**Question:** Source of Ca+2 in dentinal bridge is:

A. Dentin
B. Enamel
C. Pulp
D. Blood vessels

**Core Concept:** Dentinal bridges are formed as a response to dental caries, particularly when bacteria invade the dentinal tubules and initiate the process of caries. Calcium ions (Ca++) are essential components in the mineralization and hardening of the dental tissues, including dentin, enamel, and the dentinal bridge.

**Why the Correct Answer is Right:** The correct answer, **C. Pulp**, refers to the dental pulp, which is a soft tissue containing odontoblasts, blood vessels, nerves, and fibroblasts. When the dental caries invades the dentinal tubules, the dental pulp responds by producing dentin, which eventually forms a dentinal bridge to close the tubules and prevent further spread of caries.

**Why Each Wrong Option is Incorrect:**

A. **Dentin (A)** is a part of the dental hard tissue but does not directly contribute to the formation of dentinal bridges. The pulp is responsible for that process.

B. **Enamel (B)** is the outer, hard, and mineralized layer of the tooth and is not involved in the formation of dentinal bridges.

D. **Blood vessels (D)** are essential for maintaining the pulp's health but do not directly contribute to the formation of dentinal bridges. The formation occurs through pulp's response to dental caries.

**Clinical Pearl:** Understanding the source of calcium ions in dentinal bridges is crucial for understanding pulpal responses to dental caries and maintaining oral health. The pulp, specifically odontoblasts, plays a vital role in producing dentin and mineralized tissue to combat the invasion of cariogenic bacteria and prevent further caries progression.