Does fibroadenoma cause hardening of silicone implant?

Dear lilpil_sydney,
Fibroadenomas themselves don't contain bacteria nor increase the risk of capsular contracture.  To what I believe your plastic surgeon was alluding was that the act of removing the fibroadenoma usually requires cutting through breast tissue and breast ducts which do contain bacteria which can increase your risk of capsular contracture.  Both of your surgeons are correct in my opinion, but they are looking at things from different perspectives.

Fibroadenomas, as you know, are benign lesions. They are not infectious lesions and do not "contain bacteria".   They do not, directly "cause" encapsulation of breast implants.

 Also, as you know, different plastic surgeons will have different viewpoints and opinions.  Some will, some will not, remove benign lesions at the time of breast augmentation surgery. In our practice, lesions such as cysts or fibroadeomas that have been worked up and found to be a benign can be removed (depending on the patient's specific situation) during breast augmentation surgery (and other types of elective breast surgery). 
  Best wishes.