An Evaluation of Lip Sealing during the Daytime and Sleep

Objectives: It is important to determine whether the lips are in light and continuous contact without muscular activity in orthodontic patients for the purpose of detecting the background to malocclusions. Although there are many methods to evaluate lip sealing such as visual examination, facial photography and cephalometric radiographs, these methods make the determination for short periods only, and none evaluate the lip sealing directly. Further, there are no reports of determinations of continuous lip sealing under whole day conditions. The purpose of this study was to detect and evaluate lip sealing times directly under three different conditions (when calculating, listening to music, and when sleeping) using a newly developed device with subjects with their individual normal occlusions. Methods: Twenty-five males with their individual normal occlusions took part in the study. All subjects wore the newly developed device to detect the lip sealing and were subject to polysomnography to detect sleeping. The examination was carried out under three different conditions: when performing calculations, as an intellectual task (15 minutes); listening to music (15 minutes); and sleeping (120 minutes): The sealed lip ratio in each condition was calculated as length of time the lips were sealed / length of time recorded. Results: 1. The mean sealed lip ratio during listening to music was statistically longer than in the two other conditions. 2. Subjects with low sealed lip ratios when listening to music generally had lower sealed lip ratios under the two other conditions. Subjects who had high sealed lip ratios while both calculating and listening showed a tendency towards higher sealed lip ratio while sleeping. Conclusion: These results suggest that lip sealing in subjects with normal occlusion is different depending on the situation.