Sensitivity of Titanium Brackets to the Corrosive Influence of Fluoride-Containing Toothpaste and Tea

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1 Originl Article Sensitivity of Titnium Brckets to the Corrosive Influence of Fluoride-Contining Toothpste nd Te Winfried Hrzer, Dr Med Hbil ; Anke Schröter, Dr Med Dent b ; Tomsz Gedrnge, Dr Med Dent b ; Frnk Muschter, Dr Med Dent b Abstrct: Titnium brckets re used in orthodontic ptients with n llergy to nickel nd other specific substnces. In recent studies, the corrosive properties of fluoride-contining toothpstes with different ph vlues were investigted. The present in vivo study tested how the surfces of titnium brckets rect to the corrosive influence of cidic fluoride-contining toothpste during orthodontic tretment. Molr bnds were plced on orthodontic ptients. In these sme ptients, titnium brckets were bonded on the left qudrnts nd stinless steel brckets on the right qudrnts of the upper nd lower rches. Fifteen ptients used Gel Km contining soluble tin fluoride (ph 3.), wheres 3 used fluoride-free toothpste. The brckets were removed for evlution by light microscopy nd scnning microscopy 5.5 to. months nd.5 to months fter bonding. The qulity nd quntity of elements present were mesured by scnning microscopy. Mcroscopic evlution showed the mtte gry color of titnium brckets dominting over the silver glem of the steel brckets. The plque ccumultion on titnium brckets is high becuse of the very rough surfce. Pitting nd crevices were observed in only 3 of the 65 brckets tested. The present in vivo investigtion confirms the results of in vitro studies, but the chnges re so minor tht titnium brckets cn sfely be used for up to months. Wing surfces should be improved by modifying the mnufcturing process. (Angle Orthod ;:3 33.) Key Words: Titnium brckets; Corrosion by fluorides; Acidic toothpste INTRODUCTION The use of titnium brckets is dvntgeous in the orthodontic tretment of ptients with n llergy to nickel nd other specific substnces. However, the results of recent studies investigting the corrosive properties of fluoride-contining toothpstes differed with respect to the ph vlue of the environment.,, Boere used polriztion resistnce technique (n electrochemicl corrosion test procedure in vitro) nd observed lrge decrese in polriztion resistnce with incresing fluoride concentrtion t ph. Toumelin-Cheml et l tested the corrosive properties of fluoride-contining toothpstes on titnium in vitro nd found substntil corrosion processes in the fluoridted cidic medi. Reclru nd Meyer suggested tht fluoride ions re the only ions cting on the protective lyer of titnium nd cusing loclized pit Professor, Chirmn, Deprtment of Orthodontics, University Clinics, Technicl University of Dresden, Germny. b Postgrdute student, Deprtment of Orthodontics, University Clinics, Technicl University of Dresden, Germny. Corresponding uthor: Prof Dr Med W. Hrzer, Poliklinik für Kieferorthopädie Universitätsklinikum, TUD, Fetscherstr, D-3 Dresden, Germny (e-mil: hrzer@rcs.urz.tu-dresden.de). Accepted: October. Submitted: April. by The EH Angle Eduction nd Reserch Foundtion, Inc. ting nd crevice corrosion. He found wek glvnic currents within ph rnge of 6. to 3.5 in tests involving rtificil sliv. However, in confined res where fluoride ions were present, titnium nd other dentl lloys underwent corrosive process in the form of crevices nd pitting when the ph dropped below 3.5. Kusy et l 5 found in depth profile of titnium, oxygen, crbon, nd nitrogen tht the bulk structure ws 5%, but in the ner surfce region some to 3 Å in depth, the titnium metl ws present with ever-incresing quntities of crbon, oxygen, nd nitrogen. Therefore, the surfce of brckets is not titnium-rich lloy. Homul et l suggested tht the smooth, Teflonlike surfce of titnium, becuse of thin lyer of titnium oxide, prevents direct contct between the metllic toms on the surfce of the wire nd the brcket, thus reducing intertomic dhesion nd friction. The existing dt were obtined from in vitro experiments nd re not directly pplicble to the conditions in the orl environment. The present reserch tested the corrosive influence of cidic fluoride-contining toothpste on titnium brckets in vivo during orthodontic tretment by compring titnium nd steel mteril. MATERIALS AND METHODS Eighteen orthodontic ptients, children (men ge.5 yers) nd dults (men ge.3 yers), were selected Angle Orthodontist, Vol, No, 3

2 FLUORIDE CORROSION OF TITANIUM BRACKETS 3 TABLE. Distribution of Ptients, Kind of Toothpste, nd Orthodontic s Acidic Fluoride Toothpste (Gel Km) Fluoride-free Toothpste (Putzi) Ptients, n Twistflex Nitinol Twistflex Nitinol Children Adults TABLE. Number of Investigted Brckets nd s Vrible Twistflex wire Nitinol wire b Twistflex wire Nitinol wire Titnium Children Steel Titnium Brckets Adults Steel 3 5 Titnium 6 65 indictes fluoride in toothpste. b indictes no fluoride in toothpste Steel 3 FIGURE. Mesurement points t the brckets: brcket wing, / brcket slot, 3 t the side of brcket ( detil region of Figures nd b). for the investigtion (Tble ). All ptients received fixed orthodontic pplince with bnds t the molrs nd brckets t the incisors, cnines, nd premolrs. Titnium brckets (Denturum, Pforzheim, Germny; Germn mteril no. 3.65, titnium grde ) were used on the left side in the upper nd lower jws, wheres steel brckets were used on the right side. Two mnufcturing steps re used for the production of titnium brckets. In the first step, profile is cold rolled nd in the second step the slots re milled. All ptients were right hnded, resulting in more intensive brushing on the left jw side. This side ws chosen becuse the mechnicl stress nd clening effect of brushing the left side is higher in right-hnded ptients. For dily brushing (every morning nd evening), 5 ptients ( chil- Angle Orthodontist, Vol, No,

3 3 HARZER, SCHRÖTER, GEDRANGE, MUSCHTER FIGURE. () One of the 5 in vitro tested brckets which hd been rinsed for minutes with Gel Km solution. Brcket is shown before rinsing (region t wing, see rrow, Figure ). (b) Brcket from Figure fter rinsing. No chnge nd no sign of corrosion re present. (c) Element nlysis in titnium brcket, which ws rinsed for dys in green te solution. dren nd dults) used Gel Km toothpste (Colgte, Hmburg, Germny) contining soluble stnnous fluoride (ph 3.; group ). Three ptients ( child nd dults) served s controls nd brushed with fluoride-free Putzi toothpste (Dentl Kosmetik, Dresden, Germny). This product contins ph rnging from. to. (group ). The choice of fluoride-free dentifrice is normlly less often prcticed for dily tooth brushing, but for the methodologicl design to exclude ny fluoride influence, the use of fluoride-free dentifrice ws necessry. All ptients used sme type of toothbrushes (Orl B, Frnkfurt/Min, Germny). Nickeltitnium nd steel twistflex wires were used for orthodontic tretment. These wires were fixed to the brckets with elstomeric ligtures. However, becuse of mstiction nd occlusion, the wires moved with resulting friction nd ttrition. This ttrition is strongest in steel twistflex wires. s were dditionlly subdivided into those with nickel titnium wires nd those with steel twistflex wires (Tble ). The ptients kept written record of food intke nd tooth brushing. They were sked to note other potentil fluoride intke, eg, te. Blck nd green tes contin dditionl fluoride nd complicted the investigtions. However, mny orthodontic ptients drink te, nd for this reson, this influence ws tken into ccount. The orl hygiene sttus ws recorded every months by using the Orl Hygiene Index with plque stining (Mir -tone solution). In period of 5.5 to. months fter brcket fixtion, titnium nd steel brcket were removed from ech ptient nd tested for corrosion pitting nd crevices. These brckets were replced with new ones. All titnium brckets were removed fter tretment period rnging from.5 to months. Five titnium brckets were tested in Gel Km solution for durtion of minutes for comprison with in vitro conditions. Every minutes, the brckets were rinsed in n ultrsonic bth with % lcohol. Additionl titnium brckets nd steel brckets were tested in green nd blck te solutions (6:6 of ech brcket nd te kind). The brckets were put in green nd blck te solution with temperture of 5 C to55 C for dys. For nlysis of corrosion processes, predetermined mesurement points were recorded from the brckets before nd fter tretment (Figure ). Brckets tht becme detched during tretment were excluded from the evlution. The investigtion involved 65 titnium brckets nd steel brckets rndomized from ech group nd contct time in the mouth (Tbles nd 3). An MZ stereo microscope (Leic, Frnkfurt, Germny) nd DSM Gemini scnning microscope (Crl Zeiss, Jen, Germny) were used for microscopic nlysis. The qulity nd quntity of elements, in prticulr, fluoride, tin nd titnium, were registered on titnium nd steel brckets by scnning microscopy. Sttisticl evlution ws performed with the SPSS progrm. The results re given s rithmetic mens stndrd devition. For sttisticl nlysis, the test ws pplied (P.5) for orthodontic ptients. For microscopic Angle Orthodontist, Vol, No,

4 FLUORIDE CORROSION OF TITANIUM BRACKETS 3 FIGURE 3. Trces of mechnicl stress t the bottom of slot, point between the wings (see Figure ) of titnium brcket cused by the friction of twistflex wire. TABLE 3. Durtion of Bonded Brckets in the Mouth (Time of Fluoride Contct) Time, mo Titnium Brcket Steel Brcket indictes fluoride in toothpste;, no fluoride in toothpste. TABLE. Plque Accumultion (Brown) in Ptients With Te Consumption (Green nd Blck) Titnium brcket Steel brcket Children Te, n 5 Te, n 3 indictes fluoride in toothpste. Te Te, n 3 5 Adults Te, n TABLE 5. Chnge of Color nd Plque on Titnium Brckets (n 65) Mesuring Point/ Discolortion 3 Plque (brown) n % indictes fluoride in toothpste. b indictes no fluoride in toothpste. * P.5. b n %.* evlution, 65 titnium brckets nd steel brckets were investigted. Elements were nlyzed in 33 of 65 titnium brckets nd of steel brckets. RESULTS The Orl Hygiene Index rnged from. to. in ll ptients. Nine ptients representing the group stted tht they drnk blck or green te (Tble ). In vitro testing of the 5 brckets, which hd been rinsed for minutes with Gel Km solution, showed no chnge nd no sign of corrosion (Figure,b). In vitro testing of the brckets, which hd been rinsed for dys with green nd blck te solution, showed very smll mount of fluoride (. wt%) with high integrted error (.; Figure c). Mcroscopic evlution showed the mtte gry color of the titnium brckets dominting over the silver glem of the steel brckets. Eight weeks fter bonding, the titnium brckets hd drkened in color. Regrdless of the toothpste used, the plque ccumultion on the titnium brckets ws greter thn in steel brckets. In of 5 ptients using Gel Km, the teeth nd brckets hd yellow-brown cotings cused by the cidic stnnous fluoride in the toothpste nd encourged by the rough surfce of the titnium (Tbles nd 5). Microscopic evlution of 65 titnium nd steel brckets reveled trces of mechnicl ction cused by the friction of the wires nd ligtures t the bottom of the slot between the wings of the brckets, but there ws no significnt difference mong the brckets, wires, nd toothpstes used (Figure 3; Tbles nd 5). Microscopic signs of the corrosion process re pits, crevices, nd their extensions, but s the surfce of the titnium Angle Orthodontist, Vol, No,

5 3 HARZER, SCHRÖTER, GEDRANGE, MUSCHTER brcket is very rough becuse of the mnufcturing process (cold rolling), the corrosion process cn be identified only from n extension of existing pitting. In clinicl testing, fissures, present t the wings of 3 titnium brckets in ptients (Gel Km), seemed to be extended fter nd months, respectively. Scnning microscopy reveled tht the length of crevice ws lmost the sme fter the use of fluoride toothpste (35.5 nd 35.3 m, respectively), but the width ws doubled (.6 m to.5 m; Figure,b). In specil nlysis of elements in the crevice, no fluoride occurred (Figure c). Anlysis of the elements in titnium nd steel brckets reveled very infrequent occurrence of fluoride t the,% level, which ws detected in only titnium nd steel brckets of 3 ptients. In titnium brcket, from ptient in the group with te consumption, nlysis reveled smll mount of fluoride similr to the in vitro test. DISCUSSION The surfce structure nd the color of titnium nd steel brckets re very different. The surfce of the rolled wings of titnium brckets is very rough, nd the biocomptibility of titnium supports plque dherence. These re the resons for significntly more plque ccumultion nd more mrked chnge of color with titnium brckets. The slots of titnium brckets re not s rough s the wings becuse the slots re milled nd not rolled. Deeper nd wider crevices were found in the wings of only 3 of the 65 titnium brckets investigted (%). This ws possibly cused by the slight deformtion ssocited with the removl process of the brcket nd lso confirms the in vitro results of Boere, Toumelin-Cheml et l, nd Reclru nd Meyer. These ltter uthors reported the occurrence of corrosion potentil in fluoridted cidic medi with ph below. or 3.5. The ph of Gel Km is 3., but the findings with deeper nd wider crevices t the wings of 3 of 65 brckets re insignificnt. The resons for the differences between the in vitro nd the in vivo experiments might be the short exposure time of the fluoride ions in the toothpste to the titnium of the brckets, s well s to the heterogeneity of the outer lyers where the titnium metl ws present with incresing mounts of oxygen, nitrogen, nd crbon. The ptients were instructed to brush their teeth for 3 minutes twice dy. However, the results confirm those of FIGURE. () Scnning microscopy picture from wing of titnium brcket (region, Figure ) before bonding t the tooth. (b) Scnning microscopy picture from wing of the sme titnium brcket from Figure fter bonding nd use of fluoride toothpste for months. The length of crevice ws lmost the sme (I I), but the width ws doubled (: :). Compre Figures nd b before nd fter tretment. (c) Anlysis of elements shows no occurrence of fluoride in the crevice (spot mesurement; penetrtion depth 5 to m). Angle Orthodontist, Vol, No,

6 FLUORIDE CORROSION OF TITANIUM BRACKETS Reclru nd Meyer with respect to the crevice potentil. The presence of fluoride ions does not ffect the crevice potentil of different lloys, including titnium, when the ph vlues re between 6.5 nd 3.5. On the other hnd, t ph 3, the crevice potentil of titnium becomes negtive t 55 mv vs SCE (Sturted Colomel Electrode). Thus, titnium undergoes corrosion process in the form of crevices nd pitting from ph 3.5 onwrd. In conclusion, the ggressiveness of the environment t ph 3 is such tht it is no longer possible to mintin pssivtion zones, nd titnium will, therefore, undergo continuous degrdtion. The low rte of brckets with crevices is cused by the rinsing effect of sliv, wter, nd food tht dilutes the fluoride ion concentrtion. Anlysis of the elements in these brckets with deeper crevices reveled no fluoride. Fluoride ws found only in te-consuming ptients, but the in vitro experiments showed this to be very smll mount with high vrition. An dverse effect of the ppliction of titnium brckets is their rough nd smooth surfce with high plque ccumultion. This upper lyer is very biocomptible nd serves s depot for bcteri nd electrolytic medium for different ions. The mnufcturer should modify the production process nd mill the entire brcket, but this is only of minor influence of the plque dherence. Nevertheless, the comprison of Figures nd b shows tht the surfce of the brcket fter months is less prone to gther debris nd plque. The reson my be tooth brushing nd ttrition by hrd food. CONCLUSIONS. Titnium brckets show higher plque ccumultion nd more discolortion thn steel brckets. This is cused by the rough surfce with smooth outer lyer. Biocomptibility should be improved by modifying the mnufcturing process, but this influence is less thn in steel brckets.. In contrst to the results of in vitro investigtions, pits nd crevices re found under cidic conditions below ph 3.5 in only few brckets. The reson for this difference might be the short rection time of fluoride ions nd dilution by sliv nd liquids The combined use of titnium brckets in combintion with the use of cidic fluoride dentifrice nd fluoridted foods is completely hrmless for the brcket nd does not give rise to corrosion. ACKNOWLEDGMENTS This reserch project ws supported by Dentl Forschung e.v. nd by DENTAURUM. We thnk Prof Dr H. Worch (Institute for Mteril Science, TU Dresden) for consulttion nd support with scnning microscopy. REFERENCES. Rolsdorph MC. Klinische Aspekte bei der Anwendung von Titnbrckets [disserttion]. Freiburg, Germny University of Freiburg Br.; 6.. Boere G. Influence of fluoride on titnium in n cidic environment mesured by polriztion resistnce technique. J Appl Biomter. 5;6:3. 3. Hösch A, Strietzel R. Korrosion von Titn in thiocynt-, chloridund fluoridhltigen künstlichen Speicheln. Dtsch Zhnärztl Z. ;:6 6.. Homul DW, Homul W, Sernetz F. Pure titnium orthodontic brckets. J Clin Orthod. 6;3:. 5. Kusy RP, Whitley JQ, Ambrose WW, Newmn JG. Evlution of titnium brckets for orthodontic tretment: prt I. The pssive configurtion. Am J Orthod Dentofcil Orthop. ;: Kypreos G, Rolsdorph MC, Jons IE, Kppert HF. Clinicl spects concerning the use of titnium brckets [bstrct ]. Eur J Orthod. ;:5.. Pröbster L, Lin W, Hüttemnn H. Effect of fluoride prophylctic gents on titnium surfces. Int J Orl Mxillofc Implnts. ; :3 3.. Quigley G, Hein J. Comprtive clening efficiency of mnul nd power brushing. J Amer dent Ass. 6;65:6.. Reclru L, Meyer JM. Effects of fluorides on titnium nd other dentl lloys in dentistry. Biomterils. ;:5.. Pessler K, Bestelmeyer F, Ohnmcht P, Sernetz F. Einflüsse uf die Qulität und Eigenschften von dentlen Güssen. Dent Lbor. ;3: 5.. Toumelin-Cheml F, Rouelle F, Burdiron G. Corrosive properties of fluoride-contining odontologic gels ginst titnium. J Dent. 6;: 5.. Bsic System User s Guide: Sttisticl Pckges Socil Sciences. Chicgo, Ill: SPSS Inc; 3. Angle Orthodontist, Vol, No,