Baccetti, Tiziano

Camporesi, M.

Franchi, Lorenzo

English

Florence Research

120Angle Orthodontist, Vol 78, No 1, 2008 DOI: 10.2319/011107-11.1Original ArticleForces in the Presence ofCeramic Versus Stainless Steel Brackets withUnconventional vs Conventional LigaturesTiziano Baccettia; Lorenzo Franchia; Matteo CamporesibABSTRACTObjective: To compare the forces resulting from four types of bracket/ligature combinations: ce-ramic brackets and stainless steel brackets combined with unconventional elastomeric ligatures(UEL) and conventional elastomeric ligatures (CEL) during the leveling and aligning phases oforthodontic therapy.Materials and Methods: The testing model consisted of five 0.022-inch preadjusted brackets(second premolar, first premolar, canine, lateral incisor, and central incisor) for each of the twobracket types. The canine bracket was welded to a sliding bar that allowed for different amountsof offset in the gingival direction. The forces generated by a 0.014-inch superelastic nickel titaniumwire in the presence of either the UEL or CEL bracket/ligature systems at different amounts ofupward canine misalignment (1.5 mm, 3 mm, 4.5 mm, and 6 mm) were recorded.Results: Significant differences were found between UEL and CEL systems for all tested variables(P  .01) with the exception of the canine misalignment of 1.5 mm. The average amount ofrecorded force in the presence of CEL was negligible with 3.0 mm or greater of canine misalign-ment. On the contrary, during alignment, a force available for tooth movement was recorded inthe presence of both ceramic and stainless steel brackets when associated with UEL.Conclusions: The type of ligature used influenced the actual amount of force released by theorthodontic system significantly more than the type of bracket used (stainless steel vs ceramic).KEY WORDS: Orthodontic ligatures; Esthetic fixed appliances; FrictionINTRODUCTIONIn modern society the esthetic aspect of the ortho-dontic therapy is important because the number ofadults that undergo orthodontic therapy is increasing.1The development of appliances that combine both ac-ceptable esthetics and adequate technical perfor-mance is an important goal. Ceramic brackets weredeveloped to improve esthetics during orthodontica Assistant Professor, Department of Orthodontics, The Uni-versity of Florence, Florence, Italy; Thomas M. Graber VisitingScholar, Department of Orthodontics and Pediatric Dentistry,School of Dentistry, The University of Michigan, Ann Arbor,Mich.b Research Fellow, Department of Orthodontics, The Univer-sity of Florence, Florence, Italy.Corresponding author: Tiziano Baccetti, DDS, PhD, Diparti-mento di Odontostomatologia, Universita` degli Studi di Firenze,Via del Ponte di Mezzo, 46-48 50127, Firenze, Italy(e-mail: t.baccetti@odonto.unifi.it)Accepted: February 2007. Submitted: December 2006. 2008 by The EH Angle Education and Research Foundation,Inc.treatment, with a continuous effort to overcome sev-eral problems of these types of brackets: brittlenessleading to bracket or tie-wing failure, iatrogenic enameldamage during debonding, enamel wear of opposingteeth, and high frictional resistance to sliding mechan-ics.2–6Beside esthetics, a second desirable condition infixed appliance therapy with preadjusted brackets con-sists in the reduction of ‘‘frictional’’ forces between thebracket and the guiding archwire during both the initialtreatment phases of leveling and aligning and the slid-ing mechanics for space closure. Friction is the resis-tance to motion that exists when a solid is moved tan-gentially with respect to the surface of another con-tacting solid.7 Friction is, thus, inherent to sliding sys-tems and influences the rate of orthodonticmovement.8 During mechanotherapy involving move-ment of the bracket along the wire, friction at thebracket-archwire interface may prevent the attainmentof optimal force levels in the supporting dental tissue.Therefore, an understanding of the force required toovercome friction is important so that the appropriate121LOW-FRICTION LIGATURES FOR TWO TYPES OF BRACKETSAngle Orthodontist, Vol 78, No 1, 2008Figure 1. Ceramic bracket (AQUA) with unconventional elastomericligature (Slide). (A) Frontal view. (B) Lateral view.Figure 2. Stainless steel bracket (STEP) with unconventional elas-tomeric ligature (Slide). (A) Frontal view. (B) Lateral view.magnitude of force can be used to produce appropri-ate biologic tooth movement.9 To explain the frictionbetween wire and bracket, several variables such asbracket material, wire material, and wire section canbe studied.10–12 For instance, ceramic brackets show ahigh level of frictional resistance because the ceramicmaterial yields a higher coefficient of friction thanstainless steel due to differences in the plastic andelastic properties of the materials.7Previous research13–15 stated that friction can be de-termined also by the nature of the ligation. An inno-vative system of unconventional ligatures is an actualalternative to self-ligating brackets. Recently, uncon-ventional elastomeric ligatures (UEL) have been de-veloped to be combined with both ceramic and stain-less steel brackets.16 Once the unconventional ligatureis applied on the bracket, the interaction between theligature and the slot forms a ‘‘tube-like’’ structure,which allows the archwire to slide freely and to pro-duce its effects more readily on the dentoalveolar com-ponent. In vitro studies17,18 have compared the friction-al forces generated by the UEL and the conventionalelastomeric ligatures (CEL) with 0.014-inch superelas-tic nickel titanium wire and 0.019  0.025 inch stain-less steel wire. The amount of both static and kineticfriction was minimal (10 g) in the UEL group in thepresence of aligned brackets with both types of wires,and it was less than half of that shown by CEL in thepresence of a misaligned canine bracket.The aim of the present in vitro study was to comparethe differences in the forces available for tooth move-ment during the alignment phase of fixed appliancetherapy when utilizing either ceramic or stainless steelbrackets with either unconventional or conventionalelastomeric ligatures.MATERIALS AND METHODSAll materials used in this study were supplied by Le-one Orthodontic Products (Sesto Fiorentino, Firenze,Italy). An experimental model18 was used to assess theforces produced by:a. Esthetic ceramic brackets (AQUA) with estheticUEL (Slide) (Figure 1);b. Esthetic ceramic brackets (AQUA) with CEL (trans-parent mini modules, with an inside diameter of 1.3mm and thickness of 0.9 mm);c. Stainless steel brackets (STEP) with silver UEL(Figure 2);d. Stainless steel brackets (STEP) with CEL.The buccal segment model (Figure 3) consisted ofeither five esthetic ceramic or five stainless steel0.022-inch preadjusted brackets (Roth prescription forthe ceramic brackets and MBT prescription for thestainless steel brackets) for the second premolar, firstpremolar, canine, lateral incisor, and central incisor.The interbracket distance was set at 8.5 mm. The ca-nine bracket was welded to a sliding bar that allowedfor different vertical positions, while the other bracketswere mounted in a vice-like device. A section of0.0215  0.028 inch stainless steel wire was used toalign all the brackets.The forces generated by the testing unit consistingof wire, brackets, and either CEL and UEL were mea-sured under dry conditions and at room temperature(20  2 C) by means of an Instron 4301 testing ma-chine (Instron Corp, Canton, Mass) with a load cell of10 N. The upper end of the sliding bar bearing thecanine bracket was connected to the Instron cross-head. A 0 gram frictional force was recorded by thetesting machine when pulling the sliding bar with thecanine bracket in an upward direction in the absenceof any orthodontic wire.A round 0.014-inch superelastic nickel titanium wire(Memoria, Leone Orthodontic Products, Sesto Fior-entino, Firenze, Italy) was tested. This type of wire isfrequently used during the aligning and leveling phaseof the straight-wire technique.9 The wire was securedinto the preadjusted brackets using the two types of122 BACCETTI, FRANCHI, CAMPORESIAngle Orthodontist, Vol 78, No 1, 2008Figure 3. Experimental in vitro model with misaligned canine brack-et.ligatures: UEL (Slide) and CEL (mini modules). Theelastomeric ligatures were placed immediately beforeeach test run, to avoid ligature force decay.The Instron machine recorded the forces releasedby the archwire-bracket-ligature system following fourdifferent amounts of upward displacement of the slid-ing bar bearing the canine bracket: 1.5 mm, 3.0 mm,4.5 mm, and 6.0 mm of misalignment. The forces gen-erated by the wire with either ceramic or stainless steelbrackets with UEL and CEL were recorded. The forcesproduced by each wire/ligature combination were test-ed 20 times with new wires and ligatures on each oc-casion. A total of 320 tests were carried out (80 testsfor esthetic ceramic brackets with UEL, and 80 testsfor esthetic ceramic brackets with CEL; 80 tests forstainless steel brackets with UEL, and 80 tests forstainless steel brackets with CEL).Statistical AnalysesDescriptive statistics were calculated for the forcesgenerated by the wire/ligature combinations at the fourdifferent amounts of canine misalignment. The com-parisons between the results for the two types ofbrackets with UEL and CEL were carried out by meansof Kruskal-Wallis test with Tukey’s post hoc test (P .05) (SigmaStat 3.1, Systat Software Inc, Point Rich-mond, Calif).RESULTSThe descriptive statistics and the analysis of thecomparisons on the forces released by the orthodonticwire in the presence of ceramic brackets with UEL andwith CEL, and in the presence of stainless steel brack-ets with UEL and with CEL are shown in Table 1.At a canine misalignment of 1.5 mm, differences be-tween ceramic brackets with UEL and CEL were notsignificant for any of the tested variables. At the sameamount of canine misalignment, the differences be-tween ceramic and stainless steel brackets with UELand with CEL were not significant either.The comparison between the unconventional liga-tures and CEL in conjunction with ceramic and stain-less steel brackets showed that, in the presence ofUEL, a significantly greater amount of force was gen-erated when canine misalignment was of 3.0 mm, 4.5mm, and 6.0 mm. When the two types of brackets (ce-ramic vs stainless steel) with UEL were compared, nosignificant differences were found in the presence of1.5 mm, 3.0 mm, 4.5 mm, and 6.0 mm of misalignedcanine. The same results were found in the compari-son between the ceramic and stainless steel bracketswith CEL. The average amount of released force forboth types of brackets in the presence of CEL with 3.0mm of canine misalignment or greater was approxi-mately zero.DISCUSSIONThe aim of the present study was to compare theforces released by an orthodontic archwire in the pres-ence of two types of brackets (stainless steel bracketsand esthetic ceramic brackets) by combining themwith either conventional or unconventional elastomericligatures during the leveling and aligning phase offixed appliance therapy. A testing device similar to theone proposed recently by Franchi and Baccetti18 wasconceived to recreate clinical conditions for the level-ing and aligning phase of straight-wire technique, ie,to study the forces released during alignment of a dis-placed tooth by allowing for different amounts of ver-tical misalignment of one bracket (canine bracket) withrespect to the four remaining aligned brackets.In the presence of a 1.5-mm misaligned canine theforces produced by the two types of brackets with UELand with CEL were not statistically different, and theyranged from 95 to 120 g. Similar results were found ina previous work on stainless steel brackets.18 Startingfrom a 3.0-mm misalignment of the canine bracket, thedifference in behavior between UEL and CEL becamestatistically significant. The use of CEL produced anegligible amount of released force for alignmentwhen the tooth misalignment was greater than orequal to 3 mm, whereas the use of low-friction liga-123LOW-FRICTION LIGATURES FOR TWO TYPES OF BRACKETSAngle Orthodontist, Vol 78, No 1, 2008Table 1. Descriptive Statistics and Statistical Comparisons of the Forces (grams) Released by the Ceramic Brackets (B) With Low-FrictionLigatures (Slide) and With CEL vs Stainless Steel (SS) Brackets With Low-Friction Ligatures (Slide) and With CEL at Different Amounts ofCanine Misalignment (CM)aCeramic B.  SlideMean SDCeramic B.  CELMean SDKruskal-Wallis TestSignificance0.014 SE–1.5 mm CM 115.9 3.3 110.6 8.1 NS0.014 SE–3.0 mm CM 124.3 5.7 0.3 0.2 *0.014 SE–4.5 mm CM 115.4 5.7 0.4 0.5 *0.014 SE–6.0 mm CM 111.0 6.5 0.2 0.2 *SS B.  SlideMean SDSS B.  CELMean SD Significance0.014 SE–1.5 mm CM 97.6 7.6 91.9 2.7 NS0.014 SE–3.0 mm CM 112.4 6.7 0.1 0.1 *0.014 SE–4.5 mm CM 99.7 8.0 0.1 0.1 *0.014 SE–6.0 mm CM 116.6 12.9 0.1 0.1 *Ceramic B.  SlideMean SDSS B.  SlideMean SD Significance0.014 SE–1.5 mm CM 115.9 3.3 97.6 7.6 NS0.014 SE–3.0 mm CM 124.3 5.7 112.4 6.7 NS0.014 SE–4.5 mm CM 115.4 5.7 99.7 8.0 NS0.014 SE–6.0 mm CM 111.0 6.5 116.6 12.9 NSCeramic B.  CELMean SDSS B.  CELMean SD Significance0.014 SE–1.5 mm CM 110.6 8.1 91.9 2.7 NS0.014 SE–3.0 mm CM 0.3 0.2 0.1 0.1 NS0.014 SE–4.5 mm CM 0.4 0.5 0.1 0.1 NS0.014 SE–6.0 mm CM 0.2 0.2 0.1 0.1 NS* P  .05. NS indicates not significant.a UEL indicates unconventional elastomeric ligatures; CEL, conventional elastomeric ligatures.tures allowed for the release of an average amount offorce of 110 g and 130 g (for ceramic and stainlesssteel brackets, respectively). The statistical compari-son between the two bracket types in the presence ofUEL and CEL did not show a significant difference atany of the amounts of canine misalignment. Therefore,the type of ligature influenced the actual amount offorce released by the orthodontic system significantlymore than the type of bracket (stainless steel vs ce-ramic).The outcomes of the current study indicate thatwhen a slight amount of tooth alignment is needed (1.5mm) the differences in the performance of convention-al vs unconventional ligatures are minimal (with bothtypes of brackets), while these differences becomesignificant when correction of a misalignment greaterthan 3.0 mm is attempted. A negligible amount of forcefor alignment is actually available in the presence ofconventional ligatures and of a misalignment equal toor greater than 3.0 mm (with both types of brackets).On the other hand, the presence of UEL enablesceramic brackets to release a significant amount oforthodontic force during the aligning and levelingphases of treatment, very similarly to stainless steelbrackets. Therefore, the use of recently developed un-conventional ligatures allows the orthodontist to jointhe advantages of low-friction biomechanics to thosein the use of esthetic ceramic brackets. The clinicalinterpretation of these data, however, requires furtherconsideration. Each individual test with the Instron ma-chine was performed with new elastomeric ligatures.No attempt was made in the present study to evaluatethe effect of time and oral environment on the amountof force released in the presence of different types ofelastomeric ligatures.19,20CONCLUSIONS• The forces released by orthodontic wire in the pres-ence of esthetic ceramic brackets were similar tothose released by stainless steel brackets with bothlow-friction and conventional elastomeric ligatures.• For tooth misalignments of 3.0 mm or greater, theforce available for tooth movement was recorded inthe presence of either type of bracket only in thepresence of unconventional ligatures, while in the124 BACCETTI, FRANCHI, CAMPORESIAngle Orthodontist, Vol 78, No 1, 2008presence of conventional ligatures the amount offorce generated was negligible.REFERENCES1. Buttke TM, Proffit WR. Referring adult patients for ortho-dontic treatment. J Am Dent Assoc. 1999;130:73–79.2. Kusy RP, Whitley JQ. 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Fortschr Kieferorthop. 1990;51:106–116.14. Hain M, Dhopatkar A, Rock P. A comparison of differentligation methods on friction. Am J Orthod Dentofacial Or-thop. 2006;130:666–670.15. Thomas S, Sherriff M, Birnie D. A comparative in vitro studyof the frictional characteristics of two types of self-ligatingbrackets and two types of pre-adjusted edgewise bracketstied with elastomeric ligatures. Eur J Orthod. 1998;20:589–596.16. Fortini A, Lupoli M, Cacciafesta V. A new low-friction ligationsystem. J Clin Orthod. 2005;39:464–470.17. Baccetti T, Franchi L. Friction produced by different typesof elastomeric ligatures in treatment mechanics with thepreadjusted appliance. Angle Orthod. 2006;76:211–216.18. Franchi L, Baccetti T. Forces released during alignment witha preadjusted appliance with different types of elastomericligatures. Am J Orthod Dentofacial Orthop. 2006;129:687–690.19. Tanne K, Matsubara S, Shibaguchi T, Sakuda M. 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Forces in the presence of ceramic versus stainless steel brackets with unconventional vs conventional ligatures

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Forces in the presence of ceramic versus stainless steel brackets with unconventional vs conventional ligatures

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