The authors developed a new type of hourglass worm gearing based on the authors’ own theories [1, 2]. The worm having the developable tooth surface can be ground precisely. The pair of the tooth surfaces of the gearing have comparatively small relative curvature and contact with each other with the contact line lying perpendicularly to the relative sliding velocity. The manufactured gears showed the efficiency of 80 percent with the authors’ experimental apparatus without trouble in continuous running test over 3000 hours. Conditions are: reduction ratio, 40; center distance, 100 mm; input power, 3.7 kW; rotating speed of the worm, 1800 rpm.

The aim of this study was to determine whether chewing with closed lips improved masticatory efficiency compared with open lips. A total of 21 adults comprising 10 men and 11 women with a mean age of 26.2±3.5 years and normal masticatory function were included in the study. The study participants were instructed to chew a fresh gummy under two conditions for 30 seconds each, one after the other: the first with closed lips, and the second with open lips. The average size of the fragmented gummies was calculated and graded from 1 to 4 according to a specific scale. Masticatory efficiency was evaluated using this "gummy mastication value" and the Gnatho-hexagraph II to observe and analyse jaw movement during chewing. Differences in chewing time and mouth-opening distance were also compared. The gummy mastication value for open and closed lips mastication was 2.51±0.56 and 3.25±0.50, respectively (p<0.01). Masticatory efficiency was significantly greater during closed-lip mastication. The number of chewing strokes over 20 seconds decreased while chewing time and mouth-opening distance increased in cycle 1 with open-lip mastication. In conclusion, the present results revealed that chewing efficiency improved with closed-lip mastication, indicating that instruction to seal the lips while eating is appropriate and necessary.

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