When We Stop Brushing: How Oral Bacteria Rapidly Shift and Trigger Gum Inflammation

A close look at how dental plaque, tongue bacteria, and microbial balance shape early gingivitis

Gingivitis gum inflammation marked by redness and bleeding is often seen as a simple consequence of poor oral hygiene. But what really happens inside the mouth when brushing stops, even for a short time? A recent study published in Frontiers in Cellular and Infection Microbiology offers a detailed and surprising answer, revealing that gingivitis is not driven by plaque alone, but by complex and dynamic changes across multiple bacterial communities in the oral cavity

The Mouth as a Living Ecosystem

The human mouth hosts one of the most diverse microbial ecosystems in the body. Bacteria form structured biofilms on teeth, gums, and the tongue, coexisting with the host in a delicate balance. When this balance is disturbed a condition known as microbial dysbiosis inflammation and disease may follow.

Gingivitis represents an early and reversible stage of periodontal disease. Understanding how microbial communities shift during its onset could help improve prevention and treatment strategies, not only for gum disease but also for broader health conditions linked to oral inflammation.

What the Researchers Did

To explore these early changes, researchers conducted an experimental gingivitis study involving 41 healthy adults. After a two-week period of normal oral hygiene, participants were asked to stop all oral hygiene practices for two weeks, deliberately allowing gingivitis to develop. This was followed by a one-week recovery phase in which brushing was resumed.

Throughout the study, the team monitored plaque levels and gum bleeding while collecting samples from six different oral niches: supragingival plaque (above the gumline), subgingival plaque, interproximal plaque, gingiva, tongue surface, and saliva. Advanced genetic techniques (16S rRNA gene sequencing) were used to track changes in bacterial composition and diversity.

Rapid Microbial Changes Especially in Dental Plaque

The results showed that stopping oral hygiene led to fast and pronounced microbial shifts, particularly in supragingival dental plaque. As plaque accumulated, bacteria such as Leptotrichia and Prevotella increased, while health-associated Streptococcus species declined.

Interestingly, bacterial diversity increased not only in dental plaque but also on the tongue and in saliva. This suggests that gingivitis is not a localized phenomenon but involves coordinated changes across the oral ecosystem.

Plaque and Bleeding: Related but Not the Same

One of the most important findings of the study is that plaque buildup and gum bleeding are not driven by the same microbial factors.

• Dental plaque levels were mainly linked to the amount of bacteria (bacterial load).

• Gum bleeding, on the other hand, was more closely associated with changes in bacterial composition, especially in supragingival plaque and on the tongue.

This distinction helps explain why some people develop significant inflammation even with similar amounts of plaque and highlights why brushing alone may not fully address gingival health.

The Unexpected Role of the Tongue

The tongue emerged as a key player in gingival inflammation. Changes in tongue biofilm composition were strongly associated with gum bleeding, suggesting that the tongue may act as a reservoir influencing bacteria elsewhere in the mouth.

This finding reinforces the idea that oral hygiene should extend beyond teeth alone and that the tongue deserves greater attention in both daily care and clinical practice.

A Dynamic and Nonlinear Microbial System

Rather than changing in a smooth, gradual way, the oral microbiota showed nonlinear and sometimes abrupt shifts during gingivitis development. Some microbial changes persisted even after brushing was resumed, despite visible plaque levels returning to normal.

These patterns suggest that the oral ecosystem may approach ecological tipping points, where small disturbances can lead to disproportionate biological responses an idea increasingly discussed in microbiome research.

Why This Study Matters

This research provides a more nuanced view of gingivitis, showing that:

• Plaque and gum inflammation are biologically distinct processes.

• Multiple oral niches, especially the tongue, interact to shape clinical outcomes.

• Early microbial changes may persist beyond visible clinical recovery.

Together, these insights could inform more targeted prevention strategies, improved diagnostics, and a broader understanding of how oral health connects to systemic inflammation.

Reference

Keijser, B. J. F., van den Broek, T. J., van der Wurff, M., Dulos, R., Jagers, F., Kool, J., et al. (2025). Oral bacterial community dynamics during induction of gingival inflammation. Frontiers in Cellular and Infection Microbiology, 15, 1597690.

DOI: 10.3389/fcimb.2025.1597690