# Implementation of Fused Filament Fabrication in Dentistry
###### Abstract  
Additive manufacturing is becoming an increasingly important technique for the production of dental restorations and assistive devices. The most commonly used systems are based on vat polymerization, e.g., stereolithography (SLA) and digital light processing (DLP). In contrast, fused filament fabrication (FFF), also known under the brand name fused deposition modeling (FDM), is rarely applied in the dental field. This might be due to the reduced accuracy and resolution of FFF compared to vat polymerization. However, the use of FFF in the dental sector seems very promising for in-house production since it presents a cost-effective and straight forward method. The manufacturing of nearly ready-to-use parts with only minimal post-processing can be considered highly advantageous. Therefore, the objective was to implement FFF in a digital dental workflow. The present report demonstrates the production of surgical guides for implant insertion by FFF. Furthermore, a novel approach using a temperature-sensitive filament for bite registration plates holds great promise for a simplified workflow. In combination with a medical-grade filament, a multi-material impression ray was printed for optimized impression taking of dedentulous patients. Compared to the conventional way, the printed thermoplastic material is pleasant to model and can allow clean and fast work on the patient.  
additive manufacturing; 3D printing; fused filament fabrication; fused deposition modeling; digital workflow; dentistry +
Footnote †: journal: Medical Imaging  
11 July 2021  
time independent of the surface area covered by the object(s) and enables time-efficient production. After printing, both processes require washing of the object to remove the resin adhering to the surface. To obtain the final material properties, further post-processing by additional light-curing is necessary, which leads to the final crosslinking of the polymers [7; 8]. However, post-processing equipment, consumables, such as isopropanol for the cleaning step, and requirements for occupational safety increase the costs. The use of photosensitive resin as feedstock material also requires special precautions and trained personnel to ensure adequate printing results. Especially in the case of medical products, regulations must be strictly followed during the entire manufacturing process. Therefore, a cost-efficient process with a straight-forward workflow that offers facile handling of materials and little post-processing appears promising. Thereby regulatory compliance is alleviated and the barrier to entry for the user is lowered.  
Fused filament fabrication (FFF), which is also known by its trademark fused deposition modeling (FDM), represents a simplistic and low-cost method of additive manufacturing (AM). Invented in 1989 [9], the FFF process has experienced strong growth since the original patents began to expire from 2009 onwards. Today, both industrial customers and private users are stimulating the market. New FFF printers are available for a low budget, and the choice of materials is steadily increasing.  
In the FFF process, a thermoplastic filament is fed to a heated nozzle. This is where the material is melted, and as the nozzle moves layer by layer in the x and y directions along the geometry, the material is deposited [10]. Apart from possible support structures for steep projections, which have to be removed, no post-processing is required and the parts can be used immediately. The simplicity makes the process very attractive, as evidenced by its widespread use.  
However, FFF suffers from limited mechanical properties in build direction due to incomplete fusion of deposited strands and higher surface roughness [11]. Until now, SLA/DLP has been mainly used in dentistry, due to its superior accuracy and mechanical properties compared to FFF. Nevertheless, non-load-bearing medical devices and assistive devices with reduced accuracy requirements present a huge potential for FFF in dentistry.