**Core Concept:**
Dental caries, also known as tooth decay, is a pathological process that occurs when there is a disruption in the balance between the bacteria in the oral cavity, the food we consume, and the host response. The primary cause of dental caries is the overgrowth of acid-producing bacteria, particularly Streptococcus mutans, which can lead to demineralization of the tooth enamel.

**Why the Correct Answer is Right:**
The correct answer, **D. Streptococcus mutans**, is responsible for dental caries due to its unique ability to ferment carbohydrates, producing lactic acid as a byproduct. This acid creates an acidic environment in the oral cavity, leading to demineralization of the tooth enamel and ultimately causing dental caries.

**Why Each Wrong Option is Incorrect:**
A. **Bacteroides species:** While some Bacteroides species are present in the oral microbiota, they are not specifically responsible for dental caries.

B. **Actinomyces israelii:** Although Actinomyces species are part of the oral microbiota, they are not primarily responsible for dental caries.

C. **Streptococcus sanguis:** While Streptococcus sanguis is present in the oral microbiota, it does not specifically cause dental caries like Streptococcus mutans does.

**Clinical Pearl:**
The prevention and management of dental caries involve maintaining good oral hygiene, limiting sugar intake, and regular dental check-ups for early detection and intervention. Understanding the role of specific bacteria, like Streptococcus mutans, in dental caries helps healthcare professionals design targeted preventive strategies and treatments.