The complexity and importance of the biological structures that form the so-called pulpal dentinal complex call for considerable accuracy during restorative procedures. In practice this means accurate techniques and appropriate dental materials, able to combine protective and restorative qualities, and above all, offering biocompatibility. In order to analyze this property, a number of international studies suggest the use of sequential tests divided into three different levels: initial tests, secondary tests and usage tests in the form of in vivo and in vitro tests to observe and simulate the biological reactions to dental materials used in particular tissues. The authors publish a review of the literature regarding the biocompatibility of intermediate materials regarded as useful aids in restorative dental practice; these include paints, liners and cavity bases made from Ca(OH)2, ZOE cements, zinc phosphate, polycarboxylic compounds, glass ionomers, bonding agents and mordents. The chemical, biological, clinical and utilization parameters are outlined for each compound, paying special attention to the problem of biocompatibility and indicating the pulpal reactions reported over the past decade in connection with their use. In conclusion, while waiting for a standard international document to codify evaluation methods and classify the results obtained, these experimental data can be used to programme a more correct and safer use of materials.