When restoring two adjacent teeth, which cavity should be prepared and its restoration completed first? Can both be prepared and restored at the same time?

If possible, the cavities should be prepared one at a time. I prepare the other one after finishing the first. First, we prepare and restore the tooth in which the caries is deeper. If both are at the same depth, the more posterior tooth is prepared first. Also, if one tooth has an old filling that overhangs toward the other, or its position encroaches on the other tooth’s emergence profile, we need to prepare that tooth first.
When we prepare both at the same time, the margin of one may encroach on the other, or its contour may be insufficient, and the second filling may not turn out as we would like.
To prevent this, when a matrix is placed on one tooth, a band is also placed on the other, but this still does not fully resolve the problem.
Additionally, when both are prepared at the same time, more postoperative sensitivity may develop if the dentin remains uncovered for longer.