Stress behaviors of ceramic restorations produced from different preparation designs and various lithium disilicate materials under vertical and oblique forces: Finite element analysis

Objective: Evaluate the stress behavior and estimated lifespan of different occlusal veneer preparation and lithium disilicate ceramic restorations on maxillary premolars under vertical and oblique forces using finite element analysis (FEA). Method: 30 different study groups were created based on different preparation designs applied to maxillary premolars (O: Occlusal preparation, BO: Beveled occlusal preparation, CO: Chamfer margin occlusal preparation, BV: Buccal veneerlay preparation, TK: Full crown preparation) and six different lithium disilicate materials produced for each design (E: IPS e.max CAD, G: GC Initial LiSi, A: Amber Mill, N: Straumann N!ce, T: CEREC Tessera, R: Rosetta SM). After applying a 200 N force in both vertical and oblique directions, Von Mises stress values and distributions in enamel, dentin, and restorations, and the estimated lifespan of the enamel and dentin was evaluated with FEA. Results: It was observed that the preparation designs had the most significant effect on the stress distribution, both under vertical and oblique forces. Under vertical force, the Von Mises stress values were highest in the BVT group and lowest in the ON group for enamel; highest in the BVT group and lowest in the TKN group for dentin; and highest in the BVE group and lowest in the TKR group for restorations. Under oblique force, the Von Mises stress values were highest in the OE and OT groups and lowest in the BVT group for enamel; highest in the ON group and lowest in the TKN group for dentin; and highest in the BVT group and lowest in the TKR group for restorations. Under vertical force, the estimated lifespan of enamel and dentin were found to be similar, while under oblique force, the estimated lifespan of dentin was acceptable, but there was a significant decrease in the estimated lifespan of enamel. Conclusion: The preparation design was found to be the primary factor affecting the amount and distribution of stress, and the variation in lithium disilicate materials did not significantly affect this. The tested lithium disilicate materials were found to be interchangeable in clinical use. It was determined that oblique forces could have more harmful effects on teeth and restorations, potentially leading to failure in dental tissues in a shorter period, and that forces should be directed as vertically as possible to dental tissues. Keywords: preparation design, occlusal veneer, lithium disilicate, finite element analysis, estimated lifespan