Why is is that even those of us who practise good dental health end up with caries? Tooth enamel is the hardest bit of our body. Shouldn’t it protect our teeth well enough, given adequate care? It isn’t news that acidic foods soften tooth enamel—citrus juices, for instance. Softened tooth enamel can wear away, leaving the tooth vulnerable to cavities and sensitive to cold foods. This isn’t to say you shouldn’t sink your teeth into a juicy kinoo. After all, it has vital nutrients to offer. But you can understand what dents your enamel and find ways to help it heal. But first, know your enemy—some of those enamel scourers in your shopping come well camouflaged!

Not all acid is sour

Citrus fruits produce an obvious mouth-puckering alarm, but not all acids that attack tooth enamel in a day’s worth of meals can be detected by taste. Take your cola drink. There’s enough sugar to make it taste like candy, but as for its acidity… I hear it’s great for cleaning toilets. Then there’s the relatively novel trend of “sour sweets"—readers may recall a chewing gum ad featuring a hair-perming flavour—of which several are more acidic than orange juice.

Also Read previous Food Factors columns

More surprisingly, bland starches also attack teeth, producing lactic acid as they break down in the mouth. A 1999 study at New York University (NYU) Dental Center tested various cooked carbohydrates (popcorn, potato chips, cornflakes, bread sticks, pretzels and wheat crackers). Potato starch was the most injurious, cornflakes the least. All were less damaging than simple sugars, though, as found in a candy bar.

However, “stickiness" is also a factor to consider. Contrary to our use of “sticky" for jelly beans or chocolate, in terms of oral health, the word is better suited to cooked starches, which produce acid longer. An earlier study (NYU, 1997) compared chocolate bars, potato chips, Oreo cookies, sugar cubes, raisins and jelly beans. Lactic acid levels 30 minutes after ingestion, in order from highest to lowest, were as follows: raisin > chocolate bar > sugar cube > jelly bean > Oreo cookie > potato chip. Chewy first, crispy last. Sounds obvious? Well, two hours after eating, the order changed dramatically: potato chip > jelly bean > sugar cube > chocolate bar > Oreo cookie > raisin!

Foods that heal

If so much of what we eat softens up our tooth enamel, what keeps it from wearing out entirely? The fact that the mouth is a self-healing organ. Saliva rehardens acid-bombed enamel. Fluoride, though an acid itself in solution, is similarly protective. Some foods also help:

• A star performer is cheese. It seems not to matter much what kind: soft or hard, flavoured or plain. All do a world of good, even mixed with jammy preserves—though a 2001 NYU study confirmed cheese after sweets helped more than the other way around.

• Another good guard is bread, though a “cooked starch". Again, it doesn’t matter for oral health whether it’s white or wholemeal. However, toasting changes things, according to a study at the Department of Community Dental Health, University of Otago, Dunedin, New Zealand: Adding cheese to toasted breadcrumbs helped, but not much.

• Munching crunchy raw veggies scours away sticky soft foods and forces you to chew longer, generating saliva. Eat with your meal rather than as a starter.

After-dinner mouth guard

Fluoride is good for teeth. Food sticking to them is bad. So we should brush right after eating? Not so. It may pit softened enamel before it can harden. Instead, rinse with a fluoridated mouthwash, or even plain water. Or sip milk.

Sweet tooth?

Sugar-free diet chocolate doesn’t produce cavity-causing acids. No joy? Make it a dark, bitter chocolate (plain, with 70% cocoa). It’s better than milk or white chocolate, and much better than sugar. If you can only find milk chocolate, choosing one with nuts is better for your teeth.

Manidipa Mandal is deputy features editor at Mint