Edentulism is defined as a complete absence of teeth and is considered a disability by the World Health Organization (WHO) [1]. The prevalence of reported causes for tooth loss is as follows: caries (36.0% to 55.3%); periodontitis (24.8% to 38.1%); trauma (0.8% to 4.4%), periapical disease (7.3% to 19.1%); orthodontics (2.5% to 7.2%); and other reasons (4.5% to 9.2%) [2]. Following tooth loss, the underlying bone continues to resorb, and there are changes to patients’ facial appearance and facial height [3]. Moreover, elderly people who wear complete dentures are more likely to experience denture stomatitis, an inflammatory condition of the palatal mucosa, as well as angular cheilitis, oral candidosis, and traumatic ulcers [3]. Dental health has a significant impact on quality of life; edentulism negatively affects patients’ quality of life because it decreases chewing capacity, enervates phonetics, and impairs aesthetics [4]. The loss of chewing efficacy can result in a decreased intake of food (e.g., vegetables and fruit), which could lead to malnutrition. Simultaneously, edentulous patients cannot meet dietary recommendations [5]. In addition, edentulism can be connected with several systematic conditions such as pneumonia, adiposity, neck and head carcinoma, and a higher risk of mortality [1]. Studies showed different prevalences of edentulism. Females have higher prevalence of edentulism when compared to males, especially females with poor profit and lower degree of education [6]. In a review, Polzer et al. [7] determined that the prevalence of edentulism ranges from 1.3% to 78% for people aged 65 and older. Inter- and intracountry differences in the prevalence of edentulism exist, but comparison between nations is challenging because of different factors (e.g., erudition, economical instance, dental health competence, and beliefs and attitudes towards oral health) which can influence the outcome [3,8]. Manifestations of edentulism are constantly falling in developed countries, whilst in developing countries, the opposite trend has been observed [9]. Nevertheless, a study by Douglass et al. [10] showed increasing edentulism as a result of aging and longer life expectancy. The higher number of elderly people could be caused by demographic changes which can be seen in the majority of countries [11]. A total of 703 million people worldwide are aged 65 years and above, and it is predicted that the given number will double by 2050.

Complete dentures have been used for many years and are considered the gold standard for treating patients with this condition [4,7,12,13,14]. Although other types of prosthodontic solutions for edentulism are accessible, such as implant-supported dentures, most patients decide to wear conventional ones, mainly because of financial causes [15,16,17]. Until today, polymethyl methacrylate (PMMA) has remained the most accepted denture base resin [18,19]. PMMA conforms to some of the requirements for a perfect denture base resin, which include easy mending, optimal appearance, and a tolerable price [13,20]. Common manipulation is also one of the advantages and is started by mixing methyl methacrylate (monomer) and polymethyl methacrylate (polymer) [18]. The polymerization process of a given type of PMMA (heat-polymerized resin) is terminated after a certain exposure time to heat. Despite all the advantages, polymerization shrinkage of 6% can be interpreted as the main disadvantage [18]. Moreover, the chemical reaction between methyl methacrylate and polymethyl methacrylate is never complete. Leftovers of the residual monomer after the polymerization process can modify the mechanical properties of the material and cause allergic reactions (e.g., oedema, stomatitis, and ulcerations) [18,21].

Bonding between the denture base material and the artificial teeth is imperative for completeness of dentures and patient’s quality of life. Resin artificial teeth are used more frequently when compared to porcelain ones because of the chemical bonding that occurs and simple occlusal adaptation [22]. Furthermore, resin denture teeth are persistent to thermal changes and are less pervious to fracture under impact [22].

2. Shear Bond Strength between Milled Denture Base Materials and Artificial Teeth