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Forces released by nonconventional bracket orligature systems during alignment of buccallydisplaced teeth

Lorenzo Franchi, Tiziano Baccetti, Matteo Camporesi, and Veronica Giuntini

Florence, Italy

Introduction: The aim of this study was to analyzethe forces released by 4 types of passive stainless steelself-ligating brackets and 2 nonconventional elasto-meric ligature bracket systems compared with conven-tional elastomeric ligatures on stainless steel bracketsduring the alignment of buccally displaced teeth.

Methods: A model consisting of 5 brackets (fromsecond premolar through central incisor) was used to as-sess the forces released by the 7 bracket-ligature systemswith 0.012- or 0.014-in superelastic wires with variousamounts of buccal canine displacement (1.5-6.0 mm).The comparisons between the different types ofbracket-wire-ligature systems were performed with3-way ANOVA with the Tukey post-hoc test (P\0.05).

Results: For buccal misalignments of 1.5 and3.0 mm, both low-friction and conventional systemsreleased forces for bracket alignment ranging fromabout 30 to 160 g. For greater buccal displacements(4.5 and 6.0 mm), the low-friction systems produceda significant magnitude of force, but it dropped to 0 gfor the conventional system.

Conclusions: Nonconventional elastomeric ligaturebracket systems produced levels of force for toothmovement that were similar to those generated by pas-sive self-ligating brackets.

Read the full text online at: www.ajodo.org,pages 316.e1-316.e6.

Am J Orthod Dentofacial Orthop 2009;136:316-7

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Copyright � 2009 by the American Association of Orthodontists.

doi:10.1016/j.ajodo.2009.04.007

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EDITOR’S SUMMARY

The objectives of this study were to investigate theforces released by 4 types of passive stainless steelself-ligating brackets (SLBs) and 2 nonconventionalelastomeric ligature-bracket systems compared withconventional elastomeric ligatures on conventionalbrackets. The authors compared the force levels createdby light nickel-titanium wires used with a variety of li-gating bracket systems for alignment of a buccally dis-placed canine bracket. In reality, this was a bench studywith a typodont model and force measuring device. Nostatistically significant differences in force levels werereported between SLBs and nonconventional elasto-meric ligature-bracket systems, and no statistically sig-nificant differences were found between bracketligation systems when the canine bracket was buccallydisplaced less than 3 mm. Some readers might be con-fused by some points in the ‘‘Material and methods’’section. For example, (1) the authors measured the forcederived by the wires, not the brackets or ligatures; and(2) fixed brackets were used, so the obtained force levelswere all initial levels. The dental arch form from centralincisor to second premolar is usually curved, but thebrackets were actually fixed in a straight line by the0.0215 3 0.028-in wire and by the uncurved 0.012-and 0.014-in wires that were also used. There are majordiscrepancies between clinical treatment and this in-vi-tro simulation. The force system will be significantlydifferent because of the discrepancies of these boundaryconditions.

The authors noted that, ‘‘in this study, we did notevaluate the behavior of bracket-ligature systems withtime. We found no clinically meaningful differencein terms of the magnitude of forces generated by thevarious passive SLBs or low-friction ligature systems.’’With the same wire and the same level of tooth mis-alignment, all low-friction systems behaved similarly.They produced levels of force for tooth movementthat were similar to those generated by passive SLBs.

Fig 1. B, Close-up view with a canine bracket (Carriere)welded to the movable bar.

Fig 2. Interaction profile chart showing the forces re-leased by the various bracket-ligature combinations atthe 4 amounts of canine misalignment. The data representthe average forces released by 0.012- and 0.014-inNiTi wires.

American Journal of Orthodontics and Dentofacial Orthopedics Franchi et al 317Volume 136, Number 3

Q & AEditor: The AJO-DO no longer accepts in-vitrostudies evaluating shear bond strength in adhesivesbecause there is no relationship to in-vivo findings.Do you think there is merit in continuing bench(in-vitro) studies of new appliance systems?

Franchi: In-vitro studies still have value when theirobjective is the initial evaluation of the physical andbiomechanical features of newly developed appli-ance systems or materials. In-vivo testing with ap-propriate study designs, however, will always bethe last word on the treatment effects of new appli-ance systems.

Editor: Have you tried to design manageable in-vivo studies to evaluate fixed appliances?

Franchi: Our efforts in the last 5 years have been di-rected at developing an in-vitro testing device (simi-lar to that described in this study) that will allow us tomeasure the amount of force available for orthodon-tic movement during alignment of vertically or hor-izontally displaced teeth, with a more directclinical meaning. Classic in-vitro studies were aimedat measuring friction with various amounts of toothdisplacement. In these studies, however, the staticand kinetic frictions were evaluated solely by pullingthe orthodontic archwire through a series of alignedor misaligned brackets. In-vivo conditions are notrepresented by a pulling force that is applied to thewire during leveling and aligning.

Editor: Do you think the combination of improvedarchwires and bracket systems is starting to reduce

treatment times? Do you plan any studies along theselines?

Franchi: Recently, 2 well-designed studies(randomized clinical trials) in the AJO-DO (ScottP, DiBiase AT, Sherriff M, Cobourne M. Alignmentefficiency of Damon3 self-ligating and conven-tional orthodontic bracket systems: a randomizedclinical trial. 2008;134:470.e1-8; and Pandis N,Polychronopoulou A, Eliades T. Self-ligating vsconventional brackets in the treatment of mandibu-lar crowding: a prospective clinical trail of treat-ment duration and dental effects. 2007;132:208-15) compared treatment durations for the correc-tion of mandibular crowding with self-ligatingand conventional brackets. Both studies foundthat SLBs were no more efficient than conventionalbrackets during tooth alignment when mandibularincisor irregularity was greater than 5 mm. Formoderate crowding (irregularity \5 mm), however,SLBs produce 2.7 times faster correction. Futurein-vivo studies should elucidate whether SLBscan reduce treatment times during space closureor induce more effective transverse expansion ofthe dental arches than conventional fixed appliancetherapy.