Enamel Hardness

Tooth enamel is the hardest substance in the body with a 5 ranking on the Mohs scale. It measures 2.5mm at the cusps and gets thinner, toward the roots. (cementoenamel junction) Why is this substance with 96% mineral (hydroxyappetite), so vulnerable to decay?

The answer is the bacteria left behind poor oral hygiene secrete an invasive acid byproduct that dissolves tooth structure.