Steven, T. Fredeen
| Steven, T. Fredeen |
Steven T. Fredeen1, Niyati Reddy1, Sonaj Vardhaman1, Sukirti Dhital2, Jeongho Kim2
Mark Wolff1, Yu Zhang1
1Preventive and Restorative Sciences, University of Pennsylvania, School of Dental Medicine; 2Civil Engineering, University of Connecticut
Introduction
Porcelain-veneered-zirconia (PVZ) and Porcelain veneered lithium disilicate (PVLD) restorations have risen in popularity due to improved esthetics and biocompatibility over their PFM predecessors. However, the porcelain veneer faces the problem of chipping and delamination associated with residual stresses created during the firing process. Unfortunately, there is not a sound experimental method to directly measure residual stresses in anatomically-correct restorations. Thus, VFEM has been utilized to predict residual stresses in dental restorations. This study aims to provide a direct experimental validation to Viscoelastic Finite Element (VFEM) stress analysis of PVZ crowns using a lift-off method.
Methods
PVZ and PVLD anatomical crowns (n = 3) were CAD/CAM fabricated with an average core thickness of 0.7 mm. Porcelain, ~1.4 mm in thickness, was hand veneered using a slow cooling profile. Each crown was embedded in epoxy resin and polished down parallel to occlusal plane to obtain a flat cusp surface for Vicker’s indents (load = 4.9 N dwell time = 5 sec). The embedded crowns were further polished down incrementally and indents were placed on exposed cusps of each layer. The average crack lengths in transverse and radial direction (parallel and perpendicular to veneer core interfaces) were measured using optical microscopy to obtain the experimental stress measurements. VEFM was used to compare the predicted residual stresses by the lift-off method with the experimental measurements.
Results
Similar stresses ( ̴20 MPa), mainly in compression, were seen in experimental measurements through the layers within one-third of porcelain thickness.
Conclusion
The agreement between experimental measurements and VFEM predictions boosted our confidence in VFEM stress analysis. Once validated, the VFEM model can then be used to predict true internal stresses.