Katona, Thomas R.Wilson, DonBaldwin, James J.Chen, JieHohlt, William F.Shanks, James2024-05-242024-05-242002https://hdl.handle.net/1805/41013Indiana University-Purdue University Indianapolis (IUPUI)Orthodontic closing loops offer an efficient approach to consolidate extraction spaces. They allow for efficient tooth movement by lowering the load deflection rate, increasing potential activation, and by forming posterior anchorage units that can effectively resist displacement. The closing loop under investigation is a cross-leg delta loop. No studies have been done on this unique spring and the force systems created by altering its interbracket position. It is simple to fabricate chairside and produces fairly predictable moment to force ratios (M:F). The legs are crossed so the spring is activated in the same direction as its original bends, thus giving a more uniform distribution of stress within the spring, potential permanent deformation of the spring is decreased, reduced load deflection, and a greater overall range of activation. The cross-leg delta is simpler to fabricate than the more common T-loop since it needs two fewer bends. The material chosen for loop fabrication was 0.016 x 0.022 inch stainless steel wire due to its common use in clinic and research. Allowing for patient comfort and the fact that taller loops produce greater moment to force ratios, 7mm was chosen as the height of the cross-leg delta loop. The purpose of this study was to measure the spring generated forces and moments when altering the interbracket position of the closing loop. The null hypotheses are that there will not be any differences in the forces generated in the x (Fx) and y (Fy) directions, moments about the bucco-lingual axis (Mz), and M:F ratios in the sagittal plane (Mz:Fx) will not be altered by changing the interbracket position of cross-leg delta loops of same dimensions. A total of 120 loops, grouped as four sets of loops with 30 loops in each set: L1010, Ll 109, L1208, Ll307, were fabricated. The first two digits represent the length of the mesial leg and the last two digits represent the length of the distal leg for a total of 20mm in overall length. Each sequential set had the mesial leg increased by 1mm and the distal leg decreased by 1mm such that the most asymmetric set (L1307) had a 13mm mesial and a 7mm distal leg. The testing apparatus measured forces and moments along 3 mutually perpendicular axes (x, y, and z). Horizontal activation of the loop was performed by placing measured 1mm and 2mm stops over the wire. Data were collected from each set of loops. The cross-leg delta loops with symmetric 15° gable bends were compared for differences in moments and forces using repeated measures analysis of variance (ANOVA) models. Separate analyses were performed for Fx, Fy, Mz and Mz:Fx. Since the data was not normally distributed, a rank transformation was used. Pairwise comparisons were made using the Sidak method to control the overall significance level at 5%. Altering the interbracket position of a cross-leg delta loop did not cause major changes on the anterior and posterior forces in the x direction. Statistically significant differences in vertical forces (Fy), were much more pronounced when loops were positioned asymmetrically. Posteriorly positioned loops caused a statistically significant intrusive force on the anterior and extrusive force on the posterior segment was observed. As the loop was positioned more posteriorly, moments (Mz) acting in a clockwise direction on the anterior bracket decreased. More posteriorly positioned loops caused increased moments (Mz) in a counter-clockwise direction on the posterior bracket. As the loop was positioned more posteriorly, the M:F ratios in the sagittal plane acting on the anterior bracket decreased (Mz:Fx). More posteriorly positioned loops generated increased M:F ratios on the posterior bracket in the sagittal plane (Mz:Fx). Ideally, a posteriorly positioned closing loop would be used in a deep bite case needing maximum posterior anchorage. The intrusive force and decreased M:F ratio (Mz:Fx) on the anterior segment would cause more tipping and intrusion as space closure was carried out. The posteriorly positioned loop would generate increased moments (Mz) on the posterior bracket leading to increased M:F ratios in the sagittal plane (Mz:Fx). The extusive forces on the posterior segment would open the bite while the increased M:F ratios (Mz:Fx) would cause less tipping and increased anchorage. The study showed that altering the interbracket position of a closing loop can significantly alter the M:F ratio as well as the vertical and horizontal forces on the anterior and posterior segments. These results are important because the clinician can incorporate asymmetrically positioned loops to facilitate more efficient anchorage preparation. A posteriorly positioned loop can also generate an intrusive force on the anterior segment to help control overbite while retracting individual teeth or a segment en mass.en-USTooth Movement Techniques -- MethodsOrthodontic AppliancesDental Stress AnalysisBiomechanical PhenomenaThesis