If the chin implant gets hit by someone during a fight, will the implant break or move around?
Depending on what your surgeon likes to use, chin implants can be flexible (silicone) or solid with characteristics similar to plastic. None of these are particularly brittle. The flexible ones can withstand a lot of blunt trauma (your skin will get damaged long before the implant will). In the case of the more rigid implants, I would think that any force strong enough to crack the implant would probably cause a jaw fracture as well. It is possible to have a chin augmentation without using a synthetic implant (splitting the bone and moving a segment forward). In this case, right after the surgery you would be at higher risk for a jaw fracture from a fight. Depending on how much bone overlap and callous formation is expected, in the long term your jaw could be weaker, the same, or stronger. (Discuss this with your surgeon.)I hope that helps.
