It has been reported that TMJ inflammation causes an increase in background activity and evoked responses in C- and/or Aδ-primary afferent fibers innervated in inflamed tissues, resulting in peripheral sensitization. Long lasting hyperexcitability of the primary afferent fibers and trigeminal ganglion neurons modulate excitability of trigeminal spinal nucleus neurons, causing central sensitization. These peripheral and central changes in neuronal excitability are thought to be involved in an abnormal TMJ pain.
In order to clarify the peripheral and central mechanisms of TMJ pain, many researchers studied the neuronal activity and induction of neuropeptides in the peripheral and/or central nervous system using the rat model with TMJ inflammation. We analyzed a single neuronal activity and phosphorylated extracellular signal-regulated kinase (PERK) -LI cells in the trigeminal spinal nucleus caudalis (Vc) of rats with CFA-induced TMJ inflammation. The background activity and evoked responses of Vc neurons were increased 3 days after CFA injection into TMJ capsule, the receptive fields of these neurons expanded. These data suggest that central sensitization is induced in Vc neurons 3 days after TMJ inflammation, resulting in the acute TMJ pain.
TMJ chronic inflammation also caused strong pERK expression in dorsal portion of Vc neurons during passive jaw movement. The pERK-LI cells were increased following increase in frequency and intensity of jaw movement. These findings suggest that the dorsal portion of the rostral Vc is involved in mediating chronic pain following TMJ inflammation and that the intracellular ERK cascade is involved.

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The purpose of this study was to clarify the characteristics of gnathofunction such as masticatory muscle activities and jaw position during playing wind instruments and to examine the load to temporomandibular joints (TMJ) and masticatory musucles during playing the instruments. The subjects were eighteen brass instrument players and twelve woodwind instrument players. Electromyograms (EMG) of masseter, temporal, orbicural oris and digastric muscles were recorded and distance between lower incisal points at intercuspation and during playing wind instruments was also measured. The obtained results were as follows:
1. During playing instruments, EMG activity in masseter and temporal muscles was extremely small in comparison with those during maximum clenching, while EMG activity in orbicural oris and digastric muscles was comparatively large.
2. There was no obvious change of EMG activity in each muscle when the sound volume in playing instruments was changed.
3. There was no obvious difference of EMG activity between brass instrument and woodwind instrument group in masseter, temporal and digastric muscles. However, brass instrument group showed larger variation of activity in masseter muscles among the subjects than that of woodwind instrument group.
4. Lower incisal point of woodwind instrument group moved to inferior direction in larger distance than that of brass instrument group. However, brass instrument group showed larger variation of direction in movement than woodwind instrument group.
The results suggested that the tension of masseter and temporal muscles and compressive load to TMJ are generally small during playing wind instruments. However, it is necessary to examine the influence of individual difference further.

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A hypotheses about mechanism of tinnitus without hearing loss in temporomandibular disorders was examined by kinetic analysis of temporomandibuler joint as follows: (1) Disc displacement and disc deformation and also joint effusion in temporomandibular joint were examined by using magnetic resonance imaging, (2) Condylar positions were measured on radiographs by using the standardized axial projection and Schuller's projection. (3) Terminal hinge axis point located by using hinge locator (Almore Co.), it was X-rayed and transferred on standardized radiograph and measured the position precisely, (4) Direction and distance of condyle shift at a time of occurrence before and after occlusal treatment were analyzed three-dimensionally on articulator. Furthermore, neuro-otological examinations were done as follows: (5) Activities of the outer hair cells in cochlea were evaluated by DPOAE (distortion-product otoacoustic emission) using GSI-60 system (Grason-Stadler Co.) . And (6) Responses on efferent neural pathway throughout brainstem were examined with SR (auditory stapedial reflex in ipsi-lateral-stimuli) by using GSI-33 middle ear analyzer (Grason-Stadler Co.) . And also, (7) Functions of middle ear transmission system were evalued by TM (tympanometry) using impedance meter MA-4000 (Morita Co.), it were proved as the impedance on tympanic membrane (IMP) and peak pressure in middle ear cavity (PRS) . Those data were gathered from the twenty-five patients (female, 2lto 62 years old), they were classified into two groups by means of the presence (OMS) and/or absence (TMD) of tinnitus, and were analyzed by X²-test and Mann-Whitney U-test for comparing between these two groups.
We obtained the following results, the differences in group OMS comparing with group TMD are significantly noted as follows: (1) Relative frequency of disc deformation, (2) Mesio-distal distance of terminal hinge axis point located on standardized radiograph, (3) Vector Lat/Sag in condyle shift at disorder joint side, (4) Reflex threshold in ear at disorder joint side, (5) Reflex latency L₁ and (6) middle ear pressure in ear at opposite side. However, (7) any difference of the activities of outer hair cells in cochlea weren't noted. From these results, a worthy finding of the above mentioned study is on the difference of reflex threshold, which was significantly noted as unilateral disorder at one side, but not on both side.
Referring to these results on neural pathway in stapedial reflex, the valuable consideration is the torsion of condyle capsule stimulates trigeminal ganglion which sends projections to the superior olivary complex.

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