Dental Admissions Test (DAT) Practice Test

Which oral bacteria is primarily responsible for tooth decay?

1. Lactobacillus casei

2. Streptococcus mutans

3. Actinomyces naeslundii

4. Porphyromonas gingivalis

The correct answer is: Streptococcus mutans

Streptococcus mutans is recognized as the primary bacterial species responsible for tooth decay, or dental caries. This bacterium is particularly adept at thriving in the oral cavity where it metabolizes sugars, producing acid as a byproduct. This acid lowers the pH in the mouth, leading to demineralization of tooth enamel and ultimately resulting in cavities. The process of tooth decay begins when S. mutans adheres to the dental surfaces, often forming a biofilm known as dental plaque. In this environment, the bacteria can proliferate, especially after consumption of fermentable carbohydrates. As these bacteria produce acids, the enamel's mineral content is compromised, leading to progressive decay if left untreated. Other bacteria listed are associated with oral health but do not play as significant a role in the formation of cavities. For example, Lactobacillus casei is involved in the progression of tooth decay but is not the primary initiator. Actinomyces naeslundii is more related to periodontal disease rather than caries, while Porphyromonas gingivalis is primarily linked to periodontitis. Thus, the critical role of Streptococcus mutans in initiating dental caries underscores its importance in oral health discussions.