brushing ur teeth is for hygene purpose if i`m not wrong .
how can compair with natural or not ? 
because brushing your teeth = grooming.
if it wasn't suppose to be dirty , naturally it
wouldn't be dirty. But naturally , it get's
dirty so what do we do ? we 'un-naturalise' by brushing it. Same
goes to make up / foundation , eg there's a pimple , you're going
for a photoshoot , having pimples is natural . So
by applying make up / foundation , you 'un-naturalise' again.
So my conclusion : you can't pin-point modelling and say it's
all unnatural. Everything else is the same , isn't it ? why is
modelling different then ?
@ Deino , i hope you get where i'm coming from . (;
not trying to flame here