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Original Article

Rapid Maxillary Expansion Followed by Fixed Appliances: A Long-term Evaluation of Changes in Arch Dimensions
James A. McNamara Jr, DDS, PhDa; Tiziano Baccetti, DDS, PhDb; Lorenzo Franchi, DDS, PhDc; Thomas A. Herberger, DDSd
Abstract: The purpose of this longitudinal study was to evaluate the short- and long-term changes in dental arch dimensions in patients treated withrapid maxillary expansion (RME) followed by fixed edgewise appliances. The records of 112 patients in the treated group (TG) were compared with those of 41 untreated controls. Serial dental casts were available at three different intervals: pretreatment (T1), after expansion and fixed appliance therapy (T2), and at long-term observation (T3). The mean duration of the T1-T2 and T2-T3 periods for the TGgroup was three years two months five months and six years one month one year two months, respectively. Treatment by RME followed by fixed appliances produced significantly favorable short- and long-term changes in almost all the maxillary and mandibular arch measurements. In comparison with controls, a net gain of six mm was achieved in the maxillary arch perimeter, whereas a net gain of 4.5 mm wasfound for the mandibular arch perimeter of treated subjects in the long term. The duration of retention with a fixed lower appliance in the posttreatment period did not appear to affect the long-term outcomes of the treatment protocol significantly. The amount of correction in both maxillary and mandibular intermolar widths equaled two-thirds of the initial discrepancy, whereas treatment eliminatedthe initial deficiency in maxillary and mandibular intercanine widths. The amount of correction for the deficiency in maxillary arch perimeter was about 80%, whereas in the mandible a full correction was achieved. (Angle Orthod 2003;73:344–353.) Key Words: Orthodontic treatment; Rapid maxillary expansion; Haas expander; Edgewise therapy; Tooth-size/arch-size discrepancies; Arch perimeter; Dentalcasts

INTRODUCTION The present appeal of nonextraction treatment to correct discrepancies between tooth size and arch dimensions has
Thomas M and Doris Graber Endowed Professor of Dentistry, Department of Orthodontics and Pediatric Dentistry, School of Dentistry; Professor of Cell and Developmental Biology, School of Medicine; and Research Scientist, Center for Human Growth and Development, TheUniversity of Michigan, Ann Arbor, Mich. Private practice, Ann Arbor, Mich. b Assistant Professor, Department of Orthodontics, The University of Florence, Florence, Italy; Thomas M. Graber Visiting Scholar, Department of Orthodontics and Pediatric Dentistry, School of Dentistry, The University of Michigan, Ann Arbor, Michigan. c Research Associate, Department of Orthodontics, The University ofFlorence, Florence, Italy; Thomas M Graber Visiting Scholar, Department of Orthodontics and Pediatric Dentistry, School of Dentistry, The University of Michigan, Ann Arbor, Mich. d Private practice, Elyria, Ohio. Corresponding author: James A. McNamara, DDS, PhD, Department of Orthodontics and Pediatric Dentistry, School of Dentistry, The University of Michigan, Ann Arbor, MI 48109-1078 (e-mail:mcnamara@umich.edu).
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Accepted: November 2002. Submitted: August 2002. 2003 by The EH Angle Education and Research Foundation, Inc.
Angle Orthodontist, Vol 73, No 4, 2003
344

created a renewed interest in alternative methods of increasing arch perimeter. Rapid maxillary expansion (RME) is a viable option to create additional space in the dental arches.1–3 For example, Adkins et al1 havedemonstrated that every millimeter of transpalatal width increase in the premolar region produces a 0.7 mm increase in available maxillary arch perimeter. When the aim of RME is to relieve crowding in the dental arches, long-term appraisal of residual gain in arch perimeter is mandatory to assess the potential effectiveness of this therapeutic approach in reducing the need for the extraction of...