The health benefits of Camellia sinensis (green tea) range from improving cardiovascular health, reducing risk for Alzheimer’s and certain cancers, to supporting weight management. An interesting new Japanese study of 25,978 people, between 40 and 64 years of age, found that drinking one cup of green tea a day may improve dental health and reduce the risk of losing teeth by about 20 percent¹. 
 
Dental caries are the result of mutans streptococci (S. mutans and S. sobrinus) which feed on sucrose in the mouth and produce plaque. While they are producing plaque, mutans streptococcialso produce lactic acid, which eats into tooth enamel. This combination of plaque buildup and lactic acid is responsible for the decay of tooth enamel.
 
Another study published in the Caries Research found that epigallocatechin gallate (EGCg), one of the green tea catechins reduces the ability of S. mutans to produce the enamel-destroying acid². In this study, participants either rinsed their mouths with an EGCg solution, or with plain water, then rinsed their mouths again, 30 minutes later, with a sucrose solution. The plaque acidity of participants who pre-rinsed with the EGCg solution was significantly lower than that of participants who pre-rinsed with plain water. Less acid means less tooth decay. These results suggest that EGCg is effective in reducing acid production by mutans streptococci.
 
So drinking a cup green tea after a meal or dessert might not be a bad idea. It can fight tooth decay by reducing lactic acid production, by inhibiting plaque production, and by destroying some of the S. mutans bacteria. All this with as little as one cup of green tea!
 
References 

1. Koyama Y, Kuriyama S, Aida J, et. al.  Association between green tea consumption and tooth loss: Cross-sectional results from the Ohsaki Cohort 2006 Study.  Prev Med. 2010 Apr;50(4):173-179. Epub 2010 Jan 25.
2. Hirasawa M, Takada K, Otake S. Inhibition of acid production in dental plaque bacteria by green tea catechins. Caries Research 2006;40(3):265-70.