Lip-closing strength in children is enhanced by lip and facial muscle training

Objectives

Weakening of lip‐closing strength (LCS) associated with an incompetent lip seal (ILS) may affect the oral balance between the lip and tongue pressures. The purpose of this study was to evaluate the effects of lip‐closing training in children with lower LCS and/or abnormal habits across different age groups and to compare its effects on increasing LCS in children with malocclusion and/or oral habits.

Material and Methods

Lip‐closing training was performed by 154 Japanese children aged 3–12 years using a specialized training device at home for 3 months. Children with oral habits and/or exhibiting less than standard LCS were included. LCS was measured using a digital strain force gauge at a dental clinic at the beginning (T0) and after each month (after 3 months: T3).

Results

Children had higher LCS responses after lip‐closing training. The first month of lip‐closing training was more effective than the subsequent months. With lip‐closing training, the LCS increased from an average of 6.2 N (T0) to 11.4 N (T3) in Group I, 7.9 N (T0) to 12.8 N (T3) in Group II, and 6.8 N to 11.4 N in Group III. Anterior cross bite, including reverse bite, open bite, and tongue thrusting, significantly reduced training effects.

Conclusion

Our findings showed that lower LCS in children with ILS resulted in greater responses to lip‐closing training in a short period, but oral dysfunction, such as abnormal habits, inhibited the positive effects of training. Our results suggest that less detrimental effects of malocclusion and abnormal oral habits lip‐closing training enhances LCS in younger children.

Distribution of lip-seal strength and its relation to oral motor functions

Objectives

Lip‐seal strength, which represents the muscle strength of the lips, appears to chiefly contribute to mastication and pronunciation. However, the functional characteristics of lip‐seal strength in adults are still undefined. The present study aimed to understand not only the distribution of lip‐seal strength in adult men and women but also the effect of age on this strength and identify oral motor functions correlated with lip‐seal strength.

Materials and methods

The subjects included 339 participants (men: 170, age 39.2 ± 18.2 years; women: 169, age 43.1 ± 19.7 years). Oral motor function was evaluated for lip‐seal strength, oral diadochokinesis (ODK), tongue pressure, occlusal force, and masticatory performance. Statistical analyses included the Shapiro–Wilk, Mann–Whitney U, and Jonckheere–Terpstra tests, in addition to the Spearman's correlation analysis and curvilinear regression analysis.

Results

Lip‐seal strength did not have a normal distribution (p < 0.001). The mean ± standard deviation and median (first quartile, third quartile) of lip‐seal strength were 11.2 ± 3.4 and 10.9 (8.7, 13.2)N for the whole sample, 12.3 ± 3.4 and 11.9 (9.4, 14.4)N for men, and 10.2 ± 3.0 and 9.9 (8.0, 12.0)N for women. A significant difference was observed in lip‐seal strength between men and women (p < 0.001). Oral motor functions showed a marked correlation with lip‐seal strength, including tongue pressure, occlusal force, and masticatory performance and ODK (/pa/ and /ta/), tongue pressure, and masticatory ability in men and women, respectively. In women, lip‐seal strength declined with increase in age.

Conclusions

Lip‐seal strength was non‐normally distributed in both men and women, and lip‐seal strength was affected by age only in women. Lip‐seal strength and multiple oral motor functions were significantly correlated. Because the indicators of perioral muscle strength and performance were correlated with lip‐seal strength, lip‐seal strength may also partially reflect the condition of the perioral muscles.

Relationship between oral function and mandibular anterior crowding in early mixed dentition

The position of the dentition is considered to be determined by a combination of forces exerted by the perioral muscles and tongue. We hypothesized that mandibular anterior crowding may be related to abnormalities in the development of oral function. To determine the relationship between oral function and mandibular anterior crowding in early mixed dentition. A total of 61 children (30 boys, 31 girls) with early mixed dentition were included in this study. Height, body weight, maximum occlusal force, lip‐closing strength, and maximum tongue pressure were measured in all participants, and their dental casts and lateral cephalograms were evaluated. Little's irregularity index (LII), evaluated by dental casts, was used as an indicator of mandibular anterior crowding. Maximum occlusal force and lip‐closing strength were not significantly correlated with the LII, although they were positively correlated with maximum tongue pressure, mandibular intercanine perimeter distance, and upper central incisor (U1)‐to‐NL angle (p < .05). Maximum tongue pressure was negatively correlated with LII (p < .05). Maximum tongue pressure and LII were significantly positively correlated with the mandibular intercanine perimeter distance and U1/NL angle, and negatively correlated with the interincisal angle (p < .05 for all). Crowding of the mandibular anterior teeth was directly correlated with tongue pressure function and indirectly correlated with maximum occlusal force and lip‐closing strength.