I had 40 units of botox injected into my masseter muscles (20 ea side) with no change whatsoever. What could have gone wrong?

Thank you for the question. The masseter muscle is one of the more dense and strong muscles in the body. Shrinking the muscles mass typically requires multiple treatments, especially for men or patients with very prominent muscles. In addition, the results generally take a few weeks to become noticeable. This type of treatment is a bit different that, say, Botox for forehead lines where the results are seen in just a few days.

A good way to monitor your progress after Botox for masseter reduction is with your hands.  In the morning when you look at yourself in the mirror, put your hands on the sides of your jaw and feel the masseter muscle as you clench down.  For the first week after injection, you'll notice less and less muscle activity each day.If you still have significant movement after 1 week, then an additional treatment may be necessary to achieve full relaxation of the muscle.  Once the masseter muscle is relaxed, you'll notice your jawline begin to slim and taper with the most significant visible effects present at 1-3 months.  

You did not mention how long ago you had the Botox treatment to your masseter muscles, but it normally does take several days and sometimes a week or so to see the full effect from the injection.  If you had the treatment more than a week or two ago, it may be that you need a higher dose to relax the muscle.  I am also not sure how you are judging your results.  You may not see any decrease in size of the muscle for several months after the treatment, but within a week or so you should notice the muscle not tensing up when you try and clench.