The Morphological Characteristics, Growth, and Etiology of the Hyperdivergent Phenotype

Due to the skeletal complexity of the problem, hyperdivergent retrognathic patients are among the most difficult for orthodontists to treat. It is imperative to treat these patients for both esthetic and functional reasons. Hyperdivergent growth patterns are generally established early and most do not improve over time. The etiology appears to be environmental, due to postural adjustments related with compromised airways and weak masticatory musculature. If a lowered mandible posture is maintained in growing subjects, the dentition, dentoalveolar complex, and the mandible should be expected to compensate. Dentoalveolar heights should be expected to be excessive (i.e., supraeruption of the teeth), the ramus is shorter, the gonial angle is larger, the mandibular symphysis is taller and thinner, the mandibular plane is steeper, the mandible is retrognathic, and anterior lower face height is increased. Moreover, the jaws, especially the upper, are narrow. The most important factor underlying these developmental adaptations is true mandibular rotation. Rotation is important because it is the major determinant of the anteroposterior (AP) chin position. The detrimental skeletal changes that characterize hyperdivergent patients are ultimately due to backward or less than average true forward rotation. Theoretically, a therapeutic treatment that mimics normal growth (i.e., one that builds in true forward rotation) is desirable because it might be expected to correct not only the anteroposterior (AP) and vertical position of the chin, but also many of the other morphological maladaptations associated with the hyperdivergent retrognathic phenotype.