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Nocturnal bruxism may be secondary to nocturnal gastroesophageal reflux, occurring via sleep arousal and often together with swallowing. The physiologic link between bruxism and the increase in salivation needs to be investigated.

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ASDA, American Sleep Disorders Association; EMG, electromyogram; GER, gastroesophageal reflux; LES, lower esophageal sphincter; NREM, non-rapid eye movement; REM, rapid eye movement; RMMA, rhythmic masticatory muscle activity; SB, sleep bruxism; SD, standard deviation; UES, upper esophageal sphincter.

To date, the effect of food size on the movement of the mandibular first molars and condyles during chewing has not been fully examined due to methodological problems. The purpose of the present study was to examine the previously unknown effect of food size on masticatory jaw movement. Using a face bow, light-emitting diodes, and optical cameras, we recorded, in 16 young adults with good occlusion, mandibular movement for the first 10 strokes during the unilateral chewing of similarly shaped hard gummy jellies weighing 5 g and 10 g, respectively. The chewing cycle time for the 10-g jelly was significantly longer than that for the 5-g jelly. The jaw-closing and -opening maximum velocities, gapes at the maximum velocities, and maximum gape were significantly faster and larger when 10-g gummy jellies were chewed, compared with results with 5-g jellies, at the mandibular first molar on the chewing side and the condyle on the non-chewing side. With the exception of the velocity, similar tendencies were observed at the molar on the non-chewing side. However, such significant differences were not detected at the condyle on the chewing side. The mandibular first molar on the chewing side was that most affected by food size, and the mean value of the maximum gape coincided approximately with the height of each jelly. These results suggest that humans chew hard coherent food such that the mandibular teeth that come into contact with the food open to a height equivalent to that of the food bolus, and that the changes in movement of the other parts of the mandible are minimized, ensuring efficient mastication.

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