New diagnostic tools in orthodontics

Abstract

The discipline, science, and art of orthodontics are concerned with the face and our ability to modify its growth. Orthodontists achieve their goals by manipulating the craniofacial skeleton, with particular emphasis on modifying the dentoalveolar region, the temporomandibular joint, and the sutures. In a few patients, external orthopedic forces are applied that mirror some techniques used in medical orthopedics. Most treatments, however, focus on modifying the occlusion and controlling dentoalveolar development and abnormal vertical growth. Underlying the varied techniques that orthodontists use is the confounding but important factor of the soft tissues, particularly the facial and mandibular muscles. Orthodontists know that the lip, facial, tongue, jawopening, and large jaw-closing muscles are relevant to the clinical outcome for their patients. How these muscles affect the face depends on the region of the craniofacial skeleton. Although the craniofacial skeleton can develop completely during the fetal stage without muscle contraction or tension, the form of the individual bones changes (domed vault, high and flat zygomatic arch, mandible bent dorsoventrally, and no temporomandibular joint spaces). 1 Postnatally, the relative effect of muscle on bone depends on the region of the craniofacial skeleton and the stage of development. Mandibular muscles modify the craniofacial skeleton through 3 mechanisms: direct tension on the attached bone that extends beyond the attachment site of the muscle; developing forces on the dentition, which in turn modify the underlying and adjacent bone; and reactive forces and stresses on the condyle of the temporomandibular joint. These muscle and soft tissue forces are real. Weakening of the systemic muscles in a young child with muscular dystrophy results in a highly retrognathic mandible. 2 Normal muscle function is needed to maintain a normal face.