**Core Concept**
ZOE (Zinc Oxide Eugenol) is a type of temporary restorative material used in dentistry. It is a mixture of zinc oxide, eugenol, and other ingredients. The primary reason ZOE is not used for permanent cementation is due to its chemical properties and potential for toxicity.

**Why the Correct Answer is Right**
ZOE contains eugenol, which can inhibit the formation of secondary caries by releasing free radicals that kill bacteria. However, eugenol is also a known irritant and can cause pulpitis if it comes into contact with the dental pulp. When used as a permanent cement, ZOE can cause chronic irritation, leading to pulp damage and potential tooth loss. Additionally, ZOE does not provide adequate mechanical strength for long-term use.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because ZOE does not provide adequate mechanical strength for permanent cementation, but it is not the primary reason.
* **Option B:** This option is incorrect because while eugenol can inhibit the formation of secondary caries, it is not the primary reason ZOE is not used for permanent cementation.
* **Option C:** This option is incorrect because ZOE is not used for permanent cementation due to its chemical properties, not because it is not biocompatible.

**Clinical Pearl / High-Yield Fact**
When using ZOE as a temporary restorative material, it is essential to remove it before placing a permanent restoration to avoid chronic irritation and potential pulp damage.

**Correct Answer: C.**