I'm due to get 340-360cc silicone implants. What are the differences in Natrelle Styles 10, 15, 20, 40, 45, 110,115, and 120?

Thank you for the question.   The differences in “styles” of breast implants come down to differences in breast implant dimensions (width and projection) as well as breast implant shape. I would respectfully suggest that you  not try to become an “expert” on breast implant styles,  although it would behoove you to learn about the pros/cons of round/anatomic breast implants as well as the pros/cons of breast implants placed in the submuscular versus subglandular position. You will find much more information about these topics on this website. Generally speaking, the best online advice I can give to ladies who are considering  breast augmentation surgery ( regarding breast implant size/profile selection) is:
1. Concentrate on choosing your plastic surgeon carefully.  Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you're looking for. Ask to see lots of examples of his/her work.
2. Have a full discussion and communication regarding your desired goals  with your plastic surgeon. This communication will be critical in determining  breast implant size/type/profile will most likely help achieve your goals. 
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 or D cup”  etc means different things to different people and therefore prove unhelpful.
 The use of computer imaging technology may also be very helpful during this communication process.
3.  Once you feel you have communicated your goals clearly,  allow your plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals.  Again, in my practice, this decision is usually made during surgery.
 Best wishes. 

You have told us your cup size but not your bra
size.If you are 32 or 34 each 100 cc’s
of implant corresponds to 1 cup size change.If you are 36 or 38 each 200 cc’s of implant corresponds to 1 cup size
change.From this, you can compute the
volume required to achieve your desired goal.I always recommend small round textured silicone gel implants placed
retro-pectoral since they look and feel more natural, are more stable, less
likely to ripple or have complications needing revision.Implant profile is irrelevant in the
retro-pectoral position since the muscle compresses it.Best Wishes,Gary Horndeski, M.D.

I understand how confusing the multiple different shapes and styles of breast implants are too patients.Generally speaking round silicone breast implants are the most commonly used and often are the most natural-appearing after surgery.  Specific shapes and styles such as high profile, teardrop, shaped, all have specific indications for a special situations.The topic is so complex it is truly best if you sit down with your plastic surgeon and discuss this in detail.  Bear in mind that the round implant shape is the most commonly used and natural looking.