0099-2399/92/1807-0315/$03.00/0 JOURNAL OF ENDODONTICS Copyright © 1992 by The American Association of Endodontists
Printed in U.S.A. VOL. 18, NO. 7, JULY 1992
SCIENTIFIC ARTICLES Penetration of the Pulp Chamber by Carbamide Peroxide Bleaching Agents Jonathan S. Cooper, DDS, Timothy J. Bokmeyer, DDS, and William H. Bowles, PhD, DDS
published that have sounded a note of caution as to possible harmful effects of strong bleaching agents on the dental pulp (4-6). Many bleaching protocols in which heat is used have no direct control over the heating process; the temperature to which the surface of the tooth is subjected is not known, and certainly the temperature to which the pulp is subjected is not known. Zach and Cohen (4) used tiny thermistor probes implanted in teeth to measure the rise in pulpal temperature during the heating process. They showed that increases of only 5 to 10*C caused irreversible pulpal damage. Concentrated hydrogen peroxide solutions have now been largely replaced by carbamide peroxide gels, applied without heat. These products have been found to be quite effective as dental bleaching agents at concentrations of 10 to 15%, over a period of several days or weeks. The so-called "power bleaches," designed for in-office use only, are available in higher concentrations of 30 to 35%. Carbamide peroxide readily decomposes to produce hydrogen peroxide in situ. A recent study reported that hydrogen peroxide readily penetrates enamel and dentin and enters the pulp chamber of freshly extracted teeth (6). Because of the increased use of the carbamide peroxide bleaching agents, the purpose of this study was to determine whether peroxide from this source penetrates the pulp chamber and, if so, how it compares to penetration by hydrogen peroxide.
Hydrogen peroxide readily penetrates the pulp chamber of freshly extracted teeth. This study was undertaken to determine whether carbamide peroxide also penetrates the pulp chamber. Freshly extracted teeth were sectioned 2 to 3 mm apical to the cementoenamel junction and the coronal pulpal tissue was removed. Acetate buffer was placed in the pulp chamber to absorb and stabilize any peroxide that might penetrate. The coronal portion of each tooth was immersed in either carbamide peroxide gel or gelled hydrogen peroxide at various concentrations for 15 min at 37°C. The buffer was removed, leukocrystal violet was added, and the optical density of the resulting blue solution was determined spectrophotometrically. Amounts of peroxide found in the pulp chamber after 15 min ranged from 3.3 __. 0.3~ /~g for the 10% sample to 40.4 +_. 3.51/~g for the 30% sample.
Within the past 2 yr esthetic dentistry has focused on tooth whitening. Patient demands for white teeth have increased dramatically and a large number of tooth-whitening products have come on the market. Most of these products are intended to be dispensed and used directly by a dentist or under the direct supervision of a dentist. A few, however, are available over-the-counter or through late-night television offers, in which the patient is left on his/her own to use the products without supervision. Often, because of a desire to hurry up the process, patients use more of the product or use it for longer periods than recommended. Early efforts to bleach stained teeth employed concentrated hydrogen peroxide (35%), sometimes mixed with dilute hydrochloric acid and/or diethyl ether, sometimes also employing heat. Extrinsic stains, such as fluorotic brown stains, are much more amenable to bleaching than are intrinsic stains, such as those caused by tetracycline (1). A number of studies have demonstrated the safety and effectiveness of using hydrogen peroxide for bleaching fluorotic stains (2, 3). However, there have been a few articles
MATERIALS AND METHODS Adult human anterior teeth were collected at time of extraction, washed, and stored in water with a few drops of sodium hypochlorite added to retard bacterial growth for a few days, until enough teeth could be collected to conduct the study. The hypochlorite concentration was kept low (approximately 0.03%) to minimize any major effects on the tooth structure. The object was to merely retard bacterial growth rather than to fix the tissue. It was felt that use of a Formalin-based fixative (10%) would fix the tissue and adversely affect the diffusion of any peroxide molecules through the coronal walls of the teeth, thus diminishing the comparison of the experimental conditions with in vivo conditions.
315
316
Journal of Endodontics
Cooper et al.
Approximately 12 teeth were initially selected for use in each group. Any teeth that were found to have developmental flaws, caries, or existing restorations were discarded. The number of usable teeth remaining in group 4 was less than ideal. The roots were removed approximately 2 to 3 mm apical to the cementoenamel junction and the pulpal tissue was removed with a #4 round bur. A support wire was attached to each tooth by means of light-cured acrylic. Experimental groups consisted of teeth exposed to commercially available preparations of gelled carbamide peroxide at concentrations of 10% (White and Bright) and 15% (Nu Smile), and gelled preparations of hydrogen peroxide, 5.0% (made by gelling a diluted preparation of 30% H202) and 30% (Star Bright, gelled as per the manufacturer's directions). Into each pulp chamber was placed 25 tzl of 2 M acetate buffer to absorb and stabilize any peroxide that might diffuse into the cavity. The teeth were suspended by the wires so that the entire clinical crown was brought into contact with the peroxide gel and maintained at 37°C for 15 min. At the end of the incubation period, the contents of the pulp chamber were removed by means of a Pasteur pipette and transferred to a test tube. The pulp chamber was rinsed twice with 100-#1 portions of distilled water; the washes were added to the test solution and diluted to 3.0 ml. The hydrogen peroxide was measured according to the method described by Mottola et at. (7). Leukocrystal violet (100 #1, 0.5 mg/ml) and the enzyme horseradish peroxidase (50 ~l, 1 mg/ml) were added. The optical density of the blue color that developed was measured in a Shimadzu 210 UV spectrophotometer at a wavelength of 596 nm. A standard curve made with known amounts of hydrogen peroxide was used to convert the optical density of the colored samples into microgram equivalents of hydrogen peroxide. Control specimens were not exposed to any form of peroxide. RESULTS The carbamide peroxide molecule is 35% hydrogen peroxide (wt/wt); thus, 10% carbamide peroxide actually provides an effective concentration of 3.5% H202 and 15% carbamide peroxide effectively delivers 5.25% H202. Results are summarized in Table 1. Carbamide peroxide, 10% (group 2) delivered significant quantities of peroxide through the coronal tooth structure to the pulp chambers of the extracted teeth, even in the short exposure time of 15 rain. In groups 3 and 4, a direct comparison was made between essentially equal concentrations of peroxide from carbamide peroxide TABLE 1. Penetration of coronal wall by hydrogen peroxide* Peroxide Concentration Group
1 2 3 4 5
Carbamide (%)
Free H202 Equivalent
n
0.0 10.0 15.0 ---
0 3.5 5.25 5.0 30.0
8 10 10 5 7
(%)
Pulpal Peroxide (#g)
3.3 4.8 10.4 40.4
* All groupswere significantlydifferentfrom eachother (p < 0,001). t Mean--!-SD.
0 +_ 0.38"1 + 0.27 + 0.24 ___3.51
and hydrogen peroxide sources. Results show that significantly less peroxide reaches the pulp from carbamide peroxide sources than from free hydrogen peroxide. Comparing groups 4 and 5, while the effective peroxide concentration increased by 6-fold, the penetration increased by only 4-fold. This shows that the rate of diffusion of hydrogen peroxide through the coronal wall of the tooth is somewhat limited and that the rate of diffusion is not proportional to the concentration of hydrogen peroxide. Analysis of variance, followed by Scheffr's test for the computation of confidence intervals, showed statistically significant differences among all groups.
DISCUSSION For some "take home and wear" bleaching kits it is recommended that the tray filled with bleaching agent be worn for only 5 min/day, while others recommend that the tray be worn for up to 14 h/day. It was recently reported that the concentration of peroxide in mouth trays diminishes rapidly (8). This raises the question whether wearing the tray 14 h/ day is justified. Relatively little is known about the direct influences of many of the materials used in dentistry on molecular processes occurring in the pulpal tissue. Little is known about the effects of hydrogen peroxide on metabolic processes. From a quantitative perspective, two of the most important metabolic processes that take place in the pulp are glucose metabolism and protein synthesis, especially synthesis of collagen. Protein synthesis requires ribonucleic acid (mRNA), which is made within the pulpal fibroblasts. These metabolic reactions are catalyzed by specific enzymes, which are sensitive to variations in environmental conditions. Bowles and Thompson (5) examined the combined effects of heat and hydrogen peroxide on seven pulpal enzymes involved in the metabolism of glucose and amino acids. They found that most of the enzymes were relatively resistant to the effects of heat up to 50°C, but that nearly every enzyme tested was inhibited to some degree by hydrogen peroxide, in concentrations as low as 5%, with some enzymes being completely inactivated at that concentration. When hydrogen peroxide, in concentrations as low as 2.5%, was used in combination with heat, all of the enzymes tested were greatly decreased in activity and some were totally inactivated. Results of this study and others (5, 6) show that hydrogen peroxide, whether applied directly or derived from carbamide peroxide, readily penetrates the coronal wall of the tooth and enters the pulp chamber. These data indicate that for the same effective concentration, there is less penetration of the pulp from carbamide peroxide than from free hydrogen peroxide. The dental pulp appears to be quite resilient to indirect insult by various dental materials. However, a concern is the possibility that some patients, in their eagerness to achieve whitened teeth, will apply the material for longer periods of time or more frequently than instructions suggest and cause undesirable consequences. Dr. Cooper is in private practice in Garland, TX. Dr. Bokmeyer is assistant professor, Department of General Dentistry, Baylor College of Dentistry, Dallas, TX. Dr. Bowles is associate professor, Department of Biochemistry, Baylor College of Dentistry, Dallas, TX. Address requests for reprints to Dr. William H. Bowles, Department of Biochemistry, Baylor College of Dentistry, Dallas, TX 75246.
Pulpal Penetration by Carbamide Peroxide
Vol. 18, No. 7, July 1992 References 1. Walton RE, O'Dell NL, Myers DL, Lake FT, Shimp RG. External bleaching of tetracycline-stainedteeth in dogs. J Endodon 1982;8:536-42. 2. RobertsonWD, Melfi RC. Pulpal responsesto vital bleachingprocedures. J Endodon 1980;6:645-9. 3. Cohen SC. Human pulpal response to bleaching procedures on vital teeth. J Endodon 1979;5:134-8. 4. Zach L, Cohen G. Pulp response to externally applied heat. Oral Surg 1965; 19:515-30.
317
5. Bowles WH, Thompson LR. Vital bleaching: the effect of heat and hydrogen peroxide on pulpal enzymes. J Endodon 1986;12:108-12. 6. Bowles WH, Ugwuneri Z. Pulp chamber penetration by hydrogen peroxide following vital bleaching procedures.J Endodon 1987;13:375-7. 7. Mottola HA, Simpson BE, Godn G. Absorptiometdc determination of hydrogen peroxide in submicrogram amounts with leucocrystal violet and peroxidase as catalyst. Anal Chem 1970;42:410-1. 8. Aldana L, Wagner MJ, Frysh H, Baker F. Inactivation of tooth whitener peroxide by oral fluids [Abstract 1266]. J Dent Res 1991;70(special issue):424.
The Way It Was Necessity is the mother of invention, even in the primitive pharmaceutical "industry." Much of the diet of Amazon natives is arboreal animals. Early hunters must have quickly learned the frustration of losing a meal because the wounded animal would hang on indefinitely in the tall trees far out of reach of the marksman. Imagine their joy when the medicine man introduced a poison that could be placed on the arrow tip that would induce paralysis in a wounded animal causing it to fall helplessly down to the awaiting hunter. The natives called it curare. Which translates roughly to "he to whom it falls." John Smith
Printed in U.S.A. VOL. 18, NO. 7, JULY 1992
SCIENTIFIC ARTICLES Penetration of the Pulp Chamber by Carbamide Peroxide Bleaching Agents Jonathan S. Cooper, DDS, Timothy J. Bokmeyer, DDS, and William H. Bowles, PhD, DDS
published that have sounded a note of caution as to possible harmful effects of strong bleaching agents on the dental pulp (4-6). Many bleaching protocols in which heat is used have no direct control over the heating process; the temperature to which the surface of the tooth is subjected is not known, and certainly the temperature to which the pulp is subjected is not known. Zach and Cohen (4) used tiny thermistor probes implanted in teeth to measure the rise in pulpal temperature during the heating process. They showed that increases of only 5 to 10*C caused irreversible pulpal damage. Concentrated hydrogen peroxide solutions have now been largely replaced by carbamide peroxide gels, applied without heat. These products have been found to be quite effective as dental bleaching agents at concentrations of 10 to 15%, over a period of several days or weeks. The so-called "power bleaches," designed for in-office use only, are available in higher concentrations of 30 to 35%. Carbamide peroxide readily decomposes to produce hydrogen peroxide in situ. A recent study reported that hydrogen peroxide readily penetrates enamel and dentin and enters the pulp chamber of freshly extracted teeth (6). Because of the increased use of the carbamide peroxide bleaching agents, the purpose of this study was to determine whether peroxide from this source penetrates the pulp chamber and, if so, how it compares to penetration by hydrogen peroxide.
Hydrogen peroxide readily penetrates the pulp chamber of freshly extracted teeth. This study was undertaken to determine whether carbamide peroxide also penetrates the pulp chamber. Freshly extracted teeth were sectioned 2 to 3 mm apical to the cementoenamel junction and the coronal pulpal tissue was removed. Acetate buffer was placed in the pulp chamber to absorb and stabilize any peroxide that might penetrate. The coronal portion of each tooth was immersed in either carbamide peroxide gel or gelled hydrogen peroxide at various concentrations for 15 min at 37°C. The buffer was removed, leukocrystal violet was added, and the optical density of the resulting blue solution was determined spectrophotometrically. Amounts of peroxide found in the pulp chamber after 15 min ranged from 3.3 __. 0.3~ /~g for the 10% sample to 40.4 +_. 3.51/~g for the 30% sample.
Within the past 2 yr esthetic dentistry has focused on tooth whitening. Patient demands for white teeth have increased dramatically and a large number of tooth-whitening products have come on the market. Most of these products are intended to be dispensed and used directly by a dentist or under the direct supervision of a dentist. A few, however, are available over-the-counter or through late-night television offers, in which the patient is left on his/her own to use the products without supervision. Often, because of a desire to hurry up the process, patients use more of the product or use it for longer periods than recommended. Early efforts to bleach stained teeth employed concentrated hydrogen peroxide (35%), sometimes mixed with dilute hydrochloric acid and/or diethyl ether, sometimes also employing heat. Extrinsic stains, such as fluorotic brown stains, are much more amenable to bleaching than are intrinsic stains, such as those caused by tetracycline (1). A number of studies have demonstrated the safety and effectiveness of using hydrogen peroxide for bleaching fluorotic stains (2, 3). However, there have been a few articles
MATERIALS AND METHODS Adult human anterior teeth were collected at time of extraction, washed, and stored in water with a few drops of sodium hypochlorite added to retard bacterial growth for a few days, until enough teeth could be collected to conduct the study. The hypochlorite concentration was kept low (approximately 0.03%) to minimize any major effects on the tooth structure. The object was to merely retard bacterial growth rather than to fix the tissue. It was felt that use of a Formalin-based fixative (10%) would fix the tissue and adversely affect the diffusion of any peroxide molecules through the coronal walls of the teeth, thus diminishing the comparison of the experimental conditions with in vivo conditions.
315
316
Journal of Endodontics
Cooper et al.
Approximately 12 teeth were initially selected for use in each group. Any teeth that were found to have developmental flaws, caries, or existing restorations were discarded. The number of usable teeth remaining in group 4 was less than ideal. The roots were removed approximately 2 to 3 mm apical to the cementoenamel junction and the pulpal tissue was removed with a #4 round bur. A support wire was attached to each tooth by means of light-cured acrylic. Experimental groups consisted of teeth exposed to commercially available preparations of gelled carbamide peroxide at concentrations of 10% (White and Bright) and 15% (Nu Smile), and gelled preparations of hydrogen peroxide, 5.0% (made by gelling a diluted preparation of 30% H202) and 30% (Star Bright, gelled as per the manufacturer's directions). Into each pulp chamber was placed 25 tzl of 2 M acetate buffer to absorb and stabilize any peroxide that might diffuse into the cavity. The teeth were suspended by the wires so that the entire clinical crown was brought into contact with the peroxide gel and maintained at 37°C for 15 min. At the end of the incubation period, the contents of the pulp chamber were removed by means of a Pasteur pipette and transferred to a test tube. The pulp chamber was rinsed twice with 100-#1 portions of distilled water; the washes were added to the test solution and diluted to 3.0 ml. The hydrogen peroxide was measured according to the method described by Mottola et at. (7). Leukocrystal violet (100 #1, 0.5 mg/ml) and the enzyme horseradish peroxidase (50 ~l, 1 mg/ml) were added. The optical density of the blue color that developed was measured in a Shimadzu 210 UV spectrophotometer at a wavelength of 596 nm. A standard curve made with known amounts of hydrogen peroxide was used to convert the optical density of the colored samples into microgram equivalents of hydrogen peroxide. Control specimens were not exposed to any form of peroxide. RESULTS The carbamide peroxide molecule is 35% hydrogen peroxide (wt/wt); thus, 10% carbamide peroxide actually provides an effective concentration of 3.5% H202 and 15% carbamide peroxide effectively delivers 5.25% H202. Results are summarized in Table 1. Carbamide peroxide, 10% (group 2) delivered significant quantities of peroxide through the coronal tooth structure to the pulp chambers of the extracted teeth, even in the short exposure time of 15 rain. In groups 3 and 4, a direct comparison was made between essentially equal concentrations of peroxide from carbamide peroxide TABLE 1. Penetration of coronal wall by hydrogen peroxide* Peroxide Concentration Group
1 2 3 4 5
Carbamide (%)
Free H202 Equivalent
n
0.0 10.0 15.0 ---
0 3.5 5.25 5.0 30.0
8 10 10 5 7
(%)
Pulpal Peroxide (#g)
3.3 4.8 10.4 40.4
* All groupswere significantlydifferentfrom eachother (p < 0,001). t Mean--!-SD.
0 +_ 0.38"1 + 0.27 + 0.24 ___3.51
and hydrogen peroxide sources. Results show that significantly less peroxide reaches the pulp from carbamide peroxide sources than from free hydrogen peroxide. Comparing groups 4 and 5, while the effective peroxide concentration increased by 6-fold, the penetration increased by only 4-fold. This shows that the rate of diffusion of hydrogen peroxide through the coronal wall of the tooth is somewhat limited and that the rate of diffusion is not proportional to the concentration of hydrogen peroxide. Analysis of variance, followed by Scheffr's test for the computation of confidence intervals, showed statistically significant differences among all groups.
DISCUSSION For some "take home and wear" bleaching kits it is recommended that the tray filled with bleaching agent be worn for only 5 min/day, while others recommend that the tray be worn for up to 14 h/day. It was recently reported that the concentration of peroxide in mouth trays diminishes rapidly (8). This raises the question whether wearing the tray 14 h/ day is justified. Relatively little is known about the direct influences of many of the materials used in dentistry on molecular processes occurring in the pulpal tissue. Little is known about the effects of hydrogen peroxide on metabolic processes. From a quantitative perspective, two of the most important metabolic processes that take place in the pulp are glucose metabolism and protein synthesis, especially synthesis of collagen. Protein synthesis requires ribonucleic acid (mRNA), which is made within the pulpal fibroblasts. These metabolic reactions are catalyzed by specific enzymes, which are sensitive to variations in environmental conditions. Bowles and Thompson (5) examined the combined effects of heat and hydrogen peroxide on seven pulpal enzymes involved in the metabolism of glucose and amino acids. They found that most of the enzymes were relatively resistant to the effects of heat up to 50°C, but that nearly every enzyme tested was inhibited to some degree by hydrogen peroxide, in concentrations as low as 5%, with some enzymes being completely inactivated at that concentration. When hydrogen peroxide, in concentrations as low as 2.5%, was used in combination with heat, all of the enzymes tested were greatly decreased in activity and some were totally inactivated. Results of this study and others (5, 6) show that hydrogen peroxide, whether applied directly or derived from carbamide peroxide, readily penetrates the coronal wall of the tooth and enters the pulp chamber. These data indicate that for the same effective concentration, there is less penetration of the pulp from carbamide peroxide than from free hydrogen peroxide. The dental pulp appears to be quite resilient to indirect insult by various dental materials. However, a concern is the possibility that some patients, in their eagerness to achieve whitened teeth, will apply the material for longer periods of time or more frequently than instructions suggest and cause undesirable consequences. Dr. Cooper is in private practice in Garland, TX. Dr. Bokmeyer is assistant professor, Department of General Dentistry, Baylor College of Dentistry, Dallas, TX. Dr. Bowles is associate professor, Department of Biochemistry, Baylor College of Dentistry, Dallas, TX. Address requests for reprints to Dr. William H. Bowles, Department of Biochemistry, Baylor College of Dentistry, Dallas, TX 75246.
Pulpal Penetration by Carbamide Peroxide
Vol. 18, No. 7, July 1992 References 1. Walton RE, O'Dell NL, Myers DL, Lake FT, Shimp RG. External bleaching of tetracycline-stainedteeth in dogs. J Endodon 1982;8:536-42. 2. RobertsonWD, Melfi RC. Pulpal responsesto vital bleachingprocedures. J Endodon 1980;6:645-9. 3. Cohen SC. Human pulpal response to bleaching procedures on vital teeth. J Endodon 1979;5:134-8. 4. Zach L, Cohen G. Pulp response to externally applied heat. Oral Surg 1965; 19:515-30.
317
5. Bowles WH, Thompson LR. Vital bleaching: the effect of heat and hydrogen peroxide on pulpal enzymes. J Endodon 1986;12:108-12. 6. Bowles WH, Ugwuneri Z. Pulp chamber penetration by hydrogen peroxide following vital bleaching procedures.J Endodon 1987;13:375-7. 7. Mottola HA, Simpson BE, Godn G. Absorptiometdc determination of hydrogen peroxide in submicrogram amounts with leucocrystal violet and peroxidase as catalyst. Anal Chem 1970;42:410-1. 8. Aldana L, Wagner MJ, Frysh H, Baker F. Inactivation of tooth whitener peroxide by oral fluids [Abstract 1266]. J Dent Res 1991;70(special issue):424.
The Way It Was Necessity is the mother of invention, even in the primitive pharmaceutical "industry." Much of the diet of Amazon natives is arboreal animals. Early hunters must have quickly learned the frustration of losing a meal because the wounded animal would hang on indefinitely in the tall trees far out of reach of the marksman. Imagine their joy when the medicine man introduced a poison that could be placed on the arrow tip that would induce paralysis in a wounded animal causing it to fall helplessly down to the awaiting hunter. The natives called it curare. Which translates roughly to "he to whom it falls." John Smith
