Laura Tam, DDS, M.Sc.
© J Can Dent Assoc 1999; 65:453-5
[Minor or Transient Effects |Potenial LongTerm or Systemic Ricks|Regulations | References]
Practitioners Question:
How safe is home tooth bleaching?
Home bleaching is a popular dental procedure used to whiten teeth. Thefirst clinical study of nightguard vital tooth bleaching using a carbamide peroxideproduct was published in 1989.1 Carbamide peroxide is the most commonly usedactive ingredient in home bleaching systems. It breaks down into hydrogen peroxide andurea in aqueous solution. Although concentrations of 10% carbamide peroxide (equivalent toapproximately 3% hydrogen peroxide) are most commonly used, bleaching systems containingup to 22% carbamide peroxide are available for home use.
The safety of home bleaching has been questioned. This article looks atthe minor or transient adverse effects of home bleaching on oral tissues as well as thepotential major long-term or systemic risks of the technique on dental and soft tissues.
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Minor or Transient Effects
Tooth Sensitivity
Previously, the most common method for vital tooth bleaching used liquid hydrogen peroxidein combination with heat. This method invariably caused tooth sensitivity both during andafter the procedure. Thirty-five per cent hydrogen peroxide preparations with or withoutthe additional use of heat caused histological pulpal changes.2-4 However, thetreated pulps generally showed a reversal of these changes and repair within 60 to 92days. Hydrogen peroxide by itself has been shown to inhibit pulpal enzyme activity and maypenetrate into the pulp in very minute concentrations.4-6
Recent clinical studies of carbamide and hydrogen peroxide tooth bleachingreported varying degrees of tooth sensitivity which persisted for up to 24 to 48 hoursafter the cessation of bleaching treatment.7-10 To date, irreversible pulpchanges have not been attributed to the home use of carbamide peroxide. Irreversible pulpchanges have been reported, however, with 35% hydrogen peroxide bleaching in vitro4,11and in vivo.12
Altered Enamel Morphology
Carbamide peroxide bleaches create slight morphological changes in the enamel surface atvarious pH levels.13-15 These changes are minimal in comparison to the severemorphological changes that occur when the enamel surface is subjected to phosphoric acid.There has been one reported clinical case of significant non-reversible destruction ofpreviously sound tooth structure after using an acidic over-the-counter homebleaching system for two months.16
Reduced Bonding
Carbamide peroxide can also affect the teeth by significantly reducing the bond strengthof resin composite systems to treated enamel and dentin.17 It has beenpostulated that residual peroxide on the dentin and enamel surfaces inhibitspolymerization of the resin bonding systems. As a result, any bonding procedures should bepostponed for at least one week after the cessation of bleaching.
Problems with Restorative Dental Materials
Laboratory studies documenting the effects of bleaching agents on dental materials showclinically insignificant changes to most restorative dental materials after bleaching. Itis interesting to note that carbamide peroxide gels increase the mercury release fromdental amalgams.18 In addition, methacrylate temporary restorations becomeorange after carbamide peroxide exposure.19
Gingival Tissue Irritation
Patients may report soft-tissue irritation during home bleaching treatment. It hasbeen shown that the gingival soft tissues can undergo an acute inflammatory reactionfollowing exposure to a dilute hydrogen peroxide solution.20 Higherconcentrations (30%) of hydrogen peroxide will temporarily blanch the gingival softtissues. However, when the tray is designed to avoid soft tissue contact, no significantsoft tissue problems have been identified when the home bleaching technique with 10%carbamide peroxide is used. In addition, carbamide peroxide products are used as rinsesfor periodontal purposes and can actually reduce plaque and gingivitis scores.
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Potential Major Long-Term or Systemic Risks
In the home bleaching method, exposure to peroxide bleaching agents is notisolated to the teeth. Bleaching agents come into contact with the intraoral soft tissuesand are unavoidably swallowed. Therefore, the advent of the home bleaching technique hasraised concerns as to whether peroxide bleaching agents have detrimental long-term softtissue or systemic effects.
As an oxidant, hydrogen peroxide has been adversely associated with carcinogenesis,genotoxicity, cytotoxicity, aging and lung injury.21,22 Many of the effects ofhydrogen peroxide are attributed to its conversion to reactive oxygen radical species, thehydroxyl radical (OH) in particular. However, hydrogen peroxide is a normal intermediatemetabolite in humans that eventually breaks down into water and oxygen. The human body isequipped with a protective barrier of salivary constituents and the oral mucosa as well asvarious defence mechanisms to effectively metabolize hydrogen peroxide bothextracellularly and intracellularly. Well-conducted in vivo studies are needed todetermine the true effects of the current home bleaching technique on the human body.
Significant systemic and soft tissue consequences following exposure tohydrogen and carbamide peroxide have been demonstrated in animal and in vitro studies. Forexample, acute toxicological effects have been demonstrated in rats that have ingestedcarbamide peroxide.23,24 These studies infer that a very large ingestion ofcarbamide peroxide is potentially hazardous for humans. However, the estimated totalingestion of 10% carbamide peroxide by humans during a typical bleaching treatmentprovides a calculated safety factor of 239 for the no-observable-adverse-effect level.25Acute toxicity following material ingestion should therefore not be a clinical problemwhen adults use home bleaching products with 10% carbamide peroxide as directed.
Potential carcinogenicity of the peroxides used in bleaching agentsremains the most controversial safety issue. Studies have suggested that, when ingested,0.1 and 0.4% hydrogen peroxide increased the incidence of duodenal carcinomas in mice,26that 1.5% hydrogen peroxide increased the carcinogenicity of a known carcinogen in ratduodenums and jejunums,27 and that 3% and 30% hydrogen peroxide increased theincidence of carcinomas in hamster cheek mucosa when applied topically along with a knowncarcinogen.28 However, Marshall and others reported that low concentrations(0.75% to 3%) of hydrogen peroxide-formulations actually delayed the onset, reduced therate of tumour formation and/or reduced the incidence of tumour formation in hamster cheekmucosa.29 These studies were reviewed along with others by Li30 whoconcluded that the overall evidence suggests that the use of peroxide-containing homebleaching materials is safe when used as prescribed.
Regulations
In Canada, carbamide- and hydrogen peroxide-based bleaching systems areconsidered cosmetic preparations that are subject to the provisions of the Food and DrugsAct (FDA) and its regulations regarding composition, safety, labelling and advertising. Acosmetic is defined as any substance or mixture of substances manufactured, sold orrepresented for use in cleansing, improving, altering the complexion, skin, hair orteeth. Carbamide and hydrogen peroxide are ingredients that present an avoidablehazard and are therefore on the Cosmetic Notification Hot List. This list states thatcarbamide or hydrogen peroxide may be used as a tooth bleaching agent at a concentrationlimited to 10% and 3% respectively and must be labelled for use for no more than 14 daysunless under the supervision of a dentist. Bleaching systems that containfluoride would be considered a drug. Consequently, they are not commercially available inCanada at this time.
In the United States, hydrogen peroxide products containing 3% or lesshydrogen peroxide are approved by the Food and Drug Administration and are generallyrecognized as safe. Dentifrices delivering low concentrations of hydrogen peroxide (0.75%)or calcium peroxide (0.5%) are available over the counter. The Council on ScientificAffairs of the American Dental Association (ADA) developed Guidelines for theAcceptance of Peroxide-Containing Oral Hygiene Products in 1994 to consider thesafety and efficacy of bleaching products. If the data submitted by the manufacturers ofperoxide-containing home use whitening agents met the guideline requirements, the productwas awarded the ADA Seal of Acceptance. The Council recommends using only whitening agentsdisplaying the ADA Seal of Acceptance. Currently, these are Opalescence Whitening Gel(Ultradent), Platinum and Platinum Overnight Professional Toothwhitening System (Colgate),Nite White Classic (Discus Dental), Patterson Brand Toothwhitening Gel (Patterson DentalCo.) and Rembrandt Lighten Bleaching Gel (DenMat).
In light of the estimated millions of cases of home bleaching using 10%carbamide peroxide, the lack of documented serious adverse effects attributed directly tothis technique has contributed to its acceptance as a conservative option for toothwhitening. However, definitive conclusions regarding the safety of the carbamide peroxidebleaching method from clinically relevant in-depth bleaching studies are lacking. Dentistsmust therefore be wary of the inappropriate use of application of products by patientsthat could potentially lead to serious adverse effects not anticipated from the short-termuse of 10% carbamide peroxide bleaching products. There are reported cases of homebleaching of longer duration (up to 6 months31) with minimal side effects.However, the majority of clinical studies have been based on a shorter-term bleachingregimen. The regulations suggest that if the bleaching treatment is to be extended, thedentist should be regularly assessing the patient after two weeks.
The emphasis on dentist supervision is critical. The dentist plays a keyrole in the safe use of home bleaching materials, diagnosing the condition of thedentition and the etiology of the tooth discolouration, deciding if the home bleachingmethod is the treatment regimen to prescribe, providing the most appropriate type andamount of bleaching materials, educating and supervising the patient during bleachingtreatment, assessing the effectiveness of the treatment, and treating any adverse effects.
An in vitro study concluded that lower concentrations (5%) ofcarbamide peroxide take longer to whiten teeth but eventually achieve the same result ashigher concentrations (16%).32 Given the current regulations for approval inCanada and the United States, which suggest that 10% is the upper limit of tolerance forsafety for unprotected use, and the paucity of available safety data and clinical trialsfor bleaching systems containing more than 10% carbamide peroxide, bleaching systemscontaining more than 10% carbamide peroxide should not, at least from a medico-legalstandpoint, be used at this time for home bleaching. The use of the home bleachingtechnique should also be avoided in children, pregnant and lactating women, and patientssuffering from pathological conditions affecting the oral tissues.
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Dr. Tam is an assistant professor in the faculty of dentistry,University of Toronto.
Reprint requests to: Dr. Laura Tam, Faculty ofDentistry, University of Toronto, 124 Edward St., Toronto, ON M5G 1G6
The author has no declared financial interest in any companymanufacturing the types of products mentioned in this article.
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References
1. Haywood VB, Heymann HO. Nightguard vital bleaching. Quintessence Int1989; 20:173-6.
2. Cohen SC. Human pulpal response to bleaching procedures on vital teeth.J Endod 1979; 5:134-8.
3. Seale NS, McIntosh JE, Taylor AN. Pulpal reaction to bleaching of teethin dogs. J Dent Res 1981; 60:948-53.
4. Seale NS, Wilson CR. Pulpal response to bleaching of teeth in dogs.Pediatr Dent 1985; 7:209-14.
5. Bowles WH, Ugwuneri Z. Pulp chamber penetration by hydrogen peroxidefollowing vital bleaching procedure. J Endod 1987; 13:375-7.
6. Hanks CT, Fat JC, Wataha JC, Corcoran JF. Cytotoxicity and dentinpermeability of carbamide peroxide and hydrogen peroxide vital bleaching materials, invitro. J Dent Res 1993; 72:931-8.
7. Reinhardt JW, Eivins SE, Swift EJ Jr, Denehy GE. A clinical study ofnightguard vital bleaching. Quint Int 1993; 24:379-84.
8. Schulte JR, Morrissette DB, Gasior EJ, Czajewski MV. The effects ofbleaching application time on the dental pulp. JADA 1994; 125:1330-5.
9. Sterrett J, Price RB, Bankey T. Effects of home bleaching on thetissues of the oral cavity. J Can Dent Assoc 1995; 61:412-7, 420.
10. Tam LE. Clinical trial of three 10% carbamide peroxide bleachingproducts. J Can Dent Assoc 1999; 65:201-5.
11. Cohen S, Parkins FM. Bleaching tetracycline-stained vital teeth. OralSurg Oral Med Oral Pathol 1970; 29:465-71.
12. Glickman GN, Frysh H, Baker FL. Adverse response to vital bleaching. JEndod 1992; 18:351-4.
13. Ben-Amar A, Liberman R, Gorfil C, Bernstein Y. Effect of mouthguardbleaching on enamel surface. Am J Dent 1995; 8:29-32.
14. Bitter NC, Sanders JL. The effect of four bleaching agents on theenamel surface: a scanning electron microscopic study. Quintessence Int 1993; 24:817-24.
15. Shannon H, Spencer P, Gross K, Tira D. Characterization of enamelexposed to 10% carbamide peroxide bleaching agents. Quintessence Int 1993; 24:39-44.
16. Cubbon T, Ore D. Hard tissue and home tooth whiteners. CDS Rev 1991;84:32-5.
17. Titley KC, Torneck CD, Ruse ND. The effect of carbamide-peroxide gelon the shear bond strength of a microfil resin to bovine enamel. J Dent Res 1992; 71:20-4.
18. Hummert TW, Osborne JW, Norling BK, Cardenas HL. Mercury in solutionfollowing exposure of various amalgams to carbamide peroxides. Am J Dent 1993; 6:305-9.
19. Robinson FG, Haywood VB, Myers M. Effect of 10 percent carbamideperoxide on color of provisional restoration materials. J Am Dent Assoc 1997; 128:727-31.
20. Martin JH, Bishop JG, Guentherman RH, Dorman HL. Cellular response ofgingiva to prolonged application of dilute hydrogen peroxide. J Periodontol 1968;39:208-10.
21. Link EM. The mechanism of pH-dependent hydrogen peroxide cytotoxicityin vitro. Arch Biochem Biophys 1988; 265:362-72.
22. Imlay JA, Linn S. DNA damage and oxygen radical toxicity. Science1988; 240:1302-9.
23. Cherry DV, Bowers ED Jr, Thomas L, Redmond AF. Acute toxicologicaleffects of ingested tooth whiteners in female rats. J Dent Res 1993; 72:1298-303.
24. Dahl JE, Becher R. Acute toxicity of carbamide peroxide and acommercially available tooth-bleaching agent in rats. J Dent Res 1995; 74:710-4.
25. Li Y. Toxicological considerations of tooth bleaching usingperoxide-containing agents. JADA 1997; 128 Suppl:31S-36S. Review.
26. Ito A, Watanabe H, Naito M, Naito Y. Induction of duodenal tumors inmice by oral administration of hydrogen peroxide. Gann 1981; 72:174-5.
27. Hirota N, Yokoyama T. Enhancing effect of hydrogen peroxide uponduodenal and upper jejunal carcinogenesis in rats. Gann 1981; 72:811-2.
28. Weitzman SA, Weitberg AB, Stossel TP, Schwartz J, Shklar, B. Effectsof hydrogen peroxide on oral carcinogenesis in hamsters. J Periodontol 1986; 57:685-8.
29. Marshall MV, Kuhn JO, Torrey CR. Hamster cheek pouch bioassay ofdentifrice containing hydrogen peroxide and baking soda. J Am Coll Toxicol 1996; 15:45-61.
30. Li Y. Tooth bleaching using peroxide-containing agents: current statusof safety issues. Compend Contin Educ Dent 1998; 19:783-6, 788, 790, passim; quiz 796.
31. Haywood VB, Leonard RH, Dickinson GL. Efficacy of six months ofnightguard vital bleaching of tetracycline-stained teeth. J Esthet Dent 1997; 9:13-9.
32. Leonard RH, Sharma A, Haywood VB. Use of different concentrations ofcarbamide peroxide for bleaching teeth: an in vitro study. Quintessence Int 1998;29:503-7.
Editors note: I invite readers to send me questions aboutclinical problems experienced in everyday practice. I will seek answers to these questionsfrom recognized Canadian experts. You can send me your questions by e-mail, fax or regularmail. I look forward to hearing from you.
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