Background: Surgical correction of transverse maxillary hypoplasia, in adolescents and adults is considered the least stable orthognathic procedure. Different surgical techniques have been advocated to improve the transverse stability. However, the pattern of transverse dental and skeletal expansion and long-term stability after segmental Le Fort I osteotomy (SLFIO) and surgically assisted rapid maxillary expansion (SARME) have never been compared systematically with different fixation techniques or distraction appliances.~Purpose: Test the H0-hypothesis of no difference in transverse stability after SLFIO without fixation of the palatal vault compared to stabilizing with either a bone block graft or a biodegradable plate. Moreover, test the H0-hypothesis of no difference in transverse maxillary dental and skeletal expansion and stability after SARME with either a tooth-borne (TB) or a bone-borne (BB) distraction appliance.~Method: 60 patients scheduled for SLFIO are included in a randomized clinical trial and allocated into 3 groups; I) stabilization of the palatal vault with a bone block graft, II) fixation of the palatal vault with a biodegradable plate and III) no fixation of the palatal vault. Moreover, 30 patients undergoing SARME are randomly allocated to either a TB or a BB distraction appliance. Transverse expansion and stability is assessed by clinical and radiographic measurements evaluating differences between dental and skeletal expansion, the pattern of skeletal expansion and the long-term stability.~Primary impact goal: Long-term transverse maxillary stability after SLFIO and SARME.
To assess transverse dental and skeletal expansion and stability after SLFIO with no fixation of the palatal vault compared to stabilization of the palatal vault with an autogenous bone block graft or fixation of the palatal osteotomy site with a biodegradable plate.~To assess transverse maxillary dental and skeletal expansion and stability after SARME with a TB distraction appliance compared to a BB distraction appliance.