Just think real quick: what was the coolest thing you did today?

From a biochemical perspective—basically EVERYTHING you do is impossible and incredible and unfathomably clockwork-gorgeous. The molecular inner-workings of your day-to-day life consist of millions of perfectly-timed miracles working in brilliant synch with each other.

But I’m not going to say you ‘do’ any of those things—since you largely have no say as to what your chemicals are doing. No man, I’d say the most badass thing you consciously did today was brush your teeth.

I know brushing seems like it’s just maintenance work. You rub the gunk off your teeth in order to keep your breath socially acceptable and to stop cavities and whatever from forming. However, most toothpastes contain an ion that actually changes the chemistry of your teeth so they’re harder to hurt. Consistently brushing your teeth with the right toothpaste literally gives them a layer of chemical armor plating.

This is all because of the most insane element on the periodic table: Fluorine.

A small puff of Fluorine gas ignites iron wool on contact. GIF ripped from Periodic Videos. This entire essay was inspired by Periodic Video’s clip on Fluorine. Check them out, they’re amazing!

Fluorine is powerful stuff. So powerful that it’s basically impossible to see pure fluorine in nature. That’s because chemically, fluorine is down to react/ explode with pretty much everything. If you put it in a glass container with even a single drop of water in it, it’ll turn into hydrofluoric acid and dissolve the glass. Flourine causes everything from Iodine to Iron to straight up burst into flames through nothing but casual contact.

However, once Fluorine is done reacting with ALL THE THINGS, it becomes the resolutely stable fluoride ion. Which is a word you may recall if you’ve ever spent too much time watching toothpaste commercials or listening to crazy people complain about Fluoride in your drinking water. Everywhere you look, you see people hawking fluoride as a magic ingredient that promotes tooth health and erases cavities.

But the thing is: no one ever explains why fluoride is good for dental health. And that’s lame because the reason is so cool it’s actually hard to believe.

PART 1: YOUR TEETH ARE SO STRONG THAT THEY’RE ACTUALLY WEAK

A rough 2d representation of Hydroxylapatite. This is a HUGE simplification. To see the real deal, check this out.

The fact that your body can take basically random free-floating ions in your bodily fluids and grow honest-to-god rocks inside your gooey, soft tissues is one of those miracles of biology I talked about earlier. Your body turns the phosphate it gets from everything you eat (especially meat, cheese and nuts) into the mineral hydroxylapatite. (y’know: hi-DROCKS-ill-A-pa-TIGHT). Let’s go ahead and shorten that to ‘HAP’ for now. HAP is a compound made up of Calcium(Ca), Phosphate(PO4) and Hydroxide(OH) ions. Looking at the image I slapped together, just keep in mind that HAP is mostly Calcium and Phosphate. However, that central Hydroxide bit is going to be key later. Remember that one.

Basically, Hydroxylapatite is a crystal manufactured by cells in your mouth called ameloblasts in a repeating sequence of hexagonal(ish) rods. HAP makes up most of your tooth’s outer enamel covering. I don’t want to hit you with too many science-y words at once, so for now let’s just say that this stuff is excessively strong and hard for something grown out of your soft tissues. Hydroxylapatite is so tough that it’s harder than most metals (gold and steel come to mind) and a good number of rocks. This hardness allows people to chomp down on basically everything they come in contact with, and that’s also the reason why opening a beer bottle with your teeth isn’t as scary or damaging as it seems.

This strength has served us well for basically our entire evolutionary history, so strong in fact that we never evolved a way to heal damaged teeth. We never needed to fix busted teeth because ordinary use of teeth didn’t break them down that much. However, in the past 200ish years, people have been adding something to their diets that has uncovered an enormous, Achilles-Heel level weakness in our teeth.

PART 2: SUGAR RUINS BASICALLY EVERYTHING

I don’t have to tell you that sugar is bad for you. An overabundance of sugar in your diet can lead to everything from diabetes and obesity to liver disease. However, Sugar’s campaign of running you down starts right at your front door. Every carbohydrate you consume leads to tooth damage but sucrose (y’know, table sugar) really heads the pack on this.

Sucrose gets dissolved in your saliva and then bacteria in your mouth absolutely go to town on the stuff. Big critters like us humans process sugar using a sophisticated process called respiration, which is awesome and only produces Carbon Dioxide as a byproduct.

But bacteria use an old-school energy-making method called glycolysis. Glycolysis is a mess of a way to make energy, and ends up making a whole slew of hazardous chemicals along the way. Some bacteria make ethanol (booze) while others make acid (usually lactic acid, sometimes others). People are unlucky in that the bacteria in their mouths are the acid-making kind. Not the booze making kind.

It’s the acid that uncovers that huge weakness in your teeth, because HAP is a mineral that is INCREDIBLY prone to being dissolved by any acid. This is because phosphate is kind of a weak link in HAP’s structure. If any acid gets in the saliva on your teeth, it basically vacuums out the phosphate ions, making a whole bunch of different compounds. Without the phosphate there, HAP falls apart. This gradually crumbles down your teeth in a process called demineralization. The short of it is: sugar causes your teeth to straight up dissolve into your saliva. After a while, that acid wears down your teeth enough so the bacteria can get at the soft bits of your teeth and chow-down on them. That’s called a cavity. Left untreated—this causes the whole tooth to dissolve away entirely. We all know how agonizing this process is.

So that sucks. But that’s not the end of the story. Because science came in and stumbled upon that awesome solution I mentioned in the beginning.

PART 3: HOLY CRAP LET’S JUST CHANGE WHAT OUR TEETH ARE MADE OF

So yea, we brush our teeth to clean them and all. But, if you use flouride toothpaste, it leaves those fluoride ions floating around in your saliva. And this is where the magic of chemistry kicks in.

Remember how acid dissolves your teeth? It does that by sucking out the phosphate from the HAP in your enamel. Once that happens, the crystal structure of HAP is wide-open for change. Specifically, that central Hydroxide (OH) piece is exposed and ready to be messed with.

Now, the science gets fuzzy here—so no one really knows exactly how this happens. But, the best guess is that fluoride wants to be in OH’s little spot WAY MORE than OH does, so OH gets kicked out and fluoride slams its way into OH’s throne. Maybe. Regardless of how it happens, once fluoride joins the party, the chemical makeup of your enamel now looks sorta like this:

Basically fluorine comes in, BOOTS OUT the hydroxide ion, and takes up shop in the middle of this crystal. Like a Boss.

It’s a mineral called Fluoroapatite—or, uh—FAP…for short.

Actually—let’s go ahead and not shorten that one.

Fluoroapatite is just like HAP, only it’s a LOT more resistant to acid damage. Remember, Fluorine is insanely reactive, but once it’s finished reacting, the compounds it makes are really stable. Fluoride works the same way, holding the calcium and phosphate ions onto the crystal a lot harder than the Hydroxide ever could. Even though this doesn’t stop cavities that have already formed, it’s still powerful.

In short, acid damages your teeth, but then fluoride can come in and SAVE THE DAY, right when the minerals of your enamel are most vulnerable. Fluoride can repair acid damage and change the actual chemical make-up of your outer enamel into something stronger. Which is extra crazy because you have to damage your teeth in the first place in order for them to transform into this stronger stuff.

It’s this amazing story of how through science, people managed to find a chemical hack to heal teeth even though our bodies never figured out a natural way to.

If only my dentist had explained to me how awesome brushing my teeth was—if only I’d known that I was transforming my teeth into something more powerful via nothing short of chemical wizardry—I probably wouldn’t have to go get this root canal tomorrow morning.