**Core Concept**
Supernumerary teeth are extra teeth that develop in addition to the normal complement of teeth. They can occur in any dental arch but are most commonly found in the maxillary jaw. The most common type of supernumerary tooth is a mesiodens, which is a small, peg-shaped tooth that typically develops between the maxillary central incisors.

**Why the Correct Answer is Right**
The mesiodens is the most common supernumerary tooth form due to its developmental origin. It arises from the proliferation of epithelial cells in the dental lamina, which is a layer of cells that gives rise to the teeth. The mesiodens is usually small and peg-shaped, and it often causes crowding or impaction of the adjacent teeth.

**Why Each Wrong Option is Incorrect**
* **Option A:** Supernumerary teeth can also occur in the mandibular arch, but they are less common than mesiodens in the maxillary arch.
* **Option B:** Supernumerary teeth can be classified into several types, including mesiodens, paramolars, and distomolars, but mesiodens is the most common form.
* **Option C:** Supernumerary teeth can cause a range of problems, including crowding, impaction, and orthodontic issues, but they are not typically associated with systemic diseases.

**Clinical Pearl / High-Yield Fact**
The mesiodens is often difficult to diagnose on radiographs due to its small size and location between the central incisors. A clinical pearl is to look for a small, peg-shaped tooth between the maxillary central incisors when evaluating a patient with crowding or impaction of the anterior teeth.

**Correct Answer: C. Mesiodens**