**Core Concept**
The retention of a pin retained crown is influenced by various factors, including the design of the pin, the material properties of the crown, and the mechanical properties of the tooth. The retention can be increased by modifying the pin design to engage with the tooth structure more effectively.

**Why the Correct Answer is Right**
The retention of a pin retained crown is increased when the pin is designed to engage with the dentinal tubules of the tooth. This is achieved by creating a dovetail or a serrated design on the pin, which allows it to interlock with the dentinal tubules, increasing the shear strength of the bond between the pin and the tooth. This mechanism is critical in preventing the pin from dislodging from the tooth during mastication.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not provide any information about how the retention of the pin retained crown is increased.
**Option B:** This option is incorrect as it refers to a different type of crown retention, which is not relevant to the question.
**Option C:** This option is incorrect as it does not provide any information about how the retention of the pin retained crown is increased.

**Clinical Pearl / High-Yield Fact**
To increase the retention of a pin retained crown, dentists should design the pin to engage with the dentinal tubules of the tooth, using a dovetail or serrated design. This will increase the shear strength of the bond between the pin and the tooth, making it more resistant to dislodgment.

**Correct Answer:** D.