Lip pressure at rest and during function in 2 groups of patients with different occlusions

The influence of the forces exerted by the perioral musculature on the position of the teeth has been the object of many scientific studies. Of the forces from the soft tissues, those from the tissues in the passive resting state are believed to be more important than forces exerted on the teeth during various functions such as speech and swallowing. The aims of this study were to measure upper lip pressure at rest and during swallowing in 2 groups of patients with different occlusions and to evaluate any differences among the groups.

Fifty subjects were divided into 2 groups according to occlusal and skeletal patterns: Class I and Class II. Both groups were divided into 2 subgroups according to age: young patients (9-17 years) and adult patients (18-35 years). A force-sensing resistor device (Datalog, Flexiforce low type, Biometrics Ltd, Gwent, United Kingdom) with a transducer thickness of less of 1 mm was used for the measurements. The sensor was positioned on the midline between the maxillary incisors with a thin layer of soft wax. Labial pressure measurements were made with the lips at rest and during swallowing saliva.

The average resting lip pressure was 24.59 ± 2.55 g/cm(2); during swallowing, the mean pressure was 24.87 ± 2.45 g/cm(2). No significant difference was found between lip pressure at rest and at function or between the two groups with different occlusions and skeletal patterns. There was a significant correlation between lip pressure and age.

In healthy patients, (1) upper lip pressure does not change at rest and during swallowing, (2) upper lip pressure was similar in the 2 groups (Class I, 24.33 g/cm(2); Class II, 24.61 g/cm(2)), and (3) lip pressure was higher in adults than in young subjects. Further studies are needed to measure the pressure of the lower lip and to evaluate whether there are differences in labial pressure between subjects with labial competence and incompetence.