**1. Introduction**

Acrylic resins, which represented an important step forward in dentistry, have been used in manufacturing denture bases, artificial teeth, orthodontic appliances, maxillofacial prostheses, single-tooth or provisional restorations, as well as veneering materials, since the middle of the twentieth century [1].

Characterized by low density and thermal conductivity, good resistance to chemical solvents, acrylic resins became the most popular material for denture base fabrication because of the low fabrication cost, easy repair/reline, low weight, and aesthetical properties [2].

The most frequently used acrylic resins in dentistry are heat-cured. They seemed very promising at first, but, in time, it turned out that heat-cured acrylics had various shortcomings, such as poor resistance, dimensional stability issues, polymerization shrinkage, high degradation rate in wet environment, allergenic potential and citotoxicity due to the residual monomer, difficult processing, due to the awkward flasking and packing procedure (**Figure 1**) [3–6].

#### **Figure 1.**

*Flasking and packing of heat-cured acrylic dentures.*

Acrylic resin becomes porous and permeable after prolonged use in the mouth wet environment, also being prone to discoloration [7].

The consequence may be denture base fracture, allergic reactions, and improper seating [8].

The fracture of the acrylic denture base is a very common clinical problem, partly due to its complex geometry, which favors stress concentration in certain areas [9]. Most of upper denture base fractures are caused by fatigue and impact, whereas in case of the lower denture base, impact and low fracture toughness are the main causes [10]. One of the primary problems of acrylics is the impact failure when the denture is accidentally dropped on a hard surface and fatigue failure when the unfit denture base deforms repeatedly through occlusal forces [11].

According to literature data, 68% of the acrylic dentures break within a few years after fabrication [12].

Acrylics are also well known for their allergenic potential, their citotoxicity being mainly due to the residual monomer [13, 14].

The adverse reactions of the oral mucosa, in case of conventional acrylic resins, may also be induced by porosity (**Figure 2**), poor hygiene, degradation due to water sorption [15–17].

Inadequately cleaned dentures are subject to quick formation of a biofilm on their surface [18].

The anaerobic environment, characteristic under poorly cleaned denture bases, is associated with the proliferation of certain bacterial species, consequently leading to a pathogenic biofilm composition and inducing denture stomatitis by plaque accumulation (**Figure 3**) [19].

The often contaminated dentures of elderly patients may finally result in affecting the general health condition [20].

The high relative humidity of the oral environment, constant contact of the denture with saliva, cold and hot food and drinks, enzymes, bacteria, and the varying pH *Alternative Denture Base Materials for Allergic Patients DOI: http://dx.doi.org/10.5772/intechopen.101956*

**Figure 2.** *Porous acrylic denture base.*

#### **Figure 3.**

*Microbial flora found on the denture base surface: a. candida hyphae, b. cocci, c. mucinous conglomerate, d. trichomonas tenax (ATP Dragan coloration Ob. Im).*

levels can severely affect the physical and mechanical properties of the denture [21]. Dental base materials, and especially acrylic resins, are prone to water sorption, as they tend to form hydrogen bonds with water molecules, which also leads to deteriorated physical and mechanical properties [22].

In order to overcome these disadvantages, various attempts have been made. One of the methods considered was gold plating, which has proved to increase the retention and overcome plaque accumulation. However, the method did not prevail, as the adhesion between the acrylic resin and the gold plated layer deteriorates and abrades.

Later on, reinforced acrylic resins, characterized by better resistance and low/ none residual monomer, became available. Alternative polymer systems, such as polyamide, epoxy, styrene, acetal, polycarbonate, polyether ether ketone (PEEK), or vinyl resins, have been experimented, with promising results [23]. However, the desired denture base material has not been developed yet.
