**Core Concept**
Tetracycline, a broad-spectrum antibiotic, can cause tooth discoloration due to its binding to calcium ions and incorporation into tooth enamel. This process occurs during tooth development, resulting in permanent discoloration.

**Why the Correct Answer is Right**
The correct answer is related to the mechanism of tetracycline binding to calcium ions, which are essential for tooth enamel formation. During tooth development, tetracycline binds to calcium ions, leading to the formation of a tetracycline-calcium complex. This complex is then incorporated into the tooth enamel, causing permanent discoloration. The specific reason for this discoloration is the absorption of light in the blue and red spectrum, resulting in a yellow or brownish hue.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it does not relate to the mechanism of tetracycline binding to calcium ions or the incorporation of the tetracycline-calcium complex into tooth enamel.
**Option B:** Incorrect because it refers to a different mechanism of action of tetracycline, which is not relevant to tooth discoloration.
**Option C:** Incorrect because it is a type of bacterial resistance, not related to the mechanism of tetracycline binding to calcium ions.

**Clinical Pearl / High-Yield Fact**
To remember the mechanism of tetracycline-induced tooth discoloration, recall that tetracycline binds to calcium ions, which are essential for tooth enamel formation. This binding leads to the incorporation of the tetracycline-calcium complex into the tooth enamel, resulting in permanent discoloration.

**Correct Answer: C. Calcium-complex**