Original Article. So-Jeong Jang a ; Dong-Soon Choi b ; Insan Jang c ; Paul-Georg Jost-Brinkmann d ; Bong-Kuen Cha b

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1 Originl Article Quntittive comprison of incisl tooth wer in ptients receiving onephse or two-phse tretment for skeletl Clss III mlocclusion with nterior crossbite So-Jeong Jng ; Dong-Soon Choi b ; Insn Jng c ; Pul-Georg Jost-Brinkmnn d ; Bong-Kuen Ch b ABSTRACT Objectives: The present study imed to compre the mount of incisl tooth wer in the mxillry centrl incisors of ptients with skeletl Clss III mlocclusion nd nterior crossbite receiving onephse or two-phse tretment. The hypothesis ws tht tooth wer would differ ccording to tretment modlities. Mterils nd Methods: Mxillry dentl csts obtined before (T1) nd fter (T2) orthodontic tretment were divided into three groups. Group I consisted of csts from 21 ptients (7 mles, 14 femles; men ge 9.8 yers) who received two-phse tretment (mxillry protrction followed by fixed pplince therpy). Group II comprised csts from 37 ptients who underwent orthodontic cmouflge tretment for crossbite, subdivided ccording to ge. Group II consisted of csts from 15 dolescents (8 mles, 7 femles; men ge 13.5 yers), nd group IIb consisted of csts from 22 dults (13 mles, 9 femles; men ge 24.5 yers). Mxillry dentl csts obtined t T1 nd T2 were scnned. For ech pir of digitl imges, T2 ws superimposed on T1 using the best-fit method. Tooth wer ws quntified nd compred mong groups. Results: Significntly less tooth wer ws observed in group I compred to groups II nd IIb, but no difference ws found between groups II nd IIb. Spermn correltion nlysis reveled no significnt correltion between tooth wer nd ge, tretment durtion, or crniofcil morphology. Conclusions: Despite the long durtion of erly tretment, it cused less wer of the mxillry centrl incisors thn did orthodontic cmouflge tretment. (Angle Orthod. 2018;88: ) KEY WORDS: Tooth wer; Three-dimensionl; Clss III; Orthodontic tretment; Mxillry protrction INTRODUCTION PhD student, Deprtment of Orthodontics, College of Dentistry, Gngneung-Wonju Ntionl University, Gngneung, South Kore. b Professor, Deprtment of Orthodontics, College of Dentistry, Gngneung-Wonju Ntionl University, Gngneung, South Kore. c Associte Professor, Deprtment of Orthodontics, College of Dentistry, Gngneung-Wonju Ntionl University, Gngneung, South Kore. d Professor, Deprtment of Orthodontics, Dentofcil Orthopedics nd Pedodontics, Center for Dentl nd Crniofcil Sciences, Chrité Universitätsmedizin Berlin, Berlin, Germny. Corresponding uthor: Dr Bong-Kuen Ch, Deprtment of Orthodontics, Gngneung-Wonju Ntionl University Dentl Hospitl, Jukheon gil-7, Gngneung City, Gngwon Province 25457, South Kore (e-mil: korth@gwnu.c.kr) Accepted: November Submitted: August Published Online: December 21, 2017 Ó 2018 by The EH Angle Eduction nd Reserch Foundtion, Inc. Tooth wer is norml physiologic process tht occurs with ging, but it cn cuse dentin hypersensitivity, pulp involvement, nd compromised esthetics s consequences of the loss of hrd tissue. 1 Mny uthors hve studied the ssocitions between tooth wer nd ge, 2,3 gender, 2,4 7 bite force, 8 prfunctions, 3,7 fcil height, 8 mouth brething, 9 slivry fctors, 10 nd mlocclusion. 6,7,11,12 Tooth wer my occur during orthodontic tretment s result of occlusl interference nd brsion by orthodontic pplinces. A few studies hve investigted tooth wer occurring during 13 nd fter orthodontic tretment. 3,14 However, no report hs described tooth wer occurring during the tretment of nterior crossbite, lthough the incisors ply importnt roles in occlusl function nd dentl esthetics. Orthopedic/orthodontic tretment of young ptient with skeletl Clss III mlocclusion represents DOI: /

2 152 JANG, CHOI, JANG, JOST-BRINKMANN, CHA Tble 1. Descriptive Sttistics for Age t the Beginning of Tretment, Tretment Durtion, nd Cephlometric Chrcteristics Tretment Durtion, mo Groups Gender (No. of Subjects, Teeth) Age, y Mxillry Protrction Men (SD) Fixed Applince Men (SD) ANB, 8 FMA, 8 Group I Mle (7, 14) 10.3 (1.6) 7.0 (4.9) 25.6 (7.9) 2.3 (2.1) 27.5 (4.4) Femle (14, 24) 9.6 (1.7) 9.4 (3.0) 25.4 (7.3) 1.8 (1.4) 28.9 (5.1) Totl (21, 38) 9.8 (1.6) 8.6 (3.8) 25.5 (7.3) 2.0 (1.7) 28.2 (4.8) Group II Mle (8, 16) 13.5 (2.7) 29.5 (11.6) 1.2 (1.3) 29.3 (3.5) Femle (7, 13) 13.5 (2.4) 34.3 (12.8) 1.5 (1.0) 27.6 (2.7) Totl (15, 29) 13.5 (2.5) 31.7 (12.0) 1.4 (1.1) 28.5 (3.1) Group IIb Mle (12, 21) 26.0 (8.6) 22.6 (9.9) 2.6 (1.9) 22.3 (4.5) Femle (8, 16) 23.0 (7.2) 26.0 (4.5) 3.5 (1.2) 22.2 (7.8) Totl (20, 37) 24.8 (8.0) 24.0 (8.2) 2.9 (1.6) 22.7 (6.2) SD indictes stndrd devition. chllenge in orthodontics becuse of the uncertinty of long-term stbility. 15 Prepubertl ptients dignosed erly with Clss III problems cn be treted orthopediclly with protrction fcemsk or chin cup to normlize the underlying skeletl discrepncy, then with fixed orthodontic pplinces (two-phse orthodontic tretment). After the dolescent growth spurt, however, the therpeutic possibilities re limited to cmouflge tretment (one-phse orthodontic tretment) or surgicl jw repositioning. Most strtegies for the cmouflge of Clss III mlocclusion involve proclintion of the mxillry incisors nd retroclintion of the mndibulr incisors to improve dentl occlusion. 16 Trumtic occlusion generted during this process my cuse jiggling movement, periodontl disese, root resorption, nd lso tooth wer. 17,18 However, no quntittive study hs compred incisl tooth wer in ptients with Clss III mlocclusion treted by one-phse nd two-phse orthodontic tretment. Ch et l. 19 nd Prk et l. 13 hve shown tht the volume of tooth wer in orthodontic ptients cn be mesured by the superimposition of three-dimensionl (3D) digitl models. Prk et l. 13 introduced 3D digitl superimposition method for the quntittive evlution of cnine wer during orthodontic tretment; this study ws the first to clculte tooth wer volumetriclly using 3D reverse-engineering technology. In the present study, incisl tooth wer occurring during erly nd lte (cmouflge) interventions for skeletl Clss III mlocclusion with nterior crossbite ws evluted quntittively. The hypothesis ws tht wer of the mxillry centrl incisor would be relted to tretment modlity in these ptients. MATERIALS AND METHODS The smple consisted of pretretment (T1) nd posttretment (T2) mxillry dentl csts from 56 ptients who received orthodontic tretment to correct nterior crossbite t the Deprtment of Orthodontics, Gngneung-Wonju Ntionl University Dentl Hospitl, Gngneung, South Kore. Inclusion criteri were (1) one or two mxillry centrl incisors in n nterior crossbite occlusion, (2) skeletl Clss III occlusion (ANB, 18), (3) use of metl brckets, (4) no incisl djustment during orthodontic tretment, nd (5) stone dentl csts free of obvious distortion nd ccurtely showing the incisl surfces of the mxillry centrl incisors. The ethics committee of Gngneung-Wonju Ntionl University pproved the study protocol (IRB ). Three groups were formed ccording to tretment type nd ptient ge. Group I consisted of csts from 21 subjects (7 mles, 14 femles; men ge 9.8 yers) who hd undergone two-phse tretment (bonded rpid mxillry expnsion nd fcemsk [RME/FM], followed by fixed pplince therpy) to correct nterior crossbite. Group II consisted of csts from 15 dolescents (8 mles, 7 femles; men ge 13.5 yers) who hd received cmouflge tretment (9 with nd 6 without extrction) round the sme time s the phse II tretment of group I. Group IIb consisted of csts from 20 dults (12 mles, 8 femles; men ge 24.8 yers) who underwent cmouflge tretment (7 with nd 13 without extrction). In totl, 104 mxillry centrl incisors from 56 ptients were evluted t T1 nd T2. The distributions of ge, ANB ngle, nd Frnkfurt horizontl plne to mndibulr plne ngle (FMA) in ech group re shown in Tble 1. 3D Assessment of Tooth Wer The csts, mde of lginte (Arom Fine Plus; GC Co, Tokyo, Jpn) nd hrd stone (New Plstone II White; GC Co), were scnned using lser surfce scnning system (KOD300, ccurcy 50 lm; Orpix Co, Ltd, Seoul, South Kore). The mxillry centrl incisors were scnned with point spcing of 150 lm. The imges were then imported into 3D scn dtprocessing progrm (Rpidform XOR3t; INUS Technology Inc, Seoul, South Kore). Imges of mxillry

3 INCISOR WEAR IN CLASS III ORTHODONTIC PATIENTS 153 Figure 1. Construction of single-tooth three-dimensionl (3D) digitl model. Pretretment (A) nd posttretment (B) reconstructed 3D digitl mxillry models (left) nd extrcted 3D digitl mxillry centrl incisor models (right). centrl incisors were extrcted from the 3D digitl models (Figure 1). To evlute tooth wer, 3D imges of the mxillry centrl incisors t T1 nd T2 were superimposed using two registrtion res (lbil nd lingul middle third) with Rpidform XOR3t. This function, designted 3D surfce-to-surfce mtching (best fit method), employs lest men-squre lgorithm. The middle thirds of the incisors lbil nd lingul surfces were used s references becuse these res re considered to be rrely ffected by ttritionl wer nd gingivl conditions (Figure 2A). With reference to color br, the region nd degree of tooth wer were identified clerly (Figure 2B). As solid models were required to clculte the volume of tooth wer, four boundry plnes were constructed on ech T1 mxillry centrl incisor model (Figure 3A). The mesil nd distl plnes were creted prllel to the long xis of the crown nd 0.5 mm from the mesil nd distl contct points. The lingul plne ws constructed perpendiculr to the mesil nd distl plnes using the sme vector s ws used for the long xis. The gingivl plne ws perpendiculr to the mesil, distl, nd lingul plnes nd cut off the incisl third of the tooth. Volumetric differences between the T1 nd T2 models were then clculted for ech pir (T1 nd T2) of incisors (Figure 3B). To evlute the method error, 20 pirs of mxillry centrl incisors were selected rndomly, nd superimposition nd volume clcultions were repeted t 2- week intervls by the sme investigtor. The systemtic error ws evluted with pired t-test t significnce level of P,.05. No significnt difference between the two sets of mesurements ws detected. For ll mesurements, the method error ws tested pp using Dhlberg s formul (method error ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi d 2 =2n, where d is the difference between two mesurements Figure 2. Superimposition of pretretment (red) nd posttretment (blue) mxillry centrl incisor models. (A) Superimposition with the best-fit method using the middle third of the lbil nd lingul surfces s reference res. (B) Exmintion with reference to color br.

4 154 JANG, CHOI, JANG, JOST-BRINKMANN, CHA Figure 3. Quntifiction of the volume of tooth wer. (A) Superimposed pretretment (red) nd posttretment (blue) mxillry centrl incisor models nd boundry plnes (mesil, distl, nd gingivl) for the cretion of solid models. (B) Solid three-dimensionl geometries surrounded by the boundry plnes. The volume of tooth wer ws determined by clculting the difference between the pretretment nd posttretment models. tken on n incisor pir nd n is the number of subjects), yielding method error of 0.18 mm 3. Sttisticl Anlysis Becuse the dt were not distributed normlly, nonprmetric nlysis ws used. Gender-bsed differences within groups were exmined using the Mnn-Whitney U-test. The Kruskl-Wllis test ws used to identify significnt differences mong groups. These differences were further nlyzed using the Mnn-Whitney U-test with Bonferroni correction to reduce the possibility tht ny significnce ws due to chnce. Associtions between tooth wer nd vribles such s ge t the beginning of tretment, tretment durtion, or crniofcil morphology were ssessed by Spermn s correltion nlysis. The level of significnce ws set t P,.05 (P,.016 for the Bonferroni-corrected Mnn-Whitney U-test). RESULTS No gender-bsed difference in tooth wer ws found in ny group (Tble 2). Thus, dt from subjects of both genders in ech group were combined. Descriptive sttistics nd comprisons of tooth wer in the three groups re shown in Tble 3. The men tooth wer vlues were mm 3 in group I (RME/FM followed by fixed pplinces), mm 3 in group II (cmouflge tretment in dolescents), nd mm 3 in group IIb (cmouflge tretment in dults). The Kruskl-Wllis test reveled significnt differences mong the three groups, nd the Mnn-Whitney U-test showed significntly less tooth wer in group I thn in groups II nd IIb (both P,.01). No significnt difference ws observed between dolescents (group II) nd dults (group IIb) who received cmouflge tretment. Spermn s correltion nlysis reveled no significnt correltion between tooth wer nd ge, tretment durtion, or crniofcil morphology in groups I or II (Tble 4). DISCUSSION This report is the first to describe the quntittive nlysis of tooth wer s function of orthodontic tretment modlity. Severl reports 20,21 hve described tooth wer cused by orthodontic tretment, which should be of concern to orthodontists. The quntittive nlysis of such wer yields importnt dditionl informtion compred to conventionl tooth wer indices (TWIs). Previous studies hve employed mny different TWIs tht re simple to use but present problems relted to stndrdiztion nd quntifiction. In ddition, they re not suitble for the identifiction of minor tooth wer occurring during orthodontic tretment. In the present study, 3D superimposition method ws used tht hs the potentil to become powerful tool for the quntittive ssessment of tooth wer. 3D superimposition is used widely to evlute orthodontic tooth movement, but few studies 13 hve investigted tooth wer cused by orthodontic tretment using this method. In the present study, the method previously developed for cnines, in which the mesil nd distl boundry plnes were designted 1.5 mm from the corresponding contct points, ws modified 13 These plnes were designted 0.5 mm from the contct points in the present study to include the lrgest possible portions of the incisl edges. In future reserch, individul boundry plnes should be defined bsed on tooth shpe. Two-phse tretment of skeletl Clss III mlocclusion resulted in less mxillry centrl incisor wer thn Tble 2. Men, Stndrd Devition, nd P Vlues for Sex Differences in Ech of the Three Groups Group I Group II Group IIb Mles Femles Mles Femles Mles Femles (n ¼ 14) (n ¼ 24) Mnn-Whitney (n ¼ 16) (n ¼ 13) Mnn-Whitney (n ¼ 21) (n ¼ 16) Mnn-Whitney Vribles Men (SD) Men (SD) U-Test Men (SD) Men (SD) U-Test Men (SD) Men (SD) U-Test Tooth wer, mm (0.82) 0.93 (0.66) NS 3.86 (2.18) 3.25 (2.15) NS 4.12 (2.60) 3.77 (2.60) NS NS indictes not significnt; SD, stndrd devition.

5 INCISOR WEAR IN CLASS III ORTHODONTIC PATIENTS 155 Tble 3. Comprison of the Men Vlues of Tooth Wer in Three Groups by Kruskl-Wllis Test nd Mnn-Whitney U-Test Group I (n ¼ 38) Group II (n ¼ 29) Group IIb (n ¼ 37) Mnn-Whitney U-Test Vribles Men (SD) Men (SD) Men (SD) I-II I-IIb II-IIb Tooth wer, mm (0.75) 3.59 (2.15) 3.97 (2.57) ** ** SD indictes stndrd devition. ** P,.01. did cmouflge tretment, despite the greter totl tretment durtion of the former (Tble 3). This finding my be explined by the posterior bite block effect of the bonded RME, which minimized trumtic occlusion during crossbite correction in the first phse of tretment. One dvntge of two-phse over onephse tretment is the bility to initite fixed orthodontic therpy fter nterior crossbite correction. Wrren et l. 25 observed severe wer in subjects with Clss III mlocclusion nd edge-to-edge incisor reltionships nd suggested tht this wer ws likely ssocited with frequent contct between the mxillry nd the mndibulr incisors. Similrly, it is possible tht incisl tooth wer ws ccelerted during the edge-to-edge occlusion tht occurred trnsitionlly during the course of crossbite correction in cmouflge tretment in the present study. The results suggest tht clinicins should consider proper use of posterior bite blocks in the tretment of nterior crossbite. In ddition, overcorrection of the reverse overjet is recommended in growing ptients with Clss III mlocclusion, not only to prevent possible relpse, but lso to void tooth wer due to occlusl interference. Given the observtion period between FM/RME nd fixed pplince therpy ( months), more nturl tooth wer likely occurs during the tretment period in ptients undergoing two-phse tretment compred with those undergoing one-phse tretment. Pintdo et l. 26 investigted nturl tooth wer in 18 young dults for 2 yers using profiling system on epoxy replics. They reported men losses of mm 3 for cnines, mm 3 for second premolrs, nd mm 3 for first molrs. It seems tooth wer tht occurred during orthodontic tretment is more thn nturl tooth wer. As no quntittive dt on centrl incisor wer hve yet been published, the current findings cnnot be compred with nturl tooth wer Tble 4. Spermn s Correltion Anlysis Between the Amount of Tooth Wer nd Other Vribles Group I Tooth Wer, mm 3 Group II Vribles Correltion (r) P Correltion (r) P Age Tretment durtion ANB ngle FMA vlues. Thus, further quntittive reserch on nturl tooth wer is needed. Among subjects undergoing cmouflge tretment in the current smple, dults showed more tooth wer thn did dolescents, but this difference ws not significnt (Tble 3). Studies 27,28 hve demonstrted n increse in the microhrdness of enmel with ge, due to the reduction of enmel porosity with posteruptive mturtion. In the present study, it needs to be noted tht more incisl tooth wer ws observed in dults thn in dolescents nd subjects who underwent two-phse tretment, despite the greter posteruptive ge of the dult teeth. These results could be explined by the fct tht dults hve slower turnover rtes of lveolr bone nd greter bite force thn do dolescents. 29,30 Mny previous studies hve reported ssocitions between tooth wer nd ge, 2,3 gender, 2,4 7 nd crniofcil morphology. 8 In contrst, no significnt gender difference (Tble 2) nd no significnt correltions between tooth wer during orthodontic tretment nd ge, ANB ngle, FMA, or tretment durtion were observed in the present study (Tble 4). The results were consistent with previous results 13 tht showed no significnt correltion between cnine wer during orthodontic tretment nd ge, gender, tretment durtion, or crniofcil morphology. The mount of tooth wer during orthodontic tretment my depend on the orthodontic tretment methods nd therefore my not follow the nturl tooth wer pttern. Such sensitive chnges cnnot be mesured ccurtely by trditionl methods such s TWIs. Further reserch using more sophisticted methods, such s the 3D volumetric ssessment introduced in this study, re recommended to clrify the ssocition between tooth wer nd ge, gender, nd crniofcil morphology. CONCLUSIONS The results of the present study support the hypothesis tht incisl wer of the mxillry centrl incisor is relted to tretment modlity in ptients with skeletl Clss III mlocclusion nd nterior crossbite. Although erly tretment is lengthy, it resulted in less wer of the incisors thn did orthodontic cmouflge tretment.

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