Various studies have shown that certain components found in Cranberry Juice disrupted the adhesive properties of bacterial biofilms found in the oral cavity.
Biofilms are a way for bacteria to stick to each other and protect eacth other from harm. These bacterial congregations are sticky, and make it hard for their removal. In essence, drinking cranberry juice has been found to act as an anti-bacterial agent, breaking up these biofilms on teeth.
Having said that, don't go out and drink just any cranberry juice. Remember, many juices contain a lot of added sugar. Drink only those juices with no extra sugar. Also, take care not to drink too much. All fruit juices contain a high amount of natural sugar.
Cranberry juice can stain your teeth, so make sure you rinse with water after drinking.