February 2021

Quantification of the Masseter Muscle Hardness of Stroke Patients Using the MyotonPRO Apparatus: Intra- and Inter-Rater Reliability and Its Correlation with Masticatory Performance

Authors: Chao Song 1, Yi-Fu Yu 1, Wen-Long Ding 1, Jian-Yong Yu 2, Li Song 1, Ya-Nan Feng 3, Zhi-Jie Zhang 3


  1. Department of Rehabilitation Therapy, Zhengzhou Central Hospital Affiliated to Zhengzhou University, Zhengzhou, Henan, China (mainland)
  2. Department of Rehabilitation Medicine, Huiji District People’s Hospital, Zhengzhou, Henan, China (mainland)
  3. Rehabilitation Therapy Center, Luoyang Orthopedics Hospital of Henan Province, Orthopedic Hospital of Henan Province, Luoyang, Henan, China (mainland)

Journal: Medical Science Monitor - January 2021, 27: e928109 (DOI: 10.12659/MSM.928109)

Background: Chewing dysfunction is one of the most common serious complications after a stroke. It may be influenced by the hardness of the masseter muscle and masticatory performance; however, the association between these 2 factors is not explicit. Thus, it is meaningful to explore the functional status of the masseter muscle among stroke patients.

Objective: The main objectives of this study were to examine the intra- and inter-rater reliability of the MyotonPRO apparatus in measuring masseter muscle hardness in stroke patients and to investigate the correlation between the bilateral masseter muscle hardness and masticatory performance in these patients.

Material and Methods: A total of 20 stroke patients participated in our study. The hardness of the masseter muscle was measured by 2 physiotherapists using the MyotonPRO apparatus. Overall, each patient masticated 2 pieces of red-blue bicolor chewing gum for 20 chewing cycles each. The chewing pieces were analyzed using ViewGum software for masticatory performance.

Results: The intra- and inter-rater reliability of the MyotonPRO apparatus for measuring bilateral masseter hardness of stroke patients was excellent. The correlation analysis showed that the hardness index of the masseter muscle on the affected side was moderately correlated with the masticatory performance of the same side.


Keywords: Hardness, Masseter Muscle, Reproducibility of Results, Stroke


Our findings indicate that the MyotonPRO apparatus is a reliable tool for examining masseter muscle stiffness in stroke patients and has excellent intra- and inter-rater reliability. The masticatory function of stroke patients was significantly greater on the unaffected side than on the affected side. A negative moderate correlation was found between masseter muscle stiffness and masticatory performance. The construct validity between the stiffness of the masseter muscle and masticatory performance was established in this study.