Hi There,
I had my (second) double jaw+genioplasty surgery in November 2009, so less than 3 months ago. I still have no feeling in my chin, and my lower lip, not to mention the half-right side of my tongue.
For the tongue, and inside the cheeks, I've noticed that when I eat sweets (chocolate is my thing), I have a very strong tingling sensation for a few seconds, and when I mention it to my surgeon, he said that it was the nerves starting to reconstruct-work again, and that usually it did that with spicy foods.
So anything that will create such a sensation must be encouraged during the recovery.
For the face, such as chin, massages, from moderate-strong to feather-like soft should also help regain some sensation. From What I understand, there is two levels of feelings: deep and surface, hence the two types of massages.
I know that in certain cases, nerve damage can be irreversible. I hope this is not your case.
I am still learning to learn patience, since it's my second surgery and fourth round of braces, but I know how frustrating and worrying it can be.
Just keep hope, massage, and you will get better!

4th round of braces...
2nd jaw surgery on Nov. 23