A major objective of orthodontic treatment is the establishment of harmonious relation of dentoalveolar structures with each other and with the musculoskeletal system which surrounds it. Such relation should be functionally stable and aesthetically pleasing to patient.

Skeletal class II malocclusion is resultant of either excessive maxillary growth or due to retarded mandibular growth. Twin block appliance mainly helps in growth modification of mandible in forward direction and neuromuscular adaptation of adjacent muscles. There are evidences saying that integrity of craniocervical system may be significantly dependent on position of mandible. Mastication, speech and respiration are vitally dependent on adequate mandibular position. In addition, this is also required for correction of postural relationships with other parts of head and neck. The Twin block is able to reduce muscle tension not only in craniofacial region but also in cervical region. It is intraoral, robust and less bulky appliance. With this in mind the present study is aimed to evaluate muscle activity of sternocleidomastoid and trapezius muscle following correction of skeletal class II malocclusion with Twin Block appliance.