Recent years have witnessed an increased interest in natural food ingredients, which have effects on the oral microflora by both, promoting the growth of beneficial microbes and inhibiting the growth and metabolism of cariogenic bacteria. Among these, particular attention should be paid to polyphenols (1-6).

Polyphenols are phenolic compounds that form a large group of natural substances found in a number of plants, fruits, vegetables, seeds and the leaves of some trees. More than 8,000 phenolic compounds have been isolated from various natural products. Systematisation of these compounds is difficult due to significant variations in their structure and properties. Considering the very general chemical structure of the carbon skeleton of these compounds, flavonoids and phenolic acids derived from benzoic and cinnamic acids may be distinguished. The following subclasses, which are also highly differentiated, may be distinguished in the group of flavonoids: flavones (apigenin, hesperetin, luteolin), flavanones (naringenin, hesperedin, taxifolin), flavonols (quercetin, kaempferol, myristin, rutin), flavanols (catechin, epicatechin, epigallocatechin), isoflavones (daidzein, genistein, glycitein) and anthocyanins (e.g. cyanidin, malividine, dolphinidine) (7).

Polyphenols are commonly found in diets containing fruits, vegetables, cereals, chocolate and dry legumes. However, fruits, fruit juices, plant-based beverages, tea and coffee are the main source of these compounds (8).

Tea is a water infusion of Camellia sinensis leaves. There are many types of teas, with black, green, white, red (pu-erh) and ulung (oolong) teas being most popular. Tea leaves contain about 36% of polyphenols, most of which (about 80%) are catechins. Catechins such as epigallocatechin gallate, epicatechin gallate, epigallocatechin and epicatechin are the most important ingredients for oral health. They belong to oxidised polyphenols collectively referred to as tannins (1). A number of studies demonstrated the inhibitory effects of tea polyphenols on caries. A study in rats on a cariogenic diet supplemented with 0.1% of green tea polyphenols demonstrated a 40% inhibition of caries (9). The anticariogenic effects of extracts from different types of tea involve the inhibition of the growth of cariogenic bacteria and thus their production of acids, inhibition of bacterial glucosyltransferase activity, reduction of Streptococcus mutans adherence to dental surface as well as inhibition of salivary alpha-amylase. Polyphenols extracted from black and red tea showed in vitro activity against planktonic Streptococcus mutans and Streptococcus sobrinus as well as reduced the proportion of acid producing bacteria (10-12). A significant reduction of salivary Streptococcus mutans and Lactobacilli spp. was observed after oral rinsing (3 times a day for one week) with green tea extract (13). Awadella et al. (14) showed a significant reduction of salivary and plaque Streptococcus mutans as well as reduced gingival bleeding index (GBI) after 7 days of oral rinsing (3 x daily) with 2% green tea infusion. Oral rinsing with epigallocatechin gallate, which is one of green tea catechins, followed by oral rinsing with sucrose solution resulted in a lower decrease in plaque pH indicating reduced acid production by bacterial flora (15). Therefore, it may be suggested that drinking green tea after a meal containing fermentable carbohydrates may help maintain plaque pH above the demineralising threshold, and thus prevent caries. This is also confirmed by clinical obeservrtions showing that children habitually drinking 1-3 cups of tea daily had significantly lower DMFT and plaque index values compared to those drinking only 1-2 cups weekly (16). In vivo studies demonstrated that oral rinsing with 1.5% black tea infusion after consumption of crackers inhibited the activity of alpha-amylase, an enzyme hydrolysing starch to maltose and other low-molecular weight carbohydrates, which are the substrate for acid producing bacteria (17). Tea is also a source of fluoride, the content of which ranges between 0.34 to 3.71 ppm, depending on the species and the place of growing (18). Therefore, the anti-cariogenic activity of tea may result from both, the antibacterial effects of polyphenols and the effects of fluoride on the demineralisation and remineralisation processes.

Coffee is a source of multiple bioactive compounds, including polyphenols (tannins), caffeine and antioxidants. The content of these compounds varies depending on the type of coffee and how it is prepared. Green and roasted coffee extracts of the two most commonly used types of Coffea arabica nd Coffea robusta impair Streptococus mutans adsorption to a hydroxyapatite coated by saliva. Trygonelin, caffeine, chlorogenic acid are active compounds contained in coffee. They are adsorbed to the teeth, preventing the interaction between tooth surface receptors and bacterial adhesins. Furthermore, an inhibition of bacterial glucosyltransferase was observed (19). A similar activity was shown for boiled and unboiled aqueous solutions of commercially available coffee, both ground and instant (1, 13, 20). Anila Namboodiripad and Kori (21) showed lower DMFT (2.9) values in individuals with long-term consumption of coffee with no sugar or milk compared to those who did not consume coffee (4.0) or consumed coffee with sugar and milk (5.5). Thus coffee can help in the prevention of dental caries if consumed without additives.

Grain coffee, which is produced from roasted cereal grains, is also a source of polyphenols. Roasted barley coffee, e.g. Inka beverage containing about 72% of roasted cereal (barley, rye) as well as chicory and sugar beet, is a popular beverage. It was shown that roasted barley coffee contains anti-adhesive components, which inhibit Streptococcus mutans adsorption to hydroxyapatite (22). Roasted and ground chicory root beverage is a substitute for real coffee. It also contains polyphenols. Antimicrobial activity of 100% chicory solution against Streptococcus mutans, manifested in a reduced number of bacterial colonies, was shown. The addition of chicory to natural coffee reduced both the number of microorganisms and bacterial adhesion. Therefore, both chicory and coffee exhibit anticariogenic activity via different mechanisms of action, i.e. chicory has antibacterial activity, whereas coffee inhibits the adherence of cariogenic bacteria (23).