Masseter Botox. Will it help give my face a round shape?

Botox for masseter reduction can be a very safe and predictable way to create slimming and tapering of the jawline.  When performed by a surgeon experienced in the treatment, it will create a slimming effect in 4-6 weeks which will continue for 3-4 months.  Maximal results will be achieved with serial treatments after 4-6 months.

Hello, thank you for your great question. Botox is a neuromodulator, which will ease the contraction of your masseter muscles, softening the outer corners of your jaw. Clenching of the jaw can cause the masseter muscles to become strong and over-pronounced, similar to a weight lifter lifting weights. By easing the contraction, the muscles can remain in their relaxed position. 
Make sure you visit a doctor who is experienced in using Botox for the masseters. Although many do not have before and afters on their public websites, many will have samples for you to look at in their practice. 
Best of luck to you!

Administration of Botox to the masseter muscles will generally thin the lower portion of the face. Good luck from New York City

Generally injection of the masseter is to make the face more tapered. as far as pictures most doctors take before pictures and then at 2 weeks as there is not a change immediately after the injection

The fact is, Botox in the masseters will give your face a more oval or angular face by reducing the lateral jaw bulking of the masseter. This is preferrred for femininity more than a square or round face. Females should want the widest point to be near the lateral,upper cheeks not the lateral jawline. Botox will also help with unwanted clenching and grinding, TMJ symptoms and headaches. I often combine it with a bit of filler in the chin to elongate the face and counter-balance the squared or lower rounding of the lower face which can look more masculine (if squared)  of child-like (if round)

Botox injection in masseter is used for medical and aesthetic reasons. It reduces with time the volume of the muscles in those who have increased mass of that muscle. The effect is an increased ovality of the face particularly in those that have rather round face due to increased master volume. So, it appears from your description that your goal will unlikely be achieved with Botox. Good luck!

Botox is good for the masseter when the masseter is overdeveloped. This can happen when we grind our teeth or just naturally. It seems more common in the Asian population. Over developed masseters tend to make the jawline a bit square and bulky. Botox can reduce the size of the masseter muscle, reducing the squareness of the jaw and restoring the face to a more feminine heart shape. It can also reduce tooth grinding, TMJ pain, migraines and headaches. The results last longer that botox for the upper face; often around 8 months.  
As for photos before and after, it depends on the doctor who is treating you.