The effects of abutment taper, length and cement type on resistance to dislodgement of cement-retained, implant-supported restorations.

Purpose: The purpose of this study was to compare the effect of 20 degrees and 30 degrees of total occlusal convergence (TOC), the occlusocervical dimension, and the type of cement on the tensile resistance to dislodgement of cement-retained, implant-supported restorations.

Materials And Methods: Cylindrical preparations with TOC angles of 20 degrees and 30 degrees and occlusocervical dimensions of 4 mm (S) and 8 mm (L) were made through a machining process. The cylinders had a shoulder finish line of 1.0 mm in depth. Eight impressions were made of each machined cylinder and poured in type IV dental stone, for a total of 32 dies. Die spacer was applied to each die. A master wax pattern was designed, and the 32 wax patterns were marginated, invested, and cast in type IV gold alloy (n = 8). The gold crowns were cemented with Fleck's cement (zinc phosphate cement), Temp-Bond (zinc oxide eugenol cement), Temp-Bond plus Vaseline (30% by weight), and IMProv temporary cement (acrylic/urethane cement) under a 10-kg load and placed in a humidor at 37 degrees C for 1 hour before testing. A uniaxial tensile force was applied to the crown using an Instron machine with a crosshead speed of 5 mm/min until cement failure occurred. Analysis of variance models were fit to determine the effect of TOC, occlusocervical dimension, and cement type of the restorations on the mean tensile strength.

Results: For each type of cement, the mean tensile strengths were significantly higher at 20 degrees of TOC and 8 mm of occlusocervical dimension compared with the other preparations. At this preparation, IMProv had the highest mean tensile resistance to dislodgement (47.7 +/- 8.4 kg), followed by Fleck's (38.2 +/- 8.8 kg), Temp-Bond (35.9 +/- 4.4 kg), and Temp-Bond plus Vaseline (8.2 +/- 2.2 kg). No statistically significant difference was observed between Temp-Bond and Fleck's zinc phosphate cement when 20 degrees of TOC and 8 mm of occlusocervical dimension was used. There was no statistical difference in the mean tensile resistance to dislodgement for Temp-Bond plus Vaseline with different preparation designs (p > 0.05) except when 20 degrees of TOC and 8 mm of occlusocervical dimension was used. The mean tensile strength was significantly different between Temp-Bond and Temp-Bond plus Vaseline for each of the 4 preparation designs (p < 0.05). Among the cements tested, IMProv exhibited higher values, which were statistically different (p < 0.05). Restorations with greater occlusocervical dimension and less TOC exhibited higher tensile resistance to dislodgement.

Conclusions: Preparations with 20 degrees of TOC and 8 mm of occlusocervical dimension had significantly higher mean retentive values for all of the cements tested. Significant differences in mean tensile strength were observed, with the highest tensile resistance seen with IMProv, followed by Fleck's cement, and the lowest tensile resistance seen with Temp-Bond plus Vaseline.