Assessment of mandibular mobility is an integral part of many dental examinations. Yet, information on the maximum range of mandibular motion in large groups of patients with temporomandibular disorders (TMDs) is limited.
Therefore, we analyzed the corresponding data of 500 TMD patients who had presented at the University Center for Dental Medicine Basel. All measurements had been carried out by one examiner. The average maximal values for unassisted jaw opening, protrusion, and movement to the right and left were 49.3 mm (SD: 9.1), 8.8 mm (SD: 2.3), 9.4 mm (SD: 2.5), and 11.8 mm (SD: 3.1), respectively. Since activities such as chewing, talking, oral hygiene or even yawning require neither very wide openings nor extensive lateral or protrusive excursions, we would like to propose the following general threshold values for impaired mandibular function: maximum interincisal distance < 30 mm; maximum laterotrusion as well as maximum protrusion < 5 mm.
These cut-off values, which are lower than those traditionally suggested in the dental literature, appear to be sufficient to carry out functionally undisturbed mandibular movements. By lowering the traditionally higher thresholds, the spectrum of anatomical and functional variability is increased. In this way, patients and non-patients may be protected against medicalization, overdiagnosis, and overtreatment.

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