My FFS doctor said to avoid bone cement at all costs. The reason is that bone cement can interfere with the bone growing back together.
How deep is the hollow part of your forehead and can this be filled with a solid bone graft instead of done dust and cement?
The procedure he used on my brow is to remove the frontal bones and reshape them and replace with small screws to hold the bone in place. After 30 days, the bones grew back together. The screws are still in place and I could have them removed if I want to. Right now they cause no problems, so I just leave them there.