Neurophysiological Study on Onset Mechanism of Ear Symptoms in Temporomandibular Disorders

2002 Fiscal Year Final Research Report Summary

• Project/Area Number: 13470410
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 補綴理工系歯学
• Research Institution: Tohoku University
• Principal Investigator: SASAKI Keiichi Tohoku University, Graduate School of Dentistry, Professor, 大学院・歯学研究科, 教授 (30178644)
• Co-Investigator(Kenkyū-buntansha): TSUBOI Akito Tohoku University, Dental Hospital, Lecturer, 歯学部附属病院, 講師 (00241646) ; INAI Tetsuji Tohoku University, Dental Hospital, Lecturer, 歯学部附属病院, 講師 (60193538) ; KOBAYASHI Toshimitsu Tohoku University, Graduate School of Medicine, Professor, 大学院・歯学研究科, 教授 (80133958) ; CHIBA Toshihiko Tohoku University, Medical Hospital, Assistant Professor, 歯学部附属病院, 助手 (70280881)
• Project Period (FY): 2001 – 2002
• Keywords: temporomandibular disorders / auditory brain stem response / Guinea pig / electrical stimulation / capsicin

Research Abstract

Ear symptoms, such as tinnitus and earache, are observed frequently in the patients of temporomandibular disorders. The aim of this study was to evaluate the influence of sensory inputs from the orofacial area on the auditory neural conduction by means of recording auditory brainstem response (ABR).
Guinea-pigs were anesthetized with pentobarbital sodium (25mg/kg) intraperitoneally and used for the experiment. Animals were mounted on the stereotaxic apparatus and were inserted a earbur with a small speaker into right external auditory canal. Sonic stimulation for eliciting ABR was supplied as click sound (frequency : 9 Hz) from the speaker. Recording electrodes of ABR were attached beneath the skin at the median vertex (Cz) and the Ieft and right mastoid (Al, A2). A reference electrode was placed at occiput. Sound pressure of the sonic stimuli was 100 dB at the beginnings of the experiment and then reduced by 5 dB until all of the responses in ABR were diminished. Waves of ABR at each s ound pressure level were averaged 100 times and averaged waveforms of ABR were estimated.
Single and train rectangle constant current pulses (duration : lmec) were applied for electrical stimulation to the orofacial regions. Subcutaneus injection of Capsicin (100mg/10 μl) was used as chemical pain stimulation. Electrical and chemical stimulation were applied to the periodontal ligaments of canine, oral mucosa and masseter muscles.
Before applying stimulation, ABR was recorded as a control. ABRs were also recorded after injection of 30 μ1 of capsicin. Before stimulation, six responses ( Wave I, II, III, IV, V, VI) were obviously obserbed in recorded ABR and the latency of these responses were reduced as reducing the sound pressure. After applying the chemical stimllation, the responses of ABR were not changed. The results after applying the electrical stimulation were the same as the results of the chemical stimulation. Namely, transient electrical or chemical pain stimulation could not induce the change of ABR.
These results suggest that transient noxious stimulation to the orofacial region does not cause the ear dysfunction such as ear symptoms observed in temporomandibular disorders patients. Therefore, it suggests the need of chronic model animal experiment, in which model animal with temporomandibular disorders would be made by artificial malocclusion. The relation of orofacial symptoms and ear dysfunction should be observed in thoese experiments.