Hyrax appliance opening and pattern of skeletal maxillary expansion after surgically assisted rapid palatal expansion: a computed tomography evaluation

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The objective of this study was to evaluate, using computed tomography, correlations between Hyrax appliance opening and post-SARPE skeletal changes.

Study design

Fifteen patients underwent SARPE according to a specific protocol and were followed. Linear and angular measurements of the anterior, intermediate, and posterior portions of the maxilla were evaluated. The correlation between maxillary expansion and appliance opening was investigated.


Significant overall expansion was observed. In the anterior and intermediate portions of the maxilla, the increase in maxillary width was greater than that observed in the posterior portion. The degree of appliance opening was significantly greater than that of the skeletal expansion. Also, no linear correlation between appliance opening and regional maxillary expansion was established.


The transverse expansion of the maxilla was less than uniform. The lack of linear correlation between appliance opening and skeletal expansion is attributable to multiple factors, including those related to the device, the surgical technique, and the craniofacial deformity itself.

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