Optical and mechanical characterization of 3D-printing polymer-based resin materials for fixed dental restorations: influence of building orientation

Abstract

Color and optical properties of materials hold special significance in emulating the natural appearance of teeth. A comprehensive understanding of the characteristics of color based on visual perception and the aesthetic appearance of dental resins, derived from their optical properties, can assist dental practitioners in the selection of suitable materials and shades, facilitating the attainment of a lifelike appearance in dental restorations. 3D printing resins are frequently used for the manufacture of temporary fixed partial restorations, which should fullfil adequately the esthetic demands of patients and clinicians. However, studies addressing questions concerning color characteristics and optical properties of 3D printed restorative dental materials are scarce in the current literature. Diverse factors, including printing parameters, layer thickness, and the specific printer employed, exert influence over the final material characteristics. The printing angle, printing orientation, or build direction, which refers to the orientation of layer construction, stands as a crucial parameter during the initial stages of additive manufacturing (AM) processes, capable of aiding in modulating the anisotropy and physical vulnerabilities inherent in printed materials produced through layering fabrication techniques. It has been demonstrated that the printing orientation has an influence on both the mechanical properties and the printing accuracy of 3D-printed restorative resins. In this sense, mechanical behavior characterization of polymeric dental materials involves the assessment of both flexural strength (σf) and elastic or Young's modulus (E). Furthermore, the colorimetric behavior and optical properties of these resins could also be affected by the printing orientation of the resin structures. To date, there is a lack of information regarding how printing orientation and structural thickness affects the color, translucency and other optical properties (including scattering, absorption, light reflectance and transmittance) of 3D printed resins, justifying the need for further studies. This information is crucial for an effective management of these materials, and to meet the growing esthetic expectations of patients. In this context, the present Doctoral Thesis involves several studies designed and carried out to address and resolve the mentioned issues.