EXP ANS I O N: LESSONS FROM THE LAB By By Daryl Daryl Mathias, Mathias, CDT CDT any patients have a narrow maxillary arch. Often this requires widening to relieve crowding and provide more pleasing facial contours. Expansion appliances can widen the maxillary arch in two different ways. Teeth can be moved in a lateral direction (dental expansion) or the palate can be widened along the median palatal suture (orthopedic expansion). In pre-adolescents, the two halves of the palate have not yet fused together, so permanent widening of the palate is a relatively simple process. When lateral pres-sure is applied, the two halves push apart. New bone rapidly grows between the two plates making the expansion permanent. Here are a few of the most common expander designs: M HAAS RPE: The design Standard RPE: The Fig. 1 Rapid Palatal Expander (RPE) uses a metal screw soldered to bands. It is opened at a rate of ½ mm per day using a wire key. The screw opens laterally causing the palatal plates to push apart. The patient is instructed to open the screw ¼ turn twice per day until the desired amount of expansion is achieved. The appliance is then worn passively to act as a stabilizing device until new bone has formed along the suture. (Fig. 1) Bonded RPE: This Fig. 2 expander uses the same type of screw as the Standard RPE, but is bonded to the posterior teeth with an acrylic shell rather than soldered to bands. Some clinicians prefer this design because they feel the acrylic shell distributes the lateral force of the screw more evenly across the posterior teeth. Some also feel the shell acts as a posterior bite plate, which unlocks the patient’s occlusion allowing the screw to work with less resistance. (Fig. 2) 26 November/December 2012 JAOS Fig. 3 of this expander allows it to apply lateral force to both the teeth and the walls of the palate. This is achieved by using an acrylic-borne screw embedded in an acrylic plate. A split in the acrylic along the patient’s midline widens as the screw is turned. Heavy wires embedded in the plate are soldered to bands and run along the lingual surfaces of the patient’s posterior teeth. Some clinicians feel that the acrylic plate aids in achieving a more lateral expansion rather than the outward tipping of the posterior teeth that is sometimes associated with expanders that only push against the teeth. (Fig. 3) RPE w/Acrylic Pads: This appliance uses the same principle as the Haas in that it’s acrylic pads push against the walls of the palate as it is activated. The screw used in this design is a Standard RPE soldered to bands and embedded in acrylic. (Fig. 4) Fig. 4 Mini Screw Expander: The design of this Fig. 5 screw addresses the comfort issues some patients experience with a standard RPE by greatly reducing the bulk of the screw itself. There is some debate as to whether or not the smaller design can deliver the force required to get true separation of the palatal plates. Some clinicians feel that this design’s effectiveness is limited to dental expansion only. (Fig. 5)
Journal of the American Orthodontic Society November-December 2012: Page 26
