There are more than 500 microorganisms in the oral cavity [39, 40]. Streptococcus mutans is one of the causative bacteria of dental caries, while Porphyromonas gingivalis is considered to be the most toxic for periodontal disease. These bacteria not only cause dental diseases, but S. mutans causes infectious endocarditis, valvular heart disease and cerebral hemorrhage, and P. gingivalis causes atherosclerosis, diabetes, rheumatism, etc. Further, representative diseases affected by oral bacteria include aspiration pneumonia. The main causative bacteria of aspiration pneumonia are resident bacteria in the oral cavity, and oral streptococci and anaerobic bacteria such as Peptstreptococcus, Prevotella, and Fusobacterium are known as bacteria classified at high frequency. These bacteria are also present on tongue coating, and thus, some authors stated that cleaning tongue coating might reduce the risk of aspiration pneumonia [3, 4].
Various methods for tongue cleaning have been reported, including mechanical cleaning using a tongue scraper or toothbrush, and the application of some mouthwashes, diets, chewing gums, and tablets. The results of the previous studies are summarized as follows: 1) mechanical tongue cleaning reduced tongue coating, 2) some antibacterial mouthwashes reduced tongue coating, and 3) some diet, chewing gum and tablets also reduced tongue coating. However, many of the reported diets, gums and tablets are not commercially available in Japan. The most effective method for removing tongue coating is considered to be the combination of mechanical cleaning and disinfectant, therefore, we decided to conduct this preliminary study.
Disinfectants approved for use on the oral mucosa in Japan include 10% povidone iodine, 0.2% benzethonium chloride, and 3% hydrogen peroxide solution. However, 0.12% chlorhexidine, which is commonly used overseas to prevent VAP in intubated patients is contraindicated for mucosal use, because anaphylaxis was reported in Japan. Therefore, in this study, we selected povidone iodine, benzethonium chloride, and hydrogen peroxide solution, and water as a control, and compared their effect in reducing tongue coating bacteria when brushing the tongue with a toothbrush. Our results showed that the bacterial count was significantly decreased when brushing with povidone iodine and hydrogen peroxide solution, while 0.2% benzethonium chloride and tap water did not decrease the bacterial count. It is necessary to further study the concentration and action time of benzethonium chloride.
Povidone iodine has strong ionicity and adheres well to mucous membranes, therefore, it was considered to have a strong disinfecting effect on oral bacteria. Although there are some disadvantages such as iodine allergy, the possibility of coloring the teeth with long-term use, and the unsatisfactory taste, the use of povidone iodine for removing tongue coating was still recommended. Next, the hydrogen peroxide solution through catalase decomposes tissues, bacteria, blood, pus, etc., generates oxygen, and exhibits a bactericidal action. It was considered that the bacterial count on the tongue was decreased by the foaming reaction at the time of the decomposition, because the deposit on the tongue was physically removed and mechanically washed, and in addition, a bactericidal action was performed. The taste was also acceptable as compared to iodine, and it was considered as a recommended disinfectant for removing tongue coating.
This study had some limitations. First, this is a preliminary study using a small sample size, and it is therefore difficult to generalize the results. Next, because these methods were intended for patients with dental disease but without a systemic disease, it is unknown whether it can be applied for the removal of pathological tongue coating. In the future, it will be necessary to conduct an intervention study using a larger sample size, to evaluate the effects of removing tongue coating in patients with diseases such as aspiration pneumonia.