Temporomandibular joint (TMJ) disorders (TMDs) encompass various clinical symptoms related to the skeletal and associated structures of the TMJ as well as the muscles involved in mandibular and neck movements [1]. Acute changes in occlusion, particularly without obvious dental or periodontal pathologies, may be one of the TMD symptoms attributed to alterations in the position of the mandibles. These alterations can be caused by joint or muscle disorders [2], such as disc displacement, degenerative joint disorder (DJD), dislocation, effusion, and myalgia of masticatory muscles [3-5]. It can also be caused by bone fractures [4] or a space-occupying mass [6]. Occasionally, identifying the etiology of acute occlusal changes based on clinical presentation and routine plain radiography is often challenging.

Herein, we describe two cases of acute malocclusion related to posterior disc displacement (PDD) and complete disc tearing and discuss observations after conservative therapies.

This study was approved by the Institutional Review Board of Dankook University Dental Hospital (DKUDH IRB 2024-03-001), and the committee waived the need for written informed consent.

1. Case 1

A 65-year-old male presented to the clinic with complaints of left TMJ pain and chewing difficulty because his teeth were not fitting together properly. He reported premature contact of the posterior molars on both sides, protrusion of the mandibular anterior teeth, and inability to cut with his anterior teeth. He also reported clicking and crepitus sounds, and all these symptoms occurred during breakfast approximately 2 to 3 months ago. As contributing factors, he had a heavy and unilateral chewing habit. His medical history included taking medications for knee arthralgia. He had no history of recent trauma or dental treatments.

Clinical examination revealed a maximum mouth opening of 45 mm, mild left TMJ pain without any joint sounds, and mild tenderness in the left TMJ. On intraoral examination, the posterior and anterior teeth were in contact on both sides, along with general tooth attrition.

Considering the crepitus sound and joint pain, the clinical diagnosis was DJD of the left TMJ. Computed tomography images showing posterior erosion and superior cystic changes of the left condyle confirmed the DJD (Fig. 1). The condyle was also positioned anteriorly to the temporal fossa, and broad depression was observed in the posterior–superior aspect of the condyle. Magnetic resonance imaging (MRI), which was performed to assess space-occupying mass or disc displacement, revealed complete tearing of the left TMJ disc, and the posterior fragment of the disc was displaced posteriorly (Fig. 2). Comparing the occlusion on the dental casts, the intraoral occlusion revealed a slight mandibular deviation to the right and protrusion (Fig. 3). Thus, acute malocclusion was confirmed as resulting from the PDD of the completely separated disc.

He underwent physical therapy several times but declined splint therapy. Because he was already taking medications for knee arthralgia, further pharmacotherapy was not administered. At the 1-month follow-up, he reported pain relief but occlusal disharmony persisted. At the 4-month follow-up, he remained pain-free and often experienced initial occlusal discrepancies on the left side during meals, which improved with continued eating. The midline has been slightly restored toward the left. He declined further treatments.

2. Case 2

An 88-year-old female presented to the clinic with complaints of difficulty fully opening her mouth, crepitus sound, and left jaw pain, as well as difficulty chewing, particularly on the left side. She stated that the symptoms had started 3 days earlier in the morning after corn consumption. As a contributing factor, she had a unilateral chewing habit. She had a history of right TMJ pain and impaired mastication approximately 9 years ago. Her medical history included occasional intake of medications for leg swelling and coronary artery stent insertion approximately 2 years ago. She had no history of recent trauma or dental treatments other than scaling.

On clinical examinations, her maximum mouth opening amount was 48 mm with mild pain in the left TMJ and a clicking sound in the left TMJ. The left TMJ was tended on palpation, and left TMJ pain increased on clenching. In the intraoral examination, the posterior teeth were in contact on both sides; however, the occlusion did not appear to fit tightly into the intercuspal position. General tooth attrition was also observed.

Panoramic radiography showed osteophytic change in the right condyle and slight dislocation of the left condyle without bony changes (Fig. 4). Nonsteroidal anti-inflammatory drug and physical therapy were prescribed under the preliminary diagnosis of arthralgia of the left TMJ. At the 1-month follow-up, the pain was relieved; however, impaired mastication persisted. Upon examination of her dental casts, the intraoral occlusion revealed mandibular deviation to the right anteriorly compared with her original occlusion (Fig. 5).

PDD was suspected, and MRI was planned. Attempts to reduce the displacement through manipulation before MRI, even under general anesthesia, were unsuccessful. MRI revealed complete disc tearing of the left TMJ and displacement of the posterior disc fragment (Fig. 6). Surgical removal of the displaced fragment of the disc could be considered to restore the occlusal change; however, she declined surgery because of her elderly status. At the 3-month follow-up, she tolerated the persisting malocclusion because no significant discomfort or pain occurred.

Herein, we reported rare cases of acute malocclusion attributed to PDD of completely separated discs. In PDD, the disc is positioned posteriorly relative to the normal disc position [7], typically diagnosed through MRI. Only two reports [8,9] have documented posterior displacement caused by complete disc tearing (described as “disc fracture”). Because a fracture implies a break in solid materials and calcification was not observed in the presented cases, the term “complete disc tearing” was used instead of “disc fracture.”

In previous reports, the chief complaint of patients with PDD included acute malocclusion, particularly the inability to occlude on the affected posterior teeth [7,10,11], which is consistent with the present cases. Unlike most PDD cases that occur during yawning or wide opening [10,11], the symptoms in the present cases occurred upon awakening in the morning or during breakfast. Excessive mouth opening or adhesion of the disc in the upper joint space has been proposed as etiological factors of PDD [11,12]. Complete disc tearing was speculated to occur when the perforated disc further tears and completely separates [9]. In present cases, a disc configuration like a “C-shape” on MRI may serve as supportive evidence. In case 1, a wide disc separation was observed in the central–lateral area, whereas in the medial region, the separated fragments were closely positioned. In case 2, an inverse pattern was noted. Perforation has been suggested to be caused by increased friction in the abnormal disc–condyle relationship, particularly anterior disc displacement [13,14], and increased friction may be caused by joint overload attributed to parafunctional habits [14]. Considering the severe tooth attrition observed in both cases and the onset of symptoms in the morning, parafunctional habits such as bruxism or clenching may have been a contributing factor.

In case 1, the posterior fragment of the separated disc appeared thin and small (Fig. 2). The thinned posterior portion of the disc was probably perforated during anterior disc displacement and subsequently completely separated [14]. In case 2, the sizes of the anterior and posterior disc fragments were nearly equal and thick (Fig. 6). This suggests the possibility of central perforation followed by complete tearing, and central perforation can occur even in the normal disc position [13]. Thus, the relatively minor occlusal changes in the presented cases compared with typical PDD cases may be caused by the displacement of only partial disc fragments rather than the entire disc. Furthermore, in case 1 where a relatively smaller disc fragment was displaced posteriorly, the occlusal changes were less pronounced. Both cases also exhibited severe tooth attrition resulting in flat tooth cusps, which may have masked the occlusal changes despite the mandibular displacement.

Several conditions are considered for the differential diagnosis of PDD. Condylar resorption caused by DJD is the most common cause of occlusal changes [4,5]. Bilateral condylar resorption may lead to an anterior open bite, whereas unilateral condylar resorption can result in a contralateral posterior open bite and mandibular shift to the affected side. In case 1, DJD was evident in the left condyle; however, a mandibular shift was observed to the right side, suggesting that the DJD was not the cause of the occlusal changes. In case 2, the DJD was confirmed in the right joint; however, it appears to have remained unchanged for approximately 9 years, suggesting that it is unrelated to the recent occlusal changes. Condylar dislocation can be excluded by confirming whether the condyle extends beyond the articular eminence on the radiograph. Masticatory muscle myalgia [1,3] and joint effusion [5] may also lead to acute occlusal changes. These conditions are commonly accompanied by pain, and occlusal changes resolve when the pain subsides. When occlusal changes occur in the absence of severe pain, the differential diagnosis can be challenging, necessitating MRI.

The PDD is mainly managed by conservative therapies such as manipulation, physical therapy, splint therapy, and medications, whereas surgical interventions such as arthroscopic lavage, arthroplasty, and discectomy are commonly performed for disc perforation [13,15]. Patients with complete disc tearing previously reported were managed with conservative therapies, despite surgical approaches being recommended to restore occlusal changes, consistent with the present cases. In case 1, a slight improvement in lateral deviation was observed at the 4-month follow-up. Melis et al. [8] reported a minor reduction in the open bite of the posterior teeth, suggested to be due to adaptation. Although the original occlusion was not completely restored, both patients refused further surgical therapies because of the nearly complete alleviation of pain with conservative treatments and the tolerable impairment in chewing ability.

In conclusion, PDD-related complete disc tearing is extremely rare, and occlusal changes are the main discomfort in patients with typical PDD. However, clinically significant occlusal changes may not be apparent; thus, a comprehensive evaluation is necessary. Including the cases presented here, most cases of complete disc tearing responded well to conservative treatment, resulting in pain relief, and any residual occlusal changes are tolerable. Persistent occlusal changes or presence of significant difficulty with mastication may require surgical intervention.

No potential conflict of interest relevant to this article was reported.

The datasets used during the current study are available from the corresponding author on reasonable request.

None.