Abstract
Many advantages have been described surrounding self-ligating (SL) brackets compared to metallic conventional ligating (CL) brackets, such as: Less total treatment time, alignment efficiency, patient comfort, plaque retention, and low friction. The objective of this in vitro simulation was to know the variables that affect arch displacement in CL and SL brackets—active (ASL) and passive (PSL)—and analyze if static friction values are affected by bracket design, arch wire section, kind of ligature, and use of a friction reducer agent (FRA) in a wet state. Larger values of static friction were found in CL with metallic ligature (ML) (8.01 ± 1.08 N/mm) and elastic ligature (EL) (6.96 ± 0.48 N/mm). Lower values were found in PSL brackets combined with FRA (0.58 ± 0.21 N/mm). The study was carried out using different stereographical models of a maxillary upper right quadrant with canine, first and second premolar, and first molar bonded brackets. A section of 25 mm of 0.019 × 0.025” stainless steel arch with a rectangular section (SS) and hybrid section (HY) was inserted into the different bracket models. Static friction values were collected using a universal test machine in wet conditions and testing the effect of a friction reducer agent (FRA). To assure the reliability of the study, different wire combinations were repeated after two weeks by the same operator and a linear analysis of regression was done. Each bracket model analysis—with the different wires, use of the FRA, and comparison among brackets in similar conditions—was done using an ANOVA test with a confidence interval of 95% and comparative Post-Hoc tests (LSD). In this in vitro simulation we found higher static friction values in CL compared to ASL and PSL. In PSL, lower values were achieved. CL brackets using ML showed the highest static friction values with a great variability. In this setting, the use of HY wires did not reduce static friction values in ASL and PSL, while in CL brackets with EL friction the values were reduced significantly. An FRA combined with ASL reduced significantly static friction values but not with PSL. In the case of CL, the FRA effect was higher with SS and better than with HY wires. ML values were similar to ASL static friction. The direct extrapolation of the results might be inaccurate, since all these findings should be tested clinically to be validated.
Highlights
Self-ligating brackets (SLB) were reintroduced in the clinical orthodontic practice in late 90s [1].Some advantages were described, such as faster movements, less chair time, and less extraction need.Materials 2019, 12, 3279; doi:10.3390/ma12203279 www.mdpi.com/journal/materialsRecent systematic reviews describe only these advantages: Less time needed to ligate, less incisor protrusion, and greater transversal changes in the molar region [2,3].Knowledge of the friction concept with the use of self-ligating brackets, and its clinical evidence, may be critical to the orthodontist to be able to select the better system for treating patients
Each bracket model analysis—with the different wires, use of the friction reducer agent (FRA), and comparison among brackets in similar conditions—was done using an ANOVA test with a confidence interval of 95% and comparative Post-Hoc tests (LSD). In this in vitro simulation we found higher static friction values in conventional ligating (CL) compared to ASL and PSL
All possible combinations (Table 1) were tested and static friction values were obtained in each studied bracket
Summary
Self-ligating brackets (SLB) were reintroduced in the clinical orthodontic practice in late 90s [1].Some advantages were described, such as faster movements, less chair time, and less extraction need.Materials 2019, 12, 3279; doi:10.3390/ma12203279 www.mdpi.com/journal/materialsRecent systematic reviews describe only these advantages: Less time needed to ligate, less incisor protrusion, and greater transversal changes in the molar region [2,3].Knowledge of the friction concept with the use of self-ligating brackets, and its clinical evidence, may be critical to the orthodontist to be able to select the better system for treating patients. Friction is the resistance produced between two surfaces: The slot and the arch wire, making a movement in the same direction but in the opposite way [5]. There are two types of friction: Dynamic and static. Dynamic friction is directly proportional to the normal ligated strength, which works perpendicularly to the direction of movement between the surfaces in contact with the arch and the bracket. In vitro studies may be helpful to simulate clinical situations with different materials. Even those results must be checked clinically to confirm presumed advantages
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