Effective maxillary protraction: Hyrax expansion appliance vs. double-hinged expansion appliance
Date of Graduation
School of Dentistry
Patients with a skeletal Class III malocclusion may have one of the following conditions: midface deficiency and/or mandibular hypertrophy/prognathism. If modification of the skeletal Class III growth pattern is not effectively accomplished at an early age via maxillary protraction, then orthognathic surgery would be required to help correct the skeletal Class III malocclusion. Some of the more serious risks associated with orthognathic surgery include parasthesia, bone and tissue necrosis, and possibly death. However, if one is able to effectively protract the maxilla, the need for anterior-posterior correction of the maxilla via orthognathic surgery will be minimized if not eliminated.;The purpose of this pilot study was to evaluate the quantitative difference, if any, between the conventional protraction technique using a one-time expansion and comparing it to a protraction protocol with the double-hinged expander as advocated by Liou.1-3 The differences between the two techniques were evaluated on lateral cephalometric radiographs, in which the skeletal and dental changes with maxillary expansion and protraction were measured.;The results of this study found that both treatment groups experienced statistically significant sagittal changes as compared to the control group. But the primary reason for the improvement of the Class III malocclusion is related to the downward and backward rotation of the mandible. The Hyrax expansion group had more "A" point forward movement; however, the success may have been attributed to the higher level of compliance in this group compared to the Double-hinged expansion group. Future studies reviewing the length of time that protraction forces are placed on the maxilla can help to clarify the results of protraction facemask therapy. Finally, more long-term studies are needed in order to evaluate the stability of the immediate success of maxillary expansion and protraction facemask therapy.
Do-deLatour, Thuy B., "Effective maxillary protraction: Hyrax expansion appliance vs. double-hinged expansion appliance" (2009). Graduate Theses, Dissertations, and Problem Reports. 4456.