I am not aware of any study investigating the time in which it takes for the volume of the masseter muscle to regain its orginal size after Botox wears off, and determining whether this would take more time if someone has maintained treatment for a long while vs. just having one treatment. An expert in this treatment, such as an ENT physician, Dr. Andrew Blitzer, NYC, who deals with TMJ syndrome (jaw clenching) has a great deal of clinical experience about this treatment and has communicated with me that the masseter muscle returns to full volume in 4 to 6 months, the time depending on the dose used and the extent of atrophy the muscle developed initially after treatment.