Until around 250 years ago in the West, archaeological evidence suggests that most human beings had an edge-to-edge bite, similar to apes. In other words, our teeth were aligned liked a guillotine, with the top layer clashing against the bottom layer. Then, quite suddenly, this alignment of the jaw changed: We developed an overbite, which is still normal today. The top layer of teeth fits over the bottom layer like a lid on a box.
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