A novel method for the remote measurement of trismus in clinical trials using mobile phone cameras

Abstract

Objective: To evaluate the reliability and validity of a novel method for remotely measuring trismus. Materials and methods: We recruited 60 volunteers who took three types of photographs at a fixed restricted jaw position mimicking limited mouth opening, including one selfie and one portrait with or without a reference frame. Additionally, the interincisal distance and the width of the upper central incisors were measured with a ruler, as per common practice. Measurements of trismus were made using image analysis software comparing different types of photos and calibration methods. Intraclass correlation coefficient (ICC) and 95% limits of agreement (LoA) with 95% confidence interval were calculated to evaluate reliability and validity. Results: The proposed method demonstrated high reliability (ICC 0.998; 95% CI 0.997, 0.999). Calibration of photographs using at least a baseline photograph with an external reference frame yielded unbiased measurements and minimised variability. The use of selfies compared to portrait photos also increased variability. Conclusion: The measurement of trismus can be performed using images taken remotely by patients using their mobile phone cameras. The proposed method is highly accurate, with best results obtained by using a reference frame for calibration of portrait photographs. Clinical relevance: We propose an easy, cheap, and accurate method that allows for remote and frequent monitoring of trismus in clinical studies using patients’ mobile phones.