Effect of crown to titanium base ratio and force angle on the biomechanical behavior of dental implants with CAD/CAM zirconia and lithium disilicate crowns: a finite element analysis

Objectives: This study investigates how titanium-base (Ti-base) abutment height, crown design, and force angulation affect biomechanics in an anterior single-implant restoration, using finite element analysis. 

Material and Methods: A three-dimensional anterior maxilla model was constructed with linear elastic properties. Two Ti-base heights (3.5, 5.5 mm) and two crown heights (8, 11 mm) were tested as monolithic zirconia or bilayer (zirconia core veneered with lithium disilicate). A 146 N load was applied at the cingulum at 45° or 65°. von Mises stress (VMS) was computed in the crown, abutment, and surrounding bone. 

Results: A 3.5 mm Ti-base with an 8 mm monolithic zirconia crown (SSZ) produced the lowest crown and abutment VMS. The highest crown VMS occurred in the 11 mm bilayer crown on a 5.5 mm Ti-base (LLZEX) at 45°, while the highest abutment VMS occurred in the 3.5 mm Ti-base with an 8 mm bilayer crown (SSZEX) at 65°. An increase in crown height raises crown stresses, whereas the impact of abutment height depends on configuration and angle. In bone, 45° loading increased VMS compared with 65° across all models. 

Conclusions: In anterior single-implant models, the lowest restoration stresses were achieved with a short crown on a 3.5-mm Ti-base and monolithic zirconia. Long crowns (11 mm) increased crown stresses, and abutment height should be tailored to material and anticipated loading direction rather than adjusted by a single rule. Oblique loading consistently raised bone stress compared with 65°, underscoring the need to optimize for axial force transmission.