Originl Article Invislign nd Trditionl Orthodontic Tretment Postretention Outcomes Compred Using the Americn Bord of Orthodontics Objective Grding System Dniel Kuncio ; Anthony Mgnzini b ; Clrence Shelton c ; Ktherine Freemn d ABSTRACT Objective: To compre the postretention dentl chnges between ptients treted with Invislign nd those treted with conventionl fixed pplinces. Mterils nd Methods: This is comprtive cohort study using ptient records of one orthodontist in New York City. Two groups of ptients were identified tht differed only in the method of tretment (Invislign nd Brces group). Dentl csts nd pnormic rdiogrphs were collected nd nlyzed using the objective grding system (OGS) of the Americn Bord of Orthodontics (ABO). The cses were evluted immeditely fter pplince removl (T1) nd t postretention time (T2), three yers fter pplince removl. All ptients hd completed ctive orthodontic tretment nd hd undergone t lest one yer of retention. A Wilcoxon rnk sum test ws used to evlute differences in tretment outcomes between the groups for ech of the eight ctegories in the OGS, including four dditionl subctegories in the lignment ctegory. A Wilcoxon signed rnk test ws used to determine the significnce of chnges within ech group from T1 to T2. Results: The chnge in the totl lignment score in the Invislign group ws significntly lrger thn tht for the Brces group. There were significnt chnges in totl lignment nd mndibulr nterior lignment in both groups. There were significnt chnges in mxillry nterior lignment in the Invislign group only. Conclusions: In this smple for this period of observtion, ptients treted with Invislign relpsed more thn those treted with conventionl fixed pplinces. KEY WORDS: Invislign; Cohort study; Objective grding system; Tretment outcome; Relpse INTRODUCTION In 1999, Align Technology Inc ddressed the demnd for n esthetic lterntive to brces by developing n invisible method of orthodontic tretment (Invislign) tht uses series of computer-generted, cler, removble ligners to move the dentition. Since Former orthodontic resident, Montefiore Medicl Center/Albert Einstein College of Medicine, Bronx, NY. b Deprtment Hed, Deprtment of Orthodontics, Montefiore Medicl Center/Albert Einstein College of Medicine, Bronx, NY. c Assistnt Professor, Deprtment of Orthodontics, Montefiore Medicl Center/Albert Einstein College of Medicine, Bronx, NY. d Associte Professor, Deprtment of Epidemiology nd Popultion Helth, Albert Einstein College of Medicine, Bronx, NY. Corresponding uthor: Dr Dniel Kuncio, Montefiore Medicl Center, Deprtment of Orthodontics, 3332 Rochmbeu Ave, New York, NY 10467 (e-mil: kuncioorthodontics@nyc.rr.com) Accepted: November 2006. Submitted: October 2006. 2007 by The EH Angle Eduction nd Reserch Foundtion, Inc. then, Invislign hs been used to tret over 300,000 orthodontic ptients with vriety of mlocclusions. The primry benefit of the Invislign system is the superior esthetics during tretment compred to metl brces. Other dvntges of the system include the bility to remove ligners to et, brush nd floss, nd the superior comfort nd ese of use. 1 Bsed on cse reports, this technique ppers effective in treting mild mlocclusions nd is more visully ppeling thn conventionl brces. 2 Align hs climed tht 90% of orthodontic ptients re cndidtes for Invislign. These include ptients with mild to moderte crowding (1 6 mm), mild to moderte spcing (1 6 mm), nonskeletl constricted rches, nd those who hve experienced relpse fter fixed pplince therpy. 3 To this dte, little clinicl reserch hs been published to comprehensively study the effectiveness of Invislign tretment. The lck of such objective informtion on this product hs mde it difficult for clini- 864 DOI: 10.2319/100106-398.1
POSTRETENTION OUTCOMES IN INVISALIGN AND FIXED TREATMENT 865 cins to objectively chrcterize the efficcy of Invislign s compred to fixed pplinces. Previous literture hs focused on presenting descriptions of the product nd necdotl informtion on individul successful cses. 4 6 A recent systemtic review of Invislign reserch by Lgrvere nd Flores-Mir 7 found tht no strong conclusions could be mde regrding the tretment effects of Invislign pplinces. They concluded tht rndomized clinicl trils re the only wy to ddress the mny concerns surrounding the Invislign system. Despite the thousnds of completed cses treted with Invislign nd the mny published successful cse reports, some orthodontists feel tht this tretment cn be inferior to conventionl brces. 8 Until rndomized studies re performed, orthodontists will hve to rely on their individul clinicl experiences. Only one cse-controlled cohort study compring the tretment results of Invislign ptients to conventionl fixed pplince ptients hs been published. Using the Americn Bord of Orthodontics objective grding system (OGS), it ws reported tht the cses treted with Invislign hd men OGS score 13 points worse thn the Brces group, nd the OGS pssing rte for Invislign ws 27% lower thn for the conventionl Brces group. It ws implied tht, ccording to this mesurement technique, tretment results of brces re superior to those of Invislign nd tht Invislign did not tret ptients with lrge nteroposterior discrepncies s well. 9 However, the dt for this project were tken immeditely post tretment, with no ssessment of the long-term stbility of these cses. Despite extensive reserch, the vrious elements leding to relpse of treted mlocclusions re not completely understood, which mkes retention one of the most chllenging spects of orthodontic tretment. Although reserchers hve published retention recommendtions, they dmit tht long-term lignment is vrible nd unpredictble. In ddition, there pper to be no descriptive chrcteristics of cse or pretretment vribles tht cn ccurtely predict relpse. 10 In 2005, Nett nd Hung 11 used the Americn Bord of Orthodontics (ABO) objective grding system to mesure long-term relpse of conventionlly treted cses nd found tht overll OGS scores ctully improved. Alignment ws the only criterion tht worsened. The min objective of this study ws to ssess nd compre postretention tretment outcomes of ptients treted with the Invislign system to tretment outcomes of ptients treted with trditionl fixed pplinces. MATERIALS AND METHODS This is comprtive cohort study using ptient records of one ABO bord-certified nd Invislign-certified orthodontist in New York City. Dentl csts nd pnormic rdiogrphs from ptients were collected nd nlyzed. The posttretment records were tken immeditely fter pplince removl (T1) nd the postretention records were tken three yers lter (T2). Two groups of ptients were evluted: the Invislign group nd the Brces group. To estblish the Invislign group, ll ptients from the 2005 Invislign tretment outcome study were contcted (48 ptients). 9 Eleven returned to the clinic for postretention evlutions. A pool of ptients treted to completion with tip-edge fixed pplinces nd debonded in 2002 or 2003 ws then estblished. Becuse there were no extrction cses in the Invislign group, it ws decided to eliminte ll extrction cses from the Brces group s well. Ptients in the Brces group fitting the inclusion criteri were contcted for records in lphbeticl order. The finl smple size for both groups ws 11. Retention in the Invislign group consisted of the finl ligners. Ptients were instructed to wer retiners full time for six months, nd then nightly for t lest nother six months. In the Brces group, Essix retiners were used with the sme retention protocol. Using the OGS, ll csts nd pnormic rdiogrphs were rndomly ordered nd identifiction msked by one exminer before being evluted. Eight mesurements were mde for ech cse nd points were deducted for ny discrepncy from the idel. The mesurement ctegories of the OGS re lignment, mrginl ridges, buccolingul inclintion, occlusl contcts, occlusl reltions, overjet, interproximl contcts, nd root ngultion. The lignment ctegory, s defined by the ABO website, comprises four subctegories: mxillry nterior, mxillry posterior, mndibulr nterior, nd mndibulr posterior. 12 The number of points lost ws totled for ech ptient to give n OGS score. A perfect score is 0. A cse tht loses 30 points or fewer would be considered successfully treted cse nd will usully receive n cceptble grde on the ABO Phse III exm. 13 To ensure exminer relibility, three sets of records from ech group were ordered nd msked s previously described nd evluted by second exminer. Fisher s exct tests were used to determine the significnce of differences in distributions between the Invislign nd Brces groups with regrd to gender, ethnicity, nd if they still wer their retiners. Unpired t- tests or Wilcoxon rnk sum tests were performed to ssess the significnce of differences with regrd to ge, tretment length, nd posttretment length. Unpired t-tests or Wilcoxon rnk sum were lso used to
866 KUNCIO, MAGANZINI, SHELTON, FREEMAN Tble 1. Attributes of Ptients in Invislign nd Brces Groups (N 11) Attributes Invislign Brces P Vlue Femle ptients 10 (90.9%) 10 (90.9%).5238 Mle ptients 1 (9.1%) 1 (9.1%) Africn-Americn 7 (63.6%) 8 (72.7%).1642 White 2 (18.2%) 2 (18.2%) Hispnic 2 (18.2%) 1 (9.1%) Still wer retiners 5 (45.4%) 3 (27.2%).2384 Do not wer retiners 6 (54.6%) 8 (72.8%) Men ge t posttretment (T1) 33.97 (SD 8.98) 26.79 (SD 12.12).1337 Men ge postretention (T2) 37.05 (SD 9.20) 29.50 (SD 12.15).0942 Tretment length (y) 1.74 (SD 0.83) 2.34 (SD 0.77).0941 Postretention length (y) 3.08 (SD 0.78) 2.70 (SD 0.21).1400 T1 indictes immeditely fter pplince removl; T2, postretention time. * P.05. determine the significnce of differences between the two groups from T1 to T2. Pired t-tests or Wilcoxon signed rnk tests were used to determine the significnce of chnges within ech group between the two time points. RESULTS The Invislign group nd Brces group hd similr distributions of gender, ethnicity, ge, retiner wer, tretment, nd posttretment length. All subjects climed to hve worn their retiners for t lest one yer post tretment, six months full time (Tble 1). Tble 2 provides mens nd stndrd devitions for ech OGS ctegory by group, nd ssocited P vlues. No sttisticlly significnt differences were found between the Invislign group nd Brces group t T1 or T2 (Tble 2). The difference between the two groups with regrd to chnges from T1 to T2 ws sttisticlly significnt for totl lignment (P.034). The totl lignment of the Invislign group decresed from 5.91 t T1 to 8.81 t T2, while the totl lignment of the Brces group decresed from 8.36 to 9.73. No other OGS ctegory ws sttisticlly significnt, nor ws further brekdown of the lignment ctegory (Tble 3). With regrd to differences between T1 nd T2 within ech group, both groups showed significnt decreses in totl lignment (P.0020 for the Invislign group, P.0156 for the Brces group; Tble 4), nd mndibulr nterior lignment (P.0039 for the Invislign group, P.0313 for the Brces group; Tble 4). Only the Invislign group showed significnt difference in mxillry nterior lignment (P.0156; Tble 4). The mxillry nterior lignment of the Invislign group decresed from 0.91 t T1 to 2.00 t T2, while the mxillry nterior lignment of the Brces group decresed from 0.82 to 1.18 (Tble 2). There were no significnt differences between the mesurements performed by the two exminers. The dt listed in the tbles re from the first exminer only. DISCUSSION Becuse Invislign hs been used to tret ptients only since 1999, obtining records on subjects tht Tble 2. OGS Scores nd P Vlues for Invislign nd Brces Groups t T1 nd T2 OGS CATEGORY Invislign (T1) Brces (T1) P Vlue Invislign (T2) Brces (T2) P Vlue Totl lignment 5.91 (SD 4.09) 8.36 (SD 3.93).1665 8.81 (SD 4.97) 9.73 (SD 3.77).6344 Mxillry nterior lignment 0.91 (SD 0.83) 0.82 (SD 0.87).8051 2.00 (SD 1.26) 1.18 (SD 0.87).0928 Mxillry posterior lignment 2.09 (SD 1.58) 3.45 (SD 1.70).0650 2.36 (SD 1.75) 3.63 (SD 1.75).1031 Mnidubulr nterior lignment 1.27 (SD 1.01) 1.64 (SD 0.81).3622 2.82 (SD 1.66) 2.36 (SD 1.43).5001 Mndibulr posterior lignment 0.1.54 (SD 1.37) 2.45 (SD 1.51).1542 1.64 (SD 1.69) 2.55 (SD 1.37).1808 Mrginl ridges 5.45 (SD 2.50) 6.72 (SD 2.53).2499 5.00 (SD 2.52) 5.72 (SD 1.90).4549 Buccolingul inclintion 3.45 (SD 2.07) 2.81 (SD 2.40).5129 3.63 (SD 1.85) 2.73 (SD 2.90).3919 Occlusl contcts 8.27 (SD 4.24) 9.72 (SD 5.02).4717 7.90 (SD 5.11) 7.82 (SD 3.57).9619 Occlusl reltions 6.73 (SD 4.64) 6.90 (SD 4.83).9292 6.36 (SD 3.70) 6.36 (SD 3.95) 1.0000 Overjet 7.00 (SD 3.79) 5.45 (SD 4.29).3820 6.09 (SD 2.63) 5.36 (SD 3.44).5836 Interproximl contcts 0.55 (SD 1.21) 0.90 (SD 1.30).5055 0.36 (SD 0.67) 0.27 (SD 0.65).7502 Root ngultions 2.09 (SD 1.44) 2.09 (SD 1.70) 1.0000 2.00 (SD 1.48) 2.45 (SD 1.92).5409 Totl OGS score 39.45 (SD 10.26) 43.00 (SD 12.52).4760 40.18 (SD 10.32) 40.45 (SD 9.81).9500 OGS indictes objective grding system; T1, immeditely fter pplince removl; T2, postretention time. * P.05.
POSTRETENTION OUTCOMES IN INVISALIGN AND FIXED TREATMENT 867 Tble 3. OGS Score Chnges Between T2 nd T1 for Ptients Treted With Invislign nd Brces OGS Ctegory Invislign Chnge (T2-T1) Brces Chnge (T2-T1) P Vlue Totl lignment 2.91 (SD 1.64) 1.36 (SD 1.21).0340* Mxillry nterior lignment 1.09 (SD 1.04) 0.36 (SD 0.51).0859 Mxillry posterior lignment 0.27 (SD 0.64) 0.18 (SD 0.40).9615 Mndibulr nterior lignment 1.55 (SD 1.21) 0.72 (SD 0.79).1133 Mndibulr posterior lignment 0.09 (SD 0.54) 0.09 (SD 0.30) 1.0000 Mrginl ridges 0.45 (SD 2.30) 1.00 (SD 2.00).4726 Buccolingul inclintion 0.18 (SD 1.40) 0.09 (SD 2.30).8644 Occlusl contcts 0.36 (SD 4.63) 1.91 (SD 3.36).6244 Occlusl reltions 0.36 (SD 4.18) 0.55 (SD 3.47).2083 Overjet 0.91 (SD 3.78) 0.90 (SD 2.43).7676 Interproximl contcts 0.18 (SD 0.60) 0.64 (SD 1.21).3670 Root ngultions 0.09 (SD 0.30) 0.36 (SD 0.81).1169 Totl OGS score 0.73 (SD 5.58) 2.55 (SD 7.30).1208 OGS indictes objective grding system; T1, immeditely fter pplince removl; T2, postretention time. * P.05. met the criteri of post retention ws chllenging. Obviously, the uthors would hve preferred much lrger smple size, but these dt should provide some preliminry insight to the long-term post tretment chnges in the dentition using the Invislign system. To ensure tht both groups followed similr retention protocol, ech ptient ws sked if they followed the posttretment retention instructions nd if they continued to wer their retiners. Obviously, there will be some self-reporting errors, but ll subjects climed t lest one yer of retention (six months full time), nd there ws no sttisticlly significnt difference between the groups s to how mny still wore retiners for mintennce (Tble 1). The OGS ws chosen to mesure records in this study becuse it is stndrdized method of grding orthodontic tretment results. It provides n objective protocol to thoroughly evlute chnges in the dentition. 12,13 Since relpse is function of time, it ws essentil to equte the two groups with regrd to posttretment length. Although the Invislign group hd slightly longer posttretment length (3.08 vs 2.70 yers), this result ws not sttisticlly significnt nor considered cliniclly importnt. There ws lso no significnt discrepncy between the tretment times. As whole, ptient chrcteristics for the Invislign nd Brces groups were similr (Tble 1). An nlysis of the disprity between the groups reveled no significnt differences immeditely post tretment or post retention (Tble 2). When nlyzing the chnges between the groups during the time intervl from T1 to T2, significnt difference ws found in the lignment ctegory (Tble 3). This indictes tht the ptients treted with Invislign showed more deteriortion in the lignment of the dentition thn the ptients treted with trditionl fixed pplinces. This is cliniclly importnt becuse tooth lignment is probbly the most visully noticeble chrcteristic mesured by the OGS nd is the min reson people seek orthodontic tretment. 14 In order to investigte this finding further, the lignment ctegory of the OGS ws further broken down into mxillry nterior, mxillry posterior, mndibulr nterior, nd mndibulr posterior subctegories (Tble 3). These subctegories re not independent OGS criteri, but hve been identified by the ABO s subsets of the lignment ctegory. 12 When chnges between the groups were compred for these subctegories, no sttisticlly significnt differences were found. Even though the Invislign group did show lrger decrese in the lignment score, the men lignment of the Invislign group ws superior to the Brces group before nd fter the retention phse, but these differences were not sttisticlly significnt (Tble 2). Therefore, even though the Invislign cses relpsed more, they pper to hve the sme, if not better, overll lignment scores. With regrd to chnges within ech of the two groups, chnges in totl lignment in both groups were significnt (Tble 4). More specificlly, there ws deteriortion in the mxillry nd mndibulr nterior lignment of the Invislign group, but only in the mndibulr nterior lignment of the Brces group. Therefore, while the mndibulr nterior teeth were relpsing significntly in both groups, the mxillry nterior teeth were relpsing significntly only in the Invislign group. This finding is cliniclly significnt, becuse the mxillry nterior teeth re the most visible in the mouth. These dt re in greement with the results of Nett et l, 11 who found tht of the eight OGS ctegories, only lignment worsened postretention. Also in greement with this study, it ws found tht lmost ll of the chnges in the lignment occurred in the nterior teeth. 11
868 KUNCIO, MAGANZINI, SHELTON, FREEMAN Tble 4. Comprison of OGS Scores Within Ech Group t T1 nd T2 OGS Ctegory Invislign (T1) Invislign (T2) Invislign (P Vlue) Brces (T1) Brces (T2) Brces (P Vlue) Totl lignment 5.91 (SD 4.09) 8.81 (SD 4.97).0020** 8.36 (SD 3.93) 9.73 (SD 3.77).0156* Mxillry nterior lignment 0.91 (SD 0.83) 2.00 (SD 1.26).0156* 0.82 (SD 0.87) 1.18 (SD 0.87).1250 Mxillry posterior lignment 0.2.09 (SD 1.58) 2.36 (SD 1.75).5000 3.45 (SD 1.70) 3.63 (SD 1.75).5000 Mndibulr nterior lignment 0.1.27 (SD 1.01) 2.82 (SD 1.66).0039** 1.64 (SD 0.81) 2.36 (SD 1.43).0313* Mndibulr posterior lignment 0.1.54 (SD 1.37) 1.64 (SD 1.69) 1.0000 2.45 (SD 1.51) 2.55 (SD 1.37) 1.0000 Mrginl ridges 5.45 (SD 2.50) 5.00 (SD 2.52).6250 6.72 (SD 2.53) 5.72 (SD 1.90).1182 Buccolingul inclintion 3.45 (SD 2.07) 3.63 (SD 1.85).8125 2.81 (SD 2.40) 2.73 (SD 2.90) 1.0000 Occlusl contcts 8.27 (SD 4.24) 7.90 (SD 5.11).7734 9.72 (SD 5.02) 7.82 (SD 3.57).0977 Occlusl reltions 6.73 (SD 4.64) 6.36 (SD 3.70).6875 6.90 (SD 4.83) 6.36 (SD 3.95).2949 Overjet 7.00 (SD 3.79) 6.09 (SD 2.63).5547 5.45 (SD 4.29) 5.36 (SD 3.44).8594 Interproximl contcts 0.55 (SD 1.21) 0.36 (SD 0.67) 1.0000 0.90 (SD 1.30) 0.27 (SD 0.65).1875 Root ngultions 2.09 (SD 1.44) 2.00 (SD 1.48) 1.0000 2.09 (SD 1.70) 2.45 (SD 1.92).3125 Totl OGS score 39.45 (SD 10.26) 40.18 (SD 10.32).7578 43.00 (SD 12.52) 40.45 (SD 9.81).2275 OGS indictes objective grding system; T1, immeditely fter pplince removl; T2, postretention time. * P.05; ** P.01. There ws sttisticlly insignificnt overll improvement in mny of the ctegories within ech group, which is lso in greement with the results of Nett el l. 11 Specificlly, mrginl ridges, occlusl contcts, occlusl reltions, overjet nd interproximl contcts ll improved from T1 to T2 for both groups. Overll, the totl OGS score for the Invislign group got worse from T1 to T2, while the totl OGS score for the Brces group improved (Tble 2). This is function of the significntly worse totl lignment in the Invislign group. The men totl OGS score of the Invislign group ws superior to the men totl OGS score of the Brces group before nd fter the retention phse, lthough these differences were not sttisticlly significnt. An importnt question to come out of these findings is: why does the lignment of the ptients treted with Invislign worsen more postretention thn ptients treted with fixed pplinces? Both groups underwent similr retention protocol, which mens tht ll gingivl nd periodontl fibers were eqully s reorgnized. The difference could be in the chrcteristics of the new bone formed. 15 The current concept of n optiml force in orthodontics is bsed on the theory tht force of certin mgnitude nd durtion would be cpble of producing mximum rte of tooth movement without tissue dmge. 16 Tooth movement with the Invislign system is distnce-bsed, s opposed to forced-bsed with the fixed pplince systems. Due to sttic constrints, it is impossible to know exctly wht forces re being creted by continuous rch mechnics with fixed pplinces, but mteril properties nd stress/strin reltionships of orthodontic wires nd springs re known. 17 Even though both fixed pplinces nd Invislign cn move teeth to cliniclly cceptble positions, there is no literture s to how much force is being creted by the cler removble pplinces. Although no evidence bout n optiml force level in orthodontics is vilble in the literture t this time, the finding in this study illustrtes the need for further investigtion. One difference in the tretment protocol of the two groups ws tht the ptients treted with Invislign inserted new ligners, nd therefore new forces, every two weeks. There is no reserch supporting the 2-week intervl recommendtion, other thn Bollen et l 18 who concluded chnging ligners every other week ws more likely to led to completion of the initil series of ligners thn chnging weekly. The Brces group, on the other hnd, ws djusted usully every 4 6 weeks. Even under idel orthodontic forces, some undermining resorption of the lveolr bone will occur. Undermining resorption requires 7 14 dys, with equl time needed for periodontl ligment (PDL) regenertion nd repir. This is why orthodontic pplinces should not be rectivted more frequently thn t 3-week intervls. Activting n pplince too frequently cn produce dmge to the teeth or bone by cutting short the repir process. 17 It could be postulted tht the 2-week intervl of ligners in the Invislign system is too smll nd is leding to poor bone formtion nd more relpse. This study is subject to severl limittions. The Invislign group ws creted from pool of ptients who successfully completed tretment with Invislign ligners only. Not included were ptients whose tretment needed to be supplemented with fixed pplinces. Future studies should tke more rndom smple of Invislign ptients, s ws done with the Brces group. All of the subjects in the Invislign group were mong the first 50 ptients treted with Invislign (Dr Shelton). Any technique requires lerning curve, nd future results my be different s the clinicin gins experience. In ddition, lrger smple size from severl
POSTRETENTION OUTCOMES IN INVISALIGN AND FIXED TREATMENT 869 orthodontists would be useful in future studies. Becuse of these limittions, the generlizbility of this study is limited. CONCLUSIONS Chnges in totl lignment, s mesured by the ABO OGS, were worse postretention in ptients treted with Invislign thn in ptients treted with conventionl fixed pplinces. Within both groups, totl lignment nd mndibulr nterior lignment worsened postretention. Mxillry nterior lignment worsened postretention in the Invislign group only. In this smple for this period of observtion, ptients treted with Invislign relpsed more thn those treted with conventionl fixed pplinces, nd further investigtion is wrrnted. REFERENCES 1. Introducing Invislign. The invisible wy to strighten your teeth without brces. Avilble t: http://www.invislign. com/generlpp/gb/en/index.html. Accessed My, 2006. 2. Joffe L. Invislign: erly experiences. J Orthod. 2003;30(4): 348 352. 3. Boyd RL, Nelson G. Orthodontic tretment of complex mlocclusions with the Invislign pplince. Semin Orthod. 2001;7(4):274 293. 4. McNmr JA, Krmer KL, Juenker JP. Invisible retiners. J Clin Orthod 1985;19:570 578. 5. Wong BH. Invislign A to Z. Am J Orthod Dentofcil Orthop. 2002;121(5):540 541. 6. Vlsklic V, Boyd RL. Orthodontic tretment of mildly crowded mlocclusion using the Invislign System. Aust Orthod J. 2001;17:41 46. 7. Lgrvere MO, Flores-Mir C. The tretment effects of Invislign orthodontic pplinces: systemtic review. J Am Dent Assoc. 2005;136:1724 1729. 8. Mgnzini AL. Outcome ssessment of Invislign nd trditionl orthodontic tretment nd subsequent commentries. Am J Orthod Dentofcil Orthop. 2006;129(4):456. 9. Djeu G, Shelton C, Mgnzini AL. Outcome ssessment of Invislign nd trditionl orthodontic tretment compred with the Americn Bord of Orthodontics objective grding system. Am J Orthod Dentofcil Orthop. 2005;128(3):293 298. 10. Little RM. Stbility nd relpse of mndibulr nterior lignment: University of Wshington studies. Semin Orthod. 1999;5(3):191 204. 11. Nett BC, Hung GJ. Long-term posttretment chnges mesured by the Americn Bord of Orthodontics objective grding system. Am J Orthod Dentofcil Orthop. 2005; 127(4):444 450. 12. Americn Bord of Orthodontics Rod to Certifiction Website. Discrepncy Index for the Phse III Clinicl Exmintion. Avilble t http://www.mericnbordortho.org. Accessed My, 2006. 13. Csko JS, Vden JL, Kokich VG, et l. Objective grding system for dentl csts nd pnormic rdiogrphs. Am J Orthod Dentofcil Orthop. 1998;114:589 599. 14. Shw WL. The influence of children s dentofcil ppernce of their socil ttrctiveness s judged by peers nd ly dults. Am J Orthod. 1981;79(4):399 415. 15. Storey S. The nture of tooth movement. Am J Orthod. 1973;63(3):292 314. 16. Ren Y, Jp MC, Kuijpers-Jgtmn AM. Optimum force mgnitude for orthodontic tooth movement: systemtic literture review. Angle Orthod. 2003;73(1):86 92. 17. Proffit WR, Fields HW Jr. Contemporry Orthodontics. 3rd edition. Mosby; 2000:296 361, 594 614. 18. Bollen AM, Hung G, King G, Hujoel P, M T. Activtion time nd mteril stiffness of sequentil removble orthodontic pplinces. Prt 1: bility to complete tretment. Am J Orthod Dentofcil Orthop. 2003;124:496 501.