**2. Anatomy of the tooth**

In the second half of the nineteenth century, a large development of the field of plastic was observed. In 1869, a new material that was called 'celluloid' was presented. In 1871 that material was used as a restoration which was a turning point for the introduction of plastics for the dental industry. Despite its advantages such as ease of handling or resistance to fracture, new material was also characterized by many disadvantages including an undesirable colour change and emission of mercury causing drooling and inflammations in the mouth. Thus, in conjunction with further explorations of new material, next materials that have been proposed by researchers were phenol-formaldehyde resins [10]. As in the case of celluloid despite initial delight of dentists in these resins, it became quickly apparent that they do not meet the basic requirements. Thus in 1935, ICI company unveiled a new material which was poly(methyl methacrylate) (PMMA) also known as 'organic glass' which is associated with its transparent properties. At first, PMMA was not applied in dentistry due to many technological problems. However, in 1937, a new method of synthesis of the mentioned polymer was developed in which PMMA was obtained in the form of beads and not in the form of plates as it was previously the case. Then, a special methodology was developed aimed at combining beads of polymer with monomer in order to obtain an elastic mass. In **Figure 3**, PMMA in a

Detailed application of this polymer and the other belonging to the group of acrylates will be

form of plates (A) and beads (B) is presented.

**Figure 2.** Amalgam as a dental filling.

28 Acrylic Polymers in Healthcare

presented in subsequent parts of this chapter.

The name 'teeth' refers to the anatomical formations of complex structure occurring in the oral cavity that play an essential role in the digestive system. Teeth fulfil many functions including grinding and crushing of food which significantly facilitates its subsequent digestion and intake in the following sections of the digestive tract [11] (**Figure 4**).

**Figure 4.** Acrylic teeth.

In human oral cavities, it is possible to distinguish two types of dentitions: primary and permanent one. First of the mentioned occurs in children aged 2–6 and involves incisors, canines and molars. Primary dentition is with the time replaced by permanent one. This type includes 32 teeth, and in comparison to the previous one, it comprises additionally premolars [11]. The different types of teeth in dentition were shown in **Figure 5**.

In the construction of every tooth, three basic elements can be mentioned, i.e. crown, neck and root. Among tissues that form teeth, enamel, dentin, cementum, and pulp have to be mentioned. Enamel—the toughest tissue in the human body—in the vast majority (95%) is made of inorganic compounds. The most innervated and vascularized tissue from the abovementioned is a tooth pulp [11, 12].

Inadequate oral hygiene which consequently results in the accumulation of food debris and in the development of bacterial flora leads to the development of various types of teeth and periodontal diseases. In some cases, the process of healing of this type of illnesses is complex and lengthy. Therefore, it is necessary to develop this field of medicine whose role is to deal with functioning but also with treatment of teeth, periodontal, all tissues and any other elements contained in the oral cavity. The origins of this science should be sought several thousand years ago. Literature reports indicate that the traces of actions aimed at preventing tooth decay were discovered in the skull of young man whose remains were found more than 14,000 years ago. Areas of dentistry such as orthodontics and prosthetics also are characterized by a long tradition. The hygiene and the aesthetics of oral care were taken in ancient times. Therefore, high attention has been paid to the development of this field of medicine. With the passing of years, new elements that had to meet the growing demand on the market of dental materials have been introduced [11, 12].

Nowadays, it is necessary to use dental materials associated with artificial restorations or with technologies that in perfect way will enable a reconstruction of the missing piece of the dentition. Such materials are undoubtedly dental bridges, crowns, dentures and dental braces [11, 12].

**Figure 5.** Kinds of teeth in permanent dentition.
