A scanning electron microscopy study of the effect bleaching agents on enamel: A preliminary report Norman

C. Bitter,

University

of Southern California,

of

DDSa School of Dentistry, Los Angeles, Calif.

The effect of bleaching agents on the enamel surface was examined by scanning electron microscopy. The comparison of treated to untreated enamel revealed that the treated surface had increased surface change and porosity after the equivalent of 30 hours of exposure to the bleaching agent. The degree of alteration of enamel surface was not uniform and was influenced by cleanliness (oral hygiene) of the treated teeth and apparent variation in calcification. The enamel surface developed varying degrees of surface porosity and alteration. (J PROSTHET DENT 1992;67:8625.)

V ital bleaching of teeth has generated sufficient interest in the literaturelm4 and clinical treatment to prompt an investigation of the effect of bleaching agents on the enamel surface. Suggested techniques include the use of phosphoric acid and hydrogen peroxide solutions,5 10 % carbamide peroxide gel,?:and various commercially available products incorporating oxidizing agents. The pulpal reaction to bleaching6 and the potential oral epithelial tissue carcinogenicity of hydrogen peroxide solutions has been reported.7 This scanning electron microscopic (SEM) investigation describes the cumulative effect of enamel alteration and demineralization by bleaching agents on 14 extracted teeth.

aAssociate Professor, Department

of Restorative Dentistry.

10/l/36318

MATERIAL

AND

METHOD

Three commercially available night guard vital bleaching agents were tested (Rembrandt Lighten, Ultra White, and Natural White, Aesthete Laboratories, Laguna Niguel, Calif.). Rembrandt Lighten material has a pH of 6.8. Active ingredients are sodium citrate, carbamide peroxide, carbomer, and trolamine. The ingredients of Ultra White pretreatment solution are water citric acid, polyether, glycerine, phosphoric acid, FD & C blue dye No. 1. Whitening gel contains 10% carbamide peroxide in an anhydrous glycerol base. Ingredients in Natural White prerinse are deionized water, acetic acid, sodium benzoate, Tween 20, sodium saccharine, and menthol crystals. Oxygen bleach gel contains deionized water, hydrogen dioxide, carboxypolymethylene, TEA 99%. Pigment polishing cream contains glycerine, silica, sodium dioxide, deionized water, sorbitol, Zenothix 265, carboxymethylcellulose, sodium benzoate,

2. Photomicrograph of treated enamel surface (Rembrandt ) shows decalcification and increased porosity of the

Fig. Fig.

1.

SEM photomicrograph

of untreated enamel sur-

face (Rembrandt). (Left, Box insert, original X2,000; right, X10,000.) 352

magnification

enamel

surface.

X2,000;

right,

(Left, Box insert, X10,000.) JUNE

1992

original

VOLUME

magnification

67

NUMBER

6

EFFECT

OF BLEACHING

AGENTS

ON ENAMEL

Fig. 3. Photomicrograph of treated enamel surface (Rembrandt) shows etched, demineralization of surface. (Left, Box insert, original magnification X2,000; right, x10,000.)

Fig. 5. Surface treated with pretreatment solution for 2 minutes (Ultra White). (Left, Box insert, original magnification X2,000; right, X10,000.)

Fig. 4. Untreated (Left, Box insert, x10,000.)

Fig. 6. Surface treated with pretreatment solution followed with whitening gel (Ultra White). (Left, Box insert, original magnification X2,000; right, X10,000.)

enamel surface original magnification

(Ultra White). ~2,000; right,

methyl salicylate, menthol crystals, and sodium saccharine. Half of the enamel surface of the extracted tooth was covered with Teflon (Du F’ont Co., Wilmington, Del.) tape and half was exposed to ,the bleaching agents. The teeth were cleaned in a manner consistent with the manufacturers’ instruction and the agents were applied to the enamel surface. The teeth were stored in plastic containers in a humidor to prevent desiccation. The bleaching agents were applied to the teeth for a total of 30 hours. The teeth were not brushed at intervals, to simulate daily use or to simulate in vivo results. Therefore, tooth-brushing abrasion was not evaluated. The chemical effect on the enamel was evaluated on1.y by SEM observation. THE

JOURNAL

OF PROSTHETIC

DENTISTRY

RESULTS SEM examination revealed that the enamel surface was altered by the etching gel exposing a porous surface (Figs. 1 through 3). Bacteria may be observed in Fig. 2 just above the noted box, indicating a lack of good oral hygiene technique also noted before extraction. The insert box in Fig. 2 reveals an area of nonetched surface adjacent to the white spot. The remaining porous areas are a result of the exposure to the bleaching agents. A more extensively altered surface of another specimen can be seen in Fig. 3. Increased surface alteration and resultant porosity is evident. This alteration was not uniform throughout the surface. The untreated tooth with Ultra White material is rela853

BITTER

7. Untreated surface (Natural White). (Left, Box insert, original magnification X2000; right, X10,000.)

Fig.

9. Surface treated with prerinse, oxygen gel, and pigment polishing cream (Natural White). (Left, Box insert, original magnification X2000; right, X10,000.)

Fig.

This was created by the SEM processing, but the vertical cleavage line was notable in its presence. The results of all teeth evaluated were substantially the same as seen in these photomicrographs. It is of interest that the surface porosity varied (compare Fig. 2 and 3), demonstrating the lack of uniformity of effect. This was noted in other samples as well.

DISCUSSION

8. Surface treated with prerinse and oxygen bleach gel (Natural White). (Left, Box insert, original magnification X2000; right, X10,000.)

Fig.

tively smooth (Fig. 4). The pretreatment solution application demonstrates the common acid-etch effect on the enamel surface (Fig. 5). The effect of the whitening agent applied after the application of the pretreatment solution demonstrates a surface dissolution (Fig. 6). An untreated control for Natural White material is demonstrated in Fig. 7. ‘The prerinse and oxygen bleach gel was applied to the tooth., and surface dissolution is demonstrated (Fig. 8). The pigment polishing cream was additionally applied for 1 minute at three separate intervals and the oxygen bleach gel was reapplied thereafter. This altered enamel surface is demonstrated in Fig. 9. In several of the test samples, a fracture in the enamel was seen in the SEM at the point of demarcation of the Teflon tape separating the treated and untreated surfaces.

854

The effect of bleaching agents on teeth in this study demonstrated that surface enamel is significantly altered after 30 hours of exposure. Effects of exposure at lesser intervals of time was not evaluated. Alteration of the surface was not uniform in nature; some areas demonstrated little effect and other areas had serious dissolution of the surface. This does not coincide with the results of other investigations.” 8 The effect on the enamel surface in prolonged use of bleaching agents should be analysed. Although the depth of penetration of the bleaching agent and demineralization of the surface was not measured, the results indicate that further study of the effect of various bleaching and oxygenating agents to the enamel surface is warranted. Bleaching agents or pretreatment solutions may be acidic in nature and as such have a potential demineralizing effect on the enamel surface of teeth.

SUMMARY Bleaching of teeth has generated widespread interest in the dental and general population. The popular appeal of whitening the shade of teeth should be measured in light of the change to the enamel surface. The dissolution and increased-porosity effect of bleaching agents to the enamel surface should be seriously considered in recommending their common use and application.

JUNE

1992

VOLUME

67

NUMBER

6

EFFECT

OF BLEACHING

AGE:NTS

ON ENAMEL

2. Putt.er

CONCLUSION Further investigation of bleaching agents is indicated to determine the degree of alteration and the probable cummulative effect of continuous application of these agents to the vital tooth surfaces. The added effect of brushing in conjunction

with

weighted

in considering

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exposure

time

I thank Microanalysis, tance.

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bleaching their

to bleaching

JackWorrall of University

agents use.

should

also

agents

should

the Center for Electron of Southern California,

be studied.

Microscopy and for his assis-

Reprint

REFERENCES 1. Haywood VB, Heyman Int 1989;20:173-6.

THE

JOURNAL

be

The effect of intermedi-

H, Jordan RE. The “walking” bleach technique. J Esthet Dent 1989;1:191-3. 3. Nathanson D, Parra C. Bleaching vital teeth: a review and clinical study. Compend Contin Educ Dent 1987;8:490-8. 4. Jordan RE, Boksman L. Conservative vital bleaching treatment of discolored dentition. Compend Contin Educ Dent 1984;5:805-8. 5. Feinman RA, Goldstein RE, Garber DA. Bleaching teeth. Chicago: Quintessence, 1987. 6. Baumgartner JC, Reid DE, Pickett AB. Human pulpal reaction to the modified McInnes bleaching technique. J Endodont 1983$X527-9. 7. Weitzman SA, Weitberg AB. Effects of hydrogen peroxide on oral carcinogenesis in hamsters. J Periodontol 1986;57:685-8. 8. Haywood VB, Leech T, Heymann HO, Crumpler D, Bruggers K. Nightguard vital bleaching: effects on enamel surface texture and diffusion. Quintessence Int 1990;21:10:801-4.

HO. Night

OF PROSTHETIC

guard vital bleaching.

DENTISTRY

Quintessence

requests

to:

DR. NORMAN C. BITTER 3727 N. FIRST STREET SUITE 106 FRESNO, CA 93726

855

A scanning electron microscopy study of the effect of bleaching agents on enamel: a preliminary report.

The effect of bleaching agents on the enamel surface was examined by scanning electron microscopy. The comparison of treated to untreated enamel revea...
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