Why do we have baby teeth at all?

We’ve previously discussed WHY to fix baby teeth even though they’re going to fall out. Mainly it’s because nobody wants a small problem – which would be easy to fix when small – to turn into a big problem, i.e. pain, infection, swelling, which we’d have to fix via extraction. Numb or not, extractions aren’t as fun as Disney World. Baby teeth are important to keep regardless for the sake of speech, feeding, jaw development and for proper orthodontic spacing during transition to permanent teeth. Also, having teeth extracted can be traumatizing in the procedure itself, but also in the years to come with social perception and peer discrimination.

Why not have infinite sets of teeth?

There are animals that have only 1 set of teeth (mono-phyodont), those with 2 sets of teeth (di-phyodont, and those that have many sets of teeth (poly-phyodont). Wouldn’t it be great to have a never-ending supply of teeth in case you ever get a cavity or take the occasional hockey puck to the face? The benefit is obvious – you always have more teeth to fill any gap. The downside is that these rows of teeth on top and bottom will never occlude, will never fit together with each other. Having only 1 or 2 sets of teeth means that you end up with a stable occlusion, which allows for chewing, or comminution. Some crocodiles and snakes can go a whole year on one huge meal. They use their teeth for prehension – to seize prey head first and to swallow it whole, so having a set of teeth that’s always slightly different in how it fits together isn’t really a big issue. Mammals, being “warm-blooded” (see homeothermy), have higher metabolic need and have to eat every day, often several times! Chewing is necessary for mammals such as humans in order draw all possible nutrients from the foods we eat (so goes the theory). We are also heterodonts, which means the teeth are NOT all the same – we have incisors to cut off a bite, canines to tear, and premolars / molars with which to grind food down.

Why specifically we have 2 sets of teeth instead of 1?

That’s not a question to which we exactly have the answer. Why animals have many sets of teeth makes sense – break or lose one? Here’s another. But, again, these function only for prehension. 1 set of teeth? That’s efficient and works for rodents where there’s iron in their teeth (hence the yellow color). The tooth biochemistry is different and continues to grow throughout life and so it never (usually) gets worn down. What came first evolutionarily? Was being polyphyodonty (many sets) the way teeth first came to be and mono- and di-phyodont dentitions were offshoots of this? I don’t know how it all came to be. But we can see why it works for us: Our bodies grow a great deal from infancy. Our fingers, hands, arms, head, etc. all grow bigger as we age. This includes our jawbones, but not our teeth. They are hypercalcified structures – they don’t heal when broken, nor do they grow, but they are also VERY strong, hard to break, and hard to wear down. The baby’s mouth can only fit so many teeth, and the occurrence of small chips in teeth is high, and the occurrence of larger dental traumas is far from low – we’re cruising and bruising! Dental trauma from ages 1-3 years of age is very high as we learn to move and fall often. I’m glad those teeth are not meant for a lifetime. But as we grow, those small teeth, which had supported jaw shape during growth, aided in speech development, and allowing babies, toddlers, and children to chew food, are insufficient for the size of an adult mouth (imagine your mouth but having zero molars, nothing but empty gum space the whole back half of your mouth!). Or go the other way with it! An adult set of 32 LARGE teeth would absolutely fail to fit in a baby’s mouth. 

So, we have 2 sets, and that seems to work out pretty well. To quote Dr. Seuss, “And when you get your second set, THAT’S ALL THE TEETH YOU’LL EVER GET.”