**Core Concept**
Apical transportation is a common problem in endodontics that occurs during the root canal preparation process, where the root canal's apical foramen is compromised, leading to a reduction in the canal's apical diameter. This can result in a transportation of the canal's shape, making it more oval or elliptical.

**Why the Correct Answer is Right**
Zipping refers to the apical transportation of the root canal, where the canal's apical foramen is compromised due to excessive use of endodontic instruments, such as files or reamers. This can lead to a loss of the canal's original shape, making it more prone to fracture or perforation. The apical foramen is the narrowest part of the root canal, and zipping can occur when instruments are used too aggressively or with excessive torque, causing the canal's walls to be compromised.

**Why Each Wrong Option is Incorrect**
**Option A:** Curing is a process used in dentistry to harden or set materials, such as resin or cement. It is not related to apical transportation or root canal preparation.

**Option C:** Ledging is a term used to describe a situation where a root canal instrument becomes wedged or stuck in the canal, often due to excessive use of force or improper technique. While ledging can be a complication of root canal preparation, it is not synonymous with apical transportation or zipping.

**Option D:** Apical perforation is a serious complication that can occur during root canal preparation, where the root canal instrument perforates the apical foramen or the surrounding bone. While apical perforation is a possible consequence of zipping, the two terms are not interchangeable.

**Clinical Pearl / High-Yield Fact**
To avoid zipping or apical transportation, it is essential to use endodontic instruments with caution and control, and to maintain a gentle, continuous motion while preparing the root canal. Additionally, using a well-designed and well-fitted canal instrument can help to minimize the risk of zipping.

**✓ Correct Answer: B. Zipping. Apical transportation is also known as zipping.**