Characteristic mouth opening: a precise measurement of vertical mandibular movements

Objectives: The aim of the study was to investigate whether a composite score representing “characteristic mouth opening” (CMO) improves the precision of measuring mandibular range of motion (ROM) in patients with temporomandibular disorders (TMD) and normal controls.

Methods: Six ROM variables, unassisted opening without pain, maximum unassisted opening, maximum assisted opening, protrusive, and laterotrusive movements, were measured during the calibration training exercises within the validation study of the Research Diagnostic Criteria for TMD. One hundred eighty subjects, 165 with a minimum of one TMD diagnosis and 15 normal controls, were each measured a total of three times by six different blinded examiners. A composite score was derived as the mean for both the vertical and the horizontal ROM variables. The precision of the two resultant composite scores and the individual ROM variables was computed with the standard error of measurement (SEM).

Results: The SEMs for the individual measurements of unassisted opening without pain, maximum unassisted opening, and maximum assisted opening were 4mm, 3mm, and 3mm, respectively. For the vertical composite score of CMO, the SEM was 2mm. For the horizontal composite score, and the individual laterotrusive and protrusive movements, the SEM was 1mm.

Conclusion: Combining vertical opening measurements into a characteristic mouth opening (CMO) composite score improved the precision of measuring mouth opening. Conversely, combining horizontal ROM variables did not change the precision for these measurements. Given these results we recommend the CMO for observational studies and clinical trials due to its improved precision and therefore increased statistical power over individual measures of vertical opening. Supported by NIDCR # UOI-DE13331.