Cementum is a hard, bone-like substance that covers the roots of your teeth, the parts hidden below your gums. While the crown of your tooth (the part you can see when you smile) is covered in shiny white enamel, the roots need their own protective layer, and that's where cementum comes in.

Cementum does a crucial job: it anchors your teeth to your jawbone. Tiny fibers called periodontal ligaments attach to the cementum on one end and to the jawbone on the other, holding each tooth firmly in place like thousands of microscopic ropes. Without cementum, your teeth would have nothing for these ligaments to grip, and they'd feel loose.

Dentists care a lot about keeping cementum healthy because gum disease can expose it to bacteria. Unlike enamel, which is the hardest substance in your body, cementum is softer and more vulnerable to decay if it becomes exposed.