Gravity and repeating face mimic activity are the main reasons of sagging, line formation and loss of expression
Face sagging mainly cause by sliding of the deep facia over the zygomatic cheek bone
Facial linesstarts after sagging of cheek. Traction of mimic muscles repeatingly is another reason. Botox changes tracking lines if done correctly
Prejowl line depression shadow can be hidden by filler. Also jaw angle increase may help stretching of face.