Would the Botox injection technique affect the results to my masseter?

If the masseter muscle enlarges from teeth grinding or clenching, and my patient desires to have a more narrow face, I typically inject the masseter muscle in four quadrants as it is a large muscle and i allow for 1cm. of diffusion of effectiveness for the Botox from each injection site.The information provided in Dr. Shelton's answer is for educational purposes only and is not intended to constitute medical advice.  The information provided should not be relied upon as a substitute for consultations with a qualified health professional who may be familiar with your individual medical needs. 

Hello GataC and thanks for your question.
Injecting Masseters with Botulinium Toxin (BoTA) is a big part of my practce.
When I am treating a patient for Bruxism for the first time unlike my approach with 'cosmetic' injections, I prefer to use higher dosages. I want to know whether or not the treatment si going to work for that particular patient and not have them 'guessing' the efficacy of the treatment. With 'cosmetics' , I prefr the "less is more" approach.
Depending on the dilution factor used when reconstituting the Botulinium Toxin the number of injection points may vary. A larger dilution will result in greater spread of the solution, yet one must remember that the dose is also affected.
Generally I use 2 injection points as a  minimum with a 2.5ml dilution to 100 units of BoTA. I then inject 40 units on each side, that is 20 units at each point. 
In patients who are symptomatic and have jaw / muscle aches / pain, i will also inject 10 units in 2-3 points in the Temporalis muscles on each side.

The masseters are a big muscle contributing to a square jaw and bruxism.
Usually I use a 3 point injection to maximise coverage of the muscle.
I usually use 50units. However in patient with bigger muscles  I may need to increase dosage.
Muscle relaxants are effective in facial slimming and bruxism.