Originl Article Anchorge Control in Bioprogressive vs Stright-wire Tretment Dyse Uris ; Ftim Ibrhim Abdel Mustf b Abstrct: Orthodontic techniques with different concepts nd philosophies hve emerged to provide dequte nchorge control. The purpose of this study ws to compre the effectiveness of the Bioprogressive nd Stright-wire techniques in the control of lower nchorge. Dt were obtined from the records of 40 ptients presenting Clss I nd II mlocclusions treted with first bicuspid extrctions. One group of 20 ptients ws treted with utility rch used to set up corticl nchorge in the lower rch nd sectionl retrction mechnics for spce closure. The second group ws treted with stright wire with predjusted pplince system. Tretment evlution reveled no significnt between-group differences in the mount of skeletl growth reltive to crnil bse nd lower mesil movement of first molrs. Men lower nchorge loss ws 3.1 mm in the Bioprogressive ptients nd four mm in the Stright-wire ptients. The picl bse chnge ws the most importnt component to molr correction. Although corticl nchorge did not impede lower molr movement, it ws no less effective in controlling molr movement with prtil pplince thn ws the fully bnded Stright-wire pplince. (Angle Orthod 2005;75:987 992.) Key Words: Anchorge; Spce closure; Corticl nchorge; Biomechnics; Stright wire; Bioprogressive INTRODUCTION In orthodontic tretment, nchorge loss is potentil side effect of orthodontic mechnotherpy nd one of the mjor cuses of unsuccessful results. Its cuse hs been described s multifctoril response in reltion to the extrction site, pplince type, ge, crowding, nd overjet. 1 Therefore, clinicins throughout the yers hve mde n effort to find biomechnicl solutions to control nchorge. 2 6 Tweed, 2,6 Holdwy, 7 nd Merrifield 8 developed different types of nchorge preprtion to increse the efficcy of tretment. Although stisfctory results were ttined by these methods, the vlidity of second-order (tip-bck) bends during nchorge preprtion rised considerble controversy. 9 11 Professor nd Chir, Center for Professionl Development, Brzilin Assocition of Dentistry, Curitib, Brzil. b Former grdute student, Center for Professionl Development, Brzilin Assocition of Dentistry, Curitib, Brzil; currently in privte prctice in the United Arb Emirtes. Corresponding uthor: Dyse Uris, DDS, MSD, Associção Brsileir de Odontologi, R. Dis d Roch Filho, 625, Curitib, Pr. 80040-050, Brzil (e-mil: dyseuris@su.com.br) Accepted: August 2004. Submitted: June 2004. 2005 by The EH Angle Eduction nd Reserch Foundtion, Inc. Storey nd Smith 12 introduced new concepts of force, in which n optimum rnge of force vlues should be used to produce mximum rte of movement of the cnine without producing ny discernible movement of the molr nchor unit. This underlying concept encourged Begg 13 to put forth clinicl concept clled differentil forces in orthodontic tretment. The use of multiple teeth t the nchorge segment to form lrge counterblncing unit nd the ppliction of differentil moments hve been investigted s methods to stbilize molr position. 14 16 Retrction mechnisms 17 nd brcket designs 18 hve lso been developed to improve tooth movement nd nchorge control. Bioprogressive technique of Ricketts et l 19 tkes dvntge of bone physiology nd its rections to pplied forces. Ricketts et l 20 suggested tht by plcing the roots of the molr teeth ginst the dense nd lminted corticl bone with its limited blood supply, tooth movement is delyed nd nchorge enhnced. In terms of mechnics, the Bioprogressive technique uses sectionl rches tht could be more dvntgeous for tooth movement in force quntity nd direction, without disrupting the posterior unit. 21 Besides, the utility rch hs been one of the most efficient instruments to neutrlize the tendency of the posterior section of the rches to migrte mesilly. 22 987
988 URIAS, MUSTAFA TABLE 1. Group Tretment Group Chrcteristics n Men Age (y, mo) Men Tretment Time (y, mo) Group I Femle, 13 12.9 3.1 3.8 1.0 Mle, 7 Group II Femle, 12 15.9 6.8 3.3 0.8 Mle, 8 P vlue 1.000.180 b.089 c 2. b Mnn-Whitney. c t-test. The development of the Stright-wire pplince by Andrews 23 25 brought bout new technology with simplified mechnics, which hs llowed orthodontists to tret ptients efficiently with consistent qulity results. 26 This sliding technique, however, involves risk of frictionl binding nd temporry stops in the tooth movement cused by deformtion nd irregulrities in the rch, nd my demnd greter control of the nchorge. 17 The present study hd the purpose of chrcterizing nd compring the role of growth nd lower nchorge control in cses treted using the Bioprogressive nd Stright-wire techniques. MATERIALS AND METHODS The smple consisted of two groups of 20 subjects, ech treted t the Orthodontic Grdute Progrm, Center for Professionl Development of the Brzilin Assocition of Dentistry. Chrcteristics of the smples re listed in Tble 1. The criteri for selection were the existence of Clss I or II molr reltionship, mesiofcil pttern, more thn eight mm of lower rch length deficiency, nd requiring four first premolr extrctions. All ptients were selected on the bsis of mximum nchorge needs. Cervicl hedger ws used for upper nchorge in both groups. The lower molr nchorge ws chosen for evlution becuse its mintennce did not require ny pplince dependent on ptient complince. Group I ws treted using the Bioprogressive technique of Ricketts et l 19 (3M Unitek, 0.018 0.025- inch brcket slots) nd group II ws treted using the Stright-wire technique (Brckets, A-Compny 0.021 0.028 inch). The Roth prescription system ws used in both groups. Tretment mechnics The segmented pproch of the Bioprogressive technique consisted of utility rch, 0.016- by 0.016- inch stinless steel rch wire used to set up corticl nchorge in the lower rch. Cuspid retrction springs were followed by closing utility rches of blue Elgilloy (0.016 0.016 inch). 21 Becuse the subjects hd mixed dentition, the second molr could not yet be included in the pplince. The Stright-wire technique followed the method developed by McLughlin nd Bennett. 26 28 In this group, retrction consisted of one step retrction of the mxillry nterior segment. Second molrs were included in the mechnics. Lingul rches were used during the ligning phse in the ptients who did not hve second molrs t the strt. Dt collection Ech ptient hd two lterl cephlometric rdiogrphs tken, one before nd the other fter tretment. Trcing, superimposition, nd mesurements ll were done by hnd (with the id of digitl clipers). The liner mesurements were executed to the nerest 0.1 mm. To seprte growth from tretment, the Johnston cephlometric method 29 ws used (Figure 1). Accordingly, the sources of molr correction were ssessed by mesuring movements of the molrs reltive to bsl bone nd the trnsltory growth of the jws with respect to both the crnil bse nd one nother. Chnges tht contributed to Clss II correction (eg, mndibulr growth or distl movement of the upper molrs) were given positive sign nd those tht detrcted (eg, mxillry growth, upper nchorge loss) were given negtive sign. In this nlysis, sgittl chnges tht ffect molr correction (ie, growth, nchorge loss) cn be distinguished with respect to mgnitude nd source. Sttisticl nlysis Common descriptive sttistics were clculted for ech of the vrious mesures of tretment chnge, nd the differences between the two groups were exmined by mens of nlysis of vrince. Becuse the present study covered both sexes nd wide rnge of strting ges nd tretment times, Schulhof nd Bgh s 30 sex-specific growth curves were integrted over ech subject s period of tretment observtion. For ech yer of development, the
ANCHORAGE CONTROL FIGURE 1. Cephlometric nlysis. (A) Mxillry regionl superimposition to estimte the growth of the mxill reltive to crnil bse (Mx), mndible reltive to mxill (picl bse chnge [ABCH]), nd upper molrs reltive to mxillry bsl bone. Mndibulr dvncement (Mnd) is obtined by lgebric subtrction: Mnd ABCH Mx. (B) Mndibulr regionl superimposition to mesure the movement of the lower molrs reltive to bsl bone. (C) Dentl superimposition to mesure totl molr correction. In ech instnce, orienttion is long the men functionl occlusl plne (MFOP), nd registrtion is t R (sphenoethmoid point, mxillry internl rchitecture, lbil mndibulr symphysel rchitecture). res under the pproprite curve were divided by the re of minimum prepubertl yer (mle-femle verge). This resulted in the expected growth unit (EGU), n individulized estimte of the reltive intensity of growth tht n untreted subject of the sme ge nd sex would be expected to experience during the specified intervl. 31,32 Person s correltion coefficient (r) ws clculted to estimte the strength of the reltionship between men tretment chnges nd EGU. 989 RESULTS Method error To ddress relibility issues, the cephlometric trcings of 50% of the totl smple were rndomly selected. Differences between the originl nd the retrced cephlometric rdiogrphs were sttisticlly nlyzed using mtched pired t-test. The results of the nlysis indicted tht there were no sttisticlly significnt differences between the originl nd repeted mesurements t the 0.05 level. Mens nd stndrd devitions for the vrious components of the molr correction re summrized in Tble 2. When the movement of the lower molr crown ws ssessed, there ws no significnt difference in the mount of mesil movement between groups (Tble 2). Ptients treted by the Bioprogressive therpy presented mesil movement of the lower first molr crown of 3.1 mm (4.7 mm bodily nd 1.6 mm tipping). The ptients treted using the Stright-wire pplince presented lower molr nchorge loss of four mm (5.4 mm bodily nd 1.4 mm tipping). Reltive to the mxill, the lower molr moved mesilly 5.6 mm in the Bioprogressive group nd 6.2 mm in the Stright-wire group. This chnge is the composite effect of orthodontic intervention nd the trnsltory movement of mndibulr growth. The totl molr correction ws ssessed by the effective mount of movement of the mxillry nd mndibulr first molrs reltive to one nother. A men of 2.6 mm of molr correction (rnge 1.1 to 5.9 mm) occurred in group I nd 1.5 mm (rnge 0.7 to 5.2 mm) in group II. No significnt between-group differences were observed in the mount of mxillry or mndibulr growth mesured reltive to the crnil bse. The mndible grew forwrd 5.1 mm in the Bioprogressive group nd 4.9 mm in the Stright-wire group. The mxill ws displced 2.6 mm nteriorly through growth in both groups, nd this detrcted from the molr correction effect. The skeletl differentil resulted in net picl bse difference of 2.5 mm in group I nd 2.2 mm in group II. This is one component of the totl molr correction. The remining correction cme TABLE 2. Mx Mnd ABCH U6 (totl) L6 (totl) L6 (bodily) L6 (tipping) 6/6 EGU Mens nd t scores for Between-tretment Differences Group I Men SD Medin 2.65 5.18 2.53 3.02 3.11 4.79 1.68 2.62 3.46 1.82 2.83 1.70 1.87 1.53 1.81 1.12 2.13 2.12 2.40 4.45 2.44 3.31 2.99 5.26 1.77 2.90 3.80 High SD-medin use is recommended. b Mnn-Whitney. c ABCH indictes picl bse chnge; EGU, expected growth unit. Group II Men SD Medin P b 2.65 4.92 2.27 4.83 4.01 5.43 1.41 1.51 2.23 1.77 3.34 2.70 2.34 2.21 2.28 0.99 2.02 1.84 2.17 5.13 1.91 5.33 3.93 5.84 1.35 1.12 2.09.989.850.715.005.190.273.675.102.055
990 URIAS, MUSTAFA TABLE 3. Mx Mnd ABCH U6 (totl) L6 (totl) L6 (bodily) L6 (tipping) 6/6 Correltion Coefficients for the Reltionship Between Tretment Chnge nd Expected Growth Unit Correltion Coefficient (r) r 0.7252 r 0.6932 r 0.3783 r 0.3830 r 0.1499 r 0.1699 r 0.0713 r 0.0743 Bioprogressive Group P P.0001 P.0001 P.1001 P.0956 P.5283 P.4740 P.7653 P.7555 ABCH indictes picl bse chnge; EGU, expected growth unit. Correltion Coefficient (r) r 0.3363 r 0.5427 r 0.4504 r 0.4348 r 0.1555 r 0.1644 r 0.0313 r 0.2390 Stright-wire Group P P.1471 P.0134 P.0462 P.0554 P.5126 P.4885 P.8959 P.3103 from the differentil nterior movements of the mxillry nd mndibulr first molrs. In the Bioprogressive group the lower nchorge loss ws more thn mtched by extr nchorge loss in the mxill (3.1 nd three mm, respectively). Hence, the molr correction resulted lmost entirely from the mxillomndibulr differentil (95%). The sme occurred in the Stright-wire group (Tble 2). When tretment chnges in the Bioprogressive group were compred with those in the Stright-wire group, no sttisticl differences were found between groups, except for the upper molr movement (P.011). Group I demonstrted slightly greter growth potentil. The EGU ws 3.4 in group I nd 2.2 in group II (P.05) (Tble 2). Considering the resulting EGU, correltion ws used to exmine the reltionship between men tretment chnges nd EGU (Tble 3). A positive correltion ws seen between EGU nd mndibulr growth in groups I nd II (r 0.69, P.0001 nd r 0.54, P.0134, respectively) nd negtive reltionship to mxillry displcement in group I (r 0.72, P.0001). The picl bse chnge (ABCH) presented significnt correltion with EGU in group II ptients (r 0.45, P.04). In Figures 2 nd 3, the components of the molr correction chieved in groups I nd II re grphed s function of expected growth. It my be seen tht the mjority of the correction ws due to differentil jw growth. DISCUSSION One of the mjor concerns of orthodontics hs been the development of techniques tht could dequtely control nchorge units in the selective movement of individul teeth or groups of teeth. In the Bioprogressive therpy, lower molr nchorge is enhnced by expnding the molr roots into the dense corticl bone on their buccl surfce. 20 This technique suggests tht FIGURE 2. Group I: components of molr correction grphed s function of EGU. Averge EGU denoted by verticl interrupted line. EGU indictes expected growth unit. FIGURE 3. Group II: components of molr correction grphed s function of EGU. Averge EGU denoted by verticl interrupted line. EGU indictes expected growth unit. the use of light continuous pressure during spce closure on sectionl rches will result in less strin on the nchorge. 20,22 In the Stright-wire technique, lingul rches cn support nchorge during the leveling nd ligning phse nd during the resolution of crowding. 28 As
ANCHORAGE CONTROL 991 proper lignment of brcket slots is ttined, the nchorge needs towrd the end of the cse diminishes. 27 Although the two techniques used in this study mke use of different resources to control nchorge, the mesil movement of the molrs ws not significntly different (Tble 2). The mndibulr molrs cme forwrd 3.1 mm in the Bioprogressive group nd four mm in the Stright-wire group. It is interesting to note tht the principle of holding the molrs ginst corticl bone to improve nchorge is not supported by the present findings. A study compring nchorge loss in group of ptients treted by the Bioprogressive with group treted by the Stndrd-edgewise mechnics demonstrted similr results. 33 Other studies hve reported one-third of the mesil movement of posterior teeth on the first bicuspid extrction. 34,35 Johnston 31 found men mount of 3.8 mm of nchorge loss in the lower rch in study of Clss II extrction ptients treted edgewise. Tooth movement ccounted for 40% of the molr correction, wheres the remining 60% of the correction cme from ABCH. In similr study of three groups of ptients treted with conventionl nchorge preprtion, ten-two system, nd without nchorge preprtion, the mesil displcement of the lower molrs ws 3.2, 2.6, nd 3.4 mm, respectively. 10 In this study, 44% nd 57% of the extrction spce ws lost by mesil movement of the lower molrs in groups I nd II, respectively. Considering tht the extrction of first premolr in ech qudrnt produces pproximtely 14-mm spce in ech rch, little ws left for correction of crowding nd uprighting of lower incisors. According to Bench et l, 20 rection to tretment mechnics is dependent on the influence of the fcil pttern. Brett, 36 in study of Clss II extrction tretment by the Bioprogressive therpy, found 3.6 mm of lower nchorge loss in the mesiofcil pttern, ginst 4.5 mm in the dolichofcil nd 2.9 mm in the brchyfcil pttern. In this study, group I demonstrted slightly greter growth potentil s estimted by EGU (Tble 3). This is explined by the fct tht usully Bioprogressive tretment strts t n erlier ge. Menwhile, positive correltion ws seen between EGU nd mndibulr growth in groups I nd II, which mens tht ABCH ws more importnt thn tooth movement (Figures 2 nd 3). The contribution to the correction cme bout s by-product of the usul pttern of fcil growth. The mndible outgrew the mxill in the 20 ptients in group I nd 19 in group II. This mens tht when mndibulr growth ceses, the min source of molr correction is no longer present. Tretment my lst longer. Nevertheless, tooth movement is the key vrible, nd it my result in deficient molr correction. 10 Bien 37 concluded tht nchorge is enhnced by incresing the number of teeth in the nchorge unit, thereby incresing the root re resisting displcement. However, clinicl experience bsed on the prctice of bnding second molrs hs shown tht this is not lwys relible. This nchorge strtegy ws not supported by the present findings. Actully, the nchor unit receives the lesser mount of force per unit re long the periodontl membrne thn the nonnchor unit (cnines), which my be more physiologic. 15 Loss of nchorge my then ensue. This study demonstrted tht only prtil pplince incorporting corticl nchorge provided nchorge equl to fully bnded lower rch. Although corticl nchorge nd the concept of segmented retrction mechnics ws not demonstrted to be more efficcious thn the Stright-wire pplince, it ws not worse either. This implies tht Clss II correction, spce closure, nd the use of Clss II elstics my ll be ccomplished when the entire lower rch (second molrs) is not vilble for strp-up. In this study, estimtes of expected growth intensity derived from the integrtion of sex-specific incrementl growth curves were used to djust wide rnge of strting ges nd tretment times. 30 Therefore, the use of n untreted control group (eg, Bolton, Burlington, Michign) would possibly yield better comprisons. CONCLUSIONS The results of this study support the following conclusions: There were no differences in nchorge loss between the two groups studied even though the source of nchorge ws different. Therefore, the present results do not support the notion tht one tretment strtegy is superior to the other in terms of nchorge control. The pttern of jw growth ws similr in both groups, with higher growth expected unit in the Bioprogressive group becuse of n erlier tretment strting ge. Lower nchorge loss ws mtched by upper mesil movement of upper posterior teeth in both groups. Differentil jw growth ws the most importnt component to molr correction. REFERENCES 1. Geron S, Shpck N, Kndos S, Dvidovitch M, Vrdimon AD. Anchorge loss multifctoril response. Angle Orthod. 2003;73:730 737. 2. Tweed CH. The ppliction of the principles of the Edgewise rch in the tretment of mlocclusions. Angle Orthod. 1941;7:5 11.
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