Lips function to provide competence to the oral cavity during mastication and at rest. To accomplish this multitude of functions, they require a complex system of muscles and supporting structures. In 1942, Breitner stated that there should be a balance between the forces of the tongue from within the dental arches and compensating action of the lips and cheek musculature. He called this as functional equilibrium. The exaggerated lip eversion on the maxillary incisor makes lip seal difficult. The discrepancy between bone bases leads to hypofunction and shortening of upper and lower lips, with eversion, and closure occurs on the palatal surface of the maxillary incisors, leading to Mentalis muscle hyperfunction, as it contributes to the increase of the lower portion of the Orbicularis Oris muscle.Alfred Paul Rogers was among the first to recommend the use of muscles for correction of malocclusion.

To determine and compare the thickness of the Circumoral musculature Ultrasonographically in the Control Group (skeletal class I) and Experimental Group (skeletal class II division 1) in relaxed and contracted state.