The human tooth is made up of three main parts: the pulp, the dentin, and the enamel.
The hard, white outer part of the tooth is the enamel. It’s made of 96% of a mineral called calcium phosphate (also known as hydroxylapatite or hydroxyapatite), and it’s the hardest substance in the human body; harder even than bone. The enamel is actually a matrix of calcium rods. Since there are no blood vessels or nerves in the enamel, it cannot grow or be repaired by the body once damaged. The matrix is also brittle so that if not maintained properly the enamel can weaken and/or fracture under stressful situations (eg: grinding, trauma). When this happens, dental care is needed to repair, restore or replace the lost tooth structure.
The entire crown of the tooth-the upper portion of the tooth that’s used for chewing and that people see when you smile – is covered in enamel. The enamel is actually a thin coating on the crown of the tooth and is naturally semi-translucent or “see-through,” revealing the yellowish color of the dentin below. Many people think that teeth are naturally white, but they can actually vary in color from light yellow to a greyish white, and may actually have a sort of blue tone towards the edges of the crown where there is no yellow-colored dentin beneath.
The enamel at the gumline is often darker than that at the biting edge because the enamel is thinner in that part of the tooth and the dentin is more visible. The thinnest part of the enamel is at the junction where the crown ends and where the tooth roots extend into the gum. Most people’s canine teeth are darker than the front middle teeth.
The enamel insulates the interior of the tooth from temperature changes (eg: hot coffee, cold ice cream) and substances that could cause decay or infection. On top of the enamel is another very thin protective layer called the protein pellicle. This layer helps keep acids away from the enamel. We’ll look at the pellicle in a little more detail when we look at its role in how teeth become stained.
The dentin is a porous, yellowish-colored substance that sits below the enamel. It is softer than enamel and that means decay eats through it faster and can cause deeper cavities. The dentin is made up of connective tissue and contains microscopic “tubules” which run from the edge of the enamel down the cementum (a bone-like substance that covers the root); the tubules are narrower at the top and wider at the bottom.
The dentin is responsible for the color of your teeth more so than the enamel. We’ve already learned that the enamel, the part of the tooth that everybody sees, is translucent so it lets the yellowish color of the dentin show through. This is what gives teeth their natural shade of yellow.
The pulp is the innermost part of the tooth and is filled with soft connective tissue containing blood vessels and nerves connected to the jawbone. Because it is deep in the tooth and covered by dentin, it does not affect the color of the crown. However, it does make the root part of the tooth (below the gumline) darker in color where there is no protective dentin or enamel.