A Biomimetic Li₂Si₂O₅ Composite with High Energy Absorption for Endocrowns

Endocrowns represent a minimally invasive treatment option for endodontically treated teeth. However, in the anterior dentition, they are more likely to cause fractures in the abutment teeth due to the influence of lateral forces. Developing endocrowns that closely replicate the mechanical properties of the different components of natural teeth offers a promising strategy for improving the biomechanical performance of single-component restorations. Therefore, this study reports a novel multilevel ceramic composite achieved through fabrication of a diamond-topology lithium disilicate (LD) ceramic scaffold using vat photopolymerization, followed by toughening through potassium nitrate ion exchange (IE) and epoxy resin infiltration. This ceramic composite exhibited mechanical properties close to those of human dentin and therefore can prevent catastrophic stress-induced fractures of the abutment teeth due to enhanced toughness. Heating treatment and phase analyses were conducted to determine the optimal debinding and sintering parameters. Residual stress measurements, flexural strength testing, and microhardness evaluations were performed to assess the mechanical properties of the IE-toughened LD. In addition, the elastic modulus, compressive strength, and toughness of the ceramic composite were comprehensively characterized, using Vita Enamic and human dentin as reference materials. With the optimization of the heat-treatment and IE processes, the ceramic composite achieved a maximum compressive strength of 217 ± 11.8 MPa and a minimum elastic modulus of 3.7 ± 0.1 GPa, similar to the elastic modulus of human dentin (1.9 ± 0.4 GPa). In addition, the 0.25RD (relative density) composite group showed a maximum energy absorption of 37.7 ± 1.9 MJ/m³. The quasi in situ compression test revealed that the enhanced toughness primarily resulted from microcrack aggregation, interface delamination, and macroscopic crack splitting.