Depending on the bony maturation, various degrees of mid-palatal suture opening and skeletal expansion can be observed. At an early age, new appliances anchored on the primary teeth can be used to prevent external root resorption and excessive tipping of the first permanent molars, thus providing better stability. In adult patients, the resistance generated by the zygomatico-maxillary buttress and the maxillary articulations in general, prevent sufficient skeletal separation and, without surgical assistance, only dental tipping occurs. Surgically assisted rapid maxillary expansion using new palatal expanders anchored directly to the bone seem to achieve adequate skeletal expansion for the mature patients.