It seems to me that many of the controversies that beset orthodontics have evolved because of confusion about definitions. It would help orthodontists immensely if they could come to some kind of precise semantic agreement before disagreeing about the merits or liabilities of an appliance, technique, or philosophy. It is one thing to differ in interpretation of the same data, but quite another to be polarized in a misunderstanding about words and definitions. The first kind of disagreement can sharpen and refine knowledge, but the second simply wastes energy and time.
A prime example is the distinction between orthopedic and orthodontic forces. When some orthodontists hear the term orthopedic, they conjure up a mental image of a Herbst appliance or a Fränkel function regulator. Others insist that nothing short of a forceful displacement of bones by surgery or appliances constitutes orthopedic movement. An unequivocal definition of orthopedic function or movement would do much to clarify the topic and establish guidelines that would govern our interpretation of data.
When orthodontists in the United States began experimenting with and prescribing functional appliances more than a decade ago,1-3 the spectacular condylar growth in adolescent patients encouraged researchers and clinicians alike to believe that these appliances might somehow promote extraordinary growth of the mandible. Consequently, they placed appliances such as the Herbst, Fränkel, and bionator in a category of orthopedic apparatus. Unfortunately, in these early investigations, the animals and patients were not followed to maturity or compared to paired control groups.
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Not until the work of DeVincenzo did orthodontists begin to receive a clear picture of what was actually happening with patients who used "orthopedic" appliances.4 DeVincenzo discovered that in adolescents, these appliances could accelerate condylar growth, but that after the first year or so of acceleration, the condyles quieted down and grew abnormally less than those of the controls. At maturity, the mandibles of the experimental and control groups showed no statistical difference in length.
Apparently, the extra condylar growth that occurs with functional appliances enables a dentoalveolar adaptation that holds the occlusion in a corrected position while the entire TMJ apparatus remodels.5 Moreover, there is plenty of evidence that this corrected position will not be maintained without sharp bicuspid occlusion.5-8
Although no one, to my knowledge, disputes the clinical efficacy of functional appliances, legitimate questions have been raised regarding their ability to cause or accelerate unusual mandibular growth.9-11 Orthodontists need to settle these questions once and for all. It does not seem an insurmountable intellectual challenge to determine whether this is an actual growth phenomenon or nothing more than a mandibular functional shift that is eventually caught up by the steady, normal growth of the jaw.
For the sake of clarity, it might be better to reserve the definition orthopedic for those appliances and techniques that can permanently and measurably displace osseous tissue. These would include the rapid palatal expander that permanently enlarges the maxilla, the cervical and directional retractors that displace the entire midface, and the protraction facemask that moves the midface forward. Surgical procedures that lengthen, shorten, intrude, or extrude osseous tissues would also qualify.
Improper classification not only encourages professionals to ascribe to an appliance qualities that don't exist; it also fosters the development of enduring therapeutic myths, which in turn cause clinicians to make dangerous generalizations about diagnosis and treatment planning. For instance, it makes little sense to treat a Class II bimaxillary protrusion with a functional appliance and expect any reduction in the overall protrusion or improvement in facial esthetics. This type of malocclusion is better treated with therapies that will reduce the facial convexity, such as bicuspid extractions, retractors, or orthognathic surgery. Likewise, trying to treat adults in the same way as young patients and expecting similar adaptations of teeth and bones is presumptuous at best.
Orthodontists have a responsibility to themselves as well as to their patients to know why and through what mechanisms their corrections occur. It's more than a matter of semantics: to be satisfied with less reduces the profession's claim as an objective scientific pursuit.
LWW
REFERENCES
- 1. Pancherz, H.: Treatment of Class II malocclusions by jumping the bite with the Herbst appliance, Am. J. Orthod. 76:423-442 1979.
- 2. McNamara, J.A. and Carlson, D.S.: Quantitative analysis of temporomandibular joint adaptations to protrusive function, Am. J. Orthod. 76:593-6 11 , 1979.
- 3. Langford, N.M. Jr.: The Herbst appliance, J. Clin. Orthod. 15:559-561, 1981.
- 4. De Vincenzo, J.P.: Changes in mandibular length before, during and after successful orthopedic correction of Class II malocclusions using a functional appliance, Am. J. Orthod. 99 :241-257, 1991.
- 5. Woodside, D.G.; Metaxas, A.; and Altuna, G.: The influence of functional appliance therapy on glenoid fossa remodeling, Am. J. Orthod. 92: 181-198, 1987.
- 6. Herbst, E.: Thirty years experience with the retention joint, Zahnartzl. Rundschau 443:1515-1524, 1563-1568, 1611-1616, 1934.
- 7. White, L.W.: Current Herbst appliance therapy, J. Clin. Orthod. 23:296-309, 1994.
- 8. Pancherz, H. and Hansen, K.: Occlusal changes during and after Herbst treatment: A cephalometric investigation, Eur. J. Orthod. 8:213-228, 1986.
- 9. Gianelly, A.; Bronson, P.; Martignoni, M.; and Bernstein, L.: Mandibular growth, condyle position and Frankel appliance therapy, Angle Orthod. 53: 131-142, 1983.
- 10. Creekmore, T.D. and Radney, L.J.: Frankel appliance therapy: Orthopedic or orthodontic? Am. J. Orthod. 83:89-108, 1983.
- 11. Johnston, L.E. Jr.: Functional appliances: A mortgage on mandibular position, Austral. Orthod. J. 14:154-156, 1996.