It is the enamel, usually. There could be dentin exposed if there is decay.
Crown
enamel is the outer covering of the teeth.
The part of the tooth above the gum is the sulcus this is the neck of the tooth.
The part of the tooth that has the nerves in it is right under the crown of your tooth ''aka'' the top part of your tooth and they travel down into you gums hope this help's
The root of the tooth.
The visible portion of the tooth is called the crown. The submerged portion is called the root.
The tooth root is the part of the tooth that is embedded within the jawbone and anchors the tooth in place. It is located beneath the gum line and connects to the crown of the tooth, which is the visible part in the mouth.
No part of "tooth decay" is a structure or function.
enamel found only in the crown of the tooth ( the exposed part of the tooth ), dentin found in both the crown and the root of the tooth ( root : the embedded part of the tooth ) and cement which hold the tooth in it's place
Your teeth are fixed to your jawbone in your mouth. They sit in a curved line along your top and bottom jaws. The white part of your tooth that you can see when you smile or open your mouth is called the crown. Some of your tooth is hidden under the skin (gum) in your mouth. This is called the root and you cannot see this in your mouth. The white covering on your tooth is called enamel. Dental enamel is strong and helps to protect the tooth. Dental enamel is the hardest thing in your whole body.For further information, go to The British Dental Health Foundation link.
It's Dentin
the dentine