Can Mouthwash After Brushing Change Morning Breath?

Does adding mouthwash to toothbrushing change the way the mouth smells the next morning? In a 2015 comparative trial, the group using a mouthwash containing 0.075% cetylpyridinium chloride (CPC) had lower oral-malodor scores the following morning and four hours after cleaning than the group that brushed alone.

The study examined not only human smell ratings but also odor compounds and oral bacteria. Its aim was to assess together how adding a mouthwash changes perceived odor, sulfur compounds, and bacterial composition.

Seventy people with morning malodor were assigned to two care regimens

The trial, conducted at a university dental clinic in Brazil, included 70 participants: 30 men and 40 women, with a mean age of 24.3 years. After applying exclusion criteria concerning severe periodontal conditions, dry mouth, and other factors, participants first used the same toothpaste and toothbrush for 10 days. During this period they brushed for one minute morning and evening and refrained from tongue cleaning and other oral-care products.

Three trained examiners then smelled their morning breath and scored it from 0, no odor, to 5, extremely strong odor. People with a mean score of at least 3, indicating at least moderate oral malodor, were randomly allocated by computer to two groups of 35.

• Brushing group: brushing with fluoride toothpaste for two minutes morning and evening.
• Mouthwash group: the same brushing followed by rinsing for 30 seconds with 20 mL of mouthwash containing 0.075% CPC.

Participants followed these regimens for 21 days. Examiners were not told the group assignments, and all 70 participants completed the study. The concentrations and amounts given here are the conditions compared in the research.

Scores were lower with mouthwash both the next morning and four hours after cleaning

The final assessments took place twice: in the morning, 12 hours after the last cleaning, and four hours after performing the assigned regimen again on site. Conditions concerning eating, drinking, and strongly scented foods were standardized, and participants refrained from eating and drinking during the four-hour wait.

Initial oral-malodor scores were almost identical: 3.35 in the brushing group and 3.36 in the mouthwash group. After 21 days, both groups had lower scores than at baseline, but the mouthwash group’s scores were significantly lower.

• The next morning, 12 hours after cleaning: 1.37 in the brushing group versus 0.89 in the mouthwash group.
• Four hours after cleaning that day: 1.04 in the brushing group versus 0.53 in the mouthwash group.

The paper describes these as approximately 35% lower the following morning and 49% lower at four hours than in the control group. These are percentages comparing the groups’ mean scores, not evidence that an individual’s odor compounds were halved. Looking at the scores themselves, brushing alone improved the ratings, and the condition with added mouthwash produced still lower ratings.

Results differed between odor compounds

Instrumental measurements assessed hydrogen sulfide, methyl mercaptan, and dimethyl sulfide in gas sampled from the mouth. These are sulfur-containing compounds that contribute to odor in gaseous form.

The sum of the three compounds fell significantly from baseline in the mouthwash group and was lower than in the brushing group both the following morning and at four hours. Individually, hydrogen sulfide and methyl mercaptan also showed lower values in the mouthwash group.

For dimethyl sulfide, however, the between-group differences at follow-up were not significant. The original results text states that all three compounds decreased in both groups, but the table shows an increase in dimethyl sulfide in the brushing group. Here, the findings are read in accordance with the compound-specific table, rather than treating all odor compounds as having decreased in the same way.

A distinctive feature of this study is that human ratings and measurements of the major sulfur compounds pointed in the same direction. Rather than merely asking about a fresh feeling in the mouth, it captured differences both in odor perceived by other people and in the composition of mouth air.

Bacterial composition on the tongue and in plaque also changed

Another major aim was to examine microbial changes. At baseline and at the final four-hour assessment, the researchers collected saliva, tongue coating, and plaque from tooth surfaces and examined DNA corresponding to 40 bacterial species.

They focused on the group known as the red complex, consisting of Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola. These bacteria are associated with periodontal disease and were examined because of their involvement in sulfur-compound production.

In the mouthwash group, the proportion of this bacterial group declined from baseline. Direct comparisons also showed significantly lower proportions in the final tongue-coating and plaque samples in the mouthwash group. At the individual-species level, the proportions of the first two bacteria decreased in the mouthwash group’s saliva, tongue coating, and plaque.

What was measured was their proportion of the DNA signals for the 40 species examined. This does not represent the absolute number of all oral bacteria or a count limited to living bacteria. Nevertheless, the change in the composition of bacteria related to odor production, alongside the decline in oral-malodor scores, is an important finding.

What the trial actually compared matters

The authors concluded that adding a CPC mouthwash to brushing offers advantages in reducing oral malodor and the proportions of associated bacteria. During the study, examinations and participant interviews revealed no reported adverse effects on oral tissues.

However, the comparator was brushing alone, not an otherwise identical mouthwash without CPC. The design therefore did not isolate the effect of CPC from the act of rinsing or the other ingredients. The findings also cover 21 days in people whose morning malodor reached a specified level while they refrained from tongue cleaning. This trial alone cannot establish the effects and safety of long-term use or effectiveness for oral malodor with a wide range of causes.

The original paper also contains an inconsistency between the methods section and table notes in the description of the statistical methods used to assess changes over time. Detailed interpretations of those changes require caution. However, the main comparisons show lower values in the mouthwash group for human ratings, hydrogen sulfide and methyl mercaptan, and the associated bacterial group in tongue coating and plaque.

Summary

In this 70-person trial, adding a 0.075% CPC mouthwash to brushing for 21 days produced lower oral-malodor scores the following morning and four hours after cleaning than brushing alone. Lower values were also found in the mouthwash group for hydrogen sulfide, methyl mercaptan, and the proportions of the associated bacterial group in tongue coating and plaque.

When reading mouthwash research, considering other people’s assessments after a time interval, compound analyses, and microbial changes together, rather than only fragrance or the feeling immediately after use, makes it easier to understand what was demonstrated.

This study was funded by Colgate-Palmolive, and three coauthors were company employees at the time. The four university authors declared no financial relationship with the company, and another coauthor was described as an independent statistician.

Reference

Feres M, et al. The efficacy of two oral hygiene regimens in reducing oral malodour: a randomised clinical trial. International Dental Journal. 2015;65(6):292–302. Original article (Open full text).