Transverse effects of surgically assisted rapid maxillary expansion: a comparative study using Haas and Hyrax

Surgically assisted rapid maxillary expansion is the treatment of choice for correcting transverse maxillary deficiency in patients with skeletal maturity, although the influence of the expander type on these alterations has not been elucidated yet.

Determine the skeletal and dental transverse effects on the maxilla after completion of surgically assisted rapid maxillary expansion, with Haas and Hyrax expanders.

Thirty-eight patients (aged between 18 and 39 years) were submitted to subtotal Le Fort I osteotomy and divided into Hass and Hyrax groups (19 patients each). Measurements of maxillary width, upper intermolar width, and its inclination on the posteroanterior cephalometric radiographs were obtained in the preoperatory period (T1), after the completion of the expansion (T2), and 4 months after the completion of the expansion (T3). The intercusp and intergingival distances measured on the plaster models were obtained from the first premolars and molars, before expander cementation (M1) and after the expander removal (M2).

Both groups revealed statistically significant increase in the maxillary width, upper intermolar width, and inclination of the molars in T2 (P<0.001); T3 showed a statistically significant decrease in the maxillary width and inclination of the molars (P<0.001). The expansion presented an increment on the maxillary width of 71% from the upper intermolar width (T1-T3), and molars had vestibular inclination (P<0.05). The ratio of width increase of maxilla by the amount of device activation was of 69% for Haas and 74.5% for Hyrax.

Clinically, the transversal effects were similar for both groups.