Monolithic hybrid abutment crowns: Influence of crown height, crown morphology and material on the implant-abutment complex.

PURPOSE: This in vitro study investigated the influence of material selection, crown morphology, and vertical crown height on the biomechanical behavior of screw-retained monolithic hybrid abutment crowns (HACs).

METHODS

Ninety implants were embedded in accordance with ISO standard 14801; ninety HACs were mounted (N=90). Monolithic crowns with varying group-specific designs were luted using titanium bases. HACs were fabricated from monolithic lithium disilicate ceramic (LD) or zirconia-reinforced lithium silicate ceramic (ZLS). The crown morphology was either maxillary premolar (LD_PM, ZLS_PM) or molar (LD_MO). The three groups were further divided into three subgroups of ten specimens, each designed with a small (7.5 mm), middle (10.5 mm), and high (13.5 mm) configuration of crown heights (N=10). A load-to-failure test at 30° off-axis was conducted using a universal testing machine until failure. For statistical analysis, Kolmogorov-Smirnov and Mann-Whitney U tests were conducted (P < 0.05).

RESULTS

All LD_MO groups presented the highest failure values (808.7 to 947.9 N), followed by the LD_PM (525.8 to 722.8 N) and ZLS_PM groups (312.6 to 478.8N). A comparison between LD and ZLS materials (P < 0.001) as well as the crown morphology (P < 0.001) showed significant differences in failure values. The values in the subgroups of ZLS_PM (low, middle, high) decreased as the crown height increased. The fracture modes showed no consistent patterns across the test groups.

CONCLUSIONS

Material selection, crown morphology, and vertical crown height appear to be important factors that may influence the clinical failure values and patterns of screw-retained single implant crowns.