Bad breath can occur when patient has either gum disease or cavities in the teeth that catches food and it deteriorates giving out a foul smell. If there are multiple fillings in the mouth, it’s possible that after a person eats, some of the food gets stuck between the teeth and as it gets rotten, it gives out bad odor. The prevention is to have very healthy mouth by getting professional cleaning done in the dental office and getting all your cavities cleaned out and filled. You should also learn from your dentist or hygienist on how to take care of your oral hygiene at home. You might need to use floss and water-pic and inter-dental brush to get rid of bad odor or halitosis.