Dimensional accuracy of ceramic self-ligating brackets and estimates of theoretical torsional play

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1 Originl Article Dimensionl ccurcy of cermic self-ligting rckets nd estimtes of theoreticl torsionl ply Youngrn Lee ; Dong-Yul Lee ; Yoon-Ji R. Kim c ABSTRACT Ojective: To scertin the dimensionl ccurcies of some commonly used cermic self-ligtion rckets nd the mount of torsionl ply in vrious rcket rchwire comintions. Mterils nd Methods: Four types of inch slot cermic self-ligting rckets (upper right centrl incisor), three types of inch cermic self-ligting rckets (upper right centrl incisor), nd three types of rectngulr rchwires ( inch et-titnium [TMA] (Ormco, Ornge, Clif), inch stinless steel [SS] (Ortho Technology, Tmp, Fl), nd inch SS (Ortho Technology)) were mesured using stereomicroscope to determine slot widths nd wire cross-sectionl dimensions. The men cquired dimensions of the rckets nd wires were pplied to n eqution devised y Meling to estimte torsionl ply ngle (c). Results: In ll rcket systems, the slot tops were significntly wider thn the slot ses (P,.001), yielding divergent slot profile. Clrity-SLs (3M Unitek, Monrovi, Clif) showed the gretest divergence mong the inch rckets, nd Clippy-Cs (Tomy, Fut, Fukushim, Jpn) mong the inch rckets. The Dmon Cler (Ormco) rcket hd the smllest dimensionl error (0.542%), wheres the inch Empower Cler (Americn Orthodontics, Sheoygn, Wis) rcket hd the lrgest (3.585%). Conclusions: The lrgest mount of theoreticl ply is oserved using the Empower Cler (Americn Orthodontics) inch rcket comined with the inch TMA wire (Ormco), wheres the lest mount occurs using the Clippy-C (Tomy) comined with inch SS wire (Ortho Technology). (Angle Orthod. 2016;86: ) KEY WORDS: Torsionl ply; Cermic self-ligting rckets; Slot dimensions INTRODUCTION Andrews s stright-wire pplince system llows clinicins to move teeth in three dimensions using stright wires. 1 3 The system involves inserting rectngulr wires into rcket slots tht hve een specificlly designed ccording to prescription. Teeth cn e properly ligned, ngulted, nd inclined y mens of n intimte fit etween the wire nd the rcket slot. 4 Student, Grdute School of Clinicl Dentistry, Kore University, Seoul, Kore. Professor nd Chir, Grdute School of Clinicl Dentistry, Kore University, Seoul, Kore. c Clinicl Instructor, Deprtment of Orthodontics, Kore University Anm Hospitl, Seoul, Kore. Corresponding uthor: Yoon-Ji R. Kim, Clinicl Instructor, Deprtment of Orthodontics, Kore University Anm Hospitl, 73 Inchon-ro, Seonguk-gu, Seoul, Kore (e-mil: yn0331@kore.c.kr) Accepted: Novemer Sumitted: Septemer Pulished Online: Jnury 12, 2016 G 2016 y The EH Angle Eduction nd Reserch Foundtion, Inc. Clinicins expect tht the interction etween these two elements will provide clinicl efficiency, ssuming tht mnufcturers relily report the dimensions of the pplince nd wires. However, previous studies hve reported dimensionl inccurcies in the rckets nd rchwires, often creting excessive torsionl ply. 4 6 As result, torque is insufficiently controlled, especilly in the incisors in extrction cses, nd this compromises clinicl outcome. Self-ligtion rckets hve ecome widely used ecuse they demnd shorter chir time, cuse miniml friction, nd cn e esily mnipulted y clinicins. 7 9 Moreover, mny ptients find metl rckets unttrctive, preferring esthetic pplinces, 10 nd cermic self-ligtion rckets cn e used to this end without compromising the low-frictionl chrcteristics. 9 Despite this, few studies hve een crried out ddressing the dimensionl ccurcies of cermic selfligtion rckets. The purpose of this study ws to scertin the dimensionl ccurcies of some commonly used cermic self-ligtion rckets s well s 804 DOI: /

2 SLOT DIMENSIONS OF CERAMIC SELF-LIGATING BRACKETS 805 Tle 1. Self-Ligting Brckets nd Orthodontic Archwires Used in This Study Brcket Mnufcturer Slot Size (Inch) Clip Design Empower Cler Americn Orthodontics (Sheoygn, Wis) 0.018, Active Dmon Cler Ormco (Ornge, Clif) Pssive Clippy-C Tomy (Fut, Fukushim, Jpn) 0.018, Active Clrity-SL 3M Unitek (Monrovi, Clif) 0.018, Pssive Archwire Mnufcturer Dimension (Inch) Lot No. Low Friction TMA Ormco (Ornge, Clif) TruForce SS Ortho Technology (Tmp, Fl) TruForce SS Ortho Technology (Tmp, Fl) Empower Cler, Americn Orthodontics, Sheoygn, Wis; Dmon Cler, Ormco, Ornge, Clif; Clippy-C, Tomy, Fut, Fukushim, Jpn; Clrity-SL, 3M Unitek, Monrovi, Clif. SS indictes stinless steel; TMA, et titnium. the mount of torsionl ply in vrious rcket rchwire comintions. The specific ims were to (1) quntify the mnufcturer error in the rcket slots nd rchwires, (2) mesure the edge rounding of the wires, nd (3) clculte the mount of torsionl ply using the men vlues of the study smples. MATERIALS AND METHODS Four types of inch (0.559 mm) cermic selfligting rckets (upper right centrl incisor) nd three types of inch (0.457 mm) cermic self-ligting rckets (upper right centrl incisor) were investigted (Tle 1; n 5 20 for ech type). The following three types of rectngulr wires were selected for dimensionl nlysis of cross-sections: inch et-titnium (TMA), (Ormco, Ornge, Clif), inch stinless steel (SS) (Ortho Technology, Tmp, Fl), nd inch stinless steel (SS) (Ortho Technology), (Tle 1; n 5 10 for ech type). This nlysis included mesurements of height, width, nd corner rdii of the wire edge. A stereomicroscope (SMU-Z, Nikon, Tokyo, Jpn) ws used to mesure the dimensions of the rckets nd wire cross-sections. To this end, rckets were fixed to glss slide using wx, nd the wx llowed the rckets to e mneuvered in the stereomicroscope so tht the rcket slots could e photogrphed t perpendiculr ngle. Proper orienttion of the rcket slots ws confirmed y reviewing the imges. The reliility of the dimensions mesured with the stereomicroscope ws ssessed y conducting preliminry study of rndomly selected rckets (n 5 20) to compre the slot dimensions cquired from the scnning electron microscope (HITACHI S-4700, Hitchi, Tokyo, Jpn) nd the stereomicroscope. The results indicted no significnt difference in the slot widths of the rckets mesured with oth microscopes (P..05), vlidting the method of mesurement used in this study. The imges of the rckets mesil profiles were exported to the NIS-Elements softwre (Nikon), nd the slot-se width nd top width were mesured in millimeters, wheres the slot divergence ngle ws mesured in degrees (Figure 1). The width nd height of the wire cross-sections were lso mesured. Furthermore, ecuse the wires hd two pirs of identicl corner evels, the rdii of the two different corners of the wire cross-sections were mesured (Figure 2). The differences were clculted etween the nominl dimensions on the one hnd nd the mesured slot-se width nd top width on the other. The dimensionl error is shown in Tles 2 nd 3 s percentge error of the nominl width. Becuse of the vrious slot designs of the self-ligtion rcket systems, which re ssocited with type of wire slot interction known s either pssive or ctive, slot-height dimensions re inconsistent with the nominl dimensions, therefore they were excluded for evlution. Torsionl ply (c) ws clculted in degrees y pplying the men cquired dimensions of the rckets nd rchwires to n eqution devised y Meling et l., 11 c~rcsin½ðh 2rÞ=dŠ rcsin½h 2r=dŠ where H is the height of rcket slot, h the height of wire, d the distnce etween the centers of the two circles tht fit the corners of the wire, nd r the rdius of the wire rounding. Sttistics Dt were nlyzed using SPSS 15.0 softwre (IBM, Armonk, N.Y.). The mens nd 95% confidence intervls of the rcket slot dimensions nd rchwire cross-sections were clculted in ddition to the percentge error from the given size. The se nd top widths were compred using t-test, nd the dimensions were compred mong the rckets nd rchwires using nlysis of vrince nd Tukey s test. P vlues,.05 were considered sttisticlly significnt.

3 806 LEE, LEE, KIM Figure 1. Stereomicroscopic imges of the rckets mesil profiles tht were used to mesure the slot dimensions: slot-se width (), top width (), nd slot divergence ngle (c). (A: Empower Cler [Americn Orthodontics, Sheoygn, Wis], B: Dmon Cler [Ormco, Ornge, Clif], C: Clippy-C [Tomy, Fut, Fukushim, Jpn], D: Clrity-SL [3M Unitek, Monrovi, Clif]). RESULTS The slot dimensions of different self-ligtion rcket systems significntly differed from ech other; this ws true for oth the inch (P,.001) nd inch (P,.001) systems (Tles 2 nd 3). Slot ses Figure 2. Width, height, nd 2 corner rdii of edge evels in the wire cross-section. rnged from mm to mm in the inch rckets (Tle 2), nd from mm to mm in width in the inch rckets (Tle 3). The smllest dimensionl error ws in the Dmon Cler rckets (0.542%; Ormco), nd the lrgest ws in the inch Empower Cler rcket (3.585%; Americn Orthodontics, Sheoygn, Wis). In contrst, slot tops were wider thn the given vlue in ll types of rckets, with the gretest error in the inch Clrity-SL rckets (3M Unitek, Monrovi, Clif), which hd slot top 30.9% wider thn reported. These were followed y the inch Clippy-C rckets (Tomy, Fut, Fukushim, Jpn), which were 22.5% wider thn reported t the slot top. In ll rckets, slot tops were significntly wider thn slot ses (P,.001). All rckets hd divergent slot profile, with the inch Clrity-SL (3M Unitek) nd inch Clippy-C (Tomy) rckets showing the lrgest slot divergence ngle, with sttisticl significnce (P,.05). Tle 4 shows the sizes of the rchwire cross-sections. All wires hd mnufcturing errors of less thn 2%. The inch SS (Ortho Technology) wire nd the inch SS (Ortho Technology) wire were oversized, wheres the inch TMA wire (Ormco) height ws undersized. The inch TMA wire (Ormco)

4 SLOT DIMENSIONS OF CERAMIC SELF-LIGATING BRACKETS 807 Tle 2. Brcket Slot Dimensions of Inch Self-Ligting Brckets Bse Width*** (mm) Top Width*** (mm) Men 95% CI c Dimensionl Error, % Men 95% CI Divergence Angle*** (Degrees) Dimensionl Error, % Men 95% CI Clrity-SL Clippy-C Empower Cler The sme superscript numers within the sme column re not significntly different (P..05). Clrity-SL, 3M Unitek, Monrovi, Clif; Clippy-C, Tomy, Fut, Fukushim, Jpn; Empower Cler, Americn Orthodontics, Sheoygn, Wis. c CI indictes confidence intervl. *** P,.001 for nlysis of vrince of slot dimensions mong different self-ligtion systems. ws significntly shorter in height thn the inch SS (Ortho Technology) wire (P,.001), wheres the widths were not significntly different (P 5.342). Regrding the mount of corner eveling, the rdius of corner 1 in the inch TMA wire (Ormco) ws significntly smller (P,.05) thn in the other two types of wire. Conversely, the rdius of corner 2 did not differ mong the three types of wires. Tle 5 shows the theoreticl torsionl ply with different comintions of rckets nd rchwires. Becuse the inch TMA wire (Ormco) ws shorter in height thn the inch SS wire (Ortho Technology), the torsionl ply of the inch TMA wire (Ormco), in ll types of rckets, ws greter y degrees to degrees in the inch rckets nd y 7.49 degrees to 7.70 degrees in inch rckets. Empower Cler rckets (Americn Orthodontics), in oth the inch nd inch systems, hd the gretest torsionl ply (Tle 5). DISCUSSION Although most mnufcturers do not stte their engineering tolernces for rcket slot vritions, mnufcturing inccurcies do exist s result of errors in mnufcturing processes nd mteril prmeters. 5,12 As the slot rchwire difference is mjor contriutor to torsionl ply, the uthors imed to mesure the ctul slot sizes nd wire dimensions nd thus ccurtely quntify the theoreticl torsionl ply in cermic self-ligtion rckets. All study smples of self-ligting cermic rckets hd diverging slots, with the slot tops eing 10% to 30% wider thn the given vlue. However, the slot ses were close to the nominl widths, with dimensionl error of 1% to 2%. Regrding slot dimensions, Bhll et l. 6 reported tht inch In- Ovtion-C (Dentsply, York, Penn), Clrity-SL (3M Unitek) rckets hd slot tops tht were wider thn the given vlue y 11.4% nd 9.5%, respectively, nd tht the rcket slots diverged. According to Mjor et l., 5 In-Ovtion metl rckets (Dentsply), nd Dmon metl rckets (Ormco) were oversized, nd In- Ovtion rcket (Dentsply), slots were divergent, wheres Dmon rcket slots (Ormco) were nerly prllel. Moreover, Csh et l., 4 in their study of conventionl nd self-ligting rckets, reported tht ll rckets were lrger thn stted y the mnufcturer, with n error rnge of 5% to 24%. Regrding the slot size differences mong different self-ligtion systems, Bhll et l. 6 stted tht there ws considerle slot-size vrition mong different inch rcket systems, coinciding with our results. Tle 3. Brcket Slot Dimensions of Inch Self-Ligting Brckets Bse Width*** (mm) Top Width*** (mm) Divergence Angle*** (Degrees) Men 95% CI c Dimensionl Error, % Men 95% CI Dimensionl Error, % Men 95% CI Clrity-SL Clippy-C Dmon Cler Empower Cler , The sme superscript numers within the sme column re not significntly different (P..05). Clrity-SL, 3M Unitek, Monrovi, Clif; Clippy-C, Tomy, Fut, Fukushim, Jpn; Dmon Cler, Ormco, Ornge, Clif; Empower Cler, Americn Orthodontics, Sheoygn, Wis. c CI indictes confidence intervl. *** P,.001 for nlysis of vrince of slot dimensions mong different self-ligtion systems.

5 808 LEE, LEE, KIM Tle 4. Dimension Dimensions of Archwire Cross-Sections Men Width (mm) 95% CI Height (mm) Dimensionl Error, % Men 95% CI Corner Rdius-1 (mm) Corner Rdius-2 (mm) Dimensionl Error, % Men Men SS TMA SS SS indictes stinless steel; TMA, et titnium; CI, confidence intervl. The rchwires in our study hd dimensionl vritions within 2% of the given vlue, which is significntly less thn the errors in the cermic self-ligtion rcket slots ssessed. All width nd height mesurements of the wire cross-sections ut the height of the inch TMA (Ormco), ws greter thn stted y the mnufcturer. Our results corroorte those of Meling et l., 12 who reported tht most wires re lrger thn stted. In contrst, Fischer-Brndies 13 stted tht rchwires hd cross-sections tht were significntly smller thn stted. Although these wire-dimension vritions re reltively smll, their effect on the mount of torsionl ply my e cliniclly significnt when comined with rcket size discrepncies. Vritions in wire-edge eveling lso contriute to incresed torsionl ply. 12 In our study, corner rdii, oth within the sme wire nd mong different wires, vried depending on the wire size nd mnufcturer. Sernetz 14 suggested tht rdius of t lest 0.04 mm is needed t the edge evel to ensure ptient comfort, nd stndrdiztion of the wire evel is needed. Moreover, Meling et l. 12 reported considerle vritions in the mount of edge evel, corroorting our results. Tle 5. Theoreticl Torsionl Ply (Degrees) in Comintions of Different Rectngulr Archwires nd Cermic Self-Ligting Brckets Torsionl Ply, c ( o ) Brcket Archwire Inch Slot Inch Slot Clippy-C TMA SS SS NA Clrity-SL TMA SS SS NA Dmon TMA NA Cler SS 31.3 NA SS NA Empower Cler TMA SS SS NA SS indictes stinless steel; TMA, et titnium; NA, not pplicle. Clippy-C, Tomy, Fut, Fukushim, Jpn; Clrity-SL, 3M Unitek, Monrovi, Clif; Dmon Cler, Ormco, Ornge, Clif; Empower Cler, Americn Orthodontics, Sheoygn, Wis. Torsionl ply clcultions, using the men vlues from our study smples, reveled tht dimensionl differences in the sme-sized SS (Ortho Technology) nd TMA (Ormco) wires resulted in n pproximte 10-degree difference in torsionl ply; this ws true in oth the inch nd inch rckets. Becuse the ply ngle clculted does not tke into ccount the different physicl properties of the wires, this difference must e the result of discrepncies in the ctul dimensions etween the two wires. In fct, the inch TMA wire (Ormco) cross-section ws significntly shorter in height thn the inch SS wire (Ortho Technolgoy) (P,.01). The ccurcy of Meling s eqution for clculting theoreticl torsionl ply hs een confirmed in previous studies. For instnce, Odegrd et l. 15 compred mesured torque with tht derived from Meling et l., 12 nd they found 0.6 degrees of difference etween mesured nd clculted torsionl ply in inch wire inside inch stndrd edgewise rcket. Similr results were reported y Fischer- Brndies et l. 13 who lso compred mesured torsionl ply with tht derived using Meling s formul. Becuse Meling s formul incorportes the mount of wire evel, more ccurte torsionl ply vlues cn e yielded. However, one needs to understnd tht Meling s formul ssumes the slot wlls re prllel. In relity, most rcket slots diverge, nd when slot-se widths re used for clcultions, the ctul torsionl ply my e greter thn estimted depending on the degree of divergence. In our study, we used slot-se widths ecuse different types of rcket slot se hve similr designs, regrdless of the self-ligting mechnism; this mkes mesurements more relile. The limittion of our study ws tht torsionl ply ws not directly mesured, nd thus the possile effects of ctive-type self-ligtion rckets on torsionl ply could not e oserved. Mnufcturers clim tht when the rchwire fills the slot nd comes into contct with the ligting clip, the wire is pushed ginst the slot nd torsionl ply is decresed. Furthermore, theoreticl torque is n estimte when there is no loding. 16 As torsionl ply increses with loding, 15,17

6 SLOT DIMENSIONS OF CERAMIC SELF-LIGATING BRACKETS 809 the effects of loding on the mount of torsionl ply my provide vlule informtion. This wrrnts further reserch. CONCLUSIONS N All rcket slots studied hve divergent slot profile, with the gretest divergence eing in the Clrity-SL (3M Unitek) rcket for the inch system (P,.001), nd in the Clippy-C (Tomy) rcket for the inch system (P,.001). N In oth the inch nd inch rckets, the se of the rcket slot hs miniml dimensionl errors, rnging from 1.520% to 2.004% in the inch system, nd 0.835% to 1.482% in the inch system. However, the tops of the slots re significntly wider thn stted in ll types of rckets, with the gretest discrepncy eing in the Clrity-SL rckets (3M Unitek) oth in the inch (30.887%) nd inch (20.373%) systems. N The given cross-sectionl dimensions of the rchwires re reltively ccurte, with dimensionl vritions within 2%, wheres the mount of edge evel vried widely. N The lrgest mount of theoreticl ply is oserved using the Empower Cler inch rcket (Americn Orthodontics) comined with the inch TMA wire (Ormco) wheres the lest mount occurs using the inch Clippy-C rcket (Tomy) comined with the inch SS wire (Ortho Technology). REFERENCES 1. Uris D, Mustf FI. Anchorge control in ioprogressive vs stright-wire tretment. Angle Orthod. 2005;75: McLughlin RP, Bennett JC. Anchorge control during leveling nd ligning with predjusted pplince system. J Clin Orthod. 1991;25: Andrews LF. Stright Wire: The Concept nd Applince. Sn Diego, Clif: LA Wells Compny; Csh AC, Good SA, Curtis RV, McDonld F. An evlution of slot size in orthodontic rckets re stndrds s expected? Angle Orthod. 2004;74: Mjor TW, Crey JP, Noes DS, Mjor PW. Orthodontic rcket mnufcturing tolernces nd dimensionl differences etween select self-ligting rckets. J Dent Biomech. 2010; 2010: Bhll NB, Good SA, McDonld F, Sherriff M, Csh AC. Assessment of slot sizes in self-ligting rckets using electron microscopy. Aust Orthod J. 2010;26: Hrrdine N. Self-ligting rckets increse tretment efficiency. Am J Orthod Dentofcil Orthop. 2013;143: Morin E, Elides T, Pndis N, Jäger A, Bouruel C. Torque expression of self-ligting rckets compred with conventionl metllic, cermic, nd plstic rckets. Eur J Orthod. 2008;30: Voudouris JC, Schismenos C, Lckovic K, Kuftinec MM. Self-ligtion esthetic rckets with low frictionl resistnce. Angle Orthod. 2010;80: Rosvll MD, Fields HW, Ziuchkovski J, Rosenstiel SF, Johnston WM. Attrctiveness, cceptility, nd vlue of orthodontic pplinces. Am J Orthod Dentofcil Orthop. 2009;135: Meling TR, Odegrd J, Seqner D. On rcket slot height: methodologic study. Am J Orthod Dentofcil Orthop. 1998;113: Meling TR, Ødegrd J. On the vriility of cross-sectionl dimensions nd torsionl properties of rectngulr nickeltitnium rch wires. Am J Orthod Dentofcil Orthop. 1998; 113: Fischer-Brndies H, Orthuer W, Es-Souni M, Meyer S. Torque trnsmission etween squre wire nd rcket s function of mesurement, form nd hrdness prmeters. J Orofc Orthop. 2000;61: Sernetz F. Qulität und Normung orthodontischer Produkte us der Sicht des Herstellers [in Germn]. Kieferorthop Mittlg. 1993;7: Odegrd J, Meling T, Meling E. An evlution of the torsionl moments developed in orthodontic pplictions. An in vitro study. Am J Orthod Dentofcil Orthop. 1994;105: Senc J, Brntley WA, Pincsk JJ, Conover JP. Vriility of effective root torque s function of edge evel on orthodontic rch wires. Am J Orthod. 1984;86: Meling TR, Ødegrd J, Meling EØ. On mechnicl properties of squre nd rectngulr stinless steel wires tested in torsion. Am J Orthod Dentofcil Orthop. 1997; 111: