For deep preparations, the base indicated below composite is:

For deep preparations, pulpal medications like calcium hydroxide should be used. Previously, in a deep preparation, a calcium hydroxide liner would be placed first. Then a base would be added to provide mechanical support and stress distribution. The base would be covered with varnish at the same time the tooth structure walls were varnished (except that when using zinc phosphate cement the varnish would be applied before the cement), and the amalgam would be placed. Currently, light-cured calcium hydroxide and glass-ionomer materials are being used to both line and base relatively deep preparations. Sturdvent ed 4, pg 174