Treatments for Sensation Loss After Breast Augmentation?

I've had a BA about 9 months ago under the muscle thorugh the breast crease. My right breast has lost some sensation from the nipple down.Since I will need an implant replacement eventually I'm concerned that the 2nd surgery will cause complete sensation loss, & I was considering going a cup bigger in the future during the replacemnt.I'm very worried that the sensation may never come back are there any treatments or surgeries that will help? What are my options and what causes sensation loss?