Dentin and the Layers of Your Teeth

If you've ever experienced tooth sensitivity, you're not alone. But not everyone realizes that dentin—not enamel—is what causes tooth sensitivity. Dentin is the middle layer of the tooth (between the enamel and the pulp), and makes up the majority of the tooth's structure. In fact, dentin is what gives our teeth their color; tooth enamel (the top layer) is fairly clear!

Though many people know that enamel is the hardest substance in the body, dentin is also denser and harder than bone. The color of dentin may range anywhere from grey to black, but is typically a pale yellow. This yellow hue is generally what is seen penetrating through the tooth's enamel.

Components

In order to fully know what dentin is and how it works, it's important to understand the composition of our teeth.

Our teeth have four main parts:

• Pulp: Located at the center of the tooth, the pulp is a fully living layer made up of blood vessels and nerves. It is the softest layer of our teeth.
• Dentin: As the middle layer, dentin surrounds the tooth's pulp. Dentin is calcified, living tissue made up of tiny tubules or tubes, and is harder than pulp but softer than enamel or cementum. Dentin grows throughout the life of the tooth.
• Enamel and cementum: These hard outer layers protect the tooth and attach it to the jawbone. Enamel is the outer layer located above the gum line, and is a mineralized, non-living substance. Cementum is the outer layer below the gum line, and is partially living and non-living.

Odontoblasts, or cells located in the tooth's pulp, are responsible for dentin production.

There are four different types of dentin, characterized by the tooth growth stage at which it forms:

• Mantle Dentin: This is the first type of dentin produced. This early dentin is more elastic than other types of dentin, and provides a cushion for the enamel at the crown of the tooth.
• Primary Dentin: This type of dentin grows before the tooth erupts from the gum and fills the area of the tooth between the inner layer (pulp) and outer layer (enamel or cementum).
• Secondary Dentin: This is dentin that is formed after the tooth erupts through the gum. Secondary dentin has the same composition as primary dentin, but it grows more slowly. As it grows, the pulp chamber may decrease inside, as dentin grows inward (our teeth do not get larger as they age).
• Tertiary Dentin: This type of dentin grows when our teeth wear down, crack, or get a cavity. The growth of tertiary dentin is part of the tooth's defense mechanism to prevent against an infection or abscess.

Tooth Sensitivity

Tooth sensitivity can occur when dentin becomes exposed. This can happen either above or below the gum line. Temperature changes (hot or cold), or even acidic or sugary foods and drinks can trigger tooth sensitivity.

How does our tooth dentin get exposed? It can happen in a number of ways:

• Tooth decay can lead to worn areas or holes in tooth enamel (cavities).
• Gum disease can lead to receding gums that allow plaque and other bacteria to erode the cementum.
• Dental abrasion can happen if you brush your teeth too hard and wear away the enamel.
• Cracked or broken teeth can compromise the enamel.
• Tooth whitening procedures expose the dentin layer to bleaching agents, such as hydrogen peroxide or carbamide peroxide, and can sometimes cause sensitivity.

Sensitive teeth can be a sign of a more serious dental condition, since it means your tooth dentin is exposed. In addition to causing pain, exposed dentin leaves your tooth susceptible to infection or abscess, which could lead to the need for a root canal, or even tooth loss.

It's important to talk to your dentist if your teeth become sensitive to temperature changes or food. They can help you take steps to avoid making the problem worse.