# Implementation of Fused Filament Fabrication in Dentistry
## 2 Applied FFF Materials in Dentistry  
FFF has a huge variety of available feedstock materials. Standard materials are filaments made of semi-crystalline thermoplastics such as the most commonly used polylactic acid (PLA) and the second group of amorphous polymers like (1) acrylonitrile-butadiene-styrene copolymers (ABS), (2) polycarbonates (PC), (3) polyethylene terephthalate glycol (PETG), and (4) water-soluble materials for support structures like polyvinyl alcohol (PVA) [12].  
For medical use, filaments are available that are certified for short-term contact with skin and body fluids, such as polyphenylsulfone (PPSU) [13]. Surgical guides for oral implant insertion and bone-like models are made of a biocompatible filament made from a compound of polyamide-polyolefin and cellulose (PAPC) [14]. In addition, the manufacturing of polyetherketons like PEEK [15] with FFF printers for use in craniosulfacial implants is being evaluated [16; 17; 18]. Other filaments are certified as medical device class 1, which are products for the temporary use in the body and a low degree of invasiveness, like PETG [19], Polycaprolactone (PCL), and poly(lactic-co-glycolic acid) (PLGA) filaments [20].  
Currently, the most common application of FFF in dentistry is the production of dental models based on intraoral scans (Figure 1). Although models made by FFF are considered to have lower precision and trueness compared to SLA and DLP systems, they meet the requirement for many dental sectors [21; 22]. For example, orthodontic models require a lower accuracy than models made for the manufacturing of prosthetic restorations. Low material and equipment costs and nearly ready-to-use models without post-processing make FFF economically attractive. The model shown in Figure 1 was manufactured by using a lignin-based filament (Greentec Pro, Extrudr FD3D GmbH, Lauterach, Austria)with a material cost of approximately 1 \(\upxi\). The printing time was comparable to SLA systems, but with no need for post-processing procedures and reduced material costs up to 80%. Additionally, other materials such as gypsum-containing filaments [23; 24] can be used to produce dental models, which can also be used for thermoforming of splints.  
Another innovative application using FFF presents the manufacturing of customized impression trays [25; 26] (Figure 2a). The utilized filament (Trayfill, Bernhardt Kunstoffver-arbeitungs GmbH, Berlin, Germany) is a certified medical device class 1 and withstands autoclavation [27]. This trap was printed with material costs of about 1.70 \(\upxi\) and was therefore highly cost-effective. In order to verify the fulfillment of the required accuracy, a comparison of the STL file and the printed part was performed. Therefore, the impression tray was digitized (Keyence VL 500, Keyence, Osaka Japan) and a best-fit analysis (Geomagic Control X, 3D Systems, Inc., Rock Hill, AC, USA) was conducted (Figure 2b.) The obtained results revealed negative deviations of approximately 0.9 mm in the areas of the tuber maxillae and positive deviations of 0.2 mm in the palatal area.  
Figure 1: (**a**) Dental model of the upper jaw manufactured by fused filament fabrication (FFF), (**b**) Detailed view of highly accurate tooth structures.  
Figure 2: (**a**) Customized impression tray fabricated by means of FFF (Filament: Trayfill), (**b**) Heatmap indicating the deviation between STL file and tray.