Author’s response
In the following, I will address comments made by Drs. Swift, Heymann, Kugel and Kanca that relate to our article. I will reference these dentists as "letter writers" in my response. Following are comments regarding Dr. Swift and colleagues’ letter.
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Whitening with light.
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The letter writers were surprised that light by itself whitened teeth. One possible explanation lies in the basic nature of colored pigments. Molecules are colored because they absorb certain segments, leaving the unabsorbed light to be reflected. Colored molecules possess conjugated double-bonds that absorb visible light. Irradiation with high-intensity light could rupture some of the double bonds, rendering the molecule less absorbent and therefore less colored. All museum curators know that light bleaches paintings.
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Gingival health and tooth whitening.
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The letter writers were also surprised that the tooth-whitening treatments resulted in decreased signs of gingival inflammation. Although we do not know the reason, we do know that several pathogenic bacteria are "black-pigmented" by virtue of their having porphyrins (for example, Porphyromonas gingivalis). We also know that if we shine an intense light on these bacteria they die. It is also possible that individuals were taking better care of their teeth. Studies with carbamide peroxide usage and improved gingival health were cited to indicate that others using tooth-whitening products have observed gingival effects.
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Comparison with published results.
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The Papathanasiou study cited to suggest that light has little effect is not comparable to our study because the light source was a curing light. In our own studies, we have found that the curing light is not nearly as effective as the fixed halogen light.1
Referring to a report from the April 2000 CRA Newsletter, the letter writers suggested that whitening at the level we reported is not within "reasonable expectation." First, all lights are not equal. The particular light used in this study as manufactured by BriteSmile produces an intense irradiance of 130–160 mw/cm2 with negligible ultraviolet output over the entire one-hour period. The newsletter states that the CRA group has not evaluated the BriteSmile system. Reasonable in the mind of the letter writers or not, the level of whitening we measured was reported.
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Experimental design.
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The letter writers indicate that the number of appointments needed for a desired degree of tooth whitening for a given subject is often variable. Although this is true, in our study, the number of applications was a controlled variable. The letter writers also state that measurements at one week and one month are important. I see no problem in the time scale we selected (three months and six months). Our data clearly show that the shade increased (became darker), the L* parameter decreased (became less light) and the b* parameter increased (became more yellow) between the immediate posttreatment period and three months. I would expect the same would be true, but to a lesser extent, at one week and one month.
The letter writers suggest that a consensus approach in which one or more examiners are required to come to some level of agreement is somehow superior. This is one approach to measurement; it is not clear that it is superior. It does increase variability. It does not answer many critical questions: If the examiners differ, how are differences resolved? Are responses in some way "averaged" or "arbitrated"? If arbitrated, on what basis is the final arbitration made, or how is an average taken? Isn’t arbitration a form of bias with the loudest and most authoritative advocate being the winner? Essentially we are asking that one number be dropped. What is the statistical validation for this procedure? We have chosen the alternative of a single calibrated measurer. There are proponents for both approaches. It is not clear which is superior.
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Calibration.
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The letter writers were critical of the calibration methods used in the study. There are two aspects to calibration: precision and accuracy. Precision is virtually impossible to calibrate. This assumes a "gold standard" clinician, but no one tells us where to find one of these. We can and did measure reproducibility. This was evaluated using Vita shade tabs. The test is to obscure the tab identities, mix them up and have the evaluator attempt to arrange them in the correct order. This exercise, repeated many times, indicates that our color evaluator was reproducible 98 percent of the time.
The letter writers were mistakenly concerned that perceived calibration error would bias a study. Actually, in a blind experiment, evaluator bias in color would have a principal effect of decreasing sensitivity to detect an effect. Bias toward a particular treatment is controlled by the blinding. The statistical analysis in this study was conducted on a subject basis. The letter writers have deduced correctly that Figure 2 is an illustration of the distribution of shade of individual teeth.
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Colorimeter.
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The colorimeter was calibrated according to the manufacturer’s instructions each day. The procedure is to measure L*, a* and b* from a provided standard white plate. Analysis of these data indicates that the day-to-day instrument responses varied no more than 1 percent over the duration of the experiment.
The letter writers note that the shade guide measurements were greater than the colorimeter measurements. It has been our consistent observation that the visual discrimination by shade guide is a more statistically powerful change variable than the colorimeter. The colorimeter provides more objectivity but less sensitivity.
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Dehydration.
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The letter writers state that "prevention of dehydration with any in-office bleaching procedure is virtually impossible... ." How do the letter writers know it always occurs, and how do they measure it? The most direct method would be to take a standard volume of tooth enamel, measure the water content, whiten the tooth and take another sample and measure the water content. This is clearly a laboratory procedure, not a clinical procedure. We did report that the average L* parameter in the light-treated control at baseline was 50.54, changed to 52.95 immediately after whitening and returned to 50.66 three months later. This could easily be due to dehydration. Not having measured the water content of enamel, we were hesitant to proclaim it so.
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Images.
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The letter writers felt that the images did not illustrate the changes reported in the manuscript. Even in the published images it seems clear that there are differences in the before-and-after images. The controversy over how much difference illustrates the problems I have discussed concerning calibration and multiple examiners.
I find it grievous that the letter writers feel they must refer to our work as "devoid of scientific validation," "superficial" and "biased." That aside, it is neither what we say nor what the letter writers say that counts—it is the data. The data speak for themselves. In this case, the experiment has been conducted with the scientific rigor required of an FDA submission. It has been audited by an external auditor, reviewed by peers and published in a reputable peer-reviewed journal. If the letter writers wish to refute the findings, there is only one way: let us see your data.
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REFERENCES
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- Tavares M, Goodson JM, Stultz J, Newman MB. A comparison of four systems of tooth whitening (abstract 2440). J Dent Res 2002;81(special issue A [San Diego Abstracts]):A-308.
J. Max Goodson, D.D.S., Ph.D., Director
Clinical Research The Forsyth Institute Boston
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Whitening with light.
Gingival health and tooth...
