Can the implant cause pectoral muscle to tear from breastbone?

Without a photo it is difficult to answer your question. But the pec muscle is cut most of the time to allow the implant to sit properly. I would recommend you return to your surgeon and let him or her examine you.

The pectoralis muscle is usually detached from the sternum at its bottom portion to allow the implant to descend properly beneath the breast.Is divot is most likely caused by surgical disruption of the pectoralis muscle and not by a tear.These types of deformities can be satisfactorily treated with fat injection.

Size of an implant will be the driving force as to how much the pectoralis muscle will need if at all to be divided.  If the implant is a small implant (<400cc) then most often division of any muscle fibers is minimal.  As the implant size, volume, and diameter increases more muscle fibers will need to be divided to accommodate the device.  It sounds as if you may have some "window-shading" of the muscle and displacement of the implant.  You should discuss this with your surgeon as there are several options on how to deal with this if so desired.