The tear drop implant is relatively new to the market but already has many names: form-stable, shaped, gummy bear. There are many advantages, a few disadvantages, and some similarities with the older gel models. The shaped or "tear drop" implant provides a more natural shape that avoids the high and round upper pole. This is a strong draw for women seeking a natural rather than "augmented" look. Secondly, the stability of the implant in terms of its density and the fact that the lower pole has strong projection can also help with mild forms of breast ptosis or "droopiness": it helps "lift" that lower pole of the breast. Thirdly, the textured shaped implants have lower rates of capsular contracture. Lastly, because the silicone has a higher rate of cross-linkage, even if the implant were to rupture, the silicone doesn't run. It has the consistency of a gummy bear, hence its other nickname. A board certified plastic surgeon should thoroughly examine you and carefully discuss all the risks and benefits: tear drop implants are more expensive, and not everyone will see a huge benefit in using them, so the surgeon should discuss weighted benefits and give you other options as well. You are correct that base width is one of the parameters informing size, but as with round gel implants, the projection varies between styles. The appropriate size is determined by your anatomy and tissue quality. Too big and you risk a "bottoming out" effect with early stretching of the tissues. You are also correct about the risk of rotation. One of the reasons to select an experienced board certified plastic surgeon is that he or she will be well-versed in the proper technique for placement of the shaped implant. If the implant is not placed snugly, there is a much higher risk of rotation. The shaped implant also requires that drains be placed to avoid fluid build-up which might increase the rate of rotation. All the best to you in this process, and I hope you are thrilled with your results!