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Journal of Orthodontics, Vol. 0, 2015, 1–11
Actual versus theoretical torsional play in conventional and self-ligating bracket systems Michel Dalstra1, Henrik Eriksen1, Chiara Bergamini2 and Birte Melsen1 1
Section of Orthodontics, Department of Dentistry, Aarhus University, Aarhus, Denmark Department of Paediatric Dentistry, University of Insubria, Varese, Italy
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Objective: The aim of this study was to assess the amount of torsional play in 32 commercially available self-ligating and conventional 0.018-inch and 0.022-inch bracket systems in relation to 0.01760.022-inch and 0.01960.025-inch stainless steel wires, respectively, and compare the results with the theoretical amount of play for the given bracket/ wire combinations. Methods: Torque moments were measured in a mechanical force testing system by twisting straight pieces of stainless steel wire seated in the bracket slot in increments of 0.5u until a full torsional expression was registered. Five upper central incisor brackets from each of the 32 different bracket systems were selected for the study. Results: The result from the laboratory testing clearly showed that wire/slot play was larger than anticipated from the nominal values, especially regarding the 0.022-inch brackets and particularly in relation to the passive self-ligating brackets. The play ranged from 19.8 to 36.1u of play for the most imprecise bracket system. Conclusions: The result does not favour the use of self-ligating brackets when focussing on torque control. The actual play is larger due to oversized slots and the inability of self-ligation brackets to press the archwire into the bottom of the slot. In conventional brackets, the initial torque moment is generated by the steel ligatures pressing the arch wire against the bottom of the slot. The oversize of the slot is thus less critical in relation to the conventional than in relation to the passive self-ligation bracket. Key words: Orthodontic brackets, torque expression, torsional play Received 16 June 2014; accepted 7 November 2014
Introduction Since the replacement of orthodontic bands with bonded brackets, the biggest change within clinical orthodontics has been the introduction of the ‘straight wire’ concept, where treatment is carried out with pre-adjusted appliances incorporating first, second and third order corrections built into the bracket, making bending of the continuous arches superfluous in patients with normal anatomy of the teeth. The concept and philosophy behind this approach was developed by Andrews in 1976 (Andrews, 1989). Although initially presented as the ideal, different prescriptions have been introduced, all considered by the authors to represent the optimal (Planche, 1997). Special attention has been paid to third order correction, the torque of the anterior teeth, for several reasons. According to Andrews, correct torque of the incisors influences the sagittal occlusion, facilitating the establishment of a neutral molar relationship (Andrews, 1976a, b). The influence of upper incisor inclination on arch length was demonstrated by Hussels and Nanda Address for correspondence: B. Melsen, School of Dentistry Aarhus University, Vennelvst Boulevard 9, Aarhus, Denmark. Email: [email protected] # 2015 British Orthodontic Society
(1987), and Ghaleb and co-workers, who suggested that inclination of the upper incisors was important for attractiveness of the facial profile (Ghaleb et al., 2011). Consequently, the focus has been on the production of brackets delivering the desired torque value. The variation between prescriptions is, however, only one among a large number of factors influencing final outcome. The variations are related to the patient, tooth morphology (Dellinger, 1978; Meling et al., 1998; Miethke and Melsen, 1999; van Loenen et al., 2005), to the doctor, the bonding procedure and the vertical position (Balut et al., 1992; McLaughlin et al., 2001; Miethke & Melsen, 1999). However, a prerequisite is that the brackets are able to generate and deliver the stated torque. Many studies have focussed on the precision of brackets and wires (Siatkowski, 1999; Fischer-Brandies et al., 2000; Cash et al., 2004; Mittal et al., 2013; Sifakakis et al., 2013; Al Fakir et al., 2014), but a comparison of the ability of a broad range of commercially available bracket types and sizes to deliver
DOI 10.1179/1465313314Y.0000000126
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Figure 1 The Force System Identification testing machine showing the two fixtures (the copper cylinders). The left one is attached to the three translatory step motors and mounted with an aluminium strip with 10 brackets; the right one is attached to the three rotatory step motors and features the stainless steel torqueing wire, which at its free end is inserted in the top-most bracket
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Figure 2 Schematic illustration of the torsional moment versus torsional angle curve (solid curve). The region between a1 and a2 represents the total amount of torsional play. The residual stiffness in the play region is calculated as: RS5(M22M1)/(a22a1). Note that the curves in the following figures have been normalized with a new origin at (x0,y0)5[(a2za1)/2,(M2zM1)/2] (dotted curve)
Table 1 Overview of the available bracket systems for testing. Size (inch)
Ligation
Bracket
Producer
HQ location
0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022
SL-passive SL-passive SL-passive SL-active SL-active SL-active Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional SL-passive SL-passive SL-passive SL-passive SL-active SL-active SL-active SL-active SL-active Conventional Conventional Conventional
BioPassive Carving Discovery BioQuick Empower In-OvationR Clarity Classic Equilibrium Integra Mini Diamond Mini Master Mini Sprint Mini-Taurus Mini-Twin OmniArch Sprint Twin Mini Diamond Victory LP Victory MBT Damon MX3 Damon Q Discovery SL Empower Passive BioQuick Empower Interactive In-Ovation R Smart Clip Speed Interactive Mini Diamond Mini Master Victory LP
Forestadent Swiss Dental Specialities Dentaurum Forestadent American Orthodontics Dentsply GAC 3M Unitek ClassOne Orthodontics Dentaurum Rocky Mountain Orthodontics Ormco American Orthodontics Forestadent Rocky Mountain Orthodontics Ortho Organizers Dentsply GAC Forestadent Ormco 3M Unitek 3M Unitek Ormco Ormco Dentaurum American Orthodontics Forestadent American Orthodontics Dentsply GAC 3M Unitek Speed System Orthodontics Ormco American Orthodontics 3M Unitek
Pforzheim, Germany Schwyz, Switzerland Ispringen, Germany Pforzheim, Germany Sheboygan, Wisconsin York, Pennsylvania Monrovia, California Carlsbad, California Ispringen, Germany Denver, Colorado Orange, California Sheboygan, Wisconson Pforzheim, Germany Denver, Colorado Carlsbad, California York, Pennsylvania Pforzheim, Germany Orange, California Monrovia, California Monrovia, California Orange, California Orange, California Ispringen, Germany Sheboygan, Wisconsin Pforzheim, Germany Sheboygan, Wisconsin York, Pennsylvania Monrovia, California Cambridge, Ontario Orange, California Sheboygan, Wisconsin Monrovia, California
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promised torque has to the knowledge of the authors not yet been presented. The aim of the present is study was therefore to compare the actual and the nominal torque delivered by 32 available conventional and selfligating brackets with 0.018-inch and 0.022-inch slot width by assessing the torsional play between the bracket and a given wire in an in vitro study. Materials and methods Thirty-two commercially available bracket types represented by the upper left central incisor brackets were analysed: 20 with a nominal slot size of 0.018-inch and 12 of 0.022-inch (Table 1). The collection included both self-ligating (passive and active) brackets and brackets with conventional ligation. Torsional play was measured using the Force System Identification machine developed for the Section of Orthodontics of the Institute of Odontology, Aarhus University (Melsen et al., 1992). Movements of the
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sensors are generated by six computer-controlled incremental motors and occur stepwise with a minimal increment of 0.1 mm for translation and 0.15u for rotation. The sensors are initially positioned in a predetermined position, which is stored in a connected computer and used as the zero-position throughout the total experiment. The movement of the sensors to the desired location is controlled by the computer and carried out by the step-motors. Sixteen strain-gauges inside the sensors measure deformations, which are amplified, converted into digital signals and calibrated to forces and moments and the computer then records and stores these data. The three planes of space are represented by the x-, y- and z-axes. They are illustrated as an orthogonal right-handed coordinate system at the two sensors. The forces and moments can therefore have a positive or negative sign. The reproducibility of the system has been previously reported and was found to be within plus/minus 5% (Menghi et al., 1999).
Table 2 Overview of the mean and standard deviation (SD) values of the play and the residual stiffness within the play region for the 32 tested bracket systems, ranked after bracket size, type of ligation and increasing play. In addition, the subsets to which the different brackets within each group of brackets belong according to the post-hoc tests are denoted in roman numerals. Play (u)
Residual stiffness (cN mm/u)
Size (inch)
Bracket
Ligation
Mean
SD
Subset
Mean
SD
Subset
0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022
Carving Discovery BioPassive In-OvationR Empower BioQuick Mini-Taurus Victory LP Integra Mini Sprint Mini-Twin Sprint OmniArch Victory MBT Mini Master Twin Mini Diamond Mini Diamond Clarity Equilibrium Classic Damon Q Empower Passive Discovery SL Damon MX3 Speed Interactive In-Ovation R Empower Interactive Smart Clip BioQuick Mini Master Victory LP Mini Diamond
SL-passive SL-passive SL-passive SL-active SL-active SL-active Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional SL-passive SL-passive SL-passive SL-passive SL-active SL-active SL-active SL-active SL-active Conventional Conventional Conventional
6.4 6.6 13.4 6.2 7.1 9.1 4.7 5.5 5.5 6.5 7.2 7.3 8.6 8.9 10.4 10.8 11.5 11.6 13.7 15.5 24.1 26.6 27.4 29.4 24.5 26.7 28.0 32.8 35.2 19.3 33.2 35.9
1.6 0.6 3.5 1.3 1.0 1.2 1.2 0.7 1.1 0.8 0.7 1.1 1.2 1.7 2.1 0.7 1.2 1.0 2.1 1.3 2.7 2.3 1.7 2.0 1.6 1.4 1.1 2.3 1.8 1.7 0.4 2.6
I I II I I II I I, II I, II I, II II, III II, III III, IV III, IV, V IV, V, VI V, VI VI VI VII VIII I I, II I, II II I II II III IV I II III
5.3 3.0 1.2 4.4 4.4 3.2 6.7 5.2 3.5 11.3 16.5 4.5 12.8 9.3 4.5 15.5 17.7 10.8 11.8 14.3 11.6 3.4 19.6 3.2 12.3 8.0 12.7 8.2 7.8 17.0 12.2 34.6
2.8 2.1 1.7 4.2 5.1 3.6 3.9 2.6 3.8 2.0 5.7 2.0 4.0 3.3 6.8 6.7 4.4 6.6 3.9 3.3 5.7 2.4 3.8 2.5 8.1 4.2 5.0 2.0 2.9 5.4 4.9 8.1
II I, II I I I I I, II I I I, II, III III I I, II, III I, II, III I II, III III I, II, III I, II, III II, III II I III I I I I I I I I II
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Figure 3 Overview of the torque vs. torque angle curves for the six most extreme conventional 0.018-inch brackets with regards to torsional play. The theoretical play (4.7u) is denoted by the vertical dotted lines
The brackets were glued onto an aluminium bar in a row of ten (five brackets from the same system). Every slot was perpendicular to the long axis of the aluminium rod. This rod was fixed to the grips, allowing one bracket to be tested at the time (Figure 1). The rod with the brackets was attached to one of the sensors and either a rectangular 0.01760.022-inch (for testing 0.018-inch brackets) or a 0.01960.025-inch straight stainless steel archwire (for testing 0.022-inch brackets) (both from Ormco, Orange, CA, USA) was fixed to the rotating sensor on the opposite side and guided passively into the bracket slot. In the case of self-ligating brackets, the lock or clip was then closed and for conventional brackets the ligation was performed in a standardized way with 0.008inch stainless steel ligatures tied tightly, while the wire was pressed onto the bottom of the bracket with an instrument as done in clinical practice. Measurements of the torqueing moments and the corresponding torqueing angles were carried out while
the wire was being twisted in the bracket slot. The machine started measuring by twisting the wire in steps of 0.5u up until full moment expression was achieved (i.e. the moment vs. torsional angle curve had reached its maximal slope). The torqueing wire was then returned to its zero position and the test was repeated in the opposite direction to ensure full torsional expression of the wire in the slot in both directions. Torsional play was defined as the width of the flatter part of the curve, before full expression of the torqueing moment was reached (Figure 2). Especially for the brackets with conventional ligation, but also for some of the active self-ligating ones, some build-up of torqueing moment was observed before the full torsional moment expression was reached. The amount of this moment was divided by the amount of play of the corresponding bracket to calculate the amount of ‘residual’ stiffness (RS) in the play region (Figure 2). Moment–torque angle curves were constructed and were normalized by
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Play in conventional and self-ligating brackets
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Figure 4 Overview of the torque vs. torque angle curves for the active self-ligating 0.018-inch brackets. The theoretical play (4.7u) is denoted by the vertical dotted lines
placing the origin at the middle of the play region, both to compensate for asymmetric bracket shape in the torqueing plane and to be able to make a comparison between the different brands of brackets. The measurements were carried out on five brackets from each of the 32 different bracket systems to evaluate the intrabracket variation. The torque wire was never twisted to plastic deformation, or such that notching of the wire could give rise to scratches, which was checked by visual and tactile inspection. Statistical analysis The error of the method was assessed by measuring the torsional play twice in five Damon MX3 brackets and using the Dahlberg formula for double measurements. A statistical description was performed for both torsional play and residual stiffness and a one-way ANOVA with a Student–Newman–Keuls post-hoc test was performed to rank the data for each group of brackets in order
assess any significant differences between the brackets within each group. Results The error of the method or intra-observer variation was calculated to be 0.4u. The standard deviation of the first and second series of measurements was 1.6 and 1.8u, respectively. As the error of method was smaller than any of these two values, the method can be considered adequate for the study. The moment–torque angle curves for the various bracket size and type of ligation groups are shown in Figures 3–8. For reference purposes, the calculated amount of theoretical play is also depicted graphically: 4.7u for 0.018-inch brackets and 14.5u for 0.022-inch ones. In general, the curves run through the first (positive torque) and third quadrant (negative torque). A certain asymmetry between the curves in these two quadrants is caused by the shape of the brackets and the
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Figure 5 Overview of the torque vs. torque angle curves for the passive self-ligating 0.018-inch brackets. The theoretical play (4.7u) is denoted by the vertical dotted lines
mounting of the clip in the self-ligating brackets and deformation of the bracket. The mean and SD values of the play and ‘residual’ stiffness are shown in Table 2. In relation to the conventional brackets, very little or no torsional play could be observed in relation to the 0.018-inch and 0.022-inch slot brackets. Straight from the start, there is a build-up of torsional moment with the twisting of the wire. Among the 0.018-inch brackets, the Mini-Diamond, the Mini-Taurus and the Clarity reached the full torque expression first (Figure 3). For the 0.022-inch slot brackets the Mini Master reached full torque expression first (Figure 6). The results regarding 0.022-inch active self-ligating brackets also differed, especially when expressing negative torque as BioQuick and Smart Clip exhibited more torsional play as the three others with respect to the negative torque (Figure 4). For the 0.018-inch active self-ligation brackets, the In-OvationR was slightly
closer to the anticipated values than Empower and BioQuick (Figure 7). The passive self-ligating brackets were clearly exhibiting larger torsion play than anticipated. In the 0.018inch group, the BioPassive was the weakest and among the 0.022-inch brackets and the Damon MX3 and the Damon Q were the weakest, exhibiting almost 30u of torsional play compared to the anticipated 14u (Figures 5 and 8). The Student–Newman–Keuls post-hoc test confirmed the impression from the graphs, that the conventional brackets have no totally passive part, and even though much oversized like the Mini Diamond or Victory, they develop moments almost from the start when the archwire is being twisted in the slot (Table 2). The same, although less pronounced, was the case with the active self-ligating brackets having less actual play than the passive self-ligating brackets.
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Play in conventional and self-ligating brackets
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Figure 6 Overview of the torque vs. torque angle curves for the conventional 0.022-inch brackets. The theoretical play (14.5u) is denoted by the vertical dotted lines
Discussion Bracket prescription has been in the focus of the orthodontic world since Andrews suggested that first, second and third order corrections were transferred to the brackets, thus reducing the necessity for bending. Bending is done for three reasons: (1) to obtain the first, second and third order correction once the teeth are close to the desired position; (2) to lower the force level; and finally (3) to obtain the desired force vector. The first object should in principle be performed with the pre-adjusted brackets, but factors as variation in crown morphology, bracket positioning (Miethke and Melsen, 1999) are not taken into consideration. The second object, lowering the force level, was to a large degree taken care of when the superelastic wires were introduced (Burstone et al., 1985). The third object does, on the other hand, still require custom-made appliances (Burstone, 1977; Burstone and Koenig, 1988). Meanwhile, a large number of publications have focused
on the variation in third order correction when applying the pre-adjusted brackets, lately specifically relation to the invasion of self-ligating brackets claimed to reduce variation in ligation force (Brauchli et al., 2011; Streva et al., 2011; Brauchli et al., 2012; Major et al., 2012; Major et al., 2013; Sifakakis et al., 2014). The present study set-up was performed with the aim of measuring the actual torsional play when twisting a wire in a large number of brackets with both 0.018-inch and 0.022-inch slot dimension and with both conventional ligation with steel ligatures, passive and active self-ligation. The study focussed on the comparison of the torque, delivered by different types and sizes of brackets and did not include any analysis of the ligation materials — steel ligatures or elastics, which is consistent with the recent studies of Brauchli et al. (2012) and Al Fakir et al. (2014). Elastics are not able to cause an elastic deformation of the wire, sufficient for a seating of the wire deeply into the bracket and should therefore
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Figure 7 Overview of the torque vs. torque angle curves for the active self-ligating 0.022-inch brackets. The theoretical play (14.5u) is denoted by the vertical dotted lines
only be used when the teeth are already aligned and the wire is fitting passively into the bracket. The torque play was expressed as the difference between the negative and the positive torque angle where the torsional stiffness of the twisting wire started to be fully expressed. This amount of play does, however, not represent the ability of the bracket to deliver torqueing moments to the tooth. The data from the statistical comparison are therefore of limited value as they fail to transfer information on the initial moments developed by the twisted wire to the brackets and which was not the result of the wire loaded against the walls of the bracket, but rather generated by the wire being forced against the floor of the brackets by the ligature or the active clip. This influence of ligation with a stainless steel ligature, forcing the wire onto the bottom of the bracket is in contrast to the findings of Brauchli and co-workers, who did not find any influence on the torque, the wire exhibited in the presence or absence of ligation with
either steel ligatures or elastics (Brauchli et al., 2012). An explanation may be the difference in set-up of the experiment as their study started the measurements with the wire centred in the bracket, and with a distance between the sensor and the bracket less than the normal interbracket distance, which might not allow the 0.01960.025-inch wire to be deformed by neither the ligature nor the clip of the active self-ligating bracket (Figure 9). A moment was generated from the first twisting and occurred also when a torsion play was anticipated. This moment would initiate a tissue reaction that would lead to a root movement in the right direction. The asymmetry observed between the graphs reflecting the buccal and the lingual torque can be ascribed to geometrical asymmetries and in relation to the active self-ligating brackets also the construction of the clip. The problem of finishing in undersized arch wires was evident especially in relation to passive self-ligating
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Figure 8 Overview of the torque vs. torque angle curves for the passive self-ligating 0.022-inch brackets. The theoretical play (14.5u) is denoted by the vertical dotted lines
brackets from our study. The actual play ranges between 19.8 and 36.1u, which is up to 2.4 times that of the nominal play of 14.5u. These findings are in agreement with the results from the study of Brauchli and coworkers, in which they measured the development of torque moment in active and passive self-ligating brackets using a 0.01960.025-inch stainless steel archwire in a 0.022-inch bracket slot (Brauchli et al., 2011). The reasons for the increased play in this laboratory experiment are all related to the manufacturing process. The slot walls should be parallel, in most brackets they are not. The slot is always oversized (Cash et al., 2004). Another reason for lack of a linear relation between twist and torque could be the bracket material, which may be softer than the stainless steel archwires and can be deformed by these archwires (Morina et al., 2008). A bevelled arch wire may, on the other hand, also contribute to the initial torsion play as the reduced cross-section of the archwire allows for more twist
before firm contact is established between archwire and slot walls (Sebanc et al., 1984). In spite of the inadequate torque control with the 0.022-inch brackets, especially when passive self-ligating, finishing with a 0.01960.025-inch stainless steel archwire has been recommended (Rinchuse and Miles, 2007). In addition to the variation in torque related to the ‘hardware’, it should, however, be borne in mind that the in vivo variation is most likely even larger as the variation in dental anatomy and variation related to the positioning of the brackets are not taken into consideration (Mietke and Melsen, 1999; van Loenen et al., 2005). Torque prescriptions of upper incisors today vary from Andrews z7u to the popularly used Roth of value of z12 and Ricketts’ z22u. The 0.018-inch bracket is able to provide more torque control than the 0.022-inch one and talks in favour of the bi-dimensional system. The result from the present study does not favour the use of passive self-ligating brackets especially with a
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being pressed to the bottom of the slot, develop moment that may initiate the torqueing of the teeth although not to the full expression. The importance of selecting a prescription seems limited, as the torsional play especially in relation to passive 0.022-inch brackets over-rules the difference between various prescriptions. Conventional brackets using steel ligatures generate more torsional moment despite large play values, because the archwire is firmly pressed onto the bottom of the slot.
Figure 9 Without ligation (or with passive selfligation), the wire is free to move upwards and torque will first be generated when the wire touches the walls of the bracket (left). With ligation (or active selfligation), immediate contact with the ligation wire (or the clip of the self-ligation bracket) will create contact forces which create a torqueing moment which has to be overcome before the torque angle can be further increased
0.022-inch slot due to the oversized slots and the inability of the self-ligation to press the archwire into the bottom of the slot. The 0.018-inch brackets were in general expressing torque closer to the anticipated values, and this speaks for the application of the bidimensional system recommended by Gianelly (Gianelly et al., 1985). The 0.022-inch slot size in the lateral segment would then allow for the impact of the occlusal forces on the third order control, while the incisors would be controlled by the bracket prescription. In relation to conventional brackets with steel ligatures presses the archwire into the slot bottom, even if the slot is oversized torqueing moments will be present immediately throughout the twisting of the archwire. There is no passive moment/twist (graphically seen as a plateau) in the conventional brackets as seen in all the selfligating brackets. Conclusion The in vitro experimental testing concludes that the actual play in every tested bracket was up to 2.4 times larger than the nominal play of 14.6u and that the passive self-ligating brackets were least able to generate the desired torque. In this category, moments were only generated with respect to the bracket after a twisting 19.8u in the best bracket to 36.1u in the worst when using a 0.01960.025-inch stainless steel archwire in a 0.022inch slot. The conventional and to some degree the active self-ligating brackets did, possibly due to the wire
Disclaimer statements Contributors Dalstra: set-up of tests, data analysis, and manuscript preparation; Eriksen and Bergamini: performance of measurements; Melsen: initiation of study and final manuscript. Funding Aarhus University. Conflicts of interest The authors hereby declare that there are no conflicts of interest. Ethics approval In vitro study — no ethics approval required. References Al Fakir H, Carey JP, Melenka GW, Nobes DS, Heo G, Major PW. Investigation into the effects of stainless steel ligature ties on the mechanical characteristics of conventional and self-ligated brackets subjected to torque. J Orthod 2014; 41: 188–200. Andrews LF. The straight-wire appliance, origin, controversy, commentary. J Clin Orthod 1976a; 10: 99–114. Andrews LF. The straight-wire appliance. Explained and compared. J Clin Orthod 1976b; 10: 174–195. Andrews LF. Straight Wire: the Concept and Appliance. 1st edn. San Diego, CA: LA Wells. 1989. Balut N, Klapper L, Sandrik J, Bowman D. Variations in bracket placement in the preadjusted orthodontic appliance. Am J Orthod Dentofacial Orthop 1992; 102: 62–67. Brauchli LM, Senn C, Wichelhaus A. Active and passive self-ligation — a myth? Angle Orthod 2011; 81: 312–318. Brauchli LM, Steineck M, Wichelhaus A. Active and passive self-ligation: a myth? Part 1: torque control. Angle Orthod 2012; 82: 663–669. Burstone CJ, Koenig HA. Creative wire bending — the force system from step and V bends. Am J Orthod Dentofacial Orthop 1988; 93: 59–67. Burstone CR. Deep overbite correction by intrusion. Am J Orthod 1977; 72: 1–22. Burstone CJ, Qin B, Morton JY. Chinese NiTi wire — a new orthodontic alloy. Am J Orthod 1985; 87: 445–452. Cash AC, Good SA, Curtis RV, McDonald F. An evaluation of slot size in orthodontic brackets-are standards as expected? Angle Orthod 2004; 74: 450–453. Dellinger EL. A scientific assessment of the straight-wire appliance. Am J Orthod 1978; 73: 290–299. Fischer-Brandies H, Orthuber W, Es-Souni M, Meyer S. Torque transmission between square wire and bracket as a function of measurement, form and hardness parameters. J Orofac Orthop 2000; 61: 258–265. Ghaleb N, Bouserhal J, Bassil-Nassif N. Aesthetic evaluation of profile incisor inclination. Eur J Orthod 2011; 33: 228–235. Gianelly AA, Bednar JR, Dietz VS. A bidimensional edgewise technique. J Clin Orthod 1985; 19: 418–421. Hussels W, Nanda RS. Effect of maxillary incisor angulation and inclination on arch length. Am J Orthod Dentofacial Orthop 1987; 91: 233–239.
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Major TW, Carey JP, Nobes DS, Heo G, Major PW. Deformation and warping of the bracket slot in select self-ligating orthodontic brackets due to an applied third order torque. J Orthod 2012; 39: 25–33. Major TW, Carey JP, Nobes DS, Heo G, Melenka GW, Major PW. An investigation into the mechanical characteristics of select self-ligated brackets at a series of clinically relevant maximum torquing angles: loading and unloading curves and bracket deformation. Eur J Orthod 2013; 35: 719–729. McLaughlin RP, Bennett JC, Trevisi HJ. Systemized Orthodontic Treatment Mechanics. Maryland Heights, MO: Mosby. 2001 Meling TR, Odegaard J, Seqner D. On bracket slot height: a methodologic study. Am J Orthod Dentofacial Orthop 1998; 113: 387–393. Melsen HM, Frederiksen MMA, Godtfredsen EAKL, Melsen B. Force System Identification. Eur J Orthod 1992. Menghi C, Planert J, Melsen B. 3-D experimental identification of force systems from orthodontic loops activated for first order corrections. Angle Orthod 1999; 69: 49–57. Miethke RR, Melsen B. Effect of variation in tooth morphology and bracket position on first and third order correction with preadjusted appliances. Am J Orthod Dentofacial Orthop 1999; 116: 329–335. Mittal N, Xia Z, Chen J, Stewart KT, Liu SS. Three-dimensional quantification of pretorqued nickel–titanium wires in edgewise and prescription brackets. Angle Orthod 2013; 83: 484–490.
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Morina E, Eliades T, Pandis N, Ja¨ger A, Bourauel C. Torque expression of selfligating brackets compared with conventional metallic, ceramic, and plastic brackets. Eur J Orthod 2008; 30: 233–238. Planche P. L’evaluation des techniques pre`-enferme´es depuis Andrews. Rev Orthop Denta Faciale 1997; 31: 453–471. Rinchuse DJ, Miles PG. Self-ligating brackets: present and future. Am J Orthod Dentofacial Orthop 2007; 132: 216–222. Sebanc J, Brantley WA, Pincsak JJ, Conover JP. Variability of effective root torque as a function of edge bevel on orthodontic arch wires. Am J Orthod 1984; 86: 43–51. Siatkowski RE. Loss of anterior torque control due to variations in bracket slot and archwire dimensions. J Clin Orthod 1999; 33: 508–510. Sifakakis I, Pandis N, Makou M, Eliades T, Katsaros C, Bourauel C. Torque expression of 0.018 and 0.022 inch conventional brackets. Eur J Orthod 2013; 35: 610–614. Sifakakis I, Pandis N, Makou M, Eliades T, Katsaros C, Bourauel C. Torque efficiency of different archwires in 0.018- and 0.022-inch conventional brackets. Angle Orthod 2014; 84: 149–154. Streva AM, Cotrim-Ferreira FA, Garib DG, Carvalho PE. Are torque values of preadjusted brackets precise? J Appl Oral Sci 2011; 19: 313–317. van Loenen M, Degrieck J, de Pauw G, Dermaut L. Anterior tooth morphology and its effect on torque. Eur J Orthod 2005; 27: 258–262.
Journal of Orthodontics, Vol. 0, 2015, 1–11
Actual versus theoretical torsional play in conventional and self-ligating bracket systems Michel Dalstra1, Henrik Eriksen1, Chiara Bergamini2 and Birte Melsen1 1
Section of Orthodontics, Department of Dentistry, Aarhus University, Aarhus, Denmark Department of Paediatric Dentistry, University of Insubria, Varese, Italy
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Objective: The aim of this study was to assess the amount of torsional play in 32 commercially available self-ligating and conventional 0.018-inch and 0.022-inch bracket systems in relation to 0.01760.022-inch and 0.01960.025-inch stainless steel wires, respectively, and compare the results with the theoretical amount of play for the given bracket/ wire combinations. Methods: Torque moments were measured in a mechanical force testing system by twisting straight pieces of stainless steel wire seated in the bracket slot in increments of 0.5u until a full torsional expression was registered. Five upper central incisor brackets from each of the 32 different bracket systems were selected for the study. Results: The result from the laboratory testing clearly showed that wire/slot play was larger than anticipated from the nominal values, especially regarding the 0.022-inch brackets and particularly in relation to the passive self-ligating brackets. The play ranged from 19.8 to 36.1u of play for the most imprecise bracket system. Conclusions: The result does not favour the use of self-ligating brackets when focussing on torque control. The actual play is larger due to oversized slots and the inability of self-ligation brackets to press the archwire into the bottom of the slot. In conventional brackets, the initial torque moment is generated by the steel ligatures pressing the arch wire against the bottom of the slot. The oversize of the slot is thus less critical in relation to the conventional than in relation to the passive self-ligation bracket. Key words: Orthodontic brackets, torque expression, torsional play Received 16 June 2014; accepted 7 November 2014
Introduction Since the replacement of orthodontic bands with bonded brackets, the biggest change within clinical orthodontics has been the introduction of the ‘straight wire’ concept, where treatment is carried out with pre-adjusted appliances incorporating first, second and third order corrections built into the bracket, making bending of the continuous arches superfluous in patients with normal anatomy of the teeth. The concept and philosophy behind this approach was developed by Andrews in 1976 (Andrews, 1989). Although initially presented as the ideal, different prescriptions have been introduced, all considered by the authors to represent the optimal (Planche, 1997). Special attention has been paid to third order correction, the torque of the anterior teeth, for several reasons. According to Andrews, correct torque of the incisors influences the sagittal occlusion, facilitating the establishment of a neutral molar relationship (Andrews, 1976a, b). The influence of upper incisor inclination on arch length was demonstrated by Hussels and Nanda Address for correspondence: B. Melsen, School of Dentistry Aarhus University, Vennelvst Boulevard 9, Aarhus, Denmark. Email: [email protected] # 2015 British Orthodontic Society
(1987), and Ghaleb and co-workers, who suggested that inclination of the upper incisors was important for attractiveness of the facial profile (Ghaleb et al., 2011). Consequently, the focus has been on the production of brackets delivering the desired torque value. The variation between prescriptions is, however, only one among a large number of factors influencing final outcome. The variations are related to the patient, tooth morphology (Dellinger, 1978; Meling et al., 1998; Miethke and Melsen, 1999; van Loenen et al., 2005), to the doctor, the bonding procedure and the vertical position (Balut et al., 1992; McLaughlin et al., 2001; Miethke & Melsen, 1999). However, a prerequisite is that the brackets are able to generate and deliver the stated torque. Many studies have focussed on the precision of brackets and wires (Siatkowski, 1999; Fischer-Brandies et al., 2000; Cash et al., 2004; Mittal et al., 2013; Sifakakis et al., 2013; Al Fakir et al., 2014), but a comparison of the ability of a broad range of commercially available bracket types and sizes to deliver
DOI 10.1179/1465313314Y.0000000126
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Figure 1 The Force System Identification testing machine showing the two fixtures (the copper cylinders). The left one is attached to the three translatory step motors and mounted with an aluminium strip with 10 brackets; the right one is attached to the three rotatory step motors and features the stainless steel torqueing wire, which at its free end is inserted in the top-most bracket
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Figure 2 Schematic illustration of the torsional moment versus torsional angle curve (solid curve). The region between a1 and a2 represents the total amount of torsional play. The residual stiffness in the play region is calculated as: RS5(M22M1)/(a22a1). Note that the curves in the following figures have been normalized with a new origin at (x0,y0)5[(a2za1)/2,(M2zM1)/2] (dotted curve)
Table 1 Overview of the available bracket systems for testing. Size (inch)
Ligation
Bracket
Producer
HQ location
0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022
SL-passive SL-passive SL-passive SL-active SL-active SL-active Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional SL-passive SL-passive SL-passive SL-passive SL-active SL-active SL-active SL-active SL-active Conventional Conventional Conventional
BioPassive Carving Discovery BioQuick Empower In-OvationR Clarity Classic Equilibrium Integra Mini Diamond Mini Master Mini Sprint Mini-Taurus Mini-Twin OmniArch Sprint Twin Mini Diamond Victory LP Victory MBT Damon MX3 Damon Q Discovery SL Empower Passive BioQuick Empower Interactive In-Ovation R Smart Clip Speed Interactive Mini Diamond Mini Master Victory LP
Forestadent Swiss Dental Specialities Dentaurum Forestadent American Orthodontics Dentsply GAC 3M Unitek ClassOne Orthodontics Dentaurum Rocky Mountain Orthodontics Ormco American Orthodontics Forestadent Rocky Mountain Orthodontics Ortho Organizers Dentsply GAC Forestadent Ormco 3M Unitek 3M Unitek Ormco Ormco Dentaurum American Orthodontics Forestadent American Orthodontics Dentsply GAC 3M Unitek Speed System Orthodontics Ormco American Orthodontics 3M Unitek
Pforzheim, Germany Schwyz, Switzerland Ispringen, Germany Pforzheim, Germany Sheboygan, Wisconsin York, Pennsylvania Monrovia, California Carlsbad, California Ispringen, Germany Denver, Colorado Orange, California Sheboygan, Wisconson Pforzheim, Germany Denver, Colorado Carlsbad, California York, Pennsylvania Pforzheim, Germany Orange, California Monrovia, California Monrovia, California Orange, California Orange, California Ispringen, Germany Sheboygan, Wisconsin Pforzheim, Germany Sheboygan, Wisconsin York, Pennsylvania Monrovia, California Cambridge, Ontario Orange, California Sheboygan, Wisconsin Monrovia, California
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promised torque has to the knowledge of the authors not yet been presented. The aim of the present is study was therefore to compare the actual and the nominal torque delivered by 32 available conventional and selfligating brackets with 0.018-inch and 0.022-inch slot width by assessing the torsional play between the bracket and a given wire in an in vitro study. Materials and methods Thirty-two commercially available bracket types represented by the upper left central incisor brackets were analysed: 20 with a nominal slot size of 0.018-inch and 12 of 0.022-inch (Table 1). The collection included both self-ligating (passive and active) brackets and brackets with conventional ligation. Torsional play was measured using the Force System Identification machine developed for the Section of Orthodontics of the Institute of Odontology, Aarhus University (Melsen et al., 1992). Movements of the
Play in conventional and self-ligating brackets
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sensors are generated by six computer-controlled incremental motors and occur stepwise with a minimal increment of 0.1 mm for translation and 0.15u for rotation. The sensors are initially positioned in a predetermined position, which is stored in a connected computer and used as the zero-position throughout the total experiment. The movement of the sensors to the desired location is controlled by the computer and carried out by the step-motors. Sixteen strain-gauges inside the sensors measure deformations, which are amplified, converted into digital signals and calibrated to forces and moments and the computer then records and stores these data. The three planes of space are represented by the x-, y- and z-axes. They are illustrated as an orthogonal right-handed coordinate system at the two sensors. The forces and moments can therefore have a positive or negative sign. The reproducibility of the system has been previously reported and was found to be within plus/minus 5% (Menghi et al., 1999).
Table 2 Overview of the mean and standard deviation (SD) values of the play and the residual stiffness within the play region for the 32 tested bracket systems, ranked after bracket size, type of ligation and increasing play. In addition, the subsets to which the different brackets within each group of brackets belong according to the post-hoc tests are denoted in roman numerals. Play (u)
Residual stiffness (cN mm/u)
Size (inch)
Bracket
Ligation
Mean
SD
Subset
Mean
SD
Subset
0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022
Carving Discovery BioPassive In-OvationR Empower BioQuick Mini-Taurus Victory LP Integra Mini Sprint Mini-Twin Sprint OmniArch Victory MBT Mini Master Twin Mini Diamond Mini Diamond Clarity Equilibrium Classic Damon Q Empower Passive Discovery SL Damon MX3 Speed Interactive In-Ovation R Empower Interactive Smart Clip BioQuick Mini Master Victory LP Mini Diamond
SL-passive SL-passive SL-passive SL-active SL-active SL-active Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional Conventional SL-passive SL-passive SL-passive SL-passive SL-active SL-active SL-active SL-active SL-active Conventional Conventional Conventional
6.4 6.6 13.4 6.2 7.1 9.1 4.7 5.5 5.5 6.5 7.2 7.3 8.6 8.9 10.4 10.8 11.5 11.6 13.7 15.5 24.1 26.6 27.4 29.4 24.5 26.7 28.0 32.8 35.2 19.3 33.2 35.9
1.6 0.6 3.5 1.3 1.0 1.2 1.2 0.7 1.1 0.8 0.7 1.1 1.2 1.7 2.1 0.7 1.2 1.0 2.1 1.3 2.7 2.3 1.7 2.0 1.6 1.4 1.1 2.3 1.8 1.7 0.4 2.6
I I II I I II I I, II I, II I, II II, III II, III III, IV III, IV, V IV, V, VI V, VI VI VI VII VIII I I, II I, II II I II II III IV I II III
5.3 3.0 1.2 4.4 4.4 3.2 6.7 5.2 3.5 11.3 16.5 4.5 12.8 9.3 4.5 15.5 17.7 10.8 11.8 14.3 11.6 3.4 19.6 3.2 12.3 8.0 12.7 8.2 7.8 17.0 12.2 34.6
2.8 2.1 1.7 4.2 5.1 3.6 3.9 2.6 3.8 2.0 5.7 2.0 4.0 3.3 6.8 6.7 4.4 6.6 3.9 3.3 5.7 2.4 3.8 2.5 8.1 4.2 5.0 2.0 2.9 5.4 4.9 8.1
II I, II I I I I I, II I I I, II, III III I I, II, III I, II, III I II, III III I, II, III I, II, III II, III II I III I I I I I I I I II
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Figure 3 Overview of the torque vs. torque angle curves for the six most extreme conventional 0.018-inch brackets with regards to torsional play. The theoretical play (4.7u) is denoted by the vertical dotted lines
The brackets were glued onto an aluminium bar in a row of ten (five brackets from the same system). Every slot was perpendicular to the long axis of the aluminium rod. This rod was fixed to the grips, allowing one bracket to be tested at the time (Figure 1). The rod with the brackets was attached to one of the sensors and either a rectangular 0.01760.022-inch (for testing 0.018-inch brackets) or a 0.01960.025-inch straight stainless steel archwire (for testing 0.022-inch brackets) (both from Ormco, Orange, CA, USA) was fixed to the rotating sensor on the opposite side and guided passively into the bracket slot. In the case of self-ligating brackets, the lock or clip was then closed and for conventional brackets the ligation was performed in a standardized way with 0.008inch stainless steel ligatures tied tightly, while the wire was pressed onto the bottom of the bracket with an instrument as done in clinical practice. Measurements of the torqueing moments and the corresponding torqueing angles were carried out while
the wire was being twisted in the bracket slot. The machine started measuring by twisting the wire in steps of 0.5u up until full moment expression was achieved (i.e. the moment vs. torsional angle curve had reached its maximal slope). The torqueing wire was then returned to its zero position and the test was repeated in the opposite direction to ensure full torsional expression of the wire in the slot in both directions. Torsional play was defined as the width of the flatter part of the curve, before full expression of the torqueing moment was reached (Figure 2). Especially for the brackets with conventional ligation, but also for some of the active self-ligating ones, some build-up of torqueing moment was observed before the full torsional moment expression was reached. The amount of this moment was divided by the amount of play of the corresponding bracket to calculate the amount of ‘residual’ stiffness (RS) in the play region (Figure 2). Moment–torque angle curves were constructed and were normalized by
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Play in conventional and self-ligating brackets
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Figure 4 Overview of the torque vs. torque angle curves for the active self-ligating 0.018-inch brackets. The theoretical play (4.7u) is denoted by the vertical dotted lines
placing the origin at the middle of the play region, both to compensate for asymmetric bracket shape in the torqueing plane and to be able to make a comparison between the different brands of brackets. The measurements were carried out on five brackets from each of the 32 different bracket systems to evaluate the intrabracket variation. The torque wire was never twisted to plastic deformation, or such that notching of the wire could give rise to scratches, which was checked by visual and tactile inspection. Statistical analysis The error of the method was assessed by measuring the torsional play twice in five Damon MX3 brackets and using the Dahlberg formula for double measurements. A statistical description was performed for both torsional play and residual stiffness and a one-way ANOVA with a Student–Newman–Keuls post-hoc test was performed to rank the data for each group of brackets in order
assess any significant differences between the brackets within each group. Results The error of the method or intra-observer variation was calculated to be 0.4u. The standard deviation of the first and second series of measurements was 1.6 and 1.8u, respectively. As the error of method was smaller than any of these two values, the method can be considered adequate for the study. The moment–torque angle curves for the various bracket size and type of ligation groups are shown in Figures 3–8. For reference purposes, the calculated amount of theoretical play is also depicted graphically: 4.7u for 0.018-inch brackets and 14.5u for 0.022-inch ones. In general, the curves run through the first (positive torque) and third quadrant (negative torque). A certain asymmetry between the curves in these two quadrants is caused by the shape of the brackets and the
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Figure 5 Overview of the torque vs. torque angle curves for the passive self-ligating 0.018-inch brackets. The theoretical play (4.7u) is denoted by the vertical dotted lines
mounting of the clip in the self-ligating brackets and deformation of the bracket. The mean and SD values of the play and ‘residual’ stiffness are shown in Table 2. In relation to the conventional brackets, very little or no torsional play could be observed in relation to the 0.018-inch and 0.022-inch slot brackets. Straight from the start, there is a build-up of torsional moment with the twisting of the wire. Among the 0.018-inch brackets, the Mini-Diamond, the Mini-Taurus and the Clarity reached the full torque expression first (Figure 3). For the 0.022-inch slot brackets the Mini Master reached full torque expression first (Figure 6). The results regarding 0.022-inch active self-ligating brackets also differed, especially when expressing negative torque as BioQuick and Smart Clip exhibited more torsional play as the three others with respect to the negative torque (Figure 4). For the 0.018-inch active self-ligation brackets, the In-OvationR was slightly
closer to the anticipated values than Empower and BioQuick (Figure 7). The passive self-ligating brackets were clearly exhibiting larger torsion play than anticipated. In the 0.018inch group, the BioPassive was the weakest and among the 0.022-inch brackets and the Damon MX3 and the Damon Q were the weakest, exhibiting almost 30u of torsional play compared to the anticipated 14u (Figures 5 and 8). The Student–Newman–Keuls post-hoc test confirmed the impression from the graphs, that the conventional brackets have no totally passive part, and even though much oversized like the Mini Diamond or Victory, they develop moments almost from the start when the archwire is being twisted in the slot (Table 2). The same, although less pronounced, was the case with the active self-ligating brackets having less actual play than the passive self-ligating brackets.
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Play in conventional and self-ligating brackets
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Figure 6 Overview of the torque vs. torque angle curves for the conventional 0.022-inch brackets. The theoretical play (14.5u) is denoted by the vertical dotted lines
Discussion Bracket prescription has been in the focus of the orthodontic world since Andrews suggested that first, second and third order corrections were transferred to the brackets, thus reducing the necessity for bending. Bending is done for three reasons: (1) to obtain the first, second and third order correction once the teeth are close to the desired position; (2) to lower the force level; and finally (3) to obtain the desired force vector. The first object should in principle be performed with the pre-adjusted brackets, but factors as variation in crown morphology, bracket positioning (Miethke and Melsen, 1999) are not taken into consideration. The second object, lowering the force level, was to a large degree taken care of when the superelastic wires were introduced (Burstone et al., 1985). The third object does, on the other hand, still require custom-made appliances (Burstone, 1977; Burstone and Koenig, 1988). Meanwhile, a large number of publications have focused
on the variation in third order correction when applying the pre-adjusted brackets, lately specifically relation to the invasion of self-ligating brackets claimed to reduce variation in ligation force (Brauchli et al., 2011; Streva et al., 2011; Brauchli et al., 2012; Major et al., 2012; Major et al., 2013; Sifakakis et al., 2014). The present study set-up was performed with the aim of measuring the actual torsional play when twisting a wire in a large number of brackets with both 0.018-inch and 0.022-inch slot dimension and with both conventional ligation with steel ligatures, passive and active self-ligation. The study focussed on the comparison of the torque, delivered by different types and sizes of brackets and did not include any analysis of the ligation materials — steel ligatures or elastics, which is consistent with the recent studies of Brauchli et al. (2012) and Al Fakir et al. (2014). Elastics are not able to cause an elastic deformation of the wire, sufficient for a seating of the wire deeply into the bracket and should therefore
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Figure 7 Overview of the torque vs. torque angle curves for the active self-ligating 0.022-inch brackets. The theoretical play (14.5u) is denoted by the vertical dotted lines
only be used when the teeth are already aligned and the wire is fitting passively into the bracket. The torque play was expressed as the difference between the negative and the positive torque angle where the torsional stiffness of the twisting wire started to be fully expressed. This amount of play does, however, not represent the ability of the bracket to deliver torqueing moments to the tooth. The data from the statistical comparison are therefore of limited value as they fail to transfer information on the initial moments developed by the twisted wire to the brackets and which was not the result of the wire loaded against the walls of the bracket, but rather generated by the wire being forced against the floor of the brackets by the ligature or the active clip. This influence of ligation with a stainless steel ligature, forcing the wire onto the bottom of the bracket is in contrast to the findings of Brauchli and co-workers, who did not find any influence on the torque, the wire exhibited in the presence or absence of ligation with
either steel ligatures or elastics (Brauchli et al., 2012). An explanation may be the difference in set-up of the experiment as their study started the measurements with the wire centred in the bracket, and with a distance between the sensor and the bracket less than the normal interbracket distance, which might not allow the 0.01960.025-inch wire to be deformed by neither the ligature nor the clip of the active self-ligating bracket (Figure 9). A moment was generated from the first twisting and occurred also when a torsion play was anticipated. This moment would initiate a tissue reaction that would lead to a root movement in the right direction. The asymmetry observed between the graphs reflecting the buccal and the lingual torque can be ascribed to geometrical asymmetries and in relation to the active self-ligating brackets also the construction of the clip. The problem of finishing in undersized arch wires was evident especially in relation to passive self-ligating
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Play in conventional and self-ligating brackets
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Figure 8 Overview of the torque vs. torque angle curves for the passive self-ligating 0.022-inch brackets. The theoretical play (14.5u) is denoted by the vertical dotted lines
brackets from our study. The actual play ranges between 19.8 and 36.1u, which is up to 2.4 times that of the nominal play of 14.5u. These findings are in agreement with the results from the study of Brauchli and coworkers, in which they measured the development of torque moment in active and passive self-ligating brackets using a 0.01960.025-inch stainless steel archwire in a 0.022-inch bracket slot (Brauchli et al., 2011). The reasons for the increased play in this laboratory experiment are all related to the manufacturing process. The slot walls should be parallel, in most brackets they are not. The slot is always oversized (Cash et al., 2004). Another reason for lack of a linear relation between twist and torque could be the bracket material, which may be softer than the stainless steel archwires and can be deformed by these archwires (Morina et al., 2008). A bevelled arch wire may, on the other hand, also contribute to the initial torsion play as the reduced cross-section of the archwire allows for more twist
before firm contact is established between archwire and slot walls (Sebanc et al., 1984). In spite of the inadequate torque control with the 0.022-inch brackets, especially when passive self-ligating, finishing with a 0.01960.025-inch stainless steel archwire has been recommended (Rinchuse and Miles, 2007). In addition to the variation in torque related to the ‘hardware’, it should, however, be borne in mind that the in vivo variation is most likely even larger as the variation in dental anatomy and variation related to the positioning of the brackets are not taken into consideration (Mietke and Melsen, 1999; van Loenen et al., 2005). Torque prescriptions of upper incisors today vary from Andrews z7u to the popularly used Roth of value of z12 and Ricketts’ z22u. The 0.018-inch bracket is able to provide more torque control than the 0.022-inch one and talks in favour of the bi-dimensional system. The result from the present study does not favour the use of passive self-ligating brackets especially with a
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being pressed to the bottom of the slot, develop moment that may initiate the torqueing of the teeth although not to the full expression. The importance of selecting a prescription seems limited, as the torsional play especially in relation to passive 0.022-inch brackets over-rules the difference between various prescriptions. Conventional brackets using steel ligatures generate more torsional moment despite large play values, because the archwire is firmly pressed onto the bottom of the slot.
Figure 9 Without ligation (or with passive selfligation), the wire is free to move upwards and torque will first be generated when the wire touches the walls of the bracket (left). With ligation (or active selfligation), immediate contact with the ligation wire (or the clip of the self-ligation bracket) will create contact forces which create a torqueing moment which has to be overcome before the torque angle can be further increased
0.022-inch slot due to the oversized slots and the inability of the self-ligation to press the archwire into the bottom of the slot. The 0.018-inch brackets were in general expressing torque closer to the anticipated values, and this speaks for the application of the bidimensional system recommended by Gianelly (Gianelly et al., 1985). The 0.022-inch slot size in the lateral segment would then allow for the impact of the occlusal forces on the third order control, while the incisors would be controlled by the bracket prescription. In relation to conventional brackets with steel ligatures presses the archwire into the slot bottom, even if the slot is oversized torqueing moments will be present immediately throughout the twisting of the archwire. There is no passive moment/twist (graphically seen as a plateau) in the conventional brackets as seen in all the selfligating brackets. Conclusion The in vitro experimental testing concludes that the actual play in every tested bracket was up to 2.4 times larger than the nominal play of 14.6u and that the passive self-ligating brackets were least able to generate the desired torque. In this category, moments were only generated with respect to the bracket after a twisting 19.8u in the best bracket to 36.1u in the worst when using a 0.01960.025-inch stainless steel archwire in a 0.022inch slot. The conventional and to some degree the active self-ligating brackets did, possibly due to the wire
Disclaimer statements Contributors Dalstra: set-up of tests, data analysis, and manuscript preparation; Eriksen and Bergamini: performance of measurements; Melsen: initiation of study and final manuscript. Funding Aarhus University. Conflicts of interest The authors hereby declare that there are no conflicts of interest. Ethics approval In vitro study — no ethics approval required. References Al Fakir H, Carey JP, Melenka GW, Nobes DS, Heo G, Major PW. Investigation into the effects of stainless steel ligature ties on the mechanical characteristics of conventional and self-ligated brackets subjected to torque. J Orthod 2014; 41: 188–200. Andrews LF. The straight-wire appliance, origin, controversy, commentary. J Clin Orthod 1976a; 10: 99–114. Andrews LF. The straight-wire appliance. Explained and compared. J Clin Orthod 1976b; 10: 174–195. Andrews LF. Straight Wire: the Concept and Appliance. 1st edn. San Diego, CA: LA Wells. 1989. Balut N, Klapper L, Sandrik J, Bowman D. Variations in bracket placement in the preadjusted orthodontic appliance. Am J Orthod Dentofacial Orthop 1992; 102: 62–67. Brauchli LM, Senn C, Wichelhaus A. Active and passive self-ligation — a myth? Angle Orthod 2011; 81: 312–318. Brauchli LM, Steineck M, Wichelhaus A. Active and passive self-ligation: a myth? Part 1: torque control. Angle Orthod 2012; 82: 663–669. Burstone CJ, Koenig HA. Creative wire bending — the force system from step and V bends. Am J Orthod Dentofacial Orthop 1988; 93: 59–67. Burstone CR. Deep overbite correction by intrusion. Am J Orthod 1977; 72: 1–22. Burstone CJ, Qin B, Morton JY. Chinese NiTi wire — a new orthodontic alloy. Am J Orthod 1985; 87: 445–452. Cash AC, Good SA, Curtis RV, McDonald F. An evaluation of slot size in orthodontic brackets-are standards as expected? Angle Orthod 2004; 74: 450–453. Dellinger EL. A scientific assessment of the straight-wire appliance. Am J Orthod 1978; 73: 290–299. Fischer-Brandies H, Orthuber W, Es-Souni M, Meyer S. Torque transmission between square wire and bracket as a function of measurement, form and hardness parameters. J Orofac Orthop 2000; 61: 258–265. Ghaleb N, Bouserhal J, Bassil-Nassif N. Aesthetic evaluation of profile incisor inclination. Eur J Orthod 2011; 33: 228–235. Gianelly AA, Bednar JR, Dietz VS. A bidimensional edgewise technique. J Clin Orthod 1985; 19: 418–421. Hussels W, Nanda RS. Effect of maxillary incisor angulation and inclination on arch length. Am J Orthod Dentofacial Orthop 1987; 91: 233–239.
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Major TW, Carey JP, Nobes DS, Heo G, Major PW. Deformation and warping of the bracket slot in select self-ligating orthodontic brackets due to an applied third order torque. J Orthod 2012; 39: 25–33. Major TW, Carey JP, Nobes DS, Heo G, Melenka GW, Major PW. An investigation into the mechanical characteristics of select self-ligated brackets at a series of clinically relevant maximum torquing angles: loading and unloading curves and bracket deformation. Eur J Orthod 2013; 35: 719–729. McLaughlin RP, Bennett JC, Trevisi HJ. Systemized Orthodontic Treatment Mechanics. Maryland Heights, MO: Mosby. 2001 Meling TR, Odegaard J, Seqner D. On bracket slot height: a methodologic study. Am J Orthod Dentofacial Orthop 1998; 113: 387–393. Melsen HM, Frederiksen MMA, Godtfredsen EAKL, Melsen B. Force System Identification. Eur J Orthod 1992. Menghi C, Planert J, Melsen B. 3-D experimental identification of force systems from orthodontic loops activated for first order corrections. Angle Orthod 1999; 69: 49–57. Miethke RR, Melsen B. Effect of variation in tooth morphology and bracket position on first and third order correction with preadjusted appliances. Am J Orthod Dentofacial Orthop 1999; 116: 329–335. Mittal N, Xia Z, Chen J, Stewart KT, Liu SS. Three-dimensional quantification of pretorqued nickel–titanium wires in edgewise and prescription brackets. Angle Orthod 2013; 83: 484–490.
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Morina E, Eliades T, Pandis N, Ja¨ger A, Bourauel C. Torque expression of selfligating brackets compared with conventional metallic, ceramic, and plastic brackets. Eur J Orthod 2008; 30: 233–238. Planche P. L’evaluation des techniques pre`-enferme´es depuis Andrews. Rev Orthop Denta Faciale 1997; 31: 453–471. Rinchuse DJ, Miles PG. Self-ligating brackets: present and future. Am J Orthod Dentofacial Orthop 2007; 132: 216–222. Sebanc J, Brantley WA, Pincsak JJ, Conover JP. Variability of effective root torque as a function of edge bevel on orthodontic arch wires. Am J Orthod 1984; 86: 43–51. Siatkowski RE. Loss of anterior torque control due to variations in bracket slot and archwire dimensions. J Clin Orthod 1999; 33: 508–510. Sifakakis I, Pandis N, Makou M, Eliades T, Katsaros C, Bourauel C. Torque expression of 0.018 and 0.022 inch conventional brackets. Eur J Orthod 2013; 35: 610–614. Sifakakis I, Pandis N, Makou M, Eliades T, Katsaros C, Bourauel C. Torque efficiency of different archwires in 0.018- and 0.022-inch conventional brackets. Angle Orthod 2014; 84: 149–154. Streva AM, Cotrim-Ferreira FA, Garib DG, Carvalho PE. Are torque values of preadjusted brackets precise? J Appl Oral Sci 2011; 19: 313–317. van Loenen M, Degrieck J, de Pauw G, Dermaut L. Anterior tooth morphology and its effect on torque. Eur J Orthod 2005; 27: 258–262.
