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SHORT COMMUNICATION
Forces released during alignment witha preadjusted appliance with differenttypes of elastomeric ligaturesLorenzo Franchia and Tiziano Baccettib
Florence, Italy
Introduction: The purpose of this in-vitro study was to compare the forces generated by new nonconven-tional elastomeric ligatures (NCEL) and conventional elastomeric ligatures (CEL) during leveling and aligningphases. Methods: The testing model consisted of 5 stainless steel 0.022-in preadjusted brackets for secondpremolar, first premolar, canine, lateral incisor, and central incisor. The canine bracket was welded to asliding bar that allowed for different vertical positions. The forces generated by 3 sizes of wires (0.012-,0.014-, and 0.016-in superelastic nickel-titanium) with the 2 types of elastomeric ligatures at differentamounts of upward canine misalignment (1.5, 3, 4.5, and 6 mm) were recorded. Results and Conclusions:Significant differences between CEL and NCEL were found for all tested variables (P �.01) with the exceptionof the 0.014- and 0.016-in wires at canine misalignment of 1.5 mm. A noticeable amount of force wasgenerated with the NCEL at all 4 canine positions with all 3 wire sizes (from about 50 to about 150 g). With4.5 mm of canine misalignment or more, the average amount of released force with the CEL was
approximately zero. (Am J Orthod Dentofacial Orthop 2006;129:687-90)Adesirable condition in fixed appliance therapywith preadjusted brackets consists of the reduc-tion of “frictional” forces between the bracket
and the guiding archwire during both sliding mechanicsfor space closure and the initial treatment phases ofleveling and aligning. Clinical evidence of the favor-able effects of low-friction archwire ligatures on thebiomechanical characteristics of orthodontic treatmentcan be derived from the use of passive self-ligatingbrackets.1
Recently, an innovative elastomeric ligature (Slide,Leone Orthodontic Products, Sesto Fiorentino, Firenze,Italy) was introduced (Fig 1) that can be used onconventional brackets to produce low levels of fric-tional resistance in treatment mechanics with the pre-adjusted appliance. An in-vitro study compared thefrictional forces generated by nonconventional elasto-meric ligatures (NCEL, Fig 1) and conventional elas-tomeric ligatures (CEL, Fig 2) with 0.014-in superelas-tic nickel-titanium wire and 0.019 � 0.025-in stainless
From the Department of Orthodontics, University of Florence, Florence, Italy;Thomas M. Graber Visiting Scholar, Department of Orthodontics and PediatricDentistry, School of Dentistry, University of Michigan, Ann Arbor, Mich.aLecturer.bAssistant professor.Reprint requests to: Lorenzo Franchi, Dipartimento di Odontostomatologia,Università degli Studi di Firenze, Via del Ponte di Mezzo, 46-48, 50127,Firenze, Italy; e-mail, [email protected], June 2005; revised and accepted, July 2005.0889-5406/$32.00Copyright © 2006 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2005.11.028steel wire.2 The amount of both static and kineticfriction was minimal (�10 g) in the NCEL group withaligned brackets of both wires, and it was less than thehalf that of the CEL with a misaligned canine bracket.This study, however, referred to the outcomes of a teston the friction affecting sliding mechanics by “pulling”the orthodontic archwire through a series of aligned andmisaligned brackets. A specific way of testing shouldappraise also the role of nonconventional ligatures inallowing the expression of orthodontic forces availablefor bracket alignment. The efficiency of fixed-appliancetherapy depends on the fraction of force delivered withrespect to the force applied.3
The aim of our in-vitro study was to analyze theforces released by orthodontic archwires during thealignment phase of fixed-appliance therapy with NCELcompared with CEL.
MATERIAL AND METHODS
An experimental model reproducing the rightbuccal segment of the maxillary arch was used toassess the forces produced by the NCEL (Fig 1) andthe CEL (Fig 2). The buccal segment model (Fig 3)consisted of 5 stainless steel 0.022-in preadjustedbrackets for second premolar, first premolar, canine,lateral incisor, and central incisor (STEP brackets,Leone Orthodontic Products). The interbracket distancewas set at 8.5 mm. The canine bracket was welded to a
sliding bar that allowed for various vertical positions,687
American Journal of Orthodontics and Dentofacial OrthopedicsMay 2006
688 Franchi and Baccetti
whereas the other brackets were mounted in a vice-likedevice. A section of 0.0215 � 0.028-in stainless steelwire was used to align all brackets.
The forces generated by the testing unit consistingof wire, brackets, and elastomeric ligatures were mea-sured under dry conditions and at room temperature(20°C � 2°C) with a testing machine (4301, Instron,Canton, Mass) with a load cell of 10 N. The upper endof the sliding bar bearing the canine bracket wasconnected to the machine’s crosshead. The frictionalforce recorded by the machine when pulling the slidingbar with the canine bracket in an upward directionwithout orthodontic wire was 0 g.
Three sizes of round superelastic nickel-titanium wire(Memoria wire, Leone Orthodontic Products) were tested:0.012, 0.014, and 0.016 in. These wires are frequentlyused during the aligning and leveling phase of thestraight-wire technique.4 The 3 sizes of wires weresecured in the preadjusted brackets with 2 types ofelastomeric ligatures produced by injection molding:
Fig 1. Nonconventional elastomeric ligature (NCEL).
Fig 2. Conventional elastomeric ligature (CEL).
NCEL (Slide) and CEL (silver mini modules, with
inside diameter of 1.3 mm and thickness of 0.9 mm).The elastomeric ligatures were placed immediately beforeeach test run to prevent ligature force decay. The testingmachine recorded the forces released by the archwire-bracket-ligature system after 4 amounts of upward dis-placement of the sliding bar bearing the canine bracket:1.5, 3, 4.5, and 6 mm of misalignment.
The forces generated by the 3 sizes of wires withthe 2 types of elastomeric ligatures were recorded. Theforces produced by each wire/ligature combinationwere tested 5 times with new wires and ligatures eachtime. A total of 120 tests (60 tests for each type ofligature) were carried out.
Statistical analysis
Descriptive statistics were calculated for the forcesgenerated by the wire/ligature combinations at the 4amounts of canine misalignment. The results for the 2types of ligatures were compared with the Fisher exacttest (P �.05) with statistical software (SPSS for Win-dows, version 12.0, SPSS, Chicago, Ill).
RESULTS
The descriptive statistics and the analysis of thecomparisons on the forces released by the 2 ligaturesystems are shown in the Table. Significant differences
Fig 3. Experimental in-vitro model with misaligned ca-nine bracket.
between the CEL and the NCEL were found for all
American Journal of Orthodontics and Dentofacial OrthopedicsVolume 129, Number 5
Franchi and Baccetti 689
tested variables (P �.01) with the exception of the0.014- and 0.016-in superelastic nickel-titanium wiresat the canine misalignment of 1.5 mm.
The NCEL generated a noticeable amount of forceat all 4 canine positions with all 3 wire sizes (fromabout 50 to about 150 g). At 3, 4.5, and 6 mm of caninemisalignment, the average amount of released forcewith the CEL was approximately 0 for the 0.012- andthe 0.014-in superelastic nickel-titanium wires. A sim-ilar result was found for the 0.016-in superelasticnickel-titanium wire at 4.5 and 6 mm of canine dis-placement.
DISCUSSION
In this study, we aimed to compare the forces releasedby orthodontic archwires during the leveling and aligningphase of fixed appliance therapy with NCEL vs CEL. Aninnovative testing device was conceived to recreate clin-ical conditions for the leveling and aligning phase ofstraight-wire technique to study the forces releasedduring alignment of a displaced tooth by allowing fordifferent amounts of misalignment of a bracket (canine)in an upward direction with regard to 4 remainingaligned brackets. With a 1.5-mm misaligned canine, theforces produced by the NCEL and the CEL weresimilar, ranging from 45 to 50 g for the 0.012-in wire to90 to100 g for the 0.014-in wire, and to 115 to 130 g forthe 0.016-in wire. The comparison between the 2 types ofligatures on the amount of released force with the 0.014-and the 0.016-in wires was not statistically significant at1.5 mm of canine misalignment. Although statisticallysignificant, the average difference between the amountof force released by the 0.012-in wire with the 2 types
Table. Descriptive statistics and statistical comparisonswith 2 types of elastomeric ligatures at various amoun
CEL
Mean Median SD Minimum M
0.012-in SE, 1.5 mm CM 43.8 44.3 1.2 41.70.012-in SE, 3.0 mm CM 0.1 0.0 0.1 0.00.012-in SE, 4.5 mm CM 0.0 0.0 0.1 0.00.012-in SE, 6.0 mm CM 0.0 0.0 0.1 0.00.014-in SE, 1.5 mm CM 91.9 92.4 2.7 89.10.014-in SE, 3.0 mm CM 0.1 0.1 0.1 0.00.014-in SE, 4.5 mm CM 0.1 0.1 0.1 0.00.014-in SE, 6.0 mm CM 0.1 0.0 0.1 0.00.016-in SE, 1.5 mm CM 112.9 106.4 15.5 103.00.016-in SE, 3.0 mm CM 76.8 79.0 8.8 65.20.016-in SE, 4.5 mm CM 0.1 0.1 0.1 0.00.016-in SE, 6.0 mm CM 0.1 0.0 0.1 0.0
*P �.01; NS, not significant.
of ligatures at 1.5 mm of canine misalignment was less
than 10 g. Starting from a 3-mm misalignment of thecanine bracket, the difference in behavior between theNCEL and the CEL becomes remarkable. With regardto both the 0.012- and 0.014-in wires, the CELproduce a null amount of released forces for align-ment, whereas the NCEL generate average amountsof force of 82 and 112 g for the 2 wires, respectively.With the 0.016-in wire with a 3-mm misalignment ofthe canine bracket, the average amount of forceproduced with the NCEL was 151 g, whereas it was77 g for the CEL. At 4.5 and 6 mm of caninemisalignment, the amount of force released with theCEL was 0 g, whereas it varied from about 100 g forthe 0.012-in wire to about 110 g for the 0.014-inwire, and to about 150 g for the 0.016-in wire.
Our results indicate that, when a slight amount oftooth alignment is needed (1.5 mm), the differences inthe performance of CEL and NCEL are minimal, butthese differences become extremely significant whencorrection of a misalignment of more than 3 mm isattempted. A null amount of force for alignment isactually released with CEL and a misalignment of atleast 4.5 mm. The clinical interpretation of these data,however, requires further considerations that modulateour findings. First, the vice-like devices of the testingmachine did not allow the brackets contiguous to themisaligned bracket to move. Our results, therefore,relate to a condition that can be defined as “absoluteanchorage.” Second, each test with the machine wasperformed with new elastomeric ligatures. No attemptwas made to evaluate the effects of time and oralenvironment on the amount of force released with thedifferent types of elastomeric ligatures.5
ces (g) generated by 3 sizes of superelastic (SE) wiresanine misalignment (CM)
NCEL
Mean Median SD Minimum Maximum Significance
52.7 51.1 4.2 49.5 59.3 *82.4 81.6 1.7 80.5 84.4 *99.3 98.0 7.4 89.4 108.6 *97.7 96.1 5.5 93.2 107.2 *97.6 95.8 7.6 91.3 110.3 NS
112.4 108.9 6.7 105.8 121.6 *99.7 96.8 8.0 94.1 113.8 *
116.6 113.4 12.9 103.5 131.5 *128.3 123.4 9.4 120.4 141.2 NS151.4 150.3 6.9 144.9 159.6 *152.7 151.1 10.0 141.0 165.1 *148.2 145.5 17.4 128.0 175.4 *
of forts of c
aximum
44.70.20.10.1
95.20.10.20.2
140.285.60.10.2
Previous investigations have shown that binding
American Journal of Orthodontics and Dentofacial OrthopedicsMay 2006
690 Franchi and Baccetti
and classical friction are 2 possible factors that tend tocontrast orthodontic movement.3,6 Because of the geom-etry of the interactions between the wire and the slot, witha misaligned canine bracket, the development of a forcedefined as “binding” (contact angle � equal to or greaterthan the critical contact angle �c) can be expected at themesial aspect of the first premolar bracket, at the distalaspect of the lateral incisor bracket, and at both mesial anddistal aspects of the canine bracket.6 For all the 3 sizes ofsuperelastic wires used in this study, the contactangle � exceeded the critical contact angle �c at all 4amounts of canine displacement (the contact angle �ranged from 10° to 35.2°; the critical contact angle �c
ranged from 2.7° to 4.5°). Therefore, binding couldbe assessed for all conditions reproduced here. Re-gardless of the consistent binding, for archwiredeformations induced by bracket misalignments of 3mm or greater, the amount of force generated with
the NCEL during the aligning phase of orthodontictreatment was significantly greater than that pro-duced with the CEL.
REFERENCES
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2. Baccetti T, Franchi L. Friction produced by different types ofelastomeric ligatures in treatment mechanics with the preadjustedappliance. Angle Orthod 2006;76:211-6.
3. Kusy RP, Whitley JQ. Friction between different wire-bracketconfigurations and materials. Semin Orthod 1997;3:166-77.
4. McLaughlin RP, Bennett JC, Trevisi HJ. Systemized orthodontictreatment mechanics. Philadelphia: Mosby; 2001. p. 110-1.
5. Taloumis LJ, Smith TM, Hondrum SO, Lorton L. Force decay anddeformation of orthodontic elastomeric ligatures. Am J OrthodDentofacial Orthop 1997;111:1-11.
6. Kusy RP, Whitley JQ. Influence of archwire and bracket dimen-sions on sliding mechanics: derivations and determinations of the
critical contact angles for binding. Eur J Orthod 1999;21:199-208.
