Torquedrehmomentübertragung zwischen Vierkantdraht und Bracket als Funktion von Maß-, Form- und Härteparametern

Abstract

The aim of the study was to investigate the influence of cross section, edge geometry and structural hardness on torque transmission between square wire and bracket. For this purpose, 5 different brands of stainless steel square wire in 3 dimensions (0.016" x 0.016", 0.016" x 0.022" and 0.017" x 0.025") were inserted into edgewise brackets with a slot size of 0.018" and loaded with different torques (1 and 3 Ncm). The slot and wire geometries were analyzed by computer on ground specimens before and after loading. In addition, the Vickers hardness and micro-hardness of the unstressed and stressed metal surfaces were determined. While the slot size was very accurately maintained, the wire dimensions deviated downwards by an average of 10%. Torque transmission led to notching and bending-up phenomena on the bracket slot flanks. A torque loading of 3 Ncm increased the torque play of 0.016" x 0.022" wires by 3.6 degrees, and of 0.017" x 0.025" wires by 3.7 degrees. In the case of 0.016" x 0.016" wires, an effective torque transmission was no longer possible. The average Vickers hardness of the wires was 533 kp/mm2, and that of the brackets 145 kp/mm2. The micro-hardness in the deformation area of stressed internal slot walls increased with increasing load transmission from 204 to 338 kp/mm2. As a result of excessively small wire dimensions and plastic deformation of the brackets, a relatively large torque play occurs. Deformation and notching in the area of the internal slot walls are inconsistent with demands for recycling brackets. A standardization of bracket wire systems stating the actual torque play would be desirable.

Orthodontic Bracket Manufacturing Tolerances and Dimensional Differences between Select Self-Ligating Brackets

“…Using the same formula, the difference between the average torque play between a Speed and Damon bracket is 2.3°. These torque play differences are an idealized estimate, and actual torque play is dependent on factors such as bracket/wire friction and beveling of wire corners [2, 11–13]. …”

“…Orthodontic bracket slot profile variances have an impact on torque play and third-order torque expression [2, 3]. Typically the bracket slot height will be stated as a nominal height; previous studies have found variations between the nominally stated sizes and the measured sizes [4–9], with some brands being oversized up to 27% [10].…”

Are torque values of preadjusted brackets precise?

“…Some authors that studied orthodontic materials developed mechanical devices to conduct their researches 8,19,20 . Others used computerized systems 7 or graphic computation systems (CAD) 14 . Nevertheless, optical microscopy was frequently involved 3,6,15,24,30 .…”

“…However, in spite of incorporating ideal torque characteristics in the structure of such brackets, in some cases it is necessary to apply additional or individual torques on some teeth. This would occur due to several factors 10,27 : mechanical side-effects 25 , morphological differences in the buccal faces of teeth 4,6,9,21,22,26 , changes in the position of the brackets 2,16,22,29 , different methods of bracket manufacturing 12,30 and orthodontic wires 24 , the play between the wire and the bracket slot 3,4,7,16,24,25 , variations in the bracket designs 8 , properties of the materials constituting the brackets 7,8,11,13,23 and wires 24 and differences between the value of the torque informed by the manufacturer and the real value of the torque of the brackets 10 .…”

Measurement of Orthodontic Bracket Tie Wing Elastic and Plastic Deformation by Arch Wire Torque Expression Utilizing an Optical Image Correlation Technique

“…Accurately measuring and predicting torque expression and understanding the sources of losses are critical to providing predictable orthodontic treatment results. Several studies have measured in vitro torque expression using different devices and techniques looking at wire/bracket play, different brackets, and wire configurations, among other variables showing that torque expression was largely affected by these variables [2–5, 8, 14–21]. …”