Effects of cement on crown retention.

This study indicates that the frequent clinical technique of permanently cementing a crown without removing all traces of a temporary ZOE cement from the tooth has no adverse effect on retention. Circumferential grooving of the tooth preparation did not significantly increase retention. In contrast, cutting a shallow groove in the crown significantly improved retention. Therefore, it would appear that the grooving of the gold casting might be advantageous in conditions where the crown restoration has minimal retention. Significant improvement in retention with grooving of the restorations was accompanied by a change in the location of the cement film. The cement was retained in the crown coronal to the groove rather than on the tooth. This finding was interesting, since previous retention studies showed that adhesive failure occurred at the metal-cement interface. From this data it appears that a primary factor of crown retention is the adhesion or mechanical interlocking of the cement to the crown. This would explain why small variations in cement film thickness, such as those due to the use of die relief, have little effect on retention. In view of these findings, the current concepts on cement retention and cement adhesiveness should be reevaluated.