Clinically undetectable leakage around amalgam and composite restoration, normally referred to as microleakage, will cause a bacterial invasion of the dentinal tubules. Such an invasion demands precautions. Although without a protective base many patients do not have complaints, this does not imply that the pulp is not affected. Therefore, dentin which is exposed during dental treatment should always be sealed hermetically. Of the lining materials, calcium-hydroxide and glass-ionomer are strongly favourable among the general practitioners. Disadvantages of these popular materials justify, however, the conclusion that other linings are to be preferred.