A Long-term Study on the Expansion Effects of the Cervical-pull Facebow With and Without Rapid Maxillary Expansion

Transcription

1 Originl Article A Long-term Study on the Expnsion Effects of the Cervicl-pull Fcebow With nd Without Rpid Mxillry Expnsion Frederick A. Fenderson, DDS, MS ; Jmes A. McNmr Jr, DDS, PhD b ; Tizino Bccetti, DDS, PhD c ; Chrles J. Veith, DMD, MS d Abstrct: This study evlutes the long-term stbility of mxillry expnsion chieved by widening the inner bow of fcebow, with or without concurrent rpid mxillry expnsion (RME) (Hs type), followed by tretment with fixed edgewise pplinces. The prent smple included 154 nonextrction ptients who strted their orthodontic tretment during defined time period. The exclusion criteri reduced the number of ptients to in the cervicl-pull fcebow group () nd in the RME- group. All subjects were in the lte-mixed to erly-permnent dentition stge t the strt of tretment. Dentl csts were mesured using digitl imging system t four different times: strt of tretment (T 1 ), end of ctive tretment (T 2 ), end of retention (T 3 ), nd postretention follow up (T 4 ). The RME- protocol produced greter increse in mxillry rch width (6.1 mm) thn did the protocol (4 mm). The RME- protocol provided greter net mxillry rch perimeter increse thn did expnsion with n inner bow of cervicl fcebow. The RME- group hd three mm more rch perimeter 10 yers fter tretment completion thn did the group. The stbility of expnsion chieved with n inner bow of fcebow ws equl to tht chieved with Hs-type RME pplince. Both expnsion protocols retined 90% of the initil intermolr expnsion 15 yers fter expnsion. (Angle Orthod 2004;74:4 449.) Key Words: Rpid mxillry expnsion; Fcebow; Edgewise therpy; Arch perimeter; Irregulrity index; Cst nlysis INTRODUCTION Rpid mxillry expnsion (RME) hs been used routinely by orthodontists for the lst three decdes to widen orthopediclly the mxille of growing ptients. Arch expnsion lso hs been produced simply by widening the Grdute Orthodontic Progrm, The University of Michign, Ann Arbor, Mich.; nd privte prctice, Prescott, Ariz. b Thoms M. nd Doris Grber Endowed Professor of Dentistry, Deprtment of Orthodontics nd Peditric Dentistry, School of Dentistry; Professor, Cell nd Developmentl Biology, School of Medicine; nd Reserch Scientist, Center for Humn Growth nd Development, The University of Michign, Ann Arbor, Mich.; nd privte prctice, Ann Arbor, Mich. c Assistnt Professor, Deprtment of Orthodontics, The University of Florence, Florence, Itly; nd Thoms M. Grber Visiting Scholr, Deprtment of Orthodontics nd Peditric Dentistry, School of Dentistry, The University of Michign, Ann Arbor, Mich. d Privte prctice, Wilmington, Del. Corresponding uthor: Jmes A. McNmr Jr, DDS, PhD, Deprtment of Orthodontics nd Peditric Dentistry, School of Dentistry, The University of Michign, Ann Arbor, MI (e-mil: mcnmr@umich.edu). Accepted: September Submitted: August by The EH Angle Eduction nd Reserch Foundtion, Inc. inner bow of fcebow for over hlf century. Surprisingly, however, despite the extensive use of both methods, there hve been reltively few studies tht hve evluted the long-term stbility of either procedure when followed by phse of fixed pplinces. Numerous investigtors hve suggested using mxillry expnsion for correcting trnsverse discrepncies tht result in posterior crossbites, either unilterl or bilterl. 1 5 In ddition to correcting posterior trnsverse discrepncies, RME therpy hs been dvocted to help llevite toothsize/rch-length problems. 5 Adkins et l 6 determined tht for every millimeter of interpremolr width increse, the resultnt gin in rch length is pproximtely mm. The gin in rch perimeter resulting from orthopedic mxillry expnsion in combintion with other methods of gining rch perimeter such s interproximl reduction nd molr distliztion cn be used to help eliminte crowding in some ptients without the need to extrct permnent teeth. The long-term stbility of RME reported in the literture vries considerbly, s illustrted by the rnge of percent relpse fter retention, 0 % 7 14 (Tble 1). Mny fctors must be tken into ccount if suturl seprtion (orthopedic expnsion) is the primry objective. Argubly, the most im- 4

2 440 FENDERSON, MCNAMARA, BACCETTI, VEITH TABLE 1. Posttretment Chnges After Orthopedic Mxillry Expnsion Reference Stockfish 7 Timms 8 Linder-Aronson nd Lindgren 9 Hs 10 Mew 11 Herold 12 Brust nd McNmr 22 Smple Size Mouss et l McNmr et l Age (y) Yers Out of Tx/Ret NA indictes not vilble; Tx, tretment; nd Ret, retention. Initil 6/6 3/ Expnsion (mm) Residul 6/6 3/ Relpse (%) 6/6 3/ Sttisticl Anlysis No No Yes No No NA Yes Yes Yes portnt fctors re the ge nd level of skeletl mturity of the ptient. 15 The rigidity of the pplince lso must be considered. Studies conducted by Hicks 16 nd Krebs 17 reported tht the skeletl contributions to the increse in rch width were 16 % nd %, respectively. These two studies indicte tht lrge mount of orthodontic expnsion (tooth tipping) occurs. On the other hnd, Mouss et l 13 nd McNmr et l 14 evluted more rigid expnsion pplinces nd suggested tht orthodontic expnsion (tooth tipping) ccounts for very little of the totl expnsion. Unfortuntely, the vlidity of the conclusions reched by the mjority of studies reporting both good nd poor stbility is questionble becuse most hd lrge ge rnges, smll smples, nd/or lcked ny sttisticl nlysis. 18 The investigtions of both Gryson 19 nd Sndström et l 20 filed to show ny correltion between the chnge in mndibulr rch width nd the chnge in mxillry rch width. The few studies tht suggest RME cn influence the mndibulr dentition indicte tht the response is highly vrible. The chnges produced (if they exist t ll), therefore, do not pper to be predictble or stble to ny cliniclly significnt degree, especilly in the mndibulr intercnine nd rch perimeter dimensions. To dte, there hs been only one investigtion 21 tht exmined the trnsverse chnges ssocited with intentionl expnsion of the inner bow of cervicl hedger. It should be noted, however, tht no long-term dt were presented in this study. To summrize, the lst two decdes hve seen stedy decline in the extrction rte during orthodontic tretment, especilly in ptients with mild to moderte mounts of crowding. Mxillry expnsion, either with RME nd/or widened inner bow of fcebow, is being used with incresing frequency to gin dditionl rch length in these types of ptients. The im of this investigtion ws to compre nd test sttisticlly the effects nd stbility of two methods of tretment used to expnd the mxillry rch, cervicl-pull fcebow () with expnsion of the inner bow nd Hs-type expnder followed by the. The long-term effects on dentl cst smples tht were pproximtely 10 yers postorthodontic tretment nd pproximtely 15 yers postexpnsion therpy were evluted. MATERIALS AND METHODS The ptients who prticipted in this study were recruited from the prctice of single orthodontic prctitioner (Dr Veith). The originl prent smple included 154 nonextrction ptients who strted their orthodontic tretment between the yers 1973 nd All subjects were in the lte-mixed to erly-permnent dentition stge, nd they presented with vrible degree of contrction of the dentl rches t the time of initil observtion. The mxillry rches of these ptients were expnded with one of two pplinces: Hs-type RME pplince in conjunction with cervicl fcebow (RME-) or cervicl fcebow with expnsion of the inner bow (). In the RME- group, the fcebow ws used right fter RME tretment. The RME- group did not present with more severe constriction of the dentl rches thn the -only group. Both groups received similr fixed pplince therpy t the end of expnsion. Ech complete ptient record consisted of seril dentl csts mesured t four different times: strt of tretment (T 1 ), end of tretment (T 2 ), end of retention (T 3 ), nd postretention follow up (T 4 ). The verge end-of-tretment to postretention follow-up-intervl ws 1 yers. Ech ptient wore bnded mndibulr first-premolr-to-first-premolr retiner until well pst puberty, typiclly t lest until 21 yers of ge. Of the prent smple of 154 ptients, 52 ptients were eliminted becuse of one or more of the following exclusion criteri: dmged or unusble csts (n 2); incomplete seril csts, typiclly T 1 or T 2 cst (n 40); extensive prosthodontic reconstruction (n 3); postretention follow-up of less thn two yers (n 7). The exclusion criteri reduced the number of ptients to in group RME- nd in group. A totl of 408 mxillry nd mndibulr dentl csts of these 102 ptients were mesured t the four different stges de-

3 STABILITY OF EXPAION BY RME OR FACEBOW TABLE 2. Intervl T 1 T 2 T 3 T 4 Age Distribution (y) n Men Rnge RME- n Men Rnge scribed previously using digitl imging system. The smple ge chrcteristics re summrized in Tble 2. The group consisted of 28 mles nd 33 femles, wheres the RME- group included 14 mles nd 27 femles. Dentl cst mesurements Occlusl imges of the dentl csts were generted using video-imging hrdwre nd softwre (Bioscn OPTIMAS Imging Systems, Settle, Wsh) tht hd been modified specificlly for the nlysis of dentl csts. 22 Mesurements of rch width, rch depth, rch perimeter, incisor irregulrity, nd molr ngultion were generted with the id of the OPTIMAS softwre on both rches. Arch width. Two methods were used to determine rch width. The first method mesured the distnce between the computer-clculted centroid of one tooth nd the centroid on its ntimere. This method of mesurement ws denoted s rch width (centroid). 23 The second method mesured the distnce between point on the lingul surfce of ech tooth to homologous point on its ntimere. The mesure derived using this method ws denoted s rch width (lingul). Arch widths were mesured for the cnines, first premolrs, second premolrs, nd first molrs. Arch depth. Arch depth ws mesured from common midline point in the dentl rch (the contct point between the centrl incisors) perpendiculrly to trnsverse line connecting the mesil surfces of the cnines, first premolrs, second premolrs, nd first molrs. 23 Arch perimeter. Arch perimeter ws mesured s the sum of the lengths of line segments nterior to the first permnent molrs between the contct points of djcent teeth. 23 Incisor irregulrity index. Incisor irregulrity index ws mesured s the five summed liner displcements of the mesil nd distl ntomicl contct points of the six lower nterior teeth, s described previously by Little. 24 Molr ngultion. Molr ngultion refers to the ngle of intersecting lines drwn through the mesiobuccl nd the mesiolingul cusp tips of the mxillry nd mndibulr first molrs. Sttisticl evlution Mens nd stndrd devitions were clculted for the dentl cst vribles t T 1,T 2,T 3, nd T 4, s well s chnges between T 1 -T 2,T 2 -T 4, nd T 3 -T 4. An nlysis of vrince (ANOVA) ws used to test for significnt differences (P 4.05 nd P.01) between the mens of the two groups t the strt of tretment (T 1 ) nd to identify significnt differences for the chnges between T 1 -T 2 (expnsion effect) nd T 2 -T 4 (postexpnsion effect) for the two tretment groups. A sttisticl progrm (Systt for Windows, version 5.03) ided in the sttisticl computtions. Error of the method The order of digitiztion of the csts of ech subject ws selected t rndom, nd then ll rch dimensions on the T 1, T 2,T 3, nd T 4 csts were digitized on the sme occsion in n ttempt to reduce the systemtic error in the mesurements. 25 In n ttempt to determine how ccurtely the vrious rch dimensions could be mesured on two seprte occsions, 18 subjects csts were selected rndomly nd redigitized to clculte intrclss correltion coefficients (ICC): ICC vrince component/(vrince component men squre within), where vrince component (men squre between men squre within)/q, nd q equls the number of mesures per subject (ie, two). The men squre between used the ptient cst men squre. The ICC ws clculted using n (M)ANOVA model. The ICC s well s the men mesurement difference nd stndrd devition for ll vribles re summrized in Tble 3. RESULTS Anlysis of strting form The results of the ANOVA of pretretment vlues (Tble 4) reveled tht there were no significnt differences (P.05) between the two groups before tretment, with the exception of lrger mndibulr first interpremolr rch width dimension in the group, mesured lingully. All between-group differences were within one mm rnge. Anlysis of tretment nd posttretment effects Tble 5 summrizes the descriptive sttistics for the two groups t T 2 through T 4. Tble 6 illustrtes the chnges from pretretment to end-of-tretment (T 1 -T 2 ), end-of-tretment to strt-of-retention (T 2 -T 3 ), end-of-retention to postretention (T 3 -T 4 ), nd postretention to end-of-tretment (T 2 -T 4 ) for both groups, long with the results of the comprison of the chnges over time in the T 1 -T 2 nd T 2 -T 4 intervls between the two groups using ANOVA. Tretment (T 1 -T 2 ) Generlly, most mesurements incresed in group RME- during tretment. For exmple, mxillry intermolr width incresed n verge of 6.1 mm. Similrly, mndibulr intermolr nd mxillry nd mndibulr intercnine widths lso incresed during tretment. Tretment lso incresed both mxillry nd mndibulr rch perimeters. Specificlly, mxillry rch perimeter incresed mm. As

4 442 FENDERSON, MCNAMARA, BACCETTI, VEITH TABLE 3. Intrclss Coefficient Correltions Mesure (mm) Mx. rch width (centroid) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mx. rch width (lingul) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mn. rch width (centroid) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mn. rch width (lingul) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mx. rch depth Cnine First premolr Second premolr First molr Mn. rch depth Cnine First premolr Second premolr First molr Arch perimeter Mxillry Mndibulr Incisor irregulrity Mxillry Mndibulr Molr ngultion ( ) Mxillry Mndibulr Difference (n 18) Men ICC ICC indictes intrclss correltion coefficients; Mx., mxillry; nd Mn., mndibulr. expected, both mxillry nd mndibulr incisor irregulrities decresed. There ws very slight tipping effect or increse in mxillry molr ngultion nd slightly greter uprighting or decrese in mndibulr molr ngultion. The sme generl trends noted in group RME- lso occurred in group. The between-group differences were sttisticlly significnt for mxillry interpremolr nd intermolr widths nd mxillry rch perimeter. These mesures showed greter increse in the RME- group thn in the -only group. The chnges in the other vribles were not sttisticlly different during the expnsion intervl. Retention period (T 2 -T 3 ) Both mxillry nd mndibulr incisor irregulrities remined essentilly unchnged in both groups during the retention period. It is interesting to note tht even with fixed retiner, mndibulr intercnine width decresed slightly. Generlly, ll other mesurements lso decresed slightly, but not to significnt degree. Both mxillry nd mndibulr molr ngultions incresed by smll mount. Postretention period (T 3 -T 4 ) Both mxillry nd mndibulr incisor irregulrities incresed very slightly fter the fixed mndibulr retiner ws removed in both RME- nd groups. All other mesurements showed generl trend towrd decrese, except mxillry intermolr width nd mxillry nd mndibulr molr ngultions, which did not chnge. The mgnitude of chnge did not exceed one mm for ny of the vribles exmined. Overll posttretment period (T 2 -T 4 ) Most mesurements decresed in group RME- during the end-of-tretment to postretention period. Both mxillry nd mndibulr rch perimeters showed the lrgest mgnitude of decrese, nd mm, respectively. Mxillry nd mndibulr incisor irregulrities nd mndibulr molr ngultion incresed slightly, but not significntly. The sme generl trends noted in group RME- lso occurred in group. During the end-of-tretment to postretention intervl, the only significnt difference between groups nd RME- ws represented by the decrese in mndibulr intermolr width, which ws lrger in the RME- group; however, the mgnitude of the difference ws not cliniclly significnt ( mm). DISCUSSION Mxillry rch width In group RME-, the men mxillry intermolr tretment increse of 6.1 mm is consistent with the tretment chnges recorded in numerous investigtions 7 10,13,22 nd slightly greter thn the increse reported by McNmr et l ( mm). 14 Severl investigtions lso hve reported men mxillry intercnine tretment increses similr to the 3.9 mm reported in this study for group RME-. 9,12 14 The net posttretment gin of 5.5 mm in mxillry intermolr width (Tble 5) is similr to the net gins reported by Mouss et l, 13 McNmr, 26 nd McNmr et l. 14 In this study, the decrese in mxillry intermolr width 15 yers fter expnsion ws smll, pproximtely mm. The net long-term gin in mxillry intercnine width of

5 STABILITY OF EXPAION BY RME OR FACEBOW 443 TABLE 4. Pretretment (T 1 ): Descriptive nd Inferentil Sttistics Mesure (mm) Mx. rch width (centroid) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mx. rch width (lingul) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mn. rch width (centroid) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mn. rch width (lingul) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mx. rch depth Cnine First premolr Second premolr First molr Mn. rch depth Cnine First premolr Second premolr First molr Arch perimeter Mxillry Mndibulr Incisor irregulrity Mxillry Mndibulr Molr ngultion ( ) Mxillry Mndibulr n Men RME n Men ANOVA Significnce indictes cervicl-pull fcebow group; RME, rpid mxillry expnsion; Mx., mxillry; Mn., mndibulr; nd, not significnt. * P * three mm for group RME- lso is similr to the net gins reported by Mouss et l 13 nd McNmr et l 14 but lrger thn the net gins reported by Linder-Aronson nd Lindgren, 9 Herold, 12 nd McNmr. 26 It is interesting to note tht the mxillry intercnine width decreses significntly, pproximtely one mm, from ge 14 to 48 yers in untreted subjects. 27,28 Thus, the net gin of three mm recorded in intercnine width for group RME- represents stble increse tht is cliniclly significnt. In the literture, there is only one investigtion tht evluted the short-term effects of using fcebow to expnd the mxillry rch. Kirjvinen et l 21 reported mxillry intermolr tretment increse of 6.6 nd 5.1 mm in mles nd femles, respectively, nd mxillry intercnine increse of 4.9 nd five mm, in mles nd femles, respectively. These investigtors did not quntify the reltive mounts of tooth tipping tht my hve occurred. In this study, there ws four-mm tretment increse in mxillry intermolr width nd 3.2-mm tretment increse in mxillry intercnine width for group. Surprisingly, there ws only of mxillry first molr ngultion increse ssocited with this increse in rch width produced by the

6 444 FENDERSON, MCNAMARA, BACCETTI, VEITH TABLE 5. End of Tretment (T 2 ), End of Retention (T 3 ), nd Posttretment (T 4 ): Descriptive Sttistics T 2 T 3 T 4 -RME -RME -RME Mesure (mm) Men Men Men Men Men Men Mx. rch width (centroid) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mx. rch width (lingul) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mn. rch width (centroid) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mn. rch width (lingul) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mx. rch depth Cnine First premolr Second premolr First molr Mn. rch depth Cnine First premolr Second premolr First molr Arch perimeter Mxillry Mndibulr Incisor irregulrity Mxillry Mndibulr Molr ngultion ( ) Mxillry Mndibulr indictes cervicl-pull fcebow group; RME, rpid mxillry expnsion; Mx., mxillry; Mn., mndibulr; nd, not significnt. cervicl fcebow. The miniml chnge in mxillry molr ngultion ssocited with this cliniclly significnt mount of intermolr expnsion suggests tht the expnsion chieved using the fcebow is similr in nture to tht recorded in group RME-. In group, the net long-term gin in mxillry intermolr nd intercnine width ws 3.6 nd mm, respectively. The losses in mxillry intermolr width ( mm) nd intercnine width ( mm) postretention in this tretment group were similr to the losses recorded in group RME- for the sme dimensions. Mndibulr rch width In group RME-, the men mndibulr intermolr nd intercnine tretment increses of nd mm, respectively, re less thn the 3.3 mm intermolr nd mm intercnine width tretment increses reported by Sndström et l. 20 The chnges in rch dimensions re, however, lrger thn the two mm intermolr nd mm intercnine tretment increses reported by Mouss et l 13 nd thn the one mm intermolr nd two mm intercnine tretment increses reported by McNmr et l. 14

7 STABILITY OF EXPAION BY RME OR FACEBOW In group RME-, the net long-term increse of mm in mndibulr intermolr width is greter thn the rnge of to mm reported on ptients treted only with fixed edgewise pplinces This net increse of mm is the sme vlue reported by Mouss et l 13 nd is greter thn the vlue of mm reported by McNmr 26 nd McNmr et l 14 in ptients treted with RME in ddition to fixed edgewise pplinces. There were lrge stndrd devitions ssocited with ll the postretention mens, however, suggesting much individul vrition. The results of this study re consistent with the trends reported in the literture regrding mndibulr intercnine width. After smll ( mm) tretment increse, the resultnt net gin fter retention ws mm. The results reported by Mouss et l 13 re identicl to those found in this study. McNmr 26 nd McNmr et l, 14 however, reported net mndibulr intercnine width increse of bout mm. One possible explntion for this difference is the ge of the ptients t finl mesurement. In this study, the men ge of ptients ws 26.7 yers, wheres it ws 21 yers in the investigtions by McNmr 26 nd McNmr et l. 14 It is possible tht the norml mturtionl process of shrinking intercnine dimension hs not occurred to the sme extent in the previous studies. 14,26 In group, the men mndibulr intermolr tretment increse of mm is similr to the mm increse reported by Kirjvinen et l 21 for femles but is somewht less thn the 3.4 mm increse they reported for mles. Interestingly, the similrities nd differences between mles nd femles re reversed in the intercnine region. The men mndibulr intercnine tretment increse of mm is similr to the mm increse Kirjvinen et l 21 reported for mles nd is slightly less thn the mm increse reported for femles. The net long-term gin in mndibulr intermolr nd intercnine width in the group ws nd mm, respectively. As discussed previously, the tretment chnges reported by Kirjvinen et l 21 were similr, but they did not present ny long-term dt. Mxillry rch perimeter Before interpreting the results of expnsion therpy in terms of rch perimeter increse, it must be noted tht investigtions regrding the longitudinl chnges in rch perimeter hve shown tht this dimension decreses with ge. 23,27 40 Moyers et l 23 reported tht mxillry rch perimeter decreses pproximtely two to three mm from ges 10 to 17 yers. Crter nd McNmr 27 reported decrese of mm from ge 14 to 17 yers. More recent investigtions lso hve reported men tretment increses in mxillry rch perimeter in ptients who hd RME therpy. 6,13,14,22,26,27 In this study, the men tretment increse of mm in group RME- is similr to the 4.7-mm increse reported by Adkins et l 6 nd the 4.1-mm increse reported by Mouss et l. 13 McNmr 26 nd McNmr et 445 l, 14 however, hve reported lrger men tretment increses (rnging from 7.9 to 5.6 mm). Tking into ccount the mm decrese tht occurs nturlly in untreted ptients, 27 the rches treted with RME- effectively hd mxillry rch perimeters tht were 6.2 mm greter t the end of tretment thn would hve been expected if they were left untreted. There ws less men tretment increse in mxillry rch perimeter seen in group thn tht recorded for group RME- ( mm compred with mm). It should be noted, however, tht the mjority of ptients in group still hd their primry mxillry second molrs intct (44 of ), nd thus mjority hd leewy spce vilble. Unfortuntely, Kirjvinen et l 21 mesured rch length nd not rch perimeter, nd thus, direct comprison of the numeric vlues is difficult. Kirjvinen et l, 21 however, did record n increse in mxillry rch length of pproximtely mm. After tretment, the RME- group still hd net increse of mm in rch perimeter, wheres group showed no net gin. McNmr 26 reported net increse of 4.3 mm, wheres McNmr et l 14 recorded n increse of three mm nd Mouss et l 13 n increse of mm in RME ptients. Agin, if the norml mturtion process of decrese in rch perimeter ( mm) 27 is considered, the mxillry rch perimeter for the RME- group is five mm lrger thn in the untreted subjects. The gin produced by tretment with RME is not trnsient nd is stble long term fter tretment. This long-term net increse in mxillry rch perimeter chieved with the RME- protocol my help eliminte the need to extrct in some ptients with mild to moderte ( 6 mm) mounts of crowding in the mxillry rch. This sttement only pertins to the cquisition of vilble spce necessry for lignment; however, it does not ddress the possible need to extrct teeth for the correction of nteroposterior discrepncies. Mndibulr rch perimeter The men mndibulr rch perimeter tretment gin of mm produced by the RME- mxillry expnsion protocol ws lesser thn the vlues recorded by other investigtions. 13,14,26 Mouss et l 13 reported men tretment increse of mm, wheres McNmr indicted men tretment gin in mndibulr rch perimeter of mm (lte-mixed dentition) in ptients treted with n RME-fixed pplince protocol. 26 In this study, mndibulr rch perimeter did not decrese s much s it would hve hd these ptients not received the mxillry expnsion in combintion with fixed pplince protocols. 26,27 In group RME-, the mxillry expnsion protocol, in combintion with fixed orthodontic therpy, yielded enough dditionl spce to provide resonbly good resolution of the slight mount of mndibulr crowding present in these ptients.

8 446 FENDERSON, MCNAMARA, BACCETTI, VEITH TABLE 6. Descriptive Sttistics for Between-observtion Chnges nd Sttisticl Comprisons on T 1 -T 2 nd T 2 -T 4 Chnges Mesures Mx. rch width (centroid) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mx. rch width (lingul) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mn. rch width (centroid) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mn. rch width (lingul) Intercnine Interpremolr (first) Interpremolr (second) Intermolr (first) Mx. rch depth Cnine First premolr Second premolr First molr Mn. rch depth Cnine First premolr Second premolr First molr Arch perimeter Mxillry Mndibulr Incisor irregulrity Mxillry Mndibulr Molr ngultion ( ) Mxillry Mndibulr n Men Chnge T 1 -T 2 -RME n Men Anov significnce Chnge T 2 -T 3 (n ) indictes cervicl-pull fcebow group; RME, rpid mxillry expnsion; Mx., mxillry; Mn., mndibulr; nd, not significnt. * P.05; P Men The men gin in mndibulr rch perimeter produced by the mxillry expnsion protocol ws only mm. Kirjvinen et l, 21 who mesured rch length rther thn rch perimeter, reported very miniml tretment gin of pproximtely mm (verge of mles nd femles, nterior nd posterior rch lengths). The potentil leewy spce vilble becuse of the presence of primry second molrs (present in the mjority of subjects), however, ws not lost. In group RME-, the loss in mndibulr rch perimeter fter -mm tretment gin yielded postretention vlue tht ws essentilly the sme s the pretretment vlue. Mouss et l 13 recorded postretention vlue tht ws mm less thn the pretretment vlue. McNmr, 26 however, described net gins in mndibulr rch perimeter of mm (lte-mixed dentition) nd 4.1 mm (erly-permnent dentition) in ptients treted with n RME-fixed pplince protocol five yers postretention. Agin, one possible explntion for this discrepncy is the difference in ge of the ptients t finl mesurement. As stted previ-

9 STABILITY OF EXPAION BY RME OR FACEBOW 447 TABLE 6. Extended Chnge T 2 -T 3 Chnge T 3 -T 4 Chnge T 2 -T 4 -RME (n ) Men (n ) Men -RME (n ) Men (n ) Men -RME (n ) Men Anov significnce * * ously, the postretention mndibulr rch perimeter vlue ws smller thn the pretretment vlue in group. However, the net loss ( mm) in this group did not equl the mount of leewy spce potentilly vilble for use in some ptients. Mxillry nd mndibulr incisl irregulrity In group RME-, the men tretment decrese of five mm in the mxillry incisor irregulrity index is comprble to the 5.8-mm decrese reported by Mouss et l. The RME- mxillry expnsion protocol resolved the moderte mounts of crowding present in these ptients t the strt of tretment. In group, the men tretment decrese in mxillry incisor irregulrity index ws 5.4 mm. Kirjvinen et l 21 did not mesure incisor irregulrity, nd thus, direct comprison of the tretment effects observed in this study is not possible. In group RME-, the men mndibulr incisor irregulrity index decrese of mm is comprble to the - mm decrese reported by Mouss et l. 13 The ptients in this study hd mild mounts of crowding, s represented by the initil irregulrity index (Tble 4). It is cler, how-

10 448 FENDERSON, MCNAMARA, BACCETTI, VEITH ever, tht the RME- mxillry expnsion protocol in combintion with fixed orthodontics successfully resolved the mild mount of crowding present t the strt of tretment. In group, the men tretment decrese in mndibulr incisor irregulrity index lso ws mm. Agin, the study conducted by Kirjvinen et l 21 did not mesure incisor irregulrity. In both groups, RME- nd, during the posttretment period, the men mxillry incisor irregulrity increses of nd mm, respectively, nd the men mndibulr incisor irregulrity increses of nd mm, respectively, re comprble to the -mm increses reported by Mouss et l. 13 These chnges in mxillry incisor irregulrity during the posttretment period re similr to those tht might hve occurred nturlly with incresing ge. 27,28 The prolonged retention period most likely plyed role in the somewht greter stbility, compred with tht reported in the literture. Expnsion with the RME- protocol compred with the protocol The results of this study indicte tht the stbility of the widening chieved with the Hs-type expnder ws not sttisticlly different compred with the stbility of the expnsion chieved with the expnded inner bow of fcebow. Previous investigtions hve demonstrted tht RME pplinces produce orthopedic expnsion tht is stble fter retention when used t n ge before suturl ossifiction occurs ,26 With four nd 6.1 mm of intermolr expnsion for groups nd RME-, respectively, the loss in this dimension ws only nd mm 10 yers fter ctive tretment ended. In both groups, 90% of the totl intermolr expnsion ws mintined. These losses in the trnsverse dimension were minor nd represent good longterm stbility. The literture lso demonstrtes the long-term instbility of ny significnt mount of orthodontic expnsion (tooth tipping). If tooth tipping hd occurred with fcebow tretment, it is nticipted tht there would be more mxillry first molr tipping (s indicted by chnge in molr ngultion) during the tretment phse followed by rebound in the posttretment phse. In fct, there ws no sttisticl difference in mxillry molr ngultion between the two groups during the tretment (T 1 -T 2 ) or posttretment (T 2 - T 4 ) intervls. In this study, the net mxillry intermolr increse in group ws 3.6 mm, rgubly cliniclly significnt. The mxillry intermolr increse is much greter thn the one mm net mxillry intermolr expnsion, chieved with orthodontic-type forces, reported in the literture. 29,31,34, The mount of mndibulr intermolr width tht is gined t the end of the long-term observtion intervl is the sme for the RME nd fcebow groups ( mm). As for the increses in rch perimeters, however, the fcebow protocol is not ble to induce ny fvorble increse in either mxillry or mndibulr rch perimeters in the long term, wheres the significntly lrger postexpnsion gin in the RME group ( vs mm in the fcebow group) leds to cliniclly significnt outcome in the long term ( mm). CONCLUSIO The RME- protocol produced greter increse in mxillry rch width (6.1 mm) thn did the protocol (4 mm). The RME- protocol provided more net mxillry rch perimeter increse thn did expnsion with n inner bow of cervicl fcebow. The RME- group hd three mm more mxillry rch perimeter 10 yers fter tretment completion thn did the group. The stbility of expnsion chieved with n inner bow of fcebow is equl to tht chieved with Hs-type RME pplince, especilly when similr fixed pplince protocol follows expnsion. Both expnsion protocols retined 90% (5.5 in mm group RME-; 3.6 mm in group ) of the initil intermolr expnsion 15 yers fter expnsion therpy. The expnsion produced by both protocols does not pper to induce orthodontic tipping of nchor teeth. Mxillry expnsion by either method exerted only modest effect on mndibulr rch perimeter. Neither method produced net postretention increse. Mndibulr rch perimeters, however, were greter thn they would hve been hd these ptients not been treted. ACKNOWLEDGMENTS The uthors would like to recognize the contributions of Mr Elvis L. Evns, senior progrm nlyst, for his development nd refinement of the digitl imging system used in this project. This project ws supported in prt by the Orthodontic Fund for Excellence, Grdute Orthodontic Progrm, The University of Michign nd through funds mde vilble through the Thoms M. nd Doris Grber Endowed Professorship. REFERENCES 1. Hs AJ. The tretment of mxillry deficiency by opening the mid-pltl suture. Angle Orthod. 1965;65: Hs AJ. Pltl expnsion: just the beginning of dentofcil orthopedics. Am J Orthod. 1970;57: Wertz RA. Skeletl nd dentl chnges ccompnying rpid midpltl suture opening. Am J Orthod. 1970;58: Hrberson VA, Myers DR. Midpltl suture opening during functionl posterior cross-bite correction. Am J Orthod. 1978;74: McNmr JA Jr, Brudon WL. Orthodontics nd Dentofcil Orthopedics. Ann Arbor, Mich: Needhm Press, Inc; 2001:. 6. Adkins MD, Nnd RS, Currier GF. Arch perimeter chnges on rpid pltl expnsion. Am J Orthod Dentofcil Orthop. 1990; 97: Stockfish H. Rpid expnsion of the mxill-success nd relpse. Trns Eur Orthod Soc. 1969;45:

11 STABILITY OF EXPAION BY RME OR FACEBOW 8. Timms DJ. Long-term follow-up of cses treted by rpid mxillry expnsion. Trns Eur Orthod Soc. 1976;52: Linder-Aronson S, Lindgren J. The skeletl nd dentl effects of rpid mxillry expnsion. Br J Orthod. 1979;6: Hs AJ. Long-term posttretment evlution of rpid pltl expnsion. Angle Orthod. 1980;: Mew J. Relpse following mxillry expnsion. A study of twenty-five consecutive cses. Am J Orthod. 1983;83:. 12. Herold JS. Mxillry expnsion: retrospective study of three methods of expnsion nd their long-term sequele. Br J Orthod. 1989;16: Mouss R, O Reilly MT, Close JM. Long-term stbility of rpid pltl expnder tretment nd edgewise mechnotherpy. Am J Orthod Dentofcil Orthop. 1995;108: McNmr JA Jr, Bccetti T, Frnchi L, Herberger TA. Rpid mxillry expnsion followed by fixed pplinces: long-term evlution of chnges in rch dimensions. Angle Orthod. 2003; 73: Bccetti T, Frnchi L, Cmeron CG, McNmr JA Jr. Tretment timing for rpid mxillry expnsion. Angle Orthod. 2001;71: Hicks EP. Slow mxillry expnsion. A clinicl study of the skeletl versus dentl response to low-mgnitude force. Am J Orthod. 1978;73: Krebs A. Midpltl suture expnsion studies by the implnt method over seven yer period. Trns Eur Orthod Soc. 1964; 40: Hs AJ. Rpid expnsion of the mxillry dentl rch nd nsl cvity by opening the mid-pltl suture. Angle Orthod. 19;31: Gryson JA. Chnges in mndibulr interdentl distnce concurrent with rpid mxillry expnsion. Angle Orthod. 1977;47: Sndström RA, Klpper L, Ppconstntinou S. Expnsion of the lower rch concurrent with rpid mxillry expnsion. Am J Orthod Dentofcil Orthop. 1988;94: Kirjvinen M, Kirjvinen T, Hvikko K. Chnges in dentl rch dimensions by the use of n orthopedic cervicl hedger in Clss II correction. Am J Orthod Dentofcil Orthop. 1997;111: Brust EW, McNmr JA Jr. Arch dimensionl chnges concurrent with expnsion in mixed dentition ptients. In: Trotmn CA, McNmr JA Jr, eds. Orthodontic Tretment: Outcome nd Effectiveness. Crniofcil Growth Series, Monogrph. Ann Arbor, Mich: Center for Humn Growth nd Development, The University of Michign; 1995; Moyers RE, vn der Linden FPGM, Riolo ML, McNmr JA Jr. Stndrds of Humn Occlusl Development. Crniofcil Growth Series, Monogrph 2. Ann Arbor, Mich: Center for Humn Growth nd Development, The University of Michign; 1976; Little RM. The irregulrity index: quntittive score of mndibulr nterior lignment. Am J Orthod. 1975;68: Houston WJ. The nlysis of errors in orthodontic mesurements. Am J Orthod. 1983;83: McNmr JA Jr. The role of the trnsverse dimension in orthodontic dignosis nd tretment. In: McNmr JA Jr, ed. Growth Modifiction: Wht Works, Wht Doesn t nd Why. Crniofcil Growth Series, Monogrph 36. Ann Arbor, Mich: Center for Humn Growth nd Development, The University of Michign; Crter GA, McNmr JA Jr. Longitudinl dentl rch chnges in dults. Am J Orthod Dentofcil Orthop. 1998;114: Sinclir PM, Little RM. Mturtion of untreted norml occlusions. Am J Orthod. 1983;83: Shpiro PA. Mndibulr dentl rch form nd dimension. Tretment nd postretention chnges. Am J Orthod. 1974;66: Grdner, Chcons SJ. Posttretment nd postretention chnges following orthodontic therpy. Angle Orthod. 1976;46: Glenn G, Sinclir PM, Alexnder RG. Nonextrction orthodontic therpy: posttretment dentl nd skeletl stbility. Am J Orthod Dentofcil Orthop. 1987;92: Bishr SE, Chdh JM, Potter RB. Stbility of intercnine width, overbite nd overjet correction. Am J Orthod. 1973;63: Little RM, Wllen TR, Riedel RA. Stbility nd relpse of mndibulr nterior lignment-first premolr extrction cses treted by trditionl edgewise orthodontics. Am J Orthod. 1981;80: Uhde MD, Sdowsky C, BeGole EA. Long-term stbility of dentl reltionships fter orthodontic tretment. Angle Orthod. 1983; 53: Little RM, Riedel RA, Årtun J. An evlution of chnges in mndibulr nterior lignment from 10 to 20 yers postretention. Am J Orthod Dentofcil Orthop. 1988;93: Little RM, Riedel RA. Postretention evlution of stbility nd relpse mndibulr rches with generlized spcing. Am J Orthod Dentofcil Orthop. 1989;95: Little RM. Stbility nd relpse of dentl rch lignment. Br J Orthod. 1990;17: Little RM, Riedel RA, Engst ED. Seril extrction of first premolrs postretention evlution of stbility nd relpse. Angle Orthod. 1990;: Bishr SE, Treder JE, Jkobsen JR. Fcil nd dentl chnges in dulthood. Am J Orthod Dentofcil Orthop. 1994;106: Moorrees CFA. Dentition of the Growing Child: A Longitudinl Study of Dentl Development Between 3 nd 18 Yers of Age. Cmbridge, Mss: Hrvrd University Press; 19.. Wlter DC. Comprtive chnges in mndibulr cnine nd first molr widths. Angle Orthod. 1962;32: