**Core Concept**
Chandler's index is a measure used to assess the severity of periodontal disease. It is a scoring system that evaluates the extent of periodontal pocketing and attachment loss in a patient's mouth. This index helps clinicians to quantify the severity of periodontal disease and monitor its progression over time.

**Why the Correct Answer is Right**
Chandler's index takes into account the number of teeth with periodontal pockets and the depth of these pockets. A higher score indicates a greater extent of periodontal disease. The index is calculated by multiplying the number of teeth with pockets by the average depth of these pockets. This scoring system allows clinicians to compare the severity of periodontal disease between different patients and to monitor the effectiveness of treatment.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Chandler's index is not a measure of bleeding on probing, which is a different aspect of periodontal assessment.
**Option B:** This option is incorrect because the Community Periodontal Index of Treatment Needs (CPITN) is a different scoring system used to assess periodontal disease, not Chandler's index.
**Option C:** This option is incorrect because the Periodontal Disease Index (PDI) is another scoring system used to assess periodontal disease, but it is not the same as Chandler's index.

**Clinical Pearl / High-Yield Fact**
Chandler's index is an important tool for clinicians to assess the severity of periodontal disease and to monitor its progression over time. It is essential to use this index in conjunction with other periodontal assessment tools to get a comprehensive understanding of a patient's periodontal health.

**Correct Answer: D. A scoring system that evaluates periodontal pocketing and attachment loss.**