Influence of Soft Drinks with Low pH on Different Ni-Ti Orthodontic Archwire Surface Patterns

In luence o So D inks wi h Low pH on Di e en Ni-Ti O hodon ic A chwi e Su ace Pa e ns C. Abalos, A. Paul, A. Mendoza, E. Solano, C. Palazon, and F.J. Gil (Submi ed No embe 5, 2011; in e ised o m May 16, 2012; published online July 20, 2012) The aim o his s udy was o de e mine he influence o so d inks on he su ace o Ni-Ti a chwi es and hei co osion beha io . A chwi es wi h di e en pa e ns (smoo h, sc a ch, dimple, and c ack) we e selec ed and cha ac e ized by scanning elec on mic oscopy and lase con ocal mic oscopy. Imme sion es s we e pe o med in a ificial sali a (pH 6.7) wi h a so d ink wi h a pH o 2.5 o 28 days. The esul s showed an inc ease in he su ace de ec s and/o oughness o he dimple, c ack and sc a ch pa e ns wi h he imme sion imes, and a dec ease in co osion esis ance. A ela ionship be ween he su ace pa e n and he ex en o he co osion in Ni-Ti a chwi es wi h so d inks a low pH has been demons a ed. Pa e n should be aken in o accoun in u u e s udies, and manu ac u ing p ocesses ha p oduce su ace de ec s (especially c acks) should be a oided. Keywo ds co osion, Ni-Ti, su ace 1. In oduc ion The biocompa ibili y o nickel- i anium alloys (Ni-Ti) nea equia omic composi ion is good in a ificial sali a, Ringe s solu ion, and physiological saline solu ion (Re 1). Ne e he- less, he co osion esis ance o Ni-Ti alloys dec eases in acid sali a (Re 2-4) and chlo ine (Re 5) o fluo ide-con aining solu ions (Re 5-15). Co osi e agen s de e io a e he passi e film o he i anium oxide su ace (Re 7,12,14,15), dec easing co osion esis ance o he alloy and hence i s biocompa ibili y (Re 1-3). In he las decade, many s udies ha e examined he ac o s ha influence Ni-Ti alloys exposed o fluo ide. I is well known ha he ou e i anium oxide laye is deg aded by hyd ogen abso p ion (Re 14). Also, he e ec s o exposu e ime (Re 13, 14), fluo ide concen a ion (Re 6,7,12) and a mo e acidic pH (Re 12,14), as well as hei ela ionships, ha e been s udied (Re 13). A pH-dependen c i ical concen a ion has been defined (Re 10,11) ha can deg ade he passi e film. Ne e heless, in ela ion o ca bona ed d inks, only s udies on he enamel coa ing ha a ec s adhe ence o b acke s can be ound in he li e a u e. Such d inks a e a pa o he die o young people ecei ing o hodon ic ea men , and can also deg ade he o hodon ic a chwi e su ace. When he passi e film is b oken, co osion akes place. As a consequence, he elease o me allic ions in o he medium (Re 3,6,10,15,16), su ace mo phological changes (Re 6, 13,14) including an inc ease in oughness (Re 3,6) and ic ion coe ficien be ween he a chwi e and he b acke (Re 17), a e p oduced. In hese e ec s, he wi e su ace plays an impo an ole in co osion, al hough he published esul s a e con o e sial. P e ious s udies (Re 3,16,18) poin o su ace de ec s p oduced du ing he wi e manu ac u ing p ocess as p e e en ial co osion a eas, while o he au ho s ha e epo ed no such e idence (Re 7,19). Some in es i- ga o s (Re 20) conside a chwi e oughness o be an indica o o he endency owa d co osion, al hough o he s udies (Re 3,6,7,19) ha e ound no such ela ionship when including esidual s esses and he deg ee o homogenei y as co osion accele a o s (Re 7,19). This is o say ha di e en a chwi e su aces ha e a be e o wo se esponse o co osi e fluo ide. Thus, he a chwi e manu ac u e is a a iable in i sel (Re 6, 19). The main objec i e o his s udy was o de e mine whe he so d inks wi h a low pH cause co osion o Ni-Ti wi es. The wi e su ace, su ace de ec s, and oughness a e ela ed o he manu ac u ing p ocesses (Re 6) ha lead o di e en su ace finishes (Re 21). A second objec i e o he p esen s udy was o in es iga e he influence o he su ace (su ace de ec s and oughness), as a esul o he manu ac u ing p ocess, upon he co osion o Ni-Ti a chwi es. Di e en comme cial b ands could p esen he same pa e n. In his con ex , he influence o each pa e n upon so d ink co osion was s udied by means o su ace analysis (scanning elec on mic oscopy), oughness cha ac e iza ion (lase scanning con- ocal mic oscopy), and co osion es s. The main hypo hesis is ha di e en su ace pa e ns, de i ed om di e en manu ac- u ing p ocesses, will espond di e en ly o co osion p oduced by so d inks. C. Abalos, Depa men o Den al Ma e ials, School o Den is y, Uni e si y o Se ille, Se ille, Spain; A. Paul, Depa men o Mechanical and Ma e ials Enginee ing, School o Enginee ing, Uni e si y o Se ille, Se ille, Spain; A. Mendoza, Depa men o Pedia ic Den is y, School o Den is y, Uni e si y o Se ille, Se ille, Spain; E. Solano and C. Palazon, Depa men o O hodon ics, School o Den is y, Uni e si y o Se ille, Se ille, Spain; and F.J. Gil, Depa men o Ma e ials Science and Me allu gical Enginee ing, Technical Uni e si y o Ca alonia, Diagonal 647, 08028 Ba celona, Spain. Con ac e-mail: ancesc.xa ie [email p o ec ed]. JMEPEG (2013) 22:759–766 ASM In e na ional DOI: 10.1007/s11665-012-0311-3 1059-9495/$19.00 Jou nal o Ma e ials Enginee ing and Pe o mance Volume 22(3) Ma ch 2013—759 2. Ma e ials and Me hods 2.1 P elimina y S udy The su aces o 16 Ni-Ti a chwi es (0.016 90.022 inches) om nine comme cial b ands we e s udied in he as- ecei ed condi ion (Re 22)(Table 1). The su ace mo phology and composi ion we e e alua ed by scanning elec on mic oscopy (SEM) (Philips XL-30 Philips, Eindho en, Ne he lands) and ene gy dispe si e spec ome y (EDS) (Edax In e na ional, Mahwah, USA), while oughness was measu ed using a lase scanning con ocal mic oscope sys em (LSCM) (Leica TCS- SP2, We zla , Ge many). The a chwi es we e classified acco ding o hei su ace pa e ns using 18 a iables. Fi e a iables we e ound o be co ela ed o he pa e n: dimples, sc a ches, c acks, po es, and smoo h/no de ec . As a esul , he Ni-Ti a chwi es we e classified acco ding o hese fi e pa e ns (Table 1) depending on he p edominan su ace de ec s. The di e en su ace de ec s a e de e mined in he ollowing way: As- ecei ed ma e ial can be obse ed in Fig. 1a. Po e is a deep, usually ounded de ec . Mic opo e is a po e wi h a diame e o less han one mic ome e . Dimple is a small hole, an ellip ical o ounded dep ession on he su ace simila o he dimples in a gol ball (Fig. 1c). C ack is a long, deep fissu e wi h i egula edges and a iable wid h (Fig. 1e). Las ly, sc a ch is a long fissu e wi h smoo h edges and cons an wid h, in which he bo om is clea ly isible (Fig. 1g). 2.2 Ma e ial and Imme sion Tes Eigh Ni-Ti wi es wi h nea equia omic composi ions made by di e en manu ac u e s we e used in his s udy. Each su ace pa e n (dimple, sc a ch, c ack, po e, and smoo h/no de ec ) co esponded o wo di e en comme cial b ands (Table 1). The po ous su ace pa e n was elimina ed om his s udy because he e was only one manu ac u e . Fo he es s, use was made o fi e samples o di e en a chwi es om he same ba ch (n= 40). The samples we e 20 mm segmen s ex ac ed om he s aigh pa o he a ch. P io o imme sion es ing, each specimen was cleaned and deg eased o 5 min in ace one. Samples we e placed in a p opylene ube (15 mL) wi h 2 mL o a ificial sali a modified by Fusayama (sali a com- posi ion: NaCl (0.4 g/L), KCl (0.4 g/L), CaCl 2 Æ2H 2 O (0.906 g/L), NaH 2 PO 4 ÆH 2 O (0.690 g/L), Na 2 SÆ9H 2 O (0.005 g/L), KSCN (0.3 g/L), and u ea (1 g/L) (Re 2,3,7,8)) a pH 6.7 (mic opH 2001, C ison Ins umen S.A., Ba celona, Spain) o 28 days a 37 C. Du ing his ime, he samples we e placed in 15 mL p opylene ubes wi h 2 mL o so d ink wi h a pH o 2.5 e e y 3 days (10 days in o al). The imme sion sequence was: 1 min in so d ink ollowed by insing o a ificial sali a o 3 min (5 imes), acco ding o he Van Eygen p o ocol (Re 23). The o al imme sion ime was 50 min in so d ink co esponding o he consump ion o one can o so d ink pe day o 28 days (Re 24). Du ing his p ocess, a e each imme sion in so d ink, he specimens we e placed in esh a ificial sali a used in his expe imen . 2.3 Su ace Cha ac e iza ion The su ace opog aphy o he Ni-Ti a chwi es was exam- ined be o e and a e he imme sion es s. SEM mic og aphs and we e aken o ep esen a i e deg aded a eas o he su ace. The images we e used o measu e he su ace occupied by each de ec (dimples, sc a ches, c acks, and po es) in h ee di e en a eas o 10,000 lm 2 . The h ee measu emen s we e hen a e aged. Thus, fi e samples pe b and o wi e (n= 40) and h ee a eas pe specimen we e analyzed. The su ace oughness o he Ni-Ti a chwi es we e analyzed be o e and a e he imme sion es s by means o LSCM. The mic oscope was p e iously calib a ed using a Mi u oyo p ecision Re e ence Specimen (Code no. 178-601) wi h Ra = 3.1 lm— he e o coe ficien being below 0.3%. The images we e p ocessed using Leica Con ocal so wa e (Leica Mic o- sys ems GMBH, We zla , Ge many). Mic og aphs co espond- ing o 750 linea mic ons we e aken. Fi e a eas o 10,000 lm 2 we e andomly selec ed om each opog aphic image and he oughness was measu ed. Ra, Rms, Rp, and R alues ob ained Table 1 A chwi es used in he p elimina y and expe imen al s udies Code A chwi e Company Ba ch Composi ion(b) Pa e n NC(a) Ni inol Classic(a) 3M-Uni ek V5304 53.0/47.0 Smoo h RS(a) Reflex Supe elas ic(a) TPO 1567027 52.9/47.1 Smoo h AL(a) Align XF(a) O mco 030880842 53.4/46.6 Dimple OR(a) O honol(a) RMO A07005 52.9/47.1 Dimple NCu Ni iCu 35 O mco 07E278E 47.2/46.5/6.3(c) Dimple TS(a) Ti anol Supe elas ic(a) Fo es aden 28636946 53.9/46.1 C ack M(a) Memo ia(a) Leone 07132601 54.0/46.0 C ack TM(a) The momemo ia(a) Leone 08022001 53.9/46.1 Sc a ch G4(a) G4(a) G&H 142669 53.3/46.7 Sc a ch T Tensic Den au um 54301 56.5/43.4 Sc a ch NH Ni inol HA 3 M-Uni ek AP1FY 53.0/47.0 Sc a ch RL Rama i an Li e Den au um 60648 54.5/45.5 Sc a ch M5 M5 G&H 146755 53.3/46.6 Sc a ch TA The maloy RMO A07304 53.4/46.6 Sc a ch RH Reflex Hea -Ac i a ed TPO 1297060 53.2/46.7 Sc a ch NS Neo Sen alloy GAC H326 53.1/46.8 Po ous (a)A chwi es used in he expe imen al s udy. (b)%Ni/%Ti (w .%). (c)%Ni/%Ti/%Cu (w .%) 760—Volume 22(3) Ma ch 2013 Jou nal o Ma e ials Enginee ing and Pe o mance in each a ea we e a e aged. Ra and Rms ep esen he a i hme ical mean o he absolu e alues and he oo -mean- squa e alue o he scanned su ace p ofile, espec i ely. Rp and R in u n ep esen he highes and lowes alues o he scanned p ofile. Thus, o oughness s udies, fi e a eas om fi e samples o each a chwi e we e analyzed (n= 40). 2.4 Co osion Tes s A chwi es we e sec ioned o p oduce co osion es samples. A 25-mm leng h o each a chwi e wascu wi h s e ile o hodon ic plie s and was isola ed wi h wax a he poin o in e phase be ween he es ing solu ion and he ai . The co osion es s we e Fig. 1 Rep esen a i e SEM images o Ni-Ti wi es. As- ecei ed: (a) smoo h pa e n, (c) dimple pa e n, (e) c ack pa e n, and (g) sc a ch pa e n. So d ink- ea ed: (b) smoo h pa e n, (d) dimple pa e n, ( ) c ack pa e n, and (h) sc a ch pa e n Jou nal o Ma e ials Enginee ing and Pe o mance Volume 22(3) Ma ch 2013—761 pe o med in acco dance wi h he ISO-s anda d (Re 25) o co osion es ing. The es s we e ca ied ou wi h a Vol alab PGZ 301 po en ios a (Radiome e , Copenhagen, Denma k) con olled by Vol amas e 4 so wa e (Radiome e Analy ical, Villeu banne Cedex, F ance). The es ing solu ion was a ificial sali a and a ificial sali a wi h so d ink kep a a con olled cons an empe a u e o 37 C. The elec ical se -up used o measu e he elec ochemical pa ame e s and sample geome y is ep esen ed in Fig. 2. The e e ence elec ode was an Ag/AgCl/KCl elec ode (E= 0.222 V). The auxilia y elec ode used was a pla inum elec ode wi h a su ace o 240 mm 2 (Radiome e Analy ical, Villeu banne, F ance). The open ci cui po en ial was moni o ed o 3 h in o de o allow le eling o o he alue be o e he pola iza ion esis ance es . The Cyclic Vol amme y assay was pe o med by scanning he po en ial o he alloy o he sample a 0.25 mV/s wi h he minimum cu en se a 1 A and he maximum a +1 A, wi h a minimum ange se a 100 lA be ween 300 and +2000 mV a ound he OCP alue. Reco dings o he a ia ion in gal anic cu en densi y, po en ial, e c., we e ob ained, and he Ta el slopes we e de e mined om he E ans diag ams. In o de o de e mine hese diag ams, i is e y impo an o eco d he pola iza ion cu es in a pseudo-s a iona y manne . In his case, he 250 min o imme sion o he specimens su ficed. Open ci cui po en ial (E ocp ), co osion po en ials (E co ), and co osion cu en s (i co ) we e eco ded o he di e en samples es ed. These pa ame e s a e defined as: •Open ci cui po en ial (E ocp ): Po en ial o an elec ode measu ed wi h espec o a e e ence elec ode o ano he elec ode when no cu en flows o o om he ma e ial. •Co osion po en ial (E co ): Po en ial calcula ed a he in e sec ion whe e he o al oxida ion a e is equal o he o al educ ion a e. •Co osion cu en densi y (i co ): Cu en di ided by he su ace o he elec ode. This is he size o he anodic componen o he cu en which flows a he co osion po en ial E co . Since by defini ion he esul ing cu en is equal o ze o a ha po en ial, he ca hodic componen is o equal size, bu o opposi e sign. The measu ed esul - ing cu en being ze o a he co osion po en ial, he co - osion cu en densi y i co can only be ob ained by indi ec me hods, e.g., om he Ta el equa ion. Ta el cons an s aand ba e he Ta el p opo ionali y cons an s o anodic (oxida ion) and ca hodic ( educ ion) eac ions o a me al. 2.5 S a is ical Analysis Mean alues and s anda d de ia ions o each o he eigh b ands and he ou su ace pa e ns we e compu ed om he da a ob ained du ing su ace cha ac e iza ion, o he as- ecei ed a chwi es as well as a e imme sion es ing. Since he a chwi es used had di e en ini ial alues, in o de o ensu e alid compa ison o he s a is ical esul s i was deemed app op ia e o use he di e ence be ween he as- ecei ed and pos -imme sion es alues eco ded o each wi e es ed. Thus, he final da a e e o he inc eases o dec eases in he a ea occupied by he su ace de ec s o su ace oughness. Posi i e alues imply su ace deg ada ion, while ze o o nega i e alues indica e he absence o co osion. S a is ical analysis was ca ied ou using analysis o a iance (ANOVA) and he pos hoc Bon e oni es , o he compa ison o mean alues. S a is ical significance was accep ed o a£0.05. The da a we e analyzed using he SPSS e sion 14.0 s a is ical package (SPSS Inc., Chicago, IL, USA). 3. Resul s Table 2shows he esul s o he su ace de ec s in he as- ecei ed a chwi es. Quan ifica ion was done wi h he su ace alues o each de ec and he o al su ace de ec s o each a chwi e. The inc emen al alue also e e ed o each su ace pa e n included o he a chwi es a e he imme sion es s in sali a wi h so d ink. The e we e significan di e ences in he dimple, c ack, and sc a ch pa e ns. Figu e 1shows ep esen- a i e SEM images o he changes in he su ace pa e ns a e he co osion es s. In he sc a ch pa e n, pi ing co osion simila o co osion caused by fluo ide was obse ed (Fig. 1h). In he dimple and c ack pa e ns he e was no pi ing, bu an inc ease in he su ace occupied by de ec s was seen. The numbe o dimples (Fig. 1d) and c acks (Fig. 1 ) inc eased, espec i ely. The su ace oughness da a (LSCM) o he a chwi es in he as- ecei ed and pos -imme sion condi ions a e exp essed in Table 3. The e was a significan di e ence o he c acked pa e n, whe e he e was a 34% inc ease in su ace oughness. Fig. 2 Schema ic ep esen a ion o o hodon ic a chwi es (a) and he elec ical se -up used o measu ing he elec ochemical pa ame e s (b) 762—Volume 22(3) Ma ch 2013 Jou nal o Ma e ials Enginee ing and Pe o mance In he c ack pa e n, Ra changed om 0.35 lm in he as- ecei ed a chwi es o 0.47 lm in he pos -imme sion samples. Figu e 3p o ides ep esen a i e LSCM images o he ou pa e ns s udied. The esul s ob ained o E co ,i co , and E ocp du ing co osion es ing a e p esen ed in Table 4. The a chwi es es ed in a ificial sali a clea ly showed g ea e esis ance o co osion han hose es ed in a ificial sali a wi h so d ink. Fo he smoo h a chwi es he di e ence in E co due o imme sion in so d ink was abou 100 mV. Howe e , o he su ace wi h dimples he alue was abou 150 mV, and o he c ack and sc a ch su aces i was a ound 200 mV. The de ec s wi h mo e in e nal ene gy (c acks and sc a ches) a e mo e sensi i e o co osion. The a chwi es wi h sc a ches and c acks showed he g ea es endency owa ds co osion, wi h a e age alues o 650 mV in a ificial sali a and 850 mV wi h so d ink. The a chwi es wi h a smoo h su ace we e ound o be less esis an o co osion, wi h an E co o 515 and 600 mV, in a ificial sali a and wi h so d ink, espec i ely. The minimum cu en densi y co esponded o he smoo h pa e n (3.85 o 3.0 lA/cm 2 ), while he maximum alues we e obse ed in he sc a ch pa e ns (0.59 o 0.22 lA/cm 2 ) in a ificial sali a. The p esence o so d ink p oduced a dec ease in bo h ype o pa e ns (be ween 0.3 and 1 lA/cm 2 ). The open cu en po en ial alues showed g ea a iabili y be ween he measu emen s ob ained. Howe e , he alues o he smoo h and dimple pa e ns we e highe han hose o he c ack and sc a ch pa e ns. 4. Discussion In ela ion o he me hodological design, he equi alen o one so d ink was used as a e age daily consump ion. Ne e heless, consump ion has been es ima ed o be 12 cans pe week pe pe son (565 mL/day) (Re 26). In Ame ican eenage s be ween he ages o 12 and 19 yea s, consump ion can be as high as 600-800 mL/day (Re 27). Thus, he a e age consump ion used in his s udy can be ega ded as egula . In ela ion o he imme sion es , no p e ious s udies in ol ing he exposu e o o hodon ic wi es o ca bona ed d inks ha e been ound. Due o he lack o da a, in i o enamel exposu e p o ocols we e used (Re 23,24). Acco dingly, he co osion esul s ob ained a e no due o excessi e exposu e o he media. Fu he mo e, i is suspec ed ha du ing o hodon ic ea men , he con ac ime could be e en highe han o Table 2 Su ace a ea o de ec s and a ia ion (DDe , ob ained by sub ac ing a e age o al de ec s) be o e and a e imme sion es ing Ni-Ti a chwi es Manu ac u ing de ec s (in 10,000 lm 2 ) Pa e n DDe -sali a + so d ink C acks Po es lPo es Sc a ches(a) Dimples To al Mean SD Reflex SE 0 0 0.8 2.9 0 3.7 Smoo h 6.7 16.9 Ni inol Classic 0 174 1.9 0 25 200.1 O honol 0 228 1.5 0 6215 6444.5 Dimple 252(b) 68.2 Align XF 73.7 258 3,3 0 1302 1637 Memo ia 577.5 5.1 1.7 12.8 176 773.1 C ack 768(b) 72.7 Ti anol SE 264.5 35.6 1.3 0 0 301.4 G4 37.5 94.95 5.7 11.2 0 149.3 Sc a ch 1306(b) 46.7 The momemo ia 7.5 22.8 0.66 7.5 84.78 123.2 Dimple, c ack, and sc a ch pa e ns show s a is ically significan a ia ions (a)lm pe 100 lm in linea sc a ches. (b)Mean significan di e ence (p<0.05) by ANOVA pos hoc Bon e oni es Table 3 Su ace oughness da a and a ia ion be o e and a e imme sion es ing Ni-Ti a chwi es Su ace oughness as- ecei ed (10,000 lm 2 ) Sali a + so d ink Ra Rms R Rp Pa e n Ra Rms DRa DRms Reflex SE 0.22 0.31 2.31 1.20 Smoo h 0.32 (0.13)(a) 0.45 (0.18) 0.03 (0.01) 0.04 (0.01) Ni inol Classic 0.46 0.61 3.46 2.76 O honol 1.32 1.71 8.45 4.53 Dimple 1.01 (0.35) 1.35 (0.47) 0.01 (0.01) 0.01 (0.01) Align XF 0.70 0.95 7.60 4.09 Memo ia 0.44 0.60 4.30 2.23 C ack 0.35 (0.13) 0.48 (0.17) 0.12(b) (0.04) 0.14(b) (0.04)) Ti anol SE 0.25 0.37 3.33 1.18 G4 0.41 0.53 3.75 2.9 Sc a ch 0.42 (0.11) 0.54 (0.14) 0.01 (0.01) 0.03 (0.01) The momemo ia 0.43 0.57 3.93 2.74 C ack pa e n shows s a is ically significan a ia ions (a)S anda d de ia ions a e gi en in pa en heses. (b)Mean significan di e ence (p<0.05) by ANOVA pos hoc Bon e oni es Jou nal o Ma e ials Enginee ing and Pe o mance Volume 22(3) Ma ch 2013—763 enamel, because he b acke -a chwi e se complica es he sel - cleaning mechanisms and he sali a insing e ec . The esul s e e ed o he main objec i e o his s udy show so d ink a low pH o exe co osi e ac ion on he su ace o Ni-Ti o hodon ic a chwi es, al hough in di e en ways depending on he su ace pa e n. In p e ious esea ch wi h o he co osi e media (Re 16,19), i was shown ha he manu ac u e o Ni-Ti wi es exe s a s a is ically significan influence upon co osion esis ance, since he as- ecei ed comme cial Ni-Ti a chwi es had di e en su ace mo phologies (Re 6,7,16). The esul s ob ained ag ee wi h his influence o he manu ac u e upon co osion esis ance. Ne e heless, p e ious s udies (Re 5-7,10,12,13,16,19) ela e co osion o he b ands o a chwi es s udied, using only one o ou a chwi es om di e en manu ac u e s. This s udy may ha e some ad an ages, since a gi en pa e n indica es a gi en su ace finish, which allows us o g oup se e al b ands o manu ac- u e s wi hin he same pa e n. The su ace finish is ela ed o he manu ac u ing p ocess which, in u n, is ela ed o co osion esis ance (Re 6,22,28). The e o e, he su ace pa e n should be aken in o accoun bo h in p esen (Re 29) and in u u e co osion esea ch. Fig. 3 Rep esen a i e lase scanning con ocal mic oscope sys em (LSCM) images o Ni-Ti wi es. As- ecei ed: (a) smoo h pa e n, (c) dimple pa e n, (e) c ack pa e n, and (g) sc a ch pa e n. So d ink- ea ed: (b) smoo h pa e n, (d) dimple pa e n, ( ) c ack pa e n, and (h) sc a ch pa e n Table 4 Mean alues ob ained om po en ios a ic pola iza ion plo o di e en Ni-Ti a chwi es s udied in a ificial sali a solu ion Ni-Ti a chwi es A ificial sali a A ificial sali a + So d ink i co ,lA/cm 2 E co ,mV E ocp ,mV i co ,lA/cm 2 E co ,mV E ocp ,mV Reflex SE Smoo h 3.85 520 +555 2.87 600 +545 Ni inol Classic Smoo h 3.00 515 +568 2.84 601 +524 O honol Dimple 1.67 565 +450 1.38 691 +479 Align XF Dimple 0.88 579 +520 0.79 674 +488 Memo ia C ack 1.36 624 +401 1.08 796 +409 Ti anol SE C ack 0.67 657 +321 0.11 809 +405 Tensic Sc a ch 0.22 708 +320 +0.03 894 +307 Ni inol HA Sc a ch 0.59 606 +290 +0.24 887 +301 764—Volume 22(3) Ma ch 2013 Jou nal o Ma e ials Enginee ing and Pe o mance Ra ing o he su ace pa e ns in e ms o co osion esis ance om low o high is as ollows: c ack, sc a ch, dimple, and smoo h. In he c ack and sc a ch pa e ns, hese de ec s a e esponsible o he inc ease in o al su ace de ec s, p oducing an inc ease in he discon inui ies in he a chwi e su ace (Fig. 1 -h). In he dimple pa e n, he e is an inc ease in he numbe o de ec s, p oducing a mo e i egula su ace, bu wi hou inc easing he su ace discon inui ies (Fig. 1d). The smoo h pa e n shows no signs o co osion (Fig. 1b). The e is some deba e in he case o fluo ide co osion ( he mos widely s udied ype o co osion) be ween hose au ho s (Re 3,16,18) who conside su ace de ec s p oduced du ing he manu ac u - ing p ocess o be he cause o co osion and hose who do no (Re 7,19). Upon e iewing he esul s, i is seen ha su ace de ec s can play an impo an ole in a chwi es co osion by ca bona ed d inks. Fu he s udies a e needed o confi m his hypo hesis (in ol ing ion leaching, pola iza ion cu es, e c.). Du ing manu ac u e o he a chwi es, hose p ocesses ha lead o he o ma ion o su ace de ec s, especially c acks, should be a oided. C ack and sc a ch pa e ns p esen ed g ea e co osion beha io due o he high su ace ene gy p oduced by plas ic de o ma ion, especially in he ip, esul ing in high s ess co osion. The modynamically, he zones wi h mo e ene gy a e mo e suscep ible o elec ochemical a ack. C acks also can lead o c e ice co osion. Howe e , o he su ace pa e ns p esen ed g ea e co osion esis ance, as is he case o smoo h and dimple pa e ns. F om hese esul s i can be obse ed ha he ole o oughness in co osion beha io is no significan in compa - ison wi h he de ec s. In he fluo ide co osion mechanism, which has been ex ensi ely s udied in he las decade, he fluo ide ions can de e io a e he passi e film o he i anium oxide su ace (Re 7, 12,14,15) by hyd ogen abso p ion (Re 14), dec easing he co osion esis ance o he alloy and hence i s biocompa ibili y (Re 1-3). In his case, he ca bona ed d ink has a low pH (2.5) and con ains acids. The o al acid le el (known as i a able acid), a he han he pH, can be an impo an ac o in co osion because i de e mines he ac ual hyd ogen ion a ailabili y (Re 30) o in e ac ion wi h he passi e film, in a way simila o fluo ide co osion (Re 6,10,11,13). Mos so d inks con ain one o mo e ood acidulan s; phospho ic and ci ic acid a e common bu malic, a a ic, and o he o ganic acids also may be p esen (Re 31). These acids a e esponsible o he cha ac e - is ics o Ni-Ti a chwi es co osion p oduced by so d inks. The co osi e e ec s o so d inks a e mainly eflec ed by an inc ease in he p e-exis ing as- ecei ed su ace de ec s (Table 2). The p esen s udy eco ded he gene alized o ma ion o small c acks, simila o he pi s p oduced du ing fluo ine co osion (Re 5,13,15), bu only on he a chwi es wi h a sc a ch pa e n (Fig. 1h). The c ack pa e n yielded g ea e inc eases in su ace de ec con en om he p e-exis ing c acks (Fig. 1 ). C acks filled wi h impu i ies in he as- ecei ed a chwi es g ow and become mo e p onounced. The as- ecei ed impu i ies ha e been p e iously desc ibed and ela ed o a chwi e de e io a ion by o he au ho s (Re 32). In he absence o u he s udies, he mos p onounced so d ink e ec upon he Ni-Ti alloy is seen o be i s abili y o p oduce o enla ge c acks which gene a e su ace discon inui ies and ha e de i- men al e ec s on he passi e film (Re 15). C acks ac as c e ices ha induce co osion h ough he o ma ion o a di e en ial ae a ion cell. In he a chwi es wi h a dimple pa e n (Fig. 1c, d), and al hough an inc ease in numbe is obse ed, he e is no su ace discon inui y (c e ices) and, coupled wi h he smoo h pa e n, his is he mos co osion esis an pa e n. In u u e esea ch i would be in e es ing o measu e he e ec o ion leaching upon he a e age diame e and mass o he a chwi es in o de o be e unde s and he co osi eness and e ec s o so d ink on he passi e laye . On compa ing hese findings wi h hose ound du ing fluo ide co osion, se e al ele an di e ences a e obse ed. The mos equen conse- quences o fluo ide imme sion a e a gene al (Re 5,13-15)o localized a ack (Re 10,15) in he o m o pi s. Ano he cha ac e is ic e ec is he change in colo : da k s ains (Re 13), whi e spo s (Re 9,13-15), o da k spo s ha disappea a e he imme sion es s in as- ecei ed a chwi es (Re 12-14,32,33). Such changes in colo desc ibed du ing co osion in fluo ide media we e no ound in he p esen s udy. A hypo hesis o p o e is ha so d inks, unlike fluo ide, use p e-exis ing de ec s as nuclea ion si es o co osion-c acks being he mos impo an de ec s because o he exis ence o a c e ice. Rega ding he inc ease in oughness a e imme sion in so d ink, co ela ions wi h he c ack pa e n we e ound (Table 3). The inc ease in oughness is ela ed o co osion (Re 3,6,7), al hough no he ini ial oughness (Re 3,7,19). The esul s ob ained a e in ag eemen wi h he findings e e ed o he dimple pa e n, wi h high ini ial oughness, which does no significan ly a ec pos -imme sion oughness. Ne e heless, his is in disc epancy wi h o he in es iga o s (Re 20) who poin o ini ial oughness as a ac o ela ed o co osion. On he o he hand, he inc ease in oughness is no only ela ed o he inc ease in he numbe o de ec s. In he dimple and sc a ch pa e ns he numbe o de ec s inc ease bu no so oughness. The explana ion o his is ha he su ace occupied by he de ec s in some a chwi es ep esen s abou 10% o he o al su ace. Thus, oughness depends on he numbe o de ec s bu also on he emaining su ace. Taking in o accoun ha imme sion in fluo ide solu ion p oduces a gene alized inc ease in oughness ha is dependen upon concen a ion and pH (Re 5,6), in he as- ecei ed a chwi es wi h ew su ace de ec s he inc ease in oughness essen ially depends on he p ocesses aking place on he su ace ee o de ec s. In exposu e o so d ink, an inc ease in oughness in he c ack pa e n is obse ed whe e he numbe o p e-exis ing de ec s is significan . This inc ease can influence pos -imme sion oughness. I would be in e es ing o s udy he changes in oughness p oduced by fluo a ed solu ions and o compa e hem wi h hose p oduced by ca bona ed d inks, in he same way ha he di e ence has been s udied be ween he ac ions o chlo ide-con aining solu ions on Ni-Ti a chwi es and hose exposed o fluo ide media (Re 5). The oughe su ace condi ion in fluo ide can be asc ibed o he gene al co osion o Ni-Ti alloy in fluo ide solu ions (Re 5). As he acid media in so d ink and fluo ide a e di e en , he e should be di e ences be ween hem. I may be no ed ha he po en ials in an open ci cui o he all a chwi es adop posi i e alues, and consequen ly he Ni-Ti a chwi es s udied emain in hei immune ange. The highe he cu en densi y a a gi en po en ial, he mo e p one he ma e ial is o co osion. Smoo h and dimple pa e ns had he mos passi e (2.87, 2.84, 1.38, and 0.79 lA/cm 2 ) and sc a ch he mos ac i e (+0.03, +0.24 lA/cm 2) c i ical cu en densi y alues in a ificial sali a wi h fluo ide solu ion. The di e ences in cu en densi y a a gi en po en ial be ween smoo h and dimple pa e ns a e due o he in e nal s esses p oduced in he su ace o he Ni-Ti by he machining p ocess, which a o he co osion p ocesses. Jou nal o Ma e ials Enginee ing and Pe o mance Volume 22(3) Ma ch 2013—765 Obse ed su ace changes canno be di ec ly ela ed o changes in he mechanical p ope ies o Ni-Ti a chwi es (Re 13). Nei he su ace de ec s no oughness can be conside ed he only ac o s in ol ed in co osion; su ace esidual s ess, he amoun o esidue and he deg ee o homogenei y o mic os uc- u es (Re 5,7,19), among o he ac o s, mus also be aken in o accoun . The o hodon is should ins uc he pa ien on ca bon- a ed d ink in ake du ing ea men , sugges ing he use o a s aw o minimize he co osi e e ec on Ni-Ti a chwi es. 5. Conclusions In conclusion, so d inks wi h low pH alues exe co osi e ac ion on he su ace o Ni-Ti o hodon ic a chwi es, al hough in di e en ways depending on he su ace pa e n. A chwi es wi h c acked o sc a ched su ace pa e ns a e he leas co osion esis an . C acks as p e-exis ing manu ac u ing de ec s show he g ea es su ace de e io a ion, due o he in e nal ene gy s o ed. Howe e , he ini ial oughness o a chwi es is no ela ed o he inc ease in oughness when hey a e exposed o so d ink. The c acked su ace pa e n mo eo e shows he g ea es inc ease in oughness; he e o e, c acks should be a oided in he a chwi e su ace pa e n. The absence o s anda d su ace ea men p o ocols o Ni-Ti esul s in a iabili y in he su ace finish, which in u n esponds di e en ly o co osion. Such p o ocols should be help ul in secu ing be e quali y su aces. Acknowledgmen s The au ho s hank D . Juan Luis Ribas (LSCM expe ) and he Cen e o Technology and Inno a ion Resea ch, Uni e si y o Se ille (CITIUS), o hei collabo a ion in his s udy. Re e ences 1. D.J. We e , A.G. Veldhuizen, J. de V ies, H.J. Bussche , D.R. Uges, and J.R. an Ho n, Elec ochemical and Su ace Cha ac e iza ion o a Nickel-Ti anium Alloy, Bioma e ials, 1998, 19(7–9), p 761–769 2. J. Wang, N. Li, G. Rao, E.H. Han, and W. Ke, S ess Co osion C acking o NiTi in A ificial Sali a, Den . Ma e ., 2007, 23(2), p 133– 137 3. H.H. Huang, Y.H. Chiu, T.H. Lee, S.C. Wu, H.W. Yang, and K.H. Su, Ion Release om NiTi O hodon ic Wi es in A ificial Sali a wi h Va ious Acidi ies, Bioma e ials, 2003, 24(20), p 3585–3592 4. H.H. Huang, Su ace Cha ac e iza ions and Co osion Resis ance o Nickel-Ti anium O hodon ic A chwi es in A ificial Sali a o Va ious Deg ees o Acidi y, J. Biomed. Ma e . Res. A, 2005, 74(4), p 629–639 5. X. Li, J. Wang, E.H. Han, and W. Ke, Influence o Fluo ide and Chlo ide on Co osion Beha io o NiTi O hodon ic Wi es, Ac a Bioma e ., 2007, 3(5), p 807–815 6. H.H. Huang, Va ia ion in Su ace Topog aphy o Di e en NiTi O hodon ic A chwi es in Va ious Comme cial Fluo ide-Con aining En i onmen s, Den . Ma e ., 2007, 23(1), p 24–33 7. T.H. Lee, T.K. Huang, S.Y. Lin, L.K. Chen, M.Y. Chou, and H.H. Huang, Co osion Resis ance o Di e en Nickel-Ti anium A chwi es in Acidic Fluo ide-Con aining A ificial Sali a, Angle O hod., 2010, 80(3), p 547–553 8. Y.H. Kwon, Y.D. Cheon, H.J. Seol, J.H. Lee, and H.I. Kim, Changes on NiTi O hodon ic Wi ed due o Acidic Fluo ide Solu ion, Den . Ma e . J., 2004, 23(4), p 557–565 9. A. Ramalingam, V. Kailasam, S. Padmanabhan, and A. Chi ha anjan, The E ec o Topical Fluo ide Agen s on he Physical and Mechanical P ope ies o NiTi and Coppe NiTi A chwi es. An In Vi o S udy, Aus . O hod. J., 2008, 24(1), p 26–31 10. N. Schi , B. G osgogea , M. Lissac, and F. Dala d, Influence o Fluo ida ed Mou hwashes on Co osion Resis ance o O hodon ics Wi es, Bioma e ials, 2004, 25(19), p 4535–4542 11. N. Schi , M.Boine , L. Mo gon, M. Lissac, F. Dala d, and B.G osgogea , Gal anic Co osion Be ween O hodon ic Wi es and B acke s in Fluo ide Mou hwashes, Eu . J. O hod., 2006, 28(3), p 298–304 12. I. Wa anabe and E. Wa anabe, Su ace Changes Induced by Fluo ide P ophylac ic Agen s on Ti anium-Based O hodon ic Wi es, Am. J. O hod. Den o acial O hop., 2003, 123(6), p 653–656 13. M.P. Walke , R.J. Whi e, and K.S. Kula, E ec o Fluo ide P ophy- lac ic Agen s on he Mechanical P ope ies o Nickel-Ti anium-Based O hodon ic Wi es, Am. J. O hod. Den o acial O hop., 2005, 127(6), p 662–669 14. K. Yokoyama, K. Kaneko, K. Mo iyama, K. Asaoka, J. Sakai, and M. Nagumo, Hyd ogen Emb i lemen o Ni-Ti Supe elas ic Alloy in Fluo ide Solu ion, J. Biomed. Ma e . Res. A, 2003, 65(2), p 182–187 15. N. Schi , B. G osgogea , M. Lissac, and F. Dala d, Influence o Fluo ide Con en and pH on he Co osion Resis ance o Ti anium and I s Alloys, Bioma e ials, 2002, 23(9), p 1995–2002 16. M. Es-Souni, T. Es-Souni, and H. Fische -B andies, On he P ope ies o Two Bina y NiTi Shape Memo y Alloys. E ec s o Su ace Finish on he Co osion Beha iou and In Vi o Biocompa ibili y, Bioma e- ials, 2002, 23(14), p 2887–2894 17. A. Wichelhaus, M. Gese ick, R. Hibs , and F.G. Sande , The E ec o Su ace T ea men and Clinical Use on F ic ion in NiTi O hodon ic Wi es, Den . Ma e ., 2005, 21(10), p 938–945 18. Y. Oshida, R.C. Sachde a, and S. Miyazaki, Mic oanaly ical Cha ac- e iza ion and Su ace Modifica ion o TiNi O hodon ic A chwi es, Biomed. Ma e . Eng., 1992, 2(2), p 51–69 19. H.H. Huang, Va ia ion in Co osion Resis ance o Nickel-Ti anium Wi es om Di e en Manu ac u e s, Angle O hod., 2005, 75(4), p 661–665 20. F. Widu, D. D esche , R. Junke , and C. Bou auel, Co osion and Biocompa ibili y o O hodon ic Wi es, J. Ma e . Sci. Ma e . Med., 1999, 10(5), p 275–281 21. M. Es-Souni, H. Fische -B andies, N. Koc, O. Bo, K. Ra¨ zke. Chemische Zusammense zung, Umwandlungs e hal en und mechani- sche Biegeeigenscha en ausgewa¨hl e kie e o hopa¨dische NiTi-D a- h bo¨gen. IOK 2001, 33, p 87–106 22. A. Pau´l, C. Abalos, A. Mendoza, E. Solano, and F.J. Gil, Rela ionship Be ween he Su ace De ec s and he Manu ac u ing P ocess o O ho- don ic Ni-Ti A chwi es, Ma e . Le ., 2011, 65(23–24), p 3358–3361 23. I. Van Eygen, B.V. Vanne , and H. Weh bein, Influence o a So D ink wi h Low pH on Enamel Su aces: An In Vi o S udy, Am. J. O hod. Den o acial O hop., 2005, 128(3), p 372–377 24. J.A. on F aunho e and M.M. Roge s, Dissolu ion o Den al Enamel in So D inks, Gen. Den ., 2004, 52(4), p 308–312 25. ISO-s anda d 10993-15:2000 ‘‘Biological e alua ion o medical de ices. Pa 15: Iden ifica ion and quan ifica ion o deg ada ion p oduc s om me als and alloys’’ 26. J.D. Shenkin, K.E. Helle , J.J. Wa en, and T.A. Ma shall, So D ink Consump ion and Ca ies Risk in Child en and Adolescen s, Gen. Den ., 2003, 51(1), p 30–36 27. L. Ha nack, J. S ang, and M. S o y, So D ink Consump ion Among US Child en and Adolescen s: Nu i ional Consequences, J. Am. Die . Assoc., 1999, 99(4), p 436–441 28. C. Bou auel, T. F ies, D. D esche , and R. Plie sch, Su ace Roughness o O hodon ic Wi es Via A omic Fo ce Mic oscopy, Lase Specula Reflec ance, and P ofilome y, Eu . J. O hod., 1998, 20(1), p 79–92 29. C. Abalos, A. Pau´l, A. Mendoza, E. Solano, and F.J. Gil, Influence o Topog aphical Fea u es on he Fluo ide Co osion o Ni-Ti O hodon ic A chwi es, J. Ma e . Sci.: Ma e . Med., 2011, 22(12), p 2813–2821 30. N.X. Wes , J.A. Hughes, andM. Addy, E osion o Den ine and Enamel In Vi o by Die a y Acids: The E ec o Tempe a u e, Acid Cha ac e , Concen a ion and Exposu e Time, J. O al Rehabil., 2000, 27(10), p 875–880 31. A.J. Rugg-Gunn and J.H. Nunn, Die and Den al E osion. Nu i ion, Die and O al Heal h, Ox o d Uni e si y P ess, Hong Kong, 1999, p 32 32. M.R. G imsdo i and A. Hens en-Pe e sen, Su ace Analysis o Nickel-Ti anium A chwi e Used In Vi o, Den . Ma e ., 1997, 13(3), p 163–167 33. T. Eliades, G. Eliades, A.E. A hanasiou, and T.G. B adley, Su ace Cha ac e iza ion o Re ie ed NiTi O hodon ic A chwi es, Eu . J. O hod., 2000, 22(3), p 317–326 766—Volume 22(3) Ma ch 2013 Jou nal o Ma e ials Enginee ing and Pe o mance