Is There Much a of a Difference Between 320 Cc and 345 Cc

Hello! Thank you for your question. In
general, implant size does not
correlate with bra cup size. The cup size itself will vary from
manufacturer to manufacturer as well as who is doing the actual
measurements. Thus, cup size is never a reliable indicator for your
breast size. I typically encourage my patients not to communicate her
desires in cup size but more on the actual look and appearance. Given
your desires, a breast augmentation, with an implant or fat grafting,
would be an ideal procedure that would meet your expectations. Breast
augmentation is now the most popular procedure performed in plastic
surgery today. One tolerated very well by women with minimal downtime
and high patient satisfaction. Good
communication between you and your surgeon of your expectations is
warranted - choosing your surgeon wisely is the first step. Discussion

of your wishes and having an honest and open dialog of your procedure is
mandatory (e.g, implant type, incision, placement, etc). Your height,
weight, breast width, and body habitus will make a difference for which
implant style/projection to choose. Implant
profile will also make a difference on the projection, which will
influence overall breast/cup size. I have found

that photographs brought by the patient is helpful to get a
visualization of the appearance you wish for in terms of size, shape,
fullness, etc. In addition, your surgeon's pre and postoperative
photographs should demonstrate a realistic goal for you of results.
Sizers are helpful during an in-office consultation. Once this has
been accomplished, allow your surgeon to utilize his/her best medical
judgment during the procedure to finesse the best possible result for
you after preoperative biodimensional planning and fitting the right
implant for your breast width. This is the most important determinant
for the sizing of implants, which will provide the optimal result and
most aesthetically-pleasing result for you.Consult with a
board-certified plastic surgeon well-versed in breast procedures who
will examine and discuss with you the various options and factors to
consider and help you decide which one will be the right one for you.
Hope me that this helps! Best wishes for a wonderful result!

No there is not much difference between the two sizes you mentioned.

In my opinion, there  is no correlation between the size or model (profile) of implant used and resulting cup size.  This may have to do with several factors including: the amount of breast volume the patient starts with, the shape of the patient's chest wall (concave or convex), the type and model of breast implant selected (saline/silicone  and low/moderate/high profile), bra  manufacturer variance  in cup sizes, the  degree  of filling of the cup  with breast tissue,  and the subjective differences in patients perceptions of cup size. 
Much of the final “look” achieved after breast augmentation surgery  depends on several factors:


1. The initial shape, size (volume of breast tissue), symmetry of the patient's breasts. In general, the better the  preoperative breast appearance the more likely the breast augmentation “look” will be optimal.

2. The experience/skill level of the surgeon is important in determining the final outcome. For example, the accurate and gentle dissection of the breast implant pockets are critical in producing  long-term  well-placed breast implants. I personally think that these 2 factors are more important than any others, including type (saline or silicone)  or model (low/moderate/high profile)  of implant.

3. The type of implant used may  determine the final outcome, especially if the patient does not have significant covering breast or adipose tissue. For example, some surgeons feel that silicone implants have a more natural look and feel than saline implants because silicone gel has a texture that is similar to breast tissue. Each patient differs in the amount of breast tissue that they have.  If a patient has enough breast tissue to cover the implant, the final result will be similar when comparing saline implants versus silicone gel implants.  If a patient has very low body fat and/or very little breast tissue, the silicone gel implants may provide a more "natural" result.
On the other hand, saline implants have some advantages over silicone implants. Silicone implant ruptures are harder to detect. When saline implants rupture, they deflate and the results are seen almost immediately. When silicone implants rupture, the breast often looks and feels the same because the silicone gel may leak into surrounding areas of the breast without a visible difference.  Patients may need an MRI to diagnose a silicone gel rupture.   Saline implants are also less expensive than the silicone gel implants.
Other differences involve how the breast implants are filled. Saline implants are filled after they’re implanted, so saline implants require a smaller incision than prefilled silicone breast implants.
On May 10, 2000, the FDA granted approval of saline-filled breast implants manufactured by Mentor Corporation and McGhan Medical. To date, all other manufacturers’ saline-filled breast implants are considered investigational.
As of 2006, the FDA has approved the use of silicone gel implants manufactured by the Mentor Corporation and Allergan (formerly McGhan) for breast augmentation surgery for patients over the age of 22.

4. The size and model of breast implant used may  make a  significant difference in the final outcome. Therefore, it is very important to communicate your size goals with your surgeon.  In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as “natural” or “C cup” or "fake looking" or "top heavy" means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup  size may also be inaccurate.
I use  intraoperative sizers and place the patient in the upright position to evaluate breast size. Use of these sizers also allow me to select the breast implant profile (low, moderate, moderate plus, high-profile) that would most likely achieve the patient's goals. The patient's goal pictures are hanging on the wall, and allow for direct comparison.
I have found that this system is very helpful in improving the chances of achieving the patient's goals as consistently as possible.
By the way, the most common regret after this operation, is “I wish I was bigger”.

I hope this helps.

In our Jacksonville breast augmentation practice, we routinely perform breast augmentation revision surgery on women who wish they had gone bigger. 25 cc will not make much of a difference to your overall result. Remember the implant will look smaller inside the body.