I have a thin bottom lip and now it is disappearing completely. What treatment would resolve this? (photos)

As we age we lose fullness in our face, including the fat and the bone support.  We also lose collagen and elastin, so our skin wants to sag.  All of these things combine to make our lips look thinner as we age.  I would suggest some volume around your mouth and in your chin (Voluma, Radiesse, for example).  And some volume in the lips themselves would be helpful (Juvederm, Restylane, for example).  You may also benefit from Botox in your chin, as you have some muscle strain showing, and that pushes the lower lip up a bit.  These are all office procedures.

It is very common as we get wiser/maturer ;) that our lips become thinner and recede into our mouth. Dermal fillers such as Juvederm or Restylane are great starting points to rebuilding/recreating the lips in a natural and safe way. Best to speak with your dermatologist.