Effect of Light-Emitting Diode on Bond Strength of Orthodontic Brackets

Transcription

1 Originl rticle Effect of Light-Emitting Diode on Bond Strength of Orthodontic Brckets Serdr Üşümez, DDS, PhD ; Tmer Büyükyilmz, DDS, MSD b ; li İhy Krmn, DDS, PhD c bstrct: The im of this study ws to evlute the effect of light-emitting diode (LED) light curing on sher bond strength (SBS) of orthodontic brckets bonded to teeth. Light exposure of 40 seconds from conventionl hlogen-bsed light-curing unit ws used s control. Eighty humn premolrs were divided into four groups of 0 ech. Brckets were bonded to cid-etched teeth with Trnsbond XT light-cured dhesive. In the first group, the dhesive ws light cured for 40 seconds with conventionl hlogen unit (XL3000, 3M). In the other three groups, dhesive ws cured with commercil LED unit (Elipr FreeLight, 3M ESPE) for 0, 0, or 40 seconds. SBS of brckets ws mesured on universl testing mchine nd recorded in megpscls. dhesive remnnt index (RI) scores were determined fter filure of brckets. Dt were nlyzed using nlysis of vrince nd chi-squre tests. No sttisticlly significnt differences were found mong the SBS vlues of hlogen-bsed light-cured (3. 3. MP) nd 0- nd 40-second LED-cured ( MP nd.7 5. MP) specimens (P.05). However, 0 seconds of LED curing yielded significntly lower SBS (P.05). No sttisticlly significnt differences were found between the RI scores mong groups. The results of this study re promising for the orthodontic ppliction of LED-curing units, but further comptibility nd physicl chrcteristic studies of vrious orthodontic dhesives nd clinicl trils should be performed before vlidtion. (ngle Orthod 004;74:59 63.) Key Words: LED; Bond strength; Brcket bonding INTRODUCTION The desire to cure on demnd is driving n incresing number of orthodontic prctices to use light-cure dhesives insted of the more trditionl two-pste dhesives tht require in-office mixing. In light-cure dhesives, the curing process begins when photoinititor is ctivted. The first products were cured with ultrviolet light nd the lter versions with visible light, which hs wvelength between 400 nd 500 nm. n dvntge of visible light is the greter depth of polymeriztion chieved in shorter periods. Most dentl photoinititor systems use cmphoroquinone s the diketone bsorber, with the bsorption mximum in the blue region of the visible light spectrum t wvelength ssistnt Professor, Deprtment of Orthodontics, Fculty of Dentistry, Selçuk University, Kony, Turkey. b ssocite Professor, Deprtment of Orthodontics, Fculty of Dentistry, Selçuk University, Kony, Turkey. c ssocite Professor nd Hed, Deprtment of Orthodontics, Fculty of Dentistry, Selçuk University, Kony, Turkey. Corresponding uthor: Serdr Üşümez, DDS, PhD, Deprtment of Orthodontics, Fculty of Dentistry, Selçuk University, Cmpus, Kony 4079, Turkey (e-mil: susumez@hotmil.com). ccepted: My 003. Submitted: Mrch by The EH ngle Eduction nd Reserch Foundtion, Inc. of 470 nm. Currently, the most populr method of delivering blue light is the use of hlogen-bsed light-curing units. 3 Hlogen bulbs produce light when electric energy hets smll tungsten filment to high tempertures. 4 Despite their common use in dentistry, hlogen bulbs hve severl disdvntges. The bsic principle of light conversion by this technique is inefficient becuse the light power output is less thn % of the consumed electricl power nd becuse they hve limited effective lifetime of pproximtely 00 hours due to the degrdtion of the bulb s components by the high het generted. 3,5 7 In 995, Mills et l 3 proposed solid-stte light-emitting diode (LED) technology for the polymeriztion of lightctivted dentl mterils to overcome the shortcomings of hlogen visible light curing units. LEDs use junctions of doped semiconductors to generte light insted of the hot filments used in hlogen bulbs. 8 LEDs hve lifetime of over 0,000 hours nd undergo little degrdtion of output over this time. 9 LEDs require no filters to produce blue light, re resistnt to shock nd vibrtion, nd tke little power to operte. 3 LEDs longer lifespn nd more consistent light output compred with hlogen bulb technology show promise for dentl pplictions. 4 Previous reserch 3,0, on the dentl ppliction of LEDs compred with hlogen-bsed light-curing units demon- 59 ngle Orthodontist, Vol 74, No, 004

2 60 ÜŞÜMEZ, BÜYÜKYILMZ, KRMN TBLE. Light-Curing Units Tested Light Type Tip (mm) Energy Consumption Power Density (mw/cm ) Seril No. XL 3000 Elipr FreeLight Hlogen Light-emitting diode W 0.75 W in stndby mode Power densities re mnufcturer informtion (3M Espe). strted tht, t the sme irrdince, LEDs perform s well s or better thn hlogen lights. recent study by Dunn nd Tloumis 4 demonstrted tht the two different commercil LED light curing units provided power density of 50 mw/cm bonded brckets to etched tooth enmel s well s hlogen-bsed light-curing units. However, Dunn nd Tloumis suggested tht dditionl clinicl studies should be performed before routine use of commercil LED light curing units cn be recommended for orthodontic bonding. There is lck of informtion bout the comptibility of LEDs with orthodontic dhesives nd the optimum curing time required. Moreover, review of the literture reveled no studies bout effect of LED curing on orthodontic dhesives with vrious exposures times. The im of this study ws to evlute the effect of 0, 0, nd 40 seconds of LED light curing from commercil curing unit, which opertes t power density of 400 mw/ cm, on the sher bond strength (SBS) of orthodontic brckets bonded to teeth. Light exposure of 40 seconds from conventionl hlogen-bsed light-curing unit ws used s control. MTERILS ND METHODS Eighty noncrious humn premolrs extrcted for orthodontic indictions were used in this study. Teeth with hypoplstic res, crcks, or gross irregulrities of the enmel structure were excluded from the study. The teeth were stored in distilled wter fter extrction. The wter ws chnged weekly to void bcteril growth. The smple ws rndomly divided into four groups of 0 teeth ech. Ech tooth ws mounted verticlly in self-cure crylic so tht the crown ws exposed. The buccl enmel surfces of the teeth were polished with nonfluoridted pumice nd rubber prophylctic cups nd then wshed nd dried before the bonding procedure. 37% phosphoric cid gel (Emil Preprtor, Vivdent, Liechtenstein) ws used to etch premolrs for 30 seconds. The teeth were then rinsed with wter for 30 seconds nd dried with n oil-free ir source for 0 seconds. In ll cses tht were etched, the frosty white ppernce of etched enmel ws noticed. Bonding Eighty stinless steel premolr brckets (Generous, GC, York, P) with mesh bse surfce re of.6 mm were used for this study. fter surfce preprtion, the brckets were bonded on premolrs with Trnsbond XT (3M Unitek, Monrovi, Clif), nd ny excess resin ws removed with n explorer before the resin ws polymerized. conventionl hlogen light source (XL3000, 3M Dentl Products, St Pul, Minn) ws used for curing for totl of 40 seconds (0 seconds from the mesil nd the distl side ech) in group. In groups, 3, nd 4 commercil LED curing light (Elipr FreeLight, 3M ESPE, Seefeld, Germny) ws used for 0, 0, nd 40 seconds, respectively (totl curing time ws hlved for equl curing times from the mesil nd the distl side ech). Both units hd builtin rdiometers for testing the dequcy of light intensity emitted. In the XL3000 unit, intensity ws confirmed by blinking its green LED before ech exposure. The Free- Light unit hs five-stge LED indictor, indicting the level of intensity of light emitted, with ll five LEDs being on when the intensity is t mximum. The light intensity of the LED unit ws t its mximum before ech exposure. Descriptive informtion bout the light sources nd their respective technicl informtion re given in Tble. fter complete smple preprtion, ll smples were kept in distilled wter t 37 C for 4 hours for short-term storge. Testing Before debonding, the embedded specimens were secured in jig ttched to the bse plte of universl testing mchine (Model 500, Testometric, Lncshire, UK). chisel-edge plunger ws mounted in the movble crosshed of the testing mchine nd positioned such tht the leding edge imed the enmel-dhesive interfce before being brought into contct t crosshed speed of 0.5 mm/min. The force required to dislodge the brckets ws mesured in Newtons, nd the SBS ( MP N/mm ) ws clculted by dividing the force vlues by the brcket bse re (.6 mm ). fter being debonded, the teeth nd brckets were exmined under 0 mgnifiction. ny dhesive tht remined fter brcket removl ws ssessed nd scored ccording to the modified dhesive remnnt index (RI). 3 Sttisticl nlysis Descriptive sttistics tht included the men nd stndrd devition vlues were clculted for the test groups. onewy nlysis of vrince (NOV) nd Duncn tests were used to determine whether significnt differences in the bond strengths were present mong the groups. The chisqure test ws used to determine significnt differences in ngle Orthodontist, Vol 74, No, 004

3 LIGHT-EMITTING DIODE CURING OF ORTHODONTIC BRCKETS TBLE. Descriptive Sttistics nd the Results of the Duncn s Multiple Rnge Test Compring the Sher Bond Strengths (in MP) of the Four Groups Tested Groups Tested XL 3000, 40 s FreeLight, 0 s FreeLight, 0 s FreeLight, 40 s Men Rnge (MP) SD (MP) Test* SD stndrd devition. * Groups with different letters re sttisticlly significntly different. B 6 TBLE 3. Frequency Distribution of the dhesive Remnnt Index (RI) Scores nd the Chi-Squre Comprison of the Four Groups Tested Groups Tested XL 3000, 40 s FreeLight, 0 s FreeLight, 0 s FreeLight, 40 s RI Scores n Test* Not significnt RI scores: ll of the composite, with n impression of the brcket bse, remined on the tooth; more thn 90% of the composite remined; 3 more thn 0% but less thn 90% of the composite remined on the tooth; 4 less thn 0% of composite remined on the tooth surfce; 5 no composite remined on the enmel. frequency of RI scores of (ll dhesive remined on tooth) in ll groups, which indicted tht filures were minly in the dhesive-brcket interfce. FIGURE. Probbility of filure of different curing methods t prticulr sher stress vlues. the RI scores mong groups. Significnce for ll sttisticl tests ws predetermined t probbility vlue of.05 or less. RESULTS Sher bond strength comprisons Tble shows the descriptive sttistics for the SBSs of the four groups tested. NOV reveled sttisticlly significnt differences mong the groups tested. Furthermore, Duncn tests reveled tht the bond strength vlues produced by the conventionl hlogen (3. 3. MP), 0- second LED ( MP), nd 40-second LED (.7 5. MP) groups were not sttisticlly different. However, SBS vlues of the 0-second LED group (9. 3. MP) were significntly lower thn those of the other test groups (P.05). The survivl grph (Figure ) indictes tht hlf the brckets remin bonded t 3 MP in the conventionl hlogen nd 0-second LED groups, t.5 MP in the 40- second LED group nd t nine MP in the 0-second LED group. RI comprisons The results of the chi-squre comprisons indicted tht there were no significnt differences between the four groups tested (Tble 3) (P.750). There ws greter DISCUSSION LEDs re being ggressively mrketed; however, independent reserch hs not yet verified the potentil of this technology to replce hlogen visible light curing units. 4 Optiml cure times for LEDs nd their bility to cure ll resins re still unknown. 4 number of studies hve confirmed the potentil of LED technology for the light ctivtion of dentl mterils. Fujibyshi et l 0, detected no differences in composite hrdness nd depth of cure between the LED nd hlogen unit nd obtined deeper cure with the LED of 470-nm wvelength thn with the hlogen light t 0, 0, 40, nd 60 seconds. Mills et l 3 compred light source contining 5 LEDs with hlogen unit djusted to n irrdince of 300 mw/cm. The LED unit cured composite specimens to significntly greter depth thn did the hlogen unit when tested t 40 nd 60 seconds. 3 The LED unit used in this study hd 9 LEDs plced in three respective plnes. Men power densities of the light-curing units used in this study re presented in Tble. The hlogen-bsed light-curing unit hd higher men power density thn the LED-curing unit. However, SBS vlues chieved with the sme (40 seconds) or lower (0 seconds) LED exposures were not sttisticlly different from hlogen-bsed curing light. Fujibyshi et l demonstrted tht the qulity of light polymeriztion is not exclusively due to the light intensity. The nrrow bsorption pek of the inititor system must lso be tken into ccount. This mkes the emitted spectrum n importnt determinnt of curing light s performnce. The bsorption curve of cmphoroquinine extends between 360 nd 50 nm, with its mximum t 465 nm. It hs been shown tht within this rnge, the optiml emission bndwidth of the light source lies between 450 nd 490 nm. 5 With conventionl curing devices, mjor portion of the photons is emitted outside the optiml spec- ngle Orthodontist, Vol 74, No, 004

4 6 ÜŞÜMEZ, BÜYÜKYILMZ, KRMN trum rnge for light curing. These photons cnnot, or cn only with reduced probbility, be bsorbed by cmphoroquinine. In contrst, 95% of the emission spectrum of blue LEDs is situted between 440 nd 500 nm. Furthermore, the emission mximum of the blue LEDs used in this study is pproximtely 465 nm, which is lmost identicl to the bsorption pek of cmphoroquinine. These fctors my explin the similr SBS vlues obtined by LED with shorter exposure. t cliniclly relistic irrdinces, modestly greter depth of cure ws found when composites were polymerized with n LED lmp in comprison with hlogen lmp, despite the former hving mesured output pproximtely 70% of the ltter (76 vs 388 mw/cm when mesured between 40 nd 500 nm). 3 Knezevic et l 6 demonstrted only minor increse in conversion degree vlues when 66 stronger hlogen-curing units were compred with n LED with miniml intensity of mw/cm. This finding lso supports the importnce of considering the emission spectr of curing lmps reltive to the bsorption spectrum of cmphoroquinine when ssessing the qulity of light polymeriztion. The RI scores indicted tht, regrdless of light-curing type, most of the composite remined on the tooth fter brcket debonding. This type of filure suggests tht the wek link in the dhesive chin ws between the brcket bse nd the composite. This implies tht resin penetrted into the undercuts of the brcket bse nd ws unble to resist the sher stresses when not fully cured. However, this sitution does not bis the dt becuse the sme dhesive ws used for ll test groups, nd the reserch prmeter is the bility of different light source curing time combintions to polymerize this dhesive. Regrding sttisticlly significnt differences between short nd long curing times, it is cler tht the dherence of composite to the brcket bse ws relted to the cure of the resin. The bond between etched enmel nd composite ws generlly dequte with ny of the light-curing units evluted. ccording to the results of previous reserch, commercil LED-curing units do not polymerize ny fster thn hlogen-bsed lights. 4 However, the present study suggests tht 0 seconds of LED exposure my yield SBS vlues comprble with those obtined by hlogen-bsed units in 40 seconds. On the other hnd, when these results re compred with those of previous reserch, this commercil LED does not polymerize fster thn xenon plsm lmps. 7 Xenon plsm rc lights hve demonstrted mrkedly reduced curing times: exposures of six to nine seconds produce SBSs nd surfce hrdness vlues equl to those produced with 40-second exposures to conventionl tungsten-qurtz hlogen light. 7,8 The LEDs, however, hve certin dvntges over both hlogen- nd plsm rc curing lights. They re cordless, smller, nd lighter, with estimted lifetimes of over 0,000 hours, nd they do not require noisy cooling fn. 9 Moreover, LED technology is still developing, nd high-intensity LED-curing lights re being introduced to the mrket. ccording to Dunn nd Tloumis, 4 hlogen-bsed light-curing units my be replced by LEDs s semiconductor technology improves. Consequently, lbortory studies involving LED technology will increse. The lbortory ssessment of bond strength cnnot predict clinicl performnce, but it is vluble screening tool. The results of this study re promising for the orthodontic ppliction of LED-curing units, but further comptibility nd physicl chrcteristic studies of vrious orthodontic dhesives nd clinicl trils should be performed before vlidtion. Studies re under wy in our clinic to test the comptibility of different dhesives with LEDs under clinicl conditions. CONCLUSIONS This study investigted the effect of 0, 0, nd 40 seconds of LED exposure on the SBS of orthodontic brckets nd used 40 seconds of hlogen-bsed light exposure s control. Within the limittions of this study, the results suggest tht LED curing of 0 nd 40 seconds yields SBS vlues tht re sttisticlly similr to those of 40 seconds of hlogen-bsed curing in vitro. However, 0 seconds of LED curing resulted in significntly decresed SBS vlues. There were no significnt differences in the RI scores of ny of the light-curing units tested. Most of the remnnt composite dhesive remined on the etched enmel surfce. REFERENCES. Tirth R, Fn LP, Dennison JB, Powers JM. In vitro depth of cure of photo-ctivted composites. J Dent Res. 98;6: lthoff O, Hrtung M. dvnces in light curing. m J Dent. 000;3:77D 8D. 3. Mills RW, Jndt KD, shworth SH. Dentl composite depth of cure with hlogen nd blue light emitting diode technology. Br Dent J. 999;86: Dunn WJ, Tloumis LJ. 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5 LIGHT-EMITTING DIODE CURING OF ORTHODONTIC BRCKETS. Interntionl Orgniztion for Stndrdiztion. ISO TR 405 Dentl Mterils Guidnce on Testing of dhesion to Tooth Structure. Genev, Switzerlnd: WHO; Olsen ME, Bishr SE, Dmon P, Jkobsen JR. Evlution of Scotch bond multi-purpose nd mleic cid s lterntive methods of bonding orthodontic brckets. m J Orthod Dentfcil Orthop. 997;: Clinicl Reserch ssocites. Resin curing lights, new LED technology. Clin Res ssoc Newslett. 00;5. 5. Nomoto R. Effect of light wvelength on polymeriztion of lightcured resins. Dent Mter J. 997;6: Kenezevic, Trle Z, Menig, Sutlo J, Pichler G. Degree of conversion nd temperture rise during polymeriztion of composite resin smples with blue diodes. J Orl Rehbil. 00;8: Oesterle LJ, Newmn SM, Shellhrt WC. Rpid curing of bonding composite with xenon plsm rc light. m J Orthod Dentofcil Orthop. 00;9: Üşümez S, Buyukyılmz T, Krmn I. Effect of fst hlogen nd plsm rc light on the surfce hrdness of orthodontic dhesives for lingul retiners. m J Orthod Dentofcil Orthop. 003;3: ngle Orthodontist, Vol 74, No, 004