**Core Concept**
The pathogenesis of periapical cyst (also known as radicular cyst) is a complex process involving the interplay of inflammatory cells, bacteria, and host tissue response. It occurs as a result of pulp necrosis, leading to the formation of a cystic structure.

**Why the Correct Answer is Right**
The periapical cyst is a type of odontogenic cyst that forms as a result of the transformation of the epithelial cells lining the periodontal ligament into a cystic structure. This process is initiated by the invasion of bacteria and their byproducts into the pulp space, leading to an inflammatory response and subsequent necrosis of the pulp tissue. The epithelial cells lining the periodontal ligament then proliferate and differentiate into a stratified squamous epithelium, forming a cystic structure that encapsulates the inflammatory cells and debris.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the pathogenesis of periapical cyst. The periapical cyst is not a result of a traumatic injury to the tooth.
**Option B:** This option is incorrect because it is too vague and does not specify the role of bacteria and the inflammatory response in the pathogenesis of periapical cyst.
**Option C:** This option is incorrect because it is not a recognized mechanism of pathogenesis for periapical cyst.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that periapical cysts are the most common type of odontogenic cyst, and they often occur in association with pulp necrosis. A thorough understanding of the pathogenesis of periapical cyst is crucial for the diagnosis and management of this condition.

**Correct Answer: C. The periapical cyst is a type of odontogenic cyst that forms as a result of the transformation of the epithelial cells lining the periodontal ligament into a cystic structure, initiated by the invasion of bacteria and their byproducts into the pulp space.