Citrus fruit

 Citrus fruits and juices—a rich source of vitamin C and other nutrients—are good for you in many ways, but not when it comes to your teeth. Grapefruit and lemon juice, in particular, are highly acidic and can erode tooth enamel over time. In a 2008 study that involved soaking pulled teeth in various citrus juices, those two caused the most damage. Orange juice caused the least.

OJ is less acidic, Messina points out, and many store-bought varieties are also fortified with teeth-friendly calcium and vitamin D. "Fortified OJ is good for you on many levels," he says. "Drink it, but brush and floss as recommended." 

Chewy candy 

The stickier the candy, the worse it tends to be for your teeth. Extra-chewy candies—like taffy, caramels, or Jujyfruits—stick to (and between) teeth for a long time, allowing the bacteria in our mouths to feast leisurely on the deposited sugar. "Bacteria burns sugar to make acid, which dissolves the protective layer of tooth enamel and causes cavities," Messina explains.

Candies that are chewy, sugary, and acidic—a category that includes many "sour" varieties—deliver a "triple whammy of negatives," Messina adds, because they carry their own payload of erosive acid, in addition to that produced by the interaction of sugar and bacteria.

Hard candy

 Hard candies such as Jolly Ranchers don't cling to your teeth as readily as chewy candy, but they have their own downside: Unlike, say, chocolate-based sweets, which are chewed quickly and wash away relatively easily, hard candy dissolves slowly and saturates your mouth for several minutes at a time, giving bacteria more time to produce harmful acid. To make matters worse, many varieties of hard candy are flavored with citric acid.

Besides, if you bite down wrong on some hard candies, they can chip your teeth—something no amount of brushing or flossing can repair. They don't call 'em jawbreakers for nothing!

Pickles

Acid (typically provided by vinegar) is essential to the pickling process. It's what gives pickles their sour, salty taste—and it's also what makes them a potential hazard to tooth enamel. In one 2004 study that looked at the eating habits of English teenagers, pickles were the solid food most closely linked with tooth wear. Eating them more than once a day increased the odds of wear by about 85%.

Most of us don't eat pickles that often, however, and snacking on them every now and then isn't likely to noticeably affect your dental health, Messina says. 

Soda

It's no secret that drinking too many sugary sodas can breed cavities. What's less well-known is that the acids found in carbonated soft drinks appear to harm teeth even more than the sugar. The upshot? Even sugar-free diet sodas like Diet Coke and Diet Pepsi—which both contain citric and phosphoric acid—can erode enamel if consumed in large doses.

If you can't do without soda, your best bet is to drink it during a meal, rather than sipping it throughout the day. The food will help neutralize the acid, Messina says, and "the time of exposure to the acid is much shorter."

Sports drinks

 

 If you're in the mood for something sweet or fizzy, sports drinks and energy drinks may seem like a good alternative to soda. But Gatorade or Red Bull won't do your teeth any favors, either. These beverages are acidic, too, and are potentially even more damaging to teeth.

In a 2008 study, researchers at the University of Iowa measured enamel wear after steeping teeth in several different beverages for 25 hours. Lemon-lime Gatorade resulted in the most wear, followed by Red Bull, Coke, and Diet Coke. 

Crackers

 The refined carbohydrates found in saltines and many other types of crackers convert to sugar in the mouth very quickly, providing fodder for cavity-forming bacteria. Crackers also become mushy when chewed, turning into a paste-like goop that builds up in your molars and lodges between teeth.

If you frequently binge on crackers you may have cause for concern, but eating them in moderation isn't likely to cause any long-term problems—"as long as you do a thorough job brushing and flossing," Messina says. "Good oral hygiene will compensate for almost anything." 

Coffee

 You know those stubborn brown stains that accumulate on the inside of a coffee mug? Those give you some idea of how coffee drinking can stain your teeth over time. Coffee stains appear to be even more persistent than tobacco stains, in fact. According to one study that compared the two types of stain, coffee-stained teeth were more resistant to toothbrushing and more likely to become discolored again following a bleach treatment.

In addition to being unsightly, teeth with heavy coffee stains tend to be sticky and apt to attract food particles and bacteria, Messina says.

Tea

 Tea may seem like coffee's gentler, kinder cousin, but that's not necessarily the case when your teeth are involved. Some black tea may even stain your teeth more than coffee. Like red wine, black teas tend to have a high tannin content, which promotes staining.

Not surprisingly, teas that are less rich in tannins—green tea, white tea, and herbal tea—aren't as likely to discolor your teeth. Herbal tea may have another drawback, though: In one study, herbal tea was found to erode dental enamel substantially more than black tea did. 

Sugarless gum

Sugar-free gum helps clean teeth by stimulating the production of saliva. Saliva is nature's way of washing away acids produced by the bacteria in your mouth, and it also bathes the teeth in bone-strengthening calcium and phosphate. In addition, many varieties of sugarless gum are sweetened with xylitol, an alcohol that reduces bacteria.

You might want to stick with mint flavors, however. One 2011 study suggests that the acid used to create certain fruit flavors could damage teeth, though only slightly. "Anything we taste as sour is more acidic, but we're getting so much good out of the saliva flow, I could live with that," Messina says. 

Water

 Water, like saliva, helps wash sugars and acid off teeth. It also contains fluoride, a mineral that protects against tooth erosion and is found in toothpaste and some mouthwashes.

Fluoride occurs naturally in water (including some bottled spring water), and most tap water in the United States is also fortified with it.

Dairy

 Milk and other dairy products are the primary dietary source of calcium, which is essential for healthy teeth. Calcium is the key ingredient in a mineral, known as hydroxyapatite, that strengthens tooth enamel as well as bones. (Teeth aren't bones, technically, but they share some of the same properties.)

Dairy products—especially cheese—also contain casein, a type of protein. Research suggests that caseins, along with calcium, play an important role in stabilizing and repairing tooth enamel. 

High-fiber foods

 Leafy vegetables and other high-fiber foods promote good digestion and healthy cholesterol levels, and they also do wonders for your teeth—mostly because they require a lot of chewing.

Eating a bowl of spinach or beans is a bit like running your teeth through a car wash: All that chewing generates saliva, and the food itself physically scrubs your teeth as it's mashed up into little pieces. "It's the Milk-Bone dog biscuit benefit," Messina says.

Strawberries

 These summer berries contain malic acid, a natural enamel whitener. Here's how to make your own at-home whitening treatment: Crush a strawberry to a pulp, mix it with baking soda, and spread it on your teeth using a soft toothbrush. Five minutes later, brush it off, rinse and voila: a whiter smile. (Be sure to floss, though, as tiny strawberry seeds can easily get trapped between your teeth.)