Demineralization effects of hydrogen peroxide on bovine enamel and relation of shear bond strength of brackets

Transcription

1 Pulition Copyright Deminerliztion effets of hydrogen peroxide on ovine enmel nd reltion of sher ond strength of rkets Sntigo González-López /Crmen Lui Sores G. de Medeiros /Cmejo-Aguilr Defren /Mri Vitori Bolños-Crmon d /Purifiión Snhez-Snhez e /Mrio Menendez-Nuñez f Purpose: To mesure the deminerliztion pity of 37% phosphori id nd sher ond strength (SBS) of rkets tthed on ovine enmel t different times fter lehing with 30% hydrogen peroxide. Mterils nd Methods: Four eqully-sized piees of eh rown from 18 ovine inisors were rndomly distriuted mong 7 groups (n = 10). After lehing with 30% hydrogen peroxide 1 h, speimens were stored in rtifiil sliv 0 h, 24 h, or 1, 2, 3, or 4 weeks ee onding speimens to rkets. An unlehed group of speimens served s ontrols. Sher ond strength (SBS in MP) ws mesured with universl testing mhine. Adhesive Remnnt Index (ARI) sores were determined fter filure of rket onds. To mesure deminerlized C 2 +, four 4 x 4 mm setions from eh of 15 ovine inisors were rndomly distriuted mong 4 groups (n = 15). Speimens were stored in rtifiil sliv 0 h, 24 h or 7 dys fter lehing nd then immersed in 37% phosphori id solution. After 15 s, 30 s, nd 60 s, 5-ml liquots of solution were removed spetrophotometry. Unlehed speimens served s ontrols. Results: Lrger mounts of C 2 + were extrted from the enmel phosphori id up to 24 h fter pplition of hydrogen peroxide, when there ws lso signifint derese in rket-enmel SBS. After 1 week, there were no hnges in mounts of C 2 + extrted, nd SBS vlues returned towrds unlehed vlues. Conlusion: Lower rket-enmel SBS vlues t 24 h fter lehing re losely orrelted with the lrger mounts of C 2 + extrted from the enmel. Keywords: 30% hydrogen peroxide, sher ond strength, rkets, delifying, phosphori id, spetrophotometry. J Adhes Dent 2009; 11: XXX-XXX. Sumitted pulition: ; epted pulition: Tooth lehing hs een onsidered sfe proedure some uthors, who oserved no evidene of deleterious effets on enmel or dentin fter the longest pplitions of the highest onentrtions of hydrogen peroxide in norml linil use this purpose. 12,22,23 Nevertheless, Assoite Professor, Deprtment of Pthology nd Dentl Therpeutis, University of Grnd, Spin. Assoite Professor, Deprtment of Restortive Dentistry, University of Pri, Pri, Brzil. Assistnt Professor, Deprtment of Opertive Dentistry, University of Los Andes, Mérid, Venezuel. d Assoite Professor, Deprtment of Integrted Peditri Dentistry, University of Grnd, Spin. e Assoite Professor, Deprtment of Inorgni Chemistry, University of Grnd, Spin. f Assoite Professor, Deprtment of Orthodontis, University of Grnd, Spin. Correspondene: Dr. Sntigo González López, Deprtment of Pthology nd Dentl Therpeutis, Fulty of Dentistry, University of Grnd, Cmpus de Crtuj, E, 18071, Grnd, Spin. Fx: e-mil: sglopez@ugr.es lehing gents my dversely ffet the ond strength of omposite to id-ethed enmel. Vrious studies hve reported signifint redutions in enmel ond strength of resin omposite restortions 24 nd resin-onded rkets when onding is preeded tooth lehing. 10,20,42 These redutions re greter t higher onentrtions of lehing gent. 43 Severl investigtions hve ttempted to eluidte this derese in enmel ond strength fter lehing. Due to its low moleulr weight, hydrogen peroxide n penetrte enmel nd e retined in the lehed enmel. 1 Residul oxygen relesed from the lehing gent inhiits polymeriztion of the resin, resulting in n inomplete uring of the dhesive, nd interferes with resin infiltrtion into the ethed enmel. 15 It my theree e responsile the time-dependent redution in the qulity of resinenmel onds. 41 There is no generl greement onerning the deleterious effets of lehing gents on enmel nd dentin. Chnges to the mirostruture of surfe enmel hve een reported tht re proportionlly more severe with longer tretment times nd higher hydrogen peroxide onentrtions. 7 In ddition, lehing gents my lter Vol 11, No 3,

2 enmel mirohrdness, with loss of minerl ontent from the outer tooth struture. 2,3,47 The relese of lium nd phosphorous ions inreses with higher hydrogen peroxide onentrtions, leding to redution in the C:P rtio in lehed smples. 2 After prolonged use, the lehing gent redues the frture resistne of dentin, 39 nd these redutions re greter longer pplition times nd higher leh onentrtions. 40 Crmide peroxide hs n intrinsi deminerlizing effet. 17,29 Previous lehing with 30% rmide peroxide inreses the mount of C 2 + extrted from enmel fter ething with phosphori id, with highest losses oserved t 24 h fter lehing. 28 Mny linil proedures, eg, onding of orthodonti rkets, porelin veneers, omposite veneers, or omposite restortions, require id ething of the enmel only short time fter ompletion of lehing. The effetiveness of these proedures my e ffeted this higher deminerlizing power of phosphori id on lehed enmel. In the present study, the null hypothesis ws tht lehing tretment with 30% hydrogen peroxide does not modify either the delifying ility of phosphori id in enmel id ething or the sher ond strength of rkets to enmel. The ojetives were: 1. to determine the sher ond strength of metl orthodonti rkets onded to hydrogen peroxide-lehed enmel fter vrious postlehing intervls (immeditely, or t 24 h, 1 week, 2 weeks, 3 weeks, nd 4 weeks postlehing); 2. to evlute Atomi Asorption Spetrophotometry the delifying effets of 37% phosphori id on enmel fter linilly relevnt pplition times (15 s, 30 s, nd 60 s) following three postlehing intervls (no intervl, 24 h, nd 1 week); nd 3. to explore the reltionship etween the delifying effets of 37% phosphori id nd sher ond strength. MATERIALS AND METHODS Sher ond strength (SBS) Eighteen ovine inisors with no frtures or defets on the vestiulr enmel surfe were seleted nd stored in thymol under refrigertion until use. All roots were ut off t the ementoenmel juntion using n Autom-50 dimond utter (Autom Hrd Tissue Mirotome, Struers; Bllerup, Denmrk). Eh rown ws then ut (in the inisoervil then mesiodistl diretion) into 4 equllysized setions. Using 20-ml disposle syringes (with onil ends removed) s molds, eh speimen ws then tthed to the entrl prt of the syringe plunger using Coltene utility wx (Whledent; Mhwh, NJ, USA). The plunger ws withdrwn to leve 1-m deep ontiner tht ws then filled with trnsprent self-uring resin (Ortoryl, Denturum; Ispringen, Germny), prepred ording to the mnufturer s instrutions. During polymeriztion, the mold ws sumerged in wter to ompenste the exothermi retion. The resulting ylinder ws expressed from the mold using the syringe plunger. The exposed enmel surfe of speimens ws polished with 500- then 1200-grit silion ride pper Pulition disks in order to remove the surfe prismti enmel lyer nd otin flt surfe. Speimens were rndomly divided into seven tretment groups (n = 10). Group 1 ws n unlehed ontrol group. The other six groups were lehed with Illuminé Offie lehing gent (Dentsply Detrey; Konstnz, Germny) ording to the mnufturer s instrutions. After mixing the two omponents, the resulting gel ws pplied to the polished surfe of the enmel period of 60 min, during whih the speimens were kept in n oven mintined t 37ºC nd low reltive humidity. Although the mnufturer s inmtion leflet desries this widely used produt s 30% hydrogen peroxide, the mixed gel hs onentrtion of 15%. After lehing, speimens were wshed with undnt distilled wter nd dried with sorent pper. Groups 3 to 7 were then stored in rtifiil sliv 28 in n inutor t 37ºC the required time periods (24 h, 1, 2, 3, or 4 weeks). Group 2 ws onded immeditely. A37% phosphori id gel (3M Dentl Produts; St Pul, MN,USA) ws used to eth speimens 30 s. They were then rinsed with undnt wter nd dried with n ir syringe until the frosty white pperne of ethed enmel ws seen. MBT Vitori Series metl rkets mxillry lterl inisors (3M Unitek; Puhheim, Germny) were used, with omined surfe re of 12.2 mm?. They were tthed with Trnsond XT rket dhesive (3M Dentl Produts; St Pul, MN, USA) following the mnufturer s reommendtions. After surfe preprtion, Trnsond XT liquid primer (3M Dentl Produts) ws pplied to the ethed surfes. Suffiient onding pste ws pplied to over the rket ses. The rkets were then seted firmly on the enmel surfe nd exess resin ws removed with dentl explorer. Light uring ws done with n Astrlis 10 hlogen lmp (Ivolr Vivdent; Shn, Liehtenstein) t 700 mw/m 2 20 s. After onding, the speimens in ll groups were stored in rtifiil sliv t 37ºC 24 h to llow omplete resin polymeriztion. SBS ws tested method tht voids the genertion of leverge es (Fig 1), using n Eletrotest Model 500 universl trtion mhine (IBERTEST; Mdrid, Spin) t speed of 1 mm/min. The devie llows shrpened lde to e moved in only one diretion on the smooth surfe of the speimen, lwys utting long the rket/enmel interfe in ll speimens. After deonding, ll speimens nd rkets were exmined under 10X mgnifition nd sored on the Adhesive Remnnt Index (ARI). 6 The ARI sle hs rnge of 1 to 5. A sore of 5 indited no omposite remining on the enmel; 4: < 10% of omposite remining; 3: 10% to 90% remining; 2: > 90% remining; 1: ll of the omposite remined on the tooth, ering the impression of the rket se. Spetrophotometry Fifteen ovine inisors were stored in distilled wter with thymol rystls until use. All roots were ut off t the ementoenmel juntion using n Autom-50 dimond utter (Autom Hrd Tissue Mirotome, Struers; Bllerup, 2 The Journl of Adhesive Dentistry

3 Denmrk). Crowns were polished with silion ride pper disks on polisher (Exkt-Apprteu; Norderstedt, Germny) to otin flt vestiulr surfe, nd eh rown ws then ut into 4 eqully-sized 4 x 4 mm setions (smple speimens) s desried ove. After polishing the inner surfes to remove the dentin, smple speimens were weighed on Srtorius BL6OS preision lne (ury of ± g; Srtorius; Mugió, Itly). Mximum weight equlity mong speimens ws hieved reduing weight when neessry with 600-grit silion ride pper disks (WS 18-B, Struers,), lwys reduing the inner surfe of the setion to void modifying its geometry. An Olympus stereomirosope (Olympus Optil Espñ; Brelon, Spin) ws used to verify tht ll exposed surfes were enmel. One smple speimen from eh rown ws ssigned to one of four groups (n = 15): group I, no lehing gent (ontrol group); groups II, III, nd IV, lehed with 30% hydrogen peroxide 60 min. Groups III nd IV were then stored in rtifiil sliv 24 h nd 1 week, respetively. For lehing, speimens were immersed in 30% hydrogen peroxide (Illuminé Offie, Dentsply Detrey) 60 min, repling ll of the gel t 30 min s per mnufturer s instrutions. Speimens were wshed with undnt distilled wter nd dried with sorent pper. Group III nd IV speimens were then kept in rtifiil sliv t 37ºC the speified time period (24 h or 7 dys). Group II speimens were immersed in 37% phosphori id solution immeditely fter lehing. The 37% phosphori id solution ws prepred dissolving 311 ml of 85% phosphori id (Shrln Cemise; Brelon, Spin) with onentrtion of 1.71 g/ml in 689 ml of distilled wter to otin 1000 ml of 37% id solution with ph of 0.14, mesured with Miro ph 2000 ph meter (Crisol; Alell, Spin). A lnk 20 ml smple of phosphori id solution ws first prepred to determine C 2 + levels in the sene of speimen. All unlehed nd lehed speimens underwent the sme experimentl proedure, ie, immersion in the phosphori id solution followed onstnt gittion using mgneti multi-stirrer (SBS A-09 series C, Sientifi Bsi Solutions; Brelon, Spin) to unimly mix the C 2 + extrted into the solution. At 15 s, 30 s, nd 60 s, 5-ml liquots were removed, using lirted miropipette tht ws repled fter eh extrtion. Extrts were pled in hermetilly seled, lelled glss tues. By these mens, three extrts were otined eh smple speimen. C 2 + onentrtions in the solutions were determined Atomi Asorption Spetrophotometry (Perkin Elmer, model 5100ZL; Wlthm, MA, USA) using the flme tehnique. Extrt redings were expressed in ppm nd susequently trnsmed into mg of C 2 + lost per g of speimen pplying the following mul s desried elsewhere: 28 mg C 2 + /g = [(ppm C 2 + ) 10-3 l/ml V]/W where ppm C 2 + re ppm of C 2 + in eh time period, V is volume of solution in ml (t 15 s, V1; t 30 s, V2; nd t 60 s, V3), nd W is the weight of the smple in mg. For the 15-s period, the volume of solution (V1) ws 20 ml, wheres t 30 s, the volume (V2) ws 15 ml, sine 5 ml of solution hd previously een removed. Theree, the mg of C 2 + orresponding to 5 ml of V1 solution were dded to the mg of C 2 + otined t 30 s. Likewise, sine the volume ws 10 ml t 60 s, the mg of C 2 + orresponding to 5 ml of V1 solution plus 5 ml of V2 solution were dded to those otined t 60 s. Sttistil Anlysis The effet of storge intervl on enmel-rket SBS ws nlyzed using one-wy ANOVA nd the post-ho Dunnet s t test, with the unlehed ontrol group s the referene tegory. A three-wy ANOVA ws used to explore the reltionships mong lehing tretment, id exposure, nd extrted lium, followed two-wy ANOVA nd the post-ho Dunnet s t test. Frequenies in eh ARI tegory were lulted. The distriution of ARI sores in groups ws ompred using hi-squre test. The signifine level ws set t p < RESULTS Pulition Fig 1 SBS-testing devie tht voids the genertion of leverge es. Sher ond strength Tle 1 shows the mens nd stndrd devitions of SBS mesurements. The ANOVA reveled signifint effets (F = 9.137; p <0.001) of the time elpsed ee rket onding to enmel (lehing to onding intervl). Dunnet s t test showed signifint differenes in SBS vlues etween the ontrol group nd groups with lehing-toonding intervls of 24 h nd 1 week. SBS vlues in the 24-h group were one-third of SBS vlues in the unlehed ontrol group. After 24 h, SBS vlues egn to reover towrds unlehed ontrol vlues nd hd douled fter 1 week, lthough they remined signifintly lower thn on- Vol 11, No 3,

4 Pulition Copyright Tle 1 Men sher ond strength (in MP) eh lehing-to-onding intervl Sher ond strength (MP) Blehing-to-onding intervl Control 0 h 24 h 1 week 2 weeks 3 weeks 4 weeks Men (SD) (4.42) (7.06) (3.44) (8.99) Letters indite differenes with respet to the ontrol group. : p < 0.001, : p= (p<0.05) (11.64) (5.51) (11.31) Tle 2 Comprisons of dhesive remnnt index (ARI) mong different groups Blehing-to-onding intervl dhesive remnnt index (ARI) n Unlehed h h week weeks weeks weeks Chi-squre = , p = 0.16 trols. No signifint differenes in SBS vlues were oserved etween the unlehed ontrol group nd groups with lehing-to-onding intervl greter thn 1 week. When rkets were tthed immeditely fter lehing, SBS vlues ppered slightly lower ompred to the unlehed ontrol group, ut the differene ws not sttistilly signifint. Anlysis of filure type (Tle 2) reveled tht ll filures were dhesive long the resin/enmel interfe (ARI sore of 5) fter lehing-to-onding intervl of 24 h, with no resin remining dhered to the enmel. Frtured speimens from the other postlehing groups showed vrious types of filure (round 75% with ARI sores of 4 or 5). All of the omposite remined onded to the enmel surfe in 50% of unlehed speimens (sore of 1) ut in none of the lehed groups. The distriution of frtured speimens ross ARI tegories signifintly differed mong the groups ( 2 = ; p < 0.05). C 2 + deminerliztion phosphori id ething Tle 3 shows the umultive mounts of C 2 + extrted from the enmel speimens fter sutrting the mount of C 2 + found in the study solution without speimen. The three-wy ANOVA (lehing, id exposure time, nd smple) showed signifint differenes etween experimentl groups (F = 5.124, p < 0.002) nd id exposure (ething) times (F = , p < 0.001), with no signifint intertions. The mounts of C 2 + extrted from lehed nd unlehed speimens inresed with longer ething time, nd signifintly differed etween ll ething time periods (60 s > 30 s > 15 s). Unlehed nd lehed groups showed similr deminerliztion kinetis. The totl extrted C 2 + ws greter groups with lehing-to-ething intervls of 0 h nd 24 h thn the ontrol group, lthough this differene ws only signifint (p <0.05) the 24-h group (p < 0.10 the 0-h group). Similr mounts of C 2 + were extrted etween the group ethed t 7 dys fter lehing nd the unlehed ontrol group. For given exposure time, groups did not signifintly differ in the mounts of C 2 + extrted. DISCUSSION Contemporry lehing gents re typilly either hydrogen peroxide or rmide peroxide. In-offie lehing generlly uses reltively high levels of whitening gents short time periods. For this study, the in-offie lehing 4 The Journl of Adhesive Dentistry

5 Tle 3 Amounts of C 2+ in mg extrted (s determined spetrophotometry) in reltion to lehing-to-ething intervls nd id exposure time Blehing-to-ething intervl 15s (n=60) 30s (n=60) Aid exposure time 60s (n=60) Pulition Totl (n=180) Group I (ontrol) (0.282) (0.287) (0.456) (0.538) A Group II (B- 0 h) (0.388) (0.351) (0.740) (0.726) A Group III (B- 24 h) (0.442) (0.628) (0.803) (0.729) B Groups IV (B- 7 dys) (0.167) (0.238) (0.353) (0.473) A Totl B-E (n = 180) (0.336) (0.454) (0.622) B-E: Blehing-to-ething intervl. Different pitl letters indite sttistilly signifint differenes mong experimentl groups. In eh row, different lower-se letters indite sttistilly signifint differenes mong ething times in eh lehing group. gent Illuminè (Dentsply), usully pplied 60 min in the linil setting, ws pplied on the enmel of ovine teeth, widely reognized s relile sustitute humn teeth in this type of investigtion. 33 Although deminerliztion is fster in ovine thn humn enmel 18 nd undergoes greter erosion nd erosion-rsion, 5 it hs een desried s suitle sustitute to evlute enmel deminerliztion. 30 Pulished studies hve supported the use of ovine teeth s relile sustitute humn teeth in mirolekge 32 nd dhesion tests on enmel nd dentin, 19,33-35 otining omprle ond strength mesurements in ovine nd humn teeth. SEM oservtions showed tht the morphology of ovine nd humn teeth nd their enmel ws similr fter ething with 35% H 3 PO Bovine enmel ws used in the present study euse histologilly similr group of teeth n e more redily otined nd four equl-sized enmel setions n e ut from single ovine tooth, unlike in humn teeth, enhning omprison onditions. Nevertheless, due ution should e exerised in extrpolting results from ovine to humn teeth. Severl ftors might influene the ond strength vlues fter tooth lehing, inluding the onding tehnique, 38 the lehing gent nd its onentrtion, 43 nd the dely etween lehing nd onding. 13,37,45 Enmelrket SBS is known to depend on the point t whih the e is pplied. 25 In the present study, test method tht voids the genertion of leverge es ws used. It is well doumented tht lehing signifintly redues the immedite ond strength of omposite to enmel, 24,31,45 whih hs een relted to ltertions in the tthment surfe re, resin/enmel interfe, nd resin qulity. 26 Sundfeld et l 37 found inferior mtion of tgs, whih were shorter, thinner, less frequent, nonunim, nd poorly defined, nd lesser penetrtion of the dhesive mteril into the enmel in omprison with unlehed ontrols. Dishmn et l 15 reported high onentrtion of residul oxygen in the pores of lehed tooth enmel. This oxygen-rih lyer is 5 to 10 µm thik, nd my not only inhiit polymeriztion of the dhesive ut lso inrese the porosity of the resin mteril the relese of gseous oxygen. Resin/enmel interfes on lehed enmel my exhiit more extensive nnolekge s result of this intertion. 27 In this study, SBS vlues were lower in rkets tthed immeditely fter lehing thn in the unlehed group, ut this differene ws not signifint. However, Unlu et l 45 found signifintly lower SBS vlues speimens onded immeditely fter lehing thn unlehed speimens. This disprity my e explined their use of self-ething dhesive (Clerfil SE Bond), sine the suseptiility of dhesives to lehing my depend on the ggressiveness of the deminerliztion proess. 11 The ph of Illuminé is 6.5, muh higher thn the 1.9 of Clerfil SE Bond dhesive. When the ltter is used immeditely fter the mer, the higher ph of the Vol 11, No 3,

6 mer ould interfere with the effetiveness of the dhesive. When Uysl et l 45 used the sme dhesive protool s in the present study (ething with phosphori nd Tnsond XT), they found tht in-offie lehing with 35% hydrogen peroxide did not dversely ffet the ond strengths of rkets onded immeditely or t 30 dys fter lehing. These results re in greement with the present findings these time periods. However, they did not study onding of rkets to enmel t 24 h fter lehing, when we found the wekest SBS vlues (nd lrgest C 2 + losses during ething), whih were round one-third lower thn unlehed ontrols. One week lter, the SBS hd inresed to reh the vlue of the ontrol group, nd SBS vlues then remined the sme ll groups up to 1 month. It should e orne in mind tht the inrese in SBS might hve ourred erlier, sine it ws not evluted etween three nd six dys fter lehing. There re onerns tht tooth-whitening proedures irreversily dmge tooth struture. Blehing hs een reported to produe mirostruturl hnges to the surfe nd susurfe lyers of enmel, 23 minly lolized in the outer enmel nd diminishing in inner enmel lyers, 16 ssoited with loss of C 2 + from the enmel nd signifint deline in lium:phosphte rtios. 8 A greter loss of C 2 + is produed 37% phosphori id ething of enmel fter lehing, 24 resulting in loss of prismti m nd more extensive ething pttern. 18,22 Although the rougher surfe nd greter retention otined might e expeted to inrese the ond strength, it is in ft redued euse the hydrogen peroxide lters the orgni mtrix of the enmel, 17,21 fvoring C 2 + loss nd wekening the ethed enmel. Josey et l, 23 using light mirosopy, found tht the lehing proess resulted in loss of minerl from the enmel tht ws evident 24 h fter lehing, similr to the present finding. Although hydrogen peroxide hs high pity diffusion, 46 time intervl is required the struturl ltertion of hydroxyptite tht produes C 2 + losses, whih re oserved fter 24 h. In previous study, Mdeiros et l 28 found no signifint differene in C 2 + loss etween ontrol group nd group ethed immeditely fter lehing tretment. The ph of the 30% hydrogen peroxide gel used in their study ws 6.5, theree the deminerliztion oserved in the present study nnot e ttriuted to the low ph of the gel. We found no sttistilly signifint differenes in pir omprisons etween groups, whih my e explined the low finl onentrtion of 15% hydrogen peroxide in the lehing gel used (Illuminé Offie, Dentsply Detrey). Signifint differenes my lso hve emerged with longer exposure time, s found in previous study our group tht used n 11% finl onentrtion of hydrogen peroxide 90 min, 30 min more thn in the present study. 28 Efeoglu 17 found signifint redution in the minerl ontent of surfe nd susurfe enmel speimens fter pplition of high-onentrtion in-offie lehing 2 h, the mximum pplition time reommended the mnufturer. This deminerliztion ws lerly greter in the outer 150 µm of enmel. The quntity of ions relesed inresed with higher hydrogen peroxide onentrtions. 2 These greter C + 2 losses might e explined hnges in the hemil omposition of dentl enmel used the lehing gents. 15 Although Josey et l 23 suggested tht the loss of minerl from enmel ws sustined fter 12 weeks of storge in rtifiil sliv, it is lso widely reported tht mirostruturl hnges in lehed enmel n e reversed slivry omponents, 4,7,14 with onsequent restortion of the ond strength to enmel. 10,43 In the present study, the rtifiil sliv funtioned s reminerliztion solution. For this reson, the present findings re similr to those of Unlu 45 nd Mhdo, 13 who found tht SBS vlues nd levels of extrted C + 2 returned to levels found unlehed enmel 1 week fter the use of hydrogen peroxide nd then remined stle until the end of the study t 4 weeks. Severl methods hve een proposed to meet the linil hllenge posed the effets of lehing on ond strength. Dishmn 15 suggested tht the oxygen-rih lyer would e removed the tion of the phosphori id pplied ee pplition of resin-sed dhesive. In ontrst, Cdenro 11 proposed tht ething nd rinsing proedures do not eliminte residul oxygen from the surfe nd tht polymeriztion of the dhesive is redued. Composite-enmel ond strength ws signifintly improved the pre-onding pplition of ntioxidnt gents, eg, 10% sodium sorte, tlse or ethnol, 26 whih were limed to redue or ompletely remove residul peroxides nd other oxygen rdils. Our results demonstrte tht the redution in SBS is not solely result of the persistene of oxygen in the enmel. Thus, lowest SBS vlues were t 24 h, when the lrgest extrtion of C + 2 phosphori id ething ws oserved. Moreover, the frture ptterns oserved indited poor dhesion. Theree, the lehed enmel surfe did not llow strong nd stle ond to e med with the omposite, nd our null hypothesis must e rejeted. We reommend time intervl of lest 7 dys etween the utiliztion of peroxide lehing mterils nd restortive proedures tht require id-ething nd dhesive onding, 9 llowing suffiient time penetrtion of the dhesive system into the enmel surfe, with mtion of regulr tgs. 13 CONCLUSIONS Pulition At 24 h fter pplition of 30% (finl onentrtion 15%) peroxide, lrger mount of C 2 + ws extrted 37% phosphori id from lehed thn unlehed enmel, oiniding with signifint derese in the sher ond strength of rkets to enmel. After one week, the sheer ond strength with lehed enmel progressively reovered to the vlue oserved with unlehed enmel, nd extrted C 2 + vlues stilized. 6 The Journl of Adhesive Dentistry

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