In which direction should the ligature pigtail be tucked under the arch wire?

The ligature pigtail should be tucked under the arch wire in a distal to mesial direction to ensure that it is properly secured and does not create any interference with the movement of the teeth or the placement of other components. This method helps maintain the intended force applied by the arch wire, keeping it stable during treatment.

Tucking the ligature in this manner also minimizes the risk of injury to the oral tissues, as it prevents any sharp edges or protrusions from causing discomfort. Additionally, placing the ligature in this direction is in line with the principles of optimizing the mechanics of orthodontic treatment, ensuring that various components work harmoniously together.

The other choices do not adhere to standard practices in orthodontics. For instance, tucking the ligature mesial to distal could result in improper positioning that might lead to ineffective force application. Similarly, occlusal to gingival or gingival to occlusal orientations do not provide the necessary tension and could compromise the overall alignment and stability of the arch during treatment.