Acute anterior open bite: Case report and review of the literature


Acute malocclusion outside the setting of macrotrauma is rare and therefore difficult to manage. Although some cases of acute malocclusion have been reported in the literature, to the authors’ knowledge, there has been only one report of an acute anterior open bite. The authors review the current literature on acute malocclusion, with a focus on anterior open bite. A case of an acute-onset anterior open bite is reported, where a systematic workup with an emphasis on patient function is performed to narrow the differential diagnosis to one of an intra-articular etiology. Arthroscopic lysis and lavage with maxillomandibular fixation was performed to achieve restoration of the permorbid occlusion, which was maintained for at least 1 year.


  • An acute onset of anterior open bite with no pain or changes in mandibular range of motion is reported.

  • Due to equivocal findings, a systematic functional examination was used to narrow the differential diagnosis to an intra-articular process.

  • Stable restoration of premorbid occlusion maintained 12 months after arthroscopic lysis and lavage with temporary intermaxillary fixation.


Acute malocclusion can be caused in many ways, including mid- and lower facial fractures. Even when there is no fracture, traumatic injuries to the face occasionally produce intracapsular temporomandibular joint (TMJ) effusion or hemarthrosis. Other etiologies of acute malocclusion include repeated subluxations of the mandible, internal derangements of the TMJ, rapidly progressing condylar degeneration, and very occasionally, masticatory muscle spasm [ ]. In addition, significant occlusal changes can occur as a result of iatrogenic causes such as inappropriate use of partial-coverage oral appliances. Malocclusions can occur immediately after the triggering event, or progressively within days to months. They can manifest in different forms, and the specific features are generally dependent on the underlying etiology.

While the etiology of an acute malocclusion is usually easily identified, some can be elusive and present challenges in diagnosis and management. We present a case of an acute-onset anterior open bite with equivocal clinical findings that required extensive workup based on a combination of historical report, imaging, and functional analysis in order to reach a diagnostic conclusion.

Case report

A healthy 23-year-old female presented with a sudden-onset anterior open bite after a prolonged dental procedure. She denied any prior history of symptoms in the TMJ or muscles of mastication, known parafunction or any treatment since onset of symptoms. She denied any particular alleviating or aggravating factors. On examination, she had normal and symmetrical mandibular range of motion with soft end-feel during passive opening. Palpation revealed no joint noises and no tenderness of the bilateral TMJ lateral poles or retrodiscal areas. There was mild to moderate tenderness to palpation of the right masseter muscle near the insertion along the mandibular angle. Intraorally, there was an anterior open bite of approximately 4mm, with contacts only in the second and third molars ( Fig. 1 ). A panoramic radiograph was unremarkable except for very mild flattening of the bilateral condyles, and both condyles showed a distinct cortical outline. A cone-beam computed tomography (CBCT) scan from an outside provider demonstrated minimal to mild degenerative changes of the bilateral condyles and no other remarkable findings. Hand-articulation of the study models demonstrated that prior to this incident, the patient had stable bilateral posterior occlusal contacts with an anterior vertical overlap of 1mm ( Fig. 2 ).

Fig. 1
Occlusion on presentation. A. Right side view. B. Frontal view. C. Left side view.

Fig. 2
Hand-articulated study models showing stable intercuspation and positive anterior vertical overlap. This occlusal relationship was consistent with the patient’s recollection of her premorbid occlusion. A. Right side view. B. Frontal view. C. Left side view.

Given the history of a prolonged dental visit immediately prior to the onset of symptoms, demonstration of normal and symmetrical mandibular range of motion with no intra-articular pain or TMJ sounds, and an absence of acute changes on imaging, a presumptive diagnosis of malocclusion of muscular etiology was made. A trial course of muscles relaxant (cyclobenzaprine) was prescribed. Two months after her initial presentation, the patient continued tolerating cyclobenzaprine poorly and showed no improvement of her inter-occlusal relationship. The results of her initial examination remained unchanged, as she continued to have normal, symmetrical, and painless mandibular range of motion without any joint sounds, and with a 4mm anterior open bite.

The patient grew increasingly distressed about the lack of progress with management of her condition, and with the lack of a clear diagnosis. She also expressed fear of receiving any further dental treatments as a result of the incident. Given the lack of response to therapy directed to the masticatory musculature, further investigation into an intra-articular etiology was made utilizing magnetic resonance imaging (MRI) of the TMJ. Those images showed minimal bilateral anterior displacement of the articular discs ( Fig. 3 ), with normal mandibular translational movements and no effusion. There were no significant findings that would satisfactorily explain her anterior open bite.

Fig. 3
T1 weighted MRI views. A. Right sagittal view showing mild anterior displacement of the disc (red asterisk). Junction of the disc and retrodiscal tissue marked with red arrow. Mild degenerative changes also seen in the condyle. B. Left sagittal view with similar findings as the right side (yellow asterisk on disc, yellow arrow pointing to junction of disc and retrodiscal tissue). C. Coronal view showing normal appearing position of the discs (measurements of thickness at the medial and lateral aspects shown).
Aug 8, 2020 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Acute anterior open bite: Case report and review of the literature
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