In order to expose the glabella for reshaping, the surgeon has to make an incision across the hairline and fold the skin down over the lower face. This severs the scalp's nerve supply leading to total numbness from behind the line of incision to about the crown of the head immediately post-op.
Sensation returns gradually as the severed nerves reconnects. I am currently about 3 months post-op, and have regained full sensation in the first inch of scalp behind my hairline. Nerves heal very slowly, so the process can take many months. Some loss of sensation can indeed be permanent.
Hair loss occurs as a result of trauma at the site of incision. I had some fairly dramatic shedding in the week or two immediately after surgery, but this stopped shortly afterwards. Dr. Spiegel's technique utilizes a trichophytic closure, allowing hair to grow through the forehead incision and partially concealing the scar. This has worked pretty well in my case.
If you have what Dr. Ousterhout calls a "Type I Forehead", with a filled-in sinus cavity, then you would be eligible for an endoscopic procedure. This technique avoids much of the trauma typically caused by forehead work, since the incisions are small and the facial nerves can be avoided.
