Crown retention for non-retentive preparations using adhesive resin cements

This study examines the effect of preparing teeth with six varying convergence angles (ranging between 12 and 120 degrees) and height (1 and 2 mm) on the retention of cast gold crowns. Six groups of 4 human premolar teeth were prepared to give a flat occlusal surface in dentine with very short axial wall heights (1 or 2 mm) and variation in axial wall convergence (between 12 and 120 degrees). Impressions were recorded of the prepared teeth and custom castings made using a high copper content precious metal alloy. The castings were luted with an adhesive resin and stored in water at 37 degrees C for 24 hours prior to determining the pull-off force in an Instron Universal testing Machine at a cross head speed of 1mm min(-1). Twenty two of the twenty four tested specimens failed within the dentine of the tooth, irrespective of preparation orientation. Statistical testing using ANOVA demonstrated that there were no differences between the bond strength values for any of the preparation convergence angles or between preparations with 1 and 2 mm axial wall heights. This suggests that attachment strength of adhesively bonded castings with minimal axial wall height preparations is not influenced by the convergence angle of the preparation. The attachment strength exceeded that cohesive strength of the underlying dentine in nearly all of the adhesively luted restorations.