RESUMO
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.