Comparison of the effects two different en masse retraction mechanics used with mini screw anchorage

The purpose of this study was to compare of the treatment outcomes of two different en masse retraction mechanics used with intra-osseous anchorage provided by mini screws.Sixty Class II division 1 patients requiring maxillary two premolar extractions and maximum anchorage were included to this study. The patients were divided into two equal groups (DKL and PH). The en masse retraction of one group (DKL group) was performed by frictionless mechanics applied with prefabricated Double Keyhole Loop arch wires. The en masse retraction of other group (PH group) was performed by frictional mechanics which the force was applied with Ni-Ti Closed coil springs and Power Hooks. Mini screws with 1.6 mm diameter and 9 mm length were used as absolute anchorage unit in both groups. Lateral cephalometric radiographs were taken before (T1) and after (T2) en masse retraction of both groups.Twenty seven cephalometric measurements were used to investigate the differences between two retraction methods. The Independent samples t-test for used for pairwise comparison. Paired samples t-test was used to make an intergroup evaluation.The overall success rate of 120 mini screws used in research was % 83.3. There were statistically significant decreases at SNA, ANB, Witts appraisal, U1.PD, U3.PD, SV-A, overjet, U1i-SV, U3c-SV, UL-E, UL-SV, LL-E measurements and significant increase at nasolabial angle in both groups. There were no statistically significant differences in changes of those parameters between two groups. The decreases in U1.PD, U1-NA and overjet were significantly higher in DKL group than PH group while U1a-SV measurement decreased significantly higher in PH group. These findings indicate that PH group showed more translational movement of central incisors than DKL group.The en masse retractions of both groups were completed in almost the same time. The retraction time was 6.4 months and the retraction amount was 0.64 mm per month in DKL group. The retraction time was 6.2 months and the retraction speed was 0.62 mm per month in PH group.The effects of anterior retraction on soft tissue profile without losing any anchorage can help the clinician to perform an efficient Class II division 1 camouflage therapy.In order to retract the anterior teeth more translational, the retraction force must be applied near to the center of the resistance of anterior teeth. Vertical hooks attached to arch wire may be helpful to achieve this goal.Double Keyhole Loop arch wires are effective in space closure but they may cause undesired tipping if they are not activated properly. In order to apply optimal forces and moments the loops on this arch wire should not be activated more than 1 mm. Although, the activation method must be performed properly in order to prevent deformations on the arch wire.Key words: En masse retraction, mini screws, frictional mechanics, frictionless mechanics, Power Hook, Ni-Ti closed coil springs, Double Keyhole Loop arch wires,