Evaluation of skeletal and dental modifications after palatal expansion with two-point Hyrax appliance contact on molar teeth of 8‒13 year-old patients: A preliminary study

The current orthodontic treatments have shifted toward the principles of dentofacial orthopedics and nonextraction treatment modalities. One of these orthopedic procedures is the skeletal palatal expansion of the maxilla. The aim of this investigation was to study the skeletal and dental modifications in all the three dimensions by skeletal maxillary expansion with hyrax appliance.

In this preliminary study، 8 patients (4 males، 4 females)، aged 8–13 years (mean age 9. 7 years)، were selected. The appliance used in this study was the Hyrax screw bonded on the first molars of the maxilla. The active phase of the treatment and the retention period lasted for 2 and 4 months، respectively. Lateral and posteroanterior (PA) cephalograms were taken and traced. Measurements were carried out on pre- and post-operative study casts. Wilcoxon test was used to compare means of each variable with SPSS 10. 5 (α=0. 05).

The transverse dimension of the maxilla increased both dentally and skeletally after treatment. The mean increase in skeletal transverse dimension at maxillary molar area (4. 8 mm) was greater than that at canine area (3 mm)، which was statistically significant. In the mandibles the increase in the transverse dimension at molar area (4. 8 mm) was less than that of the maxilla. Arch perimeter of the maxilla increased significantly (3 mm) (p value = 0. 012). In the vertical dimension، the posterior maxilla exhibited more downward movement compared to the anterior maxilla. The increase in facial height was not statistically significant (p value = 0. 396). There were no significant changes in the positions of maxillary and mandibular incisors (p values = 0. 343 and 0. 397).

The Hyrax appliance، with two-point contact، was more successful in posterior palatal expansion than the anterior area without any significant effect on the facial height and the positions of anterior teeth.