Influence of the Processing Method on the Nano-Mechanical Properties and Porosity of Dental Acrylic Resins Fabricated by Heat-Curing, 3D Printing and Milling Techniques

Background: Acrylic resin-based materials are a versatile category used extensively in various dental applications. Processed by current modern technologies, such as CAD/CAM technologies or 3D printing, these materials have revolutionized the field of dentistry for the efficient creation of dental devices. However, despite their extensive use, a limited number of comparative studies exist that investigate how different processing methods—such as traditional techniques, 3D printing, and CAD/CAM milling—impact the nano-mechanical behavior and internal porosity of these materials, which are critical for their long-term clinical performance. Objectives: The purpose of this study is to evaluate the nanomechanical properties (hardness, elasticity, and stiffness) and micro-porosity of acrylic resin-based materials indicated for temporary prosthodontic appliances manufactured by new technologies (milling, 3D printing) compared to traditional methods. Methods: The hardness, elasticity, and stiffness measurements were performed by the nano-metric indentation method (nanoindentation), and the quantitative morphological characterization of the porosity of the acrylic resin samples obtained by 3D printing and CAD/CAM milling was performed by micro-computed tomography. Results: According to nanomechanical investigations, CAD/CAM milling restorative specimens exhibited the greatest mechanical performances (E~5.233 GPa and H~0.315 GPa), followed by 3D printed samples, while the lowest mechanical properties were registered for the specimen fabricated by the traditional method (E~3.552 GPa, H~0.142 GPa). At the same time, the results of porosity studies (micro-CT) suggested that 3D printed specimens demonstrated a superior degree of porosity (temporary crown—22.93% and splints—8.94%) compared to CAD/CAM milling restorative samples (5.73%). Conclusions: The comparative analysis of these results allows for the optimal selection of the processing method in order to ensure the specific requirements of the various clinical applications.