Effects of intra-core mechanical interlocks and cement type on full crown retention

This study compared the retention of full cast crowns over cores of amalgam or a Bis-GMA composite resin when cemented with a Bis-GMA composite resin cement or a zinc phosphate cement. The surfaces of two groups of Bis-GMA composite cores were mechanically altered with a groove or dimples to provide physical retention; two other groups were either etched with 1.23% acidulated phosphate fluoride (APF) or exposed to a zinc oxide-eugenol interim luting agent before crown cementation. Control groups of unaltered composite or amalgam core served as comparison standards. The zinc phosphate cement provided significantly greater retention with the amalgam core than with any of the composite cores. The APF-treated composite cores had the least retention of any of the zinc phosphate cementations. Cementation failure over the composite cores was at the core surface. Crown retention over the control and dimpled-surface composite core with the resin cement was twice that with zinc phosphate, and significantly greater than retention of castings cemented with the resin cement over amalgam cores. Retention over amalgam cores was significantly greater with zinc phosphate cement than with the composite resin cement.