What are the approximate number of units of Botox required for jaw reduction?

To slim the face, Botox is injected into the masseter muscles. Appropriate patients for treatment have significant volume of muscle, rather than a strong bony prominence at the angle of the jaw (mandible). Injecting the masseter muscle with Botox decreases the prominence of the muscle and tapers the lower face. Dosage depends on the patient's muscle volume, together with regional and cultural variations in the amount of taper than is considered desirable and attractive.  In patients with small faces and modest muscle volume, tapering can be achieved with as little as 9-12 units per side. In patients with a large muscle volume the dosage required can be as high as 20-40 units per side. Most patients get noticeable tapering of the jaw with modest dosage. It is only patients with large muscles that require the higher dosage. The "equivalent" Dysport dosage would be anywhere from 30 to 100 units per side. Your lopsided chin can be managed by either dissolving the excess filler on the longer side or adding additional filler to the shorter side. I hope this helps. Best wishes to you. 

Hi there,
Thank you for your enquiry. From what I understand, you had a Dysport treatment to slim the muscles on both sides of your lower face, close to the jaw.
This muscle is called the masseter muscle. From my experience, this muscle can vary quite a bit in size. It tends to be bigger in male patients, people who go the gym a lot or clench their teeth at night. It is also often bigger in people of Asian origin.
Botox or Dysport relaxes the muscle. The bigger the muscle, the more Dysport or Botox is often needed to relax this muscle.
What you also need to know is that 2.5 units of Dysport equal only 1 unit of Botox. So in your case, when you say you had 100 units of Dysport, that equals 40 units of Botox.
Most people require 3 injections of 5 units Botox (equals 12.5 units Dysport) on each side. This can greatly vary from person to person depending on how big the muscle is.
With regards to the dermal filler in your chin, it sounds as if you had two injections on each side of the chin. Maybe the doctor or nurse injected a slightly bigger amount on one side compared to the other. This can cause asymmetry. If this was the case, it can be easily corrected. Another option could be to dissolve the dermal filler with an enzyme called hyaluronidase.
 

Botox can be injected into these areas to create a softer look and to help with TMJ. The botox will essentially relax the muscles creating the appearance of atrophic muscles. The results will last up to 3-4 months hence you will have to re-inject roughly 3x per year. When administered by an expert injector you shouldn't have an issue with too much laxity and should know the amount of units that should be used to get the results your desire.
If you're unhappy with your final results for the filler in your chin, you can have it reversed with hyaluronidase and try a different technique next time. I recommend seeing a facial sculpting expert.
 Best, Dr. Emer