**Core Concept**
The gingival index is a method used to assess the severity of gingivitis and periodontal disease by evaluating the color, texture, and bleeding on probing of the gingiva. It is a widely used clinical tool in periodontology for evaluating the health status of the gingiva.

**Why the Correct Answer is Right**
The gingival index was developed by Löe and Silness in 1963 to provide a standardized and reproducible method for evaluating the severity of gingivitis. The index assesses the gingiva based on four criteria: presence of bleeding on probing, color, texture, and edema. The score ranges from 0 (healthy gingiva) to 3 (severe gingivitis). The gingival index is a valuable tool in clinical practice and research for monitoring the effectiveness of periodontal treatments.

**Why Each Wrong Option is Incorrect**
**Option A:** The Plaque Index, developed by Silness and Löe in 1964, is a separate tool used to assess the amount of plaque on the teeth, not the severity of gingivitis.
**Option B:** The Periodontal Index, developed by Russell in 1956, is a broader index that assesses the overall periodontal health, including gingivitis and periodontitis.
**Option C:** The Community Periodontal Index (CPI) is a simplified index used for epidemiological studies to assess the periodontal health of populations, but it is not the original gingival index.

**Clinical Pearl / High-Yield Fact**
Remember the acronym "BLEED" to recall the four criteria of the gingival index: Bleeding on probing, Loss of gingival contour, Edema, and Exudate.

**Correct Answer: C. Periodontal Index, Developed by Russell in 1956.**