Midpalatal suture split after differential and fan-type expansion: a secondary analysis from a randomized clinical trial

Objective: To compare the opening of the midpalatal suture after rapid maxillary expansion (RME) with the expander with differential opening and the fan-type expander. Methods: Rapid maxillary expansion was performed with the expander with differential opening (n=12, 8 female, 4 male, mean age of 7.75 years) and the fan-type expander (n=12, 8 female, 4 male, mean age 8.08 years). CBCT scans were acquired before (T1) and immediately after (T2) the expansion. The outcomes comprised the opening of the midpalatal suture in the anterior and posterior nasal spine. Intergroup comparisons were performed with t or Mann-Whitney U tests (P<0.05). Results: All patients showed a midpalatal suture opening with greater increases in the anterior nasal spine compared to the region of the posterior nasal spine. The split in the anterior nasal spine was similar in both groups (P=0.153), while the opening in the posterior nasal spine was 1 mm greater in the differential expansion group (P<0.001). The greater increase in the anterior region of the midpalatal suture in both groups suggested a trapezoidal shape split. Conclusions: The expander with differential opening and the fan-type expander were capable of splitting the midpalatal suture in the mixed dentition. Despite both appliances showed similar opening in the anterior nasal spine, a greater expansion in the posterior region of the midpalatal suture was observed with the expander with differential opening.