The relationship between lip-closing strength and the related factors in a cross-sectional study

Abstract Introduction No diagnostic standard for assessing lip-closing strength (LCS) currently exists for clinicians. The aim of this study is to examine patterns in age-related changes in LCS and factors associated with LCS. Methods In total, 554 children aged 3–12 years participated in this study. They had no serious dental caries and no lip or mandibular dysfunction. We measured the children's LCS with a force device, and their parents completed a 24-item questionnaire. Statistical analyses were performed using the unpaired t -test and Pearson's correlation coefficient test. Findings LCS increased significantly from 3 to 6 years of age, but reached a plateau phase from 7 to 12 years of age. Between the ages of 3–12 years, LCS rapidly increased until infancy in a similar trajectory to the general type observed in Scammon's growth curve. In the 3 to 6-year-old age group, the correlation coefficient between "Age" and LCS was higher than between other items, and "Gender" and "Drinking liquid during meals" moderately correlated with LCS in the 7 to 12-year-old age group. The acquisition of the daily habit of closing the lips during the daytime is very important among children. These results indicated that LCS in children might have two different stages, one is a period of development (3–6 years old) and the other is a stable period (7–12 years old). Clinical Relevance This device is useful clinically for measuring the LCS of both children and adults and for the understanding of oral function.