May 3, 2012 — Coffee stains return on bleached teeth, whereas cigarette stains may not. In addition, coffee stains cannot be removed by brushing alone, researchers report in an article published in the May issue of the Journal of the American Dental Association.
Soaking cows' teeth in coffee and exposing them to cigarette smoke darkened them about the same amount, but tooth brushing only lightened the smoke-stained teeth, not the coffee-stained teeth, note Juliana Zavala Bazzi, DDS, MDS, from Pontifical Catholic University of Paraná, Curitiba, Paraná, Brazil, and colleagues.
"We didn't expect that cigarette staining would be so easily removed either by tooth bleaching or toothbrushing," corresponding author Evelise M. Souza, DDS, MDS, PhD, a professor of restorative dentistry at the Pontifical Catholic University, told Medscape Medical News in an email.
Although bleaching is well established as a method of whitening teeth, there is not much research to show the susceptibility of bleached teeth to being stained once again, they note.
To test the effects of brushing and bleaching, the researchers collected 40 maxillary incisors from cows and cut them into 7 × 7-mm blocks. They embedded the blocks in epoxy resin, leaving 2 mm of tooth structure exposed.
Then the researchers flattened and polished the surfaces of the specimens with sandpaper and sealed the dentin adjacent to the exposed enamel with a resin-based composite to prevent the diffusion of staining agents into the dentin.
The authors measured the baseline colors of the samples with an Easyshade colorimeter (Vita Zahnfabrik), recording both the lightness and the magenta/green and blue/yellow spectra.
They split the teeth into 2 groups of 20 specimens each and soaked 1 group in a solution made with instant coffee for 72 hours, brewing fresh coffee daily, and put the other 20 specimens at the bottom of a glass jar with 2 tubes thrust through holes in the lid. One tube connected to a vacuum machine and the other to a cigarette holder.
The researchers lit cigarettes and sucked smoke into the jar for 10-minute stretches 4 times for all 20 teeth in the cigarette group. They then measured the change in color of the samples in both groups to see how much the samples had darkened.
Next, the researchers divided each group of specimens into 2 subgroups and brushed 1 subgroup from both the coffee and cigarette groups with toothpaste in a mechanical tooth-brushing machine.
The other subgroups were soaked in bleaching trays with White Class 6% bleach (FGM Dental Products), which, according to the manufacturer, has a neutral pH and contains 6% hydrogen peroxide, neutralized carbopol, potassium nitrate, sodium fluoride, aloe vera, calcium gluconate, stabilizers, and deionized water, the researchers write.
They repeated the bleaching for 1 hour/day for 21 days. Then they measured the color changes once again.
Dr. Bazzi and colleagues found that the coffee-stained teeth were darkened by about 19 units, whereas the cigarette smoke–stained teeth were darkened about 25 units. These changes were statistically significant.
A person with average color-matching ability can see a color shift of about 2.5 to 3.5 units, according to previous research.
Bleaching restored the cigarette-stained teeth to 7.81 units darker than their baseline color, and brushing restored them to 3.20 units darker than baseline. These changes were statistically significant (P < .05).
In the coffee-stained teeth, bleaching restored the color of the teeth to 4.31 units from baseline, which was statistically significant (P < .05), whereas brushing only got them to 17.72 units from baseline, which was not statistically significant (P > .05).
After the whitening procedures, the researchers subjected the teeth to another round of staining, using the same methods as before.
Coffee returned the teeth that had been bleached to 14.51 units from baseline, which was not a statistically significant change (P > .05); the teeth that had been brushed went up to 25.40 units from baseline (P < .05).
However, the smoked teeth that had been bleached stayed at 5.51 units from baseline, which was still significantly lighter (P < .05) than before they were bleached, and the smoked brushed teeth returned to 8.24 units darker than baseline, which was also significantly better than before being brushed (P < .05).
The researchers speculate that smoke stains are easier to remove by brushing because they do not penetrate as deeply into the enamel as coffee. They also note that the artificial saliva used in the bleaching protocol might have helped the enamel resist a second application of smoke by remineralizing it.
They did not propose an explanation for why the smoked teeth that were brushed did not darken again after being smoked a second time. However, the authors did note that they used a fluoridated dentifrice with the brushing, raising the possibility of a remineralization effect for brushing as well.
Asked to comment, American Dental Association consumer adviser Matthew J. Messina, DDS, told Medscape Medical News that the findings were no surprise.
He recommends that patients who want their teeth to stay white stop using whatever product stained their teeth. "If the habits that cause them to yellow in the first place are not changed, it will cause them to yellow again," said Dr. Messina, who has a private practice in Cleveland, Ohio.
"I was surprised that coffee would have a greater potential for restaining," he said, but noted that he was not surprised that bleaching was more effective than brushing on coffee stains. "The bleaching removes stain particles that have embedded themselves in the enamel," he said.
Dr. Messina and the authors have disclosed no relevant financial relationships.
JADA. 2012;143:e1-e7. Abstract
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Cite this: Coffee Stains Teeth More Indelibly Than Tobacco - Medscape - May 03, 2012.