**2. Alternative materials and techniques**

There has been ongoing effort to enhance the strength and fatigue resistance of acrylic resins, by means of: reinforcement with the addition of filling materials, altering the chemistry of acrylic resins, and manufacturing alternative denture base materials [24, 25].

#### **2.1 Reinforced acrylic resins**

Previous studies have shown that favorable results in improving mechanical properties such as impact and transverse strength were overcome using various types of fillers such as glass, carbon, polylactic fiber, plyometric polyamide, ultra-highmolecular-weight polyethylene, aramid, rayon, ceramic particle (barium titanate, zirconium dioxide, silicon dioxide, hydroxyapatite, titanium dioxide, and calcium carbonate), and metal plates or wires [26–33].

There are numerous studies focusing on the effect of glass fibers on the mechanical qualities of acrylic resins, which reported improvement of tensile and flexural strength and esthetic results [34–39].

Different other materials have been used for reinforcement, such as viscose fibers, mica, juta, or vegetable fibers [40–42].

#### **2.2 Alternative types of acrylic resins**

Alternative manufacturing technologies for acrylic resins, which aimed at obtaining high-quality dentures, were constantly developed, using dedicated materials. These technologies including casting, injection, light curing, microwave polymerization, CAD/CAM milling, 3D printing have been more or less utilized [43].

Thermoplastic and CAD/CAM milled acrylates have a high impact rating resistance, long-term stability, being characterized by a dense and smooth surface. It's highly biocompatible, due to the absence of residual monomer, and has very good long-term stability because of limited water retention [44].

Acrylic resins have been one of the most common commercial materials used for the manufacture of 3D printed denture bases. However, there were some technical challenges that hinder the application of polymethyl methacrylate (PMMA), such as large shrinkage, low degree of one-time curing, poor mechanical strength, low bacterial resistance, etc., limiting their clinical applications [45].

Nevertheless, great progress has been made in manufacturing alternative resin materials with outstanding properties.

#### **2.3 Light-cured urethane-based resins**

Urethane-based resins have no allergic potential, due to the absence of methyl, ethyl, propyl, and butyl groups. Manufactured by light curing, full and partial urethane dentures do not need flasking, packing, and heat curing, which are timeconsuming. The system is extremely efficient and consists of three wax-like types of resins: baseplate resin, setup resin, contour resin. A full denture base needs no more than 30 minutes to process, starting with complete setting of the master model. The "wax-up" is practically made on the denture's light-cured base, and after try-in, esthetic and phonetic approval, the final conditioning and light curing are carried out (**Figures 4**–**7**) [46].

#### **2.4 Thermoplastic resins**

Thermoplastic denture base materials include different types of hypoallergenic resins: polyamide (nylon), acetal, PEEK, epoxy, styrene, polycarbonate, vinyl, their most prominent advantages being higher elasticity, toxicological safety, and use of heat molding instead of chemical polymerization, which prevents polymerization shrinkage and related deformation [47, 48].

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

**Figure 4.** *Baseplate resin before light curing.*

#### **Figure 5.**

*Attaching the teeth to the cured baseplate, by using the setup resin.*

Thermoplastic resins are monomer-free and consequently nontoxic and non-allergenic, with high biocompatibility. They provide better resistance, esthetic appearance, and lower weight, being much more comfortable for the patient [8, 49, 50].

Their manufacture implies injection by special devices (**Figure 8**), after preheating the material (at a temperature of 200–250°C), in granular form, wrapped in special cartridges (**Figure 9**), which prevents dosage errors. The technology excludes any chemical reaction [51].

Thermoplastic materials are suitable for the manufacturing of removable partial dentures, which totally or partially eliminate the metallic framework and clasps, resulting in the so-called "metal-free removable partial dentures." If desired, any combination of the metallic framework or clasps with thermoplastic resin saddles and clasps is possible (**Figure 10**) [52, 53].

#### **Figure 6.**

*Contour resin, overlaid on the baseplate, exposed setup resin and necks of the teeth, processed using the warm air gun to create a smooth surface.*

**Figure 7.** *Final light curing.*

**Figure 8.** *Injection devices for thermoplatic resins.*

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

**Figure 9.** *Thermoplastic grain-like resins, wrapped in cartridges.*

#### **Figure 10.** *Combination between thermoplastic resin saddle, metallic and acetal clasps.*

Their indications include: removable partial dentures, preformed clasps, removable partial denture frameworks, temporary or provisional crowns and bridges, full dentures, orthodontic appliances, anti-snoring devices, mouthguards and splints [54].
