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The swallowing reflex is centrally programmed by the lower brain stem, the so-called swallowing central pattern generator (CPG), and once the reflex is initiated, many muscles in the oral, pharyngeal, laryngeal, and esophageal regions are systematically activated. The mylohyoid (MH) muscle has been considered to be a "leading muscle" according to previous studies, but the functional role of the digastric (DIG) muscle in the swallowing reflex remains unclear. In the present study, therefore, the activities of single units of MH and DIG neurons were recorded extracellularly, and the functional involvement of these neurons in the swallowing reflex was investigated. The experiments were carried out on eight adult male Japanese white rabbits anesthetized with urethane. To identify DIG and MH neurons, the peripheral nerve (either DIG or MH) was stimulated to evoke action potentials of single motoneurons. Motoneurons were identified as such if they either (1) responded to antidromic nerve stimulation of DIG or MH in an all-or-none manner at threshold intensities and (2) followed stimulation frequencies of up to 0.5 kHz. As a result, all 11 MH neurons recorded were synchronously activated during the swallowing reflex, while there was no activity in any of the 7 DIG neurons recorded during the swallowing reflex. All neurons were anatomically localized ventromedially at the level of the caudal portion of the trigeminal motor nucleus, and there were no differences between the MH and DIG neuron sites. The present results strongly suggest that at least in the rabbit, DIG motoneurons are not tightly controlled by the swallowing CPG and, hence, the DIG muscle is less involved in the swallowing reflex.

Aim: In dental treatment, to remove an instrument, such as dental mirror or to remove a dental cotton roll inserted in the gingivobuccal fold, often brings the patient discomfort or pain. To prevent these uncomfortable conditions, dental instruments or dental cotton rolls are moistened based on an empirical basis. However, there has been no research done evaluating whether discomfort is reduced by these techniques. The purpose of this study was to evaluate the effects of moistened techniques on the patientsʼ discomfort and the operatorsʼ ease. Materials and Methods:Thirty eight subjects without hyposalivation were studied. Two procedures were implemented. One was that a dry or moistened dental mirror was removed after exclusion of the buccal mucosa. The other was removal of a dental cotton roll from the gingivobuccal fold after either moistening it or leaving it dry. The subjectsʼ comfort and the operatorsʼ treatment ease were evaluated on five point scales.Results: During these procedures, the subjectsʼ comfort was significantly increased by moistening of both the dental mirror and the cotton roll. The ease of performing both procedures was also significantly increased for operators in the moistened condition. In addition, there was a significant positive correlation between the subjectsʼ comfort and the operatorsʼ ease. Conclusion:When using dental instruments and removing cotton rolls, moistening increases both the subjectsʼ comfort and operatorsʼ treatment ease.