Two-step K⁺/Rb⁺ ion exchange enabling high mechanical properties and brittle-ductile transition in 3D-printed dental lithium disilicate

Two-step K/Rb ion exchange (IE) enables high exchange depth and high stress levels. • Residual stress originates from volumetric expansion of the amorphous phase. • Mechanical properties of lithium disilicate (LD) are effectively enhanced via IE. • IE induces a transition from brittle to ductile damage mode in 3D-printed LD. • 3D-printed LD veneers after IE show an increased crack-initiation threshold. To improve the mechanical reliability of thin-walled lithium disilicate (LD) veneers, this study developed a strengthening strategy that integrates vat photopolymerization (VP) with a two-step ion-exchange (IE) process. VP was employed to fabricate thin-walled LD structures, eliminating machining-induced damage, while a sequential K⁺/Rb⁺ IE process achieved both sufficient IE depth and compressive stress, overcoming their conventional trade-off. The two-step IE process increased the flexural strength of LD by 52.0% to 448.6 ± 31.5 MPa and improved the fracture toughness by 80.4% to 2.64 ± 0.10 MPa m 1/2 . The significant enhancement in mechanical performance was mainly attributed to a 349% increase in compressive stress (CS), reaching 141.9 ± 4.4 MPa. The atomic force microscope revealed that the ultrahigh CS was attributed to the volumetric expansion of an amorphous phase. Under scratching loads of 100 mN above the brittle-ductile transition threshold (∼70 mN), the coefficient of friction of IE-processed LD increased by nearly 50%, indicating a transition in energy dissipation from brittle crack initiation to localized plastic deformation. Overall, the VP-fabricated LD, after undergoing the two-step IE processing, exhibits markedly enhanced strength and toughness. This improved mechanical performance effectively resists crack initiation and propagation caused by sharp contacts, thereby contributing to the superior long-term reliability of the LD veneers in the oral masticatory environment. Download: Download high-res image (510KB) Download: Download full-size image