Can Botox Fill in Cleft Chin?

Start with Botox and if this relaxes the mentalis muscle enough to decrease the cleft then great. If not the next step would be to fill the cleft from underneath with a commercially available filler. Unfortunately the cleft is usually there for a reason and that is that there are dermal connections to the underlying muscles and fascia. Separating those connections is usually the most effective and requires a fairly simple surgical procedure.

In general, a cleft in the chin would respond best to a volumizing filler, such as Radiesse or a combination of Radiesse and Perlane L (both of which can provide lift) and the use of microdroplets of a neuromodulator, such as Dysport, Botox, or Xeomin, to relax the surrounding musculature of the chin that may be contributing to cleft.

If the two procedures are to be performed at different treatment sessions, I would recommend that the neuromodulator be performed first and then a couple of weeks later the volumizer filler injected. Two weeks is generally sufficient time to see just how much improvement can be achieved via the neuromodulator alone. In this way a more exact amount of volumizing filler may be used. 

If, however, both procedures are being performed on the same day, it is best to inject the volumizing filler first and then the neuromodulator afterward. If performed in the opposite order there is an increased risk that the introduction of the volumizer might lead to spread of the neuromodulator outside the region into which it was injected.