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.This is largely due to the different types of ceramic materials, variability in prosthetic use, and printing parameters [4].Examples of polymers include polyether ether ketone (PEEK), polycaprolactone (PCL), polymethyl methacrylate (PMMA), polylactic acid (PLA), poly (lactic-co-glycolic acid) (PLGA), and ultraviolet (UV) resins.In a systematic review of in vitro studies, Valenti et al. [25] found that the mechanical properties of AM-printed polymeric materials were generally lower than those of materials produced by conventional methods.Wesemann et al. [26] investigated the wear resistance and mechanical properties of AM-printed occlusal appliances compared to the conventional injection molding method and found that there was a significant difference between their mechanical properties.The authors found that while their mechanical properties were satisfactory, improvements in 3D-printed metals and ceramic interfaces are required to match the precision obtained with conventional casting methods.Prpic' et al. [27] investigated the mechanical properties of AM-printed PMMA compared to conventional heat-polymerized and injection pressing PMMA, as used for denture bases.Ceramics Ceramic materials are considered a favorable material for dental restorations due to their excellent mechanical properties, biocompatibility, good abrasion and corrosion resistance, and esthetic properties.Dental Materials in 3D Print Technology Printable dental materials are rapidly advancing, with research focused on the development of additive manufacturing (AM) printing parameters to fine-tune the mechanical properties of conventionally used materials.A review by Revilla-Leon et al. [28] compared different printed alloys with conventional casting methods.4.4.1.4.2.4.3.

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4. Dental Materials in 3D Print Technology
   Printable dental materials are rapidly advancing, with research focused on the development of additive manufacturing (AM) printing parameters to fine-tune the mechanical properties of conventionally used materials. In addition, biocompatibility is important for 3D printing materials used in dentistry. Compared to conventional dental resins, 3D printing resins have been proven to have similar biocompatibility [22,23,24]. This biocompatibility can be further improved with post-processing like curing and washing [24]. In Table 2, a summary is provided of some common 3D-printed materials and their measured properties compared to their comparable conventional counterparts. The main printable materials can be categorized into synthetic polymers, metals, and ceramics.

4.1. Synthetic Polymers
Polymers are the most common materials used for dental applications due to the low cost and diverse properties and capabilities. Examples of polymers include polyether ether ketone (PEEK), polycaprolactone (PCL), polymethyl methacrylate (PMMA), polylactic acid (PLA), poly (lactic-co-glycolic acid) (PLGA), and ultraviolet (UV) resins. In a systematic review of in vitro studies, Valenti et al. [25] found that the mechanical properties of AM-printed polymeric materials were generally lower than those of materials produced by conventional methods. Wesemann et al. [26] investigated the wear resistance and mechanical properties of AM-printed occlusal appliances compared to the conventional injection molding method and found that there was a significant difference between their mechanical properties. Prpic’ et al. [27] investigated the mechanical properties of AM-printed PMMA compared to conventional heat-polymerized and injection pressing PMMA, as used for denture bases. The authors found that although the AM-printed group had the lowest flexural strength, it still met the ISO requirement of 65 MPa.

4.2. Metals
The mechanical properties of titanium (Ti) and cobalt-chromium (Co-Cr) alloys are ideal for many dental applications. A review by Revilla-Leon et al. [28] compared different printed alloys with conventional casting methods. The authors found that while their mechanical properties were satisfactory, improvements in 3D-printed metals and ceramic interfaces are required to match the precision obtained with conventional casting methods. Previous studies have noted higher hardness values for 3D-printed CoCr metal alloys (371 ± 10 HV) compared to conventional casting methods [29]. In general, an increase in fit accuracy is reported in AM-printed removable partial denture metal clasps, compared to conventional casting methods [25].

4.3. Ceramics
Ceramic materials are considered a favorable material for dental restorations due to their excellent mechanical properties, biocompatibility, good abrasion and corrosion resistance, and esthetic properties. This category can be further divided into glass, zirconia, and alumina ceramics. A challenge with 3D printing ceramics is inherent to their high melting points and introduction of cracks during the cooling processes. Additionally, the characteristics of the raw materials affect their porosity and final mechanical properties. For AM-printed ceramics, reports of their mechanical properties are inconsistent [25]. This is largely due to the different types of ceramic materials, variability in prosthetic use, and printing parameters [4]. This category of dental materials is a prime example of an area where further laboratory and clinical investigation is required to achieve widespread use.