**Core Concept**
Proper implant placement is crucial to prevent complications such as peri-implantitis, bone loss, and damage to adjacent teeth. The distance between the implant and adjacent tooth is a critical factor in ensuring the long-term success of the implant.

**Why the Correct Answer is Right**
The American College of Prosthodontists recommends a minimum distance of 1.5 mm between the implant and the adjacent tooth to prevent irritation of the periodontal ligament and to allow for adequate healing. This distance also facilitates the proper alignment of the implant and the adjacent tooth, reducing the risk of occlusal instability and promoting optimal esthetics. The 1.5 mm distance is a general guideline, and the actual distance may vary depending on the individual case and the type of implant used.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because a distance of 0 mm would not provide enough space for proper healing and could lead to complications such as peri-implantitis and bone loss.
* **Option B:** This option is incorrect because a distance of 0.5 mm may not be sufficient to prevent irritation of the periodontal ligament and could lead to occlusal instability.
* **Option C:** This option is incorrect because a distance of 2 mm may be too great, potentially leading to inadequate esthetics and occlusal instability.

**Clinical Pearl / High-Yield Fact**
When placing an implant, it's essential to consider the biologic width, which is the distance between the implant and the adjacent tooth, to prevent complications and ensure the long-term success of the implant.

**Correct Answer:** D. 1.5 mm