Japanese Journal of Oral Biology, 1998; 40: 160.

Research Pertaining to the Hardness/Softness of the Facial Muscles and the Soft Tissue of the Inner Oral Cavity

Joji Inada, Hiroshi Katayama, and Yoh Yoshida

(Osaka Dental University, Department of Physiology)

[OBJECTIVE]   The areas of the jaw and the mouth are made up of various soft tissue including, but not limited to, facial skin (including the skin of the lips), muscles (facial expression, mastication, and tongue), lips, cheeks, gums, tongue, and the mucous membrane of the palate.  In order to have normal function of the oral cavity, the characteristics of each soft tissue must be understood.   Thus, this study aims to use hardness/softness of each soft tissue as one parameter in the diagnosis of the function of the oral cavity using a newly developed tactile sensor to quantify hardness/softness.

[METHODS]   Using the tactile measurement system produced by Axiom Co., Ltd., hardness/softness measurements of the soft tissue were performed on an adult person and the data were displayed on a personal computer in real time.  Particularly, the change in the hardness/softness of the lips and of the facial muscles associated with expression and mastication near the corners of the mouth during facial activity were also examined.

[RESULTS AND DISCUSSION]   The hardness of the muscles associated with facial expression and mastication increased as the strength of their contraction increased.  After their relaxation, the hardness induced by the contraction gradually, but quite slowly, faded away.  It is thought that the change in the internal pressure of the muscles, or, in other words, their elasticity, influences the hardness of the muscles. Also, the hardness of the lips changed following activity of the muscles associated with facial expression near the corners of the mouth. (For example, when the large zygoma is raised during facial activity, the corners of the mouth are also raised, and the hardness of the upper lip increases).  From this it is thought that the degree of tension of the lips (due to extension or compression) can be known by measuring the hardness of the lips.

[CONCLUSION]   The ability of this tactile sensor to elicit the properties of the facial muscles associated with expression and mastication during facial activity has been shown.