1 Assistant professor, Department of orthodontic school of dentistry, Islamic university Tehran




Aim: The main goal of this research was to evaluate the sagittal and vertical effects of Hyrax (tooth born) and Haas (tooth-tissue born) rapid palatal expanders on dentoskeletal structures of patients with maxillary constriction characterized by bilateral posterior cross bite.
Materials and methods: A nonrondomized clinical trail of 22 patients 12 to 14 years old (mean age 12.5 years) with maxillary constriction, who were divided into two groups, was undertaken. Group-I consisted of 11 patients who received treatment by Hyrax type rapid palatal expander (RPE). Group- II composed 0111 patients who received treatment by Haas RPE. Two lateral cephalograms were taken, one before and the other after the palatal cusps of the upper posterior teeth reached the buccal cusps of lower posteriors consequent to expansion. The activation period lasted from 12-16 days with a mean value of 13.5 days. On each lateral cephalogram 8 linear and 10 angular parameters were measured, recorded and compared to a nearest of 0.5 mm and 0.5 degree respectively. Statistical analyses were performed using Kolomogrovsmirnov and paired t-test. A student t-test was used for comparison of two group.
Results: In both groups significant increases in lower anterior facial height were observed. The value (ANS-ME) was increased 1.30mm in Hyrax (P=0.009) and 1.80mm in Haas group (P=0.032). Statistically neither of the appliances showed a significant effects on sagital position of the maxilla. The mandible was rotated downward and backwards. SNB angle decreases 0.65 and 0.43 degrees in Hyrax and Haas group respectively. ANB angle was increased by means of 0.60 degree (p= 0.030) in Hyrax and 0.53 degree (p=0.08) in Haas group.
Conclussion: The maxilla kept its position sagitally, pre to post treatments, but showed inferior displacement in both groups. The mandible displayed a tendency to rotate downward and backward in both groups. Upper anteriors tipped palatally. (IJO 2006; 1: 61 - 65)