**1. Introduction**

The term probiotic comes from the Greek language meaning "for life." It was first introduced by Lilly and Stillwell in 1965 to describe substances that stimulate the growth of microorganisms. In 1971, Sperti used the probiotic term to define substances secreted by tissue, which have the ability to stimulate microbial growth. Parker first used the term probiotic in relation to its modern usage, defining it as "organisms and substances that contribute to intestinal microbial balance." Later, Fuller amended this definition by emphasizing the important role of probiotics in establishing the balance of intestinal microbial. This reformed definition emphasizes on the requirement of viability for probiotics and introduces the aspect of a beneficial effect on the host. Havenaar et al. expanded the definition further to include mono

or mixed cultures of microorganisms applied to animals or humans that improve the properties of the indigenous microflora. Salminen and Schaafsma further broadened the definition of probiotics to include dairy products such as fermented cereals, sauerkraut, and salami that contain viable probiotic microorganisms. This definition showed that probiotics benefit, effect health and nutrition of the host. Salminen and Schaafsma broadened the definition of probiotics even further by no longer limiting the proposed health effects to influences on the indigenous microflora.

Today, we know that unlike Salminen definition probiotic microorganisms are also can be find in nondairy products [1].

Candida is actually another name for fungi that define over 150 yeast species that exists harmlessly in healthy individuals. An imbalance in normal flora may lead to an overgrowth of one of these species named as *Candida albicans*, which can cause candidiasis or thrush, a fungal infection that has a widespread impact on the body's overall health and well-being. Candida is one of the normal flora substances, which is known as "beneficial flora" and also has a useful purpose in the body. When there is an imbalance in the normal flora, it can cause an overgrowth in the number of *Candida albicans*. The expression used for the overgrowth of *Candida albicans* that may lead to an infection is Candidiasis or Thrush. This is a fungal infection which is also called Mycosis through any of the species of Candida; however, *Candida albicans* is the most common one. When this infection happens, it can cause a widespread deterioration to our overall health and well-being of the body.

Oral candidiasis is a common fungal infection in the oral mucosa, caused by *Candida albicans*. Many people have this organism, and the rate of carriage increases with age [2]. Denture stomatitis, an inflammation of the denture-bearing mucosa affecting two-thirds of elderly denture wearers, is often associated with Candida. It is more common on the palatal mucosa and in female patients [3].

There are different types of denture materials and one of the most common of them is polymethyl methacrylate. Polymethyl methacrylate is a lightweight, synthetic polymer that is an economical alternative to polycarbonate. Unlike polycarbonate, polymethyl methacrylate (PMMA) does not contain potential harmful subunits, such as bisphenol-A, and is easier to handle, process, and less expensive. This chapter aims to discuss the effect of probiotic solutions on the adherence of *Candida albicans* to polymethyl methacrylate dentures.

In this chapter, we aim to talk about the effect of probiotic solutions on adherence of *candida albicans* to polymethyl methacrylate dentures.
