**Core Concept**
The periodontal ligament (PDL) is a dynamic, fibrous connective tissue that surrounds the roots of teeth and plays a crucial role in tooth support and proprioception. The PDL contains various cell types, including osteoclasts, osteoblasts, and cementoblasts, which are involved in the resorption, deposition, and maintenance of the periodontal ligament and surrounding bone.

**Why the Correct Answer is Right**
Osteoclasts are the primary resorptive cells of the periodontal ligament. They are multinucleated giant cells that originate from the hematopoietic lineage and are responsible for the breakdown of bone tissue through the activation of osteoclasts' proton pump and the release of hydrochloric acid. This process leads to the dissolution of bone minerals and the degradation of organic bone matrix.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because cementoclasts are not a recognized cell type in the periodontal ligament. Cementoclasts are a subset of osteoclasts that are involved in the resorption of cementum, but they are not a distinct cell type.

**Option B:** This option is incorrect because cementoblasts are involved in the formation of cementum, not its resorption. Cementoblasts are a type of fibroblastic cell that produces cementum, a bone-like tissue that covers the root of the tooth.

**Option C:** This option is incorrect because osteoblasts are involved in the formation of bone and cementum, not their resorption. Osteoblasts are a type of bone-forming cell that produces bone matrix and regulates mineralization.

**Clinical Pearl / High-Yield Fact**
The periodontal ligament is a dynamic tissue that plays a crucial role in tooth support and proprioception. The balance between bone resorption and deposition in the PDL is essential for maintaining periodontal health and preventing diseases such as periodontitis.

**Correct Answer: D**