Botox for over 10 years for masseter reduction, now resistant to Botox, Dysport and Xeomin?

I'm not sure what doses of Botox that you have been receiving but this area generally requires more neurotoxin to see significant effects. As we age, gravity is contributing to a downward direction of our facial tissues and perhaps a small incision "facelift" with some neck tightening of the platysma muscle along the jawline would give you the results that you are looking for. Be sure to explore all your options. Good luck.

Myobloc is a botulinum toxin B product.  It is sufficiently different that neutralizing antibodies to BTA, which are very rare for cosmetic botulinum toxin, do not block BTB.  The bad news is that the effect of myobloc is just a couple of months and it much more likely to cause systemic side effects.  Generally for this reason, it is not much of an option if you actually have neutralizing antibodies which is honestly unlikely.

I would add ultherapy and consider double dosing of one of the toxins.  Myobock will work for shorter time period and isn't a good solution.  Best, Dr. Emer.