Keys to Clinical Success with Pulp Capping: A review of the literature by Hilton is an excellent review article on both direct and indirect pulp capping. Operative Dentistry, 2009; 34-5, 615-625

The author indicated several key points that must be considered when evaluating studies on pulp capping. First, clinical pulp capping studies rarely reflect clinical reality.  Many are carried out on healthy teeth that are planned for orthodontic extraction. Second, the histologic pulp status of a tooth cannot be determined by clinical signs and symptoms.  It is also noted that studies in animals are not necessarily predictive of human outcomes.

An electron micrograph of calcium hydroxide

The conclusions to the review were:

1. Avoid exposing the pulp. The chances for tooth survival are excellent if the tooth is asymptomatic and well sealed, even if residual caries remains.
2. Control haemorrhage with water, saline or sodium hypochlorite. Water and saline are the most benign to the pulp; sodium hypochlorite is best at controlling haemorrhage and disinfecting.
3. ZOE, GI/RMGI and adhesives are poor direct pulp-capping agents and should be avoided for this application.
4. MTA demonstrates comparable results to calcium hydroxide as a direct pulp cap agent in short-term data.
5. Calcium hydroxide remains the “gold standard” for direct pulp capping. It has the longest track record of clinical success, is the most cost-effective and is the likely effective component in MTA.
6. Provide a well-sealed restoration immediately after pulp capping. This will provide protection against ongoing leakage and bacterial contamination that can compromise the success of the pulp cap.

It is also worth pointing out that MTA is hideously expensive!