AIM: The Hyrax appliance has been considered the easiest to clean maxillary expander. However, it is presumed to present the most significant dentoalveolar effects due to not present any tissue bearing contact. Is has been speculated that it would produce more buccal inclination of the posterior teeth as well as more extrusion. Therefore, it would not be indicated in patients with vertical growth patterns. This study was conducted to verify if any harmful short term effects of rapid maxillary expansion (RME) remain over time in growing patients. METHODS: Lateral cephalometric radiographs were taken before and after RME (average 2 years and 9 months) in 30 patients with an initial mean age of 7 years and 8 months and a final mean age of 10 years and 7 months. All patients were initially in the mixed dentition and presented clinical signs of maxillary constriction. They were subjected to maxillary expansion with a Hyrax appliance until overcorrection was obtained. This group was compared to a untreated control group comprising 30 patients with a initial mean age of 9 years and 9 months and a final age of 12 years and 3 months, with a mean observation period of 2 years and 9 months. RESULTS AND CONCLUSIONS: There were statistically significant differences between the two groups, both at initial and at the final observation. It was concluded that any adverse effects produced by the Hyrax appliance at the early stages of therapy do not remain over time, probably compensated by growth, muscular activity and occlusion.
Rapid maxillary expansion; Maxillary expansion; Maxillary atresia
