The association between orthodontic treatment and temporomandibular disorders has always been of great interest to oral health professionals. A change in occlusion during orthodontic treatment can affect muscles and joints surrounding the jaw, resulting in temporomandibular disorders (TMD). Multiple etiological factors have been associated with the TMDs and they may be manifested by pain and/or sound of TMJ. This book aims to provide the effect of orthodontic treatment on temporomandibular joint and muscles of mastication.