**Core Concept**
The CPITN (Community Periodontal Index of Treatment Needs) is a method used to assess the periodontal status of an individual, categorizing it into different treatment needs based on the presence and severity of periodontal disease.

**Why the Correct Answer is Right**
The CPITN involves a simple, quick, and easy-to-perform examination of six selected teeth, including the upper right and left first molars, the upper right and left central incisors, and the lower right and left first molars. The examination takes into account the presence of plaque, calculus, and periodontal pockets, which are indicators of periodontal disease. The index helps in categorizing the periodontal status of an individual into different treatment needs, which can range from no treatment required to active periodontal treatment.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the CPITN does not involve a comprehensive examination of all teeth in the mouth but rather focuses on a select few to assess the periodontal status.
* **Option B:** This option is incorrect because the CPITN is not a diagnostic tool that can identify the etiology of periodontal disease but rather a method to assess the severity and categorize treatment needs.

**Clinical Pearl / High-Yield Fact**
The CPITN is a useful tool for public health dentists and researchers to assess the periodontal status of large populations and to plan preventive and therapeutic measures.

**Correct Answer:** C. The CPITN involves a simple, quick, and easy-to-perform examination of six selected teeth to assess the periodontal status of an individual.