Original Article. Hyo-Won Ahn a ; Sung Chul Moon b ; Seung-Hak Baek c

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1 Originl Article Morphometric evlution of chnges in the lveolr bone nd roots of the mxillry nterior teeth before nd fter en msse retrction using cone-bem computed tomogrphy Hyo-Won Ahn ; Sung Chul Moon b ; Seung-Hk Bek c ABSTRACT Objective: To evlute the morphometric chnges in the lveolr bone nd roots of the mxillry nterior teeth (MXAT) fter en msse retrction with mximum nchorge (EMR-MA). Mterils nd Methods: The smples consisted of 37 femle dult ptients who hd Clss I dentolveolr protrusion (CI-DAP) nd were treted by extrction of the first premolrs nd EMR- MA. Using three-dimensionl cone-bem computed tomogrphy tken before tretment nd fter spce closure, the mxillry centrl incisors (MXCI, N 5 66), lterl incisors (MXLI, N 5 69), nd cnines (MXC, N 5 69) were superimposed using individul reference plnes. After lveolr bone re (ABA), verticl bone level (VBL), root length (RL), root re (RA), nd prevlence of dehiscence (PD) were mesured t the cervicl, middle, nd picl levels, sttisticl nlyses were performed. Results: On the pltl side, ABA significntly decresed in ll levels of MXAT (P,.001; middle of MXC, P,.01). MXCI nd MXLI exhibited greter decrese in the rtio of chnge in pltl ABA thn did MXC (cervicl, P,.01; middle nd picl, P,.05; totl, P,.001). Pltl/lbil ABA rtios decresed in MXCI (cervicl, middle, totl, P,.001; picl, P,.05) nd MXLI (cervicl, P,.001; picl, P,.05). They showed greter mounts nd rtios of chnge in VBL on the pltl side compred to the lbil side (ll P,.001). The pltl side showed more PD in the cervicl re thn did the lbil side (MXCI nd MXLI, P,.001; MXC, P,.01). Significnt root resorption occurred in MXAT (RL nd RA, ll P,.001). Conclusions: During EMR-MA in cses with CI-DAP, ABA nd VBL on the pltl side nd RL nd RA of MXCI nd MXLI were significntly decresed. (Angle Orthod. 2013;83: ) KEY WORDS: Alveolr bone; Root; Mxillry nterior teeth; En msse retrction; Extrction spce closure; 3D-CBCT INTRODUCTION Grdute PhD student, Deprtment of Orthodontics, School of Dentistry, Seoul Ntionl University, Seoul, South Kore. b Privte Prctice nd Clinicl Professor, Deprtment of Orthodontics, School of Dentistry, Seoul Ntionl University, Seoul, South Kore. c Professor nd Chir, Deprtment of Orthodontics, School of Dentistry, Dentl Reserch Institute, Seoul Ntionl University, Seoul, South Kore. Corresponding uthor: Dr Seung-Hk Bek, Deprtment of Orthodontics, School of Dentistry, Dentl Reserch Institute, Seoul Ntionl University, Yeonkun-dong #28, Jongro-ku, Seoul, South Kore (e-mil: drwhite@unitel.co.kr) Accepted: June Submitted: April Published Online: October 15, 2012 G 2013 by The EH Angle Eduction nd Reserch Foundtion, Inc. There re two concepts in orthodontic tooth movement in terms of lveolr bone remodeling. If the lveolr bone is remodeled with coordintion of resorption nd pposition, tooth movement nd bone remodeling occur t 1:1 rtio, nd the tooth remins in the lveolr housing. This kind of tooth movement is known s with-the-bone. 1 However, if blnce between resorption nd pposition of the lveolr bone is not estblished during tooth movement, the tooth will move out of the lveolr housing, which is referred to s through-the-bone. 2 Bilveolr protrusion is one of the most common chief complints in Asin orthodontic ptients. The conventionl tretment modlity is extrction of the first premolrs nd retrction of the nterior teeth with mximum nchorge. 3,4 However, excessive retrction 212 DOI: /

2 ALVEOLAR BONE AND ROOT OF MAXILLARY ANTERIOR TEETH 213 of the nterior teeth my result in itrogenic sequele such s root resorption, lveolr bone loss, dehiscence, fenestrtion, nd gingivl recession. 5 8 Therefore, morphometric evlution of the lveolr bone nd roots of the nterior teeth fter en msse retrction my be good model with which to explin the therpeutic limittion of orthodontic tooth movement nd to define the with-the-bone nd through-thebone concepts. Conventionl two-dimensionl (2D) lterl cephlogrms hve severl limittions in terms of investigting the chnges in the lveolr bone nd roots, especilly in the nterior region, s result of the midsgittl projection. 5,9 11 The dvent of cone-bem computed tomogrphy (CBCT) hs mde it possible to qulittively nd quntittively evlute the height nd thickness of the lveolr bone nd the length nd thickness of the root. 8,12 15 To the uthors knowledge, few studies hve investigted the lveolr bone nd root of the individul teeth ccording to customized reference plne using CBCT imges. Therefore, the purpose of this study ws to evlute the morphometric chnges in the lveolr bone nd roots of the mxillry nterior teeth (MXAT) fter en msse retrction with mximum nchorge (EMR-MA) using superimposition of individul teeth with CBCT imges. MATERIALS AND METHODS This retrospective study ws performed under the pprovl of the Institutionl Review Bord (IRB) of KyungHee University Dentl Hospitl (IRB No.: KHD IRB ). The smples comprised 37 femle dult ptients with Clss I dentolveolr protrusion (men ge yers; tretment durtion yers; SNA, 81.4u; SNB, 77.8u; mxillry centrl incisor [MXCI] to SN, 127.7u; IMPA, 98.9u; Tble 1). These ptients were treted by single orthodontist with extrction of the four first premolrs nd sliding mechnics using EMR-MA. Working wire ws inch stinless-steel wire without extr torque, nd inch stright-wire pplince with Roth setup (Clippy-C, Tomy, Futb, Fukushim, Jpn) ws used. Conventionl nchorge such s TPA nd/ or hedger nd elstic chins with force of 200 g ws used. The mount of retrction of MXCI ccording to every 1 mm of nchorge loss of the mxillry first molr (MX1 to MX6 rtio) ws mm (Tble 1). The inclusion criteri for smpling were s follows: skeletl nd dentl Clss I reltionships, mild nterior crowding (rch length discrepncy of #3mm), lbioversion of MXCI (MXCI-SN. 120u), nd controlled tipping movement of the MXCI from superimposition of Tble 1. Cephlometric Chrcteristics of the Smples (N 5 37, Femles) Vribles Ethnic Norm Men SD Age t stge (yer) NS Durtion of orthodontic tretment, (T2-, yer) NS Skeletl horizontl SNA, u SNB, u ANB, u Skeletl verticl Posterior/nterior fcil height rtio, % SN to mndibulr plne ngle, u Dentl MXCI-SN, u IMPA, u Interincisl ngle, u Chnges of MXCI DEdge-AP, mm NA DEdge-V, mm NA DRoot-AP, mm NA DRoot-V, mm NA Dxis chnge, u NA Anchorge vlue DMX6M-AP, mm NA MX1 to MX6 rtio NA Ethnic norm is the men vlues of Koren femle dults. SD indictes stndrd devition; MXCI, mxillry centrl incisor; D, difference between pretretment () nd postretrction (T2); Edge- AP, sgittl distnce from the verticl reference plne (VRP) to the incisl edge of the MXCI (MXCIE); Edge-V, verticl distnce from the horizontl reference plne (HRP) to the MXCIE; Root-AP, sgittl distnce from the VRP to the root pex of the MXCI (MXCIA); Root- V, verticl distnce from the HRP to the MXCIA; xis chnge, ngulr chnge of the incisor long xis of the MXCI to the SN plne; MX6M-AP, sgittl distnce from the VRP to the most mesil point of the mesil surfce of the mxillry first molr crown; nd MX1 to MX6 rtio [(DEdge-AP)/(DMX6M-AP) 3 (21)], the mount of retrction of MXCIE ccording to every 1 mm of nchorge loss of the mxillry first molr crown. NA mens not pplicble. the lterl cephlogrms before tretment () nd fter spce closure (T2) (Tble 1; Figure 1). The exclusion criteri included tooth size nomly, periodontl problems, spcing or moderte to severe crowding, nd root resorption of the MXAT before orthodontic tretment. To evlute the lveolr bone ccurtely, CBCT imges were tken t the nd T2 stges (Implgrphy, Vtech, Seoul, Kore; cm field of view, 90-kVp tube voltge, 4.0-mA tube current, 0.2-mm isotropic voxel size, nd 24-second scn time). The obtined dt were nlyzed by InVivoDentl (Antomge, Sn Jose, Clif). To set n identicl reference plne in the nd T2 stges, three-dimensionl (3D) superimposition of the mxillry centrl incisors (MXCI, N 5 66), mxillry lterl incisors (MXLI, N 5 69), nd mxillry cnines (MXC, N 5 69) ws

3 214 AHN, MOON, BAEK Figure 1. Reference plnes nd vribles on the lterl cephlogrm. Reference plnes: Horizontl reference plne (HRP), horizontl plne ngulted 7u clockwise to the Sell-Nsion plne pssing through Sell; Verticl reference plne (VRP), perpendiculr plne to the HRP pssing through Sell. Vribles: (1) Dedge- AP, the mount of chnge in the sgittl distnce (Dsgittl distnce) from VRP to the incisl edge of the mxillry centrl incisor (MXCIE); (2) Dedge-V, the mount of chnge in the verticl distnce (Dverticl distnce) from HRP to MXCIE; (3) Droot-AP, Dsgittl distnce from VRP to the root pex of the MXCI (MXCIA); (4) Droot-V, Dverticl distnce from HRP to MXCIA; (5) Dxis, the ngulr chnge of the long xis (LA) of MXCI; nd (6) DMX6M-AP, Dsgittl distnce from the VRP to the most mesil point of the mesil surfce of the mxillry first molr. performed s follows (Figure 2). First, the long xis of ech nterior tooth ws set on the sgittl imge t the stge. Next, 3D superimposition ws performed by the best-fit method using two sets of homologous lndmrks in ech CBCT imge nd mnul refinement process. Then the T2 imge ws reoriented on the sme coordinte xis s the imge. Definitions of lndmrks, reference plnes, nd vribles re given in Figure 3. The lveolr bone re (ABA) ws mesured t the cervicl, middle, nd picl levels, respectively. Trisection of the root length into the cervicl, middle, nd pex levels ws duplicted in the T2 stge to gurntee the sme slice levels s those in the stge. Verticl bone level (VBL), root length (RL), root re (RA), nd prevlence of dehiscence (PD) were mesured both on the pltl nd lbil sides. The percentge of VBL to RL, the rtio of ABA chnge, nd the rtio of pltl to lbil ABA were clculted. All of the mesurements were repeted by the sme opertor fter 2 weeks. The difference rnged from 0.27 mm to 0.35 mm for liner mesurements, from 0.25u to 0.47u for ngulr mesurements, nd from 0.31 mm 2 to 0.48 mm 2 for re mesurements, Figure 2. Three-dimensionl (3D) superimposition of cone-bem computed tomogrphy (CBCT) imges of the right mxillry centrl incisor (MXCI) bsed on its long xis (LA) nd clinicl crown between the pretretment () nd postretrction (T2) stges. (A) Setting of LA of the MXCI on the sgittl imge t the stge. (B) After 3D superimposition by the best-fit method between the two sets of homologous lndmrks in the nd T2 imges, mnul refinement process ws performed. (C) Reorienttion of the T2 imge with the sme LA of the imge through 3D superimposition (left: rw imge; right: reoriented imge t the T2 stge). ccording to Dhlberg s formul. 16 The men of the two mesurements ws used for this study. Independent t- test, pired t-test, one-wy nlysis of vrince (AN- OVA) with Duncn s multiple comprison test, nd crosstb nlysis were performed for sttisticl nlyses. RESULTS Amount nd Rtio of Chnges in the Lbil nd Pltl ABA (Tble 2) On the lbil side, ABA incresed in the middle level of MXCI (P,.001) nd in the middle nd totl levels of MXLI (P,.001 nd P,.05, respectively). However, on the pltl side, ABA decresed in ll levels of MXCI (ll P,.001), MXLI (ll P,.001), nd MXC (cervicl, picl, totl, P,.001; middle, P,.01).

4 ALVEOLAR BONE AND ROOT OF MAXILLARY ANTERIOR TEETH ; picl, 42% nd 47% vs 26%, P,.05; totl, 50% nd 52% vs 25%, P,.001), MXCI exhibited greter mount of chnge in ABA (DABA mount) thn did MXC only in the middle level (24.3 mm 2 vs 22.3 mm 2, P,.05). Figure 3. (A) Lndmrks nd reference plnes: (1) Incisor edge or cnine tip point; (2) root pex (RA) point; (3, 4) cementoenmel junction (CEJ) points; (5, 6) lveolr crest (AC) points; (7) CEJ line ( line tht connects points 3 nd 4); (8) intersection point between long xis (LA; line from points 1 to 2) nd CEJ line; (9) intersecting line perpendiculr to LA t the cervicl third of root length (LCTRL); (10) intersecting line perpendiculr to LA t the middle third of root length (LLTRL); (11) intersecting line perpendiculr to LA t RA (LARL); (B) Vribles: A, root length (distnce from points 2 nd 8); B, root re (root re below CEJ line); C nd D, verticl lveolr bone level (distnce from CEJ to AC prllel to LA); E nd F, cervicl lveolr bone re (ABA); G nd H, middle ABA; I nd J, picl ABA; nd K nd L, totl ABA on the lbil (E + G + I) nd pltl sides (F + H + J). Pired vribles re the lbil nd pltl sides. Although MXCI nd MXLI showed significnt decrese in the rtio of chnge in ABA (DABA rtio) compred to MXC on the pltl side (cervicl, 78% nd 80% vs 48%, P,.01; middle, 60% nd 55% vs 18%, P, Pltl to Lbil ABA Rtio (Tble 3) Although pltl to lbil ABA rtios (P/L-ABA rtios) decresed in ll res of MXCI (cervicl, middle, totl, P,.001; picl, P,.05) nd in some res of MXLI (cervicl, P,.001; picl, P,.05), MXC did not show differences in ny of the res between the nd T2 stges. Differences in DP/L- ABA rtio mong MXCI, MXLI, nd MXC were not significnt in ny of the res. VBL of the Alveolr Bone (Tble 4) At the stge, the mounts nd rtios of VBL (VBL mount nd VBL rtio, respectively) were greter on the lbil side thn on the pltl side in MXAT (MXCI nd MXLI, P,.001; MXC, P,.01). At T2 stge, the VBL mount nd VBL rtio of MXAT incresed both on the pltl nd lbil sides. Although MXCI nd MXLI exhibited greter DVBL mount nd DVBL rtio on the pltl side thn on the lbil side, MXC did not exhibit differences in DVBL mount between the lbil nd pltl sides (DVBL mount; MXCI nd MXLI, P,.001; DVBL rtio; 1.6% vs 29.3%, 4.9% vs 36.1%, 8.3% vs 15.3%, MXCI nd MXLI, P,.001; MXC, P,.05). In comprison of DVBL on the pltl side, MXCI nd MXLI showed higher vlues thn MXC in terms of Tble 2. Comprison of the Amounts of the Alveolr Bone Are Between the Pretretment () nd Postretrction (T2) Stges in Ech Tooth nd the Amounts of Chnge during the nd T2 Stges nd Rtio Among the Mxillry Anterior Teeth Alveolr Bone Are Lbil side Mxillry Centrl Incisors (N 5 66, Group 1) TD DT/ Mxillry Lterl Incisors (N 5 69, Group 2) TD Men SD Men SD Rtio P-Vlue Men SD Men SD DT/ Rtio P-Vlue Cervicl Middle *** *** Apicl Totl * Pltl side Cervicl *** *** Middle *** *** Apicl *** *** Totl *** *** Pired t-test ws performed to compre the vlues in the nd T2 stges. b One-wy nlysis of vrince (ANOVA) with Duncn s multiple comprison test ws performed to ssess the differences in the mount (T2-, DT) nd rtio (DT/) of chnge in the cervicl, middle, picl, nd totl levels. SD indictes stndrd devition. In multiple comprison, the mxillry nterior teeth were llocted into group 1 (mxillry centrl incisors), group 2 (mxillry lterl incisors), nd group 3 (mxillry cnines). The rtio of the chnges in the lveolr bone re ws computed s follows: [mount of the chnges in the lveolr bone re (T2-, DT)/mount of the lveolr bone re t stge]. * P,.05; ** P,.01; *** P,.001.

5 216 AHN, MOON, BAEK the mount nd rtio (ll P,.001). However, on the lbil side, MXC hd greter DVBL mount thn did MXCI (P,.05). Root Resorption (Tble 5) Although significnt root resorption occurred in MXCI, MXLI, nd MXC (RL, ll P,.001; RA, ll P,.001), the mounts of decreses in RL nd RA did not differ mong MXCI, MXLI, nd MXC. PD in the Cervicl Are (Tble 6) Root exposure (dehiscence) in the cervicl re occurred more frequently on the pltl side thn on the lbil side (MXCI nd MXLI, P,.001; MXC, P,.01). In ddition, there ws higher percentge of dehiscence in MXLI nd MXC thn in MXCI on the lbil side (14% nd 12% vs 2%, P,.05) nd in MXCI nd MXLI thn in MXC on the pltl side (67% nd 68% vs 32%, P,.001). DISCUSSION The findings tht ABA incresed in the middle level of MXCI (P,.001) nd in the middle nd totl levels of MXLI (P,.001 nd P,.05, respectively) on the lbil side nd decresed in ll the levels of MXAT (P,.001; middle of MXC, P,.01) on the pltl side (Tble 2) imply tht en msse retrction of the MXAT might result in tooth movement through-the-bone. This impliction ws confirmed by the fct tht P/L- ABA rtios decresed in ll res of MXCI (cervicl, middle, totl, P,.001; picl, P,.05) nd in some Tble 2. Extended res of MXLI (cervicl, P,.001; picl, P,.05) fter retrction (Tble 3). The increse in DABA mount on the lbil side ws much lower thn the decrese in DABA mount on the pltl side (4% vs 250% in MXCI, 24% vs 252% in MXLI; Tble 2), which mens tht bone pposition in the tension re of the inner side of the lbil lveolr bone ws not sufficient nd/or bone resorption occurred on the outer side of the lbil lveolr bone. Sriky et l. 8 reported tht the pposition process in the inner corticl plte of the lbil lveolr bone is somewht slower thn the resorption process in the outer corticl plte of the lbil lveolr bone. The decrese in ABA of MXCI nd MXLI ws more significnt in the cervicl region of the pltl side (278% nd 280%, respectively; Tble 2) becuse the MXAT of the smples showed controlled tipping movement pttern, leding to greter ccumultion of pressure in the lveolr crest region on the pltl side. However, on the lbil side, the middle re of MXCI nd MXLI showed greter increse in ABA thn did the cervicl re, where more tension existed (27% vs 210%, 65% vs 4%, respectively; Tble 2). The reson tht the cervicl re did not show n increse in ABA on the lbil side seems to be n inflmmtory periodontl response concentrted in the cervicl re, resulting in loss of VBL in spite of the greter tensionl force. Therefore, the entire lveolr housing, not merely the bone in the picl zone, should be considered when clinicin tries to define the therpeutic limits for orthodontic tooth movement. 8 At the stge, VBL on the lbil side ws greter thn tht on the pltl side in ll of the MXAT (MXCI Comprison of the Amount of Chnge During nd T2 nd Rtio Mxillry Cnines (N 5 69, Group 3) Among the Mxillry Anterior Teeth in the Levels of Ech Side TD Amount Rtio DT/ Men SD Men SD Rtio P-Vlue P-Vlue b Multiple Comprison P-Vlue b Multiple Comprison *** ** (2,1), **.0373* (1,2), (2,3).0190* (1,2), *** * (2,1), *** *** (2,1), 3

6 ALVEOLAR BONE AND ROOT OF MAXILLARY ANTERIOR TEETH 217 T2 Tble 3. Comprison of the Pltl to Lbil Alveolr Bone Are Rtio Between the Pretretment () nd Postretrction (T2) Stges in Ech Tooth nd the Amounts of Chnge During the nd T2 Stges Among the Mxillry Anterior Teeth Mxillry Lterl Mxillry Centrl Incisors (N 5 66) Incisors (N 5 69) Pltl/Lbil Alveolr Bone T2 Are Rtio Men SD Men SD P-Vlue Men SD Men Cervicl *** Middle *** Apicl * Totl *** Pired t-test ws performed. b One-wy nlysis of vrince (ANOVA) with Duncn s multiple comprison test ws performed. SD indictes stndrd devition. The pltl to lbil lveolr bone re rtio in the cervicl, middle, picl, nd totl levels ws clculted s follows: pltl lveolr bone re/lbil lveolr bone re. * P,.05; *** P,.001. Tble 4. Comprison of the Amount nd Rtio of the Verticl Bone Level of the Alveolr Bone Between the Pretretment () nd Postretrction (T2) Stges in Ech Tooth nd the Amounts of Chnge During the nd T2 Stges Among the Mxillry Anterior Teeth Mxillry Centrl Incisors (N 5 66, Group 1) TD Mxillry Lterl Incisors (N 5 69, Group 2) Verticl Bone Level Men SD Men SD P-Vlue Men SD Lbil side Amount, mm * Rtio, % ** Pltl side Amount, mm *** Rtio, % *** Comprison of the vlues between P-Vlue c Amount, mm.0001***.0000***.0001*** lbil nd pltl sides Rtio, %.0001***.0000***.0001*** Pired t-test ws performed to compre the vlues in the nd T2 stges. b One-wy nlysis of vrince (ANOVA) with Duncn s multiple comprison test ws performed. c Independent t-test ws performed. SD indictes stndrd devition. In multiple comprison, the mxillry nterior teeth were llocted into group 1 (mxillry centrl incisors), group 2 (mxillry lterl incisors), nd group 3 (mxillry cnines). The rtio of the verticl lveolr bone loss ws computed s follows: [(mount of the verticl loss of the lveolr bone/root length) 3 100]. * P,.05; ** P,.01; *** P,.001. Tble 5. Comprison of Root Resorption in Terms of Root Length nd Root Are Between the Pretretment () nd Postretrction (T2) Stges in Ech Tooth nd the Amounts of Chnge During the nd T2 Stges Among the Mxillry Anterior Teeth T2 Mxillry Lterl Mxillry Centrl Incisors (N 5 66) Incisors (N 5 69) T2 Men SD Men SD P-Vlue Men SD Men SD Root length *** Root re *** Pired t-test ws performed. b One-wy nlysis of vrince (ANOVA) test ws performed. SD indictes stndrd devition. *** P,.001. nd MXLI, P,.001; MXC, P,.01; Tble 4). These findings re consistent with those of Nhm et l., 13 who reported VBL rtios of 19.3% nd 15.0% for the lbil nd pltl spects of the MXAT, respectively. The finding tht t the T2 stge, MXCI nd MXLI showed greter VBL nd higher PD on the pltl side thn on the lbil side compred to MXC (Tble 4) might result from the discrepncy in the direction of tooth movement in reltion to the lbiolingul long xis of the roots mong MXCI, MXLI, nd MXC (Figure 4). Dehiscence is mjor bony defect tht is difficult to discern on conventionl 2D rdiogrphs. 17 A previous CBCT study 18 defined dehiscence s the bsence of corticl bone round the root in t lest three sequentil views. In our study, dehiscence ws determined when the ABA covering the cervicl root

7 218 AHN, MOON, BAEK Tble 3. Extended Mxillry Lterl Incisors (N 5 69) Mxillry Cnines (N 5 69) Comprison of the Amount of Chnge During T2 T2 nd T2 Among the Mxillry Anterior Teeth SD P-Vlue Men SD Men SD P-Vlue P-Vlue b *** * Tble 4. Extended TD Mxillry Lterl Incisors Comprison of the Amount of Chnge (N 5 69, Group 2) Mxillry Cnines (N 5 69, Group 3) During nd T2 Among the Mxillry T Anterior Teeth Men SD P-Vlue Men SD Men SD P-Vlue P-Vlue b Multiple Comprison ** **.0271* (1,2), (2,3) * *** *** ***.0001*** 3, (1,2) *** ***.0000*** 3, (1,2).0000***.0012** ***.0012**.0410* Tble 5. Extended Mxillry Lterl Incisors (N 5 69) Mxillry Cnines (N 5 69) P-Vlue T2 Comprison of the Amount of Chnge During nd T2 Among the Mxillry Anterior Teeth Men SD Men SD P-Vlue P-Vlue b.0000*** *** *** ***.3445 ws zero. In spite of this strict definition of PD, strikingly higher PD in the cervicl re on the pltl side ws shown fter spce closure (67% of MXCI, 68% of MXLI, nd 32% of MXC, respectively; Tble 6). Becuse the upper prts of the roots of MXAT re supported by thin lveolr bone 13 they re vulnerble to dehiscence during retrction. However, potentil limittion of this result cn exist in the risk of overestimting dehiscence. A previous study 19 reported tht the positive predictive vlue of dehiscence ws only 0.51 nd tht lveolr bone height could be mesured with n ccurcy of 0.6 mm using CBCT with voxel size of 0.38 mm t 2 ma. Moreover, since dditionl bone remodeling continues slowly fter ctive tooth movement, the results from this study should be interpreted conservtively when one is pplying them to the clinicl sitution. Since ptients with dentolveolr protrusion usully hve thin nd elongted nterior lveoli nd/or bony defect before tretment, 8,11,13 pushing the tooth ginst

8 ALVEOLAR BONE AND ROOT OF MAXILLARY ANTERIOR TEETH 219 Tble 6. Comprison of the Prevlence of Dehiscence in the Cervicl Are Between the Lbil nd Pltl Sides in Ech Tooth nd Among the Mxillry Anterior Teeth on Ech Side t the postretrction (T2) Stge Mxillry Centrl Incisors (N 5 66) Incidence, No. % Mxillry Lterl Incisors (N 5 69) Mxillry Cnines (N 5 69) Incidence, No. % Incidence, No. % P-Vlue Lbil side Cervicl * Middle Apicl Pltl side Cervicl *** Middle Apicl Comprison of the prevlence of dehiscence in the cervicl re between the lbil nd pltl sides P-vlue.0000***.0000***.0066** Cross-tb nlysis ws performed. If the lveolr bone re covering the root decresed to zero t the T2 stge, it ws considered to represent dehiscence. * P,.05; ** P,.01; *** P,.001. Figure 4. Direction of tooth movement from the pretretment () to the postretrction (T2) stges (solid rrow). The lbiolingul long xis (LA) of the mxillry nterior teeth t the T2 stge ws used s reference for the sgittl imge (dshed line). the thin corticl bone my cuse root resorption nd/or n lveolr bone defect (Figure 5). If the brcket prescription with excessive root torque is used in the MXAT, excessive root movement cn cuse greter risk of root resorption nd PD of the lbil or pltl corticl plte. 7 For these ptients, retrction of the nterior teeth using bsolute nchorge with orthodontic mini-implnts my not lwys be the right nswer. If lbioversion of the incisors is excessive nd the lveolus is thin, retrction of the nterior teeth combined with corticotomy of the lveolr bone cn offer n effective lterntive with which to minimize the risk of uncontrolled movements of the nterior teeth. 3,4,11 Another importnt issue is whether or not the repir of lveolr bone loss is possible fter spce closure nd during the retention period. In this study, some ptients who were ble to undergo CBCT t the debonding stge did not show spontneous bone pposition on the lbil nd pltl sides (Figure 6). Figure 5. Exmples of the sgittl imges of the mxillry centrl incisor (MXCI) (A), mxillry lterl incisor (MXLI) (B), nd mxillry cnine (MXC) (C) t the pretretment () (left imge) nd postretrction (T2) stges (right imge).

9 220 AHN, MOON, BAEK Figure 6. Exmples of the mxillry centrl incisor (MXCI) (A), mxillry lterl incisor (MXLI) (B), nd mxillry cnine (MXC) (C) t the pretretment (), postretrction (T2), nd debonding stges.

10 ALVEOLAR BONE AND ROOT OF MAXILLARY ANTERIOR TEETH 221 Previous studies 6,8,20,21 reported tht once the corticl plte hd been penetrted by the root, recovery of the well-defined dense corticl plte would not occur. Therefore, longitudinl studies re needed to investigte whether repir of the lveolr bone defect tkes plce fter spce closure nd during the retention period nd to identify discrimintive fctors for good nd poor cpcity for lveolr bone remodeling. CONCLUSION N During EMR-MA in ptients with Clss I dentolveolr protrusion, the ABA nd VBL on the pltl side nd the RL nd RA of the MXCI nd MXLI were significntly decresed. REFERENCES 1. Melsen B. Biologicl rection of lveolr bone to orthodontic tooth movement. Angle Orthod. 1999;69: Vern C, Zffe D, Sicilini G. Histomorphometric study of bone rections during orthodontic tooth movement in rts. Bone. 1999;24: Bek SH, Kim BH. Determinnts of successful tretment of bimxillry protrusion: orthodontic tretment versus nterior segmentl osteotomy. J Crniofc Surg. 2005;16: Lee JK, Chung KR, Bek SH. Tretment outcomes of orthodontic tretment, corticotomy-ssisted orthodontic tretment, nd nterior segmentl osteotomy for bimxillry dentolveolr protrusion. Plst Reconstr Surg. 2007;120: Ten Hoeve A, Mulie RM. The effect of ntero-postero incisor repositioning on the pltl cortex s studied with lmingrphy. J Clin Orthod. 1976;10: Winwright WM. Fciolingul tooth movement: its influence on the root nd corticl plte. Am J Orthod. 1973;64: Wehrbein H, Fuhrmnn RAW, Diedrich PR. Periodontl conditions fter fcil root tipping nd pltl root torque of incisors. Am J Orthod Dentofcil Orthop. 1994;106: Sriky S, Hydr B, Ciğer S, Ariyürek M. Chnges in lveolr bone thickness due to retrction of nterior teeth. Am J Orthod Dentofcil Orthop. 2002;122: Fuhrmnn RAW, Wehrbein H, Lngen HJ, Diedrich PR. Assessment of the dentte lveolr process with high resolution computed tomogrphy. Dentomxillofc Rdiol. 1995;24: Hndelmn CS. The nterior lveolus: its importnce in limiting orthodontic tretment nd its influence on the occurrence of itrogenic sequele. Angle Orthod. 1996;66: Vrdimon AD, Oren E, Ben-Bsst Y. Corticl bone remodeling/tooth movement rtio during mxillry incisor retrction with tip versus torque movements. Am J Orthod Dentofcil Orthop. 1998;114: Kim Y, Prk JU, Kook YA. Alveolr bone loss round incisors in surgicl skeletl Clss III ptients. Angle Orthod. 2009;79: Nhm KY, Kng JH, Moon SC, et l. Alveolr bone loss round incisors in Clss I bidentolveolr protrusion ptients: retrospective three-dimensionl cone bem computed tomogrphy study. Dentomxillofc Rdiol. 2011; Epub hed of print. 14. Kook YA, Kim G, Kim Y. Comprison of lveolr bone loss round incisors in norml occlusion smples nd surgicl skeletl Clss III ptients. Angle Orthod. 2011; Epub hed of print. 15. Lee KM, Kim YI, Prk SB, Son WS. Alveolr bone loss round lower incisors during surgicl orthodontic tretment in mndibulr prognthism. Angle Orthod. 2012;Epub hed of print. 16. Dhlburg G. Sttisticl Methods for Medicl nd Biologicl Students. New York, NY: Interscience Publiction; Siriwt PP, Jrbk JR. Mlocclusion nd fcil morphology: is there reltionship? An epidemiologic study. Angle Orthod. 1985;55: Ygci A, Veli I, Uysl T, Ucr FI, Ozer T, Enhos S. Dehiscence nd fenestrtion in skeletl Clss I, II, nd III mlocclusions ssessed with cone-bem computed tomogrphy. Angle Orthod. 2012;82: Leung CC, Plomo L, Griffith R, Hns MG. Accurcy nd relibility of cone-bem computed tomogrphy for mesuring lveolr bone height nd detecting bony dehiscences nd fenestrtions. Am J Orthod Dentofcil Orthop. 2010; 137: Duterloo HS. Orthodontic tretment nd remodeling of the bone tissue of the lveolr process (proceedings). Rev Belge Med Dent. 1977;32: Remmelink HJ, vn der Molen AL. Effects of nteroposterior incisor repositioning on the root nd corticl plte: followup study. J Clin Orthod. 1984;18:42 49.