7. What should be considered before a tooth whitening treatment?
The SCCP opinion states:
Bottenberg (2004) points out: “Tooth bleaching is not just a simple cosmetic operation. It is important to diagnose correctly the cause of the staining or discoloration, to establish a prognosis whether the stain can be removed or not, to give the patient a complete clinical examination in order to establish other oral health problems be they related or not to the discoloration, and to counsel the patient about the best way of treating or not treating this esthetical problem.” “Before bleaching is performed, defective restorations should be replaced. All tooth and restoration surfaces must be thoroughly cleaned and adequate oral hygiene instruction are to be given to the patient.
Hydrogen peroxide has well-known irritation, in higher concentration even corrosion, potential (esp. mucus membranes). Danger of irritation in the oral cavity and gastric tract if swallowed. Mucosal irritation is commonly observed as a side effect in clinical studies and consumer complaints.
Conditions such as pre-existing tissue injury or the concurrent use of alcohol and/or tobacco while using tooth whiteners may also exacerbate their toxic effects. Hydrogen peroxide, even at concentrations as low as 3%, may be especially harmful to oral tissues if they have been previously injured (Rees and Orth, 1986). Therefore, particular care should be taken in administering bleaching agents to patients with gingivitis, periodontal disease, or pre-existing gingival lesions, and to those using alcohol and tobacco (Tipton et al., 1995). This mixed exposure may be of concern since smokers are likely candidates for tooth bleaching.
Ulceration of gastric mucosa was observed in rats 1 hour after gavage with a dose corresponding to 5.4 mg/kg bw of hydrogen peroxide while no effects were found at 1.8 mg/kg bw of hydrogen peroxide. The ratio between the “no effect level” in rats and the dose after use of mouth-rinses containing 0.1% hydrogen peroxide and tooth whitening products containing 6% hydrogen peroxide are low. In relation to this it should be noted that in the case of gel strips, it has been reported that the user occasionally may swallow the strip. This will result in an exposure of about 12 mg hydrogen peroxide. In several of these cases, consumers reported minor gastrointestinal symptoms.
Clinical studies have mostly been designed to assess efficiency of external tooth-bleaching and the risk of adverse effects has not been the main focus in these studies. In the clinical studies published on tooth-bleaching that address adverse effects, the number of participants were small and many studies did not have control groups. This is considered inadequate, since for a case-reference study that should detect a doubling of the risk for an adverse effect occurring at a level of 1:1000 in the reference group, the study group must have at least 1000 people, and for detection of a 10% increase in the risk, more than 10.000 people must be enrolled in the study (Dahl and Pallesen, 2003). Although the first articles on night guard bleaching with hydrogen or carbamide peroxide were published nearly 20 years ago, and the these products have been in the market place for many years in some countries, there have so far been no systematic epidemiological studies to assess possible long term effects. It is also of concern that only one 28-day study has been reported with adolescents (12 – 18 years old). Therefore, a number of potential adverse effects of external tooth-bleaching cannot be assessed as this time.
Tobacco use and alcohol abuse are the main risk factors for cancer in the oral cavity (IARC, 1988, 2004, 2007). Since hydrogen peroxide can act as a promoter, it may increase the risk of oral cancer in persons that already have an elevated risk due to tobacco use, alcohol abuse, or genetic predisposition. The risk may further increase with repeated exposure to tooth whiteners. Based on a case report, it has been suggested that users of tooth whiteners should be further studied with regard to oral cancer (Burningham et al., 2004).
All bleaching materials demonstrate diffusion of hydrogen peroxide through dentin. Few investigators have addressed the possible pathophysiological effects on oral and pulpal tissues from long-term treatment. The dental pulp is vulnerable through exposed dentin in patients with gingival retraction, attrition, cervical abrasion, and leaking restorations, and the gingiva may be exposed directly to hydrogen peroxide gels during treatment. Significant amounts of hydrogen peroxide diffuse through dentin after application of carbamide peroxide and hydrogen peroxide-based bleaching agents (Hanks et al., 1993).
The bleaching procedure produces a transient reduction on the bond strengths of enamel and dentin immediately following bleaching. Because of the transient reduction in bond strength, dentists should delay restoration placement for periods of one to two weeks after bleaching to ensure sufficient bond strength and retention on teeth.
Data from laboratory studies documented increased mercury release from dental amalgams exposed to carbamide peroxide solutions for periods ranging from 8 hrs to 14-28 days. The amount mercury released varied with type of amalgam and type of bleaching agent and ranged from 4 to 30 times higher in saline controls. However, the clinical significance of the loss of mercury from amalgam is unclear. It is concluded that bleaching of teeth containing amalgam restoration should be approached with caution (Swift and Perdigao, 1998).
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