Volume 57, Nzlmber 3, March, 1970
Palata,l expansion: Just the beginning of dentofacial orthopedics
J. Haas, D.D.S., MS. Falls, Ohio
mong the most remarkable aspects of palate expansion is the predictability of occurrences during treat,ment and results following treatment. If the suture opens, as it invariablywill in patients who are under 16 or 17 years of age, certain expected phenomena occur : 1. Anteroposteriorly, the opening of the midpalatal suture is parallel; inferosuperiorly, the opening is triangular with the apex being in the nasal cavity. 2. The central incisors react as expected, considering that they are linked by elastic transseptal fibers. As the suture opens, the crowns converge whilethe roots diverge. When the crowns come into contact, the continued pull of the fibers causes the roots to converge toward their original axial inclinations. During this cycle, which usually takes about 4 months, the axial inclination of these teeth may vacillate as much as 50 degrees. 3. The alveolar processes bend and move laterally with the maxillae, while the palatal processes swing inferiorlyat their free margin. The effect is a dental arch expansion and an increase in intranasal capacity. 4. When the midpalatal suture opens, the maxilla always moves forward and downward. This is probably due to the disposition of the maxillocranial sutures. Sicherl calls attention to the fact that these sutures are oriented in such a. manner that growth would produce a downward and forward vector ofmaxillary movement. Since these hafting zone sutures are disengaged by the palatal expansion procedure, an effect
Presented dontists, at the sixty-third St. Louis, Missouri, annual April meeting 26, 1967. of the American Association of Ortho-
J. Orthodont. ikfQrch1970
similar to immediate growth is manifested in a downward and forward displacement of themaxilla. 5. The change in maxillary posture invariably causes a downward and backward rotation of the mandible which decreases the effective length of the mandible and increases the vertical dimension of the IOWW face. The downward and forward conduction of the maxilla improves the Class III closed-bite skeletal pattern because of the obviously improved spat.ial relationship of the maxilla, and,as a result of the accompanying downward and backward rotation of the mandible, the effective length of the mandible is reduced and lower facial height increases. The posterior cross-bite is corrected by lat.eral and bending movements of the alveolar processes. The a.nterior cross-bite is partially or completely ameliorated by the forward shift of the maxilla and the clockwise rotation of themandible. The transposition of the maxilla affects the Class III open-bite skeletal pattern with both favor and disfavor. Its effect is favorable in that the maxillomandibular dysplasia becomes less severe. Unfortunately, however, as the mandible rotates, the skeletal and dental open-bite deteriorates. The downward and forward maxillary displacement makes the Class II, Division 1 skeletal patterndecidedly worse with regard to the maxillomandibular relationship, since the maxilla is now farther forward and the mandible is farther backward. Most deep-bite Class II skeletal patterns are not affected too adversely if the mandible possesses good characteristics. Thus, if the mandibular rotation can be held, it will aid in bite opening. The open-bite case, regardless of classification, is alwaysaffected adversely by maxillary expansion. However, this need only be temporary and should not be considered a contraindication to t,he procedure if factors requiring the treatment are present in the case.
Indications for the procedure
Rapid maxillary expansion by opening of the midpalatal suture is cxtremely advantageous in the treatment of (1) both surgical and nonsurgical Class III cases,...