What Would Cause Pressure/pain on Breast Crease? 450cc, Saline Under Muscle, Crease Incision? (photo)

You need to be more patient in your healing phase especially with larger implantation as you demonstrate in the posted photo

The picture you provided does not show classic bottoming out or ptosis of the crease.  There is a slight but natural appearing asymmetry of the crease with the left being somewhat lower than the right.It takes six months to fully recover from a breast augmentation.  Then what you see is what you get.  That is the best time to treat such things as breast asymmetries if you are still concerned.As for the discomfort, nerve regeneration or umbilical vein thrombosis are possible causes.  Neither are dangerous and both resolve on their own.Discuss these issues with your plastic surgeon.  He or she will take you through this.I hope this helps.

After having an augmentation with large (450cc are large) implants, it is not uncommon for the pressure resulting from the stretching tissues to cause pain. This is commonly felt along the inframammary fold as this area bears the weight of the implant. It can take several months for this types of discomfort to resolve as the breast adjusts to the implant size. Adherence to postoperative instructions and follow up with your plastic surgeon are advised.

I wouldn't be concerned unless you start running a fever or there is a noticeable change in breasts. Everything you describe sounds like part of the healing process. You are still fresh from surgery and you may experience odd sensations over the next several months. The nerves stretch rapidly to accommodate the implants and it takes time for them to calm down. 

Most likely, pain at the incision at 6 weeks is related to the nerves returning to full function. Sometimes after surgery, patients will experience numbness or changes in sensation. This will recover and can have times where the sensation is increased. I would massage the area to desensitize. As for the feeling of the fold, I would address this with your surgeon as there is nothing one can tell from a photo.
Best of luck,
Vincent Marin, MD
San Diego Plastic Surgeon