How Much Can Toothpaste Change Odor Compounds the Next Morning?

Feeling refreshed after brushing and having fewer odor-causing compounds can be investigated separately. A 2011 study analyzed gases in the mouth after two toothpastes were used and compared how much of the sulfur compounds remained the next morning.

The test formula contained 0.1% o-cymen-5-ol, 0.6% zinc chloride, and sodium fluoride. Compared with a sodium-fluoride control toothpaste, the sum of hydrogen sulfide and methyl mercaptan was 27.0% lower the next morning after one week of use, in a comparison adjusted for baseline values.

A trial in which the same people used both toothpastes

The study took place at one center in the United Kingdom. Eighty-nine people were screened, and 78 were randomly assigned to two sequences of use. At randomization, there were 18 men and 60 women, with a mean age of 46.3 years. Seventy-five people were included in the efficacy analysis, and 10 did not complete the full study schedule. The number analyzed and the number who completed the study are not the same.

Participants were generally in good oral and overall health and were required to have hydrogen sulfide concentrations above 300 ppb in mouth air on at least three assessments. This allowed comparison in people in whom the odor compound was repeatedly detected.

Each person first used one toothpaste morning and evening for seven days, followed by a gap of 7–21 days and then seven days with the other toothpaste. Comparing the same people under two conditions in this way is called a crossover trial. Both toothpastes were white and supplied in coded white tubes, and the examiner was not told which product was which.

The 12-hour measurement was the next morning, followed by measurements after brushing again

On the first day of each period, three mouth-air samples were taken before use to establish a baseline. Participants then continued brushing morning and evening, and on the morning of day eight, mouth air was collected approximately 12 hours after the previous evening’s brushing.

At the site, they brushed for one minute with the assigned toothpaste, moved the remaining toothpaste-containing slurry around the mouth for another 10 seconds, and spat it out. Measurements were then taken immediately afterward and one, two, and three hours later. In other words, the study did not follow a single morning brushing continuously for 12 hours: it combined an overnight measurement with measurements after brushing again the next morning.

Participants avoided strongly scented foods and other specified items before testing, and gas was collected according to a defined sampling procedure. Gas chromatography measured hydrogen sulfide and methyl mercaptan separately. What the paper calls total VSC is the sum of these two compounds.

Lower concentrations were also found the next morning

With the test formula, hydrogen sulfide, methyl mercaptan, and their sum were significantly lower than with the control at every time point examined. Comparisons of the sum, accounting for baseline values, sequence of use, and other factors, were as follows.

• The next morning, at 12 hours: 27.0% lower than the control.
• Immediately after brushing that morning: 91.8% lower than the control.
• At one hour: 81.1% lower.
• At two hours: 64.8% lower.
• At three hours: 57.5% lower.

These are relative differences between formulations in concentrations analyzed after log transformation, with adjustment for change from baseline. They do not mean that perceived freshness or the intensity of bad breath perceived by other people changed by the same percentages.

For the individual compounds the next morning, hydrogen sulfide was 28.5% lower and methyl mercaptan 23.7% lower with the test formula than with the control. Meanwhile, the control formula also reduced the sum at one to three hours relative to its pre-use baseline. Thus, additional differences were found with the test formula against a background of changes also occurring with brushing.

Was odor merely covered by fragrance, or were the compounds reduced?

One reason the study used instrumental analysis was that a toothpaste’s flavor and fragrance could influence human assessments of breath odor. Measuring specific compounds allows their amounts in mouth air to be assessed separately from the impression created by the product’s scent.

For the combination of o-cymen-5-ol and zinc chloride, the authors cited previously reported antibacterial activity and the chemical neutralization of odor compounds by zinc as background mechanisms. The present trial showed a reduction in sulfur compounds with a toothpaste containing this combination.

However, it did not directly track bacterial counts or individual reactions, nor did it include conditions using each ingredient alone. These results therefore cannot separate how much each ingredient contributed or establish whether their combination produced a synergistic effect.

What remains outside the odor and safety assessments

Hydrogen sulfide and methyl mercaptan are important indicators in oral-malodor research, but breath also contains other compounds. This trial did not measure human sensory ratings, participants’ feelings of freshness, or changes in daily life. Its conclusions should first be read as findings about the concentrations of the two compounds measured.

During the trial, 31 adverse events were reported in 26 people; 12 were oral events, all mild. Oral events considered related to the products were one case of lip tingling with the test formula and two events, dry mouth and sore gums, with the control. There were no serious adverse events.

Each formula was used for one week, and participants were selected for hydrogen sulfide levels above a specified threshold. The study reports effects and observed adverse events under those conditions, and should be distinguished from a broad assessment of long-term use or oral malodor arising from different causes.

Summary

After one week of using the test toothpaste containing o-cymen-5-ol and zinc chloride, hydrogen sulfide and methyl mercaptan were lower than with the control toothpaste not only immediately after brushing but also the next morning. For the sum of the two compounds, the baseline-adjusted difference between formulations the next morning was 27.0%.

The noteworthy feature of this research is that it measured odor-compound amounts after a time interval, separately from lingering fragrance or a feeling of freshness. When considering what a toothpaste does to odor, it matters what was measured, when it was measured, and what comparator was used.

The study was funded by GlaxoSmithKline Consumer Healthcare, and four of the five authors were affiliated with the company at the time. The external author received no additional payment for preparing the manuscript, and the company-affiliated authors declared no potential conflicts of interest.

Reference

Payne D, Gordon JJ, Nisbet S, Karwal R, Bosma ML. A randomised clinical trial to assess control of oral malodour by a novel dentifrice containing 0.1%w/w o-cymen-5-ol, 0.6%w/w zinc chloride. International Dental Journal. 2011;61(Suppl 3):60–66. Original article (Open full text).