Dental caries (tooth decay) is one of the most prevalent chronic diseases among people around the world.
About 92% of the world's adults have dental caries in their permanent teeth, and in Japan,
more than 99% of people between the ages of 35 and 55 have dental caries.
The number of dental caries patients tend to increase with the increase in sugar intake,
and it is expected that more people will be affected in the future.
Dental caries often cause toothaches and sometimes tooth loss, which can seriously damage people's quality of life and health. Dental caries are generally caused by the infection of certain gram-positive indigenous anaerobic bacteria, such as Streptococcus mutans, which, when they reach the surface of healthy teeth, settle on the tooth surface and form a biofilm composed mainly of glucans. When S. mutans reaches the surface of a healthy tooth, it settles on the tooth surface and forms a biofilm consisting mainly of glucans. Once settled, S. mutans breaks down free sugars to produce acid, which lowers the pH and causes demineralization of the tooth.
Needless to say, no one wants to have dental caries. However, the world is filled with many temptations of sweets. Even though we brush our teeth every day, many patients are suffering from dental caries. Among them, dental health is a matter of life, especially for elderlies. As the aging society grows, dentistry needs to be more and more advanced.
The traditional approach to the management to prevent dental caries is brushing teeth. In case it is not enough, removing dental plaque in the dental clinic. However, the dental plaque cannot be removed completely because the plaque near the periodontal pocket is likely to leave unbrushed. Temporary preliminary approaches are rinsing Chlorhexidine, treating fluoride, and so on. But these substances like Chlorhexidine have a transitory effect, while fluoride has a risk of dental fluorosis.
Nowadays, novel approaches have been developed to maintain oral biofilm homeostasis. One of them is “Probiotics.” Probiotics is defined as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host” by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO).
So far, some strains have proved to inhibit the proliferation of cariogenic bacteria. S. salivarius, L. rhamnosus GG, L. reuteri, and Bifidobacterium DN-173 010 have all been shown to have the potential to alter colonization of cariogenic bacteria, and contribute to the prevention of dental caries. Some strains reported producing bacteriocins and hydrogen peroxide.
On the other hand, based on the Cartagena Protocol and the Rio Declaration on Environment and Development, a few researches for recombinant probiotics targeted enteric pathogens. And there is no example of the approach of probiotics using transgenic microorganisms to prevent dental caries. Of course, it needs strict risk management to use transgenic species in an uncontrolled environment, but if it is conquered, it has great potential to develop a new approach to dairy tooth management.
By the way, natural products are paid attention as antimicrobial agents that use mouth washing instead of chemically synthesized substances. The advantages of using natural products, especially phytochemicals and their derivatives, include inexpensiveness because of abundant sources, low level of cytotoxicity, high chemical diversity, and so on.
Among them, cinnamaldehyde is renowned as an antibiotic from Cinnamon. This compound reported antimicrobial activity, suppressing biofilm formation, reduced aggregation against S. mutans[9,10].
 The National Institute of Dental and Craniofacial Research. Dental Caries (Tooth Decay) in Adults (Age 20 to 64). https://www.nidcr.nih.gov/research/data-statistics/dental-caries/adults (2018), Date accessed Oct.22.2021.
 Ministry of Health, Labour and Welfare, Summary of the Results of the Survey on Dental Diseases in 2008. Japan, (2016).
 Xuedong, Z. Dental caries: Principles and management. Dental Caries: Principles and Management (2016). doi:10.1007/978-3-662-47450-1.
 Hill, C. et al. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat. Rev. Gastroenterol. Hepatol. 11, 506–514 (2014).
 Burton, J. P., Chilcott, C. N., Moore, C. J., Speiser, G. & Tagg, J. R. A preliminary study of the effect of probiotic Streptococcus salivarius K12 on oral malodour parameters. J. Appl. Microbiol. 100, 754–764 (2006).
 Söderling, E. M., Marttinen, A. M. & Haukioja, A. L. Probiotic Lactobacilli interfere with Streptococcus mutans biofilm formation in Vitro. Curr. Microbiol. 62, 618–622 (2011).
 Çaglar, E. et al. Effect of yogurt with Bifidobacterium DN-173 010 on salivary mutans streptococci and lactobacilli in young adults. Acta Odontol. Scand. 63, 317–320 (2005).
 Mandal, S. M., Silva, O. N. & Franco, O. L. Recombinant probiotics with antimicrobial peptides: A dual strategy to improve immune response in immunocompromised patients. Drug Discov. Today 19, 1045–1050 (2014).
 Ribeiro, M., Malheiro, J., Grenho, L., Fernandes, M. H. & Simões, M. Cytotoxicity and antimicrobial action of selected phytochemicals against planktonic and sessile Streptococcus mutans. PeerJ 2018, 1–17 (2018).
 He, Z., Huang, Z., Jiang, W. & Zhou, W. Antimicrobial Activity of Cinnamaldehyde on Streptococcus mutans Biofilms. Front. Microbiol. 10, 1–11 (2019).