Lip function: a study of oral continence.

Oral continence is achieved through the harmonious interplay of several factors of which the most important are the lip sensitivity, the strength of the orbicularis oris muscle and the height of the lip curtain. Forty-four persons with varying degrees of oral incontinence and diverse lip disorders were then examined and compared against the normal values. Significantly low values for all three factors found in the orally incontinent patients supported our hypothesis that the normality of these factors is essential for the maintenance of the oral seal. Central causes of dribbling, such as mental retardation and salivary over-secretion, irrespective of etiology, are not considered here.