The surface of our teeth is made of a hierarchical structure of very small and very organised crystals. Individual atoms are organised into 50-nanometre-wide crystal rods, which are organised into 4 micrometre wide prisms, which are organised into overlapping layers that make your teeth hard enough and tough enough to last a lifetime. It’s an amazing material and a lot of my research is about trying to copy it. Rather than waste any more words trying to explain, here’s a video that does a much better job!