Analyzing the mechanism of masticatory muscle pain with experimental muscle pain models

2001 Fiscal Year Final Research Report Summary

• Project/Area Number: 11672004
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Surgical dentistry
• Research Institution: Keio University
• Principal Investigator: WAJIMA Kouichi Keio Univ., School of medicine, Assistant Professor, 医学部, 講師 (70138105)
• Co-Investigator(Kenkyū-buntansha): TAGAMI Aki Keio Univ., School of medicine, Assistant, 医学部, 助手 (30276373) ; KOGAI Hideki Keio Univ., School of medicine, Instructor, 医学部, 助手 (60205359)
• Project Period (FY): 1999 – 2001
• Keywords: Experimental muscle pain model / Centrally suppression of muscle contraction / Antinociceptive mechanism / Exteroceptive Suppression / The low-threshold mechanosensitivity / thermal thresholds / cutaneous sensorv perception threshold

Research Abstract

The purpose of this research is to analyze the factors which contribute the onset of muscle pain.
Experimental muscle pain model was composed of 30 minutes sustained clenching at 10% maximal voluntary contraction for following tests.
A decreased or abolished Second Exteroceptive Suppression (ES2) was found in chronic tension-type headache patients and proposed as a tool of diagnosis and research in muscle disorders. It was seemed that low ES2 suppression ratio means less suppressed of muscle activity and high ratio means well suppressed of muscle activity. ES2 of masseter muscle activity points towards a central pathogenic mechanism and hyperactivity of muscle is possibly caused centrally. The potency of ES2 as a diagnostic tool of suppression of muscle hyperactivity is confirmed.
The changes of cutaneous sensory perception thresholds were evaluated in the muscle pain model. The low-threshold mechanosensitivity (LTM) and thermal thresholds were evaluated over the site of masseter muscle bilaterally. Four stimulation qualities for evaluating thermal thresholds were recorded; the cool detection threshold (CDT), the warm detection limit (WD), the heat pain detection (HPD), and the heat pain tolerance (HPTO). These facial sensory perception thresholds were compared before and 6, 24 hours following the clenching. We found that (1) the pain intensity of masseter muscle recorded as VAS significantly developed directly after sustained clenching, (2) LTM was greatest at baseline and significantly decreased, and became least directly after sustained clenching, keeping same levels until 24h after clenching at the site of clenching. At the mirror site in the contralateral face LTM decreased gradually in 6 and 24 h after clenching. (3) Cool detection threshold did not differ during 6h after clenching, but significantly increased in 24h after clenching at the both site. WDT, HPT and HPTO didn't show any significant differences.