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Picture this: you're gorging on leftover Halloween candy. You take a bite of a fun-size chocolate bar and instead of sugary goodness, you get a flash of blinding pain in your tooth! What's the deal?

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Sugar is supposed to be one of the best things in life. But you might have bitten into something really sweet only to have it betray you.

Instead of sugary deliciousness, you got immediate, sharp, eye-watering pain. Sure, eating lots of sugary food can cause cavities that don't feel great, but that wasn't some sort of insta-cavity. What you experienced was a consequence of dentin hypersensitivity — or having sensitive teeth as it’s known in the toothpaste aisle.

Pain due to this condition is more commonly caused by consuming hot or cold things, but it can also be caused by eating really sweet stuff. But what makes sugar so special? To understand this, it helps to know a little about tooth anatomy in general.

Your teeth have three main layers. There’s an outer layer of hard enamel, an inner layer of pulp, which contains blood vessels and nerves, and a layer of dentinin between. Dentin is pretty hard, but unlike enamel, it’s porous.

It contains microscopic, fluid-filled tubules that run from the pulp to the underside of the enamel. Even though tooth enamel is the hardest substance in your body, it can still be damaged, like if you grind your teeth, have cavities, or drink lots of acidic sodas. If your enamel is worn away, your dentin and its tubules can be exposed.

And sometimes, the combination of sweet stuff and exposed dentin equals pain. It’s because of your old friend from science class: osmosis. Osmosis is the movement of something like water across a selectively permeable barrier.

It goes from the side where there’s less stuff dissolved to the side with more stuff. Or, in official terms, from the side with a lower concentration of solutes to one with a higher concentration. Osmosis likes things to be equal.

Now, say you bite into something very sweet, like a piece of leftover candy corn. That snack touching the outside of your exposed dentin has highly concentrated solutes in the form of sugar molecules. And the dentin acts as the selectively permeable barrier.

The fluid in your dentin’s microtubules rushes out of your tooth towards the sugar. And that flow stimulates the nerves in the pulp of your tooth, causing shooting pain. Other solutes, like salts or even sugar substitutes, are often better dissolved than sugar, and are in lower concentrations in food and drink, so they don't cause as much fluid to rush through the dentin.

That means they cause less nerve stimulation and less pain. Really, though, you’re much more likely to experience pain in response to cold or hot things which contract or expand the fluid in those tubules than you are in response to sugar. When we talked to Dr.

Kenneth Markowitz of the Rutgers School of Dental Medicine, he said sweet foods are actually a relatively weak stimulus for tooth pain. Usually, they only trigger pain when the tooth’s inner pulp and its nerves are already inflamed. That means your tooth was in trouble before you bit into that candy corn — maybe because of a cavity or defective filling.

So if your sweet tooth is causing you agony, you should probably go see a dentist. And then, you can get back to eating all that candy tear-free. Thanks for asking, and special thanks to Kenneth Markowitz for his insight into all of this.

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