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Open Access Open Badges Research article

Reliability and validity of self-assessment of mouth opening: a validation study

Daniel Satnam Singh Saund1, David Pearson1 and Thomas Dietrich2*

Author Affiliations

1 Specialist Registrar Oral Surgeon, University of Birmingham, St Chads Queensway, Birmingham, B4 6NN, UK

2 The School of Dentistry, University of Birmingham, St Chad’s Queensway, Birmingham, B4 6NN, UK

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BMC Oral Health 2012, 12:48  doi:10.1186/1472-6831-12-48

Published: 12 November 2012



The objective of this study was to evaluate the reproducibility and validity of patients’ mouth opening measurements in a research setting.


Firstly, 68 patients made repeated self-measurements of mouth opening using a cardboard scale (Therabite Range of Motion Scale – TRMS). Secondly, 80 patients enrolled in a clinical trial on morbidity after lower third molar surgery, made daily assessments during the postoperative week. Patients’ measurements were then compared to gold-standard clinicians’ measurements.


Reliability of patients’ measurements was excellent with an intraclass correlation coefficient of 0.92. The patient’s measurements correlated well with the gold-standard clinician’s measurements, both for the first 68 patients (Pearson’s rho ranging from 0.86 to 0.90, p < 0.0001) as well as for the 80 patients enrolled in the clinical trial (rho = 0.82, p < 0.0001 at day 2, rho = 0.83, p < 0.0001 at final visit).


TRMS can be used by patients to produce reproducible and valid mouth opening measurements.

Reproducibility; Validity; Measurement; Scale; TheraBite