Flexural Strength and Hardness Analysis of 3D-Printed vs. Milled Resin Composites Indicated for Definitive Crowns

The growing use of 3D-printed dental restorations has created a need to understand how the mechanical behaviour of definitive 3D-printed resin composites compares with milled counterparts. This study compared the mechanical properties of 3D-printed and milled definitive crowns and examined the factors affecting these properties. The 3D-printed materials (Permanent Crown Resin: PCR, VarseoSmile Crown Plus: VCP, and Crowntec: CT) and milled blocks (Brilliant Crios: BC, Shofu Block HC: HC, and Grandio Blocs: Gr) were tested. Filler content was evaluated using the ash method (<i>n</i> = 3), and flexural strength (FS) and flexural modulus (E<i>_f</i>) were assessed using a three-point bending test (<i>n</i> = 10). Martens hardness (HM), indentation modulus, and Vickers hardness were determined using the Martens indentation test (<i>n</i> = 24). Vickers hardness was also measured with the Vickers indenter tester (<i>n</i> = 24). Statistical analysis investigated differences between materials and methods, and correlations between filler weight and mechanical properties (α = 0.05). FS of milled blocks, Gr (244.5 MPa), BC (225.5 MPa), and HC (155 MPa), were higher than that of the 3D-printed resin composites: PCR (143.6 MPa), CT (140.9 MPa), and VCP (128 MPa). Measured mechanical properties of the milled blocks were significantly higher than those of the 3D-printed materials (<i>p</i> < 0.001). HM of the 3D-printed materials was similar (≈217 N/mm²), while HM of the milled blocks ranged from 434.7 to 858.4 N/mm². The 3D-printed materials showed comparable properties; however, milled blocks differed significantly (<i>p</i> < 0.05). Filler content was strongly associated with FS and HM. Within the limitations of this study, the milled resin composites showed markedly higher strength and hardness, while 3D-printed materials may be suitable for low-to-moderate load clinical scenarios. Further studies to evaluate the long-term performance of the 3D-printed resin composites are recommended.