After breast augmentation has the surgery affected nipple sensation?

It is possible. One of the potential risks of breast augmentation surgery is decrease or loss of nipple sensation. The published risk is about 10%. The nerve that gives the nipple sensation can be injured when the pocket that will contain the implant is created. If the nerve is injured or worse yet cut, there may be temporary or permanent loss of nipple sensation.
Nipple sensation. Depends on the incision, the dissection, submuscular versus subglandular and how far the depth of the dissection. The nerve supply to the nipple come primarily from the 3-5th intercostal nerves and this nerve should be saved to keep the sensation intact.
Yes. Change or loss of nipple/areola sensation is a known complication of breast augmentation surgery, regardless of the approach used. If loss of nipple/areola sensation would be devastating to a patient, i suggest she avoid breast surgery altogether.
It may. Generally speaking, it is uncommon for patients to experience long term loss of nipple sensitivity but it does occasionally occur and can range from 4-8%.
Temporary. Nipple sensation may change (higher or lower) after breast augmentation for about 3 months, and then it usually returns to normal. It is unlikely that there will be a permanent change, unless it was more than just an augmentation or you get very large implants. http://www.dassmd.com/breast-augmentation/index.html.
Sensation. There is always a small chance (5-10%) that there can be altered feeling after breast implant surgery. The nerves that provide feeling to the nipple and areola can be injured or bruised during surgery. Most of the time this is temporary but can last up to a year or 2. Some patients will have decreased feeling, while others have pins and needles or even increased sensitivity or pain.