Introduction

Functional appliances (FAs) are orthodontic/orthopedic appliances designed to treat patients with dental malocclusions and skeletal imbalances (e.g., retrognathia and prognathia). Despite the relatively long history of FA treatment, there continues to be controversy as to their mode of action, due in part to conflicting findings between investigators.

These appliances have been more commonly used in Europe than in the United States. American orthodontists were more likely to treat with fixed appliances or braces, whereas Europeans have been more interested in altering masticatory function to correct malocclusions, usually with the use of removable appliances. There are numerous designs all generally known as “functional appliances.” Some of these include specialized features for dental arch expansion, altering the facial vertical dimension, myofunctional therapy, and so on. The theoretical basis of FA treatment is in general the principle that a “new pattern of function,” dictated by the appliance, leads to the development of a “new morphological pattern” (Ricci, 1983). This new functional pattern is, presumably, generated by the sagittal and vertical alteration of the mandibular position in young patients (usually in early mixed dentition stages), resulting in orthodontic (primarily affecting dental units) and orthopedic (structural alterations affecting bone) adaptations to a new jaw position (Figure 15.1).