Obvious transition line while smiling - will fillers help or will I need a revision? (Photo)

No fillers at all indicated, would be even dangerous (blindness, research about this risk) or deforming (granulomas).

You suffer from one deformity that's well known after a non complete facelift is applied, it is named as clear windseep / vertical-lateral sweep deformity. Essentially the surgeon is not very skilled or profficient in facelifts or either wanted to go home sooner than the is paid for, hence the facelift is incomplete, partial, does not encompass the entire face (as it should, obviously), leading to visibility of a clear and nitid frontier between what was "ironed" and the part that's flaccid and untreated, that's the line you perceive.

Solution? Finding a real facelift surgeon doing deep plane and COMPREHENSIVE techniques, he'll redrape the cutaneous cover of your face terminating this deformity for good.

See the link attached to this answer some further explanations of the sweep deformity and cases of my own already corrected.