Citation: Farkas, A.Z.; Galatanu, S.-V.; Nagib, R. The Influence of Printing Layer Thickness and Orientation on the Mechanical Properties of DLP 3D-Printed Dental Resin. Polymers 2023, 15, 1113. https://doi.org/10.3390/ polym15051113 Academic Editor: Ali Reza Zanjanijam Received: 20 January 2023 Revised: 13 February 2023 Accepted: 21 February 2023 Published: 23 February 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). polymers Article The Influence of Printing Layer Thickness and Orientation on the Mechanical Properties of DLP 3D-Printed Dental Resin Andrei Zoltan Farkas 1 , Sergiu-Valentin Galatanu 2, * and Riham Nagib 3 1 Department of Mechatronics, Polytechnic University of Timisoara, 1 Mihai Viteazul Blvd., 300222 Timisoara, Romania 2 Department of Mechanics and Strength of Materials, Politehnica University of Timisoara, 1 Mihai Viteazu Blvd., 300222 Timisoara, Romania 3 Orthodontics Research Center ‘ORTHO CENTER’, Department of Orthodontics, “Victor Babes” University of Medicine and Pharmacy Timisoara, Eftimie Murgu Sq. 2, 300041 Timisoara, Romania * Correspondence: sergiu.galatanu@upt.ro Abstract: Technological advances are closely related to the development of new materials and their processing and manufacturing technologies. In the dental field, the high complexity of the geometrical designs of crowns, bridges and other applications of digital light processing 3D-printable biocompatible resins is the reason for the need for a deep understanding of the mechanical proprieties and behavior of these materials. The aim of the present study is to assess the influence of printing layer direction and thickness on the tensile and compression proprieties of a DLP 3D-printable dental resin. Using the NextDent C&B Micro-Filled Hybrid (MFH), 36 specimens (24 for tensile strength testing, 12 for compression testing) were printed at different layer angulations (0 ◦ , 45 ◦ and 90 ◦ ) and layer thicknesses (0.1 mm and 0.05 mm). Brittle behavior was observed in all specimens regardless of the direction of printing and layer thickness for the tensile specimens. The highest tensile values were obtained for specimens printed with a layer thickness of 0.05 mm. In conclusion, both printing layer direction and thickness influence mechanical proprieties and can be used to alter the materials’ characteristics and make the final printed product more suitable for its intended purposes. Keywords: C&B Micro Filled Hybrid; dental resin; 3D printing; tensile test; compression test 1. Introduction Technological advances are closely related to the development of new materials and their processing and manufacturing technologies [1]. Three-dimensional (3D) printing is a technology that has enabled the manufacturing of complex structures, with comparatively short times and less material consumption when compared to classical manufacturing technologies [2]. In recent years, in more and more fields, an increasing emphasis has been placed on additive manufacturing techniques [3]. More formally known as additive manufacturing (AM), 3D printing, besides being adopted for rapid prototyping, is also used for rapid manufacturing and shows great potential for applications in aerospace engineering, biomedical engineering, and conceptual model preparation. The 3D printing market is constantly on the rise, and it is projected that it will continue to thrive in the future [4]. Digital light processing (DLP) is a vat-photopolymerization-based 3D printing tech- nology where full layers of photosensitive resin are irradiated and cured with projected ultraviolet (UV) light. The final product is a three-dimensional part created layer by layer. Recent breakthroughs in polymer chemistry have led to a growing number of UV-curable elastomeric photo resins developed exclusively for VAT photopolymerization [5–7]. DLP 3D printing technology is used to produce fine components due to its high precision and efficiency, being advantageous for fabricating complex structures used in various fields, including dentistry [8]. The novel elastomeric photo resins combined with Polymers 2023, 15, 1113. https://doi.org/10.3390/polym15051113 https://www.mdpi.com/journal/polymers