CBCT imaging is primarily used in studies investigating morphological changes in osseous (bony) components of the TMJ. CBCT provides high diagnostic quality images providing detailed information on majority of disorders causing morphological changes with the joint surfaces of the mandibular and temporal components of the TMJ. Primarily, CBCT is the investigation of choice in detection and assessment of developmental abnormalities of TMJ, traumatic injuries, remodeling changes, degenerative changes, ankylosis and tumors. It can also provide information regarding changes in joint spaces which indicate towards internal derangement.
CBCT imaging however is unable to provide information regarding soft tissues, which need to be investigated using CT or MRI. The cartilaginous, muscular and capsular components of the TMJ are best imaged using MRI.
Developmental abnormalities
Bifid condylar head
Anteroposterior sections at 300µm show right condylar head with a concave depression (notch) along the posterosuperior aspect of the articular surface. The 2 lobes formed with the superior aspect of the condylar head are oriented in a mediolateral plane and show fairly demarcated cortical lining. Thinning of the condylar head along the anterioposterior plane is noted in the area of notching.
The left condylar head also shows a concave depression or notch along the superior articular surface. The 2 resultant lobes formed in the mediolateral plane show fairly demarcated cortical lining. Prominent thinning of the left condylar head is noted along the anterioposterior plane in the area of notching
Unilateral hypoplasia involving the right condylar process, mandible and right temporal bone : Hemifacial microsomia
3d reconstructed images, sagittal images and coronal images at 300µm show facial asymmetry. Unilateral, structural defect involving the right condylar process and right sigmoid notch region of mandible is noted. Morphological defect involving the condylar head and neck is noted. Prominent antegonial notch is noted with the right side. The zygomatic process of the right temporal bone is shorter. The defect partially involves the tympanic, styloid and petrous portion of the right temporal bone.
The right coronoid process shows thinning and sclerosis. Potential surgical defect involving ramus is noted at the level of the sigmoid notch area. Bicortical screws (2) are noted with the right ramus corresponding to horizontally impacted 47,48 region.
The mandible shows deviation to the right side. The occlusal cant is deviated with the left side. Anterior open bite is noted.
Hypoplasia with left condylar head
Lateral sections at 250µm show left condylar process with a small sized head showing irregular cortical lining and localized areas of erosion along the superior articular surface. The left condylar process also shows a comparatively small sized neck region. The left articular fossa shows fairly defined cortical margins. Flat appearance is noted with the left articular eminence. Irregular cortical lining is noted along the posterior slope of the left eminence.
The right condylar process shows a round shaped head with diffuse cortical periphery. The right articular fossa shows fair cortical lining. Flat morphology is noted with the right articular eminence.
Internal derangements
Internal derangement with the TMJ implies a mechanical disturbance which interferes with the functioning of a joint which is caused most commonly due to articular disc displacement. The causes of disc displacement includes structural abnormality with the articular disc, traumatic injury, oral para-functional habits. Derangement may or may not be associated with relevant symptoms.
As mentioned earlier, the disc itself is not visualized with CBCT imaging, however the resultant changes in the position of the related condylar head can be observed. Anterior, medial and lateral disc displacements are more common than posterior disc displacement. The most common type of displacement is anterior, usually a combination of anteriolateral/ anteriomedial.
The disc displacement is functionally categorized into 'with' and 'without reduction' depending upon its return to normal superior position during the mouth opening process. In disc displacement with reduction, the displaced disc in the closed mouth position, returns to a superior position resuming the normal condyle-disc relationship during the process of mouth opening. The associated symptoms usually include presence of "clicking" as the disc returns to its normal superior position i.r.t the condylar head.
Disc displacement without reduction presents with a disc which retains its displaced position and does not revert to its normal superior position during mouth opening movements. The loss of normal disc-condyle relationship integrity may cause inability to open the jaw or a locked jaw in the open position. In such cases, the disc may be structurally deformed or damaged which needs to be further investigated using MRI.
Anterior disc displacement with reduction
Lateral sections at 250µm in the closed mouth position show right condylar process with moderate degenerative changes involving the condylar head. The right articular eminence and right articular fossa also show remodeling changes.
The left condylar process also shows moderate to severe degenerative changes. The left articular eminence and fossa show remodeling changes.
In the closed mouth position, the right condylar head is located within the articular fossa, but is positioned posteriorly showing reduced posterior joint space with the right TMJ. This is potentially suggestive of anterior disc displacement with the right TMJ.
Reduced superior joint space is noted with the left TMJ. In the open mouth position, the condylar heads are located below the articular eminence on either sides suggestive of fair translation. Approximation of the bony surfaces is noted along the lateral aspect with the left TMJ in the open mouth position. This could be suggestive of suspected partial medial disc displacement with the left TMJ along with moderate degenerative changes involving the left condylar head.
Posterior disc displacement with reduction
Lateral sections at 250µm in the closed mouth position show right condylar head located anteriorly within the right articular fossa, below and distal to the posterior slope of the articular eminence. Increase in the posterior and superior joint space is noted.
The left condylar head is positioned within the left articular fossa. It is located below and distal to the posterior slope of the left articular eminence. Increase in the posterior and superior joint space is noted. This is suggestive of articular disc displacement.
Lateral sections in the open mouth position show right and left condylar heads located slightly anterior to the anterior slope of the articular eminence on either sides.
Anteroposterior (AP) sections show condyle and articular fossa relationship in the coronal plane. AP sections at 250µm in the closed mouth position show right condylar head positioned laterally i.r.t the right articular fossa. The left condylar head is also positioned laterally i.r.t the left articular fossa. Increase in the medial joint space and reduced lateral joint space is noted. This is suggestive of a potential posteriomedial disc displacement.
Remodeling and degenerative changes with the TMJ
Lateral sections at 300µm show flattening with the superior articular surface i.r.t the right condylar head. Localized concavity with corticated margin is noted with the distal slope of the right condylar head. Irregular cortical lining is noted along the articular surface of the right articular eminence.
Flattening is noted with the articular surface of the left condylar head and left articular eminence. Fairly demarcated cortical lining noted with the articular surfacs. This is suggestive of potential moderate degenerative changes with both TMJ's.
Oral Radiology : Principles and interpretation 5th edition White & Pharoah
Normal radiographic appearances and variations – HM Worth
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