# Ergonomic Sports Mouthguards: A Narrative Literature Review and Future Perspectives
## 2 Narrative Literature Review Search Strategy
### Additive Manufacturing  
With the rise of digital dentistry and the advancement of CAD/CAM (computer-aided design/computer-aided manufacturing) technology, additive manufacturing has been proposed to produce mouthguards. This is due to the incorporation of new materials and improvements in their replication, as well as the ability to provide individualized solutions with greater accuracy, coupled with the advancement of technical knowledge in this field [8; 42; 43]. This approach serves to reduce the drawbacks associated with conventional techniques used to create EVA mouthguards, which often involve pressure and vacuum molding. These traditional methods can lead to drawbacks such as reduced final thickness and delamination, especially when incorporating multiple layers of EVA during the molding process [42]. Although additive manufacturing offers innovative solutions for fabricating mouthguards, it is essential to evaluate whether the available materials exhibit mechanical performance comparable to conventional mouthguards made from EVA. This evaluation pertains to factors such as stress absorption, stress distribution, tensile strength, flexural strength, toughness, hardness, fluid absorption, material solubility, and biocompatibility [42; 44]. However, only a limited number of studies in the literature have addressed the fabrication of mouthguards using additive manufacturing techniques [8]. Existing studies indicate that there are currently no discernible benefits in terms of the mechanical behavior of the available materials for 3D-printed mouthguards that surpass the performance of EVA [8; 42]. Nevertheless, it is worth noting that the impact testing methodologies used are still simplified [42]. Moreover, the market offers various polymer types that require testing due to their distinct compositions. Additive manufacturing presents advantages in terms of customization and control over the final device, distinguishing it from conventional methods [45]. Given the advantages of additive manufacturing in producing intraoral mouthguards, it becomes evident that this technique can offer favorable retention, appearance, and comfort, producing outcomes similar to conventionally fabricated custom-made mouthguards. Figure 4: Reinforced mouthguard finishing procedure. However, when considering occlusal balance, it has been observed that 3D-printed mouthguards exhibit balanced occlusal contacts, providing a symmetrical bilateral occlusion in centric occlusion. This is in contrast to conventionally fabricated mouthguards, which may show variations in thickness [45]. This characteristic enables proper stability of the device within the intraoral environment and facilitates better distribution of absorbed forces during traumatic impacts. Figure 5 shows the steps for fabrication of a 3D-printed mouthguard with Dima print mouthguard resin (Kulzer & Co. GmbH, Wehrheim, Germany). Figure 5: Steps for fabrication of a 3D-printed mouthguard. **(A)** Imported file after individualized case planning. **(B)** File placement for 3D printing. **(C)** The 3D printing process in Dima print mouthguard resin using a Cara 3D printer (Kulzer & Co. GmbH, Wehrheim, Germany), following manufacturer’s recommendations. **(D)** Washing process in isopropyl alcohol following printing. **(E)** Cure processing. **(F,G)** The mouthguard after completing all manufacturing procedures. Additive manufacturing has displayed such promising growth potential that has spurred the development of intelligent printed materials, known as 3D-printed smart materials. These materials possess the capability to adapt to external conditions such as pH, humidity, and temperature by utilizing their shape memory effect. This advancement is considered significant progress in the field and opens up avenues for further research in this area, with the potential for future clinical implementation [43]. There is still no consensus in the literature regarding materials that can be considered safe as alternatives for EVA in the production of mouthguards.