Methods: Fifteen regular platform NobelReplace™ 15° Esthetic abutments (Nobel Biocare) were mounted in acrylic resin blocks. Abutments of heights of 5mm, 4mm and 3mm were prepared by machining. A master wax pattern was designed with features to allow for subsequent retention testing of the casting. Fifteen wax patterns were marginated, invested, and cast in type III gold alloy. The castings were cemented with TempBond (zinc-oxide eugenol) or TempBond Clear (urethane resin composite). Samples were subjected to a pull-off test using an Instron Universal testing machine at a crosshead speed of 0.5mm/min. Following testing of standard abutments, circumferential groove preparations (0.25-0.5mm in depth and 0.5mm in height) were made on the axial surface and the abutments sandblasted with 50 microns aluminium oxide. These abutments had their castings cemented and tested using the same sequence. Analysis of variance models were used to determine the effect of height, circumferential grooves and cement type on the retention of restorations.
Results: The mean retentive force for comparable abutments was significantly increased (P<0.001): when circumferential grooves were used for both cements at any given abutment height; when TempBond was used with grooved abutments and when the abutment height was increased from 3mm to 5mm especially for grooved abutments. No statistically significant difference was observed when TempBond Clear was used with a 4mm height abutment.
Conclusion: Within the limitations of this study, it was concluded that circumferential grooves provide a significant increase in retention and TempBond is more retentive than TempBond Clear in this group. It is at the clinician's discretion to select the appropriate abutment design and cement, based on the retentive requirements for the clinical situation.