When you eat a large amount of food in one sitting, like during a typical meal, your mouth produces a lot of saliva, which helps to wash away the food particles that decay your teeth, says Dr. Pankaj P. Singh, founder and CEO of Arch Dental Associates in New York City. When you snack on smaller meals you don't produce as much saliva, which means your teeth aren't getting naturally cleaned as well, says the doctor.

In addition to that, most people snack on carbohydrate-rich foods. Chips, crackers, and other carb-laden foods are especially bad for our teeth, as "fermentable carbohydrates work with bacteria to begin the decay process and eventually destroy teeth," says Singh. "All carbohydrates eventually break down into simple sugars: glucose, fructose, maltose, and lactose," he says. "And when they do, they are converted by the bacteria in your mouth into plaque -- the primary trigger of gum disease and cavities." The snack food on Dr Singh's don't-eat list that shocked us most? Bananas. Their "chewy, adhesive texture" makes it easier for them to get caught between teeth or under the gum line, where bacteria can accumulate.

Most of us assume that if our soda is sugar-free, it isn't hurting our teeth. The docs say this is a wrong assumption. It's actually the acids in these drinks, such as citric and phosphoric, that are damaging your enamel, says Dr. Singh. "Consuming these highly acidic drinks on a regular basis means your teeth are under continual acid attack, a process that can lead to tooth erosion."

If you do give in and have a soda, Singh suggests sipping on water immediately after you indulge, which helps neutralize the acid.

While popping oral contraceptives might be a great way to keep you from an unwanted pregnancy, the Pill actually tricks your body into thinking it's pregnant -- which isn't good news for your teeth.

During pregnancy, your hormones change a lot and because of this, many women suffer periodontal disease -- an infection that occurs when your immune response can't compensate for the amount of bacteria in your mouth, says Dr. Nicholas Toscano, a periodontist in New York City.

If you must take the Pill, Dr. Toscano recommends you see the dentist every three months for cleaning, as opposed to the normal six-month interval.

"People think the harder the bristles, and the more aggressive they brush, the better," says Toscano. "But this just isn't the case. The dental care industry offers toothbrushes in soft, medium, and hard, and honestly, I don't know why they sell [hard toothbrushes]. It's got to be a way to just make more money," says Toscano.

So what's so wrong with a good, hard scrubbing? Hard toothbrush bristles and over-aggressive brushing cause gums to recede, exposing the root of the tooth and causing your teeth to look old, says Toscano. Singh agrees. "The plaque and bacteria that build up on your teeth can be more effectively removed with a softer, gentler scrub."

Swimming -- a sport many agree is one of the best exercises you can do -- can hurt your teeth? Yep, you read that right.

Singh says that swimming in pool water that is excessively chlorinated can erode and stain tooth enamel. "Excessive chlorine lowers the pool's pH level, making it dangerously acidic," he says. So if you're a frequent swimmer, pack a toothbrush along with that towel of yours. "Brushing your teeth and using a fluoride rinse immediately after swimming will help," says the doctor.