a new technique with sodium hypochlorite to increase bracket shear bond strength of...

8/10/2019 A New Technique With Sodium Hypochlorite to Increase Bracket Shear Bond Strength of Fluoride-releasing Resin-

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A New Technique With Sodium Hypochloriteto Increase Bracket Shear Bond Strength ofFluoride-releasing Resin-modified GlassIonomer Cements: Comparing Shear BondStrength of Two Adhesive Systems WithEnamel Surface Deproteinization BeforeEtchingRoberto Justus, Tatiana Cubero, Ricardo Ondarza, and Fernando Morales

By eliminating the organic substances from the enamel surface before etch-ing (deproteinization), orthodontic bond strength can theoretically be in-creased because the resulting etch-pattern is predominantly type 1 and 2,

instead of type 3. Fluoride-releasing resin-modified glass ionomer cements(RMGIs) might then routinely be used to bond brackets, instead of compos-ite resins. Reducing the incidence of white spot lesions, a major currentiatrogenic effect of orthodontic treatment, is a worthy cause which might beachieved due to the fluoride-releasing properties of RMGIs. The objective ofthis study was to determine whether deproteinization of human dentalenamel surfaces, with 5.25% sodium hypochlorite (NaOCl) before etching,increases orthodontic bracket shear bond strength (SBS) of 2 adhesivesystems: a composite resin and a RMGI.

Seventy-six extracted human premolars were cleaned, and randomlydivided into 4 groups (2 experimental and 2 control), with 19 premolars ineach group. In group 1 (experimental) and group 2 (control), brackets werebonded to the teeth using Transbond XT (3M Unitek Orthodontic Products,

Monrovia, CA) and in group 3 (experimental) and group 4 (control), FujiOrtho LC (GC America, Inc., Alsip, IL) was used. The buccal surfaces of thepremolars in experimental groups 1 and 3 were deproteinized with 5.25%NaOCl for 1 minute followed by rinsing, drying, and acid etching for 30seconds. Subsequently, the acid was rinsed off, the enamel was dried (andremoistened in the Fuji Ortho LC groups), and orthodontic brackets werebonded, either with primer and composite resin, or with RMGI. The sameprotocol was used in the 2 control groups (2 and 4), except that NaOCl wasnot used. The teeth were then stored in distilled water at room temperaturefor a maximum of 24 hours, thermo-cycled 500 times, between 5C and 55C,placed in a controlled Water Bath, at 37C for 24 hours, mounted on acrylicrings, and debonded using a universal testing machine. The enamel surfaces

were examined at 10 magnification to determine the amount of residualadhesive remaining on the tooth. An analysis of variance was used to

From the Department of Orthodontics, Intercontinental University, Mexico City, Mexico.Address correspondence to Roberto Justus, DDS, MSD, Ave. Ejrcito Nacional 530-502, Colonia Polanco, Mxico City, Mxico, 11560.

Phone: 52-55-55457170; E-mail:[email protected] 2010 Elsevier Inc. All rights reserved.1073-8746/10/1601-0$30.00/0doi:10.1053/j.sodo.2009.12.006

66 Seminars in Orthodontics, Vol 16, No 1 (March), 2010: pp 66-75
mailto:[email protected]:[email protected]


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nonfluoride-releasing composite resins to bondbrackets, rather than using fluoride-releasingRMGIs.

Orthodontists are aware that RMGIs provide asustained fluoride release following bonding

(for as long as the bracket is maintained on theenamel), that glass ionomer acts as a continuousfluoride pump, and that fluoride does protectenamel from developing WSLs.17-25 If RMGIs

were routinely used to bond brackets, the inci-dence of WSLs might dramatically decrease.Schmitt et al26 studied the effect of a fluoride

varnish on ex vivo human enamel demineraliza-tion, adjacent to brackets bonded with RMGIcement. They concluded that the RMGI reducedenamel demineralization as effectively as the var-nish. In vitro data suggest that RMGIs are moreeffective at inhibiting enamel demineralizationadjacent to orthodontic brackets, than fluoride-releasing resins.27

The objective of the present research was toinvestigate whether deproteinization of theenamel surface would increase SBS when usingFuji Ortho LC, a fluoride-releasing RMGI. Acomposite resin adhesive, Transbond XT, wasused as a control.

Espinosa et al28 showed that wetting and/orconditioning the enamel surface with 5.25% so-dium hypochlorite (NaOCL) for 1 minute, be-fore acid etching, increased the quality of the

etching pattern because NaOCl eliminated theorganic matter from the enamel surface (depro-teinization). The authors demonstrated that it isthis outer organic layer that prevents conven-tional 37% phosphoric acid from effectivelyetching the surface, resulting in inconsistentetch patterns and an unreliable enamel surfacefor orthodontic bonding. Type 1 and 2 etchingpatterns resulted when NaOCL was used,

whereas type 3 etching pattern predominatedwhen NaOCl was not used.

From the above mentioned description, it can

be speculated that increased SBS might beachieved by deproteinizing the enamel surfacewith 5.25% NaOCl, before etching with 37%phosphoric acid. If SBS can be increased withNaOCl, then RMGIs could be routinely used tobond brackets, instead of composite resin,thereby possibly reducing the incidence of WSLsdue to the fluoride-releasing property of RMGIs.

Up to the writing of this article, no researchhas been published evaluating whether depro-

teinization of human dental enamel surfaces,with 5.25% NaOCl before etching, increasesorthodontic bracket SBS. Thus, it was suggestedthat such an investigation was appropriate andmeaningful to further study this potential bene-

fit to patients.

Materials and Methods

Teeth

Seventy-six, freshly extracted, human premolarswere collected, cleaned, and stored in distilledwater at room temperature, a maximum of 6months and a minimum of 3 days. To meet thecriteria for use in the study, the teeth were se-lected only if they had intact buccal enamel, had

not been pretreated with chemical agents (eg,H2O2), had no surface cracks from extractionforceps, and were caries-free. The premolars

were randomly divided into 4 groups, (2 exper-imental and 2 control), with 19 premolars ineach group. In group 1 (experimental) andgroup 2 (control), brackets were bonded to theteeth using Transbond XT (primer plus compos-ite resin), and in group 3 (experimental) andgroup 4 (control), Fuji Ortho LC (a RMGI ce-ment) was used for bonding.

Brackets

Standard orthodontic premolar 0.018 metalbrackets (Gemini, 3M Unitek, Monrovia, CA),

with a 100-gauge mesh, were used in this study.The average surface area of the bracket base

was 7.9 0.3 mm2. This was determined by thefollowing laboratory procedures. A thin sheetof aluminum foil was used to make 10 imprintsof the bracket mesh of a bracket selected atrandom from this study. The 10 imprints were

cut around the mesh periphery with fine scis-sors. Gloves were used throughout the proce-dure to prevent skin contamination of the alu-minum. Each aluminum imprint was then held

with pliers and cleaned with an alcohol-im-pregnated cotton roll. The 10 imprints werethen weighed using a microscale. The meshsurface area was determined by applying amathematical formula to each of the recorded

weights.

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Groups Tested

Group 1 (Experimental), Premolars Bonded

With Transbond XT Resin, Using NaOCl

The buccal surfaces of the premolars were

cleaned with a nonfluoridated prophylaxis pasteand rubber prophylactic cups for 10 seconds,rinsed, dried, and deproteinized with 5.25%NaOCl (Clorox, The Clorox Co, Oakland, CA;pH 12.5) for 1 minute using a microbrush(Fig 1), followed by rinsing, drying, and acidetching with 37% phosphoric acid for 30 sec-onds. Subsequently, the acid was rinsed off, theenamel was dried, a thin layer of primer wasapplied with a microbrush, and light cured for20 seconds. The composite resin was thenplaced on the bracket mesh covering the entirebase of the bracket, without bubbles or voids,and the bracket was then applied to the toothusing sufficient force to produce a flash ofexcess adhesive around the bracket to ensure auniform thickness of adhesive. This procedureensured similar conditions as encountered inthe actual clinical environment. Excess adhesive

was removed with a sharp scaler, and the bracketwas light cured with a halogen light for 40 sec-onds (10 s on each side).

Group 2 (Control), Premolars Bonded With

Transbond XT Resin, Without Using NaOCl

The same protocol was used in this controlgroup, except that NaOCl was not used.

Group 3 (Experimental), Premolars Bonded

With Fuji Ortho LC, Using NaOCl

The buccal surfaces of the premolars werecleaned with a nonfluoridated prophylaxis pasteand rubber prophylactic cups for 10 seconds,deproteinized with 5.25% NaOCl for 1 minuteusing a microbrush, followed by rinsing, drying,and acid etching with 37% phosphoric acid for30 seconds. Subsequently, the acid was rinsedoff, the enamel was dried, and then remoistened

with artificial saliva (Viarden, Co, Mxico) ap-plied with a microbrush. This step ensured thatthe bonding surface was not desiccated. FujiOrtho LC (an RMGI) was mixed according tothe manufacturers instructions, and placed onthe bracket mesh covering the entire base of thebracket, without bubbles or voids. The bracket

was then applied to the tooth using force suffi-cient to produce a flash of excess adhesivearound the bracket to ensure a uniform thick-ness of adhesive. This procedure ensured similarconditions as encountered in the actual clinicalenvironment. Excess adhesive was removed witha sharp scaler, and the bracket was light cured

with a halogen light for 40 seconds (10 s on eachside).

Group 4 (Control), Premolars Bonded With

Fuji Ortho LC, Without Using NaOCl

The same protocol as in group 3 was used in thiscontrol group, except that NaOCl was not used.

Storing and Thermo-Cycling

Test specimens were prepared at 23C 2Cand stored in distilled water at room tempera-ture for 24 hours. They were then thermocycledbetween 5C and 55C for 500 cycles. The expo-sure to each bath was 25 seconds. The 2 transfertimes between the 5C and 55C baths were 5seconds each. Following thermocycling, the pre-

molars were placed in distilled water in a con-trolled water bath (incubator), at 37C, for 24hours. This was done to discriminate betweenthose materials that can and those that cannot

withstand a wet environment. A rectangularwire, measuring 0.017 0.025, was ligature tiedto each premolar bracket. This wire acted as amounting jig while the premolars were embed-ded in acrylic placed in aluminum rings to beable to test them with the Universal Testing

Figure 1. Clinical example of enamel deproteiniza-tion with 5.25% NaOCl for 1 minute (applied with amicrobrush) to increase bracket shear bond strength.(Color version of figure is available online.)

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To determine statistical significance an anal-ysis of variance F ratio (Fisher test) was used.This test detected that a statistical significantdifference existed between the 4 groups as the Fexperimental value was higher (3.56) than the F

critical value (2.74) (P 0.05). To determinewhich of the groups had significant differences,a Tukey test was used. The result indicated thatthe transbond groups had no statistical differ-ence, as the experimentalTvalue was 1.29 whilethe criticalTvalue was 3.56 (P 0.05). The Fujigroups did have statistical difference becausethe experimental T value was 3.93, which ishigher than the criticalTvalue (3.56,P 0.05).

Adhesive Remnant Index

The failure modes of the 2 types of adhesives arepresented inTable 2.The 2 comparisons of the ARI scores be-

tween the 2 Transbond XT groups was 2 6.41. This value was lower than the 2 critical

value of 9.49, indicating that they did not differsignificantly (P 0.05) from each other.

The 2 comparisons of the ARI scores be-tween the 2 Fuji Ortho LC groups was 2 24.08. This value was greater than the 2 critical

value of 9.49, indicating that they differed sig-nificantly (P 0.05) from each other. The ex-perimental group, in which NaOCL was used,had a significantly greater amount of adhesiveremaining on the enamel than the controlgroup.

Pilot SEM Study

Comparison of the enamel surfaces of the exper-imental and control groups (5 premolars in eachgroup) shows that the enamel conditioned withNaOCl produced a qualitatively rougher enamelsurface (Fig 2)than the enamel in which NaOCl

was not used (Fig 3). The SEM images from theexperimental group (using NaOCL) show a bet-ter etch pattern (types 1 and 2) than the imagesof the control group, in which NaOCl was notused (type 3 etch pattern).

Discussion

The present study evaluated 2 contemporary ad-hesive systems marketed for use to bond orth-

Figure 2. A SEM of enamel wetted with 5.25% NaOClfor 1 minute, and conditioned with 37% phosphoricacid for 30 seconds. Observe types 1 and 2 etchingpatterns.

Table 2. Frequency Distributions of the ModifiedARI Scores of the Four Groups

Group n

Modified ARIScorea

1 2 3 4 5

1. Transbond XT with NaOCl 19 6 1 4 4 4

2. Transbond XT withoutNaOCl 19 7 2 8 2 0

3. Fuji Ortho LC with NaOCl 19 0 5 11 2 14. Fuji Ortho LC without NaOCl 19 0 0 1 11 7

X2 6.41 for the Transbond groups;P 0.05; X2 24.08for the Fuji groups;P 0.05. ARI, adhesive remnant index;n, sample size.a1, all adhesive remained on the tooth with the imprints ofthe bracket base; 2, 90% of the adhesive remained on thetooth; 3, 10%-90% of the adhesive remained on the tooth; 4,10% of the adhesive remained on the tooth; 5, no adhesiveremained on the tooth.

Figure 3. A SEM of enamel conditioned with 37%phosphoric acid for 30 seconds (no NaOCl was used).Observe type 3 etching pattern.



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odontic bracketsa RMGI, Fuji Ortho LC, and aprimer and/or composite resin system, Trans-bond XT. The main objective of the study was todetermine whether NaOCl, applied for 1 minutebefore etching, increases bracket SBS.

By conditioning the enamel with 5.25%NaOCl, followed by a 30-second etching with37% phosphoric acid, the present findings indi-cated that the mean SBS of brackets bondedusing Fuji Ortho LC was 9.64 5.01 MPa, whichexceeds the clinical recommendation by Rey-nolds,29 which is a minimum tensile bondstrength of 5.9-7.8 MPa. In contrast, the Fujigroup in which NaOCl was not used had a muchlower mean SBS (5.71 3.87 MPa). Thus, if theclinician wishes to use RMGI to prevent WSLs, itis recommended, based on the findings of thepresent study, to deproteinize the enamel sur-face with 5.25% NaOCl for 1 minute beforeacid-etching as there was a statistically significantdifference between the 2 Fuji Ortho LC groups.

The SBS increased 3.9 MPa in the Fuji exper-imental group (with NaOCl), while increasingonly 1 MPa in the Transbond XT experimentalgroup. The authors believe that the small in-crease in the experimental Transbond XT groupis because a primer is used in this system. Eventhough the etching pattern is probably type 3

when no NaOCl is applied, the primer pene-trates the microporosities created during the

acid-etching process on the enamel surface. Thisallows for the incorporation of small resin tagsinto the enamel, thereby creating microscopicmechanical interlocks between the enamel andresin providing as a result adequate SBS. In con-trast, the Fuji material does not use a fluidprimer. Thus, if RMGIs are to be used, it isimperative that the enamel etching pattern be oftype 1 or 2 (to increase SBS), and not of type 3.The authors consider that the application ofNaOCl to achieve a better etching pattern isimportant for RMGIs to be clinically useful.

Enamel deproteinization is a prudent step in theoverall bracket bonding procedure, whetherRMGIs or resin composites are used. An im-proved marginal seal of the bracket base to theenamel is obtained because of types 1 and 2acid-etching patterns produced with the aid ofthe NaOCL application. WSL formation mightbe minimized due to this improved seal.

As the test specimens in the present studywere stored in distilled water, the organic ele-

ments on the enamel surfaces might have beenpartially lost. Thus, the authors believe that thein vivo application of NaOCl might result ingreater SBS than demonstrated in this ex vivostudy.

The ARI scores indicated that the bracketsbonded using Fuji Ortho LC without NaOClfailed in a different mode than those bondedusing the Transbond XT adhesive system andthe Fuji with NaOCL. In general, bond failurefor brackets bonded using Fuji Ortho LC with-out NaOCl occurred at the enamel-adhesive in-terface, whereas brackets bonded using NaOClfailed more often at the bracket-adhesive inter-face. These results were significant. The impor-tant result was that the ARI scores for the FujiOrtho LC group (with NaOCl), and the Trans-bond XT groups were similar.

Bracket failure at each of the 2 interfaces hasits own advantages and disadvantages.7 Bracketfailure at the bracket-adhesive interface is advan-tageous as it indicates good adhesion to theenamel. However, considerable chair time isneeded to remove the residual adhesive, withthe added possibility of damaging the enamelsurface during the cleaning process. In contrast,

when brackets fail at the enamel-adhesive inter-face, less residual adhesive remains on theenamel, but then bracket failure probably oc-curs more often during treatment, disrupting

chair time and prolonging the duration of orth-odontic treatment.

The SEM results showed that the enamel sur-face, conditioned first with NaOCl and followed

with phosphoric acid, was qualitatively rougherthan when no NaOCl was used. Etching patternsof types 1 and 2 were observed on enamel sur-faces of premolars conditioned with NaOCl fol-lowed by acid-etching (Fig 2). Etching patternsof type 3 were observed in premolars where noNaOCl was used (Fig 3). These results aresimi-lar to the ones reported by Espinosa et al28 in

2008. Etching of enamel with 37% phosphoricacid after eliminating the organic elements fromthe enamel surface probably produces longeradhesive tags that penetrate the enamel. Thelonger tags greatly increase the mechanicalretention of adhesives to the enamel, particu-larly of RMGIs, as demonstrated in the presentstudy.

RMGIs provide the advantages of sustainedfluoride release and the ability to bond brackets

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in a moist environment (due to their hydro-philic properties). The latter advantage is partic-ularly useful for bonding attachments to secondmolars. These molars are not being routinelybanded, probably due to the difficulty/pain in-

volved. This occurs due to the tissue impinge-ment of bands distal to these molars. If thesemolars are bonded with resin composite, thebonds frequently fail due to saliva contamina-tion of the enamel surface during the bondingprocedure. The American Board of Orthodon-tics has determined that many of the finishingproblems in the clinical cases presented for cer-tification arise in second molars.30 By bondingattachments on second molars with RMGIs, the

American Board of Orthodontics candidatescould improve their chances of passing Ameri-can Board of Orthodonticss clinical examina-tion. Bonding second molars with RMGIs has agreater chance of success than bonding withresin composites, because it has been docu-mented that the presence of humidity on theenamel surface, during the bonding procedure

with RMGIs, increases bond strength.However, RMGIs do have some disadvan-

tages. Wetting the enamel surfaces with NaOClfor 1 minute (to increase SBS) and mixing FujiOrtho LC powder and liquid, takes additionalchair time. This adhesive requires a longer timeto set than composite resin, and it has a lower

SBS in the first half hour after bonding, al-though it increases 20-fold within the first 24hours.4 Thus, clinicians need to consider theproperties of RMGIs to be able to use themsuccessfully. It is hoped that manufacturers inthe future will develop RMGIs with better initialbond strength. Because of the recent improve-ments in the fluoride-releasing capabilities andthe SBS of RMGIs, it has been suggested thatthese adhesives should play a greater role (ie, bemore widely used) in bonding orthodonticbrackets in the future.31

Clinical Recommendations

Once Fuji Ortho LC liquid/powder has beenmixed, the operator has less than a minute ortwo (depending on room temperature) to posi-tion the brackets before the adhesive begins toharden. This probably occurs due to the ambi-ent light (as it is light-cured). It is thereforerecommended to prepare adhesive for only 2

teeth at a time. NaOCl should also be applied to2 teeth at a time. The saliva suction tip should bepositioned in such a fashion as to suction awayall NaOCl excess. As RMGIs take a longer timeto set (24 h) than composite resins, the authors

recommend tying a very light wire (0.010 SS) ora NiTi wire, as the initial wire to avoid accidentaldislodging of brackets immediately after fullbonding due to the low initial bond strength ofRMGIs. When tying in the initial arch-wire, fullbracket engagement should be avoided in se-

verely malaligned teeth. When bonding brack-ets, care should be taken to avoid maxillary teethfrom biting against lower arch brackets, prevent-ing accidental dislodgement.

The authors agree with Forsberg et al32 whodemonstrated that the labial enamel of teethligated with an elastomeric ring may exhibit asignificantly higher number of microorganismsin the plaque than incisors ligated with steel

wire. It is then understandable that WSLs occurso frequently, both due to the widespread use ofelastomeric rings, or chains, to tie arch-wires,and to the use of nonfluoride releasing bondingadhesives.

Using a systematic review, Benson et al33 con-cluded that there is some evidence that the useof a daily NaF mouth rinse, or a glass ionomercement, for bonding brackets might reduce theoccurrence and severity of WSLs during orth-

odontic treatment.This article is being published in the hope

that it will create awareness among cliniciansthat they might diminish the incidence of WSLsby using NaOCL in combination with fluoride-releasing RMGIs.

Conclusions

Significantly greater bracket SBS can be ob-tained with Fuji Ortho LC if the enamel sur-face is wetted for 1 minute with 5.25%

NaOCL, before etching. When 5.25% NaOCL is used to deproteinize

the enamel surface, brackets bonded with FujiOrtho LC have comparable SBS to bracketsbonded with Transbond XT.

With 5.25% NaOCL use, the ARI scores aresimilar when either Transbond XT or FujiOrtho LC is used to bond brackets.

Applying 5.25% NaOCL to the enamel surfaceeliminates the organic elements. This effect



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allows the acid etchant to penetrate more ef-fectively into the enamel, creating type 1 and2 etching patterns. The increased bondingstrength allows the orthodontist to use fluo-ride-releasing RMGIs as bonding adhesives to

be able to possibly protect enamel from devel-oping WSLs, which is a major iatrogenic effectof orthodontic treatment. Combining clinicalaims and experience with the best availableevidence should be an important goal of everyclinician.

Additional research is needed to determinethe real clinical benefits of fluoride-releasingRMGIs. In vivo testing of the effectiveness ofRMGIs to prevent WSLs would be a worth-

while endeavor.

AcknowledgmentsThe authors wish to express their gratitude to Dr. JorgeGuerrero from the Universidad Nacional Autnoma deMxico (Dental Materials Department) and to Ana Lilia Solisfrom the Instituto Nacional de Rehabilitacin (MicroscopyDepartment).

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