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&#95;PM, ZLS&#95;PM) or molar (LD&#95;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&#95;MO groups presented the highest failure values (808.7 to 947.9 N), followed by the LD&#95;PM (525.8 to 722.8 N) and ZLS&#95;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&#95;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.