Aside from dental caries, this normally indicates a problem in the stomach. There is a condition in Chinese medicine called 'Stomach Fire' which refers to excessive heat in the stomach caused by food stagnating and fermenting. You may wish to read the article on heartburn for more information about this.

Bad breath can be caused by excessive heat in the Stomach, and the fermentation of the stomach contents. Often the tongue has a thick yellow coating. There may be accompanying burning pain around the stomach region, especially if there is acid regurgitation.