How much more can you over fill a saline implant past the maximum fill?

Filling a saline implant with a greater volume reduces rippling and decreases the diameter of the implant allowing for more volume at a reduced diameter.  I usually fill to the recommended max, but many other plastic surgeons I have worked with have overfilled.  There have not been any cases of manufacturer warranty issues of which I am aware.

Thank you for the question.   
Some general thoughts regarding overfilling saline breast implants may be helpful to you: 
Saline breast implants are usually filled within a range provided by the breast implant manufacturer. Utilizing saline volumes in the UPPER range of the manufacturer's recommendations helps cut down on concerns such as breast implant rippling. Sometimes, patients who are looking for a certain "round, fake look" benefit from the use of overfilled saline implants.  This involves filling the saline implants past the range provided by the manufacturer.  I have found, through significant experience, that for the appropriately selected patient,  very nice outcomes can be achieved safely.  I have also found that saline breast implants can be overfilled significantly past what your current implants are filled to, without an increased rate of deflation.  Of course, the use of overfilled saline breast implants does have some potential drawbacks such as a firmer feel.  Furthermore, careful patient selection is key; not every patient is a good candidate for "extra-large" breast augmentation. I hope this helps.