Patients with low-back pain can be evaluated immediately by means of an electrical tool that produces bony vibration to the lumbar spinal processes (Yrjama M, Vanharanta H. Bony vibrotactile stimulation: A new, non-invasive method for examining intradiscal pain. European Spine Journal 1994;3:233-235). In the rehabilitation of masticatory disturbance and dysphagia, an electric toothbrush is commonly used as an oral motor exercise tool for the facilitation of blood flow and metabolism in the orofacial region in Japanese hospitals. However, subjects receiving vibration in the facial regions reported increased salivary secretion. We attempted to develop an oral motor exercise apparatus modified by a headphone headset that was fixed and could be used for extended periods. The vibration apparatus of the heating conductor is protected by the polyethyle methacrylate (dental mucosa protective material), and electric motors for vibration control of the PWM circuit. We examined the amount of salivation during vibration stimuli on the bilateral masseter muscle belly, using a cotton roll positioned at the opening of the secretory duct for 3 min. Although the quantity of salivation in each subject showed various and large fluctuations in the right and left sides of the parotid and submandibular and sublingual glands, one or more of the salivary glands were effectively stimulated by 89 Hz vibration. The reported apparatus will be useful as an additional method in orofacial rehabilitation.

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We previously found that the greatest salivation response in healthy human subjects is produced by facial vibrotactile stimulation of 89 Hz frequency with 1.9 μm amplitude (89 Hz-S), as reported by Hiraba et al. (2012, 20011, and 2008). We assessed relationships between the blood flow to brain via functional near-infrared spectroscopy (fNIRS) in the frontal cortex and autonomic parameters. We used the heart rate (HRV: heart rate variability analysis in RR intervals), pupil reflex, and salivation as parameters, but the interrelation between each parameter and fNIRS measures remains unknown. We were to investigate the relationship in response to established paradigms using simultaneously each parameter-fNIRS recording in healthy human subjects. Analysis of fNIRS was examined by a comparison of various values between before and after various stimuli (89 Hz-S, 114 Hz-S, listen to classic music, and “Ahh” vocalization). We confirmed that vibrotactile stimulation (89 Hz) of the parotid glands led to the greatest salivation, greatest increase in heart rate variability, and the most constricted pupils. Furthermore, there were almost no detectable differences between fNIRS during 89 Hz-S and fNIRS during listening to classical music of fans. Thus, vibrotactile stimulation of 89 Hz seems to evoke parasympathetic activity.

We examined the effect of vibrotactile apparatus in patients with Sjögren's syndrome and others with reduced salivation in comparison to normal subjects. The most effective salivation in normal subjects was produced by 89 Hz vibrotactile stimulation with 9.8 μm amplitude on the parotid or submandibular glands vibrotactile stimuli. First, we examined by measuring the weight of dental cotton rolls positioned at the opening of the secretory duct for total salivation 3 min during resting, and then after 5-min intervals, the weights were measured every 3 min of vibrotactile stimulation on salivary glands. Furthermore, we measured facial temperature around vibrators after 2 min of vibration. We investigated 10 poor salivation patients with Sjögren's syndrome (8 patients) defined by examinations (contrast study or scintigraphic test) and others (2 patients). About 50% of patients with poor salivation gained recognition for good results, although they had periods of shortterm (3 months) and long-term effects (6-7 years) during recuperation. Furthermore, facial skin temperatures on both sides of parotid glands were decreased in Sjogren's syndrome after vibration, although their temperatures were increased following recovery. Although the mechanism is not clear, we think that vibrotactile stimulation gives activation to salivary glands under the rising facial temperature.

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