**Question:** The inorganic component of subgingival plaque is derived from

A. saliva
B. blood
C. tooth surface
D. systemic calcium and phosphate

**Correct Answer:** D. systemic calcium and phosphate

**Core Concept:** Subgingival plaque is a biofilm that forms on the tooth surface, primarily composed of bacteria. The inorganic component of plaque is essential for its mineralization and maturation.

**Why the Correct Answer is Right:** The inorganic component of subgingival plaque is derived from systemic calcium and phosphate, which are transported to the oral cavity via blood and saliva. Calcium and phosphate ions are essential for the formation of hydroxyapatite crystals, which are the primary mineral component of plaque. These ions contribute to the mineralization of plaque, allowing it to mature and harden.

**Why Each Wrong Option is Incorrect:**

A. Saliva: While saliva plays a crucial role in plaque formation by providing nutrients and a favorable environment, it is not the primary source of the inorganic component. Calcium and phosphate ions are derived from the systemic circulation.

B. Blood: Similar to option D, blood supplies calcium and phosphate ions, which are essential for plaque mineralization. Plaque formation occurs both in the oral cavity and in the bloodstream.

C. Tooth surface: The tooth surface is where the plaque forms, but it is the systemic calcium and phosphate ions that contribute to the inorganic component of plaque.

**Clinical Pearl:** Understanding the origin of inorganic plaque components is vital for preventing and managing gingivitis and periodontal diseases. Maintaining good oral hygiene, reducing plaque accumulation, and promoting healthy systemic calcium and phosphate levels are crucial in preventing these conditions.