How sturdy are silicone implants under the muscle for bedroom play?

Implants are placed under great pressure when tested for safety. Literally tons of pressure are applied on an implant, and held there for a while, to see if they’re able to withstand it. The amount of pressure applied during sexual activity (even rough play) would not even come close to what is applied during testing, so you shouldn’t be worried about it. It’s more your actual breast tissue that you should be concerned about damaging.

1 month is a safe amount of time before the breasts are able to be used during foreplay and intercourse. IF you have no nipple sensation yet, then your partner can badly injure you, as you would expect, because the normal pain feedback is diminished. Make sure you have someone who is understanding of this and cooperative and safe. It can take up to a year for all of the nerve endings to wake up. Nipple numbness is very rare, though I have certainly seen it after breast augmentation. 

Breast implants are designed to withstand significant amount of force. In other words, rupture of the implants would require significant force, unlikely to be sustained during sexual activity. Best wishes.