**Core Concept**
Restoration margins refer to the areas where tooth preparations meet the restorative material, such as amalgam or composite resin. The location of these margins can significantly impact the health of the surrounding periodontal tissues. In particular, the interaction between the restoration margin and the plaque-retentive areas of the tooth can lead to inflammation and other periodontal problems.

**Why the Correct Answer is Right**
Plaque-retentive areas are those that harbor bacteria and are difficult to clean. When a restoration margin is placed in a plaque-retentive area, such as the cervical margin of a tooth, it creates a trap for bacteria, leading to an accumulation of plaque and subsequent inflammation. This is because the margin acts as a "microenvironment" that fosters the growth of bacteria, which in turn causes an inflammatory response. The location of the restoration margin is critical in determining the extent of inflammation, with plaque-retentive areas being the most problematic.

**Why Each Wrong Option is Incorrect**
**Option A:** Subgingival margins, while problematic, are not necessarily plaque-retentive. The subgingival location can lead to inflammation, but it is not the most problematic location in terms of plaque retention.

**Option B:** Supragingival margins are not typically associated with plaque retention, as they are above the gum line and easier to clean.

**Option C:** Occlusal margins are not typically associated with plaque retention, as they are on the chewing surface of the tooth and are not as prone to harboring bacteria.

**Clinical Pearl / High-Yield Fact**
When designing restorations, it is essential to consider the location of the restoration margin in relation to the plaque-retentive areas of the tooth. Placing margins in these areas should be avoided whenever possible to minimize the risk of inflammation and other periodontal problems.

**Correct Answer:** C.