Teardrop implants occasionally rotate, what is the risk of putting new teardrop implants in?

There are many choices available to you. You have shaped implants that have changed position? Consider an MRI to see if they have an interior crack or rupture. The implants carry a warranty and may be replaceable on their shilling. We have had quite a few happy limeys cross the pond for shopping bargains, change of implants or nips and or tucks. The Sientra implant may sit more securely in the pocket. Do you want to change the size or shape or your implant or just the rotation?

Anatomic or Tear drop implants require precise pocket dissection.  They are textured and should integrate into the tissue, moving less compared round implants.  If you have movement, then possibly there is seperation of the implant from the capsule.  It would not be wrong to try tear drop again, but the same thing could happen again.

It is a common misconception that anatomical implants look natural and round implants do not.  It's the choice of the implant size and projection that determine if the look is natural.  Of course all of the implants should be under the muscle to look more natural.  Anatomical implants look natural in the upright position.  But laying down they maintain the same shape which is not what a natural breast does.  A natural breast flattens when the woman is laying down so in my option a round breast implant such as the MP+ style of implants look more natural.   There is a 5% chance that anatomical implants will rotate.  Why deal with an additional 5% complication rate which requires reoperation.  If you are set on only having an anatomical implant, the pocket must be closed so the implant has less chance of rotation.  Also implants with a more aggressive texturing such as the 410 and Sientra brand tends to incorporate better and rotate less. 

Tear drop implants will keep on rotating.  Thus makes no sense to replace them since issues will remain.  Your plastic surgeons guided you correctly.  Round implants are excellent choice and do not create the problem of rotation.

I am sorry to hear about the problem you are experiencing. Besides careful "design" of the breast implant pocket to match the selected breast implant,  there is not much that can be done to prevent "anatomic" breast implant rotation. Although I cannot give you specific advice without viewing photographs and a full communication of your goals, I can tell you that many patients achieve a very nice outcome with breast augmentation surgery, without "looking fake". Of course, careful communication of goals and careful  selection (based on pre-operative communication and careful measurements) of breast implant type/size/profile/position will be key. Best wishes.