Dentoskeletal Effect Induced by Hyrax Screw Used in Maxillary Molar Distalization: Before- After Study in Class II Patients

Maxillary molar distalization with intraoral or extraoral appliances is a common treatment modality in non-extraction treatment plan. In this study, an appliance with hyrax screw was used for maxillary molar distalization. Our purpose was to evaluate the amount of molar distalization, type of molar movement, effects on anterior teeth, and amount of changes in lower anterior facial height. Patients and 24 class II patients (13 females, 11 males) with bilateral half cusp class II molar relationship were participated. The appliance was made by hyrax screw for producing distalization force. Pre and post distalization lateral cephalometric radiographs and dental casts were evaluated. Lateral cephalograms and study models were obtained before treatment and after 12 weeks activation of the appliance (one turn per week). Cephalometric measurement demonstrated that, first molars tipped 2.9 degrees and displaced 1.76 mm. First premolar and upper incisor tipped 3.4 and 4.2 degrees, displaced 2.9 and 2.4 mm respectively. All of these results were statistically significant. The mean of maxillary first molars distaliztion was 2.6 mm per side in approximately four month. The mean of first maxillary molars tip was 3.93˚ and the mean of anchorage loss at the first premolars was 1.95 mm, but the crowns tipped 3.45˚ mesially. Lower anterior facial height (ANS-GN) and mandibular plan angle (GO-GN) increased, 0.7 ± 0.21 mm and 0.76 ± 0.32 degree, respectively, but were statistically insignificant. It can be concluded that proposed appliance can correct class II molar relationship. Molars displaced distally by bodily movement and tipping.