Teeth are weird. We're essentially soft, fleshy organisms, but the energy we need to survive comes packaged in things that require cutting, tearing, and grinding. So evolution found a bizarre workaround. In the fleshy part of our mouth where food comes in we grow jagged rows of crystals.
Yes, teeth are crystals. Specifically, they're tightly packed sodium phosphate crystals, laid down column after column on the dentin core that serves as their anchor point. (Why people prefer the dull word "enamel" instead of "sodium phosphate matrix" is beyond me.) This is a colorized electron microscope photo of a sodium phosphate crystal on a tooth. Wonderful isn't it?
The fact that teeth are crystals is really important. Keep it in mind for the rest of this post! It's the reason teeth chip so cleanly. Apply too much force to the tooth, and it breaks along the lines of the crystal matrix. Your crystal teeth are the hardest thing in your body, being made 96% of minerals, with a bit of water and some fleshy stuff making up the remainder. Unlike most other parts of your body, they aren't connected to the nervous system and don't get any blood flow. They're just inert crystals, sitting in your mouth all day. Some people have even started putting decorative crystals on their teeth. Crystals on crystals!
So, here we are, with a mouth full of crystals that are essentially out of reach of the body's healing systems. Unlike muscles, bones, or organs, you don't get any do-overs when you damage a tooth. It's just a rock. This is where the problems start.
The teeth are there for one simple purpose; to be the first step of digestion, breaking down large pieces of food into smaller pieces of food that your tongue expertly packs up into little balls and sends down your esophagus. This means that your teeth are on the front lines of dealing with all the crazy stuff we're shoving down our gullets. All day long they're sunk into different starches and proteins, and splashed with acidic compounds like tea, coffee, juices, and sodas. The rest of your mouth is backed up by the immune system's multilevel defense systems, but your teeth are out there on their own.
With all the flavors and nutrients of food and drink also comes a payload of bacteria. Bacteria are amazing at finding their niche in the ecosystem, and a group of about 25 of them, the oral streptococci, make their living colonizing the surfaces of your teeth and gums. These little guys attach themselves to the crystal substrate, waiting for your, and their, next meal.
I think most people, when they approach tooth brushing and flossing, have in the back of their mind that leftover food is the problem. Getting that sesame seed out from between your teeth is nice, but the main reason to brush and floss is to break up the biofilm of bacteria on your teeth. Biofilm is the key word here. Bacteria don't float around as individual units, they form in thin sheets, creeping across surfaces. If you've seen mold grow on bread or pond scum on the surface of a lake, you've seen a biofilm in action.
If left alone, mouth bacteria will quickly form a biofilm on your teeth. This is why if you haven't had the chance to brush in a while, your teeth get that slimy, fuzzy feeling. And if you introduce sugars to a biofilm covered tooth, acid production goes through the roof, the tooth decays quickly and the bacteria make progress in their march all the way down to the dentin core of your tooth.
So, the first thing to take away here is that your job as a brusher and flosser is to remove biofilm, not food. My sink has a drain catch which I hadn't washed in a few weeks. I pulled it out and took a photo of the biofilm that had grown over it. This biofilm is really easy to get rid of. A few passes with a sponge or brush and it was gone.
The same goes for your teeth. Removing biofilm is a gentle process. You need a soft toothbrush, and you need to go slowly, without force. Brushing your teeth is not like scouring a pot; it's much more akin to removing algae from the glass of an aquarium. It's important to be thorough. Because missing a spot consistently allows that area to spread out and recolonize the crystal matrix more quickly between cleanings. I think the common word for biofilm, plaque, is making matters worse here. Plaque sounds like something hard, something that must be polished and shined with a lot of elbow grease. Something like... well... a plaque.
Ban the word plaque from your mind, keep the word biofilm; it's more accurate, more descriptive, and gives you a good sense of the light touch you need to disperse it.
Great, so now you know to gently remove bacteria biofilm buildup after a meal, problem solved. NO NO NO.
The bacteria in your mouth don't sit around waiting for you to finish your meal before they start theirs. They're hungry, and they're extremely fast. The second a sugar hits your mouth they're off to the races, metabolizing and producing acid within minutes. So if you have that piece of toast at 7:30 am and don't brush your teeth until 8:30 am before leaving the house, you've given the bacteria biofilm a full hour to chow down and soak your teeth in acid.
The solution is to brush your teeth before eating. If you break up that biofilm before any food hits your mouth, you drastically reduce the amount of acid byproduct. Brush before breakfast, before lunch, and before dinner. But especially before breakfast. Don't give an entire night's worth of biofilm the chance to hammer away on your teeth for the hour before brushing after the morning meal. In fact, because the teeth have been softened up by the acid bath, you can actually cause more damage to the crystal matrix if you brush hard after eating, and your good intentions for your teeth will have backfired completely.
Throughout this post, I've left out an important piece of the puzzle. While the body can't heal teeth, there is a natural process which can reverse some of the damage of tooth decay. It's referred to simply as remineralization, and it happens when the mouth has a neutral pH and the right mix of minerals in the saliva. The minerals will attach to broken parts of the crystal matrix and act like an epoxy, reconnecting damaged areas and fortifying the surface.
Until recently, remineralization was a minor help in the fight against tooth decay. That all changed with the discovery that the negative ion of flourine, called flouride, is remarkably good at getting the teeth to remineralize. In the 1950s the first fluoride toothpastes were approved by the FDA, and around the same time flouride was added to municipal water supplies (water fluoridation is only of benefit to young children with developing teeth).
It's hard to understate how dramatic a change flouride has been to our dental health as a species. It changed everything. With some old fashioned flossing and brushing and a little modern chemistry you can live your entire life without getting a cavity. This was an impossibility just 100 years ago. When you brush your teeth with fluoridated toothpaste you're delivering a one-two punch to the oral streptococci living on your teeth. You're both breaking up their precious biofilm AND depositing fluoride epoxy in their little hidey-holes, making the enamel harder and more resistant to future acid attacks. This is the reason incidence of cavities has plummeted in the past half century.
However, most of us lose a lot of the benefits of fluoridated toothpaste by making a simple mistake. If you over-rinse after brushing, you're washing away the fluoride before it has a chance to remineralize. All that good bonding agent is going down the drain. This is especially true if you're using a harsh mouthwash as the last step of brushing.
The answer, and I know this is shocking, is to not always rinse after brushing. Spit out the excess saliva and toothpaste, but don't swish any more water around. You'll have a chalky feeling in your mouth for a few minutes, but that's the point, your teeth are getting a good chance to bond with the fluoride molecules and form stronger enamel. Soon after your saliva will break up any remaining chalkiness and you'll feel like normal.
This no rinse method only works if you use the correct amount of toothpaste, which is about the size of a pea. Big gobs of toothpaste don't clean any better, and they mean unnecessarily high amounts of fluoride in your mouth that force you to rinse. I know having a mouth with leftover toothpaste in it isn't feasible all the time, so go ahead and rinse if you need to, but once in a while do a no rinse brushing, your teeth will thank you for it.