Is my square, wide jaw caused by the muscle or bone? (Photo)

I have had a very square and wide jaw since childhood. I received 50 units of Botox per side last year but the results only brought the width down a little and it was back to the same size in six months. I have consulted two doctors and one said the width was caused by the masseter and the other said bone. Which do you think it is and how can I slim down my face to a more oval shape permaneantly? Thank you!