This decision depends as much on what the surgeon can accomplish using either the round or the anatomically contoured implants as on which type of implants to use.
Assuming the breast pockets are dissected in to the inferior or lowermost extent in the exact same manner, the shaped implants will impart more fullness at the top, and provide a more natural, gently curving slope to the augmented breast. For this to happen, however, the lowermost portion of the dissection or pocket must be the same no matter which mammary implants you use. If a surgeon habitually dissects low enough inferiorly to drop round breast prosthesis low enough that upper pole fullness is lost, that surgeon will likely favor the teardrop shaped, or anatomically shaped implant to compensate for that dissection. For anatomically shaped or contoured implants to do what they were intended for, pocket dissection has to extremely precise. This is because contoured breast implants are not symmetric; they have a top and bottom. If the subglandular or submuscular pockets are too wide, the shaped implants can shift or even flip, imparting asymmetry and even worse an unnatural shape to the augmented breast. Even though shaped mammary implants are textured, this is still no guarantee against malposition. Finally using the round type of breast implants can impart more medial or inner breast fullness. This significantly improves cleavage, because more fill volume winds up toward the more central part of the breast.