Whats the difference between double bubble and bottoming out?

Double bubble is a description of the shape of the lower breast that occurs when there is an indentation in the lower part of the breast where the breast tissue stops and where the implant continues.  This indent is usually secondary to the preexisting shape of the breast called tuberous or constricted.  The original lower crease of the breast is high therefore there is limited tissue to cover the implant which can result in the double bubble. 



Double bubble is also used to describe bottoming out because the look can be somewhat similar.  However, with bottoming out, or pseudoptosis, the nipple and areola are high and often are visible above the bra or bathing suit.  The bottoming out is secondary to the implant resting too low from over dissection by the surgeon or a capsule that is simply not strong enough to hold the implant. 

Great question.  A double bubble is always the result of dissecting a pocket for the implant lower than the existing inframammary fold, essentially creating a new inframammary fold.  The old fold remains visible  with the implant bulging out between the old fold and the new fold creating the "bubbles" of bulging implant below and breast tissue above the original fold.  Bottoming out is when there is more volume below the nipple than above the nipple, causing the nipple to point upward.  This is most often seen, again, with overdissection of the implant pocket below the natural limits of the breast in order to fit a larger (and heavier) implant.  It can also happen in the absence of overdissection in those  patients who naturally have a long distance from their nipple to the fold if the implant diameter is not wide enough to provide enough upper pole volume to balance the lower pole.  Using a round implant in these patients may require too wide an implant being used which can result in symmastia (uniboob) and lateral displacement.  These patients are usually best served with a tall, shaped implant that will better fit their anatomy and also resist inferior displacement over time due to their textured surface.  

Both are problems associated with implant malposition where with bottoming out the implant and the fold have lowered too much. A double bubble deformity is associated with capsular contracture and elevation of the implant with skin overdraping it. Both require breast revision specialist to correct. Best of luck