**2.6 CAD/CAM milled and 3D printed removable dentures**

CAD/CAM systems, which enable manufacturing 3D objects, have been used in dentistry since 1980, at first for fixed prosthodontic restorations [67].

In the 1990s, the fabrication of removable prosthodontic restorations was attempted, using both 3D printing and milling technologies [68, 69].

They offer many advantages to both dentists and patients, such as reduced number of appointments and easily available spare dentures, as digital data are saved [70–72].

Compared with the traditional methods, the lab work can be completed more conveniently and cost-effectively. The high initial cost of the milling machine may be overcome by referring the data to a milling center, which will handle the actual manufacturing.

Currently, both CAD/CAM methods: substractive milling and additive printing, are being used for removable dentures manufacturing [73, 74]. By milling, the denture may be obtained as one item, teeth and denture base in a single body [75], or separate pieces, the artificial teeth requiring subsequent bonding to the denture base [76]. The latter is the most frequently used at present, as it allows using commercially available artificial teeth, with better esthetics and physical properties [77, 78].

In case of 3D printing, the light-curing resin used is quickly converted from a liquid to a solid under the action of ultraviolet or visible light. The emergence of nanomaterials provides a new way to improve the performance of 3D printed acrylics [79]. By incorporating TiO2, antibacterial effects have been obtained [80].

Cellulose nanocrystals were attempted to reinforce acrylic resins for 3D printing, with improved mechanical and antibacterial properties and no significant cytotoxic effect [81].

**Figure 16.** *3D printed high-precision models.*

**Figure 17.** *3D printed working model for manufacturing a removable partial denture.*

Light curing is a green technology and the main molding method involved in 3D printing of resin-based dental materials. When irradiated with light, the photosensitive resin undergoes stacking and curing [82].

It consists of three main technologies: stereolithogaphy, digital light processing (DLP), and fused deposition modeling (FDM). The distinctive feature of DLP technology is the diversity of materials, from thermoplastics to resins and ceramics, even zirconia paste. FDM, one of the cheapest and most popular 3D printing technologies in dentistry, enables using polylactic acid, polycarbonate, polyamide, acrylonitrilebutadiene-styrene copolymers [83].

Besides full dentures and frameworks for removable partial dentures, 3D printing dental resins are also indicated for crowns and bridges, high-precision working models (**Figures 16** and **17**), splints, custom trays.
