My face is too thin after botox to masseter muscles. Is it permanent?

From a safety standpoint, one of the best features of Botox is that its effects are always temporary.  It works by relaxing muscles, and in your case the masseter muscle.  In 3-4 months your masseter muscles will begin to regain bulk as they begin to "work out" once again after the Botox has worn off.  

No. These results are not permanent. Botox masseter treatments require maintenance for long term improvement. Wait this out and give things 3-6 months to improve. Filler is always an option if the end result is still too thin for you. However, you are likely to see the Botox effect wear off completely. Best.

It is unlikely that the result will be permanent. When the Botox wears off in 4 to 5 months, the muscle may be slightly less full but will return to normal fullness over time as the muscle exercises through your normal facial movements. Volume replacement with products such as Sculptra can be used to restore lost facial volume.I hope this was helpful.