by David A. Hall
originally published in Quintessence International,
Volume 22, Number 9 (September 1991), pp. 679-686

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(We have not reproduced the entire article here but have published an abridgement. Additionally, the original article was published with photographs of all the bleaching cases, which are not included here.)

Introduction:

The bleaching of vital teeth is a procedure that has been gaining in patient popularity as well as professional acceptance over the past several years. The results have been pleasing to the patients, and the techniques employed have proven to be conservative means of treating tooth discolorations.

The oldest technique, introduced 20 years ago, involves the application of concentrated hydrogen peroxide (eg, Superoxol, Union Broach Co) to the teeth with cotton pledgets and then heat treatment with a warming device. The heat accelerates the release of oxygen by the peroxide, and it undoubtedly accelerates the bleaching action of the oxygen on the tooth structure.

The newest technique involves the use of a solution of carbamide peroxide in a gel. A splint is made to fit tightly over the teeth of one arch. The gel is placed in the splint, and the splint is worn for a number of hours each day for several weeks, depending on how much lightening is desired. This system apparently relies on an extended period of contact between the bleaching agent and the teeth to accomplish the bleaching.

A third technique involves the use of a "bleaching light." Concentrated hydrogen peroxide is applied to teeth that have been carefully isolated with a tight rubber dam and etched with 37% phosphoric acid. While the teeth are kept wet under a thin layer of gauze, the bleaching light is placed 13 to 15 inches from the teeth. The light is set initially at a medium intensity and later adjusted according to the patient's reported sensitivity level.

Some clinicians have questioned the accepted vital bleaching techniques and have pointed out the lack of controlled scientific studies to establish the prudence of certain steps, the effectiveness of the bleaching. or its long-term effects. This study attempts to fill that void by examining the most controversial step in the bleaching light procedure, etching the teeth prior to the application of the bleaching solution. ....

Method and materials:

Ten patients were selected for this study.... An arch of each patient's mouth was then selected for bleaching. This arch was divided at the midline; one quadrant would be etched prior to bleaching and the other would not be etched. ... The patients were randomly assigned into one of two groups—in one group teeth on the left side were etched, and in the other group teeth on the right side were etched. A small piece of rubber dam material was placed between the central incisors to help contain the etchant. To conceal from the patient which side of the mouth was the experimental side and which was the control, the control teeth were treated with plain tap water and this was rinsed off the teeth in a similar manner to the etchant.

The bleaching procedure was followed for four to five appointments, spaced approximately 3 weeks apart, for each patient.

Approximately 3 weeks after the final bleaching appointment, each subject's teeth were evaluated by the operator. For this evaluation, no review was made beforehand to learn which side had been etched; thus the evaluation was done blindly. In addition, an independent dentist, who had no other role in the study, was employed to give a second, completely blind evaluation approximately 3 weeks after the first. Each quadrant of the patient's dentition was graded for lightness against the contralateral quadrant and the opposing quadrant.

Differences were graded qualitatively according to a rough numerical scale: 0 = no difference; 0.5 = barely perceptible difference; 1 = perceptible difference; 2 = small difference; 3 = distinct difference. The quantification of the differences was not regarded as critical to the study—the objective of the study was to determine if there was any difference at all, and if so, which side was lighter—the experimental side or the control.

Results

Results were averaged by assigning a positive value to the difference in lightness if the etched quadrant was lighter and a negative value to the difference if the control quadrant was lighter. The sum of these values was then divided by the number of patients.

In comparing the etched quadrant to the control quadrant, the operator found the control quadrant to be lighter, on the average, by a score of 0.2. Comparison of the bleached arch (using the lighter quadrant, if there were a difference between the etched and control quadrants) to the unbleached arch revealed that the bleached arch was lighter by an average score of 2.6.

The independent evaluator found no net difference between the etched quadrant and the control quadrant. According to the independent evaluator, the bleached arch was lighter than the unbleached arch by an average score of 2.8.

Discussion

The hypothesis of the author, in beginning this study, was that etching the teeth as part of the bleaching treatment would enhance the lightening effect of the bleaching. This study, however, failed to corroborate that hypothesis. Those teeth that were etched sometimes lightened slightly more and sometimes lightened slightly less than the teeth that were not etched.

Even when the patients were separated into a group that avoided staining substances during the bleaching and a group that ignored this caution, there was no clear pattern. Not one patient was found to have a distinct or even a small difference between their etched and control teeth. One patient, patient 6, was evaluated by the independent evaluator as having the teeth in the etched quadrant lighter by a perceptible difference than the teeth in the control quadrant. According to the evaluation by the operator, the difference in this patient and in all the other patients were smaller or the control teeth were lighter.

Admittedly, the judgments of color value used in this study are poorly quantified on a rather crude scale. This scale was adopted on the premise that clinically significant differences of value are clear, easily perceived differences. To the bleaching patient, the bleaching effect must be at least perceptible, which is a number 1 on this scale, preferably distinct, a number 3 on the scale, or even dramatic, which is beyond the range of this small scale. Therefore, a barely perceptible difference, with a value of 0.5, would not be esthetically significant.

If there is indeed a benefit for some patients in an increased lightening effect that comes from etching the teeth prior to the application of Superoxol, conceivably the same benefit could be attained by not etching and by increasing the number of bleaching sessions.

The potentially adverse effects of etching the teeth must also be considered. If the teeth are etched, they have to be polished, and polishing removes some enamel. The amount removed is not known. Clearly, it would be desirable to retain as much of this glossy, fluoride-rich surface layer of enamel as possible. Additionally, etching has the potential to increase the sensitivity of the patient to the procedure. Finally, in many states, etching is not a delegatable function. The time required for the dentist to interrupt a procedure being performed on another patient to apply the etchant is cost that needs to be considered in the total fee for the procedure, in addition to the cost of the time for the polishing.

In this study, where differences between the etched quadrant and the control quadrant were perceived, the patient was offered the chance to have additional bleaching visits and the treatments reversed: to etch the control quadrant to not etch the quadrant that had been etched during the study. However, none of the patients elected to have this reversed procedure performed. None felt there was enough difference between the quadrants to warrant any treatment.

Conclusion

Although the sample size of the study was too small to draw any quantifiable conclusions, it is the opinion of the author that, if potentially detrimental effects of etching and polishing the teeth are weighed against the absence of a clear pattern of greatly enhanced lightening, the weight of the argument is against the use of etchant.

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