Would Dermal Fillers Remove Deep Forehead Lines Unaffected by Botox?

Typically dermal fillers are not used on the forehead. Lasers can be a good adjunct to Botox in the forehead. In rare cases you can use fat injections

I like to use Botox in conjunction with dermal fillers, as the lines are caused by constant movement, so no matter what treatment you do, nothing will ever get rid of them if the muscles keep moving and bringing the lines back.  Once the lines are relaxed I will do a combination of dermal fillers and lasers to soften their appearance.  Studies have shown that combining filler with Botox is superior to improving lines created by movement and present at rest than either one alone.

If the lines are deep at baseline, Botox can take time to fully soften them. Supplementing with filler in the short term is a good answer. I would recommend going to a place that knows filler well, so as to match the right filler with the areas of concern. Fine lines do better with certain fillers (Belotero, etc) and deeper lines, where more volume is necessary, do well with others (Radiesse in the right anatomical areas, etc). Best of luck.