**Core Concept**
Gingivitis is an inflammatory condition of the gingiva, characterized by the accumulation of dental plaque, leading to the activation of immune cells and the release of inflammatory mediators. This results in the clinical signs of gingivitis, which are typically reversible with proper oral hygiene and treatment.

**Why the Correct Answer is Right**
The clinical signs of gingivitis appear due to the activation of polymorphonuclear leukocytes (PMNs) and macrophages in response to the bacterial components of dental plaque. The release of cytokines and other inflammatory mediators leads to the characteristic symptoms of gingivitis, including redness, swelling, and bleeding of the gingiva. The gingival crevice (sulcus) becomes more pronounced, and the gingiva may become painful to the touch.

**Why Each Wrong Option is Incorrect**
**Option A:** Gingivitis typically does not involve the periodontal ligament or the alveolar bone, which are affected in periodontitis.
**Option B:** Gingivitis is not a condition characterized by the loss of teeth, which is a hallmark of periodontal disease.
**Option C:** Gingivitis is not a condition of the hard tissues of the teeth, but rather an inflammatory response to bacterial plaque on the gingiva.

**Clinical Pearl / High-Yield Fact**
It's essential to note that gingivitis is reversible with proper oral hygiene and treatment, whereas periodontitis can lead to irreversible damage to the periodontium.

**Correct Answer:** D. 2-3 weeks after plaque accumulation