The Bleaching “C Factor”
Shade assessment is critical in predicting outcomes, planning treatment
Harald O. Heymann DDS, MEd
Since the introduction of “nightguard vital bleaching” to the literature in 1989, tooth whitening has assumed an increasingly important role in the contemporary private practice. Tooth whitening, both in-office or at-home, is likely the most conservative and cost-effective procedure for improving patient appearance. But regardless of the tooth whitening approach employed, shade assessment is critical for predicting treatment outcomes as well as evaluating the need for future tooth bleaching procedures.
All patients who are evaluated by their dentists for tooth whitening procedures should have their teeth shades assessed prior to and after whitening. Although the results of tooth whitening vary widely among patients, and no predictions of outcomes are absolute, the results of shade assessments can provide valuable information regarding the likely causes of tooth discoloration and the potential for success. Furthermore, once optimal tooth whitening has been achieved, identifying the postoperative shade of the treated teeth is imperative for use in future bleaching procedures.
Because the teeth tend to regress or darken slightly from their immediate posttreatment shade, final shade assessment should not be undertaken until approximately 2 weeks after cessation of treatment. This time interval will facilitate more accurate shade selection and matching if subsequent esthetic restorative procedures are needed. Moreover, studies demonstrate that resin bond strengths to bleached enamel drop precipitously immediately after tooth whitening procedures. For that reason, resin bonding procedures should be delayed for a period of 1 to 2 weeks post-bleaching to ensure that optimal results will be attained.
Shade assessment is also critical in determining if and when re-treatment with tooth whitening is necessary. This observation is particularly true for patients whose tooth discolorations are from exposure to chromogenic drinks or foods such as coffee, tea, red wine, or dark fruits.
A very critical factor in shade assessment is the determination of the nature of the stain. For example, when using a Classic Vita Shade Guide (Vita Zahnfabrik, Bad Zäckingen, Germany), if the patient’s teeth fall within the “A” or “B” shade ranges where various degrees of yellow chroma predominantly are found, it is highly likely that the origin of the discoloration is from chromogenic drinks or foods. Clinically, this determination means that the patient’s teeth likely can be whitened successfully in a relatively short period of time, depending on the whitening approach that is selected.
An assessment of a patient’s teeth that indicates a shade in the “C” range is a bit of a “red flag” that warrants additional questioning. Many patients have a medical history that involves the past use of minocycline (a tetracycline analog) for the treatment of dermatologic conditions, such as acne. Systemic minocycline use has been shown to exhibit the potential to cause hyperpigmentation and generalized discoloration of permanent teeth that is manifested as a mild, gray discoloration. The severity of the stain is generally related to how long the drug was administered. Staining is thought to be caused by oxidation of the drug once it is absorbed into collagenous tissues such as bone, dentin, and pulp.
Although this discoloration is very difficult to resolve with tooth whitening procedures, clinical studies do reveal that long-term tooth whitening under the strict supervision of a dentist can result in the reduction or elimination of tetracycline staining. However, short-term tooth bleaching procedures that are effective for the removal of acquired stains from chromogenic foods are NOT going to get the job done in these situations. The removal or reduction of minocycline staining generally requires months of treatment with nightguard vital bleaching. Because protracted treatment regimens are required to treat stains from minocycline, lower concentrations of whitening agents, such as 10% carbamide peroxide, with suitable desensitizing agents in their composition (eg, potassium nitrate and neutral sodium fluoride) are recommended for treatment. It is important to note that long-term bleaching treatments of this type require strict dentist supervision to monitor tissue health and/or the incidence of tooth sensitivity.
About the Author
Harald O. Heymann, DDS, MEd, is a professor at the School of Dentistry at the University of North Carolina in Chapel Hill, North Carolina.
An assessment of a patient’s teeth that indicates a shade in the “C” range is a bit of a “red flag” that warrants additional questioning.
