## 1 Introduction  
The use of additive manufacturing (AM), or 3D printing, has expanded significantly within dentistry, particularly in the fabrication of prosthodonic devices such as occlusal nightguards, complete and partial dentures, and temporary fixed prostheses. This innovative technology offers the advantage of rapid workflow, customization to patient-specific needs, and the potential for cost reduction (Figure 1). In restorative dentistry, materials used in additive manufacturing are called printable biomaterials and are available as acrylates, resin-based composites, and, more recently, ceramic-infiltrated composites [1]. The additive methods most frequently applied in dentistry are stereolithography (SLA) and digital light processing (DLP) technology. Each process uses light to activate the polymerization of the printable resin. While SLA uses UV light, DLP uses a high-power LED to start the chain reaction of the monomers [2]. The introduction of 3D-printed materials into clinical practice raises concerns about the biological safety of these materials, especially regarding the release of residual monomers from the polymerized products [2]. Residual monomers, primarily from acrylic-based resins, can be cytotoxic. Since prosthodonic devices are intended for long-term use, often in direct contact with sensitive oral tissues, releasing these monomers poses a health concern [3]. Consequently, evaluating the cytotoxic effects of these materials is essential to ensure the safety and efficacy of 3D-printed dental prostheses. This review aims to systematically evaluate the cytotoxicity of 3D-printed materials used in dental prosthetics, focusing on identifying and synthesizing existing research findings while highlighting areas where further study is needed. This paper seeks to contribute to the safe and effective integration of 3D printing technologies in dental care by comprehensively analyzing the cytotoxic risks and mitigation strategies associated with these innovative materials. As with directly photocured resin-based composites, 3D printable resins are not fully converted to the polymeric chain after exposure to light. This deficiency in the degree of conversion must be overcome by a post-curing process, usually, a light oven that uses extra-time light exposure and heat to improve the degree of conversion of these materials (Figure 2). However, complete conversion is rarely achieved, and the free unreacted monomers represent a well-known risk to biological properties [4]. The extensive range of available 3D printing polymer materials from different manufacturers, each using a slightly different manufacturing and curing protocol, might lead to different outcomes regarding these materials' mechanical and biological properties [5]. Three-dimensional printing materials can be indicated for surgical guides or custom trays to be used quickly (Figure 3). Other appliances, such as interocclusal nightguard devices and complete and partial dentures, may be produced using these materials, and long-term use occurs [1]. While mechanical properties have been widely investigated and documented [6], and data from these experiments are more easily translated to clinical practice,  
Figure 1: Three-dimensional printing workflow diagram demonstrating the steps in fabricating a dental device. the biological behavior of 3D printing materials has a complex methodology, which may confuse the dentist about their biological safety [7; 8]. Some published papers present data on the biocompatibility of printable resins for temporary and permanent prosthetic devices. Different methodologies can assess the biological response, such as inflammatory response, oxidative stress, biofilm interaction, cytotoxicity, genotoxicity, cell adhesion, cell proliferation, and cell viability [7; 8].