A 3,5-year-old child has symmetrical face, the middle part is predominant in proportions, swallowing is infantile, breathing is nasal. In the oral cavity the dentition corresponds with the age norms, the sagittal fissure is 3 mm, every tooth in the lateral part has its anatagonist, the lower teeth touch the hard palate. Miogymnastics with Dassa orbicularis oris activator is recommended. What function is normalised by this apparatus in the given case?