Teeth Are Harder Than Steel

Hardness of various materials
Infographic created by Grok

Did you know that on a modified Mohs hardness scale that runs from 1 to 10, tooth enamel would rank at 5? That's harder than mild steel at 4.0 to 4.5 and softer than glass at 5.5.
Hardness (resistance to localised plastic deformation and scratching) is just one of several material properties, including strength (ability to withstand applied stress without failure), toughness (the ability to absorb energy before fracturing), ductility (the ability to be stretched) and malleability (the ability to undergo plastic deformation such as being beaten or rolled into shape).
The scale isn't a linear one, and is a qualitative, ordinal scale, meaning it only ranks minerals in order from softest to hardest without using uniform gaps between the numbers. So for instance, diamond at 10 is about four times harder than corundum at 9. Glass is about 25% harder than tooth enamel.
If a material is hard, it doesn't necessarily mean it's strong. Glass is harder than steel, but brittle and not tough. However, it's strong in compression, but not in tension.

Further Reading