Sonaj Vardhaman
| Sonaj Vardhaman |
Sonaj Vardhaman1, Larissa Alves2, Camila Rodrigues2, Brian Lawn3
1Department of Preventive and Restorative Sciences, University of Pennsylvania, School of Dental Medicine ; 2Department of Dental Materials and Prosthodontics, Sao Paulo State University; 3Material Measurement Laboratory, National Institute of Standards and Technology
Introduction
Flaws produced in the restoration that result in fracture can be intrinsic (introduced during ceramic processing) or produced by occlusal adjustments with burs or during mastication. These sharp defects generate stress concentration in the dental restorations which can damage the ceramic surface, making them behave differently since it is not as strong as its initial form and ultimately affecting the longevity of the restoration. This study evaluated the damage tolerance of CAD/CAM ceramics when subjected to sharp defects induced from controlled indentation with different loads.
Methods
Disc shaped specimens were obtained from five ceramics [Vitablocks Mark II (FEL), Empress CAD (LEU), IPS e.max CAD (LDS), Zpex (3Y-TZP) and Zpex Smile (5Y-PSZ)]. The samples were cut, sintered and polished to 1 μm finish. Each sample was subjected to a Vickers indentation with loads ranging from 0.1 to 100 N. The samples were subsequently loaded in a piston-on-three-ball test set-up. Optical microscope images were taken prior to as well as after the bending test. Flexural strength versus indentation load data was plotted to determine the strength degradation behavior.
Results
All ceramics underwent strength degradation due to damage. From the strength drop point, 3Y-TZP and FEL degraded 46% while 5Y-PSZ, LDS, and LEU degraded ~64-69%. Optical images revealed although low loads did not degrade the strength, they were sufficient to initiate cracks. A given indentation load was observed to produce different size damages in each material.
Conclusion
3Y-TZP and feldspathic ceramics are the materials that tolerate damage without compromising their strength and degrade less once the strength starts to drop. The strength of 3Y-TZP is higher than other ceramics after indentation loads, followed by 5Y-PSZ, lithium disilicate, leucite-reinforced, and feldspathic.