A SEM evaluation of a 6% hydrogen peroxide toothwhitening gel on dental materials in vitro

Bruce Schemehorna,*, Carlos Gonzalez-Cabezasa, Andrew Joinerb

aIndiana University School of Dentistry, Oral Health Research Institute, 415 Lansing Street,Indianapolis, Indiana 46202, USAbUnilever Oral Care, Quarry Road East, Bebington, Wirral CH63 3JW, UK

Received 4 September 2003; revised 14 October 2003; accepted 15 October 2003

KEYWORDSTooth bleaching; Tooth

whitening; Hydrogen

Peroxide; Alloys;

Composite; Amalgam;

Porcelain; Gold; In vitro

model

Summary Objectives. The aim of this study was to evaluate the effects of a novel 6%hydrogen peroxide gel on the surface morphology of dental gold, amalgam, porcelainand composite.Methods. Admixed high-copper amalgam and hybrid resin composite specimens

were prepared in extracted teeth using standard clinical procedures. Feldspathicporcelain and type III gold specimens were prepared in a mould using standardlaboratory procedures. One half of the specimens were covered with nail varnish toserve as the control side, leaving the other half exposed. The specimens weretreated with pooled whole saliva (1 h), followed by the peroxide gel (20 min), rinsingwith water and returning to saliva. This cycling protocol was continued until a totalof 28 treatments with the peroxide gel were completed. The samples were preparedfor SEM.Results. There were no observable differences at 200 £ and 2000 £ magnifi-

cations between the control and peroxide gel treated sides on any of the materialstested.Conclusions. There were no significant effects of the 6% hydrogen peroxide gel on

the surface morphology of any of the dental materials tested.q 2003 Elsevier Ltd. All rights reserved.

Introduction

The use of patient-administered, peroxide contain-ing bleaching products is becoming increasinglypopular for whitening stained teeth since theirintroduction by Haywood and Heymann.1 As theseproducts contact tooth structures for extendedperiods of time and possibly inadvertently comeinto contact with dental materials, the effects ofbleaching products on dental hard tissues and dental

materials has attracted much attention in theliterature. Some studies report alterations in thesurface morphology of the dental hard tissues anddental materials, and also changes in their chemicaland physical properties, whereas other studies havefound no changes.2 –5 With this contrasting picture,it is therefore important for any newperoxide-basedformulation to be extensively evaluated for itseffects on dental hard tissues and dental materials.

Theaimof thecurrent studywas toevaluate, usingSEM, the effects of a new tooth whitening productcontaining 6% hydrogen peroxide on the surfacemorphology of the following dental materials: TypeIII gold alloy, porcelain, amalgam and composite.

0300-5712/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.doi:10.1016/j.jdent.2003.10.012

Journal of Dentistry (2004) 32, 35–39

www.elsevier.com/locate/jdent

*Corresponding author. Tel.: þ1-317-274-8822; fax: þ1-317-274-5425.

E-mail address: bschemeh@iupui.edu

Materials and methods

Specimens and treatments

Admixed high-copper amalgam (Dispersalloy,Dentsply, York, PA) and hybrid resin compositespecimens (Herculite, Kerr, Orange, CA) ðn ¼ 5=groupÞ were prepared in extracted teeth usingstandard clinical procedures. The feldspathicporcelain (Creation, Jensen, North Haven, CT)and type III gold (Firmilay, Jelenko, Armonk, NY)specimens were prepared in a mould usingstandard laboratory procedures. One-half of thespecimens were covered with nail varnish (Avon,Regal Red, USA) to serve as the control side,leaving the other half exposed. The specimenswere then treated by immersion into pooledwhole human saliva at 37 8C for 1 h to form aninitial pellicle layer. The five specimens of eachgroup were then immersed into the 6% hydrogenperoxide gel (Xtra Whitea, Unilever Oral Care)(5.0 g) at 37 8C for 20 min. The specimens werethen rinsed well and lightly brushed with a softtoothbrush to remove any residual gel. They werethen placed back into saliva for 1 h at 37 8C. Afterthis period, the specimens were treated onceagain with the peroxide gel as outlined above.Overnight the specimens were immersed in saliva.Four treatments were performed the first day andsix treatments were performed each of thefollowing four days for a total of 28 treatmentswith at least 1 h of saliva immersion betweentreatments.

SEM analysis

Specimens were air-dried in a desiccator. Theresin composite and porcelain specimens werecoated with gold–palladium alloy to a 200 Athickness (Desk II Cold Sputter Unit, DentonVacuum LLC, Moorestown, NJ). Specimens wereanalyzed in high vacuum conditions using a SEM(JSM-5310LV, JEOL Ltd, Peabody, Mass) at 20 Kv,10 spotsize, and a 12 , 14 mm working distance.Digital images were obtained from secondaryelectrons. Four secondary electron images weretaken from representative areas of the controland treated sides of each specimen and at twodifferent magnifications (200 £ and 2000 £ ).Images were coded and compared in a blindfashion. Observable differences were classified asmild, moderate or severe. The specimens werethen uncoded and the affected side and materialwere identified.

Results

Typical SEM images of the dental gold alloy,amalgam, porcelain and composite are shown inFigs. 1 –4, respectively. No differences wereobserved between the control and experimentalsides on any of the restorative materials tested. Inthe porcelain group, one of the five specimenspresented an irregular area that did not seem to berelated to the treatment. In the composite group,one specimen presented an apparent mild effect onthe control side (varnish covered side).

Discussion

The use of the SEM for viewing the surface ofspecimens is ubiquitous across all scientific dis-ciplines and it offers a rapid method to identify anymorphological surface changes in the materials ofinterest. In the current study, no significant effectswere observed on the surface morphology of gold,porcelain, amalgam and a composite after28 £ 20 min treatments with a 6% hydrogen per-oxide gel. Two specimens, one porcelain and oneresin composite, presented observable differencesbetween the control and experimental sides. Theporcelain specimen presented an irregular area inthe experimental side that seemed to be an artifactcreated during the preparation of the specimenrather than as a result of treatment. The resincomposite specimen showed the irregular area inthe control side. Since, it is very unlikely that atreatment effect would have taken place under theprotective varnish, we hypothesized that theobservation is related to an incomplete removal ofthe varnish before the SEM analysis.

These results contrast to in vitro studies wherechanges have been observed using SEM.5,6 However,even where changes have been observed by SEM theclinical relevance has been described as uncertain.5

The reason for the contrasting results on dentalmaterial properties by other workers is unclear. Itmay be speculated that this is due to differences instudy design or the vast array of home-use bleach-ing products and their differences in formulation.2

Indeed, Price et al.7 reports large differencesbetween 26 commercially available tooth whiteningproducts in terms of their peroxide concentration(up to 35%) and pH range (3.67–11.13). Thus, theimpact of any new tooth whitening product ondental material integrity needs to be fully charac-terised prior to launch.

The quantity of bleaching product used in thecurrent study can be considered to be in excess ofa Marketed as Signal/Mentadent/Pepsodent/Aim Xtra White.

B. Schemehorn et al.36

Figure 1 SEM images of gold alloy; A 6% hydrogen peroxide gel, 200 £ ; B control, 200 £ ; C 6% hydrogen peroxide gel,2000 £ ; D control, 2000 £ (original magnifications).

Figure 2 SEM images of amalgam; A 6% hydrogen peroxide gel, 200 £ ; B control, 200 £ ; C 6% hydrogen peroxide gel,2000 £ ; D control, 2000 £ (original magnifications).

A SEM evaluation of a 6% hydrogen peroxide tooth whitening gel on dental materials in vitro 37

Figure 3 SEM images of porcelain; A 6% hydrogen peroxide gel, 200 £ ; B control, 200 £ ; C 6% hydrogen peroxide gel,2000 £ ; D control, 2000 £ (original magnifications).

Figure 4 SEM images of composite; A 6% hydrogen peroxide gel, 200 £ ; B control, 200 £ ; C 6% hydrogen peroxide gel,2000 £ ; D control, 2000 £ (original magnifications).

B. Schemehorn et al.38

the in vivo situation since there was no elution ofthe gel from the surface of the dental material. Thisis in contrast to the in vivo situation where it isknown that peroxide levels within bleaching pro-ducts are depleted during use.8 Thus, the exper-imental design in the current study was anexaggeration of what is anticipated under normaluse, and can be used as further confirmation of thesafety of this product when used according to themanufacturer’s instructions.

In conclusion, there were no observable signifi-cant effects of the 6% hydrogen peroxide gel on thesurface morphology of gold, porcelain, amalgamand composite dental restorative materials tested.

References

1. Haywood VB, Heymann HO. Nightguard vital bleaching.Quintessence International 1989;20:173—176.

2. Swift EJ, Perdigao J. Effects of bleaching on teeth andrestorations. Compendium of Continuing Education in Den-tistry 1998;19:815—820.

3. Walsh LJ. Safety issues relating to the use of hydrogenperoxide in dentistry. Australian Dental Journal 2000;45:257—269.

4. Yap AUJ, Wattanapayungkul P. Effects of in-office toothwhiteners on hardness of tooth-colored restoratives. Operat-ive Dentistry 2002;27:137—141.

5. Bailey SJ, Swift EJ. Effects of home bleaching products oncomposite resins. Quintessence International 1992;23:489—494.

6. Rotstein I, Cohenca N, Mor C, Moshonov J, Stabholz A. Effectof carbamide peroxide and hydrogen peroxide on the surfacemorphology and zinc oxide levels of IRM fillings. Endodonticsand Dental Traumatology 1995;11:279—283.

7. Price RBT, Sedarous M, Hiltz GS. The pH of tooth-whiteningproducts. Journal of the Canadian Dental Association 2000;66:421—426.

8. Sagel PA, Odioso LL, McMillan DA, Gerlach RW. Vital toothwhitening with a novel hydrogen peroxide strip system:design, kinetics, and clinical response. Compendium ofContinuing Education of Dentistry 2000;21:S10—S34.

A SEM evaluation of a 6% hydrogen peroxide tooth whitening gel on dental materials in vitro 39