Evaluation of Retention of Complete Metal Copings : Effect of Progressive tapers in tooth preparation with Glass Ionomer & Zinc Posphate cement on retention

An in vitro study evaluated the retention of metal copings prepared with five different tapers and luted with two different cements. Eighty extracted human maxillary premolar teeth with measured dimensions & sound surfaces were selected for the study.crown preparations were done using a high speed hand piece which was stabilized by a specially fabricated customized holding device that can be moved in horizontal plane to obtain the desired degree of taper for the preparation. The crown preparation with different tapers 0, 3, 6, 9& 12 degrees respectively were achieved. Die Preparation, wax pattern fabrication, investing the wax pattern & casting procedures were carried out & metal copings were luted with glass ionomer cement and zinc phosphate cement.The breaking load was recorded when the metal coping got separated from the tooth. The force at failure was recorded in kilograms and it was concluded that the use of glass ionomer cement did not result in increased retentive strength over zinc phosphate cement,choice of cement for crowns prepared within this ideal range (3-6 degree taper) might be of limited clinical significance& 50% reduction in retention with 12 degree taper.