Abstract: Objective To compare the effects of conventional and hybrid Hyrax appliances on arch widths, dentoalveolar and basal bone. Methods 30 patients requiring maxillary expansion were randomly divided into two groups. A conventional hyrax appliance was applied in one group, consisting of 15 patients (8 boys, 7 girls; mean age (14.1±2.5) years), and a hybrid hyrax appliance was used in the other group of 15 patients (9 boys, 6 girls; mean age (13.9±2.6) years). Conebeam computed tomography records were taken before and 3 months after expansion, and dental arch width, dentoalveolar, and basal bone variables were measured on the rebuild 3D images. The pairedsamples test was used to evaluate treatment changes for both groups. The independentsamples test and the t test were used to compare the variables between the two groups. Results Significant basal bone changes and increases in dental arch width were observed in both groups. However, the widths between the first and second premolars were significantly greater in conventional Hyrax appliance than those in hybrid Hyrax appliance. There were no significantly differences in buccal and palatal alveolar bone thickness changes of the first molar between the two groups, whereas changes of the first premolars significantly differed between the two groups. No significant intergroup difference was found in the absolute dental tipping. Conclusions The two rapid expansions are both effective methods for a narrow maxilla treatment. However, the conventional hyrax appliance can result in greater expansion in the premolar dental arch width and the buccal and palatal alveolar bone thickness.

Key words: conventional Hyrax appliances, hybrid Hyrax appliances, dental arch widths, alveolar bone thickness, basal bone width