The transversal sagittal maxillary expander (TSME) is a fixed device designed to develop arch form in patients with constricted dental arches. The present article describes a modified TSME appliance, the activation method, the therapeutic benefits as well as clinical advantages. The appliance has two molar bands, a Hyrax-type transverse expansion screw, one 0.045-inch wire extending from the molar band to the palatal surface of the central incisor in the emiarch crossbite and an 8 mm-Hyrax-type screw attached to this wire between the molar band and the incisor. A buccal arm with a terminal loop is welded to the band in the emiarch and it is extended to the labial surface on the central incisor on the side opposite to the crossbite and the maxillary midline deviation. The modified TSME appliance described in this paper are specifically designed for anteroposterior and transverse development. It has a sagittal effect on the maxillary alveolar process and at the same time allow to restore the correct transverse maxillary diameters.