**Core Concept**
The question is testing the understanding of the consequences of a severe blow to a permanent anterior tooth, specifically the frequency of fracture. The underlying anatomical principle is the structure and composition of the tooth, particularly the enamel and dentin.

**Why the Correct Answer is Right**
A severe blow to a permanent anterior tooth can lead to tooth mobility, but frequent fracture is less likely due to the tooth's anterior position and the presence of the labial bone plate, which provides additional support. The labial bone plate is a thin layer of cortical bone that covers the anterior surface of the roots of the anterior teeth, providing a degree of protection against vertical forces. Additionally, the anterior teeth have a more curved root shape, which helps to distribute forces and reduce the likelihood of fracture.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because tooth fracture is not the most common consequence of a severe blow to an anterior tooth.
* **Option B:** This option is incorrect because while tooth fracture can occur, it is not the most frequent outcome in this scenario.
* **Option C:** This option is incorrect because the labial bone plate provides additional support to the anterior teeth, making fracture less likely.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the position and structure of the anterior teeth make them less susceptible to fracture compared to posterior teeth. This knowledge can be useful in clinical practice when assessing patients with dental trauma.

**Correct Answer:** D.