I am 5'10 and 114pounds. Very thin. Is 400cc silicone implants too much for my body?

It sounds as if you are not communicating very well with your surgeon. This can lead to problems and I would suggest having a consultation with another surgeon to see if you are able to communicate more effectively. Ideally you should be able to look at before and after photos of patients that have a similar build and frame as yourself and get a good idea of what you might look like with different sized implants. Most likely 400 cc implants will be too big for you if you are wishing to have a conservative C cup breast. If the implants are placed under the muscle (where I personally think that they should be), then the tear shaped implants do not offer a more natural look than a properly sized round implant. 

Thank you for the question.
In regards to specific size/profile of breast implant, despite good intentions, online consultants will not be able to provide you with  meaningful specific advice.  Ultimately, in person consultation with well experienced board-certified plastic surgeons will be necessary. Careful measurements, dimensional planning, and careful communication will be key.
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.  Again, have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining which operation and/or 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" or "classy and sexy" etc 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.  The use of computer imaging may be very helpful during this communication phase.
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.  The use of temporary intraoperative sizers with the patient in the upright position makes selection of the best breast implant size/profile relatively easy.
I hope this, and the attached link, helps.

Hi Ali,There is no one perfect size that you must select.  There are many choices depending on your aesthetic preferences, your height, and your frame.  We have our patients try on implants of various sizes.  This helps them see what they might look like after the procedure.  This way, you can select an implant that looks nice to your eye and is proportional with your figure.  We also use the Vectra 3D system to simulate various implants.  This is a second  way to show you how you may look with the different implants.  In the end, the choice of implant is up to you.  There is no such thing as you are going to small.  The surgeon's role is to guide you to a range that fits your frame and minimizes the risk of  complications down the line.  We are located in Wayne, NJ and would be happy to set up a consultation to review your questions.  I hope this is helpful.  Take care.Dr. Parham Ganchi - NJ Plastic Surgeon