Treatment effects and short-term relapse of maxillomandibular expansion during the early to mid mixed dentition

Introduction: The treatment effects and the short-term (0.9 ± 0.45 years) relapse potential of phase I slow maxillary expansion, with a bonded palatal expander or a quad-helix appliance combined with a mandibular banded Crozat/lip bumper and followed by 12 to 15 months of retention, were examined. Methods: Pretreatment (8.8 ± 1.7 years) and posttreatment (11.1 ± 1.7 years) models of 54 patients were used to evaluate treatment effects. Posttreatment (11.0 ± 1.3 years) and follow-up (11.9 ± 1.4 years) models of 23 patients who returned for phase II treatment were used to evaluate relapse over the 11 months, during which no retention was used. The models were digitized, and 15 measures were computed. Results: Significant treatment increases were observed for all measurements in both arches. Treatment gains in arch perimeter (6%-8%) were due more to increases in intermolar width (11%-15%) than to increases in arch depth (5%). Posttreatment relapse was significant (P <.05) for all measures except mandibular intercanine width and maxillary molar arch depth. After accounting for normal growth, net changes (pretreatment to follow-up) indicated significant increases for all measures except maxillary molar arch depth. In addition to maintaining leeway space, the maxilla and the mandible showed net perimeter gains of 2.9 and 1.0 mm, respectively. Conclusions: Slow maxillary expansion combined with a mandibular banded Crozat/lip bumper during the early mixed dentition produced clinically useful increases in arch dimensions that subsequently underwent mild-to-moderate amounts of relapse after removal of all retention appliances.