Probe-nov5.p65

BYBONNIE J. CRAIG, Dip.D.H., M.Ed., RDH, Director, and
LISA SUPEENE, Dip.D.H., RDH, 3rd Year BDSc Student
As primary oral health care providers, dental hygienists often Dental Hygiene Degree Completion (BDSc) Program
provide information about dental treatments and procedures Faculty of Dentistry, University of British Columbia
to the public. Dental tooth whitening is a subject about which many people seek information and advice, so it is important KEY WORDS: tooth bleaching/efficacy/adverse effects; for dental hygienists to possess current and accurate knowl- hydrogen peroxide/toxicity, tooth whitening: efficacy, effects edge about tooth whitening products and procedures. This article provides information from the scientific literature that will help dental hygienists field questions and promote careful ABSTRACTPersonal appearance is important in today’s society. Many A MedLine search over a 25-year period was conducted. This products and procedures, including tooth whitening, are paper provides a literature review that examines the efficacy of being marketed to the public as a method for enhancing tooth bleaching and its effects on hard and soft oral tissues, personal appearance. People frequently ask dental profes- the psychological impact of dental aesthetics, the impact of sionals whether tooth whitening is effective and whether bleaching agents on selected restorative materials, and possi- it would be appropriate treatment for them. In order to ble health issues surrounding tooth whitening.
field the public’s questions and promote informed choices, dental hygienists must be knowledgeable about tooth whit- A MedLine search over a 25-year period was conducted to Personal appearance is very important in society. Dentists are locate studies about the efficacy, effects and biological safety called upon to respond to requests from patients who wish to of tooth whitening products and procedures. The search enhance their smiles.1 The effect of a smile can be so significant resulted in approximately 60 articles. Additional articles that advertising experts refer to this phenomenon as “smile power”.2 were obtained through article references. The objective of the research was to prepare a literature review on tooth Social and psychological research has shown that appearance plays an important role in determining the quality of our inter- actions with others and is an important aspect of nonverbal The literature revealed that teeth can be bleached approxi- communication.2,3 How people look can affect how they see mately two shades but a second follow-up treatment is usu- themselves, what others think of them, and how they attract ally required after one to three years. In-office and at-home others to them. By enhancing their appearance, people can bleaching techniques were studied. Bleaching materials change the impression they make on others. Physical attrac- were found to adversely affect dental hard tissues. Some tiveness and self-evaluation have been positively correlated.2,3 evidence was provided to support the view that short-term effects of tooth whitening on tooth pulps appear to be re- Research has shown that throughout their lives attractive indi- versible. Long-term effects of bleaching agents on hard and viduals have significant advantages over those perceived by soft tissues remain unknown. Evidence shows there is a reduction in enamel-composite resin bond strength in teeth treated with peroxide agents though the clinical signifi- The influence of cosmetics in promoting psychological well- cance of this bond reduction is not known. Safety issues being and to the importance of self-perceived attractiveness is concerning the impact of peroxide agents on human oral beginning to be recognized and understood in health care. Stud- mucosal antioxidant defense mechanisms were identified.
ies have shown that when increased attention is placed on appearance, patients’ adjustments to illness and recuperation The writers’ research found little consensus in much of times are affected positively.3 In dentistry, Jenny et al. con- the research. A number of significant areas of concern have firmed that dental esthetics impact on the perceived levels of not yet been thoroughly investigated. Long-term scientific self-confidence in assessments of personality characteristics.4 human studies are recommended to address the unan- Cosmetic dentistry appears to be emerging as a health service.
swered questions about the efficacy, effects and biological Researchers agree that more investigation into psychological factors associated with appearance is needed.
P R O B E S C I E N T I F I C J O U R N A L n N O V E M B E R / D E C E M B E R 1 9 9 9 n V O L U M E 3 3 , N U M B E R 6 flat appearance that is not aesthetically pleasing. Some tetra- cycline stains may appear lighter after bleaching but do not become whiter. Researchers agree that brown-orange and yel- To date the process of stain formation is not well understood.
low tooth stains in older adults bleach the fastest and easiest Pellicle-coated enamel is known to have a net negative charge, though similarly coloured stains in teens and young adults do so permitting selective adhesion of positive ions to tooth not respond as well. Blue-gray stains are significantly more surfaces. This is believed to play a critical role in the deposi- difficult to eliminate. Moderate to dark stains, and those caused tion of stains on tooth surfaces.5 It seems likely that ions from by tetracycline, have been found to be the least likely to food and drink containing tannins as well as chromogens such respond.8 Reports indicate that vital night guard bleaching as copper, nickel, and iron, attach to the negative charge on techniques can achieve acceptable esthetic results.12–16 The the pellicle-coated enamel, causing dental stains.
effects of both at-home and in-office bleaching are unlikely to be permanent. Follow-up treatments have often been found to The mechanism of action of bleaching is also unclear. Bleach- be necessary in between one and three years.12–16 ing is an oxidation reaction. The enamel to be bleached donates electrons to the bleaching agent.2 Ten per cent car- bamide peroxide breaks down to 3% hydrogen peroxide and 7% urea. The hydrogen peroxide metabolizes into water and free radicals of oxygen. These free radicals possess a single To date, studies examining the adverse effect of peroxides on electron, which is thought to combine with the chromagens the microhardness of dental hard tissues have shown conflict- ing results. Rotstein et al. subjected human premolars to solu- tions of 30% hydrogen peroxide, 10% carbamide peroxide, sodium perborate, and three commercially-prepared bleach- ing agents (utilizing 10-15% carbamide peroxide with pH ranges from 6.0 to 6.5).17 Results showed that most of the Documented reports on the efficacy and prognosis of tooth bleaching agents caused changes in the levels of calcium, phos- whitening consist largely of clinical and anecdotal observa- phorus, sulfur, and potassium in the hard tissues. Alterations tions. There is a lack of consensus among researchers about in the inorganic components of hydroxyapatite are the result the results of in-office and at-home tooth bleaching.6,7 Haywood of changes in the calcium/phosphorus ratio found within the and Heymann were the first to report on the procedures and hydroxyopatite crystals of dental hard tissues. The decrease results of an at-home vital tooth bleaching system utilizing was more significant in cementum and dentin than in enamel.
night guards and 10% carbamide peroxide.8 This technique This was in all likelihood due to differences between the or- resulted in a lightening the teeth by the shade guide equiva- ganic and inorganic matter of the tooth. It was concluded that lent of approximately two shades. No detrimental effects on bleaching materials may adversely affect dental hard tissues.
the teeth or gingiva were observed and no significant tissue problems, odour or bad taste were reported. Prior to Hayward Lewinstein et al. also studied the microhardness of human and Heymann’s report, in-office bleaching techniques were enamel and dentin.18 Thirty per cent hydrogen peroxide was most commonly used. The in-office technique involved acid used at 37oC and 50oC. This study found a reduction in the etching the enamel with 37% phosphoric acid. This was microhardness of enamel and dentin. The hardness reduction followed by the application of 30–35% hydrogen peroxide was time-related and results were statistically significant on applied with supplementary heat using a specially designed dentin following a five-minute treatment and on enamel after lamp or a contact instrument. The literature records that in- a fifteen-minute treatment (p<0.05). Researchers suggested office bleaching appears to be preferred by dentists because that the use of high concentrations of hydrogen peroxide should the procedure can be more readily controlled and monitored.
However, at-home bleaching has become increasingly popu- Shannon et al. evaluated the effect of three 10% carbamide lar because it is easy to use, time-saving and cost-effective.9–11 peroxide bleaching agents with different pH values on enamel There is well documented evidence that shows the microhardness and surface morphology following 16 hours of unpredictability of tooth bleaching results. The degree of whit- daily exposure for two and four weeks.19 Unlike other studies, ening or lightening that can be achieved, the length and this was a combined in vitro and in vivo study. Results indi- number of treatments required, the type of stain that will cated that there were no statistically significant differences respond, and how long the results of bleaching last, are diffi- between the microhardness values of the subject and control cult to predict. Bleaching tooth stain that requires prolonged groups at two weeks or at four weeks, although hardness treatment may result in a whiter but chalkier, rather dull and values of subjects were less than those of controls. There was an increase in microhardness at four weeks, which may have P R O B E S C I E N T I F I C J O U R N A L n N O V E M B E R / D E C E M B E R 1 9 9 9 n V O L U M E 3 3 , N U M B E R 6 resulted from exposure of the enamel to artificial saliva.
to the findings of Cohen.21 This may be explained by differ- Remineralization potential exists with saliva substitutes con- ences between canine and human teeth. The two studies agree taining calcium and phosphate ions. Scanning electron that the observed pulpal changes were reversible. Although microscopy showed differences in surface topography of enamel clinical observations and scientific literature report short-term, treated with bleaching solutions. These changes were observed minimal hypersensitivity to in-office and at-home bleaching in surfaces treated with the lower pH carbamide peroxide agents treatments, there have been studies published that raise con- and appeared as pitting and/or enamel erosion. Enamel cerns about possible harmful effects of some bleaching agents remineralization resulting from exposure to saliva may modify Glucose metabolism and protein synthesis, especially collagen Attin et al. observed an initial significant loss of enamel synthesis, are the two most central metabolic processes occur- microhardness after bleaching.20 Rehardening of the enamel ring in the pulp. These metabolic reactions are catalyzed by after treatment was attributed to the remineralization capacity enzymes that are sensitive to changes in environmental condi- of saliva. Furthermore, results showed a decrease in enamel tions.29 Bowles and Thompson examined combined effects of surface hardness in those samples treated with highly concen- heat and hydrogen peroxide on pulpal enzymes and found that most of the enzymes were relatively resistant to the effects of heat up to 50oC. 27 However, nearly every enzyme tested was inhibited to some degree by hydrogen peroxide. At concentra- tions as low as 5% some enzymes were completely inactivated.
Studies have been conducted to examine the penetration of Results indicated that a combination of heat and hydrogen per- hydrogen peroxide and carbamide peroxide into the pulp oxide might increase the permeability of the pulp and potentiate chambers of teeth. Human and canine studies showed that the effects of hydrogen peroxide on the pulp. While the pulp both low (10%) and high (35%) concentrations of bleaching appears to be quite resilient, there is concern for patients who agents readily penetrate the pulp chamber.21-24 may apply bleaching agents for longer periods of time or more frequently than recommended in order to hasten the achieve- Cohen applied 35% hydrogen peroxide and heat for 30-minute ment of whiter teeth. The long-term effects of frequent or pro- sessions to human teeth due to be removed for orthodontic longed use of bleaching agents on pulps are unknown.26–29 treatment.21 Varying degrees of sensitivity, lasting from 24–48 hours, were reported by 78% of the subjects. Twenty-two per The reasons for tooth sensitivity during vital tooth bleaching cent reported no sensitivity. Histological findings in both the are not clear. Studies are inconclusive regarding the pulpal experimental and control groups showed that, except for considerations of vital tooth bleaching. What is clear, how- moderate vasodilation and aspiration of odontoblast nuclei into ever, is that case selection is critical. Considerations prior to the dental tubules, all pulps were normal. There were no initiating tooth whitening procedures should include assess- histological findings to explain the sensitivity experienced by ment of the condition of existing restorations, cervical erosion, the subjects. A possible explanation may be that pressure builds enamel cracks, and the estimated duration and repetition of in the pulp chamber as a result of the heat applied, causing bleaching required to obtain and maintain the desired effect.30 the sensation of pain. The sensitivity, moderate vasodilation and aspiration of odontoblasts into the dental tubules appeared Seale exposed the canine teeth of dogs to 35% hydrogen per- oxide with and without heat.23 The control teeth either received While there is a record in the literature of in-office and at- heat only or had no treatment at all. Histological examinations home tooth bleaching, many questions remain unanswered re- following exposure were conducted at 3, 15, and 60 days.
garding the effects of bleaching agents on both tooth struc- Application of heat only caused some vasodilation in the tures and restorative materials and procedures.31 The literature canine tooth pulps but no other pulpal changes. The applica- is consistent in demonstrating a reduction in the enamel-com- tion of hydrogen peroxide with and without heat caused some posite resin bond strength in teeth previously treated with some initial severe pulpal changes that included obliteration of form of peroxide agent.31–34 Disagreement occurs with respect odontoblasts, hemorrhage, inflammation and internal to the duration of this reduction, ways to reverse this effect, resorption of dentin. The 60-day histological examination and the clinical significance, if any, of the reduced bond strength.
showed only a few changes in otherwise normal pulps.
Apparently the pulps were able to recover within that time.
Dishman et al. studied the effects of 25% hydrogen peroxide The severity of pulpal change reported by Seale is in contrast on human teeth.31 Results showed a reduction in enamel- P R O B E S C I E N T I F I C J O U R N A L n N O V E M B E R / D E C E M B E R 1 9 9 9 n V O L U M E 3 3 , N U M B E R 6 composite bond strength that was time dependent. Although be limited to the surface of the enamel and may not be a factor reductions in bond strength appeared to last less than 24 hours, if the surface layer of the enamel is removed following bleach- bond strength tested one month after bleaching was signifi- ing. This procedure is thought to be effective since polymeri- cantly lower in the group that was bonded one week after zation of bonding agents is known to be inhibited by oxygen.
bleaching than in the control group. This evidence indicates If the oxygen-rich surface layer of enamel is removed, the resin- that there may be a longer-term effect on the enamel-compos- enamel bond strength returns to near normal. The exact depth ite bond strength from bleaching. The significance of this is of this layer is not known, but must be greater than 5–10 microns, otherwise the acid etching prior to bonding would remove this oxygen-rich layer of enamel.31 Titley et al. reported a statistically significant reduction in bond strength in bovine teeth following treatment with 35% hydro- gen peroxide.32 They also showed that the reduction in bond strength could be moderated to varying degrees by water immersion following exposure to the bleaching agent. How- Methods of tooth whitening have existed for more than 100 ever, the immersion time required to totally eliminate the years.35 During the last decade increased attention to techniques effect on bond strength was undetermined.
of bleaching has raised safety concerns.36 The review by Goldstein and Kiremidjian-Schumacher found 246 citations by Titley et al. studied the effect of 10% carbamide peroxide at cross-referencing hydrogen peroxide with toxicity.36 There are pH 4.7 and 7.2 on bovine teeth.33 The purpose of the study safety concerns associated with the potential biological effects was to test whether the less concentrated peroxide (10% of free radicals, specifically free radicals of oxygen, that are carbamide peroxide) commonly used in most at-home tooth- by-products or intermediates of hydrogen peroxide metabo- whitening products yielded the same effect as previous stud- lism.35 A search of the literature shows a lack of any conclu- ies utilizing 35% hydrogen peroxide. The results of the shear sive findings and often contradictions about the toxicity of bond strength tests revealed a statistically significant differ- hydrogen peroxide. The oxidative process is thought to be ence (p<0.01). There were no statistically significant differ- associated with the development of carcinogens, aging, stroke, ences due to exposure time (3 hours vs. 6 hours) or pH (4.7 vs.
liver disease, and other degenerative diseases.35–39 Although 7.2). Although this study demonstrated a reduction of shear hydrogen peroxide has been in widespread use for many years bond strength due to exposure to 10% carbamide peroxide, as an antiseptic in the healing of wounds, as a whitening agent the reduction in bond strength was substantially less than where for teeth, and as an adjunct in periodontal therapy in combi- 35% hydrogen peroxide was used. The investigators stated that nation with salt and/or sodium bicarbonate, concerns persist the results are not conclusive regarding the clinical significance of the reduction of enamel adhesive strength due to exposure to 10% carbamide peroxide products. They did recommend a The most common side-effects of tooth bleaching techniques delay of at least 24 hours for restorative treatment following are transient thermal sensitivity and oral irritation or ulcera- any bleaching procedures using peroxide-based agents.
tion.30,40,41 A few reported cases have shown severe reactions to vital tooth bleaching.24,25 The greater concern for safety re- Stokes et al. conducted shear bond strength tests on human lates to the subtle biological reactions that take place rather teeth treated with 35% hydrogen peroxide and 10% carbamide than the clinically observable reactions.
peroxide.34 It was determined that the shear bond strengths of resin-enamel bonds following treatment with both types of There is an oxygen paradox in aerobic life. While oxygen is peroxide were significantly lower than the controls. The use of essential for higher life forms, it is also toxic to all aerobes lower concentration carbamide peroxide (10%) posed similar under certain conditions.36,39 During respiration, humans hazards to resin bonding as with the 35% hydrogen peroxide.
metabolize oxygen into water. In this metabolic process, chemi- cal reactions occur that result in the formation of water and Researchers explain the reduction in the adhesive strength of by-products. A small fraction (2–5%) of the total oxygen con- the peroxide-treated enamel as the interactions occurring at sumed by all humans is diverted and forms semi-reduced forms the resin-enamel interface. There is evidence of voids in the of oxygen. These “activated oxygen species” are generally bonding resin possibly caused by gaseous bubbles resulting unstable, very reactive, and will act as chain carriers in chemi- from the oxidizing reaction of peroxide entrapped in the sub- cal reactions. At least three such chemical species are involved surface layer of the enamel. Elimination of the trapped perox- in oxygen free radical damage in biological systems: hydrogen ide, achieved by leaching in water, may cause an increase in peroxide, superoxide, and the hydroxyl free radical.37,39 adhesive strength of the enamel surface.32,33 Decrease in adhe- Superoxide and hydrogen peroxide participate in oxidative sive strength following various bleaching regimens appears to reactions, which damage lipids, proteins and nucleic acids.37 P R O B E S C I E N T I F I C J O U R N A L n N O V E M B E R / D E C E M B E R 1 9 9 9 n V O L U M E 3 3 , N U M B E R 6 All tissues are constantly subjected to oxidative stress because tabolism of hydrogen peroxide yields oxygen free radicals. These they exist in an aerobic or oxygen-rich environment. Nature free radicals are very reactive and mobile. If they are able to has created enzymes (SOD, catalase, peroxidase) and antioxi- gain access to connective tissue, the free radicals may adversely dants (ascorbate, vitamin E, glutathione) which help the body affect gingival fibroblasts and their ability to maintain the tis- defend against the effects of oxidation. Biological systems sue and participate in healing.42 Just how susceptible tissue is exist in a state of dynamic equilibrium where the antioxidant to oxidative stress depends on the magnitude of the stress and defense capacity counteracts the oxidative damage potential.
the antioxidant status of the tissue. A pre-existing tissue in- When the antioxidative capacity of the system is overwhelmed, jury, chronic inflammation or the concurrent use of alcohol and/or tobacco while using tooth whiteners may exacerbate their toxic effects.40,42–44 Animal studies have raised the issue Weitzman et al. investigated the effects of 3% and 30% hydro- of potential health concerns related to prolonged hydrogen per- gen peroxide alone and in combination with a known carcino- oxide use.45 Overt signs of hydrogen peroxide toxicity in dental gen, DMBA (9,10-dimethyl-1,2-benzanthracene, an analogue tooth whitening have not been recognized and researchers have to a known ingredient in tobacco).40 Four hydrogen peroxide yet to definitively determine the long-term effects of hydrogen solutions were applied topically to the buccal mucosa of peroxide when used in tooth bleaching agents.
Syrian hamsters twice a week for 22 weeks. All animals treated with 30% hydrogen peroxide alone exhibited hyperkeratosis and hyperplasia, and four of nine revealed hyperchromatic cells and mild dysplasia. In animals treated with DMBA alone, three What is evident from a review of the literature is the lack of of seven developed epidermoid carcinoma. Six of eleven ani- consensus in much of the research. Many areas of concern mals treated with DMBA together with 3% hydrogen peroxide have not yet been thoroughly investigated. It is well-docu- and all animals treated with DMBA plus 30% hydrogen perox- mented that teeth can be bleached. Most authors conclude ide developed carcinomas. It was concluded that long-term that retreatment is necessary but disagree on the intervals of exposure to hydrogen peroxide can itself induce pathologic time between treatments with reports ranging form one to changes and may augment the oral carcinogenesis associated three years. Transient clinical side-effects such as thermal with DMBA. It is not known if exposure to hydrogen peroxide sensitivity and mucosal irritation have been reported. Bleach- from tooth bleaching can deplete or overwhelm human oral ing agents exert some changes in hard and soft oral tissues mucosal antioxidant defense mechanisms. Although animal and in restorative materials, although it is uncertain if these studies cannot be generalized to humans, these results sug- changes are clinically significant. The short-term effects on gest that caution should be exercised especially in concomi- dental hard tissues and pulpal tissues appear to be reversible.
tant use of tooth bleaching agents containing hydrogen perox- Questions about the frequent and/or long-term use of bleach- ide for patients who are tobacco users.
ing agents and their impact on dental hard tissues, pulpal Rees and Orth reported that 3% hydrogen peroxide delayed tissues and oral soft tissues remain. Hydrogen peroxide agents the healing of wounds, caused leukoplakia, ulcerations on the pose some health risk concerns when used in biological tongue, alveolar, and labial mucosa, and eroded papillae.41 systems. The impact of hydrogen peroxide on human oral Evidence suggests that hydrogen peroxide may be harmful to mucosal antioxidant defense mechanisms is not yet completely oral tissues even when used for short time periods, and that understood. Long-term scientific human studies are needed.
with chronic use, injury may be more severe.
Because dental tooth whitening is likely to continue to be an There is a strong association between oxygen free radicals and available treatment option, dental hygienists can use the cur- the development of cancer, although the exact mechanism is rent literature to educate the public about the pros and cons not well understood.38 Carcinogens develop in a two-step proc- of tooth whitening agents and procedures. When bleaching ess, initiation and promotion. Free radicals are thought to play procedures are to be implemented, dental hygienists can a role in both processes. During initiation, changes occur in ensure that the client is a non-smoker with healthy periodon- the genetic material of cells. DNA strand breakage is mediated tium, has no cervical erosion or enamel cracks, and has intact by active oxygen species such as hydrogen peroxide, which restoration margins. Clients should be provided with custom- damage specific amino acids in proteins. Initiated cells can fitted bleaching trays with viscous bleaching gel and be remain dormant. An influx of oxidative potential could possi- advised to follow instructions very carefully. Clients should bly promote already-initiated cells to express themselves.
be firmly reminded not to retain the trays with bleaching agent in their mouths overnight while sleeping, nor to increase the amount Dental tooth bleaching involves the use of various concentra- of bleaching agent or the frequency of their use of bleaching agents tions of hydrogen peroxide or carbamide peroxide. The me- without first consulting a dental professional.
P R O B E S C I E N T I F I C J O U R N A L n N O V E M B E R / D E C E M B E R 1 9 9 9 n V O L U M E 3 3 , N U M B E R 6 23. Seale, N.S., McIntosh, J.E., Taylor, A.N.: Pulpal reaction to bleaching of teeth in dogs. J Dent Res 60: pp. 948–953, 1981 1. Philip, D.S.: Incorporating cosmetic dentistry into a general 24. Seale, N.S., Wilson, C.F.: Pulpal response to bleaching of practice. J Can Dent Assoc 60: pp. 682–686, 1994 teeth in dogs. Pediatr Dent 7: pp. 209–214, 1985 2. Goldstein, R.E.: Esthetic dentistry — a health service. J 25. Glickman, G.N., Frys, H., Baker, F.L.: Adverse response to vital bleaching. J Endodontics 18: pp. 351–354, 1992 3. Graham, J.A., Jouhar, A.J.: The importance of cosmetics in 26. Zach, L, Cohen, G.: Pulp response to externally applied the psychology of appearance. Int J of Dermatology 22: pp.
heat. Oral Surg 19: pp. 515–530, 1965 27. Bowles, W.H., Thompson, L.R.: Vital bleaching: the effect of 4. Jenny, J., Cons, N.C., Kohout, F.J., Jacobsen, J.R.: Relation- heat and hydrogen peroxide on pulpal enzymes. J Endod 12: ship between dental aesthetics and attributions of self- confidence. J Dent Res 69: p. 204 Abstract # 761, 1990 28. Bowles, W.H., Ugwuneri, Z.: Pulp chamber penetration by 5. Nathoo, S.A.: The chemistry and mechanisms of extrinsic hydrogen peroxide following vital bleaching procedures. J and intrinsic discoloration. JADA 128: pp. 6S–9S, 1997 6. Goldstein, R.: Bleaching teeth. New materials — new role.
29. Cooper, J.S., Bokmeyer, T.J., Bowles, W.H.: Penetration of JADA Special Issue: pp. 44E–52E, 1987 the pulp chamber by carbamide peroxide bleaching agents.
7. Nathanson, D., Parra, C.: Bleaching vital teeth: a review and clinical study. Compend Contin Educ Dent 8: pp. 490– 30. Nathanson, D.: Vital tooth bleaching: sensitivity and pulpal considerations. JADA 128: pp. 41S–44S, 1997 8. Haywood, V.B., Heymann, H.O.: Nightguard vital bleach- 31. Dishman, M.V., Covey, D.A., Baughan, L.W.: The effects of ing. Quintessence Int 20: pp. 173–176, 1989 peroxide bleaching on composite to enamel bond strength.
9. Clinical Research Associates Newsletter. Provo, Utah: 32. Titley, K.C., Torneck, C.D., Ruse, N.D., Krmec, D.: Adhesion 10. Clinical Research Associates Newsletter. Provo, Utah: of a resin composite to bleached and unbleached human Clinical Research Associates, December 1989 enamel. J Endodontics 19: pp. 112–115, 1993 11. Clinical Research Associates Newsletter. Provo, Utah: 33. Titley, K.C., Torneck, C.D., Ruse, N.D.: The effect of carba- Clinical Research Associates, December 1990 mide-peroxide gel on the shear bond strength of a microfilmResin to Bovine Enamel. J Dent Res 71: pp. 20–24, 1992 12. Feinman, R.A., Goldstein, R.E., Garber, D.A.: Bleaching 34. Stokes, A.N., Hood, J.A.A., Dhariwal, D., Patel, K.: Effect of peroxide bleaches on resin-enamel bonds. Quintessence Int 13. Holmstrup, G., Palm, A.M., Lambjerg-Hansen, H.: Bleach- ing of discolored root-filled teeth. Endodont Dent Traumatol4: 197–201, 1988 35. Li, L.: Toxicological considerations of tooth bleaching using peroxide-containing agents. JADA 128: pp. 31S–35S, 1997 14. Friedman, S., Rothstein, I., Lihfeld, H., Stahholz, A., Heling, I.: Incidence of external resorption and esthetic results in 36. Goldstein, G.R., Kiremidjian-Schumacher, L.: Bleaching: is it 58 bleached pulpless teeth. Endodont Dent Traumatol 4: pp.
safe and effective? J Prosth Dent 69: pp. 325–327, 1993 37. Floyd, R.A., Carney, J.M.: Free radical damage to protein 15. Walton, R.E., O’Dell, N.L., Myers, D., Lake, F.T., Shrimp, and DNA: mechanisms involved and relevant observations R.G.: External bleaching of tetracycline stained teeth in on brain undergoing oxidative stress. Annals of Neurology dogs. J Endodont 8: pp. 536–542, 1982 16. Meyers, D., O’Dell, N.L, Lake, F.T., Bell, R.A., Barenie, J.T.: 38. Varga, M.: Understanding the role of oxyradicals in general The effectiveness of bleaching for the removal of tetracy- and in toxic hepatic damage can help safer drug design.
cline from rat incisors. J Pedod 4: pp. 227–235, 1980 Medical Hypotheses 39: pp. 133–136, 1992 17. Rotstein, I., Dankner, E., Goldman, A., Heling, I., Stabholz, 39. Floyd, Robert A.: Role of oxygen free radicals in carcinogen- A., Zalkind, M.: Histochemical analysis of dental hard esis and brain ischemia. FASEB J 4: pp. 2587–2597, 1990 tissues following bleaching. J Endodontics 22: pp. 23–25, 40. Weitzman, S.A., Weitberg, A.B., Stossel, T.P., Schwartz, J., Shklar, G.: Effects of hydrogen peroxide on oral carcinogen- 18. Lewinstein, I., Hirschfeld, Z., Stabholz, A., Rotstein, I.: esis in hamsters. J Perio 57: pp. 685–688, 1986 Effect of hydrogen peroxide and sodium perborate on the 41. Rees, T.D., Orth, C.F.: Oral ulcerations with use of hydrogen microhardness of human enamel and dentin. J Endodontics peroxide. J Perio 57: pp. 689–692, 1986 42. Tipton, D.A., Braxton, S.D., Dabbous, M.K.: Effects of a 19. Shannon, H., Spencer, P., Gross, K., Tira, D.: Characteriza- bleaching agent on human gingival fibroblasts. J Perio 66: tion of enamel exposed to 10% carbamide peroxide bleaching agents. Quintessence Int 24: pp. 39–44, 1993 43. Weitzman, S.A., Weitberg, A.B., Nederman, R., Stossel, T.: 20. Attin, T., Kielbassa, A.M., Schwanenberg, M., Hellwig, E.: Chronic treatment with hydrogen peroxide: is it safe? J Perio Effect of fluoride treatment on remineralization of bleached enamel. J Oral Rehab 24: pp. 282–286, 1997 44. Marshall, M.V., Cancro, L.P., Fischman, S.L.: Hydrogen 21. Cohen, S.C., Parkins, F.M.: Bleaching tetracycline-stained peroxide: a review of its use in dentistry. J Perio 66: pp. 786– vital teeth. Oral Surg Oral Med Oral Pathol 29: pp. 465–471, 45. Morris, A.L.: Factors influencing experimental carcinogen- 22. Cohen, S.C.: Human pulpal response to bleaching proce- esis in the hamster check pouch. J Dent Res 40: pp. 3–14, dures on vital teeth. J Endod 5: pp. 134–138, 1979 P R O B E S C I E N T I F I C J O U R N A L n N O V E M B E R / D E C E M B E R 1 9 9 9 n V O L U M E 3 3 , N U M B E R 6

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