Dental plaque is an adherent deposit of bacteria and their products, which forms as a white greenish or even yellow film on all tooth surfaces. Dental plaque accumulates naturally at stagnant or retentive sites formed after one or two days with no oral hygiene (Nada HA et al., 2008).Dental caries is the single most prevalent and costly infectious disease worldwide, affecting more than 90% of the population in the US. The development of dental cavities requires the colonization of the tooth surface by acid producing bacteria such as Streptococcus mutans, in conjunction with the frequent ingestion of a cariogenic high sucrose diet, the substrate for acid and glucan production by organisms. The elevated amounts of acid and glucans modulate the establishment of cariogenic organisms within tightly adherent biofilms known as dental plaque (Catalan MA et al., 2011). Tooth surfaces colonized with S. mutans are at a higher risk for developing caries (Pannu P. et al., 2013).Dental caries is an irreversible microbial disease of the calcified tissues of the teeth, which is characterized by demineralization of the inorganic portion and destruction of the organic substance of the tooth, which often leads to cavitation. Dental caries is a multifactorial disease, which is caused by host, agent, and environmental factors (Kt S. et al., 2013).Streptococcus mutansare gram positive cocci bacteria. These facultative anaerobes are commonly found in the human oral cavity. It grow at temperatures of between 18-40 oc. Streptococcus mutans are a cariogenic microorganism that breaks down sugar for energy and produces an acidic environment, which dematerializes the superficial structure of the tooth. The result of the conversion disintegrates the coating of the tooth then later dissolves the calcium molecule creating hole (Whiley RA. and Beighton D. 2013; Jav ND. et al., 2013).It can be isolated from individuals either with or without a history of caries, but the development of dental carries dependent on the bacterial load strain variation of Streptococcus mutans (Smith B et al., 19998; Zhang L. et al., 2009). 2. MATERIAL AND METHODS 2.1. Study Area and Period The study was conducted at Jimma University specialized hospital, which is located around 352 km