Temperature Rise During Orthodontic Bonding With Various Light-curing Units An In Vitro Study

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1 Originl Article Temperture Rise During Orthodontic Bonding With Vrious Light-curing Units An In Vitro Study Aslihn Uzel ; Tmer Buyukyilmz b ; Mustf Kylioglu c ; Ilter Uzel d ABSTRACT The purpose of this in vitro study ws to investigte the temperture chnges in the pulp chmber during brcket bonding using three different light sources. Brcket bonding ws performed on one lower first premolr nd one lower centrl incisor t two different distnces (surfce nd 10 mm). The mesurements were tken with J-type thermocouple wire, plced in the pulp chmber nd connected to dt logger. Anlysis of vrince reveled tht pulp chmber temperture chnges were influenced by the light source, the tooth type, nd the distnce from the tip of the light guide to the brcket surfce. Hlogen induced significntly higher intrpulpl temperture chnges thn light-emitting diode nd Xenon Plsm Arc (PAC) (P.000). The temperture increse ws significntly higher when the light-guide tip ws positioned t the surfce of the teeth thn t the 10-mm distnce with ll light-curing units (P.000). All light-curing units produced higher intrpulpl temperture increse in the mndibulr incisor thn in the premolr. Power PAC produced significntly higher het chnges in the incisor thn in the premolr. Orthodontic bonding with different light-curing units did not exceed the criticl 5.5 C vlue for pulpl helth. (Angle Orthod 2006;76: ) KEY WORDS: Temperture rise; Pulp chmber; Orthodontic bonding; Light curing INTRODUCTION The light-initited resins hve become the most populr dhesives for mjority of orthodontists becuse of the reduced contmintion risk, ccurte brcket plcement, nd esier excess dhesive removl during bonding. 1 7 In the 1990s, rpid light-curing lterntives for conventionl hlogen units, such s Qurtz Tungsten Hlogen (QTH), Xenon Plsm Arc (PAC), nd the light-emitting diode (LED), were introduced in orthodontics, prllel with generl dentistry. 2 4,6 8 However, concerns hve been rised tht these new cur Lecturer, Deprtment of Orthodontics, Fculty of Dentistry, University of Cukurov, Adn, Turkey. b Associte Professor, Deprtment of Orthodontics, Fculty of c Reserch Assistnt, Deprtment of Orthodontics, Fculty of d Professor nd Hed, Deprtment of Orthodontics, Fculty of Corresponding uthor: Aslihn Uzel, DDS, PhD, Deprtment of Orthodontics, Fculty of Dentistry, Çukurov University, Blclı, Adn 01330, Turkey (e-mil: sliuzel@cu.edu.tr) Accepted: April Submitted: Mrch by The EH Angle Eduction nd Reserch Foundtion, Inc. ing lights my induce temperture rise tht could be detrimentl to pulp vitlity during photoctivtion. It is known tht ny increse in pulpl temperture exceeding 5 C to6 C my result in irreversible tissue dmge. 9 Previous in vitro studies hve shown the therml effect of different light sources in generl dentistry Goodis et l 17 tested six visible light curing units nd found tht the lmps do cuse temperture rise within the pulp chmber, nd the longer the lmp is used, the higher the temperture rise. Hnnig nd Bott 18 used Clss II restortive preprtion on molr nd mesured the temperture chnges in the pulp chmber with eight different curing units. Their findings indicte tht the potentil risk for het-induced pulpl injury during composite resin polymeriztion is incresed with the high-energy light sources when compred with the low-energy light-curing units. Powell et l 16 showed tht in vitro pulp chmber temperture increse from lser units were significntly lower thn tht from the conventionl curing lights. Trle et l 19 mesured the temperture rise in the composite smples with three different light sources, nd becuse of very short exposure time, they found slight temperture rise with the high-power plsm light. Such investigtions showed tht het genertion my vry depending on the light source, exposure 330

2 TEMPERATURE RISE WITH VARIOUS LIGHT-CURING UNITS TABLE 1. Group Experimentl Groups of the Study Number of Mesurements Tooth Type Light-curing Unit Distnce I 5 Premolr Hlogen Surfce II 5 Premolr Hlogen 10 mm III 5 Premolr LED Surfce IV 5 Premolr LED 10 mm V 5 Premolr PAC Surfce VI 5 Premolr PAC 10 mm VII 5 Lower incisor Hlogen Surfce VIII 5 Lower incisor Hlogen 10 mm IX 5 Lower incisor LED Surfce X 5 Lower incisor LED 10 mm XI 5 Lower incisor PAC Surfce XII 5 Lower incisor PAC 10 mm LED indictes light-emitting diode; PAC, Xenon Plsm Arc. time, composite resin thickness relted exothermic rection, nd the distnce between the light source nd the pulp. 10,17,20,21 However, there re severl fctors in restortive dentistry tht vry from those in orthodontic bonding procedures. 3 First, in bonding orthodontic brckets or retiners, the distnce from the pulp is greter becuse of the lck of ny cvity on the insulting enmel. Second, the orthodontic ttchments (brckets, tubes, etc) re present between the light sources nd the enmel. Third, the dhesive lyer is very thin, pressed between the brcket nd the tooth. Oesterle et l 3 crried out n unpublished pilot study nd suggested using the xenon plsm light with short durtions, especilly on teeth tht hve thin enmel such s the lower incisors. However, the pulp temperture chnge fter curing with different light sources nd their effect on tooth type hs not been investigted for orthodontic bonding procedures. The im of this in vitro study ws to investigte the temperture chnges in the pulp chmber of premolr nd lower incisor during brcket bonding using three different light sources. 331 MATERIALS AND METHODS In this in vitro study, two different types of humn teeth (premolr nd lower incisor) were irrdited t two different distnces (surfce nd 10 mm) with three visible light curing units. Twelve experimentl groups were prepred (Tble 1). A single-root lower first premolr nd lower centrl incisor were used in ll experimentl trils. Brckets (Omni Arch, GAC, Bohemi, NY) were bonded using Trnsbond XT (3M/Unitek, Monrovi, Clif) dhesive nd light cured with Hlogen light for 40 seconds, with LED light for 20 seconds, nd with Plsm Arc light for five seconds. The light units nd technicl detils re shown in Tble 2. Orthodontic bonding ws performed without cid etching to enble n esy removl of the brcket nd to void enmel loss during repeted debonding procedures. In pilot study, we tested the effect of cid etching on the pulp chmber temperture chnges. A different lower premolr ws bonded five times with cid etching using the plsm rc, nd surfce nd pulpl tempertures were mesured s described bove. The men vlues of the temperture increses were (with cid etching) nd (without cid etching, V group). Mnn-Whitney U-test did not indicte sttisticlly significnt differences between both vlues. Therefore, ll further mesurements were tken without cid etching. Light exposures were performed ccording to the mnufcturers instructions (Tble 2). For temperture mesurements, the roots of the premolr nd the incisor were resected nd pulp residues were removed retrogrde. A J-type 0.36-inchdimeter thermocouple wire (Omeg Engineering Inc, Stmford, Conn) ws inserted into the pulp chmber of the smple tooth to mesure temperture chnges. The thermocouple mintined contct with the dentin by thin lyer of silicone het-trnsfer compound (ILC P/N , Wkefield Engineering, Wkefield, Mss). Its position in the pulp chmber ws checked rdiogrphiclly. The root stub ws then secured with composite resin, nd the smple tooth ws mounted in the cover plte of wter bth ( C) (Nuve, Ankr, Turkey). The thermocouple wire ws connected to dt logger (XR440-M Pocket Logger, Pce Scientific, Mooresville, NC) during the brcket bonding procedure. Intrpulpl temperture chnges were recorded every two seconds. The recordings were strted t the sme time with light curing nd were ended when the temperture hd strted to drop from its mximum level. The collected dt, vilble in both tbulr nd grphic form, were monitored in rel time nd trnsferred to computer. TABLE 2. Light Sources Used in the Study Light-curing Unit Output of Light Tip (mw/cm 2 ) Dimeter of Tip (mm) Smrt-lite Dentl Curing Light (Benlioglu Dentl Inc, Ankr, Turkey) Ortholux LED Curing Light (3M/Unitek Orthodontic Products, Monrovi, Clif) Power PAC Plsm Curing Light (Americn Medicl Technologies, Corpus Christi, Tex) LED indictes light-emitting diode; PAC, Xenon Plsm Arc. Exposure Time (s)

3 332 A. UZEL, BUYUKYILMAZ, KAYALIOGLU, I. UZEL TABLE 3. Results of ANOVA Compring Men Vlues of Temperture Increses of Experimentl Groups Light-curing Unit Tooth Type Surfce Temperture Increse ( C) 10 mm Hlogen Lower premolr * * Lower incisor * * LED Lower premolr * * Lower incisor * * PAC Lower premolr * * Lower incisor * * LED indictes light-emitting diode; PAC, Xenon Plsm Arc; ANOVA, nlysis of vrince. * Distnce difference significnt (P.001), Curing unit difference significnt (P.001), Tooth type difference significnt (P.05). Five mesurements were obtined from ech group. The difference between the strting nd the highest temperture redings ws tken, nd the five clculted temperture chnges were verged to determine the men temperture increse. The light outputs of the curing units were checked before ech testing procedure with Hilux rdiometer (Benlioglu Dentl, Ankr, Turkey). Although the hndheld rdiometers mesure the light output within nrrow bnd, this ws used to mesure the wvelengths considered effective for curing. 22 There ws no mesurble reduction in light intensity for ny light during the experiment. Anlysis of vrince (ANOVA) ws performed to determine the effect of tooth type, light-curing unit, nd distnce on the temperture rise. The post hoc nlyses were mde using the lest significnt difference (LSD) test to determine which groups were significntly different. SPSS 10.1 (Chicgo, Ill) ws used for ll sttisticl nlyses in which P.05 ws dpted s the criticl significnce level. FIGURE 1. Temperture increses in the pulp chmber of the premolr nd the incisor with three light sources t two distnces. RESULTS Tble 3 shows men vlues, stndrd devitions, nd the sttisticl significnces of the temperture increse for ll the three vribles (light-curing unit, tooth type, nd distnce). The ANOVA nd LSD tests reveled tht pulp chmber temperture chnges were influenced by the light-source type, tooth type, nd the distnce from the tip of the light guide to the brcket surfce. Hlogen induced significntly higher intrpulpl temperture chnges thn did the LED nd PAC (P.000). The difference between Hlogen nd PAC ws sttisticlly significnt t ll but the 10-mm distnce. When the light-guide tip ws positioned t the surfce of the lower incisor, there ws no sttisticlly significnt difference between LED nd PAC. The lower incisor ws ffected more thn the premolr, but the differences were sttisticlly significnt only with PAC t two distnces (P.001) nd with LED t the 10-mm distnce (P.05). The temperture incresed significntly more t the surfce thn t the 10-mm distnce with ll light-curing units (P.000). The grphic presenttion of the results is shown in Figure 1. DISCUSSION The therml effect of light sources is well known, but informtion bout pulp chmber temperture chnges during orthodontic bonding procedures is scrce. Publictions in restortive dentistry showed tht the direct comprison of the light sources het effect is very difficult, if not impossible, becuse of the gret vribility of investigted mterils nd exposure times. Trle et l 19 found tht high-power plsm light leds to lower temperture increses thn do Hlogen or LED in composite smples becuse of very short exposure time. However, the results of other studies showed tht light source with high-energy output (Plsm Arc Light) cused significntly higher temperture chnges thn with the low-energy output lights (Hlogen nd LED) under dentin disks. 23,24 Hofmnn et l, 11 using deflecting disc technique, recorded tht the heting from rdition during polymeriztion ws lower with LED light thn with QTH. Studies on pulpl het chnges were lso different in severl spects. Weerkoon et l 10 exmined the het chnges ssocited with stndrdized Clss V restortions on the buccl surfce of extrcted pre-

4 TEMPERATURE RISE WITH VARIOUS LIGHT-CURING UNITS 333 molr teeth using curing time of 40 seconds. They concluded tht LED lights produced less therml insult on dentl pulp thn did the hlogen lmps. Hnnig nd Bott 18 studied Clss II restortive preprtions on molr nd recorded tht the risk for het-induced pulpl injury ws incresed using the high-energy light source (Plsm Arc Light) t 10 seconds s compred with the low-energy light-curing units (Hlogen units) t 40 seconds. In this study, we used n orthodontic bonding setup to mimic the clinicl sitution nd found the effect of different energy outputs on dentl pulp. The therml effect on the pulp tissue depends on the vritions in the enmel nd dentin thickness of the pulp chmber wll. 10,25 Lower incisors exhibit higher risk of therml dmge becuse of thinner enmel nd dentin thickness on the lbil side. 21,26 However, vritions within ech tooth cn lso ffect the therml response. 25 Accordingly, in this study only one lower premolr nd one lower incisor were used to control the thickness of the lbil pulp wll nd to eliminte ny possible structurl differences. To represent the clinicl environment, the smple teeth were irrdited t distnce of 10 mm nd t the surfce. 20 Five mesurements were obtined from ech group. There ws no need to increse the number of mesurements becuse of the very low vlues of the stndrd devitions (Tble 3). Our results showed sttisticlly significnt differences mong the three light-curing units tested (Tble 3). Hlogen with the longest exposure time induced significntly higher intrpulpl temperture chnges thn did the LED or PAC. These findings conflict with the concern of incresing het-induced pulpl injury risk with high-energy output lights, but revel the importnce of exposure time. 18,23,24 The criticl vlues reported for pulpl injury were not exceeded in ny of the experiments of this study. 9 However, there re only few in vivo studies vilble in the literture reporting on the criticl vlues for pulp injury, nd one should be creful in the interprettion of these findings. 9,21,25 Comprison of tooth types reveled tht the temperture increse ws higher in the lower incisor thn in the premolr with ll three curing units. These findings were in ccordnce with the previous results. 21,26,27 Sttisticlly significnt differences were found only with the PAC t two distnces nd with the LED t 10 mm. The temperture increse ws significntly higher t the closer distnce with ll light-curing units (Tble 3). However, the temperture vlues mesured in this study cnnot be directly pplied to temperture chnges in vivo. The design of this study did not consider het conduction within the tooth becuse of the effect of blood circultion in the pulp chmber nd fluid motion in dentin tubules. 18 In ddition, the surrounding periodontl tissues cn promote het convection in vivo, limiting the intrpulpl temperture rise. 27 On the other hnd, ctul temperture increses might be higher in clinicl conditions in younger teeth. Therefore, extensions to this study will consider histologicl investigtion of the humn pulp to evlute the effects of the light curing during orthodontic bonding in clinicl conditions. Future histologicl investigtions re needed to clrify the therml threshold for pulpl injury, not just to investigte the effect of light curing but lso fter other orthodontic procedures such s stripping, reshping, dhesive removl, nd therml debonding. CONCLUSIONS Hlogen light induced significntly higher intrpulpl temperture chnges thn did the LED nd PAC. The temperture increse ws significntly higher t closer distnces with ll light-curing units. All light-curing units produced higher temperture increse in the pulpl chmber of the mndibulr incisor thn in the premolr t both distnces. High-energy output lights produced significntly higher het chnges in the incisor thn in the premolr. Orthodontic bonding with light-curing units did not exceed the criticl 5.5 C vlue for pulpl helth. ACKNOWLEDGMENTS The uthors would like to thnk Professor Nzn Alprsln for her ssistnce with sttisticl nlyses nd Dr Aslihn Usumez for providing the dt logger. REFERENCES 1. Gottlieb EL, Nelson AH, Vogels DS. Study of orthodontic dignosis nd tretment procedures. Prt 1. Results nd trends. J Clin Orthod. 1996;12: Oesterle LJ, Newmn SM, Shellhrt WC. Comprtive bond strength of brckets cured using pulsed xenon curing light with 2 different light-guide sizes. Am J Orthod Dentofcil Orthop. 2002;122: Oesterle LJ, Newmn SM, Shellhrt WC. 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