**Core Concept**
The question is testing the understanding of a characteristic dental anomaly, specifically a progressive increase in mandibular length and interdental spacing in an adult patient. This condition is associated with a specific genetic disorder that affects the development and growth of the jaw bone.

**Why the Correct Answer is Right**
The correct answer is **Hyperdontia**. Hyperdontia is a condition characterized by the presence of extra teeth in addition to the normal complement of teeth. This condition can cause an increase in the length of the mandible and interdental spacing due to the abnormal growth and development of the jaw bone. The presence of extra teeth can also lead to crowding and malocclusion, which can affect the alignment and function of the teeth.

**Why Each Wrong Option is Incorrect**
**Option A:** **Hypodontia** is a condition characterized by the absence of one or more teeth, which would not explain the increase in mandibular length and interdental spacing.

**Option B:** **Dental fluorosis** is a condition caused by excessive ingestion of fluoride during tooth development, leading to changes in tooth enamel, but it does not affect the length of the mandible or interdental spacing.

**Option C:** **Gingival fibromatosis** is a condition characterized by the overgrowth of gum tissue, which can cause spacing between teeth, but it does not explain the increase in mandibular length.

**Clinical Pearl / High-Yield Fact**
In patients with hyperdontia, it is essential to assess the overall dental and skeletal development to determine the best treatment plan, which may include orthodontic or surgical interventions.

**Correct Answer:** C. Hyperdontia