**Core Concept**
Polymerization shrinkage is a significant concern in dental composite restorations, leading to stress and potential damage to the tooth structure. It occurs due to the contraction of the polymer chains as they undergo cross-linking during the curing process.

**Why the Correct Answer is Right**
The polymerization shrinkage of composite materials is a well-documented phenomenon, causing stress in the range of 3-7 MPa. This value can vary depending on the specific composite material, curing conditions, and thickness of the restoration. A commonly cited average value is around 5 MPa, which is the correct answer. This stress can lead to microleakage, marginal breakdown, and eventually, secondary caries. The polymer chains contract and pull away from the surrounding tooth structure as they cross-link, resulting in a tensile stress of approximately 5 MPa.

**Why Each Wrong Option is Incorrect**
**Option A:** 1 MPa is too low, as it would not cause significant stress or damage to the tooth structure. While some studies report lower values, 1 MPa is generally not a reliable estimate.
**Option C:** 15 MPa is too high, as it would likely lead to catastrophic failure of the restoration and potentially cause tooth fracture. This value is not supported by most studies on polymerization shrinkage.
**Option D:** 30 MPa is excessively high and would definitely result in catastrophic failure of the restoration. This value is not even in the range of reported values for polymerization shrinkage.

**Clinical Pearl / High-Yield Fact**
A key factor influencing polymerization shrinkage is the thickness of the composite restoration. Thicker restorations tend to experience more shrinkage stress, making it essential to minimize the thickness of the composite to minimize stress and prevent damage to the tooth structure.

**✓ Correct Answer: B. 5 Mpa**