Originl Article Tretment time, outcome, nd nchorge loss comprisons of self-ligting nd conventionl brckets Ferdinnd M. Mchiby ; Xingfu Bo b ; Lihu Zho c ; Min Hu d ABSTRACT Objective: To compre the tretment time, outcome, nd nchorge loss mong orthodontic ptients treted by self-ligting brckets (SLBs) nd conventionl brckets (CBs). Mterils nd Methods: A retrospective cohort study compred 34 ptients (SLB group) treted by SmrtClip brckets (3M Unitek, Monrovi, Clif) to 35 ptients (CB group) treted by conventionl predjusted Victory series brckets (3M Unitek) nd ligted by stinless steel wire ligtures. Pretretment (T1) nd posttretment (T2) lterl cephlogrms were trced nd nlyzed using Pncherz sgittl-occlusion nlysis to obtin skeletl nd dentl chnges in the mxill nd the mndible. The dentl cst models were ssessed by the Peer Assessment Rting (PAR) Index for the tretment outcomes. Results: The men tretment time for SLBs (19.19 months) did not show sttisticlly significnt difference from 21.25 months of CBs; the tretment time nd pretretment PAR scores were strongly correlted. There ws no difference in nchorge loss between the SLB nd CB groups. There were significnt dentl nd skeletl chnges mong dolescent orthodontic ptients regrdless of the brcket used. The lingul inclintion of the mndibulr incisors in the CB group ws 3.62u more thn in the SLB group (P,.01). Conclusions: The tretment time nd nchorge loss re not influenced by the type of brcket used. There re significnt dentl nd skeletl chnges mong dolescent orthodontic ptients regrdless of the brcket used. There is significntly greter lingul inclintion of mndibulr incisors in the CB group thn in the SLB group. (Angle Orthod. 2013;83:280 285.) KEY WORDS: Self-ligting brckets; Anchorge loss INTRODUCTION Self-ligting brckets (SLBs) hve severl supposed dvntges over conventionl brckets (CBs) nd re recently populr in orthodontic clinics worldwide. Of Americn orthodontists, 33% reported tht more thn 70% of their ptients were treted using SLBs. 1 Postgrdute student, Jilin University College of Dentistry, Chngchun, Chin. b PhD student, Jilin University College of Dentistry, Chngchun, Chin. c Employee prctitioner, Bihe Stomtologicl Hospitl, Chngchun, Jilin Province, Chin. d Professor nd Hed, Orthodontic Deprtment, Jilin University College of Dentistry, Chngchun, Chin. Corresponding uthor: Professor Min Hu, Jilin University College of Dentistry, 1500, Qinghu Rod, Chngchun City, Jilin Province, Chin (e-mil: humin@jlu.edu.cn) Accepted: July 2012. Submitted: April 2012. Published Online: August 17, 2012 G 2013 by The EH Angle Eduction nd Reserch Foundtion, Inc. Pssive nd ctive self-ligting pplinces with different ligting mechnisms hve been introduced, presumbly to llow for efficient sliding mechnics by reducing the force required for tooth movement owing to friction reduction nd bsence of binding of ligtures on the rchwire. 2 The reported dvntges of SLBs over CBs include greter ptient comfort during tretment, fewer visits to orthodontists, overll shorter tretment time, improved nchorge stbility, less need for extrctions, nd better outcomes in term of occlusl nd fcil esthetics. 3 Some reported dvntges, however, re lcking evidence due to conflicting findings. Wheres some in vitro nd retrospective clinicl studies reported significnt dvntges of self-ligting over conventionl-ligting brckets, 4 6 the prospective clinicl studies found no significnt differences especilly on tretment time nd number of visits required for orthodontic tretment. 7,8 Extrction of some teeth is indicted to resolve spce deficit in conditions with severe crowding nd nterior teeth protrusion. Anchorge control is of 280 DOI: 10.2319/041912-326.1
SELF-LIGATING BRACKETS VS CONVENTIONAL BRACKETS 281 Figure 1. Illustrtion of the force delivery method used during en msse spce closure. prmount importnce to chieve the tretment gol in extrction cses. There re four nchorge situtions defined by the rtio of incisor retrction to molr protrction in the nteroposterior dimension. These include minimum, moderte, mximum, nd bsolute nchorge. 9 The superiority of SLBs over CBs in some spects is uncertin. Since Victory series nd SmrtClip brckets hve the sme tip nd torque vlues, we therefore investigted their effectiveness nd efficiency for possible differences between the two brcket systems bsed on their ligtion styles. Our study imed t compring the tretment time, outcome, nd nchorge loss mong orthodontic ptients treted by SLB SmrtClip nd CB Victory series brckets. MATERIALS AND METHODS Ethicl pprovl for the study ws obtined from the Jilin University Scientific Committee. We compred groups of ptients rndomly selected from pool of completed cses treted by the sme investigtor t the orthodontic clinic of the Jilin University College of Dentistry between 2007 nd 2011. The ptients were treted under the sme protocol dopted by the institution with the following rchwire sequence: nickel titnium 0.012-inch, 0.014-inch, 0.016-inch, 0.018 3 0.025-inch, 0.019 3 0.025-inch, nd stinless steel (SS) 0.019 3 0.025-inch in brckets with 0.022 3 0.028-inch slot. The first group (SLB) consisted of 34 ptients treted by SmrtClip (3M Unitek, Monrovi, Clif) brckets. The second group (CB) consisted of 35 ptients treted by conventionl predjusted Victory series brckets (3M Unitek) tightly ligted with SS 0.020-inch ligtures. During spce closure, n elstic chin with SS 0.025-inch ligture wire ws tied on the first molr hook to the nterior rch hook plced between the cnine nd lterl incisor nd used for en Figure 2. Schemtic digrm of liner vribles used in Pncherz sgittl cephlogrm nlysis. msse trction of nterior teeth in both the SLB nd CB groups (Figure 1). The elstic chins were chnged on monthly ppointment bsis. The study used ptients cse notes to extrct demogrphic informtion, tretment durtion, ppointments, nd clinicl informtion for inclusion nd exclusion criteri. Pretretment nd posttretment lterl cephlogrms nd dentl cst models were exmined for tretment outcome vribles. The requirements for inclusion in this study were ptients needing extrction of four first premolrs, without trnsverse discrepncies, use of conventionl first molr nchorge, nd no previous history of orthodontic or orthognthic surgery. We excluded cses bsed on lck of dt required for our reserch, use of dditionl nchorge reinforcement (mini-implnt, hed ger, trnspltl rch, lingul rch, intermxillry elstics, pendulum, twin block, nd Nnce nd ny removble pplinces during ctive tretment), missing three or more ppointments, nd uncler pretretment or posttretment lterl cephlogrms. Pretretment (T1) nd posttretment (T2) lterl cephlogrms were trced on cette pper by the sme investigtor, nd ll complete cephlogrm trcings were proofred by second resercher; the two reserchers discussed the loction of lndmrks in cses of uncertinty. Cses with uncler rdiogrphs were excluded. Skeletl chnges s well s dentl chnges in the mxill nd the mndible were obtined using the Pncherz sgittl-occlusion nlysis (Figure 2). 10 The incisor positions were lso investigted by mesuring the
282 MACHIBYA, BAO, ZHAO, HU Tble 1. Demogrphics of the Smple Groups t the Strt of Tretment SLB CB Totl Men ge of ptients t the strt of tretment, y (SD) 15.31 (3.39) 15.94 (4.04) 15.64 (3.74) Ptients by sex, N (%) Mle 12 (17.39) 9 (13.04) 21 (30.43) Femle 22 (31.88) 26 (37.68) 48 (69.57) Pretretment PAR score (SD) 33.73 (6.36) 34.14 (6.38) 33.94 (6.33) Proclintion of upper nd lower incisors before tretment, degree (SD) Ui/Mx plne ngle 120.44 (6.14) 120.57 (5.16) 120.51 (5.66) Li/Mn plne ngle 98.09 (5.41) 98.89 (5.58) 98.50 (5.57) SLB indictes self-ligting brcket; CB, conventionl brcket; PAR, Peer Assessment Rting. ngle between the mxillry plne nd the upper incisors long xis (Ui/Mx plne ngle), nd the ngle between the mndibulr plne nd the lower incisors long xis (Li/ Mn plne ngle). The cephlogrm vribles mesured were: Ui/Mx plne ngle (degree), Li/Mn plne ngle (degree), mxillry centrl incisor (Ui-Y) (mm), mndibulr centrl incisor (Li-Y) (mm), mxillry permnent molr (Um-Y) (mm), mndibulr permnent molr (Lm-Y) (mm), mxillry bse (A-Y) (mm), nd mndibulr bse (Pg-Y) (mm). Mesurements were mde by hnd to the nerest 0.5 mm or 0.5u. Imges of bilterl structures were bisected. Chnges in the vrious mesuring points were clculted s the difference between the T1 nd T2 position. We used the Peer Assessment Rting (PAR) Index to mesure the tretment outcome on dentl cst models. All mesurements were done by the sme investigtor who ws blinded both to brcket type nd ptient nmes. Both pretretment nd posttretment weighted PAR scores were clculted ccording to the British weightings system, nd the overll improvement in PAR score s percentge reduction ws computed. Descriptive nd nlyticl sttisticl nlyses were performed with SPSS for Windows, version 13.0 softwre (SPSS Inc, Chicgo, Ill). The dt showed norml distribution tendency; hence, we pplied prmetric sttisticl nlysis, with the level of sttisticl significnce set t P,.05. By pired smples t-test, we tested for significnt differences between the men scores of cephlogrms vribles nd PAR scores before nd fter tretment. The independent smple Student s t-test ws used to detect significnt differences between men scores of SLB nd CB on tretment durtion, percentge PAR score reduction, nd cephlogrm vrible chnges. We rndomly selected cephlogrms nd dentl cst models for error study to test the exminer s ccurcy nd consistency in evluting the study models nd rdiogrphs. Thirty-five cephlogrms s well s 30 dentl cst models were mesured twice t the intervl of 5 dys to obtin two sets of dt. The pired smples t-test showed no significnt men differences between the two series of records, with method error of less thn 0.5 mm nd 1.0u. 11 RESULTS The study included 69 completed cses with men ge of 15.64 6 3.74 yers t the strt of tretment. There were no significnt group differences by sex, ge, pretretment PAR score, nd proclintion of incisors. Only 4.8% nd 4.0% of prticipnts in the SLB nd CB groups, respectively, hd skeletl Clss II (2-5 mm Wits pprisl of jw dishrmony) occlusion. Severe occlusl discrepncies were not included due to dditionl orthodontic pplinces used sometimes in the course of their tretment. Tble 1 shows the smple demogrphic distribution. On comprison of the positions of cephlogrm points before nd fter tretment in both the SLB nd CB groups, there were significnt differences between the T1 nd T2 mesurements in the SLB group for the positions of the mxillry bse, the mxillry centrl incisor, the mxillry molr, nd the mndibulr molr, ll t P,.001. In the CB group, there were significnt differences between the T1 nd T2 mesurements for the positions of the mndibulr bse (P,.001), the mxillry molr (P,.001), the mndibulr molr (P,.001), nd the mndibulr centrl incisor (P 5 0.008). The difference in PAR score before nd fter tretment ws not ffected by the brcket type used; however, there ws strong correltion between the tretment durtion nd pretretment PAR score, r 5 0.87, P,.001. The rithmetic men nd stndrd devition for tretment durtion percentge PAR reduction nd cephlogrm vrible chnges were clculted (Tble 2). The independent smple t-test for tretment durtion, reduction in PAR score, nd cephlogrm vrible chnges re shown in Tble 3.
SELF-LIGATING BRACKETS VS CONVENTIONAL BRACKETS 283 Tble 2. The Men nd Stndrd Devition for Tretment Durtion, Peer Assessment Rting (PAR) Reduction, nd Cephlometric Vrible Chnges After Tretment Vrible Men SD Men SD Tretment durtion, mo 19.19 3.93 21.25 6.27 PAR reduction, % 86.33 8.79 85.75 9.59 Ui/Mx plne ngle, degree 9.48 7.53 10.38 6.31 Li/Mn plne ngle, degree 2.23 6.16 5.85 3.43 Mxillry centrl incisor (Ui-Y), mm 21.13 3.62 21.04 4.09 Mndibulr centrl incisor (Li-Y), mm 20.73 2.77 20.04 3.79 Mxillry permnent molr (Um-Y), mm 5.68 2.09 5.33 2.59 Mndibulr permnent molr (Lm-Y), mm 4.8 2.49 4.53 3.1 Mxillry bse (A-Y), mm 2.7 2.4 2.07 3.93 Mndibulr bse (Pg-Y), mm 2.89 2.89 2.76 4.62 DISCUSSION SLB SLB indictes self-ligting brcket; CB, conventionl brcket. Very low friction with self-ligting brckets hs been demonstrted clerly nd quntified in work by vrious uthors. 12,13 It is ssumed, therefore, tht low friction in vitro, is ssocited with more rpid spce closure nd reduced tretment time in vivo. The results of this study demonstrte tht the time required to complete orthodontic tretment is not significntly different between the pssive SmrtClip brckets nd the conventionl Victory series brckets tied with stinless steel ligtures (Tble 3). Although some previous studies hve reported up to 6 months of tretment time reduction by SLBs, 5,6 our finding is in keeping with other studies tht found no differences in tretment time between the two brcket systems. 7,14 The differences in verge tretment durtions my be due to different criteri for ending ctive tretment nd type of ptients enrolled in the studies. Our study found 2.06 months of tretment time reduction by self-ligting brckets; this difference, however, is not sttisticlly significnt. Although the men PAR reduction is not ffected by the brcket type in this study (Tble 3), there is strong positive correltion between tretment time nd pretretment PAR score. The higher the pretretment PAR score, the longer the time required for completing orthodontic tretment. The findings re consistent with the rndomized clinicl tril by DiBise et l., 7 nd other uthors who reported the degree of tooth displcement rther thn brcket type to be the most significnt fctor influencing lignment rte. 14,15 Anchorge conservtion is mong the sid dvntges of self-ligting over conventionl brckets. 6,16 CB Tble 3. Differences in Tretment Chnges Between SLB nd CB Groups (34 SLB nd 35 CB Ptients), Independent Smples t-test Vribles Men Difference Lower Upper P Tretment durtion, mo 22.05 24.57 0.46.11* PAR reduction, % 0.58 23.93 5.09.62 Ui/Mx plne ngle, degree 0.91 22.45 4.24.59 Li/Mn plne ngle, degree 3.62 1.21 6.03.00* Mxillry centrl incisor (Ui-Y), mm 20.09 21.95 1.76.92 Mndibulr centrl incisor (Li-Y), mm 20.69 22.3 0.9.38 Mxillry permnent molr (Um-Y), mm 1.36 20.78 1.49.53 Mndibulr permnent molr (Lm-Y), mm 0.27 21.08 1.63.69 Mxillry bse (A-Y), mm 0.62 20.94 2.18.43 Mndibulr bse (Pg-Y), mm 0.13 21.72 1.98.89 SLB indictes self-ligting brcket; CB, conventionl brcket; PAR, Peer Assessment Rting. * Equl vrinces not ssumed; P,.05. Friction reduction during sliding mechnics is supposed to reduce the force needed to move teeth during orthodontic tretment, which in turn lowers the reciprocl force on nchor tooth or unit. This phenomenon is expected to improve nchorge nd fvor physiologic tooth movement, which my produce more stble tretment outcome. 16 Although there ws significnt mesil movement of first molrs in both self-ligting nd conventionl brckets in our study, the loss of nchorge between the two groups ws not significntly different (Tble 3). The results in this retrospective study my be ffected by unrecorded dditionl rch wire bending nd interrch elstics use during tretment. However, we went through ll dentl record detils to exclude ll possible fctors tht could cuse bis this study, s mentioned in our methodology. Mezomo et l. 17 in clinicl study reported no nchorge differences between self-ligting nd conventionl brckets. They, however, reported lower verge loss of nchorge since the nchor ws ginst cnine retrction s opposed to en msse trction in our study. Other studies hve reported one third of the mesil movement of posterior teeth onto the first premolr extrction. 18,19 The loss of nchorge in this reserch is higher in the mxill thn mndible for both SLB nd CB groups; this my be explined by the well-known fct of the mxill hving lower bone density thn the mndible. 20,21 Clinicins should expect more nchorge loss in the mxill thn in the mndible; hence, reltively more effort is required to enforce nchorge in the mxill thn in the mndible during orthodontic tretment. We ssessed chnges in the cephlometric vribles before nd fter tretment irrespective of the
284 MACHIBYA, BAO, ZHAO, HU brcket type. We noted mesil displcement for the skeletl lndmrk points A nd Pg. The chnges were not significntly different between brcket types, but the skeletl chnges re not surprise due to growth potentil mong dolescent ptients mking up the smple men ge of 15.64 yers. It is lso consistent with the observtion by Uris nd Mustf. 22 These skeletl chnges were tken into ccount by employing the Pncherz cephlogrm nlysis, which llows for detection of tooth movement within the jw despite skeletl growth chnges. 10 The proclintion of the lower incisors, mesured by the chnge in ngle between the mndibulr plne nd the lower incisors long xis, showed significnt difference between the two brcket systems. There ws more lingul inclintion in the CB group by n verge of 5.85u ngle reduction compred to 2.23u in the SLB group. We lso noted 0.9u greter reduction of the ngle between the upper incisors nd the mxillry plne in the CB group, which ws not significntly different. Although our findings my be influenced by the multiple fctors determining torque expression in the clinicl sitution like the interbrcket distnce 23 nd verticl positioning of the brckets on the tooth, 24,25 the observtion my be ttributed to difference in rchwire-slot interction of the two brcket systems; the stinless steel wire ligture keeps the rch wire tighter in the slot thn the pssive SmrtClip SLB. An ctive ligting mechnism seems to reduce the mount of rchwire ply in the brcket slot. 26 The 26u torque MBT Verstile+ pplince prescription for lower incisors rottes the tooth on the long xis moving the crown in the lingul direction. More lingul inclintion in the CB group my be the result of better torque expression in this group thn in the SLB group. This my be one of the resons for the observtion. Since there re mnufcturer-reported reported differences in the 0.022-inch slot size, 27 the mnufcturing slot size dimension difference between the CBs nd SLBs my be nother possible explntion for the difference in torque expression observed in the study. The results of this study re not in greement with n investigtion tht exmined mxillry centrl incisor inclintion with conventionl nd Dmon brckets nd reported no significnt torque difference on incisors mong ptients treted by the two types of pplinces. 28 This observtion is probbly due to the difference in torque vlues between CBs with Roth prescription nd the Dmon SLBs compred to the brckets with MBT prescription used in our reserch. Becuse one person treted ll ptients with the sme stndrds of brcket positioning nd tretment protocols nd the strict inclusion criteri, we re optimistic tht our study is relible. The findings re consistent with Morin et l. 29 nd Fleming et l. 30 Self-ligting brckets re reported to present reduced torquing moments compred with conventionl brckets in experimentl studies; however, this is difficult to confirm in clinic due to multiple fctors in ply. Both the SLBs nd CBs used in this study hve MBT Verstile+ Applince prescription (ie, 26u torque, 0u tip, nd 1.5 mm in/out for ll mndibulr incisors). Our findings highlight the possibility of reching different torque bsed on the brcket ligtion system despite hving the sme torque nd tip prescription. CONCLUSIONS N The tretment time, percentge PAR reduction, nd nchorge loss re not influenced by the type of brcket. N There re significnt dentl nd skeletl chnges mong dolescent orthodontic ptients regrdless of the brcket used. N There is more lingul inclintion of mndibulr incisors in the CB group thn in the SLB group. REFERENCES 1. Prettymn C, Best AM, Linduer SJ, Tufekci E. 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