What happens if one of my breast implants hardens and the other doesn’t? Do both need to be removed?
Implant won't harden. Implants don't get hard, ever. But the scar around them can tighten, thicken, and make the breast feel quite firm (capsular contracture--cc). When cc occurs, it can be due to an old silicone implant rupture (the newest ones don't leak and rupture rarely), bleeding around one side, bacteria (not infection) around one side, such as from dental work, etc. If old replace both. If new, correct the cc!
How old are implants. This answer is complex and requires analysis of several issues such as: how old are your implants? Size satisfaction? Degree of sagging? For example if your implants are only one year old, i would advise single sided replacement but if 10 years old, i would probably consider remove and replacing both with replacement or fat grafting.