Auxiliary retention for complete crowns provided by cement keys.

1. Cement keys were an effective means of increasing the retention of complete cast gold crowns to preparations in extracted teeth. 2. Single grooves placed in either the dentin or in the crown alone were not effective in increasing retention in 30-degree crowns. In 7-degree crowns, a single groove in the crown gave better retention than a single groove in the dentin. 3. Crowns with a 7-degree taper had greater retentive strengths than 30-degree crowns treated identically. The retentive strength of 7-degree crowns with cement keys approached the tensile strength of zinc phosphate cement.