Finite element analysis of stresses in fixed prosthesis and cement layer using a three-dimensional model.

Context: To understand the effect of masticatory and parafunctional forces on the integrity of the prosthesis and the underlying cement layer.

Aims: The purpose of this study was to evaluate the stress pattern in the cement layer and the fixed prosthesis, on subjecting a three-dimensional finite element model to simulated occlusal loading.

Materials And Methods: Three-dimensional finite element model was simulated to replace missing mandibular first molar with second premolar and second molar as abutments. The model was subjected to a range of occlusal loads (20, 30, 40 MPa) in two different directions - vertical and 30° to the vertical. The cements (zinc phosphate, polycarboxylate, glass ionomer, and composite) were modeled with two cement thicknesses - 25 and 100 μm. Stresses were determined in certain reference points in fixed prosthesis and the cement layer.

Statistical Analysis Used: The stress values are mathematic calculations without variance; hence, statistical analysis is not routinely required.

Results: Stress levels were calculated according to Von Mises criteria for each node. Maximum stresses were recorded at the occlusal surface, axio-gingival corners, followed by axial wall. The stresses were greater with lateral load and with 100-μm cement thickness. Results revealed higher stresses for zinc phosphate cement, followed by composites.

Conclusions: The thinner cement interfaces favor the success of the prosthesis. The stresses in the prosthesis suggest rounding of axio-gingival corners and a well-established finish line as important factors in maintaining the integrity of the prosthesis.