Rapid maxillary expansion in growing patients. Hyrax versus transverse sagittal maxillary expander: a cephalometric investigation

The aim of this retrospective study was to cephalometrically evaluate and compare the skeletal and dental effects of a transverse sagittal maxillary expander (TSME) and a Hyrax-type expander (RME) in children with maxillary hypoplasia. Fifty subjects (26 males and 24 females), aged from 6 to 15 years, with a maxillary crossbite caused by basal apical narrowness, were divided into two equal groups. Twenty-five were treated with a TSME and the other 25 with a RME. For each patient, a lateral cephalogram was obtained before treatment (T0) and at the end of the retention period (T1). Changes in the two groups during the observation period were calculated, compared, and statistically analysed with a paired samples t -test. In the TSME group, SNP-A, I SN, and I FH and in the RME group SN-SNP.SNA, N-Me, and U6.PP displayed a statistically significant increase (P < 0.05). The increase in SNP-A, I SN, and I FH in the TSME group was significantly greater following treatment than in the RME group. The results support the use of the TSME to produce skeletal changes and dentoalveolar modification and to correct maxillary hypoplasia. It was also demonstrated that in patients with an anterior open bite, the use of the TSME is not contraindicated as the anterior vertical dimension did not increase significantly.