Introduction: To evaluate the effects of tooth-borne and tooth-bone-borne rapid maxillary expansion (RME) on soft tissue with stereophotogrammetry. Methods: 32 patients (15 males, 17 females) who met inclusion criteria were divided into two groups. In the first group, tooth-borne RME appliance (Hyrax) was applied to 16 patients (9 males, 7 females mean age 13.4 ± 1.3 years) and in the second group, tooth-bone-borne RME appliance (Hybrid Hyrax) was applied to 16 patients (6 males, 10 females mean age 13.05 ±1.24 years). A simple electronically generated randomization was performed before trial commencement using the Random Allocation Software program. Allocation concealment involved numbered, sealed, and opaque envelopes prepared before trial commencement. One envelope was sequentially opened for each participant during recruitment. Each envelope contained a card with the name of 1 expander. The initials of the name of the participant, the type of expander, and the date of allocation were identified in the external surface of the envelope. One operator was responsible for the randomization process, allocation concealment, and implementation. The primary outcomes of this study was assessment of changes in soft tissues before RME (T0) and post-retention (T1) period by stereophotogrammetry. Independent and dependent sample t tests were used to compare intra- and inter-group differences at P<0.05 significance level.
