**Core Concept**
The concept of center of rotation for tipping refers to the point around which a tooth or a group of teeth rotates when subjected to an external force. This is a fundamental principle in orthodontics and prosthodontics, where understanding the center of rotation helps in planning and executing treatment strategies.

**Why the Correct Answer is Right**
The center of rotation for tipping is indeed located at the long axis of the tooth. This is because the long axis is the line that passes through the center of the tooth, perpendicular to the surface of the tooth. When a force is applied to a tooth, it tends to rotate around this axis, rather than pivoting around a point on the surface of the tooth. This is due to the distribution of stresses and moments along the length of the tooth. The long axis of the tooth acts as a fulcrum, around which the tooth rotates when subjected to an external force.

**Why Each Wrong Option is Incorrect**
**Option A is incorrect because** it states that the center of rotation for tipping is at the long axis of the tooth, which is actually the correct answer. However, **Option B is incorrect because** the B-L axis (bucco-lingual axis) refers to the line that passes through the center of the tooth, perpendicular to the long axis. This is not the center of rotation for tipping. **Option C is incorrect because** the M-D axis (mesio-distal axis) refers to the line that passes through the center of the tooth, perpendicular to the bucco-lingual axis. This is also not the center of rotation for tipping. **Option D is incorrect because** infinity is not a valid location for the center of rotation for tipping.

**Clinical Pearl / High-Yield Fact**
When planning orthodontic treatment, it's essential to identify the center of rotation for tipping to determine the most effective way to move teeth. Understanding the concept of center of rotation can help clinicians avoid unnecessary complications and achieve better treatment outcomes.

✓ Correct Answer: A. Long axis of tooth