**Core Concept**
The clinical crown is the portion of the tooth that is visible in the oral cavity, whereas the anatomical crown is the entire structure that includes the portion below the gum line. The difference between these two measurements is due to the presence of the periodontal tissues, including the gingiva and the periodontal ligament.

**Why the Correct Answer is Right**
As the tooth emerges to the occlusal plane, the periodontal tissues, such as the gingiva and the periodontal ligament, cover the root surface, increasing the clinical crown height. This is because the periodontal tissues are added to the tooth structure, making the clinical crown appear longer than the anatomical crown. The periodontal ligament is a fibrous connective tissue that attaches the tooth to the surrounding bone, and it is an integral part of the periodontal tissues that contribute to the increase in clinical crown height.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the increase in clinical crown height is not due to the addition of cementum, which is a thin layer of bone-like tissue that covers the root surface. While cementum does play a role in tooth attachment, it is not the primary factor contributing to the increase in clinical crown height.
* **Option B:** This option is incorrect because the increase in clinical crown height is not due to the formation of secondary dentin, which is a type of dentin that forms in response to injury or aging. While secondary dentin can contribute to an increase in tooth structure, it is not the primary factor contributing to the increase in clinical crown height.

**Clinical Pearl / High-Yield Fact**
It is essential to understand the difference between the clinical and anatomical crown, as this distinction is crucial in various dental procedures, including restorative dentistry and periodontal therapy. The periodontal tissues play a critical role in maintaining the health and function of the tooth, and their presence can affect the outcome of various dental treatments.

**Correct Answer: C. The increase in clinical crown height is due to the presence of periodontal tissues, including the gingiva and the periodontal ligament.**