Comparison of the Inclination Changes of the Upper First Molars Following Treatment with Two Types of Hyrax Tooth-Borne Expanders: 3D-Printed and Laboratory-Fabricated

Background: Rapid maxillary expansion (RME) is widely utilized to correct transverse maxillary deficiency in growing patients, yet traditional tooth-borne appliances frequently induce undesirable dental tipping and anchorage loss. Methods: A two-year non-randomized prospective clinical study evaluated and compared the dentoalveolar changes in the upper first molars following RME using two tooth-borne expanders: a conventional Hyrax expander (CHE; n = 47) and a digitally designed metal-printed tooth-borne expander (DDMPTBE; n = 35). Measurements of jugal width and upper first molar inclinations were performed using cone-beam computed tomography (CBCT) images before treatment and after a three-month retention period. Results: Analysis of covariance (ANCOVA) controlling for baseline variables demonstrated that both appliances achieved comparable, statistically significant increases in jugal width. However, significant differences were observed in molar inclination changes: the CHE group experienced a greater increase in buccal inclination (unadjusted mean (Standard deviation–SD) increase of 6.56° for the left molar and 5.96° for the right molar; adjusted mean (Estimated marginal means–EMM) increases of 7.58° for the left molar and 6.14° for the right molar), whereas the DDMPTBE group exhibited less change in buccal inclination (unadjusted mean (SD) increase of 1.43° for the left molar and 0.32° for the right molar; adjusted mean (EMM) increases of 0.08° for the left molar and 0.07° for the right molar). Conclusions: Although both expanders effectively increase the jugal width, the findings demonstrate a significant association between appliance type and molar inclination changes, with the CHE linked to increased buccal tipping of the anchorage molars, whereas the DDMPTBE is associated with smaller inclination changes.