Three dimensional evaluation of the skeletal, dental and periodontal effects of hyrax and hybrid hyrax expansion appliances

The purpose of this study is to investigate skeletal, dental and periodontal effects of tooth-borne expansion appliance (Hyrax) and tooth-bone anchored expansion appliance (Hybrid Hyrax) via cone-beam computed tomography. Twenty-five individuals, in need of expansion due to maxillary constriction, were included in our study. Hyrax was used in the 1st group, consisting of 13 patients (mean age of 14.3 ± 2.3 years), and Hybrid Hyrax was applied to the 2nd group with 12 patients (mean age of 13.8 ± 2.2 years). Photographs, dental models and cone-beam computed tomography (CBCT) records were taken from all of the patients before expansion (T1) and 3 months post-expansion (T2). Skeletal, dentoalveolar and periodontal evaluations were made on CBCT images using MIMICS® software program. In the evaluation of data, SPSS 21.0 statistical software was used. Skeletal measurements were increased significantly in both Hyrax and Hybrid Hyrax groups. It was also found that the interdental distances showed significant increases in both groups. However, the distances between 1st and 2nd premolars increased more in Hyrax group compared to Hybrid Hyrax group. With both expansion appliances, buccal bone thicknesses of anchored teeth decreased and palatal bone thickness of the anchored teeth increased. When changes in buccal and palatinal bone thicknesses of the left 1st premolars were compared, significant differences were seen between the groups (p<0.001). Absolute dental tipping did not show any significant difference between the groups (p>0.005). In conclusion, Hyrax and Hybrid Hyrax expansion appliances can be used efficiently for the treatment of maxillary constriction. However, when compared to Hybrid Hyrax appliance, more expansion can be achieved with Hyrax appliance in II the premolar region. On the other hand, Hybrid Hyrax appliance doesn't cause any significant change in the bony support of 1st premolars.