**Core Concept**
Systemic fluoride works by incorporating into the hydroxyapatite crystals of tooth enamel, making teeth more resistant to acid attack and decay. This process is known as fluorapatite formation.

**Why the Correct Answer is Right**
Systemic fluoride is ingested orally and absorbed into the bloodstream, where it is distributed to the bones and teeth. Once in the teeth, it replaces hydroxide ions in the hydroxyapatite crystals, forming fluorapatite. This substitution increases the crystal's resistance to acid dissolution, thereby reducing the incidence of dental caries. The process of fluorapatite formation is a key mechanism by which systemic fluoride exerts its cariostatic effects.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because topical fluoride, not systemic fluoride, is primarily involved in the process of saliva and plaque formation.
**Option B:** This option is incorrect because while fluoride can inhibit the activity of certain enzymes involved in the caries process, it does so indirectly through the formation of fluorapatite.

**Clinical Pearl / High-Yield Fact**
It's essential to note that excessive ingestion of systemic fluoride can lead to dental fluorosis, a condition characterized by white or brown discoloration of the teeth. This highlights the importance of monitoring fluoride intake to avoid adverse effects.

**Correct Answer: C.**