The first method of capping exposed pulps, using gold foils, was described by Pfaff in 1756. Thereafter, numerous agents for direct pulp capping have been recommended. Until the end of the 19th century, most materials were used empirically with the idea that the pulp tissue must be irritated by etching or cauterization to heal. Later, more attention was drawn to disinfecting agents, because it became obvious that microorganisms were the reason for pulp inflammation - but these agents were cytotoxic. Since insufficient or inappropriate diagnoses were made before treatment, even necrotic pulps were capped. The first scientific clinical study to compare different capping materials was made by Dätwyler in 1921, whereupon zinc oxide-eugenol showed the best results. One year later, Rebel performed the first animal experiments with disastrous results, so he regarded the exposed pulp as a doomed organ. In 1920 Hermann, introduced calcium hydroxide for root canal fillings. Between 1928 and 1930 he studied the reaction of vital pulp tissue to calcium hydroxide to prove that it was a biocompatible material. Since then, calcium hydroxide has been recommended by several authors for direct pulp capping, but it took until the middle of 20th century until it was regarded as the standard of care.