Why are dental sealants placed on teeth?

Tooth decay is caused by the bacteria found in dental plaque (the white film that forms on a person's teeth). In general, the longer dental plaque remains on a tooth's surface the more likely it will be able to form a cavity. The idea behind brushing teeth is that dental plaque that has accumulated on a tooth's surface is scrubbed off. Some teeth however, related to aspects associated with their anatomy, are harder to clean than others.

Some back teeth, especially molars, can be difficult for a person to clean because the grooves found on their chewing surface (the tooth's "pits and fissures") are deep and narrow. Even though the person brushes their teeth not all of the dental plaque that is present is cleansed off because the individual bristles of their toothbrush are simply too large to gain access into the depths of the tooth's grooves. Because some plaque has not been cleaned away, the tooth is at risk for the formation of decay.

By bonding plastic resin (the dental sealant) into the grooves of a tooth a dentist can create a tooth surface that is smoother. There are no longer any locations on the chewing surface of the tooth that the bristles of a toothbrush can't access and clean. Since dental plaque can be removed more easily and effectively, there is much less of a chance that tooth decay will form.

Another difficulty associated with a tooth having deep grooves is that in some instances the thickness of the enamel that lies at the base of the grooves is thinner than the enamel that encases other aspects of the tooth. This means that not only can deep narrow grooves make it more likely that tooth decay will form (because the tooth can't be cleansed effectively) but also that any decay that does form will have an easier time of penetrating through enamel layer (because it is less thick) and progressing on into the inner aspects of the tooth.