**Core Concept**
Zinc oxide-eugenol cement is a widely used dental restorative material, but it can be difficult to remove from instruments. The correct choice for cleaning this cement requires an understanding of its chemical composition and properties.

**Why the Correct Answer is Right**
Eugenol, a key component of zinc oxide-eugenol cement, is soluble in certain essential oils. Oil of orange (d-limonene) is a specific essential oil that can effectively dissolve and remove zinc oxide-eugenol cement from instruments. This is because d-limonene has a high solubility for eugenol, making it an ideal choice for cleaning contaminated instruments. The other options, essential oil, white rosin, and clove oil, do not have the same level of solubility for eugenol and are therefore ineffective for this purpose.

**Why Each Wrong Option is Incorrect**
**Option A:** Essential oil is too general a term and does not specifically refer to a solvent effective against zinc oxide-eugenol cement.
**Option B:** White rosin is a type of rosin used in dentistry, but it is not effective for dissolving zinc oxide-eugenol cement.
**Option C:** Clove oil, while containing eugenol, is not as effective a solvent for zinc oxide-eugenol cement as oil of orange.

**Clinical Pearl / High-Yield Fact**
When cleaning instruments contaminated with zinc oxide-eugenol cement, it's essential to use a solvent that can effectively dissolve the eugenol component. Oil of orange is a specific and effective choice for this purpose.

**✓ Correct Answer: D. Oil of orange**