Glass Ionomer Cements as Luting Agents for Orthodontic Brackets

Transcription

1 Originl Article Glss Ionomer Cements s Luting Agents for Orthodontic Brckets K. S. Coups-Smith, DDS, Dip Ortho ; P. E. Rossouw, BSc, BChD, BChD (Hons-Child Dent), MChD(Ortho), PhD, FRCD(C) b ; K. C. Titley, BDS, LDSRCS(Eng), Dip Pedo, FRCD(C), MScD c Abstrct: The objectives of the present study were to () ssess the sher bond strengths of resinreinforced glss ionomer Fuji Ortho LC nd GC Fuji Ortho cements under differing conditions nd () compre their bonding performnce with tht of conventionl resin composite bonding systems. A smple of 64 bovine incisors ws divided into groups of teeth ech nd bonded with SPEED centrl incisor brckets. Enmel surfces of the teeth in the two experimentl groups were conditioned ccording to the mnufcturer s instructions; moreover, groups unconditioned before bonding were lso included under both wet nd dry conditions. A self-cure composite resin (Phse II) nd light-cure composite resin (Trnsbond XT) served s controls nd were etched with % phosphoric cid nd bonded in dry field. After incubtion t C for 4 hours nd for seven dys, the specimens were tested to filure with sher force in n Instron mchine. The Adhesive Remnnt Index (ARI) ws used to ssess the mount of resin left on the enmel surfces fter debonding. Selected specimens were exmined using scnning electron microscopy. Sttisticl nlyses included nlysis of vrince tests, t-tests, nd correltion coefficient clcultions nd showed tht no significnt difference existed between the glss ionomer cements under wet or dry conditions, provided the enmel ws conditioned with % polycrylic cid before bonding. Both glss ionomer cements were thus cceptble for bonding. Trnsbond XT hd the highest men sher bond strength irrespective of the incubtion period. A positive correltion ws obtined between the ARI scores nd bond strength. (Angle Orthod ;: ) Key Words: Resin-reinforced glss ionomer cements; Orthodontic brckets; Sher bond strength INTRODUCTION Direct bonding of orthodontic brckets hs virtully replced the fitting nd cementing of bnds. Contemporry bonded fixed orthodontic pplinces show improved esthetics, nd the design lso enhnces orl hygiene. The elimintion of tooth seprtion t the beginning of tretment nd closure of bnd spces t the end of tretment re dditionl dvntges of the bonded pplince. Interproximl enmel contouring during ctive tretment with bonded pplince in plce is lso possible. The contributions of Formerly with the University of Toronto, now in Privte Prctice in London, Ontrio. b Formerly with the University of Toronto, now Professor nd Clinic Director, Deprtment of Orthodontics, Bylor University. c Professor, Discipline of Peditric Dentistry, University of Toronto. Corresponding uthor: P. Emile Rossouw, BSc, BChD, BChD (Hons-Child Dent), MChD(Ortho), PhD, FRCD(C), Deprtment of Orthodontics, Bylor College of Dentistry, Gston Avenue, Dlls, TX 546 (e-mil: erossouw@tmbcd.edu). Accepted: December. Submitted: September. by The EH Angle Eduction nd Reserch Foundtion, Inc. enmel etching 4 nd direct bonding 5 to the orthodontic profession hve thus mde tretment more efficient. The trditionl cementing gents for orthodontic brckets re resin mterils, which were developed in the mid- 9s. 6, For clinicl success, these mterils need to be pplied in dry field nd lso require cidic conditioning of the enmel surfce. 6 As these resin cements hve evolved, it hs been shown tht filled (composite) resins not only provide stronger bonds thn do unfilled resins but lso possess improved therml expnsion properties. 6 Composite resins cn tke up to 4 hours to rech the mximum bond strength, however, sufficient bond strength exists fter only few minutes hve elpsed (especilly with light polymeriztion), llowing the immedite plcement of rchwires without debonding of the brckets, which is convenient for both the ptient nd clinicin. These resin cements exist s chemiclly utopolymerizing pste-pste nd utopolymerizing no-mix systems, visible light polymerized systems, nd dul cure systems., Disdvntges of the resin-bsed systems, however, include loss of enmel during cid conditioning,,4 loss of the fluoride-rich surfce enmel during debonding,,5 8 nd deminerliztion of enmel round the brckets becuse of poor ptient com- Angle Orthodontist, Vol, No 4, 46

2 GLASS IONOMER CEMENTS FOR ORTHODONTIC BONDING plince with respect to orl hygiene. 9 In summry, resin cements hve proved to be strong, durble, nd relible gents for the ttchment of orthodontic brckets to teeth. More recently, however, glss ionomer cements hve been developed, dvocted, nd mrketed for cementing orthodontic brckets to teeth. Generl dentists hve been successfully using glss ionomer mterils s luting, lining, nd restortive gents for the pst 5 yers. For orthodontists, there ppers to be multiple benefits in using glss ionomer cements s cementing gent. These include the relese of fluoride with its known cries-inhibiting properties nd its bility to bsorb fluoride from sources such s fluoride toothpste, thus rechrging its fluoride reservoir. Furthermore, cid conditioning is not required so tht both bonding nd debonding procedures hve the cpcity to reduce itrogenic dmge to enmel,,4 nd the bonding field does not hve to be dry, thus incresing the speed nd ese of brcket plcement. It is of concern, however, tht bond strengths for glss ionomer cements re not of the sme mgnitude s those for the conventionl resin cements nd s result the filure rte of brcket ttchment to teeth is higher.,5 Using n in vitro bovine model developed in this lbortory, the present study ws designed to compre the sher bond strengths of two recently introduced glss ionomer cements with those of two conventionl resin cements, s well s to test the vibility of reusing prepred specimens. The in vitro environment ensured the development of stndrdized technique, which lso llowed for the control of vribles. The scnning electron microscopic exmintion of the filed sher bonds between the tooth nd brcket surfces during the present study improved the interprettion of the results. 4 MATERIALS AND METHODS Tooth preprtion Bovine incisor teeth were decoronted, the coronl pulps removed with dentl explorer, nd the crowns thoroughly wshed free of blood nd orgnic debris in running tp wter. The teeth were divided into groups of 5, plced in continers with 5 ml of distilled wter, nd frozen t C until required. The freshly extrcted frozen teeth were llowed to thw t room temperture, rinsed in running distilled wter for minutes, nd their pulp chmbers filled with wtersoked sponges. The teeth were then embedded in polymethyl methcrylte (PMMA), which ws mixed in ccordnce with the mnufcturer s instructions nd poured into mould.5 cm in dimeter nd two cm in depth. During the embedding process, it ws ensured tht the lbil surfce projected bove nd prllel to the surfce of the PMMA nd tht the teeth were kept wet. The embedded teeth were then stored in distilled wter t 4 C before surfce preprtion nd brcket ppliction. A smple of previously embedded teeth ws lso stored t 4 C in distilled wter contining thymol crystls (to inhibit bcteril growth). The fesibility of reusing teeth for this type of project fter proper storge is not known. Brckets nd cementing mterils Mxillry left centrl incisor SPEED brckets were used in this study (Strite Industries, Cmbridge, Ontrio, Cnd). Previous investigtions hve shown tht the bses of these brckets re reltively flt, hve 6-guge foil mesh bses, nd men bse surfce re of.4. mm.,8 Two composite resin cements were used s controls. These were the utopolymerizing Phse II (Relince Orthodontic Products Inc., Itsc, Ill), nd the visible light cured Trnsbond XT (M Unitek Dentl Products, Monrovi, Clif). Two glss ionomer cements comprised the experimentl mterils: the utopolymerizing resin-reinforced GC Fuji Ortho nd the visible light cured resin-reinforced Fuji Ortho LC (GC Corportion, Tokyo, Jpn). Enmel surfce preprtion Before brcket plcement, the enmel surfce of ech embedded tooth ws initilly ground flt with wter-irrigted #8 grit SiC pper. The finl test surfce ws prepred by using wter-irrigted #6 grit SiC pper. The enmel surfces were observed under light microscope t 5 mgnifiction to ensure tht enmel surfce is intct nd, for the reused teeth, tht ll residul resin is removed nd no underlying dentin is exposed. The teeth tht did not meet these criteri were discrded. Experimentl protocols The experimentl protocols used in this study re summrized in Tble. Ech experimentl group consisted of embedded teeth. All resin nd glss ionomer cements were mixed nd pplied to the brckets nd enmel in ccordnce with the mnufcturers instructions. Where cid conditioning of the enmel surfce ws required before resin cement ppliction, the surfces were conditioned in the following wy. The enmel surfce ws dried with n electric hir dryer (Hndi-Dri, Lncer Pcific, Crlsbd, Clif) nd the surfce conditioned with % orthophosphoric gel for seconds (Phse II gel etch, Relince Orthodontic Products). The conditioned surfce ws then rinsed for seconds with running distilled wter nd dried with the hir dryer for seconds fter which the brcket ws cemented in position. The glss ionomer cements were pplied in either dry or wet environment to surfces, which were unconditioned or conditioned with % polycrylic cid. The enmel surfce of teeth in ll groups ws first dried with n electric hir dryer. The groups tht were designted for conditioning Angle Orthodontist, Vol, No 4,

3 48 COUPS-SMITH, ROSSOUW, TITLEY TABLE. Men Sher Bond Strengths (MP) of Fresh nd Reused Teeth, Resin Controls, nd ll Glss Ionomer Cement Test Conditions t 4 h nd d Group Fresh Teeth Reused Teeth Control Control Experiment Experiment Mteril Phse II Phse II Trnsbond XT Phse II Fuji Ortho LC Fuji Ortho LC Fuji Ortho LC Fuji Ortho LC GC Fuji Ortho GC Fuji Ortho GC Fuji Ortho GC Fuji Ortho Environment Wet Wet Wet Wet SD indictes stndrd devition; SBS, sher bond strength. Surfce Tretment Etched (% phosphoric cid) Etched (% phosphoric cid) Etched (% phosphoric cid) Etched (% phosphoric cid) Conditioned (% polycrylic cid) Unconditioned Conditioned (% polycrylic cid) Unconditioned Conditioned (% polycrylic cid) Unconditioned Conditioned (% polycrylic cid) Unconditioned n Men SBS SD 4 h d were conditioned with % polycrylic cid (GC Ortho Conditioner, GC Corportion) for seconds. The conditioner ws then rinsed with running distilled wter for seconds nd then the conditioned enmel surfce ws dried with hir dryer for seconds. For teeth tht were to be tested in conditioned dry environment, the brckets were then bonded to this dried surfce. A wet environment ws creted for teeth tht were to be tested in such n environment. The dry conditioned surfce ws moistened using cotton swb soked in distilled wter before the brckets were cemented. For teeth tht were ssigned to groups in which the enmel surfce ws not conditioned, the brckets were bonded to either dry (electric hir drier) or wet (moistened cotton swb) surfce similr to tht previously described. Brcket plcement Irrespective of the cement used or the preprtion of the enmel surfce, the brckets were plced in the following mnner: The bse mesh surfce of ech brcket ws coted with cement, tking cre tht no voids or ir bubbles were included. The coted brcket ws then plced by hnd on the enmel surfce. The slot in the brcket ws then engged by the weighted guide pin of semidjustble rticultor (Teledyne Hnu, Bufflo, NY) to which stone cylinder ws ttched (6 g). This rrngement ensured tht ll brckets were bonded using stndrdized force nd llowed the investigtor s hnds to be free to remove excess cement flsh with shrp explorer. Brckets tht were cemented with visible light cured cements were exposed to the light source for seconds on ech of the four sides of the brcket bse for totl exposure time of 4 seconds. Brckets tht were cemented with utopolymerizing cements were llowed to bench set for five minutes. This technique is similr to tht described by McColl, 8 in which the thickness of the cement ws shown to be consistently low. Teeth in ll groups were stored in distilled wter t C for either 4 hours or seven dys fter which they were sher tested to filure. To inhibit bcteril growth, crystls of thymol were dded to the storge wter. As indicted, n initil investigtion ws crried out to see whether teeth used in previous investigtion could be reused, nd these groups were sher tested fter seven dys. Sher bond strength testing The embedded specimens were clmped in n Instron Universl Testing Mchine (Model 4, Instron Corp., Cnton, Mss) so tht the brcket ws t 9 to the verticl plne, nd the incisl edge of the tooth ws below the compression cell. A shrpened chisel blde ws plced in onekn compression cell nd positioned t the brcket-enmel interfce. Using crosshed speed of.5 mm/min, the bonds were sher tested to filure. The sher force ws recorded in Newtons nd then converted to megpscls. Resin loction The Adhesive Remnnt Index (ARI) system of Artun nd Berglnd 8 ws used to evlute the mount of cement left on the tooth surfce fter debonding. In this study, both the tooth surfce nd the brcket bse were exmined under light microscope t 5 mgnifiction. To estblish intrnd interopertor relibility for the ARI index, 4 specimens were rndomly selected nd ssessed t two different times by the reserchers. Angle Orthodontist, Vol, No 4,

4 GLASS IONOMER CEMENTS FOR ORTHODONTIC BONDING 49 Scnning electron microscopy Before scnning electron microscopic exmintion, ech tooth nd its debonded brcket were plced in bsolute lcohol for seven dys fter which they were llowed to irdry. They were then mounted on scnning electron microscope (SEM) stud in such mnner tht the enmel surfce nd the brcket bse could be viewed nd sputter coted with three nm of pltinum in Polron SC 55 coting unit (Interntionl Scientific Instruments Inc., Snt Clr, Clif). The specimens were exmined nd photogrphed in Hitchi S-5 SEM t n operting voltge of kv t mgnifictions of (Hitchi Ltd., Mito City, Jpn). Sttisticl nlysis The men sher bond strengths nd stndrd devitions were clculted for ech group. Initilly, n independent two-tiled t-test ws performed to determine whether difference existed between fresh nd reused teeth. A four-fctor nlysis of vrince (four-wy ANOVA) ws used to evlute whether there were ny significnt differences between utopolymerizing nd light-cured glss ionomer cements, wet nd dry environments, conditioned nd unconditioned enmel surfces, nd sher bond strengths fter 4 hours nd fter seven dys. A three-wy ANOVA ws used to compre resin cement control groups with the glss ionomer cement groups with respect to the setting mechnism, the time elpsed before debonding, dry environment, nd the tretment of the enmel surfce. A test of interction between the effects of the vribles ws included in ANOVA design, nd if n interction occurred, the min effects were retested t ech fctor level using the LSMEANS test. To determine the inter- nd intropertor differences when ssigning ARI scores, n error study ws performed using pired t-test nd correltion nlysis. A Kruskl- Wllis nonprmetric ANOVA test ws performed to determine the reltionship between men sher bond strength nd men ARI score. This ws followed by Spermn correltion test to ssess whether the vribles were perfectly relted. The level of sttisticl significnce for ll tests ws P.5. The SAS system ws used for the nlysis of the dt (prog GLM, version 6., 994, Cry, Clif). RESULTS Fresh vs reused teeth The results showed tht the men sher bond strength for reused teeth ws not sttisticlly significntly different from tht for fresh teeth (P.5). This result thus justifies the use of correctly prepred reused teeth (Tble ). Sher bond strengths The sher bond strengths re shown in Tble. The control resin cement groups showed tht the light-cured Trnsbond XT produced higher sher bond strengths t 4 hours nd seven dys thn did Phse II. Both resin cements showed tht sher bond strengths incresed over sevendy period when compred with those recorded t 4 hours, nd these differences were sttisticlly significnt (P.5). The sher bond strengths of the utopolymerizing GC Fuji Ortho were consistently higher thn those recorded for Fuji Ortho LC under ll enmel surfce preprtion conditions (Tble ). The results lso showed tht wet unconditioned surfces consistently produced higher sher bond strengths thn did dry unconditioned surfces. Wet or dry conditioned surfces, however, produced higher sher bond strengths thn did unconditioned wet or dry surfces. With the exception of Fuji Ortho LC dry conditioned nd GC Fuji Ortho dry unconditioned, sher bond strengths were higher t seven dys thn those recorded t 4 hours. In ddition, GC Fuji Ortho produced sher bond strengths tht were comprble with those of Phse II when the surfces were wet or dry nd conditioned with polycrylic cid (Tble ). When comprisons were mde between Fuji light cured nd GC Fuji Ortho pplied under similr surfce conditioning t 4 hours nd seven dys, it ws found, with one exception, tht there were no significnt differences between the cements (Tble ). The exception noted ws tht fter seven dys, GC Fuji Ortho demonstrted significntly higher sher bond strength thn did Fuji light cured, where the enmel surfce hd been dried nd conditioned with polycrylic cid, P.5. On the other hnd, withinmteril comprisons for the glss ionomer cement mterils between 4 hours nd seven dys showed tht significnt differences existed in sher bond strength for Fuji Ortho light-cured wet conditioned nd wet unconditioned nd for GC Fuji Ortho wet conditioned enmel surfces (Tble ). In ll three instnces, there ws n increse in sher bond strength. It should be noted, however, tht sher bond strength incresed over seven dys wherever the enmel surfce hd been conditioned. Resin loction The error study, to determine whether differences existed when ssigning ARI scores, showed tht there ws strong interopertor (r.9; P.8) nd intropertor greement over two time periods (r.98; P.). The men ARI scores for ech of the test conditions re shown in Tble 4. The Kruskl-Wllis nonprmetric ANOVA nd Spermn correltion tests indicted tht in generl liner reltionship existed between the men sher bond strength nd ARI scores for ech time intervl. In other words, s Angle Orthodontist, Vol, No 4,

5 44 COUPS-SMITH, ROSSOUW, TITLEY TABLE. Comprison of the Effect of the Mteril When the Environment nd the Surfce Tretment re Constnt t 4 h nd d Time n Environment/Surfce Tretment Men SBS SD (MP) Fuji Ortho LC GC Fuji Ortho P vlue 4 h d /conditioned /unconditioned Wet/conditioned Wet/unconditioned /conditioned /unconditioned Wet/conditioned Wet/unconditioned * SD indictes stndrd devition; SBS, sher bond strength. * Sttisticlly significnt difference (P.5). TABLE. Comprison of the Effect of the Time when the Mteril, the Environment, nd the Surfce Tretment re Constnt Mteril n Environment/Surfce Tretment Men SBS SD (MP) 4 h d P vlue Fuji Ortho LC GC Fuji Ortho /conditioned /unconditioned Wet/conditioned Wet/unconditioned /conditioned /unconditioned Wet/conditioned Wet/unconditioned *.* *.644 SD indictes stndrd devition; SBS, sher bond strength. * Sttisticlly significnt difference (P.5). TABLE 4. The Comprison of Men Sher Bond Strengths (MP) nd the Distribution of ARI scores for ech Test Condition Time Mteril n Men SD (MP) ARI Score Men ARI SD 4 h Trnsbond XT dry/etched Phse II dry/etched Fuji Ortho LC dry/conditioned Fuji Ortho LC dry/unconditioned Fuji Ortho LC wet/conditioned Fuji Ortho LC wet/unconditioned GC Fuji Ortho dry/conditioned GC Fuji Ortho dry/unconditioned GC Fuji Ortho wet/conditioned GC Fuji Ortho wet/unconditioned d Trnsbond XT dry/etched Phse II dry/etched Fuji Ortho LC dry/conditioned Fuji Ortho LC dry/unconditioned Fuji Ortho LC wet/conditioned Fuji Ortho LC wet/unconditioned GC Fuji Ortho dry/conditioned GC Fuji Ortho dry/unconditioned GC Fuji Ortho wet/conditioned GC Fuji Ortho wet/unconditioned SD indictes stndrd devition; ARI, Adhesive Remnnt Index. Angle Orthodontist, Vol, No 4,

6 GLASS IONOMER CEMENTS FOR ORTHODONTIC BONDING 44 the men sher bond strength increses so does the ARI score becuse these vribles re positively correlted. SEM results The results of SEM of both brcket nd enmel surfces illustrte the ARI scores where the luting mteril used ws Fuji Ortho LC. An exmple of n ARI score of shows tht ll the cement is left dhering to the brcket bse with none on the enmel surfce (Figure,b). An ARI score of indicted tht less thn hlf the dhesive ws left on the enmel surfce (Figure,b). A score of indicted tht more thn hlf the dhesive ws left on the tooth (Figure,b), nd score of showed tht ll the dhesive ws left on the tooth with distinct impression of the brcket mesh (Figure 4,b). Similr criteri were used to ssess ARI scores for both glss ionomer cements nd resin control cements. DISCUSSION It hs been shown in this study tht embedded bovine incisor teeth cn be reused in studies to ssess men sher bond strengths of orthodontic brckets to enmel. This finding is both cost-effective nd time sving becuse bovine incisor teeth re expensive to hrvest nd the embedding process cn tke considerble mount of time. Cre must be tken, however, to ensure tht no dentin is exposed during the regrinding of the enmel surfce. A bonded brcket must withstnd both the forces of mstiction nd the orthodontic forces tht it is subjected to in the orl environment. It is lso clinicl requirement tht the bond should rech sufficient strength shortly fter brcket bonding to llow rchwire plcement t the bonding ppointment. This mechnochemicl bond must be durble enough to lst over the period of ctive tretment. It hs been estblished tht tensile bond strengths of dhesives in the rnge of six to eight MP re required for successful clinicl bonding. 6 It hs lso been determined tht there is no significnt difference (P.5) in the stress required to produce bond filure by either tensile or sher test model. It is thus not unresonble to use these guidelines when considering the sher bond strengths recorded in this study. 9 The results of this study show tht in wet or dry environment, with conditioned enmel surfces (either polycrylic or phosphoric cid), sher bond strengths of the mgnitude required for clinicl success cn be chieved. The evidence tht glss ionomer cements cn be plced in wet environment is equivocl. Silvermn et l showed tht brckets cn be plced successfully in wet environment, wheres Rossouw et l demonstrted tht the presence of contminnts such s sliv severely compromises sher bond strength. The results further indicted tht bond strengths incresed from 4 hours to seven dys, but in ll instnces, the initil short-term sher bond strengths exceeded the minimum requirements outlined by Reynolds. 6 FIGURE. ARI score of showing () no dhesive on enmel surfce nd (b) ll the dhesive on brcket bse. Angle Orthodontist, Vol, No 4,

7 44 COUPS-SMITH, ROSSOUW, TITLEY FIGURE. ARI score of showing () less thn 5% dhesive, but not, on enmel surfce nd (b) more thn 5% dhesive on brcket bse. FIGURE. ARI score of showing () more thn 5% dhesive, but not %, on enmel surfce nd (b) less thn 5% dhesive on brcket bse. Angle Orthodontist, Vol, No 4,

8 GLASS IONOMER CEMENTS FOR ORTHODONTIC BONDING 44 There is thus no pprent contrindiction to plcing rchwires t the initil bonding ppointment when using glss ionomer cements s the cementing medium. Cution should be exercised becuse too high sher bond strength levels crry the consequent risk of enmel frcture during the debonding process. It hs been shown tht this cn occur with tensile bond strengths s low s 9. MP. 9, No enmel frctures were recorded s result of sher bond strength testing to filure in this study, despite the fct tht 6 of groups of specimens demonstrted men sher bond strengths greter thn 9. MP. It should further be noted tht these groups included both the resin controls nd the glss ionomer cements. The use of rotry instruments to remove residul cement fter brcket debonding my dmge the enmel surfce. Becuse the superficil enmel surfce hs lso been shown to be rich in fluoride, removl of dherent residul cement my lso compromise future cries resistnce. This study hs confirmed tht the ARI system is user-friendly nd esy to interpret, despite the criticism tht it is subjective evlution. As result it hs been shown tht low ARI score is the preferred result fter debonding becuse it indictes tht the mount of dhesive remining on the enmel surfce is miniml nd tht the risk of itrogenic dmge to the enmel surfce is minimized. The results obtined in this study indicte tht s sher bond strength decreses so does the ARI score, indicting tht less cement is left dhering to the enmel. The scnning electron microscopic observtions support these findings. The sher bond strengths, however, indicte tht these cements meet the clinicl requirements recommended by Reynolds. 6 Similrly, becuse glss ionomer cements contin nd lech fluoride, nd tht the fluoride content cn be restored by topicl ppliction, residul retined cement my not be disdvntge, provided tht ptient esthetics re not compromised.,,4 The results of this study suggest tht glss ionomer cements provide sufficiently high sher bond strengths to retin orthodontic brckets under clinicl conditions nd, t the sme time, could provide reservoir of fluoride, thereby reducing the criogenic potentil of plque-retining orthodontic ttchments. REFERENCES FIGURE 4. ARI score of showing () ll the dhesive on enmel surfce with imprint of bse design in cement nd (b) no dhesive on brcket bse except tht in the retentive foil mesh. Compre with Figure b.. Beton WG. Cermic brckets. Ont Dent. 99;6:4 5.. Fields HW. Bonded resins in orthodontics. Peditr Dent. 98;4: Fricker JP. A month clinicl evlution of light ctivted glss polylkenote (ionomer) cement for the direct bonding of orthodontic brckets. Am J Orthod Dentofcil Orthop. 994;5: Buonocore MG. A simple method of incresing the dhesion of crylic filling mterils to enmel surfces. J Dent Res. 955;4: Newmn GV. Epoxy dhesives for orthodontic ttchments. Progress report. Am J Orthod. 965;5:9. Angle Orthodontist, Vol, No 4,

9 444 COUPS-SMITH, ROSSOUW, TITLEY 6. Reynolds IR. A review of direct orthodontic bonding. Br J Orthod. 95;: 8.. Proffit WR. Contemporry Orthodontics. St Louis, MO: CV Mosby Co.; 986: Newmn GV. Adhesion nd orthodontic plstic ttchments. Am J Orthod. 969;56: Ostertg AJ, Dhuru VB, Ferguson DJ, Meyer RA. Sher, torsionl, nd tensile bond strengths of cermic brckets using three dhesive filler concentrtions. Am J Orthod Dentofcil Orthop. 99;: Schiffer A, Jost-Brinkmnn PG, Miethke RR. The tensile strength of brcket dhesives depending on the dhesive lyer thickness n in vitro study. Fortschr Kieferorthop. 99;5:9.. Zchrisson BU. Bonding in orthodontics. In: Grber TM, Vnrsdll RL, eds. Orthodontics Current Principles nd Techniques. St. Louis, MO: Mosby-Yer Book Inc.; 994: Urbe H, Rossouw PE, Titley K, Ymin C. The effect of different cid conditioning gents on metl, cermic, nd polycrbonte brckets bonded to bovine enmel. Angle Orthod. 999;69:6 4.. Diedrich P. Enmel ltertions from brcket bonding nd debonding: study with the scnning electron microscope. Am J Orthod. 98;9: Wng WN, Lu TC. Bond strength with vrious etching times on young permnent teeth. Am J Orthod Dentofcil Orthop. 99; : Koch G, Freiberger P. Fluoride content of outermost enmel lyers in teeth exposed to topicl fluoride ppliction. Odontol Revy. 9;: Koch G, Petersson LG. Fluoride content of enmel surfce treted with vrnish contining sodium fluoride. Odontol Revy. 9; : Brown CR, Wy DC. Enmel loss during orthodontic bonding nd subsequent loss during removl of filled nd unfilled dhesives. Am J Orthod. 98;4: McColl G. The Reltionship Between Bond Strength nd Bse Surfce Are Using Conventionl nd Micro-Etched Foil-Mesh Bses [diplom thesis]. Toronto, Ontrio: Fculty of Dentistry, University of Toronto; Zchrisson BU, Zchrisson S. Cries incidence nd orl hygiene during orthodontic tretment. Scnd J Dent Res. 9;9: Ogrd B, Roll G, Arends J. Orthodontic pplinces nd enmel deminerliztion Prt I: Lesion development. Am J Orthod Dentofcil Orthop. 988;94:68.. McCourt JW, Cooley RL, Brnwell S. Bond strength of light cure fluoride-relesing bse-liners s orthodontic brcket dhesives. Am J Orthod Dentofcil Orthop. 99;:4 5.. Silvermn E, Cohen M, Semke RS, Silvermn M. A new lightcured glss ionomer cement tht bonds brckets to teeth without etching in the presence of sliv. Am J Orthod Dentofcil Orthop. 995;8: 6.. Geiger AM, Gorelick L, Gwinnett AJ, Benson BJ. Reducing white spot lesions in orthodontic popultions with fluoride rinsing. Am J Orthod Dentofcil Orthop. 99;: Kusy R. Letter to the editor. Am J Orthod Dentofcil Orthop. 994;6:A. 5. Cook PA. Direct bonding with glss ionomer cement. J Clin Orthod. 99;8: Fjen VB, Duncnson MG, Nnd RS, Currier GF, Angolkr PV. An in vitro evlution of bond strength of three glss ionomer cements. Am J Orthod Dentofcil Orthop. 99;9:6.. Rezk-Leg F, Ogrd B, Arends J. An in vitro study on the merits of two glss ionomers for the cementtion of orthodontic bnds. Am J Orthod Dentofcil Orthop. 99;99: Artun J, Berglnd S. Clinicl trils with crystl growth conditioning s n lterntive to cid-etch enmel pretretment. Am J Orthod. 984;85: Fowler CS, Swrtz ML, Moore BK, Rhodes BF. Influence of selected vribles on dhesion testing. Dent Mter. 99;8: Rossouw PE, Penuvchev AV, Kulkrni K. The influence of vrious contminnts on the bonding of orthodontic ttchments. Ont Dent. 996;:5.. Retief DH. Filure t the dentl dhesive-etched enmel interfce. J Orl Rehbil. 94;: Zrrinni K, Eid NM, Kehoe MJ. The effect of different debonding techniques on the enmel surfce: n in vitro qulittive study. Am J Orthod Dentofcil Orthop. 995;8: Brudevold F, Grdner DE, Smith FA. The distribution of fluoride in humn enmel. J Dent Res. 956;5: Forsten L. Fluoride relese from glss ionomer cement. Scnd J Dent Res. 99;85:5 55. Angle Orthodontist, Vol, No 4,