If wishes were horses: functional appliances and growth modification

Lysle E Johnston
Progress in Orthodontics 2005, 6 (1): 36-47

OBJECTIVES: Aside from the common observation that functional appliances work, the literature has little to say about the means by which a correction is achieved and whether or not it differs from that produced by a single phase of fixed-appliance treatment. There seems to be relatively little interest in these basic questions. The purpose of this communication is to explore and discuss the action of functional appliances in light of their interaction with the gross mechanisms of craniofacial growth. It is hoped that a collegial discussion will ensue.

RESULTS: Normally, the mandible outgrows the midface, even in Class II patients. This favorable pattern of growth, however, produces maxillary dentoalveolar compensations that prevent the excess mandibular growth from having any marked effect on the malocclusion. Functional appliances may avoid this mesial movement of the maxillary dentition by dissociating mandibular displacement from the condylar growth that normally accompanies it. By producing an anterior functional shift that corrects the Class II relationships all at once and by maintaining this advanced position long enough for the condyles to grow back into the fossae, functional appliances can make clever use of the normal pattern. No "extra" growth may be necessary. Relative to untreated controls, their ultimate effect is in the midface, rather than the mandible. Moreover, the final correction may not differ significantly from that produced by fixed appliances or by two-phase treatments in which the first phase is some sort of extra-oral traction to the midface.

CONCLUSION: Functional appliances may utilize the normal pattern of facial growth, rather than some sort of mandibular "growth modification," to achieve a molar correction. As a result, their ultimate effect may not differ from that produced by the various one- and two-stage alternatives. The choice of which to use may well prove to be a simple practice-management decision.

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