lterations in human enamel surface 1 bleaching Richard

S. McGuckin,

Dental Branch, University

DDS,

MSC,~ J. F. Babin,b

morphology

following

and B. J. Meyerb

of Texas Health Science Center, Houston, Tex.

Extracted intact human teeth (n = 4) were treated for 30 days by three protocols: Home 1 (Proxigel, n = 4) for 8 hours daily, Home 2 (White & Bright, n = 4) for 24 hours with 3 minutes of stannous fluoride gel, or an Office protocol (n = 4) using 30% hydrogen peroxide (Superoxol) warmed by a high-intensity light while the controls remained untreated. “Home” bleaching agents contain approximately 10% carbamide peroxide. After treatment, the coronal surfaces were examined with a scanning electron microscope (SEM) at 2000 power magnification, and the surface topography was measured by a profilometer. The SEM photomicrographs of the controls and office-treated groups were similar to previously reported descriptions, while the home bleached surfaces appeared similar to each other. Profilometric analysis was used to examine surface roughness and surface waviness. Mean surface roughness in microns was: control, 1.9; Home 1,0.6; Home 2,O.g; and Office, 0.6. Surface waviness was ranked control > office > Home 1 = Home 2. Enamel surface alterations were evident after the three bleaching methods. The differences between the office and home-treated surfaces were unrelated to the pH of the bleaching agents. (J PROSTHET DENT 1992;68:754-60.)

ital bleaching is rapidly gaining popularity with patients and dentists as a conservative technique to lighten natural teeth.l Unfortunately, clinical use has preceded scientific investigations of possible consequences, and numerous current references to vital bleaching are anecdotal. There are two methods for bleaching vital teeth. One is an office procedure that stipulates isolation of the teeth, application of 30 % hydrogen peroxide (HsOs), and warming by a heat source, usually a high-intensity light.2 Although immediate results are commonly noted after the first treatment, several weekly treatments are required to achieve lighter shades3and retreatment may be indicated to maintain the desired shade. A serendipitous discovery4 recently confirmed that overthe-counter (OTC) peroxide-based oral antiseptics had the potential to lighten teeth. The procedure, colloquially named “Home bleaching,” uses vacuum-formed trays to maintain the bleaching agent surrounding the teeth. The tray is worn 8 to 24 hours daily, depending on the technique variation prescribed by the dentist or followed by the patient. These OTC products contain, among other ingredients, approximately 10 % carbamide peroxide (CHsNsHsOs) in an anhydrous glycerol base.5 Manufacturers have rapidly introduced special esthetic bleaching products in the marketplace. Enamel and dentin have demonstrated high permeabil-

aAssociate Professor, Department thodontics. bDental student (IV). 10/l/41421

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ity to hydrogen peroxide,6 but the method by which peroxides permeate enamel and dentin has not been identified. Enamel has “micropores? that presumably allow peroxides to pass, but other mechanisms probably coexist. Dentinal tubular morphology, with its accompanying fluid and physiologic characteristics including high moisture content (28 vol. %),8 encourage ready physical passage, dilution, and chemical reaction of peroxides. Bleaching is believed to result from an intricate oxidative reaction.4,g This investigation used scanning electron microscopy (SEM) and surface texture analysis to describe clinically relevant morphologic alterations of enamel surfaces treated by three vital bleaching techniques. MATERIALS

AND

METHODS

Three bleaching agents were selected for this investigation. Each agent represents a different clinical technique and a presently available product. Thirty percent hydrogen peroxide (Superoxol, Union Broach, York, Pa.) is indicated only for professional application because of the potential for soft tissue damage. The bleaching action is accelerated by (1) pretreatment with either phosphoric (HaPOh) or hydrochloric (HCl) acid2 to increase enamel porosity and (2) warming the hydrogen peroxide within physiologic limits of the pulp to hasten the reaction.3 Proxigel (Reed & Carnrick, Piscataway, N.J.) is an OTC or nonprescription oral antiseptic that has been used for home bleaching,lO and that contains approximately 10% carbamide peroxidell and Carbapol,5 a thickening ingredient that reportedly delays oxygen release.5White & Brite (Omni Products International, Gravette, Ark.) also contains 10% carbamide peroxide (but not Carbapol) and is only available professionally.

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I. Materials

Table

/---

Item

WA’fNESS

source

Nail varnish

ROUGHNESS ROUGHNESS SPACING Fig.

1.

Surface characteristics.24

Proxigel NDC 0021-0150-12 Superoxol Item No. 39800 White & Brite NDC 217-3800-60 Tin-Gel

Scotch Gel

Table I lists the bleaching agents in this investigation, their lot numbers, and sources of supply. The pH and fluoride content of each product are presented in Table II. The pH was determined by a pH meter (pH meter 26; Radiometer, Copenhagen, Denmark, and West Lake, Ohio), and the fluoride ion content was measured by a millivoltmeter (Model 811, Orion Research, Boston, Mass.) with a fluoride ion-specific electrode. Both instruments were calibrated before the research. Fourteen intact extracted human central incisors were used as specimens. The roots were dbbrided of periodontal fibers, while extrinsic stains and accretions were lightly scaled from the coronal surfaces. The remaining debris was removed from the entire tooth with a slurry of medium-grit pumice (Moyco, Philadelphia, Pa.) and a webbed prophy cup. The roots were covered with two coats of nail varnish to limit the areas exposed to the bleaching agents. The specimens were randomly subdivided into four groups. All specimens were treated and stored on 30 ml screw-top vials at an ambient room temperature of approximately 20’ C. The entire experimental regimen was completed in 30 days, and teeth not immediately subjected to active bleaching treatment were stored in isotonic saline containing 0.2 % sodium azide (NaNs) to prevent bacterial growth.12 All storage media were changed daily, and the control specimens (n = 2) that remained untreated were retained in storage media. Specimens in the Home 1 group (n = 4) were treated for 30 days with Proxigel, an OTC oral antiseptic described by Haywood and Heyman. lo Treatment was limited to an average immersion of 8 hours per day, and the bleaching agent was removed by rinsing the specimen in running tap water for 30 seconds. Specimens were placed in storage media until the next daily treatment. Teeth in the Home 2 group (n = 4) were treated with White & Brite according to the manufacturer’s instructions. This group of teeth was treated daily for 24 hours, except for a 30-second rinse in tap water to remove the bleaching agent. This was followed by a a-minute immersion in a 4% stannous flouride gel (Tin-Gel, Preventive Dentistry Support Center, Houston, Texas), that was later

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Table

II.

Lot/Expiration

Aristocrat Brooklyn, N.Y. Reed & Carnrick Piscataway, N.J. Union Broach York, Pa. Omni Products International Gravette, Ark. Preventive Dentistry Support Center Houston, Texas 3M Dental Products Division St. Paul Minn.

date

Enamelettes Lots 9013 & 9017 Exp 9/91 & 11/91 Lot 13058

Lot 9753

Lots 8DE, 9EM, 8CR

Fluoride concentration and pH of bleaching

products PH Product Superoxol Proxigel Unknown White & Brite Tin-Gel

Lot No.

Test

8191 11/91 9013 9017

3.0 3.0 4.7 4.7

13508 Unknown

6.2 3.4

*

t

Fluoride (rgkm) Not tested 0.2 Not tested 75.8

4.0

4.3-4.8

5.3

6.1-6.7

36.1 1000

*Data from Miller MC, Mabrito CA. Reality Now 199O;B:l. JrDatafrom Christiansen GC. Clin Res Assoc Newsletter 1989;13:1-3. These data reproduced by permission. These data were current at the time of publication.

removed by rinsing the specimens for 30 seconds in tap water. The specimens were then returned to fresh bleaching solution. Office specimens (n = 4) were subjected to four treatments, 7 days apart, using a known clinical technique.2,3 The facial surfaces were pumiced as previously described. The tooth was rinsed for 30 seconds,etched for 20 seconds with 37% phosphoric acid gel (Scotch Gel, 3M Dental Products Division, St. Paul, Minn.), and rinsed for 30 seconds in running tap water. The specimens were wrapped in a single layer of cotton gauze and were arranged on a rubber dam. A bleaching light (New Image, Union Broach, York, Pa.) was positioned approximately 20 cm from the specimens. A thermometer ensured that temperature did not exceed 40.5’ Cl3 in the illuminated area. The gauze was saturated with 30% hydrogen peroxide (Superoxol), and the exposure time for each treatment was 30 minutes. After treatment, each specimen was rinsed for 30 seconds in running tap water and the facial surfaces were pumiced.

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Fig. 2. Control labioincisal enamel surface (original magnification X2000).

Fig. 3. Office-bleached labioincisal enamel surface (original magnification X2000). The specimens were replaced in storage media after a 30-second rinse in running tap water to remove the pumice. When the bleaching regimen was completed after 30 days, the coronal portions were separated from the roots at the cementoenamel junction. In preparation for sectioning, the coronal surfaces were wrapped with plastic wrap and secured by cellophane tape to prevent cutting debris from contaminating the enamel surface. The crowns were treated with Pel-Dry II material (Ted Pella Inc., Redding, Calif.), an alternative to critical point drying, to minimize topographic distortion. The crowns were then sputter-coated with approximately 500 pm of gold (E5000 Polaron, Hatfield, Pa.), and were examined at 2000~ with a SEM (JSM 829, JELL, Tokyo, Japan). Surface analyses were performed for the specimens with a Talysurf 10 profilometer (Rank Taylor Hobson, Leicester, England) at the labioincisal surfaces in approximately 756

BABIN,

AND

MEYER

Fig. 4. Labiogingival surface of the office-bleached specimen shown in Fig. 3 (original magnification x2000). the same surface area examined by the SEM. The path measured by the stylus is known as a “traverse.” All traverses were made from the incisal toward the gingival, approximately parallel to the long axis of the natural crown. Impulses from the stylus were amplified to produce a gauge reading and a graph. The magnification or amplification for the graph was ~2000 vertically and x10 horizontally. Curvatures with radii greater than 0.08 mm could not be measured. “Surface roughness” refers to small-scale surface irregularities, while “waviness” describes the depth of the surface topography, a larger scale irregularity (Fig. 1). The roughness average (Ra) of the surface was calculated by the instrument for each traverse. Wave spacing on the graph can be used to characterize a surface by estimating the distance between wave crests, while waviness can be gauged from the depths of the waves.

RESULTS Scanning

electron

microscope

Fig. 2 illustrates the appearance of the enamel.surface at the labioincisal surface of one control specimen. The bacterial pellicle was removed, but scattered isolated large particles 1 to 3 pm in size remained on the surface. The enamel surface appeared ridged and scored, and scattered depressions were evident. Fig. 3 shows a typical labioincisal enamel surface after treatment by the office protocol. This surface exhibited a muted texture of rounded enamel rods with depressed rod boundaries. This resembled a type II acid etching pattern. The projections were approximately 3.0 to 3.5 pm in diameter. Fig. 4 shows the faciogingival third of the same tooth. Although this surface was smoother than its incisal counterpart, random voids were evident in the enamel that were absent in the incisal surfaces. All topographic features appeared to have been removed from the gingivofacial enamel surface. The enamel was deeply scored with many ranNOVEMBER

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Fig. B. Labioincisal enamel surface after home L bleaching treatment (original magnification X2000).

Fig. 6. Labioincisal enamel surface after treatment with home 2 protocol (original magnification x2000).

domly oriented scratches, but there was no evidence of definable enamel prisms that would have been previously exposed by acid etching. A representative portion of labioincisal enamel of a tooth treated by the Home 1 protocol is shown in Fig. 5. The gingival surface was not represented becauseit was similar in appearance. The enamel appeared to have intermittent depressions of various diameters and depths. Widely spaced, randomly oriented scratches were also evident and scattered debris littered the surface, but there were fewer particles than the controls. Fig. 6 demonstrates the labioincisal enamel of a tooth treated by the Home 2 method. The gingival surface was not illustrated because it was identical to the incisal surface. A deposit of small particles (approximately 0.5 to 1.0 pm in size) was evenly distributed acrossthe entire surface. Although the particles were smaller, the deposit was denser than the control surfaces. The underlying enamel surface topography displayed a mixed background of sparse, randomly oriented scratches and depressions of various sizes.

with the office protocol. The surface roughness (Ra = 0.69 pm) of this specimen was less than that of the control, but the tracing was not sufficiently long to draw conclusions regarding wave spacing or waviness. A typical profilometric graph of a Home l-treated enamel surface is presented in Fig. 9. This specimen exhibited surface roughness (Ra = 10) but less waviness than other specimens. The wave spacing appeared at 20 to 25 pm intervals. The surface topography profile of Home Z-treated enamel is shown in Fig. 10. This surface, from the same tooth as in Fig. 6, recorded an Ra of 1.0 pm, but the waviness was the least prominent of all specimens. However, the wave spacing was similar to other enamel surfaces treated with home bleaching. The profilometer apparently was incapable of detecting the particulate deposit observed on the SEM photomicrographs.

Profilometric

data

When all roughness averages for each group were compiled, the mean Ra (in microns) for each group was: Control, 1.6; Office, 0.6; Home 1,0.6; and Home 2,O.g. Similarly, the observed waviness for each group was ranked: Control > Office > Home 1 = Home 2. Representative tracings of each group were recorded for comparison. Fig. 7 shows a typical profilometer tracing for a control surface. The tracing was made on the same specimen exhibited in Fig. 2, and in approximately the same location as the SEM. The Ra for this specimen was 1.4 pm, and this surface depicted minimal waviness; however, conclusions could not be drawn about spacing from the wave pattern. Conversely, Fig. 8 shows a specimen that was treated THE

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DISCUSSION The changes on human premolar enamel surfaces after treatment with 35 % hydrogen peroxide have been investigated by Titley et all4 Torneck, et all5 also documented similar changes in 35 % hydrogen peroxide-treated bovine enamel. Haywood et al. I6 observed surface alterations caused by one “home” product on human enamel. There have been no current studies that have used profilometry, nor has there been research that concurrently compared other bleaching products. In this investigation we examined, described, and compared surfaces before initiating clinical enamel bonding procedures. Examination of prepared flat reference surfaces from which changes could be assessedwas not clinically relevant. Topographic alteration of the surface of bovine enamel has been demonstrated by Torneck et a1.15after treatment with 35 % hydrogen peroxide. Other investigators14,I5 have 757

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RABIN,

AND

MEYER

Pig. 7. Control surface tracing. This surface is characterized by both surface roughness and waviness, but the roughness average (Ra) of this specimen was 1.4 ym. The mean Ra for all control surfaces was 1.6 km. Control specimens also possessed the greatest waviness. Each grid measured 250 pm horizontally by 125 pm vertically.

Fig. 8. Traverse of office-bleached labioincisal enamel. The Ra of this specimen was 1.0 pm, whereas the mean Ra for this groups was 0.6 pm and this treatment group ranked second in waviness.

discovered a precipitate on specimens that has been attributed to the peroxide. The present specimens exhibited surface debris, but those deposits were in different configurations depending on the bleaching agent. Energydispersive x-ray microanalysis and x-ray diffraction analysis of the particles might be helpful in examining these deposits. The same investigators 14,l5 observed increased “porosity” on surfaces treated with phosphoric acid followed by 35% hydrogen peroxide. The changes consistent with increased porosity were also noted in this study at gingival surfaces of similarly treated specimens. The porosity could have resulted. from the action of acid or the peroxide, which

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has a low pH (Table I), or from both agents acting synergistically. Patterns in acid-etched enamel were described by Silverstone et a1.i7 Type 1 etching patterns reflected a loss of prismatic centers, type 2 patterns exhibited a preferential loss from the periphery of enamel prisms, and type 3 patterns were unrelated to enamel prisms. It was not determined if the muted enamel prisms in Fig. 3 could be attributed to phosphoric acid, the 30% peroxide, or to pumicing after treatment. The office bleaching protocol3 suggests polishing the enamel after treatment to burnish the enamel to diminish hypersensitivity and reduce surface discoloration. In this

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Fig. 9. Surface traverse of home l-treated

enamel. This surface displayed waviness and a surface roughness of 1.0 pm. The mean Ra for similarly treated surfaces was 0.6 pm, and their waviness was similar to the effect of other home bleaching agents.

Fig. 10. Profilometric traverse of enamel treated with home 2 bleaching. The Ra for this surface was 1.0 pm, and mean Ra for the groups was 0.9 pm. The home agents exhibited least waviness.

protocol,7 pumice and a webbed prophy cup were used. Sealing was not apparent in the gingival third of the officebleached teeth when pumice was used as a polish and the porosity remained. The surface effect attributed to the pH of the bleaching agent was inexplicable, because lower pH agents should be more aggressive in attacking enamel. The effect of the bleaching agent pH may have been enhanced by acid pretreatment but mitigated by post-treatment polishing. In general, the closer the pH was to 7.0, the smoother the surface, and this indicated that the bleaching agents had a specific effect on enamel despite their neutrality. The pH of the Tin-Gel agent (pH = 3.4) may explain the surface differences in the Home 2 group. There were no distinct effects on waviness or wave spacing when all the products were compared.

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The manufacturers of Home 2 suggest daily treatment with an adjunctive product (Perio-Med), a stannous fluoride (SnFs) concentrate. A stable 4% stannous fluoride gel (Tin-gel) was substituted because of its known composition. The increased particulated debris associated with the Home 2-treated specimens may be a by-product of the SnFs reaction18 or an artifact. However, various investigatorslg have contended that SnFs did not leave a precipitate. Interestingly, all the bleaching agents contained fluoride (Table I), but at substantially lower concentrations than those present in the Tin-Gel agent. The fluoride, or fluoride acting in concert with the peroxide, could explain the various ubiquitous particulate debris on all specimens. Profilometric analysis complemented the information of the SEM investigations, providing the third dimension of depth. It would be highly desirable but technically difficult

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to compare profile measurements on precisely the same surfaces examined by the SEM. In this investigation, the same region of each tooth was corn-pared by both investigative methods. Profilometric studies permitted surface roughness measurements that were unavailable from photomicrographs. Waviness or wave spacing also cannot be detected from a photomicrograph. The wave spacing of 20 to 25 ym was seen on several “home” bleaching specimens, but this periodicity closely resembled the spacing of perikymata,20 the enamel surface ridges of incremental growth lines, the striae of Retzius. This investigation concentrated on enamel surface alterations, but it is likely that subsurface structural and physiologic alterations can occur in both enamel and dentin. In enamel, this effect would presumably be analogous to the subsurface alterations created by phosphoric acid etchings and related to the enamel pore system.i7 Ruse et al.si investigated chemical changes to bovine enamel after treatment with 35 7%hydrogen peroxide and did not document increased oxygen in the mineral structure. Structural effects have been confirmed22 in rat dentin after the tooth was treated with 35% hydrogen peroxide and heat, but unfortunately the effect of either variable was not assessed. While surface porosity was observed during SEM examinations, it must not be confused with physiologic permeability that regulates the flow of fluid through semipermeable barriers. Nevertheless, differences in enamel permeability after vital bleaching deserve additional research.

Enamel surface alterations were evident with all the bleaching agents used in this study regardless of the pH level of the agents. Surface alterations were irregular and varied with each solution. There was a tendency toward smoother enamel surfaces when home bleaching agents were applied. The potential relationship between surface alteration by vital bleaching agents and enamel bonding warrants additional investigation.

REFERENCES 1. Christiansen GC. Tooth bleaching: home use products. Clin Res Assoc Newsletter 1989;13:1-3. 2. McEvoy SA. Chemical agents for removing intrinsic stains from vital teeth. I. Technique development. QuintessenceInt 1989;20:323-8. 3. Feinman RA; Goldstein RL, Garber DA. Bleaching teeth. Chicago: QuintessencePublishing, 1987:14.

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4. Albers HF. Home bleaching. ADEPT Rep 1991;2:9. 5. Hayman VB. Nightguard vital bleaching: current information and research. Esthet Dent Update 1990;1:20-5. 6. Bowles WH, Uguneri 2. Pulp chamber penetration by hydrogen peroxide following vital bleaching procedures. J Endodont 1987;13:375-7. 7. Silverstone L. The structure and characteristics of human dental enamel. In: Smith DC, Williams DF, eds. Biocompatability of dental materials. Boca Raton, Fla.: CRC press, 1982:57. 8. Linde J, ed. Dentin and dentinogenesis.Boca Raton, Fla.: CRC Press, 1984. 9. Davies AK, Cundall RB, Dandiker Y, Slifkin MA. Photooxidation of tetracycline adsorbedon hydroxyapatite in relation to the light-induced staining of teeth. J Dent Res 1985;64:936-9. 10. Haywood VB, Heyman HO. Nightguard vital bleaching. Quintessence Int 1989;20:173-9. 11. Christiansen GC. Tooth bleaching: home use products. Clin Res Assoc Newsletter 1989;13:1-3. 12. Potos PG, D&-Arnold AM, Williams VD. The effect of microbial contamination and pH changesin storage solutions during in uitroassays of bonding agents. Dent Mater 1990;6:154-7. 13. Pohto M, Scheinin A. Microscopic observations on living dental pulp. II. The effect of thermal irritants on the circulation of the pulp in lower rat incisor. Acta Odontol Stand 1958;16:315-27. 14. Titley K, Torneck CD, Smith DC. The affect of concentrated hydrogen peroxide solutions on the surface morphology of human tooth enamei. J Endodont 1988;14z69-74. 15. Torneck CD, Titley KC, Smith DC, Adibfar A. The influence of time of hydrogen peroxide exposure on the adhesion of composite resin to bleached bovine enamel. J Endodont 1990;16:123-8. 16. Haywood VB, Leech T, Heyman HO, Crumpler D, Bruggers K. Nightguard vital bleaching: effects on enamel surface texture and diffusion. QuintessenceInt 1991;21:801-4. 17. Silverstone LM, Saxton CA, Dogon IL, Fejerskov 0. Variation in the pattern of acid etching of human dental enamel examined by scanning electron microscope. Caries Res 1975;9:373-87. 18. Kochavi D, Gedalia 1,Anaise J. Effect of conditioning with fluoride and phosphoric acid on enamel surfaces as evaluated by scanning electron microscope. J Dent Res 1975;54:304-9. 19. Sheykholeslam Z, Bouonocore MG, Gwinnett AJ. The effect of fluorides on the bonding of resins to phosphoric acid etched bovine enamel. Arch Oral Biol 1972;17:1037-45. 20. Silver&one LM. The structure and characteristics of human dental enamel. In: Smith DC, Williams DF, eds. Biocompatability of dental materials. Boca Raton, Fla.: CRC Publishing, 1982:40. 21. Ruse ND, Smith DC, Torneck CD, Titley KC. Preliminary surface analysis of etched, bleached, and normal bovine enamel. J Dent Res 1990;69:1610-13. 22. Ledoux WR, Malloy RB, Hurst RVV, McInnes-Ledoux P, Weinberg R. Structural effects of bleaching on tetracycline-stained vital rat teeth. J BROSTHET DENT 1985;54:55-9.

23. Miller MC, Mabrito CA. Bleaching-patient administered. Reality Now 1990$3:1. 24. Instruction manual. Leicester, England: Rank Taylor Hobson, 1989. Reprint

requeststo:

RICHARD S. MCGUCKIN, DDS, MSc UNIVERSITY OF TEXAS HEALTH SCIENCE CENTER DENTAL BRANCH PO Box 20068 HOUSTON, TX 77225

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Alterations in human enamel surface morphology following vital bleaching.

Extracted intact human teeth (n = 4) were treated for 30 days by three protocols: Home 1 (Proxigel, n = 4) for 8 hours daily, Home 2 (White & Bright, ...
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