Aquafresh Science Academy

The large surface area of the tongue dorsum provides a unique environment that promotes accumulation of microorganisms and oral debris. It has recently been shown that there is a direct relationship between the distribution of bacteria on the tongue, bacterial load and oral malodor. The effect of tongue cleaning on this complex interaction has also been revealed in research and is discussed below.

• Topographic distribution of bacteria on the tongue
• Relationship between bacterial load and oral malodor
• Effect of tongue cleaning on bacterial load

Topographic distribution of bacteria on the tongue

In their paper in The Archives of Oral Biology (2008), Allaker et al provided the first detailed mapping of the tongue surface in relation to the bacteria associated with oral malodor. The study analysed the type and load of bacteria present in cultures collected from six areas of the human tongue.

Results showed that:

• on the dorsum of the tongue, there was a trend towards increasing bacterial load when moving from the anterior to the posterior surface of the tongue
• the most heavily colonised tongue site was the dorsal posterior to the circumvallate papillae
• the relative proportions of bacterial group remained similar at each site, with Streptococcus salivarius being consistently lowest.

To hear Dr Allaker discuss the findings from this study go to the IADR/CED Symposium section.

Bacterial counts by tongue area (CFU/sample x10⁵)

Relationship between bacterial load and oral malodor

In several studies, it has been identified that the dorsal posterior of the tongue makes the primary contribution to oral malodor (summarised in Bordas et al 2008). However, in the past little attention has been paid to the area posterior to the circumvallate papillae (DPCP). In order to investigate this, an organoleptic assessment using an intensity scale where 0=no malodor and 5=very strong malodor was performed. Subjects were subdivided into those with slight/moderate malodor (intensity score 1–3) or strong malodor (intensity score 4–5). Their study revealed that:

• subjects with strong malodor had higher levels of total anaerobes, Gram-negative anaerobes and volatile sulfur compound (VSC) producing bacteria recovered from the DPCP than those with slight/moderate malodor
• total aerobe and Streptococcus salivarius numbers were higher at the DPCP in the slight/moderate group than in the strong malodor group.

Visit the IADR/CED Symposium section to see Dr Allaker discuss the findings of this study.

Effect of tongue cleaning on bacterial load

At the IADR/CED Symposium on oral malodor, Dr Allaker highlighted that most odor-causing bacteria are found beyond the reach of normal oral hygiene procedures. To further investigate this, Bordas et al’s Archives of Oral Biology paper (2008) studied whether tongue cleaning provided an improved method of reducing tongue bacterial load compared with tooth brushing.

After collecting and analysing samples of tongue coating before and after tooth cleaning, they found that:

• tooth brushing alone had no significant impact on tongue bacterial populations
• tooth brushing and tongue scraping consistently, but modestly, reduced bacterial populations
• tooth brushing and thorough tongue cleaning with a high speed aspiration device resulted in highly significant reductions in bacteria.

Further reading

Allaker RP, Waite RD, Hickling J et al. Topographic distribution of bacteria associated with oral malodor on the tongue. Arch Oral Biol 2008; 53 (suppl 1): S8–S12.

Bordas A, McNab R, Staples AM et al. Impact of different tongue cleaning methods on the bacterial load of the tongue dorsum. Arch Oral Biol 2008; 53 (suppl 1): S13–S18.