20 November 2019

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Resistance to the cyclic fatigue of two CAD/CAM ceramic materials: preliminary analysis on simulators

Massimo Gagliani

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Premolars are the most difficult elements to restore and have a high failure rate due to their anatomical position and the forces they undergo. 
Therefore the choice of the material to restore these elements must be well thought out. With the introduction of the CAD / CAM system, different materials are available with the aim of ensuring resistance and aesthetics to the teeth. Among these we find lithium disilicate (LD) and ceramic infiltrated polymer (PICN). 
But which of these two guarantees a better resistance to cyclic fatigue?
Homaei et al in their study try to answer to this question and they investigated the resistance to cyclic fatigue of restored premolars with these two different types of dental CAD/CAM ceramics.

Materials and Methods
A restored premolar with a full coverage crown has been digitized. The volumetric shape of the teeth and crown tissues has been recreated in Mimics®. They were transferred to IA-FEMesh for mesh generation and the model was analyzed with Abaqus. Through these software combinations it was possible to simulate a clinical situation to assess the distribution of stress on the restorations themselves, subsequently it was possible to hypothesize the duration of the premolars restored with the two different materials

Results
The expected duration was 1,231,318 cycles for LD with a fatigue load of 1,400 N, while that for PIC was 475,063 cycles with a load of 870 N. The peak value of the maximum principal stress occurred in the occlusal contact areas ( antagonist) (LD: 172 MPa and PIC: 96 MPa) and in the central fossa (LD: 100 MPa and PIC: 64 MPa) and for both ceramics these were the areas of failure most often seen in the experiment. As far as the adhesive layer was concerned, the maximum shear stress was observed in the shoulder area (LD: 53.6 MPa and PIC: 29 MPa).

Conclusion 
The resistance to cyclic fatigue and the failure modes of the ceramic crowns are better in lithium disilicate group than PICN ones. So, for what concern premolars restorations, it's better to choose LD than PICN.

For additional informations: Numerical fatigue analysis of premolars restored by CAD/CAM ceramic crowns