Exploratory Investigation of Biaxial Flexural Strength and Fracture Characteristics of 3D-Printed Leucite-Reinforced BisGMA/TEGDMA Composites

The mechanical properties of 3D-printed dental resin materials are critical for their clinical success. Unfilled resin materials used in 3D printing for dental applications often exhibit reduced biaxial flexural strengths (BFSs) due to differences in material composition and printing processes. This article aims to evaluate and compare the BFS and fractographic characteristics of SLA-printed unfilled resin (UR) and composite (C) materials, and to identify factors influencing their mechanical properties.Two experimental groups were fabricated: an unfilled resin group (URG) and a leucite-reinforced composite group (CG; 35 wt% filler). The filler percentage is in an attempt to explore the possibility of slightly surpassing an already 3D printed 30 wt% ceramic composite concentrate-resin. Disc-shaped specimens (<i>n</i> = 20 per group) were printed using SLA and post-cured according to the manufacturer's recommendations. BFS was measured using the ball-on-ring test. Weibull analysis and scanning electron microscopy (SEM) were used to assess strength reliability and fracture features. X-ray diffraction (XRD) was used to confirm the crystalline phase of the leucite filler against International Centre for Diffraction Data (ICDD) standards. One-way ANOVA and Tukey's multiple comparisons were conducted after confirming data normality and homogeneity of variances at <i>p</i> < 0.05.XRD analysis confirmed the presence of tetragonal potassium aluminum silicate (leucite) phase, aligning with ICDD reference codes. The mean BFS of the URG (228.83 MPa) was significantly higher than that of the CG (91.62 MPa). The URG exhibited brittle fracture with various hackle markings and minimal phase delamination, indicative of high flexibility and energy absorption due to increased TEGDMA ratio. The CG showed lower BFS values, with fractographic features such as porosities, minor filler particle agglomeration, and phase delamination due to settling filler particles. SEM images revealed a homogeneous distribution of filler particles in CG but also showed micro-cracks and voids that compromised its mechanical integrity. Weibull analysis revealed a higher Weibull modulus for URG (10.26) compared with CG (5.48), indicating more consistent mechanical performance.The URG showed significantly higher BFS than the CG, likely due to greater elastic deformation and energy absorption from its higher TEGDMA content. In contrast, the CG's lower BFS was linked to porosity and filler particle settling during printing. SEM analysis revealed challenges in achieving uniform filler distribution and adequate curing. Future studies should focus on optimizing filler properties, conversion rates, and incorporating nanofillers to enhance the flexural strength of 3D-printed dental composites.