Comparison of the stabilities of reverse-l level and upper row fixation of resorbable screws in the sagittal split ramus osteotomy

The purpose of this study is to evaluate the biomechanical strength of the sagittal split ramus osteotomy models, which are provided with screws with reversed L-shape and with 3 screws on the upper border. For this purpose, it was aimed to evaluate the biomechanical restraint effect which was applied to the different positions of the screws. In our study, we used 20 polyurethane models (Synbone®, Malans, Switzerland), which were manufactured to mimic the spongiosal bone on the cortical surface of the external surface and were prepared with bilateral sagittal split osteotomy. For the standardization of the screw locations in the models with osteotomies, the crest top, osteotomy lines and distances between each other were measured and marked with calipers. For the standardization of the steel apparatus to be used for the forces to be experimentally applied to the models, the extreme end of the angulus mandibular was marked. The study was carried out with 20 polyurethane jaws. The study was divided into two groups: "Group 1", in which three bicortical screws were placed in the upper level, and "Group 2", in which screws were placed in the inverted L configuration. On the hemi-mandibular side, a 2.0 mm diameter, 15 mm long triple resorce screw (LactoSorb®, Walter Lorenz Surgical, Jacksonville, FL, USA) was inserted in the inverted L shape. Other ten models were fixed with 2.0 mm diameter and 15 mm length three resorbable screws (LactoSorb, Walter Lorenz Surgical, Jacksonville, FL, USA) in the upper row. The test setup for the biomechanical test consisted of a fixation device to fix the model to the test device, a servohydraulic tester to perform the flush test, and a computer to which this device was connected. The sample is gripped by jaws and subjected to preloading. The compression test was carried out with a test speed of 2 mm / min, 5 mm / min and 10 mm / min. The pneumatic mandibles were placed in order to be tested on the fixation device previously prepared. The prepared test setup consisted of a base rigidly connected to the servohydraulic tester and two vertical pieces enabling it to be dimensionally placed on top of it. The distal vertical part was used for the proximal fragment and the anterior vertical part was used for the fixation of the distal fragment of the hemi-bodies. Stabilization of proximal fragments was achieved by the screw on the distal vertical part. The anterior cut teeth of the hemi-mandibular were fitted to the steel piece on the vertical part to provide stabilization. All hemi-mandibles were placed so that the distance between the vertical line passing through the rotation center in the proximal segment and the vertical component of the osteotomy line was equal to the experimental setup. To apply the pushing force, the steel propellant piece was attached to the moving part of the servohydraulic test device, aligned to the extreme end of the angular mandible. During the test procedure, a 10 Nt preload was carried out to allow the blank in each hemi-mandibular system to be retrieved and the standard measurement start as much as possible. The load was then maintained at 10 Nt and the experiment started with zero displacement. Following this procedure, continuous linear force was applied until the distal and proximal fragments were separated from each other. The resulting displacement data was digitally recorded to allow measurement of displacement values at specified force ranges with specially prepared software for the servohydraulic tester (testXpert II, Zwick Roell, Germany). The maximum force averages applied to Group 2 were statistically significantly higher than Group 1 (p <0.05). There was no statistically significant difference between the groups in terms of maximal pushing force reaching distance measurements (p> 0.05). Although the force averaged for the 2 mm advance to Group 2 was higher than the Group 1, this difference was close to meaningful but not statistically significant (p> 0.05). The maximum force averages applied to Group 2 for 4 mm advance, 6 mm advance, 8 mm advance and 10 mm advance were statistically significantly higher than Group 1 (p <0.05). Group 1; There was no statistically significant correlation between maximum applied pushing force and maximum pushing force resultant distance (p> 0.05). In group 2, there was no statistically significant relationship between the maximum applied pushing force and the maximum pushing force resultant distance (p> 0.05). We propose that placement of screws in the reverse-L mechanism will provide more stability in the incoming chewing forces compared to the placement of 3 bicortical resorbable screws in the order of top row and sequential placement on resilient fixation screws after bilateral sagittal split ssteotomy.