How to make my forehead straighter? (Photos)

I  would advise against using implants or fillers for this issue. This is something that only you notice. If you have a problem then it will look abnormal and others will notice. The only thing that you should consider is a hairline advancement which will shorten the slant and make it less obvious. This is done with the Irregular Trichophytic incision so no scar is seen. 

The culprit is either a high hairline, genetically rounded forehead, or bone loss.

Depending on which it is (determined by facial analysis) the treatment will be different.

For the first one we can lower the hairline with a forehead lift. The latter two can be corrected with filler or even better with fat grafting.

Hope this helps.

Best of luck,

DrC

Decreasing the slant of your upper forehead is best done by the application of either bone cements or a custom implant for a permanent and assured solution. This is done through a more posterior scalp incision or one right along the frontal hairline.