**2.5 Polyether ether ketone**

PEEK is a ketone-based semi-crystalline thermoplastic with excellent mechanical and chemical resistance properties, used in dentistry since 2002, for crowns, implant superstructures, fixed partial dentures, and removable partial denture frameworks and clasps (**Figure 14**) [60–63].

PEEK is highly biocompatible, insoluble, lightweight, with superior resistance to wear and fracture and elasticity comparable to bone. It may be optimized by adding

*Alternative Denture Base Materials for Allergic Patients DOI: http://dx.doi.org/10.5772/intechopen.101956*

#### **Figure 13.** *Acetal framework and clasps; acetal splint.*

#### **Figure 14.** *Removable partial denture with PEEK framework and clasps.*

#### **Figure 15.** *CAD/CAM milled PEEK framework.*

ceramic nanoparticles. The material may be injected (grains) at 400°C or milled (disks) using a CAD/CAM system (**Figure 15**) [44]. Recently, 3D printing using PEEK materials has been utilized. Direct-ink writing 3D printing uses soluble epoxyfunctionalized PEEK (ePEEK) and fenchone, but the most widely used technique is fused deposition modeling (FDM), which requires increases in the nozzle and heating bed temperatures for PEEK materials [64–66].
