Functional Orthopedics

For many years, in a presentation entitled, “Fitting the Punishment to the Crime,” Dr. Northway has lectured on various functional appliances and their effect on dentoalveolar structures. While it is his belief the much of the change that is found is similar to or an enhancement of the “compensatory changes” that Bjork describes, there are patients that demonstrate remarkable skeletal changes that would not have been predicted through normal growth. Many of these cases have been extensively documented; and, in preparation for an Angle presentation, Dr. Northway compared forty-three consecutively treated headgear/activator cases with the cases Dr. James McNamara used in his article, “Skeletal and dental changes following functional regulator therapy on class II patients“, Am J Orthod 1985 Aug; 88(2):91-110.

Using digitized cephalometry, Dr. Northway showed that the headgear/activator had about the same amount of anteroposterior correction as the Frankel appliance; but, while the Frankel had a greater than normal mandibular growth response, the headgear/activator provided a distalizing and impacting effect on the maxilla. This material was presented as, “A Comparison of Treatment Effects: Function Regulator and High Pull Activator in Class II, division 1 Malocclusions” at a meeting of the Eastern Component of the Edward H. Angle Society, New York, March 1986.

Abstract:

In an effort to study the differences in response between the Frankel function regulator (FR) and the high-pull headgear activator (TC), Dr. James McNamara allowed us to compare his sample of Class II, division 1 patients (some not treated and some treated with the Frankel appliance) with our collection of individuals for whom it was decided to treat with a TC appliance. Forty-four consecutive cases were traced and digitized according to the directions detailed by McNamara in his study ( AJO, get details, date, etc.).

Our findings reveal the following:

1. The FR provides an increase of more than one millimeter per year in mandibular length (Co-Go and Co-Gn); the TC does not.
2. The forward development of the maxilla was restrained by both appliances, more so by the TC in anteroposterior position, and especially in maxillary length. (A pt. to Na perp., A pt. To PTM, SNA, and SNB)
3. Both appliances provided improvements in dental and dentoalveolar relationships of about 1.5mm per year. (A-B to FOP, U.I. to FOP, and upper molar to FOP)
4. While neither appliance altered upper face height, they both rendered significant increases in lower face height. (Me to Pal. Plane and SN-MP)
5. While the FR caused the lower incisor to flare, uprighting occurred in the Activator group and both appliances caused uprighting of the upper incisor. (Long axis of upper incisor to FOP)
6. While both appliances reduced relative eruption of the incisors, and the Activator did for the upper molar, both appliances allowed the lower molar an exaggerated amount of extrusion. (Perpendicular measures from dental cusp tips to Palatal and Mandibular Planes)
7. The Activator group experienced a shortening of upper incisor length, relative to the upper lip. (U.I. to U.L.) The high-pull headgear activator provides less of a “gummy smile” than the Frankel in the correction of maxillary dental protrusions.

Summary:

It needs to be borne in mind that the cases selected for treatment with the activator were subjectively judged to posses Class II malocclusions most significantly impaired by either maxillary extrusion or protrusion. This sample of consecutively treated cases demonstrates the activator’s rather profound effect on the maxilla en route to the correction of anteroposterior problems. The FR, on the other hand, has a greater impact on the mandible than on the maxilla (by design). For both appliances, the greatest impact (the handle) is on the dento-alveolar structures.