title: Changes in arch form following surgically-assisted rapid maxillary expansion (SRME).
abstract: OBJECTIVE
  Surgically-assisted rapid maxillary expansion is a frequently employed procedure for expanding the maxilla in adults to treat pronounced transversal discrepancies of the upper jaw. Several studies have shown how the position of the anchorage teeth changes due to SRME. However, there is little detailed information available on the transversal movement of each tooth, its change in inclination and subsequent alterations of the arch length, width and sagittal arch form.
  
  
  METHODS
  In our study we investigated those changes in 31 patient casts after SRME, following the active phase, and after a 3-month retention period whereby the Hyrax appliance remained blocked in situ. The casts were examined using a 3-dimensional reflex microscope.
  
  
  RESULTS
  After active treatment the second molars moved 28% less than the amount of total expansion. At 9.6 degrees (first bicuspid) and 11.6 degrees (first molar), the anchorage teeth were also more buccally tipped than the second molars (7.4 degrees ). Unlike with conventional maxillary expansion, the measured increase in arch length here corresponded to the amount of anchorage teeth expansion. The sagittal arch decreased significantly during the retention phase in those teeth in front of and behind the anchorage teeth. Three months later we found that only 68% of the original expansion had occurred in the canines and second molars. The inclination of the teeth decreased slightly but significantly. We observed an only temporary increase in the sagittal dimension after appliance activation. There was an average loss of 0.83 mm at the end of the retention phase. Moreover, the anterior dental arch length only experienced a 50% increase in space over the expansion achieved initially.
  
  
  CONCLUSIONS
  To minimize relapse rates in cases of severe crowding, we recommend that the canines and second molars be included in the appliance.
authors.affiliation: Department of Orthodontics, Dental School, University of Leipzig, Germany. krek@medizin.uni-leipzig.de
authors.forename: Karl-Friedrich
authors.initials: KF
authors.lastname: Krey
authors.forename: Frank
authors.initials: F
authors.lastname: Walter
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Dannhauer
mesh_terms: D003131:Combined Modality Therapy; D003724:Dental Arch / Q000002:abnormalities* / Q000473:pathology / Q000601:surgery*; D006801:Humans; D008310:Malocclusion / Q000473:pathology* / Q000628:therapy*; D019647:Oral Surgical Procedures / Q000379:methods*; D010155:Palatal Expansion Technique; D016896:Treatment Outcome