The Safety of Tooth Whitening

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One of the most important concerns for any new dental procedure is its safety. The dentist must have absolute confidence and security in the dental treatments being recommended to his patients.

Safety is normally established in one of two ways: the product can be tested on animals in order to predict its toxicity in humans, or in the case of a material that has previously been used for human treatment, Lhe record of the product can be examined for deleterious side effects.

As may be expecLed, some concerns have properly been raised regarding the safety implications of vital tooth whitening. It has been implied in the most general of terms that carbamyl peroxide* may be toxic, dangerous, and oncogenic, but no applicable applicable scientific evidence has been advanced to support these views.12 The issue has been further clouded by assertions that dentistry has no experience with these whitening materials. All of this ignores the scientific data that has been recorded over the last forty-five years. In fact, both animal and human studies, short and long-term, have evaluated the question of the safety of carbarnyl peroxide in the oral cavity.

The testing revealed that earbamyl peroxide not only promotes gingival healing, but is actively antiplaque in nature and may be anticariogenic. It is true that the focus of the earbamyl peroxide testing in past years was to evaluate the material as an antiseptic (and not as a tooth whitening agent), but the intraoral conditions under which the tests were accomplished are identical to Lhe situations that are present with whitening procedures.

Carbamyl peroxide is not a substance new to dentistry, nor was its development for dental purposes accidental. Aqueous hydrogen peroxide has long been used by Lhe dental profession; its lack of toxicity and minimal side effects, combined with both cleansing and bactericidal properties, made it particularly attractive for intraoral use. A major flaw in the character of hydrogen peroxide is its extremely rapid breakdown upon contact with body tissues, a reac

* The terms carbamyl peroxide, urea peroxide, and per hydro! urea have often l>eeii used interchangeably in the past by various authors.

tion that is greatly accelerated by the enzymes peroxidase and catalase, which are commonly found in the body. The search for improved materials led to the investigation of more stable and longer acting peroxides.3

Carbamyl peroxide was determined to have a much slower rate of reaction,. especially at room and oral temperatures (hydrogen peroxide in warm concentrated solutions lacks stability). The carbamyl peroxide was found to be active after twenty minutes of body tissue contact. The foaming that is observed at the initial application (or reapplication) of whitening solutions is an oxygenated foam resulting from the catalysis of the peroxide product. When the peroxide is held to intraoral surfaces by a glycerin solution, the effective reaction time is significantly prolonged.

Ambrose reported favorably on the use of carbamyl peroxide in the cleansing of teeth prepared for restorations.4 Arnim recorded the improvement in plaque control provided by carbamyl peroxide in anhydrous glycerol; in the absence of any other means of hygiene, four minutes of rinsing per day provided significant plaque reduction with no negative side effects reported.5

Manhold evaluated four commercially available oxygenating agents as applied to wounded rat tissue. The oxygenating agents all helped to promote faster healing than would be expected normally.6 Of all the agents tested, carbamyl peroxide offered not only the fastest, but the most complete healing.

In 1982, another rat study determined that the anticariogenic effectiveness of the oxygenating topical agents was related to their ability to release active oxygen rather than their ability to neutralize plaque acid.7 Carbamyl peroxide was found to be highly effective in reducing plaque accumulation and caries incidence.

Carbamyl peroxide has even been tested with neonates. It was used to treat oral candidiasis of the newborn and was found to be very effective and without adverse effects.55 A 10% preparation of carbamyl peroxide in anhydrous glycerin is equivalent in action to 3% aqueous hydrogen peroxide, yet far more stable and predictable.

In the following studies, one of the most important points to note is the total time of experimental oral contact with the carbamyl peroxide. This can help the dentist to establish whether the times that he recommends for the complete home whitening procedure fall within the acceptable established and researched parameters. Currently available techniques require from 40 to 300 hours of oral exposure over a period of several weeks.

Williams advocated the use of carbamyl peroxide against pharyngeal and throat infections.9 The total contact time over one week was about 10 hours, and to ensure that the material was adequately distributed, the patients swallowed it after gargling. It was observed that the minimal side effects were transitory, that the treatment was analgesic, and that tissue irritation was reduced.

The clinical effectiveness of carbamyl peroxide in reducing plaque and gingival inflammation was researched with institutionalized patients by Zinner et al.10 The total treatment time was 15 hours over four weeks. No side effects were reported.

In the course of selecting an oral hygiene supplement for the severely handicapped, car-bamyl peroxide was used as a rinse five times per day for three weeks.11 Even when the formula was used at twice the recommended dosage and frequency, no irritation or inflammation was produced in the subjects.

Fogel and Magill reported on the application of carbamyl peroxide in anhydrous glycerol for orthodontic caries prevention.12 Seventy full-banding patients participated in this study for periods ranging from two to three years. The material was applied four times daily, and patients were instructed not to rinse afterward, resulting in an effective tissue-contact time of up to two hours per day. The total exposure over the entire orthodontic treatment time was 1500-2300 hours per patient. The sequelae were positively anticariogenic, and there were no deleterious side effects observed.

In 1971 Shipman investigated the effects on the gingiva of an 11% carbamyl peroxide gel solution over a period of one month (11 hours of tissue contact time) and pronounced the material safe.13 Kashck evaluated the effect of brushing a carbamyl peroxide into the gingiva in order to deliver the material into the sulcus.14 The 45 hours of tissue-contact time over three months significantly reduced plaque scores when compared to brushing with a control toothpaste. In 1976, a recommendation was made that carbamyl peroxide should be considered as a routine oral hygiene adjunct.15 In another study, sixty orthodontic patients rinsed with carbamyl peroxide over a period of three nronths (90 hours of tissue exposure). Significant plaque reductions were observed and no adverse reactions were noted.16 Carbamyl peroxide played a significant role in reducing gingival inflammation and gingivitis in a study which involved a tissue contact time of 33 hours over twenty days.17 No side effects were observed in any of the subjects. Given the above studies, and others that have reached the same conclusions, it would appear that the safety of 10-15% carbamyl peroxide in anhydrous glycerin is well established, and that it does not pose any threat, local or systemic, to the healthy patient.18 24

Thus, although the home tooth whitening system is a new dental service, the safety and efficacy of the materials used in the technique are actually well documented. It is an impossibility for any new modality to be created with a history of safety, but the home bleach technique comes as close to that concept as possible.

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