Gummy bear or anatomical implants are shaped like a breast. Hence they have texturing on the implant surface to adhere the implant to the breast tissue to prevent rotation. If these implants rotate, it produces an unsightly appearance as the fuller portion of the implant is now higher up.
Traditional silicone implants are hemispherical but assume a breast like shape when the person is in an upright position. Hence even if the implant flips around, it is of no consequence as it still maintains its shape.
Given its natural shape, there is a tendency to think that anatomical implants are better. However a recent study found that plastic surgeons were only 50% correct in predicting if a woman had anatomical or traditional implants when shown a photograph. Traditional implants have the same width and height; anatomical implants can be shaped such that they can be wider than tall, taller than wide etc.
In most patients this is of no consequence. However, uncommonly some women an have unusually shaped chest wall where a shaped implant is preferable. Besides, texturing on the implant surface has been related to a rare form of cancer called ALCL (Anaplastic large cell lymphoma). This has not been observed with smooth surfaced implants.
In most women traditional implants give as good a result as anatomical implants without the risks of rotation and ALCL.