Modulation of jaw tapping force in response to unexpected changes in vertical jaw position

Mihoko Tanaka, DDS, Tetsurou Torisu, DDS, PhD, Kazuko Noguchi, DDS, PhD, Yoshihisa Yamabe, DDS, PhD, and Hiroyuki Fujii, DDS, PhD

Division of Removable Prothodontics and Management of Oral Function, Department of Development Reconstructive Medicine, Course of Medical and Dental Sciences, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan

Purpose: The purpose of the present study is to investigate the modulation of jaw tapping force to unexpected changes in the occlusal vertical dimension.
Materials and Methods: A device to change the vertical jaw position at tapping (VJPT) was applied to eight healthy subjects, and they were instructed to perform rhythmical jaw tapping movements. The VJPT was increased or reduced during repeated tapping, and tapping frequency (Hz), closing distance (mm), peak tapping force (N), and time to peak force (ms) were examined.
Results: The closing distance was smaller immediately after an increase than after a decrease in the VJPT. The peak tapping force was greater in the first trial than that in the second or third trial after an increase in the VJPT, but it was smaller in the first trial than in the second trial after a decrease in the VJPT. The time to peak force decreased in the second trial compared with the first trial after a decrease in the VJPT, but no difference was observed after an increase in the VJPT.
Conclusion: The results indicate that, when the vertical dimension is changed unexpectively, the jaw tapping force is likely to change markedly immediately without changing the maximum jaw gape. This modulation appears to be almost completed in first two to three trials after a change in VJPT, and a feedback and a feed-forward mechanisms are considered to be involved in it. (Int Chin J Dent 2006; 6: 21-28.)

Key Words: anticipation, force, jaw tapping movement, modulation, vertical jaw position.