Analysis of en-masse retraction compared with two-step retraction of the anterior segment using microscrew implant anchorage in extraction cases

The purpose of this randomized prospective clinical study was to investigate the treatment effects of en-masse retraction compared with two-step retraction of maxillary anterior teeth with microscrews as absolute anchorage units in patients undergoing extraction of first premolars.Sixteen subjects requiring high anchorage for space closure were included in the study and microscrew implants measuring 1,2 mm in diameter and 8 mm in length were placed between right and left first molars and second premolars buccaly to provide skeletal anchorage. The patients were randomly divided into two groups each consisting of 8 patients. In the first group (6 women, 2 men, mean age 18,5), space closure was achieved by en-masse retraction of maxillary anterior teeth. In the second group (6 women, 2 men, mean age 19,7), the retraction procedure was performed in two steps: canine retraction with microscrews followed by incisor retraction with bull-loops. Lateral cephalograms and cast models were taken from each patient before retraction (T1) and after space closure (T2). Independent t-test, Wilcoxon test, Student?s t test and Mann Whitney U test were used for statistical analysis.Successful closure of the extraction spaces without any anchorage loss was achieved with microscrews in 7,3 months for the en-masse retraction group and in 8,1 months for the two-step retraction group. All 32 microscrews (100%) remained stable until the end of the retraction period. Even though there was no significant difference in treatment times, the first group showed greater incisor retraction rate (0,74 mm per month) than the second group (0,57 mm per month). 5,25 mm retraction, 3,63° tipping and 0,81 mm intrusion of the central incisors were observed in the first group. The central incisors of the second group showed 4,63 mm retraction and 7,13° tipping and no intrusion. Only the difference in tipping movement of the incisors was statistically significant between two groups (p<0,05). Therefore, 0,88 mm significant retrusion of A- point was seen in the first group (p<0,05). On the other hand, 0,88° significant decrease in mandibular plane was found in the second group (p<0,001). No significant maxillary first molar movement was noted in the first group thus no anchorage loss occurred. The first molars in the second group showed 0,63 mm distal tipping which was considered significant (p<0,001). Both groups showed approximately 2 mm of upper and lower lip retrusion. Cast model measurements proved 2,38 mm decrease of intercanine distance in the first group (p<0,001), 2,75 mm decrease in the second group (p<0,01), no change of intermolar distance in both groups.En-masse retraction of the upper anterior teeth with microscrew implants showed faster rate of tooth movement, more translational incisor retraction, no molar movement and reduction of A-point. On the other hand, two-step retraction of upper anterior teeth showed more tipping of the incisors, distal tipping of upper molars and reduction of mandibular plane angle.