Effect of a modified Herbst appliance on maxillofacial morphology

Abstract

Cases of skeletal maxillary protrusion can be classified into those in which there is overgrowth of the maxilla and those in which there is undergrowth of the mandible. At the time of treatment for skeletal maxillary protrusion with mandible undergrowth during the growth period, functional appliances are often used to stimulate forward growth or remodeling of the temporomandibular joint region. However, it is difficult to stimulate forward growth of the mandible during the period from late adolescence to adulthood. During this time orthodontic treatment is usually in the form of either surgical orthodontics or distoclination of the maxillary incisors. Functional appliances used during the growth period include the Frankel (FR-2), the twin block, the bionator, and Herbst appliances. Although almost all of these are removable, among them, the Herbst appliance is a fixed type. The Herbst appliance was introduced by Emil Herbst for the purpose of stimulating protrusive growth in an underdeveloped mandible. McNamara performed experiments in growing monkeys, and in recent years, Pancherz et al. 9 published clinical reports on the subject. Since the Herbst appliance is a fixed Angle Class II improvement device, effective treatment does not require cooperation of the patient. 11 We studied the influence of the modified Herbst appliance on late mandible growth and development in subjects who had completed growth.