Abnormal function of the temporomandibular joints and related musculature. Orthodontic implications. Part II.

Abstract

Timing of mandibular growth and orthodontic treatment are coincidental, not cause-and-effect. Comparison of cephalometric radiographic tracings made before, during, and after treatment has shown no evidence that orthodontic forces can either arrest or stimulate growth of the condyle. Conversely, the growth behavior of the condyles can have a profound effect on the time required to achieve an orthodontic correction and on the anatomic and functional relationships at the end of treatment and later. Mandibular growth at the moment of orthodontic force application can have important effects on facial growth and function. If there is no growth, the mandible may rotate downward and backward, and condyle displacement and clicking can occur. Future growth rarely leads to recovery of such alterations. With adequate growth at the moment of orthodontic force application, the freeway space is maintained and horizontal tooth movement does not alter mandibular position. The position of the maxillary incisors in the face must be based on many considerations going far beyond arbitrary conformity to some "standard" values based on averages. Functional relationships and their effects on the joints are one of those considerations, along with esthetics. Dynamic thinking requires that maxillary incisors not be over-retracted, anticipating continued growth of the condyle that can reposition the body of the mandible and lower incisors downward and forward. This can occur before, during, or many years after treatment. If a tight incisor relationship is established, or develops naturally, in the early or midteens, and the condyles later outgrow the maxilla, clicking may well develop. Anterior translation of the mandible with the new growth is impeded by the incisors, so posterior displacement of the condyles occurs instead. This is most likely to occur in straight ("good") faces. Facial morphology, or pattern, has an impact on function. In the straight facial pattern, these problems usually involve incisor interference. In convex faces, the problems more often involve vertical molar interferences. Each of these presents its own unique problems and treatment requirements.