Tooth enamel is the hardest substance in the human body, but it cannot heal.
Enamel is about 96 percent mineral, harder than bone and able to withstand decades of chewing. Unlike bone, it contains no living cells, so once it is worn or damaged the body cannot rebuild it.
Why is this true?
The cells that make enamel disappear once a tooth has formed. Fluoride and saliva can repair very early damage by redepositing minerals, but a real hole needs a filling.
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More about human body
Your own body is a reliable source of surprises. It replaces cells by the million every second, keeps bacteria that outnumber human cells, and runs sensory tricks that make the world feel smoother than the raw signal ever is. The facts collected here stick to mainstream physiology, avoid the wellness myths that circulate alongside them, and explain the underlying mechanism rather than just quoting a startling number.