therapeutic planning.15 The main combined views are submental (or submento-vertex), transpharyngeal, transmaxillary, reverse Towne, posterior–anterior, and lateral teleradiography.3,13,15

Despite their lower cost, technical simplicity, and lower levels of radiation, the use of combined radiographic images has become less common due to increasing use and availability of accurate images such as cone-beam computed tomography, which assess hard tissues in the three anatomical planes and are widely used in dental diagnosis.13,15

CT comprises a set of images obtained through a sophisticated and highly accurate technique, compared to plane radiographs.2 Recently, cone-beam computed tomography (CBCT) technology has been used for dental diagnosis due to its specific use for the maxillofacial region.3,21 Its main advantage is the observation of boney joint structures in the sagittal, coronal, and axial planes,1,21 in addition to the possible image manipulation at different depths and three-dimensional reconstruction14,21 through specific software. The examination time varies between 10 and 70s, and the radiation dose is much lower compared to the helical technique.3,21

The main indications of CBCT include structural assessment of bone components of the TMJ, which precisely determines the location and extent of boney alterations: fractures, neoplasms, and ankylosis; erosive degenerative, pseudocystic, and osteophytic alterations; presence of asymptomatic bone remodeling; evaluation of post-surgical conditions; hyperplasia of condylar, coronoid, and styloid processes; persistent foramen of Huschke; as well as intraarticular calcification derived from synovial chondromatosis or metabolic arthritis.2,14,15

Hard tissues, teeth, and bones are well demonstrated and measured in their real morphological condition, with minimal noise and artifacts.1,18,22 However, few details are provided on soft tissue and it is not possible to evaluate the joint disc.3,22

Significant disadvantages are the cost of the examination and exposure to significant levels of radiation compared to conventional radiographic techniques.1,14,15,18

Fig. 2 shows morphological alterations in joint bone components diagnosed by the CBCT technique.

Figure 2.

Cone-beam computed tomography (CBCT) assessment of different TMJs in the coronal (a, e) and parasagittal (b–d) views. (a) Coronal view showing extensive erosion. Note the presence of bone sclerosis, cortical irregularities, and osteophytic formation in (b), (c), and (e). The presence of subchondral cysts can be observed in (c) and (e). Advanced flattening of bone components and decreased joint space are recorded in (d). Advanced degenerative osteoarthritis alteration is observed in e. Three-dimensional reconstructions (f–h) show osteophytes (f, g), advanced erosion (g) and hyperexcursion of the mandibular condyle (h). (i) The coronal view of the right and left TMJ shows alteration of the mandibular condyle and hyperdense images in the joint spaces compatible with synovial chondromatosis.

(0.5MB).

MRI has been the method of choice to study disease processes involving the TMJ soft tissues,2,20,23 such as the articular disc, ligaments, retrodiscal tissues, intracapsular synovial content, adjacent masticatory muscles, as well as cortical and medullary integrity of bone components.1,3,15,22

The technique allows three-dimensional analysis in the axial, coronal, and sagittal planes. It is considered the gold standard for assessing disc position and is highly sensitive for intraarticular degenerative alterations.3,20,23

The clinical conditions that suggest its use include persistent symptoms of joint or pre-auricular pain, presence of clicking and crepitation noises, functional alterations such as lateral projections of the condyle during mouth opening, frequent subluxations and dislocations, limited mouth opening movement with terminal stiffness, suspected neoplastic processes, and presence of osteoarthritic symptoms or asymptomatic osteoarthrosis.1,2,13,15

This diagnostic test protocols usually include the recording in the MHI and MMO position, using weighted T1, T2, and proton density (PD), in the sagittal and coronal planes.15 With T1-weighted images, it is possible to obtain excellent anatomic detail; proton density results in satisfactory spatial resolution of joint disc injuries, and is an excellent choice for the evaluation of medial and lateral disc displacements.20 T2-weighted images record the presence of joint effusion and medullary bone edema.2,3,20

The main advantages include detecting soft tissue alterations, necrosis, edema, presence or absence of invasion, and lack of exposure to ionizing radiation.2,3,15,16,20

MRI is also indicated for the assessment of the integrity and anatomical relation of neural structures, which, when compressed by tumor or vascular processes, can produce orofacial pain by demyelination and deafferentation.2,3,13,14,16

Its disadvantages are related to the high cost and the need for sophisticated facilities. It is contraindicated in claustrophobic patients, those with pacemakers and metallic heart valves, ferromagnetic foreign bodies, and pregnant women.14,15,23

Fig. 3 illustrates morphological joint disc and bone structures alterations diagnosed by MRI.

Figure 3.

Different MRI assessments disclosing previous joint disc displacement, with no reduction in the parasagittal views. One can observe compressive deformation of the joint disc in (a), also during dynamic comparison of the mandibular condylar movement in (b) and (c). Osteophytic formations (d–f), subchondral cyst (d), and severe change in form (f) define the diagnosis of osteoarthritis degenerative alterations in bone components. The presence of hyperintense T2-weighted images defines the diagnosis of effusion in (b–f).

(0.29MB).

The use of US examination, especially by high-resolution imaging equipment, can be a useful option in the assessment of disc position in internal TMJ disorders.4,23 Although it has considerable diagnostic sensitivity, it has insufficient specificity to identify osteoarthrosis. The findings related to morphological alterations show that the method still does not have accuracy for the cortical and articular disc morphological diagnosis.24 However, the method is able to identify effusion in patients with inflammatory condition associated with pain, verified by MRI.23,24

Even with limitations, it can become a useful option for the initial study of the internal dysfunctions of the TMJ,15,23 particularly in patients with contraindications to MRI.14 Moreover, it is less expensive, allows real-time visualization without the use of ionizing radiation, and is quick and comfortable.4,23,24

US assessment is commonly used in the differential diagnosis of glandular and adjacent structures alterations, such as the TMJ and the masseter muscle. The symptoms present in cases of sialadenitis and sialolithiasis can be mistaken for Eagle syndrome, TMD, myofascial pain, nerve pain, and other orofacial pain conditions.

Another indication of the US assessment is the correct location of joint spaces for infiltrative therapies, arthrocentesis, and viscosupplementation (Fig. 4a and b). It shows, dynamically and in realtime, the location of joint components, providing adequate lubrication and washing, which are verified by the increase in joint space after treatment.25

Figure 4.

Other imaging techniques. (a) Ultrasound examination of the TMJ25 used during the arthrocentesis assessment. Note the arthrocentesis needle as a hyperechoic point (white arrow). (b) Ultrasound examination of the TMJ showing the joint disc and condyle. (c) Tomographic axial view28 showing mass of soft tissue growth in the left TMJ region extending to the ipsilateral pterygoid region. Infra-temporal space with absence of condylar process, the presence of hyperdense areas, swelling, and asymmetry. (d) PET/CT assessment in axial view28 showing high metabolic activity in the left TMJ region. Images reproduced with permission of the authors’ copyrights25,28 by Elsevier.

(0.48MB).

Nuclear medicine facilitates establishing a diagnosis by detecting minute concentrations of radioactive pharmacological substances that determine osteometabolic alterations expressed in imaging exams.26

Bone scintigraphy is indicated to define neoplastic activity, metabolic disorders, and bone growth,14,26,27 as well as to evaluate synovitis and osteoarthritis.18 It is an examination with considerable sensitivity, low invasiveness, and high organ specificity, with low levels of radiation.27 It has some advantages over radiographies, conventional CT, and MRI because it provides an estimate of metabolic and inflammatory activity.26,27 It can facilitate an early diagnosis and is less costly than CT and MRI. However, it does not differentiate among bone scar disorders, infections, osteoarthritic manifestations, or tumors.15

Positron-emission tomography (PET) is usually indicated for the assessment and staging of metastatic tumors. It is able to provide accurate functional, morphological, and metabolic information.28 Three-dimensional images facilitate anatomical visualization and can significantly reduce the time required for diagnosis, in addition to properly direct treatments by ensuring that the therapies are appropriate.15

Currently, single photon emission computed tomography with technetium-99m methylene diphosphate (SPECT/CT with 99m Tc-MDP) is largely employed.26 This technology allows for multiplane image acquisition and 3-D display. The radiotracer 99m Tc is able to reflect the local osteometabolic rate, while the anatomic mapping is obtained by tomographic technique.26 As in the PET, anatomical and functional data are fused into a single image28 (Fig. 4c and d). Its main advantage is its sensitivity and specificity.26,28

Nuclear medicine examinations differ by the radiotracers/radioisotopes used, image capture technique, radiation dose, sensitivity, and presentation of results.15