Retention of metal ceramic crowns cemented with resin cements: effects of preparation taper and height.

This study investigated the effect of varying crown preparation taper and height on the retention of metal ceramic crowns cemented with resin cements. In part 1, 32 extracted molars were divided into four groups. All groups received complete-veneer crown preparations, two with a 12-degree wall angle and two with a 35-degree wall angle. Crowns were cemented with zinc phosphate and dentin-bonded resin cements. After 24 hour water storage at 37 degrees C, the crowns were separated in tension. Crowns cemented with zinc phosphate were cleaned and recemented with another dentin-bonded resin cement and after similar storage, the crowns were separated. Mean separation forces of resin-cemented crowns were higher than those of crowns cemented with zinc phosphate cement. Mean separation force of 35-degree crowns cemented with one dentin-bonded resin cement was found to be significantly higher than for the 12-degree crowns cemented with zinc phosphate cement. In part II, 32 extracted molars were divided into two groups of complete-veneer crown preparations (group I preparations were 3 mm high and group II were 5 mm high). Crowns for all teeth were cast and cemented with zinc phosphate. After 48 hours' water storage at 37 degrees C, the crowns were separated in tension. Crowns and teeth were then cleaned and each group was subdivided into 2 equal subgroups. In one subgroup of teeth with 3 mm and in one with 5 mm high preparations, the crowns were recemented with one of the two resin cement systems and the other two subgroups were recemented with the other resin cement. After 48-hour water storage, the crowns were separated. Mean separation forces of the resin-cemented crowns were greater than those of crowns cemented with zinc phosphate. Also, mean separation force of 3 mm crowns cemented with one resin cement was significantly greater than the 5 mm crowns cemented with zinc phosphate. Cohesive dentin fracture on separation was observed with some resin-cemented crowns but never with crowns cemented with zinc phosphate.