Relationship between frontal craniofacial morphology and horizontal balance of lip‐closing forces during lip pursing

The objectives of this study were to quantitatively evaluate the relationship between frontal craniofacial morphology and the horizontal balance of the lip‐closing forces (LCF) generated during maximum voluntary pursing‐like movements in patients with mandibular deviation. Thirty‐one subjects (median age 25·4 ± 8·9 years) without a history of orthodontic treatment were randomly selected from among the orthodontic patients who visited our hospital. Lip‐closing forces was recorded in eight directions during maximum voluntary pursing‐like lip‐closing movements. The subjects were divided into the deviation (two males and 11 females) and non‐deviation groups (four males and 14 females). There was no significant difference in the total LCF between the deviation and non‐deviation groups. In the deviation group, the mean LCF value on the deviation side of the upper lip was significantly lower than that detected on the non‐deviation side of the upper lip, while the mean LCF value for the deviation side of the lower lip was significantly higher than that for the non‐deviation side of the lower lip. In contrast, no significant difference in upper or lower lip LCF was detected between the deviation and non‐deviation sides in the non‐deviation group. The difference in the LCF generated in the lower lip between the deviation and non‐deviation sides was significantly positively correlated with mandibular menton deviation and significantly negatively correlated with the difference in maxillary height between the deviation and non‐deviation sides. These results suggest that the horizontal balance of the upper and lower lip LCF produced during pursing‐like lip‐closing movements in patients with mandibular deviation is related to frontal craniofacial morphology.