Dental Education Lecture: Tooth Structure
In last lecture, we talked about a small painless cavity gradually developing into a large one causing severe pain. Today we are going to use drawings to show you how this happens.
Fig. 1 shows the frontal view of a lower front tooth. Every tooth has two major portions: crown (exposed in our mouth) and root (inside gums). The junction between the crown and root is called neck. Let us cut the tooth into two halves, take off the front half and look at the cross section (Fig.2). The outer layer of our crown is enamel, the hardest structure in our body, whereas the outer layer of the root is cementum. The major part of tooth is made of dentin (yellow). In the middle of the tooth is pulp, so called nerve. This is the only soft tissue of our tooth. The other three (enamel, cementum and dentin) are hard tissues. The pulp needs two layers of hard tissues for protection.
Arrowhead in Fig.2 indicates the edge of the lower front tooth. As we get older, our teeth become shorter due to wear and tear. The enamel may be gone with dentin exposure (Fig.3). The nerve is pretty close to outside (mouth). We may experience cold, hot and sour sensitivity. If we do not brush or floss properly, a cavity develops on the side of the tooth (black, Fig.3). Early on it is far from the nerve. You do not have any problem. Once the cavity gets big and deep (black, Fig.4), our nerve becomes irritated, angry and red-faced. Single arrowhead in Fig.4 indicates a small opening of the late cavity into the nerve.
The nerve may also be violated and exposed by severe chip due to a blow from your enemy, bike or car accident. Double arrowheads points to exposure area due to chip. Once the nerve is exposed and inflamed, we have to take it out, the procedure, commonly known as root canal. We will discuss more about root canal and other treatment to the tooth problems next time.
Xin Wei, DDS, PhD, MS 1st edition 01/26/2009, last revision 04/18/2012