Not all teeth are white
The colour of your teeth varies. Not everyone has white teeth. In fact, many people have shades of yellow.

The enamel protects the tooth. Underneath is the darker dentine. The reddish core consists of pulp tissue, nerves and blood vessels.

Enamel is lighter
The enamel is usually the whitest part of the tooth. It is actually a transparent substance. The dentine below it is more yellow and not as transparent as enamel. As a result, the colour of the dentine reflects through the enamel, giving the tooth a yellowish tinge. The more yellow the dentine, the more colour the tooth has, and vice-versa. This is the natural appearance of the tooth.

  
When light reaches a tooth, it is reflected through the transparent enamel. The underlying dentine gives the tooth its colour. If the dentine is lighter the tooth will appear lighter and whiter.

Can you paint the teeth white?
Painting a layer of white on a tooth would make it appear unnatural due to the loss of the enamel’s natural transparency.

The colour of our teeth changes over time. Even though the enamel is hard, there are microscopic cracks that allow substances to enter the tooth. Sometimes, the gum recedes and exposes the root surface that consists of dentine and cement. This makes the tooth appear more yellow, especially in the part closer to the gum line.

The natural colour of a tooth is created by a reflection of light travelling through the transparent enamel. The colour of the tooth is a combination of its different layers, including the dentine. If a dentist painted one tooth white it would appear white, but completely unnatural.

At the gum line there is no enamel. If the gum recedes, the more yellow dentine becomes visible.

 
Crowns made of an opaque inner core (as above to the left with gold below the ceramic material) often get a dark halo around the border towards the gum (arrows). This I because the light that should pass through the tooth and reflect doesn’t get through and hence makes the area appear darker. To the right the metal ceramic crown has been changed to a full ceramic crown with a more translucent core that reflect the light more natural (arrows). 

Mimicking a natural look
A repair or replacement of a damaged tooth must mimic the layers of enamel and dentine. Certain materials like ceramics are better at mimicking a natural tooth.

Alternatives
Today, bleaching procedures help rectify yellow and discoloured teeth. Your dentist will be able to guide you on what is possible and best for your dental health.