Why every cavity in your teeth leads to irreparable brain damage
and what you can do to stop it
I went to the dentist for the bi-annual visit, expecting them to do their usual quick once-over before turning me loose again. Instead, the guy started murmuring a bunch of really worrisome stuff while picking around in my mouth. He paused and called for a bunch of X-rays.
That worried me a lot. Why?
I’d recently been exposed to this tweet:
Beyond that, I’ve always been moderately spooked by x-rays. It started with an exchange I had with my childhood dentist.
“Why do I need this vest?”
“It’s lead, it blocks the x-rays to make this whole thing safe.”
“Are the rays dangerous?”
“Yeah, but it’s okay. The vest protects you.”
“This vest doesn’t cover me all the way though. Do you have a bigger one?”
“No, that’s the only vest. Hold still.”
He didn’t inspire a lot of confidence during that exchange. If you look up x-ray exposure limits, the results don’t help much either:
There’s an established “recommended dose,” but they appear to completely waive this if the x-rays are ‘properly diagnosed.’
“You can survive an unlimited amount of x-ray radiation as long as it was prescribed by a board-certified doctor.”
I never went to med school or anything, but that doesn’t seem right.
Fortunately, my tsunami of neuroticism was stopped in its tracks by the dentist trying to put the little x-ray bite guard in my mouth. I passively decided to just let it happen. My dentist is a cool boomer guy and I didn’t want him to think I was a hippie freak. I let him line the cancer-gun up and obliterate my thyroid forever.
He examined the results for a while and came back with some bad news.
“Lukas, it looks like you’ve cracked a tooth.”
WHAT? I haven’t had a cavity in 15 years so these people must be making up new stuff on me to pay the bills. There’s no way.
I asked him if I could see some pictures to verify. He complied. Much to my irritation, there was indeed a crack in my tooth. The rearmost molar, no less - one of the biggest and coolest teeth in my entire mouth.
I asked how this was even possible - “Aren’t molars supposed to be kinda tough?”
“Yeah, they’re supposed to be. You actually have a lot of craze lines in your teeth though - I’ve been meaning to check on something for a while. Hold up.”
He came back with a gadget that looked like this:
“The average person exerts a bite force of about 1-200 PSI on the surface of their teeth. There’s a ton of variability in how the human jaw can be constructed though, so leverages aren’t the same across everyone. Some people just have bigger jaw muscles, too. The highest we ever measured was in the 1200s. I want to test yours before we decide how to proceed with that tooth.”
“What’s it gonna tell you?”
“Different restoration techniques should be used for the heavy biters. There’s a lot of stuff that looks really pretty but might only last a few weeks in the mouth of a gorilla.”
Seems fair. He gave me the little plate and I chomped down.
“Over 900! No wonder your teeth are cracking.”
Well, that sucks. Like, it’s not ideal for my teeth, obviously. But it’s also just annoying being within the range of “really high” without being the highest.
I try to either be the highest of the lowest in everything I do. Middling results never feel good. I coped by telling myself I could get over 1200 if I did some jaw curls.
I asked what the results told him and he let me know it pretty much locked me in for a gold crown. I wasn’t too happy about that. The crown part, at least. The gold bit was super cool.
“Tooth restoration,” as dentists call it, usually follows a given path. First, you get a cavity. This needs a filling. We used to do this with a combination of metals called amalgam, but anymore we use composite resins that match the color of the tooth. This was a big win for the holistic health freaks (me) because even though doctors assured us the only time we were at risk of mercury exposure was during the installation, we (I) assumed they were wrong and the mercury leached somehow. Normal people celebrated too because amalgam fillings look hideous.
Teeth experience a fairly strenuous loading cycle, so we’ve developed techniques to mechanically lock the filling in. Ever wondered why fillings always have those weird squiggly outlines? It’s an intentional design decision to minimize stress risers near the center of your teeth. There’s a lot of nuance going into the preparation - you want the inner walls angled slightly too, so the filling can’t lift out. The bottom of the channel needs to be damn near perfectly flat, or you risk unevenly loading the tooth and breaking off a cusp (below). There’s ton of little quirks based on the location of the cavity and the structure of the enamel in the region.
It’s not perfect. Fillings eventually delaminate from the sides of your teeth and pull away, giving bacteria just enough room to sneak in and start forming a new cavity. When this starts happening the filling gets replaced.
On average, you'll need a new filling in 5-10 years. It could last 1 year or it could last 100 depending on a number of factors, but on average that's how long people can expect.
Every time you replace a filling, you’re taking out more material. Most teeth can handle 2 or 3 fillings, but there’s a point where you’ve taken so much from the original tooth that the structure can’t maintain itself anymore. If you keep expanding the filling at this point you risk fracturing what’s left of the tooth down the base and jumping straight to root canal.
So fillings only last 10 years (on average) and you can only get 2-3 per tooth. You’re a healthy young guy who expects to still be alive in 30 years. What happens after your third filling needs to get replaced?
You get a crown. The dentist makes a mold of your tooth before drilling off ~1mm of material from the entire surface, removing most all enamel. Next he's going to try and replace the stuff he drilled off with a replacement. Smaller dental offices usually send the mold they took to a lab that can mill out a little tooth-cap from the mold he took. This takes a while, so in the meantime he'll give you a resin temporary crown and schedule another appointment in a few weeks when the lab's replacement comes in.
Bigger offices might have a CEREC machine that lets them either 3D print or mill their own caps in-house. CEREC is one of those acronyms where they clearly just started with a word they thought sounded cool and then made up words for the letters retroactively, so I could tell you what the words mean but it wouldn’t help you understand what it is. Basically though, it’s a big expensive machine that can use digital models to create crowns from ceramic.
Offices with a CEREC can get the whole crown done in a single visit but their material selection is usually more limited. You’ve gotta watch out for these guys, because dentists with access to a CEREC tend to see crowning as the solution to nearly every dental issue. When you've got a really big, expensive hammer, everything looks like a nail.
Crown materials get to be a controversial subject between dentists, but my powerful gorilla-jaw made the decision easy - gold. With all the advancements in ceramic and nanomaterials, it’s still the best we’ve got from a durability standpoint. You can laser-etch a texture on the inside of a gold crown that lets the sealants used bond more effectively than with any other material. This means properly installed gold crowns are less likely to come loose than other varieties.
Gold has an additional advantage because dentists just really like working with it. It’s a soft, malleable material in comparison to all its ceramic and porcelain competitors, so it makes their job easy. Their job being easy increases the chances they'll do it right. I've also heard some love working with gold so much the waive the additional cost over a ceramic alternative just to have a chance to work with the stuff.
The other popular option for molars is zirconia, but it’s more difficult to seal to a tooth and cracks more readily. It’s also harder than gold, which might sound good but actually kind of sucks. If you put something substantially harder than a tooth in your mouth and chew a bunch it tends to wear on the enamel of your original teeth.
Gold crowns have the additional advantage of letting you remove less tooth material on the side, because gold can be made extremely thin without cracking and molars tend to experience low side-loading. But why would you care about removing less material?
Just like fillings, crowns have a lifespan.
Also like fillings, replacing them requires the dentist remove even more tooth material. See how this goes? All this dentist stuff shaves down your tooth. You’ve got a limited amount of it, so at some point these procedures shave through it all and get to the pulp. When that happens you’re locked in for either a root canal or an extraction because exposed pulp represents a massive infection risk.
Root canals are a worst-case scenario. That’s what we’re trying to avoid here. Root canal is essentially total loss of the tooth. The dentist goes in and seals the tooth off from the blood supply at its base before drilling out all remaining pulp and filling the tooth with a cementlike filler material before putting a crown over the top. It’s basically dental taxidermy, the poor shell of your little tooth gets worn like a coat.
A lot of people say “oh, what’s wrong with that? It still works. Like, I can still chew with it, right? Why do my teeth need to be alive?”
It can chew, sort of. For a while.
Teeth are complicated. The pulp acts like a mini water-pump and exerts hydrostatic pressure outward on the enamel to improve resilience. When you clear it out and replace it with a non-reactive cement, the structure of the tooth gets a lot weaker. It can’t feel now, either - this leads people to chew harder than they otherwise would, because it doesn’t hurt when they bite down too strongly. Both factors combined mean root canalled teeth get cracked much more frequently than your natural teeth. Cracks in root-canalled teeth are infection risks, but they’re also mechanical problems - a lot of times the tooth just breaks off or shatters before anyone notices.
“But Lukas, who cares? You’ve written 5000 words now expressing complete terror over every common dental procedure in existence. Why does it matter if you lose one tooth?? We have like 300.”
Losing a tooth horrifies me for a lot of reasons.
Reason number one: tooth loss causes changes in brain volume and cognitive function.
(You don’t need to read the full text in the image below, but it agrees with me. Just trust me bro.)
This finding gets replicated in a bunch of mouse and rat studies that attempt to parse out correlation vs causation by measuring the animal’s brain volume initially, removing some teeth and then re-measuring. Grey matter volume always went down.
Losing teeth literally causes your brain to shrink.
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