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Leaching of hydrogen peroxide from bleached bovine enamel
0099-2399/92/1810-0488/$03.00/0 JOURNAL OF ENDODONTICS Copyright © 1992 by The American Association of Endodontists
Printed in U.S.A.
VOL. 18, NO. 10, OCTOBER1992
Leaching of Hydrogen Peroxide from Bleached Bovine Enamel A. Adibfar, DDS, A. Steele, DDS, C. D. Torneck, DDS, MS, K. C. Titley, BDS, MSD, and D. Ruse, PhD
Accurately weighed bovine enamel slabs were individually immersed in 2 ml of 35% hydrogen peroxide for 1, 3, 5, 30, or 60 rain. A control group was obtained by individual immersion of bovine enamel slabs in 2 ml of saline for 60 min. All samples were washed, dried, acid-etched with 37% phosphoric acid for 60 s, then washed and dried again. Two milliliters of double-distilled water were used for individual sample leaching. Leaching was done for 1, 5, 10, 20 min, or 7 days for the experimental groups and for 7 days for the control group. The samples of one of the experimental groups were leached for a second time for 1 min. A total of 112 samples was used in this study. Hydrogen peroxide was spectrophotometrically identified and quantifled in all leaching solutions based on the oxidation reaction of leuco-crystal violet buffer solution by hydrogen peroxide, a reaction catalyzed by horseradish peroxidase. The results revealed a significant difference in the quantity of leached peroxide between bleached samples (irrespective of the duration of leaching) and control, saline-treated ones. No difference was observed in the quantity of leached peroxide between releached samples and control, saline-treated ones. However, these were small, random, and numerically insignificant. Statistically significant differences were also noted among some of the experimental groups. They were thought to hold no clinical significance. The results suggested that upon immersion, the complete leaching of peroxide from bleached enamel occurs rapidly.
the prior-to-attachment exposure of the enamel to concentrated (30%) HP for periods longer than 5 min (2, 3). Scanning electron microscopic examination of tooth surfaces of samples that failed during tensile and shear bond strength tests revealed that the decrease in attachment was caused by peroxide-resin interactions at the enamel surface. This suggests that peroxide during bleaching is absorbed/adsorbed by enamel and that it remains present at, or near, the surface of enamel despite brief periods of washing and drying such as occur in clinical practice. Other investigations have shown that adequate attachment can be restored when the peroxide-treated enamel is immersed in water for 7 days prior to resin application (4). In this case, scanning electron microscopic examination of tooth surfaces of samples which failed during tensile and shear bond strength tests revealed no differences between the morphological appearance of HP and saline-treated specimens. This suggests that peroxide diffuses into and out of enamel as a function of time and environmental peroxide concentration. The aim of this investigation was to identify and quantify the peroxide released from bleached bovine enamel upon immersion. MATERIALS AND METHODS The method selected for the qualitative and quantitative determination of leached HP was the one described by Mottola et al. (5). The method is based on the oxidation reaction of leuco-crystal violet buffer solution by HP, a reaction catalyzed by horseradish peroxidase. The color change of the solution, as a result of the oxidation reaction, is used to demonstrate the presence of HP. Spectrophotometric measurements of the absorbance at 596 nm of the colored solutions are used for the quantitative determination of HP. A commercially available generic 30 to 35% solution of HP (Fisher Scientific, Neapean, Ontario) was obtained and stored at 4°C in a tightly capped brown bottle. Normal saline solution (0.9% sodium chloride; Travenol Canada Inc.) was used as the control reagent. A commercially available etching gel (ScotchBond Etching Gel; 3M Canada Inc.), containing 37% phosphoric acid, was used as the etching agent. The reactant solution was obtained by dissolving 50 mg of leucocrystal violet (Fisher Scientific) in 80 ml of 0.5% hydrochloric acid. The solution was then further diluted to 100 ml with 0.5% HC1. A solution of 10 mg of horseradish peroxidase (Sigma Chemical Co., St. Louis, MO) in l0 ml of double-
Concentrated (30 to 35%) hydrogen peroxide (HP) solution has been the most commonly used agent for the professional bleaching of discolored vital and nonvital teeth (I). The recent introduction of home bleaching products has enhanced public and professional interest in using bleaching to improve tooth coloration for cosmetic reasons. Previous investigations have shown that the attachment of a light-cured resin to bovine enamel was adversely affected by
488
Vol. 18, No. 10, October 1992
Leaching Peroxide from Bleached Enamel
TABLE 1. Data points for the spectrophotometric calibration curve
489
TABLE 2. Sample preparation procedures Steps
No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
HP (ug)
Absorbance at 596 nm
0.0 0.6 0.8 1.0 1.3 1.6 2.0 2.5 3.0 3.5 4.0 4.5 5.0 6.0 8.0 10.0 12.0 14.0
0.000 0.676 0.704 0.760 0.830 0.994 1.018 1.073 1.318 1.444 1.631 1.735 1.861 2.099 2.624 2.752 2.807 2.868
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absorbance at 596 nm FIG 1. Calibration curve for the determination of leached HP.
distilled water (DDW), prepared just before being needed, was used as the catalyst for the reactant solution. The buffer solution was made by mixing equal volumes of 2 M sodium acetate and 2 M acetic acid solutions,(Fisher Scientific, Fairlawn, N J). Glacial acetic acid (Fisher Scientific) was used to adjust the final pH to 4.5. The concentration of peroxide in the experimental and control solutions was determined by spectrophotometry using a Ultraspec II model 4050 (LKB Biochrom Ltd., Cambridge, England) spectrophotometer. The absorbance of the solutions was determined at 596 nm..Hellma Optical (Fisher Scientific) glass cells (360 to 2500 nm) were used to contain the various
Group
No. of Samples
Bleach (min)
Leach
Releach (min)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 Control
8 8 8 8 8 8 8 8 8 8 8 8 8 8 8
1 3 5 5 5 5 5 5 30 30 30 60 60 60 --
7 days 7 days 1 min 5 min 10 min 20 min 7 days 7 days 10 min 20 min 7 days 10 min 20 min 7 days 7 days
-------1 --------
solutions during spectrophotometric determinations. A calibration curve, relating weight of HP in mg to spectrophotometric absorbance at 598 nm was obtained and the equation of the best fit line was then computed. Standard HP solutions for the spectrophotometric calibration curve were obtained through successive dilutions of the 30% HP stock solution with DDW. After the first dilution to 0.1 M the solution was standardized by idiometric titration. Incisors were obtained from young cattle at a local abattoir. Only young animals having no more than four erupted permanent incisors were selected. The teeth were transported in cold water to the laboratory where they were cleaned and decoronated with a band saw. The coronal pulp was removed with a dental explorer and the crowns were washed in water. The teeth were then stored in water in a tightly sealed container at 4°C until required, a period not exceeding 6 months. Enamel slabs were obtained from the lingual enamel of bovine incisors. Dentin was removed using a high-speed rotary diamond bur and a light magnifier was used to verify its removal. Four samples of approximately equal weight were obtained from each incisor. The enamel samples were ground flat using 600 grit SiC paper on a water-irrigated grinding wheel. The ground samples were washed with distilled water (DW) for 15 s, dried with compressed air for 15 s, and accurately weighed using an analytical balance. The weight of the samples ranged between 0.06 and 0.096 g. Fifteen groups, 14 experimental and 1 control, of eight specimens each were prepared according to the sample preparation protocol presented in Table 1. For the experimental groups, each enamel slab was bleached in 2 ml of HP for the time period indicated in Table l, whereas for the control group a 60-min immersion in 2 ml of saline was used. The samples were then rinsed with D W for 1 min, dried with compressed air for 30 s, acid-etched for 60 s, rinsed with DW for 30 s, and dried with compressed air for 30 s. Each sample was then leached in 2 ml of D D W for the time period indicated in Table 1. The samples in group 8 were leached again for a second time in 2 ml of D D W for 1 min. After leaching, 1 ml of leuco-crystal violet solution, 0.5 ml of horseradish peroxidase solution, 4 ml of buffer solution, and 2.5 ml of DDW were added to the 2-ml leaching solution
490
Adibfar et al.
Journal of Endodontics TABLE 3. Leached HP, mean and SD (in/~g/100 mg enamel) Leaching Time
Bleaching Time (min)
1 min
5 min
10 min
20 min
7 days
0--control
--
--
- -
- -
---13.67 _+ 0.66
---13.86 ___0.82 --
0.43 ___0.10 13.34 __+1.14 13.51 ___0.73 12.01 _+ 0.99 0.45 ___0.09 (after 1 min releaching) 15.33 ___1.42 13.32 ___1.06
1 3
5 5
- -
- -
14.64 + 1.34
15.02 _+ 1.64
- -
- -
30 60
m
of each specimen, bringing the total volume to 10 ml. These "reactant solutions" still containing the enamel samples were vortexed for 5 s and their absorbance at 596 nm was spectrophotometrically determined. The weight of HP was calculated by substituting the absorbance value into the equation of the calibration curve. The results were then normalized to reflect mg of leached HP per 100 mg of enamel. The data collected were analyzed statistically. RESULTS The calibration curve relating the weight of HP to spectrophotometric absorbance is shown in Fig. 1 and the actual data points are summarized in Table 2. The equation of the line of best fit obtained by computing was: Y = 0.25052 - 0.035894
e -x
+
1.4204 x 2
where X is the value of the absorbance at 596 nm and Y is the weight of HP in milligrams. The results (mean and SD) of the spectrophotometric determinations obtained in this study, expressed as mg of leached HP per 100 mg of enamel are given in Table 3.
DISCUSSION Previous investigations have shown that the bond strength between a light-cured resin and bovine enamel was markedly reduced when the enamel had been bleached shortly before resin application (2, 3). However, it has been demonstrated that longer exposure of peroxide-treated enamel to water, prior to resin application, could restore the bond strength values to prebleach levels (3). The SEM appearance of failed shear- and tensile-tested, bleached specimens suggested that the reduction in attachment was due to an interaction between the resin and the peroxide which may have been absorbed along the interprismatic pathways of the enamel surface and subsurface. Since leaching in water seemed to eliminate this effect, it was considered important to identify and quantitatively determine the amount of peroxide released from bleached enamel as a function of leaching duration. The experimental method selected to identify and quantify the released peroxide (5) is based on the high molar absorptivity of leuco-crystal violet, which renders the method particularly suitable for the detection of minute concentrations of peroxide. Furthermore, the procedure is relatively simple and the required spectrophotometer is readily available.
- -
12.78 + 0.49 12.47 ___1.20
12.85 ___1.35 12.88 _+ 1.40
The results obtained in this study demonstrated that there was a significant difference in the amount of released peroxide by bleached and control, saline-treated bovine enamel sampies. However, no significant difference was identified in the amount of released peroxide by releached and control, salinetreated bovine enamel samples. These findings suggested that during the first leaching procedure a complete desorption of absorbed/adsorbed peroxide had taken place. The small concentrations of peroxide identified in the control, saline-treated bovine enamel samples could be the result of the environmental oxidation of the leuco-crystal violet. Statistical analysis of the data by a one-way analysis of variance method (due to lack of relevance, the actual results were not included in this report) revealed differences in the amount of released peroxide by different experimental groups. However, considering the random distribution of these differences and the numerical proximity of the data, it could be speculated that these statistically identified differences have no clinical relevance in terms of their impact on the bond strength between bovine enamel and restorative resins. What is considered to be clinically significant was the apparent rapidity of the leaching action. The results obtained have shown that the absorbed/adsorbed peroxide was almost completely released even during short leaching treatments. Another clinically significant consideration is that despite the observed rapidity of the leaching process, brief periods of rinsing and drying failed to eliminate the enamel-absorbed/ adsorbed peroxide. Immersion in water of bleached bovine enamel, however, even for a period as short as 1 min, resulted in significant if not complete elimination of absorbed/adsorbed peroxide. Compared with rinsing, immersion represents a stable environment which could be more conducive to ionic transport. Clinically, therefore, immersion is expected to effect bond strength between enamel and restorative resins more than rinsing. Further studies should be conducted to assess the possibility of enamel-absorbed/adsorbed peroxide elimination by extended rinsing as well as the effectiveness of saliva as a leaching agent. This investigation was supported by the Dean's Fund for Dental Research, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
The authors would like to acknowledge the secretarial assistance of Edith Tveit and the cooperation of Dr. H. Umeback in the undertaking and publishing of this study. Dr. Adibfar and Dr. Steele are associates, Department of Endodontics, Dr. Tomeck is a member of the Department of Endodontics, and Dr. Titley is a member of the Department of Pediatric Dentistry, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada. Dr. Ruse is a member of the
Vol. 18, No. 10, October 1992 Department of Oral Biology, Faculty of Dentistry, University of British Columbia, Vancouver, BC, Canada. Address requests for reprints to Dr. Calvin D. Tomeck, Department of Endodontics, Faculty of Dentistry, University of Toronto, 124 Edward Street, Toronto, Ontario, M5G 1G6, Canada.
References
1. Walton RE. Bleaching of discoloured teeth. In: Walton RE, Torabinejad M, eds. Principles and practice of endodontics. Philadelphia: WB Saunders, 1989.
Leaching Peroxide from Bleached Enamel
491
2. Titley KC, Torneck CD, Smith DC, Adibfar A. Adhesion of composite resin to bleached and unbleached bovine enamel. J Dent Res 1988;67:15238. 3. 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 Endodon 1990;16:123-8. 4. Torneck CD, Titley KC, Smith DC, Adibfar A. Effect of water leaching on the adhesion of composite resin to bleached and unbleached bovine enamel. J Endodon 1990;17:156-60. 5. Mottola HA, Simpson BE, Gorin G. Absorptiometric determination of hydrogen peroxide in submicogram amounts with leuco crystal violet and peroxidase as catalyst. Anal Chem 1970;3.
You Might Be Interested To Know We have all heard some variation of the saying, "Medicine is an art, not a science." It is interesting to note that not too long ago the reverse of this saying may have been more appropriate. In the time of Leonardo Di Vinci artists did not have their own guilds (unions), but belonged to the Guild of St. Luke, which was the organization for physicians and apothecaries. The reason for this is that the pigments used by the artists were often purchased from apothecaries. Apparently, at this point in history, painting was considered more science than art. John Smith
Printed in U.S.A.
VOL. 18, NO. 10, OCTOBER1992
Leaching of Hydrogen Peroxide from Bleached Bovine Enamel A. Adibfar, DDS, A. Steele, DDS, C. D. Torneck, DDS, MS, K. C. Titley, BDS, MSD, and D. Ruse, PhD
Accurately weighed bovine enamel slabs were individually immersed in 2 ml of 35% hydrogen peroxide for 1, 3, 5, 30, or 60 rain. A control group was obtained by individual immersion of bovine enamel slabs in 2 ml of saline for 60 min. All samples were washed, dried, acid-etched with 37% phosphoric acid for 60 s, then washed and dried again. Two milliliters of double-distilled water were used for individual sample leaching. Leaching was done for 1, 5, 10, 20 min, or 7 days for the experimental groups and for 7 days for the control group. The samples of one of the experimental groups were leached for a second time for 1 min. A total of 112 samples was used in this study. Hydrogen peroxide was spectrophotometrically identified and quantifled in all leaching solutions based on the oxidation reaction of leuco-crystal violet buffer solution by hydrogen peroxide, a reaction catalyzed by horseradish peroxidase. The results revealed a significant difference in the quantity of leached peroxide between bleached samples (irrespective of the duration of leaching) and control, saline-treated ones. No difference was observed in the quantity of leached peroxide between releached samples and control, saline-treated ones. However, these were small, random, and numerically insignificant. Statistically significant differences were also noted among some of the experimental groups. They were thought to hold no clinical significance. The results suggested that upon immersion, the complete leaching of peroxide from bleached enamel occurs rapidly.
the prior-to-attachment exposure of the enamel to concentrated (30%) HP for periods longer than 5 min (2, 3). Scanning electron microscopic examination of tooth surfaces of samples that failed during tensile and shear bond strength tests revealed that the decrease in attachment was caused by peroxide-resin interactions at the enamel surface. This suggests that peroxide during bleaching is absorbed/adsorbed by enamel and that it remains present at, or near, the surface of enamel despite brief periods of washing and drying such as occur in clinical practice. Other investigations have shown that adequate attachment can be restored when the peroxide-treated enamel is immersed in water for 7 days prior to resin application (4). In this case, scanning electron microscopic examination of tooth surfaces of samples which failed during tensile and shear bond strength tests revealed no differences between the morphological appearance of HP and saline-treated specimens. This suggests that peroxide diffuses into and out of enamel as a function of time and environmental peroxide concentration. The aim of this investigation was to identify and quantify the peroxide released from bleached bovine enamel upon immersion. MATERIALS AND METHODS The method selected for the qualitative and quantitative determination of leached HP was the one described by Mottola et al. (5). The method is based on the oxidation reaction of leuco-crystal violet buffer solution by HP, a reaction catalyzed by horseradish peroxidase. The color change of the solution, as a result of the oxidation reaction, is used to demonstrate the presence of HP. Spectrophotometric measurements of the absorbance at 596 nm of the colored solutions are used for the quantitative determination of HP. A commercially available generic 30 to 35% solution of HP (Fisher Scientific, Neapean, Ontario) was obtained and stored at 4°C in a tightly capped brown bottle. Normal saline solution (0.9% sodium chloride; Travenol Canada Inc.) was used as the control reagent. A commercially available etching gel (ScotchBond Etching Gel; 3M Canada Inc.), containing 37% phosphoric acid, was used as the etching agent. The reactant solution was obtained by dissolving 50 mg of leucocrystal violet (Fisher Scientific) in 80 ml of 0.5% hydrochloric acid. The solution was then further diluted to 100 ml with 0.5% HC1. A solution of 10 mg of horseradish peroxidase (Sigma Chemical Co., St. Louis, MO) in l0 ml of double-
Concentrated (30 to 35%) hydrogen peroxide (HP) solution has been the most commonly used agent for the professional bleaching of discolored vital and nonvital teeth (I). The recent introduction of home bleaching products has enhanced public and professional interest in using bleaching to improve tooth coloration for cosmetic reasons. Previous investigations have shown that the attachment of a light-cured resin to bovine enamel was adversely affected by
488
Vol. 18, No. 10, October 1992
Leaching Peroxide from Bleached Enamel
TABLE 1. Data points for the spectrophotometric calibration curve
489
TABLE 2. Sample preparation procedures Steps
No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
HP (ug)
Absorbance at 596 nm
0.0 0.6 0.8 1.0 1.3 1.6 2.0 2.5 3.0 3.5 4.0 4.5 5.0 6.0 8.0 10.0 12.0 14.0
0.000 0.676 0.704 0.760 0.830 0.994 1.018 1.073 1.318 1.444 1.631 1.735 1.861 2.099 2.624 2.752 2.807 2.868
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10
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2
6.
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~
4
2
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,
0.000,25
•
i
•
i
•
i
•
i
•
,
0.500.751.001.251,501.75
•
|
,
i
•
i
,
2.00 2.25
i
,
i
•
i
2.502.753.00
absorbance at 596 nm FIG 1. Calibration curve for the determination of leached HP.
distilled water (DDW), prepared just before being needed, was used as the catalyst for the reactant solution. The buffer solution was made by mixing equal volumes of 2 M sodium acetate and 2 M acetic acid solutions,(Fisher Scientific, Fairlawn, N J). Glacial acetic acid (Fisher Scientific) was used to adjust the final pH to 4.5. The concentration of peroxide in the experimental and control solutions was determined by spectrophotometry using a Ultraspec II model 4050 (LKB Biochrom Ltd., Cambridge, England) spectrophotometer. The absorbance of the solutions was determined at 596 nm..Hellma Optical (Fisher Scientific) glass cells (360 to 2500 nm) were used to contain the various
Group
No. of Samples
Bleach (min)
Leach
Releach (min)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 Control
8 8 8 8 8 8 8 8 8 8 8 8 8 8 8
1 3 5 5 5 5 5 5 30 30 30 60 60 60 --
7 days 7 days 1 min 5 min 10 min 20 min 7 days 7 days 10 min 20 min 7 days 10 min 20 min 7 days 7 days
-------1 --------
solutions during spectrophotometric determinations. A calibration curve, relating weight of HP in mg to spectrophotometric absorbance at 598 nm was obtained and the equation of the best fit line was then computed. Standard HP solutions for the spectrophotometric calibration curve were obtained through successive dilutions of the 30% HP stock solution with DDW. After the first dilution to 0.1 M the solution was standardized by idiometric titration. Incisors were obtained from young cattle at a local abattoir. Only young animals having no more than four erupted permanent incisors were selected. The teeth were transported in cold water to the laboratory where they were cleaned and decoronated with a band saw. The coronal pulp was removed with a dental explorer and the crowns were washed in water. The teeth were then stored in water in a tightly sealed container at 4°C until required, a period not exceeding 6 months. Enamel slabs were obtained from the lingual enamel of bovine incisors. Dentin was removed using a high-speed rotary diamond bur and a light magnifier was used to verify its removal. Four samples of approximately equal weight were obtained from each incisor. The enamel samples were ground flat using 600 grit SiC paper on a water-irrigated grinding wheel. The ground samples were washed with distilled water (DW) for 15 s, dried with compressed air for 15 s, and accurately weighed using an analytical balance. The weight of the samples ranged between 0.06 and 0.096 g. Fifteen groups, 14 experimental and 1 control, of eight specimens each were prepared according to the sample preparation protocol presented in Table 1. For the experimental groups, each enamel slab was bleached in 2 ml of HP for the time period indicated in Table l, whereas for the control group a 60-min immersion in 2 ml of saline was used. The samples were then rinsed with D W for 1 min, dried with compressed air for 30 s, acid-etched for 60 s, rinsed with DW for 30 s, and dried with compressed air for 30 s. Each sample was then leached in 2 ml of D D W for the time period indicated in Table 1. The samples in group 8 were leached again for a second time in 2 ml of D D W for 1 min. After leaching, 1 ml of leuco-crystal violet solution, 0.5 ml of horseradish peroxidase solution, 4 ml of buffer solution, and 2.5 ml of DDW were added to the 2-ml leaching solution
490
Adibfar et al.
Journal of Endodontics TABLE 3. Leached HP, mean and SD (in/~g/100 mg enamel) Leaching Time
Bleaching Time (min)
1 min
5 min
10 min
20 min
7 days
0--control
--
--
- -
- -
---13.67 _+ 0.66
---13.86 ___0.82 --
0.43 ___0.10 13.34 __+1.14 13.51 ___0.73 12.01 _+ 0.99 0.45 ___0.09 (after 1 min releaching) 15.33 ___1.42 13.32 ___1.06
1 3
5 5
- -
- -
14.64 + 1.34
15.02 _+ 1.64
- -
- -
30 60
m
of each specimen, bringing the total volume to 10 ml. These "reactant solutions" still containing the enamel samples were vortexed for 5 s and their absorbance at 596 nm was spectrophotometrically determined. The weight of HP was calculated by substituting the absorbance value into the equation of the calibration curve. The results were then normalized to reflect mg of leached HP per 100 mg of enamel. The data collected were analyzed statistically. RESULTS The calibration curve relating the weight of HP to spectrophotometric absorbance is shown in Fig. 1 and the actual data points are summarized in Table 2. The equation of the line of best fit obtained by computing was: Y = 0.25052 - 0.035894
e -x
+
1.4204 x 2
where X is the value of the absorbance at 596 nm and Y is the weight of HP in milligrams. The results (mean and SD) of the spectrophotometric determinations obtained in this study, expressed as mg of leached HP per 100 mg of enamel are given in Table 3.
DISCUSSION Previous investigations have shown that the bond strength between a light-cured resin and bovine enamel was markedly reduced when the enamel had been bleached shortly before resin application (2, 3). However, it has been demonstrated that longer exposure of peroxide-treated enamel to water, prior to resin application, could restore the bond strength values to prebleach levels (3). The SEM appearance of failed shear- and tensile-tested, bleached specimens suggested that the reduction in attachment was due to an interaction between the resin and the peroxide which may have been absorbed along the interprismatic pathways of the enamel surface and subsurface. Since leaching in water seemed to eliminate this effect, it was considered important to identify and quantitatively determine the amount of peroxide released from bleached enamel as a function of leaching duration. The experimental method selected to identify and quantify the released peroxide (5) is based on the high molar absorptivity of leuco-crystal violet, which renders the method particularly suitable for the detection of minute concentrations of peroxide. Furthermore, the procedure is relatively simple and the required spectrophotometer is readily available.
- -
12.78 + 0.49 12.47 ___1.20
12.85 ___1.35 12.88 _+ 1.40
The results obtained in this study demonstrated that there was a significant difference in the amount of released peroxide by bleached and control, saline-treated bovine enamel sampies. However, no significant difference was identified in the amount of released peroxide by releached and control, salinetreated bovine enamel samples. These findings suggested that during the first leaching procedure a complete desorption of absorbed/adsorbed peroxide had taken place. The small concentrations of peroxide identified in the control, saline-treated bovine enamel samples could be the result of the environmental oxidation of the leuco-crystal violet. Statistical analysis of the data by a one-way analysis of variance method (due to lack of relevance, the actual results were not included in this report) revealed differences in the amount of released peroxide by different experimental groups. However, considering the random distribution of these differences and the numerical proximity of the data, it could be speculated that these statistically identified differences have no clinical relevance in terms of their impact on the bond strength between bovine enamel and restorative resins. What is considered to be clinically significant was the apparent rapidity of the leaching action. The results obtained have shown that the absorbed/adsorbed peroxide was almost completely released even during short leaching treatments. Another clinically significant consideration is that despite the observed rapidity of the leaching process, brief periods of rinsing and drying failed to eliminate the enamel-absorbed/ adsorbed peroxide. Immersion in water of bleached bovine enamel, however, even for a period as short as 1 min, resulted in significant if not complete elimination of absorbed/adsorbed peroxide. Compared with rinsing, immersion represents a stable environment which could be more conducive to ionic transport. Clinically, therefore, immersion is expected to effect bond strength between enamel and restorative resins more than rinsing. Further studies should be conducted to assess the possibility of enamel-absorbed/adsorbed peroxide elimination by extended rinsing as well as the effectiveness of saliva as a leaching agent. This investigation was supported by the Dean's Fund for Dental Research, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
The authors would like to acknowledge the secretarial assistance of Edith Tveit and the cooperation of Dr. H. Umeback in the undertaking and publishing of this study. Dr. Adibfar and Dr. Steele are associates, Department of Endodontics, Dr. Tomeck is a member of the Department of Endodontics, and Dr. Titley is a member of the Department of Pediatric Dentistry, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada. Dr. Ruse is a member of the
Vol. 18, No. 10, October 1992 Department of Oral Biology, Faculty of Dentistry, University of British Columbia, Vancouver, BC, Canada. Address requests for reprints to Dr. Calvin D. Tomeck, Department of Endodontics, Faculty of Dentistry, University of Toronto, 124 Edward Street, Toronto, Ontario, M5G 1G6, Canada.
References
1. Walton RE. Bleaching of discoloured teeth. In: Walton RE, Torabinejad M, eds. Principles and practice of endodontics. Philadelphia: WB Saunders, 1989.
Leaching Peroxide from Bleached Enamel
491
2. Titley KC, Torneck CD, Smith DC, Adibfar A. Adhesion of composite resin to bleached and unbleached bovine enamel. J Dent Res 1988;67:15238. 3. 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 Endodon 1990;16:123-8. 4. Torneck CD, Titley KC, Smith DC, Adibfar A. Effect of water leaching on the adhesion of composite resin to bleached and unbleached bovine enamel. J Endodon 1990;17:156-60. 5. Mottola HA, Simpson BE, Gorin G. Absorptiometric determination of hydrogen peroxide in submicogram amounts with leuco crystal violet and peroxidase as catalyst. Anal Chem 1970;3.
You Might Be Interested To Know We have all heard some variation of the saying, "Medicine is an art, not a science." It is interesting to note that not too long ago the reverse of this saying may have been more appropriate. In the time of Leonardo Di Vinci artists did not have their own guilds (unions), but belonged to the Guild of St. Luke, which was the organization for physicians and apothecaries. The reason for this is that the pigments used by the artists were often purchased from apothecaries. Apparently, at this point in history, painting was considered more science than art. John Smith