Would exchanging 450 CC saline implants to 405 CC gel implants deliver a noticeable difference in size?

I would suggest going down to 300-350 cc's, since about 150 cc's is an increase/decrease in cup size in the average bra. Only going down 45 cc's will still keep you in the same bra most likely.

Dear Terrific509044,
breast implant type and sizing selection is a complicated process and requires a detailed consultation that includes a discussion of your goals, a detailed examination, and a lengthy discussion. But the decision will always start and end with the patient. When it comes to sizing, we have all of our patients find 3 photos of their desired breast size. We ask for naked breast photos because clothing can obscure the true size (push up bras). Next, we consult with patients and go over the photos and take detailed breast measurements during a physical exam. Next, we using a sizing algorithm to determine a range of implants that will work based on the exam and the measurements.Lastly, during the operation, we use silicone sizers in the operating room to see how the size actually looks in the breast. We sit the patient up in the operating room, while asleep of course, and compare the sizer result with their desired look photos. If it is too small, we start the process over with a slightly larger implant. We don't stop until we get the perfect match.Of all of my breast augmentation patients, every one of them has been happy with their size due to this detailed and meticulous process. You don't want to invest time and money into a result that is either too big or too small.You should discuss your concerns with a board-certified plastic surgeon and make sure that your surgeon understands your goals.
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

You should know that we have no idea about cup sizes; it's impossible to predict and any formulas you may come across are completely made up. Your proposed size change from 450 to 405 is a 10% reduction in volume, and will likely be unnoticeable. This is especially the going from a lower to higher projecting device. As an aside, why would your surgeon recommend a profile change? Is she concerned you may sag? You should keep the current profile and drop at least 15 to 20% in volume to see a small change. It is true that swapping saline for silicone can lead to the appearance of a smaller device even when the volumes are the same, modern highly cohesive implants with more optimal fill will not have that same effect.