Additive manufacturing of lithium disilicate glass-ceramic by vat polymerization for dental appliances

The objectives of this study were to evaluate the mechanical properties of lithium disilicate components produced by additive manufacturing (AM) and to assess the effect of build orientation on the resistance to fracture. Oversized bars were printed with a glass-filled photoactive resin using a digital light processing technique. After sintering and post-processing, flexure and chevron notch fracture toughness bars were obtained in three principal orientations (0°, 45°, and 90°) with respect to the build direction. Mechanical properties were obtained according to the relevant ASTM standards. The hardness, indentation fracture resistance, and elastic modulus were measured for each orientation, and a Weibull analysis was conducted with the flexure responses. Fractography of the fracture surfaces was performed to identify the failure origins. The 0° orientation exhibited characteristic strength, Weibull modulus, and elastic modulus of 313 MPa, 4.42, and 168 ± 3 GPa, respectively, which are comparable to lithium disilicate materials from traditional processes. However, build orientation contributed significantly to the flexure strength, elastic modulus, and Weibull modulus; the characteristic strengths for the 45° and 90° build orientations were 86 MPa and 177 MPa, respectively. The primary contribution to the orientation dependence was the number of residual build layer-related flaws from incomplete union between printed layers. Of note, hardness and the fracture toughness were not dependent on build orientation. AM of lithium disilicate materials can achieve the mechanical properties of materials produced by traditionally processing. Thus, while further process development is warranted, the outlook for dentistry is promising.