Physico-Mechanical Properties of Definitive and Interim 3D Printed Resin Restorative Materials with Different Print Orientations

Abstract

Statement of the problem. Advancements in digital dentistry have significantly transformed dental prostheses manufacturing, particularly with the integration of additive manufacturing technologies such as 3D printing. While additive manufacturing offers advantages like design flexibility, material efficiency, and reduced waste compared to subtractive methods (milled), challenges persist in understanding how parameters such as print orientation influence the physico-mechanical properties of 3D printed resin materials. Moreover, the performance of interim and definitive 3D printed materials over short- and long-term usage remains underexplored. Aim. This study aimed to evaluate the impact of print orientation (0°, 45°, and 90°) on the physical and mechanical properties of definitive and interim 3D printed resin materials after short- and long-term hydrolytic ageing. This research also sought to compare the performance of 3D printed materials with subtractively manufactured materials to identify potential advantages and limitations of additive manufacturing in dental applications. Methods. Specimens were printed with varying print orientations (0°, 45°, and 90°) and compared with milled counterparts. The materials were categorized into definitive and interim types to assess their performance across different applications. A series of standardized tests were conducted to evaluate key physico-mechanical properties, including flexural strength (FS), flexural modulus (FM), surface hardness (HM), indentation modulus (EIT), edge strength (ES), water sorption, solubility, and monomer elution. Specimens were immersed in distilled water and artificial saliva at 37°C for 24 hours and extending up to 3 months to simulate clinical conditions. Advanced imaging techniques, including optical and scanning electron microscopy, were used to analyse surface morphology and fracture behaviour. Filler content was also analysed. Results. Specimens printed at a 90° orientation demonstrated the highest flexural FS and FM both initially and after 3 months of ageing. This orientation also achieved the highest ES after 48 hours of immersion in artificial saliva. However, print orientation did not influence HM or EIT after 3 months of ageing. Sorption and solubility were also influenced by print orientation, while monomer elution was not. All materials printed at 90° met the FS, sorption, and solubility requirements stated by ISO 4049.Definitive 3D printed materials consistently outperformed interim 3D printed resins in terms of mechanical properties. Interim 3D printed materials showed significantly higher sorption, solubility, and monomer elution than definitive 3D printed resins. But most materials were within the ISO 4049 limit. The definitive milled material exhibited the highest mechanical properties among all tested materials except for ES where definitive 3D printed materials performed better than the definitive milled material at a 0.5 mm distance from the edge. Interim milled materials displayed mechanical properties comparable to definitive 3D printed resins. However, ES for all interim materials was not reported, as they exhibited severe plastic deformation under loading. The definitive milled resin exhibited higher sorption compared to the 3D printed resins but demonstrated significantly lower monomer elution. The interim milled material displayed sorption values intermediate between those of the definitive and interim 3D printed materials but with lower monomer elution levels as well. A strong positive correlation was observed between filler weight and FS/FM, as well as between filler weight and HM and EIT. Conversely, filler weight correlated negatively with sorption and solubility. No significant correlation was observed between filler weight and monomer elution and between filler weight and edge strength. Significance. This study underscores the critical role of material type, manufacturing method, and print orientation in determining the physico-mechanical properties of dental restorative materials. Definitive 3D printed materials exhibited performance comparable to or better than interim and milled counterparts in certain parameters, demonstrating their potential for clinical applications in fixed dental prostheses. The superior flexural strength and modulus of definitive 3D printed materials at a 90° orientation underscore the importance of optimizing print orientation to maximize material performance. Furthermore, the adherence of all tested materials printed at 90° to the ISO 4049 standards confirms the clinical viability of this technique. The superior strength and hardness of definitive milled resins compared to their 3D printed counterparts, emphasize their continued relevance in applications requiring high durability. However, the comparable performance of interim milled and definitive 3D printed materials in terms of flexural strength and hardness suggests that 3D printing can serve as an effective alternative to milling for interim applications. The correlation between filler weight and key properties, such as flexural strength, hardness, and modulus, offers valuable insights for material formulation and selection. Meanwhile, the negative correlation between filler weight and sorption/solubility indicates that optimizing filler composition can enhance material longevity by reducing water-related degradation. Additionally, findings on sorption, solubility, and monomer elution confirm the biocompatibility of definitive 3D printed materials, supporting their adoption in restorative dentistry. This research emphasizes the growing potential of 3D printing with opportunities for further innovation in dental applications.