Dental Education Lecture: Tooth Whitening
We always want our teeth to be as white as possible, like Hollywood movie stars. Sometimes we wonder why our teeth look so yellowish near gum line (at the neck of the tooth, see Fig. 1 of Bleaching for Tetracycline Teeth). We are going to use illustration to show you why and introduce two types of tooth whitening.
Fig.1 and 3 are the front and side views of a lower front tooth, respectively. Every tooth has two major portions: crown and root. Between them is the neck (Fig.1). The neck is pointed by two arrowheads in Fig.3. Fig.2 and 4 are cross sections of Fig.1 and 3, respectively. There are three hard tooth structures: enamel, dentin and cementum and one soft tissue: pulp (commonly known as the nerve). The bulk of the tooth is the dentin, which is somewhat yellowish, whereas the enamel is transparent (clear, no color). Since the tooth is widest at the neck, the area looks the most yellowish if we look at the tooth as indicated by two long arrowheads in Fig.4. This is pretty normal.
But as we get old and/or do not pay to attention to oral hygiene for a long time, stain from our food and drink gradually deposits on our tooth surface and penetrates into our tooth structure (arrowheads in Fig.5). After we apply bleaching (whitening) material to the surface of our tooth (arrowheads, Fig.6) for a while, the tooth returns to its normal color. We call this type of bleaching as external.
Sometimes our tooth changes color because something is wrong inside it as shown in Fig.7. Our pulp (nerve) is dead (black). The dying pulp releases nasty stain to make our tooth dark inside out (dark gray). Bleaching is not effective if we apply bleaching material to the surface of the tooth. So we need to adopt a special bleaching mode: called internal.
The internal bleaching starts with root canal therapy to get rid of dead nerve, source of tooth darkening. The doctor makes a hole in the back of the tooth (arrowhead, Fig.8), removes the dead nerve, enlarges the canal, rinses the canal repeatedly with household bleach and fill the space with a brown material. Steps of root canal therapy are discussed in detail in lectures Root Canal Therapy II and Pain after Root Canal. Repeated rinsing with household bleach helps whitening a lot (light gray in Fig.8), but it is not enough and the dark color will rebound. The doctor applies or teaches you to how apply bleaching material into the middle of the tooth (arrowhead in Fig.9). The tooth further returns to its normal color (yellow). The last step of treatment is to place white filling material in the hole (double arrow, Fig.10), making the tooth look whiter. See cases of tooth whitening here.
Xin Wei, DDS, PhD, MS 1st edition 02/01/2009, last revision 03/31/2010