An indirect pulp cap is usually done to take the place of a root canal in very decayed teeth. It is made when most of the decay on the permanent tooth is removed. When a dentist finds extensive decay very close to the pulp (nerve,) the risk of the pulp exposition by the infected decay is high. This infection will result in the need for a root canal. In this case dentists leave the last little bit of decay in there and place a sedative temporary filling. Usually Intermediate Restorative Material (IRM) is used as a temporary filling material until the patient is ready for a proper, more permanent restoration.
After a few months, the temporary filling and the decay are removed. If the tooth has no signs or symptoms of pulpal necrosis or abscess and has a good blood supply, the pulp may repair itself. When the bulk of the nasty decay is removed and just a small part is left but is limited, it has no nourishment from the mouth, so how is this possible? After this procedure the remaining decay can be removed without pulp exposure.
This dental procedure is not always effective, but in some cases the dentist should attempt it; it is more likely to work in a younger patient.
Unlike an indirect pulp cap, during a direct one, an actual exposure of the pulp takes place. For the stimulation of the secondary dentin formation a medicament like Calcium hydroxide or Mineral Trioxide Aggregate (MTA) is placed inside. With a direct pulp cap no evident decay is left, but it leads to small mechanical or traumatic exposures.