Introduction: Friction generated at the bracket/archwire interface during sliding mechanics can reduce the efficiency of orthodontic movement. The ligation method employed to tie the archwire to the bracket plays an important role in determining this friction. Methods: This study compared the frictional force generated by four different types of selfligating brackets (Time ® , Damon 2 ® , In-Ovation R ® and Smart Clip ® ) with a group of conventional orthodontic brackets (Dynalock ® ) that require the use of traditional elastomeric ligatures (ExDispens-A-Stix ® ), which served as the control group. Static friction force was measured using an EMIC DL ® 500 universal testing machine using stainless steel round 0.018-in and rectangular 0.017x0.025-in archwires. Results: ANOVA and Tukey's test showed low levels of friction in the four self-ligating brackets in tests with the 0.018-in wire (P <0.05). However, the results noted when the self-ligating brackets were tested using 0.017x0.025-in archwires showed high resistance to sliding in the self-ligating groups. AbstractAbstract: Friction. Orthodontic brackets. Self-ligating brackets. Sliding mechanics.
O bjective: To compare the static frictional forces generated at the bracket/wire interface of stainless steel brackets with different geometries and angulations, combined with orthodontic wires of different diameters. Material and Methods: The frictional forces were evaluated with three different types of metal brackets: a passive self-ligating (SmartClip™, 3M/Unitek, Monrovia, USA), with a modified slot design (Mini Uni Twin™, 3M/Unitek, Monrovia, USA) and conventional (Kirium, Abzil, São José do Rio Preto, Brazil). The samples were mounted in a testing device with three different angulations and tested with 0.014" and 0.018" stainless steel wires (American Orthodontics, Sheboygan, USA). The static frictional force was measured using a universal testing machine (DL 500, eMIC ® , São José dos Pinhais, Brazil) with a crosshead speed of 1 mm/min. Statistical analysis was performed by two-way ANOVA followed by Bonferroni's post hoc test. Results: There was a significant difference (p<0.05) in static friction when the three types of brackets were tested with the same wire size. The wire diameter influenced friction only when the brackets had a 10° angulation (p<0.05). The angulation influenced friction (p<0.05) when the brackets were associated with a 0.018" wire. Conclusion: Brackets with a modified slot design showed intermediate static frictional force values between the conventional and self-ligating brackets tested.
Experimental stress analysis can be conveniently investigated by classical shadow Moire technique. Moire is a non‐contact and non‐destructive technique, with a fast digitisation process. The phenomena of Moire fringes are the result of the projection of the fringes of a ruling on a certain object. It has measurement accuracy comparable with other systems and also low cost. The present study offers new algorithms for phase evaluation in measurements. Several phase‐shifting algorithms with an arbitrary but constant phase‐shift between captured intensity signs are proposed. The algorithms are similarly derived as the so‐called ‘Carre algorithm’. The idea is to develop a generalisation of Carre algorithm that is not restricted to four images. Errors and random noise in the images cannot be eliminated, but the uncertainty caused by their effects can be reduced by increasing the number of observations. An experimental analysis of the mistakes of the technique was made, as well as a detailed analysis of mistakes of the measurement. The advantages of the proposed algorithm are its precision in the measures taken, speed of processing and the immunity to noise in signs and images.
The present work offers new equations for phase evaluation in measurements. Several phase-shifting equations with an arbitrary but constant phase-shift between captured intensity signs are proposed. The equations are similarly derived as the so called Carré equation. The idea is to develop a generalization of the Carré equation that is not restricted to four images. Errors and random noise in the images cannot be eliminated, but the uncertainty due to their effects can be reduced by increasing the number of observations. An experimental analysis of the errors of the technique was made, as well as a detailed analysis of errors of the measurement. The advantages of the proposed equation are its precision in the measures taken, speed of processing and the immunity to noise in signs and images.
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