Tuesday, December 6, 2011

Esthetic dentistry article 7.92.QI

History, safety, and effectiveness of current bleaching techniques and applications of the nightguard vital bleaching technique

Van B. Haywood*

This article reviews the literature on the use of hydrogen peroxide in three profession­ally administered bleaching techniques from historical, technique, and safety viewpoints. Safety over time, absolute safety, and relative safety of nonvital bleaching, in‑office vital bleaching, nightguard vital bleaching, and over‑the‑counter bleaching kits are compared. The advantages and disadvantages of different bleaching options, as well as indications for individual or combined use of the techniques, are discussed. In addition, specific indications for the use of the nightguard vital bleaching technique are presented. (Quintessence Int 1992;23:471‑488.)


The purpose of this article is to evaluate the safety of the various techniques for bleaching teeth in general, and the newer nightguard vital bleaching technique specifically, as well as provide examples of some of the applications of the nightguard vital bleaching technique. Bleaching techniques may be classified by whether they involve vital or nonvital teeth and by whether the procedure is performed in the office or has an at‑home component.

Hydrogen peroxide, in various concentrations, is the primary material currently used by the profession in the bleaching process. Current in‑office techniques for vital teeth and the "walking bleach" technique for nonvital teeth typically use a 30% to 35% concentration of hydrogen peroxide.1 The majority of the products currently on the market for the nightguard vital bleaching technique use a 10% carbamide peroxide solution.2 A 10% carbamide peroxide degrades into 3% hydrogen peroxide and 7% urea, and hydrogen peroxide can be considered its active ingredient.3 The urea may provide some beneficial side effects, because it tends to raise the hydrogen ion concentration (pH) of the solution.4 Some products marketed directly to consumers, over the counter (OTC), use 6% hydrogen peroxide solutions in a gel form.

Hydrogen peroxide naturally occurs in the body, even in the eyes, in low concentrations.5 It is manu­factured and regulated by the body, and often involved in wound healing.6‑9 In higher concentrations, it is bacteriostatic,10 and in very high concentrations is mutagenic,11-13 possibly by disrupting the DNA strand. However, the body has mechanisms for immediate repair of natural damage,l4 low concentrations of hydrogen peroxide do not cause serious problems,15 the carcinogenic capabilities of hydrogen peroxide are more often caused by other peroxide derivatives,16 and the body uses the peroxidases6,7 and other mecha­nisms17 for regulating hydrogen peroxide. Also, other conditions are often required to allow action by hydro­gen peroxide on cells.18 Because hydrogen peroxide occurs extensively within the body, and because it has been used topically for many years,19 it has been studied extensively. The understanding of the role of hydrogen peroxide offers clues to understanding many of the body's actions at the cellular level and to under­standing the naturally occurring inflammation and healing processes.

The mechanism of action of hydrogen peroxide in tooth bleaching is considered to be oxidation, although the process is not well understood.20 It is felt that the oxidizers remove some unattached organic matter from the tooth without disolving the enamel matrix, but also may change the discolored portion to a color­less state.21 There is some concern that continued longterm treatment will result in dissolution of the enamel matrix,22 but reports to date on nightguard vital bleaching techniques have not supported this theory.23,24 Tetracycline stains are more resistant to oxidation because the molecule is tightly bound to the mineral in the enamel prism matrix during formation and hence is less accessible to immediate action (Cren­shaw M: Personal communication). Teeth stained with tetracycline therefore require prolonged treatment times before any results are demonstrated and often are unresponsive to the procedure.

Generally, bleaching is considered an elective process, although there are other indications that may make bleaching a necessity.

Safety over time

The first area to consider when evaluating safety is how long the technique has been used, and the obser­vations that have been made over that time. Esthetic dentistry was a popular topic in the late 1800s, including such presentday concepts as recontouring of teeth; the portion proposed to be removed was shaded with indict ink for patient approval.25 Recontouring and bleaching were recommended procedures, along with gold inlays and porcelain inlays, to avoid the waste of sound tooth structure by the casual crowning of the tooth.26,27 Dentistry was in an era of affluence, and esthetics was a prime consideration. Dentists were concerned that too many teeth were being crowned, about the inappropriate use of base metal in restora­tions, about proper uses of better pins in teeth, and about the need for better use of the rubber dam.27

From the middle 1800s until early 1900, the reputable dental journals contained 40 to 60 articles a year on tooth bleaching. The chemistry seemingly was well understood, the eminent leaders of the profession con­ducted experiments showing the safety of bleaching to the tooth, and the plea for conservative dentistry and preservation of tooth structure was ever the standard. Prominent dental leaders and editors of major textbooks gave lectures supporting bleaching,28 and chapters or sections in operative dentistry textbooks were devoted to this treatment.293l The discussions concerned whether or not bleaching worked, the appropriate indications, how long it lasted, and the relative safety of the various procedures.

Practitioners speaking against bleaching argued that it took too long to occur and was too technique sensi­tive to perform. They argued that because the teeth often reverted back to their original color, bleaching was not worth the effort, and they would rather crown the tooth.28 Those practitioners in favor of bleaching demonstrated the scientific approach to the application of the different bleaching techniques to avoid failure and minimize relapses, reported longevity averaging 6 to 25 years, and stated that professional dentists gave the needed time to get the best, most conservative treatment for their patients.28

As early as 1848, nonvital tooth bleaching with chloride of lime was practiced.32 Truman is often cred­ited with introducing, well before 1864, the most effective technique for bleaching nonvital teeth, which used chlorine from a solution of calcium hydrochlo­rite and acetic acid.28 The commercial derivative of this, later known as Labarraque's solution, was a liquid chloride of soda.26,33 Numerous other bleaching agents were also successfully employed on nonvital teeth in the late 1800s, including aluminum chloride,34,35 oxalic acid,26,36-38 pyrozone (etherperoxide),39 hydrogen dioxide (hydrogen peroxide or perhydrol),40 sodium peroxide,40 sulphorus acid,28 sodium hypophosphate,35 chloride of lime,35,41 and cyanide of potassium.42 All these substances were considered either direct or indirect oxidizers, which acted on the organic portion of the tooth, except for sulphorus acid, which was a reducing agent.28 It later came to be recognized that the most effective direct oxidizers were Pyrozone (Mc Kesson & Robbins), Superoxol (Merk), and sodium dioxide, while the indirect oxidizer of choice was a chlorine derivative.30,43

The bleaching agents were categorized according to which stains they were most effective in removing. Iron stains were removed with oxalic acid,44 silver and copper stains with chlorine,29 and iodine stains with ammonia.45 The stains of metallic salts from metallic restorations such as amalgam were considered the most resistant to bleaching. Although cyanide of potassium would easily remove such metallic stains, its use was not recommended because of its being a very active poison.41 It was recognized that restorations were not affected by bleaching, but the bleaching would remove the stains around margins and under esthetic restorations that were leaking, giving them a longer esthetic life.29 Earlier concerns of the profession about the potential dissolution of teeth from the caustic nature of some of the materials had been disproved by laboratory experiments and clinical observation.41

Techniques that allowed the practitioner to perform the procedures in-office44 or place the medicament and change it at subsequent appointments were de­scribed.33 Sodium peroxide and hydrogen dioxide were used independently or together to bleach teeth; sodium peroxide actually had the advantage of giving the most natural translucency to the nonvital teeth.40 It had long been recognized that some stains were more resistant to treatment than others, and great care was taken during endodontic therapy to avoid allowing the pulpal tissues to bleed into the chamber, since this caused the tooth to discolor.46

Although most of the early dental literature focused on bleaching nonvital teeth, vital teeth were also treated, as early as 1868, with oxalic acid,36 and later hydrogen peroxide47 or Pyrozone.39 By 1910, these vital bleaching techniques generally included the use of hydrogen peroxide with a heating instrument or a light source.47 The steps to ensure patient comfort, including the covering of the eyes, the number of appointments, four or five, and the minimum of 3‑day intervals between appointments, as well as the favorable prognosis, were well documented and recognized by the profession.46‑48

As early as 1893, it was common knowledge that a 3% solution of Pyrozone (etherperoxide), the aqueous solution of hydrogen dioxide, could be used freely as a mouthwash by both children and adults and that, in children with pitted teeth, it had the beneficial side effect of reducing caries and bleaching the teeth.49 It was reported that the 5% solution could be used in a like manner to bleach teeth, but that the 25% solution, the most effective bleaching agent, should be used carefully, to prevent contact with the soft tissue, because of its caustic nature.49

Since there were few manufacturing companies in the 1800s, most dentists were excellent chemists, and mixed a variety of solutions in their offices. When the manufacturing industry began to develop in the 1900s, this versatility was lost to the profession, and the choices of materials to the profession were limited to those offered by the manufacturing companies. Super­oxol was introduced by a manufacturing company early in the 1900s, and later became the chemical used by the majority of dentists because of its safety, although it was recognized that hydrogen peroxide bleaching sometimes left a yellow or brown tinge in some teeth, which the other, previously used materials had not,28 and that Pyrozone (etherperoxide) was the more effi­cient bleaching material.50

From about 1913 until 1940, which included the time of World War I, the Depression, and World War II, very little was written about bleaching. However, articles began to appear in the 1940s and 1950s as the United States began to recover economically, as com­munications improved nationally, and as the profession began treating fluorosis, tetracyclinestained teeth, and discolored teeth saved by endodontic therapy rather than lost to extraction. In the 1940s, hydrogen peroxide and ether were again used on vital teeth.5l

Pyrozone continued to be used effectively for nonvital teeth in the late 1950s and early 1960s,52 as was sodium perborate.53 In the late 1960s, Nutting and Poe54,55 elected to use Superoxol instead of Pyrozone, for safety, and combined it with sodium perborate to achieve a synergistic effect. They recommended use of Amosan (Knox Mfg Co), a sodium peroxyborate mono­hydrate, because it released more oxygen than did sodium perborate. They also advised that the gutta­percha be sealed before the procedure was initiated.

Also in the late 1960s, a successful technique for home bleaching using a 10% carbamide peroxide, delivered in a customfitting mouth tray, was discov­ered by Klusmier.56 Although he presented several table clinics at the Arkansas State Dental Society and the Southwestern Orthodontic Society (Klusmier B: Personal communication), this technique went rela­tively unnoticed until Haywood and Heymann2 de­scribed the technique in March 1989 and a similar product was introduced by a manufacturing company that same month.57,58 For the first time, this technique offered the possibility of whiter vital teeth to a wider section of the general patient population at a lower cost, with much less danger and fewer side effects, than any of the previous options. Since that time, numerous other products and techniques making claims for bleaching teeth have been introduced.22,57 These options include variations on the dentistpre­scribed/homeapplied techniques, as well as "bleaching kits" sold directly to consumers in stores for unsuper­vised home use. The nightguard vital bleaching techniques and the OTC bleaching kits have kindled a resurgence of interest in tooth bleaching and have reopened the questions asked 100 years ago: Does it work, is it safe, what are the indications, and how long does it last?

Current safety

Nonvital bleaching

The walking bleaching technique is probably the most popular option for bleaching nonvital teeth, and no major problems of safety were initially observed other than those associated with the handling of the material and the potential for burns from the high concentration of hydrogen peroxide. This technique involves sealing a mixture of 30% hydrogen peroxide and sodium per­borate in the pulp chamber and changing the solution every 2 to 7 days.

The inoffice alternative treatment for bleaching non­vital teeth usually involves a single appointment in which 30% hydrogen peroxide is activated by a heating instrument, which is more efficient. However, later in the 1970s, external resorption was noted in the cervical areas of nonvital bleached teeth.59,60 Early reports linked this to overzealous use of heating instruments or to previous trauma to the tooth.61,62 Onset was 1 to 7 years posttreatment, and the tooth was often lost.

Although the etiology of the resorption is still un­known, later reports have questioned the heat and trauma theories and proposed that the resorption may result from exiting of the peroxide through the tooth where the enamel and cementum do not join.63 Approx­imately 10% of teeth do not have an intact cemento­enamel junction (CEJ). This theory, along with the observation that pressure in the chamber often causes transient pain, reaffirm that a base material should be placed, before the peroxide is inserted, over the exposed root canal filler and over areas that might communicate with the CEJ. However, placement of this base often means that a portion of the tooth that is discolored will have to be masked with the base material and possibly will not lighten.

A significant drop in pH has been observed in the cervical area of the tooth from passage of the peroxide through the tooth and its exit at the CEJ.63 Later ob­servations have indicated that the resorption is not ac­tually at the CEJ, but is more apical.64 This observation, along with experience gained using calcium hydroxide in the treatment of resorption and incomplete root for­mation, have led to the practice of filling the pulp chamber with calcium hydroxide powder after the completion of the bleaching to alter the pH and halt the potential osteoclastic activity.63 More recent re­ports have recognized the greater potential for cervical resorption from the combination of heat and 30% hydrogen peroxide over either treatment alone.65 For these reasons, the safer nonvital bleaching technique appears to be the walking bleaching technique, rather than the inoffice technique using a heating instrument.

Another approach to treatment involves using sodium perborate alone, rather than in conjunction with hydrogen peroxide, as the primary bleaching agent.66 Although this may be a slower process, it is potentially less destructive to the tooth and hence safer.67

It is unclear why these resorption problems should appear so late in the history of nonvital bleaching, but their recent appearance raises the possibility that changes in materials for root canal fillers, sealers, or bleaching, or a wide variation by practitioners in ad­ministration of the technique, may be the cause. At this time, the walking bleaching technique seems reasonably safe, with only a slight chance of cervical resorption. The benefit of treatment is relatively great (considering the cost of a crown or veneer, the preser­vation of remaining tooth structure, the potential for an esthetic outcome, the avoidance of a subsequent weakening of the tooth, and the finite life of the other restorative possibilities), and the risk is small. Precau­tions include sealing the rootfilled portion preopera­tively with a material such as polycarboxylate cement, placing calcium hydroxide powder in the chamber postoperatively for 14 days, and following the patient for a number of years with frequent recall radiographs. If there is any evidence of resorption, it may be ar­rested with calcium hydroxide treatment, and the tooth can be crowned (with or without extrusion of the tooth to manage the defect).68

Vital bleaching

For any vital bleaching procedure, patients are classi­fied by whether they have tetracyclinestained teeth, or teeth stained from other reasons. Tetracycline­stained teeth are the least responsive to bleaching, depending on the severity of the stain.69 With external bleaching, tetracyclinestained teeth generally get lighter, but not whiter. Some clinicians have recently advocated intentional endodontic therapy on those teeth, with the use of the walking bleach, to overcome this problem.70 While the esthetic result appears to be much better than that of external bleaching, this ap­proach raises questions about the success of the endo­dontic therapy over time, the longevity of the walking bleaching technique, and the potential of the treat­ment or retreatment to cause cervical resorption.

The most popular technique for the inoffice bleach­ing of vital teeth involves 35% hydrogen peroxide, etching the teeth with phosphoric acid to facilitate bleaching, and either a heating element or a light source to enhance the action of the peroxide.1,71 Be­cause this technique must be accomplished without anesthesia to allow the patient's pain threshold to determine the appropriate heat level, there have been numerous studies on the effects of both the heat and the concentrated hydrogen peroxide on the pulp.72,73 Although there is insult to the tissue, most of the research has shown that the pulp remains healthy, and the insult is reversible in approximately 2 months.74,75 The observations of many clinicians who have per­formed this procedure over many years attest to the fact that pulpal necrosis is not associated with vital bleaching.1 Research in this area has shown how easily the hydrogen peroxide, because of its low molecular weight, passes through the enamel and dentin to the pulp.76

More current clinical studies have eliminated the etching with phosphoric acid,77 and the most recent products on the market advocate no use of heat or light for the reaction.57

A number of studies have evaluated the effect of bleaching with this high concentration on dentin and enamel and have found some hints of structural changes in tetracyclinestained teeth.78 However, the most important observation has been the decrease in bond strengths of composite resin to bleached, etched enamel immediately after the bleaching process.79 Later studies in this area have attributed the decrease to residual peroxide left immediately in the tooth or on the surface.80

The main safety advantages of the inoffice vital bleaching technique are that, although it uses caustic chemicals, it is totally under the dentist's control, the soft tissue is generally protected from the process, and it has the potential for bleaching quickly in situations in which it is effective. Disadvantages are primarily the cost, the unpredictable nature of the result, and the unknown duration of the treatment. The unsafe features include the potential for soft tissue damage to patient and provider, the discomfort of rubber dam, the temperature on the pulp, and the resultant post­treatment sensitivity. Although early concerns about pulpal response were identified, subsequent research seems to have shown that although this high concen­tration of hydrogen peroxide causes changes, they are reversible.4 If etching is performed, polishing is required after each visit, with some enamel loss.

It is well accepted that this technique works, but the patient must be counseled that, although the result may be permanent, the process more likely will have a 1 to 3year duration, at which time the treatment will need to be redone. Also, it cannot be determined prior to treatment whether the teeth will respond, and treatment may take as many as four to six treatments. The laborintensive nature of the treatment, which in turn requires a higher fee, coupled with the discomfort to the patient and uncertainty of the outcome, keep this method of bleaching from being a treatment that is widely accepted, although it can be successful.

Recent innovations for inoffice bleaching include chairsidemixed gels, some of which are activated by composite resin curing lights (Hi Lite Dual Activated Bleaching System, Shofu). According to the manufac­turer, this lightactivated material changes color when the bleaching process is completed, which should take only 3½  minutes. Chemical composition and effects on tooth structure of this technique are unknown at this date. Other gel forms do not use heat or light. Although they require approximately the same treat­ment time as the conventional Superoxol bleaching technique, the gels are much easier to manage clini­cally.

Nightguard vital bleaching or dentistprescribed/home­applied bleaching

The most recently introduced vital bleaching technique, originally called nightguard vital bleaching (NGVB),2 but also referred to as home bleaching or dentistmonitored bleaching, has created a resurgence in the area of bleaching, primarily because of its relative ease of application, the safety of the materials used, the lower cost, its general availability to all socio­economic classes of patients, and the high percentage of successful treatments. It may be more appropriately termed a "dentistprescribed/homeapplied" tech­nique. Because the 10% carbamide solution is equiva­lent to a 3% hydrogen peroxide solution, this solution is approximately one tenth the concentration of the solutions used for "power," or inoffice, bleaching. Results are generally seen in 2 to 3 weeks, and the final outcome is complete in 5 to 6 weeks.3 However, treatment times vary extensively, and much depends on the amount of time per day that the patient chooses or is able to apply the technique. Later products have offered solutions of hydrogen peroxide that range from 1% to 10% and carbamide peroxide solutions that are either 10% or 15% concentration.8l The details of this technique have been reported in many articles.2,3,22,56,57,82,83

Numerous articles have attested to the efficacy of the technique, which has been successful in clinical trials for approximately 91% of persons with mate­rially or genetically discolored teeth, and somewhat less successful in 91% of persons with tetracycline­discolored teeth. Tetracyclinestained teeth generally get lighter, but not whiter. Nightguard vital bleaching generally has the same indications and prognosis as conventional, inoffice bleaching, but can be accom­plished at a much lower cost and with fewer side effects, such as tissue burns and sensitive teeth, in the general patient population. A recent survey of 7,617 dentists indicated a success rate of greater than 90% for the technique; ninety percent of the responding dentists use a 10% carbamide peroxide.84

Specific questions as to the safety of NGVB were recently addressed in an article by Haywood and Hey­mann.4 The controversial element that the nightguard vital bleaching technique adds to conventional bleaching options is the potential for contact of the soft tissue during treatment and from ingestion of the material. This contact sometimes results in one of the two common side effects, an irritation of the gingival tissue. More than half the time, this irritation is related to an illfitting prosthesis. Other times, it is the tissue's re­sponse to the peroxide.

There are numerous reports of the effects of hydrogen peroxide on tissue.85-87 However, those effects are gen­erated by conditions that exceed greatly the time and dosage of peroxide used in this bleaching technique.4 The previously mentioned survey confirmed that one third of patients bleaching their teeth in the home manner did not have side effects, while those that did experienced either transient tooth sensitivity or gingi­val irritation.84 The fit of the guard was a major cause of gingival irritation. Reports from industries that make hydrogen peroxide state, "It is improbable that humans will be exposed to high oral doses of H2O2 due to the acute toxicity of concentrated solutions and the corrosivity of H2O2 to mucous membranes. An in­dividual would theoretically have to drink daily 23 mL of 35% hydrogen peroxide for a lifetime to develop the lesions seen in mice."20 Hydrogen peroxide is approved as safe for use as human food additive with no residues.

More recent studies directly evaluating the effects of 10% carbamide peroxide on tissues and in animals systemically have indicated that the effects of 10% carbamide peroxide on tissue are less than or equal to those of many other accepted dental medicaments, such as eugenol,88 or other dental procedures.4 The most conclusive evidence to date has been the work of Woolverton et al89 establishing the nonmutagenic nature of 10% carbamide peroxide, the safe level of ingestion, and the minimal effects on cell lines. Even in tray designs that seek to avoid covering the attached gingiva, the interdental papillae are still exposed to the solution. Hence, the total avoidance of soft tissue con­tact is impossible as the technique currently stands. Conclusions from evaluations of the other studies indicate that toxicity and mutagenicity of hydrogen peroxide are dose related,90 and the concentrations used in the athome bleaching technique are not of sufficient strength to warrant concern about the soft tissue.4 In fact, although a high, sudden dose of hydro­gen peroxide is toxic to cells, a lower dose over a longer time allows cells to adjust and actually ultimately tolerate a higher dose than that which originally would have been toxic.91 Also the long history of clinical usage of the solutions with soft tissue contact ranging from 7 days to 3 years, in patients ranging from new­born infants to geriatric patients, has demonstrated no problems.4

Various effects of carbamide peroxide on teeth have been studied.92-94 Generally, these reports find the effects to be nonexistent or to be no worse than those already found with inoffice bleaching. Although there have been varying reports concerning the effect on enamel, there does not seem to be a significant effect on the morphology of the enamel surface outside the normal variation of enamel.92,93,95 No published re­ports have demonstrated any change in hardness of enamel, nor have studies at the University of North Carolina shown any significant concerns.96 Studies that evaluate change in the surface must take into account the remineralization potential in the mouth, which may negate any potential changes. There has been one observation that toothbrush abrasion was more significant in the presence of bleaching agents,97 while yet another slightly different study showed brushing with the solutions had no effect.95 Another report has shown the athome bleaching procedure to be a controlled oxidation process in which the organic phase of the enamel is mobilized without producing grossly unacceptable enamel surface topography.23 Clinically, there is no apparent loss, and the tooth retains its glossy appearance. There have been reports of internal matrix changes from bleaching with 35% hydrogen peroxide after laboratoryinduced tetracycline staining, but there is no direct correlation between this study and the milder hydrogen peroxide, nor have these changes been demonstrated to have any clinical significance. Studies directly on dentin and enamel with 10% carbamide peroxide materials have demon­strated no structural loss.24

The effects on the pulp were extensively evaluated in the previous generation of bleaching with 35% hydrogen peroxide, and the lower concentration of peroxide would not be expected to be as detrimental to the pulp. The effects on pulp have not been directly evaluated with the weaker peroxide solutions, but the research on 35% hydrogen peroxide has shown effects that are reversible over time, with no clinical conse­quence other than immediate, but transient, sensitivity. Clinical trials on nightguard vital bleaching techniques in progress at the University of North Carolina have found no predictors of sensitivity relative to patient age, pulpal size, presence of exposed dentin or cemen­tum, caries, or leaking restorations. The limitation for how young the child is able to be treated is related more to the available number of permanent teeth to retain the guard and the desire not to impede the erup­tion of permanent teeth as they attempt to rapidly enter the oral cavity than to pulpal sensitivity. The occasional mild tooth sensitivity associated with night­guard vital bleaching is attributed to the easy passage of the hydrogen peroxide and urea through the enamel and dentin to the pulp and the resulting mild irritation. This ceases on termination of treatment.4 Because the concentration of hydrogen peroxide is lower, certain patients that could not tolerate the inoffice bleaching because of discomfort have found the nightguard vital bleaching technique to be acceptable.

Effects on restorative materials have been limited primarily to composite resins, both with color change and surface integrity.94 Basically, there is no appreciable change in the color of any restorative material clinically. Although there have been conflicting reports recently in this area as to composite resins,98-101 the ability of the colorimeters to measure differences is limited, and this color difference has not yet been calibrated to clini­cally detectable changes. Clinicians must assume there will be no color change in any material (although the stains may be removed from the surface and margins of porous composite resins, etc), and patients should be advised of the potential need for replacement of any esthetic restorations if the shade of the composite resin is not clinically acceptable postbleaching.3 Reports of the dissolution of a portion of the matrix have also concluded that it may be clinically inconsequential.102 Since the composite resin may have to be replaced afterward, any loss may be of no significant concern. Whether this bleaching technique will have a significant effect on the longterm wear of posterior composite resins103 is still unknown, because other reports have shown that composite resin hardens after exposure to bleaching solutions.98 Porcelain, amalgam, and gold have not responded with either color change or alter­ation of structure, so they are considered unchanged by the bleaching process.94

Of current interest to the clinician is the effect of bleaching on bond strength of etched enamel to com­posite resin. Earlier reports had associated a decrease in bond strength of treated enamel to composite resin with bleaching using 35% hydrogen peroxide.79 This occurrence has also been confirmed with the 3% per­oxide,104 but has been related to the residual oxygen in the tooth, and the bond has been shown to increase, approaching the original strength over time.4,104 More recent studies of the 35% inoffice bleaching techniques have also attributed this loss to residual peroxide tempor­arily remaining in the tooth or to surface changes.80 Another study of home bleaching techniques demon­strated that roughening the surface slightly also elimi­nates this phenomenon.105 Generally, etching and bonding should be delayed at least 14 days after termi­nation of bleaching until further studies can determine a more precise waiting time.

Safety to the occlusion and the temporomandibular joint during the bleaching process must also be consi­dered. Typically, occlusal problems during NGVB may be mechanical or physiologic. Mechanically, the patient may occlude on only posterior teeth, rather than on all teeth simultaneously. Sequentially removing posterior teeth from the guard until all the teeth contact will rectify the problem, and avoid the potential for joint disturbances. If the patient exhibits bruxism, he or she usually will wear a hole in the appliance over time, and another will have to be made. There has been no success to date in fabricating an occlusal device for bruxism that can also serve as a wellfitting guard for bleaching. Physiologically, if the patient has pain in the joint, the posterior teeth can be removed from the guard until only anterior guidance is remaining, and the patient's wear time should be reduced or limited to the day only.

Another area of concern with safety is how often the procedure will have to be administered. Current research at the University of North Carolina on longevity of the result indicates that, although the change may be permanent, the patient will probably need retreatment in 1 to 3 years. It has been noted that retreatment involves significantly less time than the original treatment.

Overthecounter bleaching kits

The newest systems that claim to bleach teeth are bleaching kits sold directly to consumers. These kits are described as a threestep process: a 15second pre­treatment acetic rinse, a 1 to 2minute application of a 6% hydrogen peroxide gel with a cotton swab on the facial surfaces of the teeth, and an application of a toothwhitening pigment.l06

Early concerns have been expressed as to whether the process actually works, especially as it is shown in television advertisements.107 Although results shown in advertisements seem dramatic, the manufacturers' literature reports that bleaching may take from 2 days to 2 weeks, and sometimes up to 60 applications, for successful lightening. No reports from dental studies have demonstrated any effectiveness.22 In a screening project for the US Federal Trade Commission at the University of North Carolina, administration of the OTC technique, on patients who had already success­fully bleached one arch with the dentistprescribed/ homeapplied technique in a clinical bleaching study, did not effect any change after one, two, 14, or 60 applications. One report has shown that there is no harm to composite resins from any of the bleaching agents, including this type of system.l08

A more disturbing concern relates to the safety of the material and technique. A recent report cites the dissolution of enamel in a young person using the technique.l09 Although the person was also a heavy cola drinker, this result raises the question of the safety of unsupervised use of a treatment as well as the lack of baseline data. If the material is not effective as a bleaching treatment, this lack of success could further foster abusive use in an attempt to achieve results. In those patients who have other problems resulting in dissolution of enamel, this could be an additional in­sult.

It may be this lack of proof of efficacy and safety with some techniques that has prompted both the American Dental Association to advise caution and the US Food and Drug Administration to issue warning letters to manufacturers requesting data supporting their claims.110 Further determination of both efficacy and safety of these OTC bleaching kits and other variations of the conventional NGVB technique are certainly indicated. However, the ruling by the US
Food and Drug Administration is directed toward manufacturers, and does not restrict, limit, or affect bleaching treatments performed in a legitimate dentist­patient relationship (US Food and Drug Administra­tion: Personal communication).

Relative safety of the nightguard vital bleaching technique

Safety of nightguard vital bleaching must be assessed relative to that of the other bleaching techniques, but it also must be compared to the safety of other accepted dental practices. With teeth, as with any living tissue, there will always be a response to treatment. The ques­tions are the riskbanefit of the treatment and what is known from observations and studies on other dental treatments.111 The question of safety is always a dose­overtime relation,112 as has been noted in the questions of fluoride toxicity1l3,114 and the recent amalgam and mercury concerns.115 Other areas in dentistry are also currently being examined for their safety. These indude concerns about the nickelberyllium content of non­precious metals,116 the carcinogenicity of nickel,117,118 and the reported toxicity of Sargenti techniques.119

As to the concern of the effect of materials on the pulp and other tissues, it has been shown that one in five teeth that receive a crown will need root canal therapy,l20 73% of the single pins placed in teeth cause a fracture in the dentin that communicates directly with the pulp,l2l and heat on the pulp from restora­tions and direct provisional restorations has adverse effects.122 Dentists observe postoperative pain from the cementation of crowns or ceramic inlays with glass­ionomer or zinc phosphate cements,l23-126 hypersen­sitivity reactions to polyether impressions,l27 and aller­gic reactions to the poly(methyl methacrylate) acrylic resins.l28 It has been shown that poly(methyl metha­crylate) is cytotoxicl29 and produces nonneoplastic lesionsl30 and that some glassionomer cements exude cytotoxic substances even after a hardening period of 48 hours.l3l In the more esthetic materials, it has been shown that all composite resin is cytotoxic in its unset form and when incompletely cured,132 and some com­posite resin is even cytotoxic if cured for less than 60 seconds.l33 The cytotoxicity of orthodontic adhesives has been demonstrated even after 2 years,l34 and the cytotoxicity of orthodontic solder joints to tissue has been shown.135 Recently, Gluma 3 (Miles Inc) has been identified as a mutagenic agent,136 the cytotoxicity of dentinal bonding agents has been demonstrated,l37,138 and detrimental effects of dentinal bonding agents on the pulp have been cited.l39-l4l Although the relative thickness of remaining dentin determines the cytotoxic effects of composite resinl42 and glassionomer ce­mentl43 on the pulpal tissues, it is impossible to know how much dentin is present in the mouth. There is also the danger of damage to the gingival tissues from in­discriminate use of the microabrasion technique,144 as well as with the conventional inoffice bleaching techniques.l45

As to effects of other dental treatments on the surface of teeth or restorations, 5 to 50 µm of enamel is re­moved during a prophylaxisl46 and 5 to 50 µm of enamel is removed at banding and debanding of ortho­dontic appliances.l47 Hence, even a possible effect on the surface of enamel from bleaching may be considered negligible compared to the 5 to 10µm loss of enamel from every rubber cup prophylaxis over the life of a patient,l48 including the loss of the fluoriderich layer. Merely etching the enamel dissolves at least 10 µm in addition to the 25 to 50 µm that is etched.l49 Treatment with microabrasion to remove stained enamel results in 12 µm of enamel loss with the first 5second applica­tion, and an average of 26 µm of loss for every succes­sive 5second application.150 Acidulated phosphate fluoride, which contains hydrofloric acid, is capable of etching porcelain in the mouth (Bayne S: Personal com­munication). It has also been shown that judicious use of the Cavitron can remove resinbonded fixed partial dentures or other cemented prostheses.151

As to overall safety, it is reported that 8% of patients are allergic to latex gloves.152 Studies on the previous effects of eugenol in periodontal dressings on bone have resulted in a change in the formulation to non­eugenolcontaining periodontal dressings.153 However, no significant clinical problems from the use of the eugenolcontaining periodontal dressings on soft tissue has been identified in the literature. Detrimental ef­fects of hydrogen peroxide on the bone have been reported, but it is unlikely that the nightguard vital bleaching techniques would ever be used in patients with exposed bone.l54 Recent reports have described the toxic effects of zinc oxideeugenol cement to the pulp,l55,156 the dangers and toxicity of sodium hypo­chlorite,l57,158 the toxicity of endodontic obturation materials,l59,160 and allergic reactions to implants.161 This, in conjunction with the radiation from normal exposure of radiographs, the potential for an allergic reaction to local anesthetic, the hazards of eye damage from composite resin curing lights, and the hearing loss caused by the high‑speed handpiece, make dental treatment full of risk‑banefit judgments in the light of current knowledge. Even the choice between a direct pulp cap or endodontic therapy,l62 between placement of another foundation or a casting,l63 or to remove a questionable restoration, which takes more tooth structure and weakens the tooth,l64 is subjective but significant in the long‑term safety and health of the tooth.

One concern often expressed about the nightguard vital bleaching technique is the potential danger of making bleaching materials available to patients at home, where abuse may occur. It is important to dis­tinguish between nightguard vital bleaching (dentist­prescribed/home‑applied), and OTC kits available directly to consumers. In the "prescribed" method, the materials are held in a custom‑fabricated guard, and approximately 1 to 2 oz is used in a 4‑ to 6‑week period.3 If the patient uses more than 2 oz during that time, the dentist should reevaluate the patient's appli­cation technique. The availability of the dentist for monitoring, the slowness of the treatment, and the contained environment reduce the potential for abuse. Clinical trials have also indicated there is a level of lightness beyond which the teeth do not pass. Hence the treatment is somewhat self‑limiting over time. Patients could continue for extended periods of time, but at this time there is no clinical evidence that this is occurring. There is always the potential for abuse by some persons, but there is the same potential danger of abuse from ingestion of fluoride‑containing tooth­paste or rinses, alcohol‑containing mouthwashes, and aspirin, even when these materials are correctly pre­scribed.

On the other hand, OTC kits place the consumer in a position of diagnosing the reason for discoloration of their teeth, as well as prescribing a treatment that has no professional evaluation of the baseline standard, the side effects, or the results. Unsupervised or exces­sive use of any material has potential for harm, espe­cially in certain persons in whom the physiologic status of the teeth and saliva or psychological status exaggerates otherwise reasonable treatment responses. These effects are seen in the case of toothbrush abrasion or the detrimental erosive effects of excess consumption of carbonated drinks and fresh citrus fruits on enamel and dentin. Most unknown about the OTC kits is the effect of the prerinse on enamel over time.l09 Further research and unbiased reports are needed to establish the appropriateness of claims for both safety and effi­cacy.57 The safer option currently available is a system where there is some establishment of indications for treatment by a trained professional, baseline recording of data, fabrication and insertion of a custom‑fitted mouthguard, monitoring of treatment, availability for questions, evaluation of success or concerns, and in­struction in application.

Some concern also has been expressed about the safety of wearing the guard. However, the history of dentures, mouthguards for sports, Hawley or Frankle appliances, orthodontic positioners, bite splints, and other occlusal devices that have served dentistry so well over the years make this an unreasonable concern.l65

Indications and applications for nightguard vital bleaching

The primary indication for the nightguard vital bleach­ing technique has been for persons dissatisfied with the original color of their otherwise sound teeth (Figs 1 and 2). Special concerns are for staining related to ingestion of tetracycline as an antibiotic during tooth formation or as an acne treatment during the teenage years (Figs 3 and 4). Other persons interested in bleaching originally had lighter teeth, but now the teeth have been darkened by age, coffee, tea, smoking, or other staining habits (Figs 5 and 6). Brown fluorosis stains are generally responsive, but white spots are unaffected (Figs 7 and 8). Other motivations for treat­ment may warrant consideration. These may include bleaching to avoid any of the developmental personality changes in young persons who are ostracized by their peers for having discolored teethl66; persons in public contact areas whose appearance greatly influences their success; or persons who are so dissatisfied with their present appearance that they are considering more invasive procedures, such as bonding, veneers, or crowns. In these instances, bleaching should be con­sidered as an alternative procedure, not as an elective procedure. Bleaching can also prolong the life of un­esthetic but otherwise acceptable dentistry.

Other indications include single teeth that have darkened from trauma, but are still vital or have a poor endodontic prognosis because of the absence of a radiographically visible canal. If all the other teeth are the appropriate color, the section of the guard cover­ing the adjacent teeth can be removed so that material is placed only on the darkened tooth3 (Figs 9 to 11). If all the teeth are slightly darkened, but one is still darker than the remaining teeth, then a conventional­style guard is constructed and all the teeth are bleached (Figs 12 and 13). Because it has been ob­served that teeth lighten to a certain point, then main­tain that color, the treatment is merely continued on the darker tooth until it approaches or matches the other lightened teeth.

Other options presented in the literature for treat­ing the single darkened tooth have included intentional endodontics or creating an artificial pulp chamber and bleaching the tooth with the walking bleaching technique.22,70 Because of the slight potential for cervi­cal resorption, the loss of tooth structure, and the less than 100% chance of success with endodontics, home bleaching should be considered the first choice for altering the color of these teeth.

Often the walking bleaching technique is desirable to ensure the removal of debris and discolored restora­tive materials from the pulp chamber. However, occa­sionally a tooth that has previously been bleached by the walking bleaching technique and sealed with a finished etched composite resin will discolor. In this instance, the first treatment considered should be bleaching the tooth externally with the nightguard vital bleaching technique, especially if the lingual access has since been covered by another restoration, such as an etched‑metal, resin‑bonded fixed partial denture retainer (Fig 14). External bleaching avoids unnecessary removal of an acceptable dental restora­tion, and the loss of tooth structure during the process, which weakens the tooth, and prevents additional insult to the cervical area from another 35% hydrogen peroxide treatment. Even after successful treatment with a walking bleach, often the bleached tooth is more yellow than the other teeth. Nightguard vital bleaching then can be used to harmonize the colors of the vital and nonvital teeth. Teeth that are endodontically treated, but have such a thin portion of remaining dentin at the cervical area that there is concern about potential cervical resorption from use of the 35% hy­drogen peroxide, are also amenable to the nightguard vital bleaching technique as the first choice of treat­ment.

The nightguard vital bleaching technique should be considered as the first choice of treatment for any dis­colored teeth, even those considered for the place­ment of porcelain or other esthetic veneers. Attempt­ing nightguard vital bleaching first may avoid the need for veneers. However, even if the technique is unsuc­cessful in achieving the desired shade, or if there are other indications for veneers other than the tooth color, bleaching may lighten the underlying tooth base and make the subsequent veneer more esthetic, as well as allow the patient to evaluate the results of the more conservative option first. Home bleaching can be used prior to placement of single porcelain‑fused tometal or ceramic crowns, fixed partial dentures, or removable partial dentures to offer a lighter, younger­looking shade, as well as to eliminate some of the dif­ficult crack lines or characterizations that are not eas­ily duplicated in ceramic restorations. Nightguard vital bleaching can minimize the discoloration of the stained incisal edges of mandibular teeth and minimize the effects of whitespot lesions by lightening the tooth structure adjacent to the whitespot lesion.

Not only is nightguard vital bleaching effective as a preoperative treatment, but it is also effective post­treatment to lighten natural teeth to match existing ceramic crowns, fixed partial dentures, or Dicor resto­rations (Dentsply International) (Figs 15 and 16). This lightening can be achieved to match crowns to adjacent teeth in one arch or to teeth in the opposing arch. Bleaching can also increase the longevity of three­quarters crown abutments, onlays, or resinbonded fixed partial denture abutments that have darkened more than their originally matched porcelain poetic (Figs 17 and 18). Bleaching has even been used successfully to increase the life of previous composite resin bonding by lightening the underlying tooth structure to com­pensate for the wear of the composite resin or to lighten the apparent color of veneers already cemented by light­ening the underlying tooth structure. This lightening effect is due to the ability of the carbamide peroxide to pass freely through enamel and dentin and to per­meate to all parts of the tooth, even those protected by restorations.92

Although the success and acceptance of the night­guard vital bleaching technique has been phenomenal, it has not eliminated the inoffice bleaching.167 Some patients' lifestyles do not lend themselves to extended treatment times, or outsidetheoffice appliances. Also, they may not be willing to wait the time for home bleaching to be effective. They may not be con­cerned about the greater financial investment of in­office bleaching or may not be able to wear the guard and tolerate the taste of the solutions used in night­guard vital bleaching. In these situations, inoffice bleaching is indicated. It is also indicated if the patient does not respond well to the nightguard vital bleach­ing regimen. In clinical trials at the University of North Carolina, a single inoffice bleaching treatment, delivered after a lack of response to nightguard vital bleaching, followed by continuation of the nightguard vital bleaching treatment, has achieved results that neither technique showed independently. In those cases, the teeth were not etched, and neither heat nor light was employed. Other recommendations include beginning bleaching with the inoffice treatment, fol­lowed by the home treatment.167

Other clinical pilot studies at the University of North Carolina have shown reduction in the buildup of chlorhexidine stains when a 10% carbamide peroxide is used in an alternating fashion with the mouthwash. Other preventive opportunities being explored have included using the nightguard vital bleaching system to attempt to reduce the incidence of root caries that is unresponsive to traditional fluoride and tray sys­tems.168 This caries is often related to xerostomia and is a sequelae to radiation therapy, chemotherapy, med­ical problems, or aging.165 There is hope to evaluate the nightguard vital bleaching application in nursing homes or hospitals, where attendants may be able to add this application technique to the oral hygiene reg­imen of patients with inability to perform adequate oral hygiene measures.169


The profession should neither propose a sweeping con­demnation nor offer a sweeping endorsement of bleaching any more than it should any other treatment option or medicament used in dentistry. Bleaching techniques that have been shown to be reasonably and relatively safe and effective, both in current usage and over time, should be accepted as a reasonable treat­ment option,84,170 knowing the risks and benefits. Con­tinued research should be undertaken on these and all other dental treatments. These accepted techniques include the nonvital bleaching with 35% hydrogen peroxide and/or sodium perborate (but without heat), inoffice vital bleaching with 35% hydrogen peroxide (but without etching), and nightguard vital bleaching (dentistprescribed/homeapplied bleaching) with 10% carbamide peroxide materials or similar products. Conversely, claims that any use of hydrogen peroxide will bleach teeth and that all techniques are safe can­not be accepted blindly. Especially in question are the OTC bleaching kits and toothpastes containing car­bamide peroxide. Effectiveness and safety of the bleaching technique must evaluate not only the prod­uct but also the delivery method and treatment time.

Unbiased research is still the best avenue for sifting through the claims and reports to achieve a better un­derstanding of what is correct and what it incorrect.57 Over time, the understanding of temporomandibular joint function has changed radically, the correlation between occlusion and pain has altered, the change from pins to slots in amalgam restorations has occur­ red, the noncrowning of anterior, endodontically treated teeth has been advocated, and the nonposting of endodontically treated anterior teeth, unless the post is needed to retain the preparation form of the crown, has been reported. So must the dental profes­sion be ever vigilant for changes that provide the most conservative esthetic treatment options for patients. More importantly, the profession should continually examine these treatment options in the light of new evidence or techniques, always applying the same stand­ards of safety to all treatment options.

Fig 1 Natural teeth with discoloration primarily confined to the maxillary arch. Color matching of composite resin restorations or crowns on the maxillary arch would be dif­ficult at best.

Fig 2 Results of nightguard vital bleaching of the maxillary arch. The mandibular arch is left untreated. No sensitivity was reported, although there was exposed dentin.

Fig 3 Vital teeth mildly discolored from tetracycline inges­tion.

Fig 4 Maxillary arch lightened with NGVB, while the man­dibular arch serves as the control.

Fig 5 Vital teeth discolored by heavy tobacco use, with craze lines and stained restorations.

Fig 6 Maxillary arch lightened with NGVB. The mandibular arch is untreated. Craze lines and stains around composite resin restorations are less noticeable.

Fig 7 Maxillary central incisors exhibiting both brown fluorosis stains and white spots.

Fig 8 After NGVB bleaching, the brown areas are removed. The white areas remain, but are less noticeable.

Fig 9 Design of the NGVB tray to limit the application of the material to the single, discolored tooth.

Fig 10 A single, vital discolored tooth. The color of the remaining teeth is acceptable to the patient.

Fig 11 After NGVB, the single tooth more closely matches the other teeth. The color of the adjacent teeth is un­changed.

Fig 12 A single, severely discolored vital tooth with no radiographic evidence of a pulp canal. Other teeth are slightly discolored.

Fig 13 Results of NGVB on the entire maxillary arch. Al­though not a perfect color match, the severely discolored tooth better blends with the rest of the teeth.

Fig 14 The lateral incisor has been treated endodontically and with the walking bleach technique years ago; the pon­tic no longer matches the natural dentition. This is a good indication for NGVB.

Fig 15 Dicor restorations placed on the four incisors are noticeable because of the yellowed canine.

Fig 16 The NGVB technique is applied until the canine more closely blends the natural posterior teeth with the crowned incisors.

Fig 17 An otherwise acceptable porcelainfusedtometal crown no longer matches the color of the adjacent teeth after years of service.

Fig 18 Maxillary arch is lightened with NGVB until the porcelainfusedtometal crown is less noticeable.


1. Feinman RA, Goldstein RE, Garber DA: Bleaching Teeth. Chicago, Quintessence Publ Co, 1987.

2. Haywood VB, Heymann HO: Nightguard vital bleaching. Quintessence Int 1989;20:173176.

3. Haywood VB: Nightguard vital bleaching: current informa­tion and research. Esthet Dent Update 1990;1(2):712.

4. Haywood VB, Heymann HO: Nightguard vital bleaching: how safe is it? Quintessence Int 1991;22:515523.

5. Spector A: Oxidation and aspects of ocular pathology. CLAO J 1990;16(suppl l):S8S10.

6. Carlsson J: Salivary peroxidase: an important part of our defense against oxygen toxicity. J Oral Pathol 1987;16: 412416.

7. Ericson T, Bratt P: Interactions between peroxide and sali­vary glycoprotein: protection by peroxidase. J Oral Pathol 1987:16;421–424.

8. Berglin EH, Carlsson J: Effects of hydrogen sulfide on the mutagenicity of hydrogen peroxide in Satmone& typhimurium strain TA102. Mutat Res 1986;175:59.

9. Berglin EH, Carlsson J: Potentiation by sulfide of hydrogen peroxideinduced killing of Escherichia coli. Infect Immun 1985;49:538543.

10. McNally JJ: Clinical aspects of topical application of dilute hydrogen peroxide solutions. CLAO J 1990;16(suppl 1):S46S52.

11. ZieglerSkylakakis K, Andrae U: Mutagenicity of hydrogen peroxide in V79 Chinese hamster cells. Mutat Res 1987;192(1):6567.

12. Kensese SM, Smith LL: Hydrogen peroxide mutagenicity towards Salmonella typhimurium. Teratogenesis Carcinog Mutagen 1989;9:211218.

13. AbuShakra A, Zeiger E: Effects of Salmonella genotypes and testing protocols on H2O2induced mutation. Mutagenesis 1990;5:469473.

14. Cantoni O, Murray D, Meyn RE: Effect of 3aminoben­zanide of DNA strand break rejoining and cytotoxicity in CHO ceils treated with hydrogen peroxide. Biochim Biophys Acta 1986;867:135143.

15. White WE Jr, Pruitt KM, ManssonRahemtulla B: Peroxidasethiocyanateperoxide antibacterial system does not damage DNA. Antimicrob Agents Chemother 1983;Feb: 267272.

16. KleinSzanto AJP, Slaga TJ: Effects of peroxides on rodent skin: epidermal hyperplasia and tumor promotion. J Invest Dermatol 1982;79:3034.

17. Starke PE, Farber JL: Endogenous defenses against the cytotoxicity of hydrogen peroxide in cultured rat he ato­cytes. J Biol Chem 1985;260:8692.

18. Starke PE, Farber JL: Ferric iron and superoxide io~ns are required for the killing of cultured hepatocytes by hydrogen peroxide. J Biol Chem 1985;260:1009910104

19. Stindt DJ, Quenette L: An overview of glyoxide liquid in control and prevention of dental disease. Compend Contin Educ Dent 1989;9:514520.

20. Material Safety Data: Hydrogen Peroxide 35%. FMC Corpora­tion, 1988, pp 19. ,

21. Feinman RA, Madray G, Yarborough D: Chemical, optical, and physiologic mechanisms of bleaching products: a review. Practical PenodontAesthet Dent 1991;3:3237.

22. Albers HF: Home bleaching. ADEPTReport 1991;2(1):917.

23. Covington JS, Friend GW, Lamoreaux WJ, et al: Carbamide peroxide tooth bleaching: effects on enamel composition and topography. J Dent Res 1990;69:175 (abstr No. 530).

24. Covington JS, Friend GW, Jones JE: Carbamide peroxide tooth bleaching: deep enamel and dentin compositional changes. J Dent Res 1991;70:570 (abstr No. 2433).

25. How WS: Esthetic dentistry. Dent Cosmos 1886;28:741745.

26. M'Quillen JH: Elongation and discoloration of a superior central incisor. Dent Cosmos 1868;10:225227.

27. Kirk CE: Chemical principles involved in tooth discolora­tion. Dent Cosmos 1906;48:947954.

28. Kirk EC: The chemical bleaching of teeth. Dent Cosmos 1889;31:273283.

29. Kirk EC: An American Textbook of Operative Dentistry, ed 2. Philadelphia, Lea Brothers, 1990, pp 540560.

30. Marshal JS: Principles and Practice of Operadve Dentistry. Philadelphia, JB Lippincott Co, 1901, pp 464 476.

31. Burchard HH: A Textbook of Dental Pathology and Therapeu­tics. Philadelphia, Lea & Febiger, 1898.

32. Dwinelle WW: Ninth Annual Meeting of American Society of Dental Surgeons. Article X. Am J Dent Sci 1850;1:5761.

33. Woodnut C: Discoloration of dentine. Dent Cosmos 1861;2:662.

34. Harlan AW: Proceedings of the American Dental Associa­tionTwentyThird Annual Session. Dent Cosmos 1884;26:9798.

35. Harlan AW: The dental pulp, its destruction, and methods of treatment of teeth discolored by its retention in the pulp chamber or canals. Dent Cosmos 1891;33:137141.

36. Latimer JS: Notes from the discussion of the Society of Den­tal Surgeons in the city of New York. Dent Cosmos 1868:10: 257258.

37. Bogue EA: Bleaching teeth. Dent Cosmos 1872;14:13.

38. Chapple JA: Hints and queries. Dent Cosmos 18M;19:499.

39. Atkinson CB: Fancies and some facts. Dent Cosmos 1892; 34:968972.

40. Kirk EC: Hints, queries, and comments: sodium peroxid. Dent Cosmos 1893;35:12651267.

41. Barker GT: The causes and treatment of discolored teeth. Dent Cosmos 1861;3:305311.

42. Kingsbury CA: Discoloration of dentine. Dent Cosmos 1861; 3:5760.

43. Franchi GJ: A practical technique for bleaching discolored crowns of young permanent incisors. J Dent Child 1953;20:6869.

44. Atkinson WH: Bleaching teeth, when discolored from loss of vitality; means for preventing their discoloration and ulceration. Dent Cosmos 1862;3:7477.

45. Stellwagen TC: Bleaching teeth. Dent Cosmos 1870;12: 625627.

46. Prinz H: Recent improvement in tooth bleaching. Dent Cosmos 1924;66:558560.

47. Fisher G: The bleaching of discolored teeth with H2O2. Dent Cosmos 1911;53:246247.

48. Rosenthal P: The combined use of ultraviolet rays and hydrogen dioxide for bleaching teeth. Dent Cosmos 1910;52:246.

49. Atkinson CB: Hints, queries, and comments: pyrozone. Dent Cosmos 1893;35:330332.

50. Pearson HH: Successful bleaching without secondary discol­ouration. J Can Dent Assoc 1951;17:200201.

51. Smith MS, Mcinnes JW: Further studies on methods of removing brown stains from mottled teeth. J Am Dent Assoc 1942;29:571.

52. Pearson HH: Bleaching of discolored teeth. JAm Dent Assoc 1958;56:6465.

53. Spasser HF: A simple bleaching technique using sodium per­borate. NY Dent J 1961;27:332334.

54. Nutting EB, Poe GS: A new combination for bleaching teeth. J Southern Calif Dent Assoc 1963;31:289.

55. Nutting EB, Poe GS: Chemical bleaching of discolored endodontically treated teeth. Dent Clin North Am 1967; Nov:655662.

56. Haywood VB, Drake M: Research on whitening teeth makes news. NC Dent Rev 1990;7(2):9.

57. Haywood VB: Overview and status of mouthguard bleach­ing. J Esthet Dent 1991;3:157161.

58. Goldstein FW: New "at home" bleaching technique intro­duced. Cosmetic Dent GP 1989;June:67.

59. Harrington GW, Natkin E: External resorption associated with bleaching of pulpless teeth. J Endod 1979;5:344348.

60. Lado EA, Stanley HR, Weisman Ml: Cervical resorption in bleached teeth. Oral Surg Oral Med Oral Pathol 1983;55:7880.

61. Montgomery S: External cervical resorption after bleaching a pulpless tooth. Oral Surg Oral Med Oral Pathol 1984;57:203206.

62. Goon WWY, Cohen S, Borer RF: External cervical root resorption following bleaching. J Endod 1986;12:414 418.

63. Lado EA: Bleaching of endodontically treated teeth: An update on cervical resorption. Cen Dent 1988;36:500501.

64. Friedman S, Rotstein 1, Libfeld H, et al: Incidence of exter­nal resorption and esthetic results in 58 bleached pulpless teeth. Endod Dent Traumatol 1988;4:2326.

65. Madison S, Walton R: Cervical root resorption following bleaching of endodontically treated teeth. J Endod 1990:16; 570574.

66. Holmstrup G, Palm AM, LambjergHassen H: Bleaching of discoloured rootfilled teeth. Endod Dent Traumatol 1988;4: 197201.

67. Warren MA, Wong M, Ingram TA 111: An in vitro compari­son of bleaching agents on the crowns and roots of discol­ored teeth. J Endod 1990;16:463467.

68. Latcham NL: Postbleaching cervical resorption. J Endod 1986;12:262264.

69. Jordan RE, Boksman L: Conservative vital bleaching treat­ment of discolored dentition. Compend Contin Educ Dent 1984;5:803808.

70. Abou‑Rass M: The elimination of tetracycline discoloration by intentional endodontics and internal bleaching. J Endod1982;8:101.

71. Goldstein RE: Bleaching teeth: new materials‑new role. J Am Dent Assoc 1987;115(special issue):44E‑52E.

72. Zach L, Cohen G: Pulp response to externally applied heat. Oral Surg Oral Med Oral Pathol 1965;19:515‑530.

73. Nyborg H, Brannstrom M: Pulp reaction to heat. J Prosthet Dent 1968;19:605‑612.

74. Cohen SC: Human pulpal response to bleaching procedure on vital teeth. J Endod 1979;5:134‑138.

75. Seale NS, Mcintosh JE, Taylor AN: Pulpal reaction to bleaching of teeth in dogs. J Dent Res 1981;60:948‑953.

76. Bowles WH, Ugwuneri Z: Pulp chamber penetration by hydrogen peroxide following vital bleaching procedures. J Endod 1987;8:375‑377.

77. Hall DA: Should etching be performed as a part of a vital bleaching technique? Quintessence Int 1991;22:679‑686.

78. Ledoux WR, Malloy RB, Hurst RVV, et al: Structural effects of bleaching on tetracycline‑stained vital rat teeth. J Prosthet Dent 1985;54:55‑59.

79. Titley KC, Torneck CD, Smith DC, et al: Adhesion of com­posite resin to bleached and unbleached bovine enamel. J Dent Res 1988;67:1523‑1528.

80. Torneck CD, Titley KC, Smith DC, et al: The influence of time of hydrogen peroxide exposure on the adhesion of com­posite resin to bleached bovine enamel. J Endod 1990;16:123‑128.

81. Haywood VB: Nightguard vital bleaching: history and prod­ucts update. Part 1. Esthet Dent Update 1991;2(4):63‑66.

82. Haywood VB: Nightguard vital bleaching, letter. Quintes­sence Int 1989;20:697.

83. Darnell DH, Moore WC: Vital tooth bleaching: the white and brite technique. Compend Confin Educ Dent 1990;11: 86‑94.

84. Christensen GJ: Home‑use bleaching survey‑1991. Clin Res Assoc Newsletter 1991;15(10):2.

85. Wietzman SA, Weitberg AB, Stossel TP, et al: Effects of hydrogen peroxide on oral carcinogenesis in hamsters. J Periodontol 1986;57:685‑688.

86. Dorman HL, Bishop JG: Production of experimental edema in dog tongue with dilute hydrogen peroxide. Oral Surg Oral Med Oral Pathol 1970;38–43.

87. Martin JH, Bishop JG, Guentherman RH, et al: Cellular response of gingiva to prolonged application of dilute hydro­gen peroxide. J Penodontol 1968;39:208–210.

88. Woolverton CJ, Fotos PG, Mokas MJ, et al: Evaluation of eugenol for mutagenicity by the mouse micronucleus test. J Oral Pathol 1986;15:450–453.

89. Woolverton CJ, Haywood VB, Heymann HO: A toxicologic screen of two carbamide peroxide tooth whiteners. J Dent Res 1991;70:558 (abstr No. 2335).

90. Cantoni O, Murray D, Meyn RE: Effect of 3‑aminoben­zamide on DNA strand‑bread rejoining and cytotoxicity in CHO cells treated with hydrogen peroxide. Biochim Biophys Acta 1986;867:135–143.

91. Winguist L, Rannug U, Rannug A, et al: Protection from toxic and mutagenic effects of H2O2 by catalase induction in Salmonella typhimurium. Mutat Res 1984;141:145‑147.

92. Haywood VB, Leech T, Heymann HO, et al: Nightguard vital bleaching: effects on enamel surface texture and diffu­sion. Quintessence Int 1990;21:801‑806.

93. Haywood VB, Houck V, Heymann HO: Nightguard vital bleaching: effects of varying pH solutions on enamel surface texture and color change. Quintessence Int 1991;22:775‑782.

94. Hunsaker KJ, Christensen GJ, Christensen RP: Tooth bleaching chemicals‑influence on teeth and restorations. J Dent Res 1990;69:303 (abstr No. 1558).

Scherer W, Cooper H, Ziegler B, et al: At‑home bleaching system: effects on enamel and cementum. J Esthet Dent 1991;3:54‑56.

96. McCracken MS: Effects of vital bleaching on the hardness of enamel. Presented at the American Dental Association Stu­dent Table Clinic, Seattle, Oct 1991.

97. Kalili T, Mito R, Caputo AA, et al: In vitro toothbrush abrasion and bond strength of bleaching enamel. J Dent Res 1991;70:546 (abstr No. 2243).

98. Friend GW, Jones JE, Wamble SH, et al: Carbamide peroxide tooth bleaching: changes to composite resins after prolonged exposure. J Dent Res 1991;70:570 (abstr No. 2432).

99. Monaghan P, Lee E, Lautenschlager EP: At home vital bleaching effects on composite resin color. J Dent Res 1991; 70:570 (abstr No. 2435).

100. Kao EC, Peng P, Johnston WM: Color changes of teeth and restorative materials exposed to bleaching. J Dent Res 1991; 70:570 (abstr No. 2436).

101. Tenaglia CA, Yaman P, Razzoog ME: Effect of vital tooth bleaching agents on enamel and composite. J Dent Res 1991; 70:475(abstr No. 1674).

102. Christensen GJ: Tooth bleaching, home‑use products. Clin ResAssoc Newsletter 1989;13(12):1.

103. Bailey SJ, Swift EJ Jr: Effects of home bleaching products on resin composites. J Dent Res 1991;70:570(abstr No. 2434).

104. McGuckin RS, Thurmond BA, Osovitz S: In vitro enamel shear bond strengths following vital bleaching. J Dent Res 1991;70:377 (abstr No. 892).

105. Cvitko E, Denehy GE, Swift EJ Jr, et al: Bond strength of composite resin to enamel bleached with carbamide peroxide. J Esthet Dent 1991;13:100‑102.

106. Stanton D: Discoveries. Dentist 1990;April:47.

107. Lyons P: Tooth‑bleaching scam. Good Morning America, transcript No. 1044, June 14, 1990.

108. Bailey SJ, Swift JS Jr: Effects of home bleaching products on composite resins. Quintessence Int 1992;23:489 494.

109. Cubbon T, Ore D: Hard tissue and home tooth whiteners. CDS Review 1991;85(5):32‑35.

110. Berry J: FDA says whiteners are drugs. ADA News 1991; 22(18):1,6,7.

111. Bantin DW, Robertson JM: Dealing with risks in the dental office. J Am Dent Assoc 1991;122:16‑17.

112. Meryon SD: The influence of surface area on the in vitro cytotoxicity of a range of dental materials. J Biomed Mater Res 1987;21:1179‑1186.

113. Banting DW: The future of fluoride: an update one year after the national toxicology program study. J Am Dent Assoc 1991;123:86‑91.

114. Mason JO: Too much of a good thing? [Questions about fluorosis explored.] J Am Dent Assoc 1991;122:93‑96.

115. Mackert JR Jr: Dental amalgam and mercury. J Am Dent Assoc 1991;122:54–61.

116. Hildebrand HF, Veron C, Martin P: Nickel, chromium, cobalt dental alloys and allergic reactions: an overview. Biomaterials 1989;10:545–548.

117. Pierce LH, Goodkind RJ: A status report of possible risks of base metal alloys and their components. J Prosthet Dent 1989;62:234–238.

118. Garattini G, Grecchi MT, Vlasasina A: Toxico‑allergic phenomena connected to the use of nickel‑containing alloys. Mondo Ortod 1990;15:639‑644 (in Italian).

119. Arenholt‑Bindslev D, Horsted‑Bindslev P: A simple model for evaluating relative toxicity of root filling materials in cul­tures of human oral fibroblasts. Endod Dent Traumatol 1989; 5:219‑226.

120. Felton D, Madison S, Kanoy E, et al: Long term effects of crown preparation on pulp vitality. J Dent Res 1989;68:1009 (abstr No. 1139).

121. Webb EL, Straka WF, Phillips CL: Tooth crazing associated with threaded pins: a 3‑dimensional model. J Prosthet Dent 1989;61:624–628.

122. Tjan AH, Grant BE, Godfrey MF III: Temperature rise in the pulp chamber during fabrication of provisional crowns. J Prosthet Dent 1989;62:622–626.

123. Klausner LH, Brandau HE, Charbeneau GT: Glass‑ionomer cements in dental practice: a national survey. Oper Dent 1989;14:170–175.

124. Grund P, Raab WH: Pulp toxicity of the acid components of acid‑base reaction cements. Dtsch Zahndrztl Z 1990;45:608–610 (in German).

125. Hickel R: The problem of tooth hypersensitivity following the placement of acid‑etch retained inlays. Dtsch Zahnarztl Z 1990;45:740–742 (in German).

126. Grund P, Raab WH: Pulp toxicity of luting cements. Dtsch Zahnarzd Z 1990;45(11):736–739 (in German).

127. Hensten‑Pettersen A, Nilner K, Moller B: Guinea pig maximization test with a polyether impression material. Scand J Dent Res 1990;98:356–362.

128. Kaaber S: Allergy to dental materials with special reference to the use of amalgam and polymethylmethacrylate. Int Dent J 1990;40:359–365.

129. Horowitz SM, Gautsch TL, Frondoza CG, et al: Mac­rophage exposure to polymethyl methacrylate leads to mediator release and injury. J Orthop Res 1991;9:406–413.

130. Chan PC, Eustis SL, Huff JE, et al: Two‑year inhalation car­cinogenesis studies of methyl methacrylate in rats and mice: inflammation and degeneration of nasal epithelium. Toxicol­ogy 1988;52:237–252.

131. Muller J, Bruckner G, Kraft E, et al: Reaction of cultured pulp cells to eight different cements based on glass ionom­ers. Dent Mater 1990;6:172–177.

132. Caughman WF, Caughman GB, Dominy WT, et al: Glass ionomer and composite resin cements: effects on oral cells. J Prosthet Dent 1990;63:513–521.

133. Ito Y, Kaga M, Oguchi H: Correlation between the illumina­tion time and cytotoxicity of light‑cured composite resins. Shoni Shikagaku Zasshi 1989;27:854–863 (in Japanese).

134. Tell RT, Sydiskis RJ, Isaacs RD, et al: Long‑term cytotoxic­.ity of orthodontic direct‑bonding adhesives. Am J Orthod Dentofac Orthop 1988;93:419–422.

135. Gjerdet NR, Kallus T, Hensten‑Pettersen A: T~ssue reac­tions to implanted orthodontic wires in rabbits. Acta Odontol Scand 1987;45:163‑169.

136. Li Y, Noblitt TW, Dunipace AJ, et al: Evaluation of mutagenicity of restorative dental materials using the Ames salmonella/microsome test. J Dent Res 1990;69:1188‑1192.

137. Furuya K: Electron microscopic study of canine dentin and odontoblast following the insertion of various composite resin monomers. FuLuoka Shika Daigaku Gakkai Zasshi 1989;16:572‑599 (in Japanese).

138. Arenholt‑Bindslev D, Horsted‑Bindslev P, Philipsen HP: Toxic effects of two dental materials on human buccal epithelium in vitro and monkey buccal mucosa in vivo. Scand J Dent Res 1987;95:467~74.

139. Yamaguchi S, Ishikawa 1, Masunaga H, et al: Effects of com­posite resin materials on gingiva and pulp. Nichidaikoko Kagaku 1989;15:315–327 (in Japanese).

140. Swift EJ Jr: Pulpal effects of composite resin restorations. Oper Dent 1989;14:20–27.

141. Meryon SD, Brook AM: In vitro cytotoxicity of three dentine bonding agents. J Dent 1989;17:279–283.

142. Hanks CT, Craig RG, Dichl ML, et al: Cytotoxicity of den­tal composites and other materials in a new in vitro device. J Oral Pathol 1988;17:396–403.

143. Hume WR, Mount GJ: In vitro studies on the potential for pulpal cytotoxicity of glass‑ionomer cements. J Dent Res 1988;67:915–918.

144. Croll TP, Killian CM, Miller AS: Effect of enamel microab­rasion compound on human gingiva: report of a case. Quin­tessence Int 1990;21:959–963.

145. Goldstein CE, Goldstein RE, Feinmann RA, et al: Bleach­ing vital teeth: state of the art. Quintessence Int 1989;20:729–737.

146. Tinanoff N, Wei SHY, Parkins FM: Effect of a pumice prophylaxis on fluoride uptake in tooth enamel. J Am Dent Assoc 1974;86:384­–389.

147. Radlanski RJ: A technic for cementing orthodontic bands; SEM research on the enamel and filling damages and a pro­tective wax technic to avoid them. Fortschr Kieferorthop 1990;51:277–283 (in German).

148. Pus MD, Way DC: Enamel loss due to orthodontic bonding with filled and unfilled resins using various clean‑up techniques. Am J Orthod 1980;77:269–283.

149. Silverstone LM: The acid etch technique: in vitro studies with special reference to the enamel surface and the enamel­resin interface, in Silverstone LM, Dogon IL (eds): Proceed­ings of an Internafional Symposium on the Acid Etch Technique. St Paul, Minn, North Central Publ Co, 1975, pp 13–19.

150. Waggoner WF, Johnston WM, Schumann S, et al: Microabra­sion of human enamel in vitro using hydrochloric acid and pumice. Pediatr Dent 1989;11:319–323.

151. Jordan RD, Krell KV, Aquilino SA, et al: Removal of acid­etched fixed partial dentures with mod)fied ultrasonic scaler tips. JAm Dent Assoc 1986;112:505–507.

152. Hensten‑Pettersen A, Jacobsen N: Perceived side effects of biomaterials in prosthetic dentistry. J Prosthet Dent 1991;65:138–144.

153. Eber RM, Shuler CF, Buchanan W, et al: Effect of periodon­tal dressings on human gingival fibroblasts in vitro. J Peri­odontol 1989;60:429–434.

154. Ramp WK, Arnold RR, Russell JE, et al: Hydrogen peroxide inhibits glucose metabolism and collagen synthesis in bone. J Periodontol 1987;58:340–344.

155. Kanca J III: An alternative hypothesis to the cause of pulpal inflammation in teeth treated with phosphoric acid on the dentin. Quintessence Int 1990;21:83–86.

156. Fotos PG, Woolverton CJ, Van Dyke K, et al: Effects of eugenol on polymorphonuclear cell migration and chemi­luminescence. J Dent Res 1987;66:774–777.

157. Becking AG: Complications in the use of sodium hypochlo­rite during endodontic treatmedt: report of three cases. Oral Surg Oral Med Oral Pathol 1991;71:346–348.

158. Kaufman AY, Keila S: Hypersensitivity to sodium hypochlo­rite. J Endod 1989;15:224–226.

159. Taoka Y: Cytotoxicity of dental filling materials in primary cultured cells derived from human dental pulp (in vitro). Shika Zairyo Kikai 1989;8:763–782 (in Japanese).

160. Briseno BM, Willershausen B: Root canal sealer cytotoxic­ity on human gingival fibroblasts. I. Zinc oxide‑eugenol­based sealers. J Endod 1990;16(8):383–386.

161. Mitchell DL, Synnott SA, VanDercreek JA: Tissue reaction involving an intraoral skin graft and CP titanium abutments: a clinical report. Int J Oral Maxillofac Implants 1990;5:79–84.

162. Maryniuk GA, Haywood VB: Placement of cast restorations over direct pulp capping procedures: a decision analytic ap­proach. J Am Dent Assoc 1990;120:183–188.

163. Maryniuk GA, Schweitzer SO, Braun RJ: Replacement of amalgams with crowns: a cost‑effectiveness analysis. Com­munity Dent Oral E:pidemiol 1988;16:263–267.

164. Maryniuk GA: Estimating prosthodontic treatment costs: a probability approach. Int J Prosthodont 1988;1:281–285.

165. Seals RR Jr, Dorrough BC: Custom mouth protectors: a re­view of their applications. J Prosthet Dent 1984;51:238–242.

166. Jenny J, Cons NC, Kohout FJ, et al: Relationship between dental aesthetics and attributions of self‑confidence. J Dent Res 1990;69:204 (abstr No. 761).

167. Garber DA, Goldstein RE, Goldstein CE, et al: Dentist monitored bleaching: a combined approach. Practical Perio­dontAesthet Dent 1991;3(2):22–26.

168. Firestone AR, Schmid R, Muhlemann HR: Effect of topical application of urea peroxide on caries incidence and plaque accumulation in rats. Caries Res 1982;16:112–117.

169. Shapiro WB, Kaslick RS, Chasens Al, et al: The influence of urea peroxide gel on plaque, calculus and chronic gingival inflammation. J Periodontol 1973;44:636‑639.

170. Golub‑Evans J: AACD survey finds bleaching safe and effec­tive. Dent Today 1991;August:34‑37.

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