How to Minimize Rectangular/square Face or Strong Jaw Bone?

Thank you for your question. Botox or Dysport can be a very effective
way to contour the jaw line by reducing the masseter shadow through the
outer jaw skin. In addition, it can reduce symptoms of jaw clenching or
grinding of teeth at night time. This is an advanced technique that
requires a strong understanding of the underlying anatomy. Some side
effects can results in some very unintented effects. This can include
affecting the smile due to diffusion of the Botox into neighboring smile
muscles. Over treatment can also overweaken your jaw muscles making it
harder to chew food and causes your jaw muscles to relax too much when
you sleep.The injection technique does vary by physical exam and
the goals of the treatment. I ask my patients to place their hands
along the sides of their face over their masseter muscles and clench
on/off so they can feel the masseter muscles bouncing against their
hands. I also ask them to repeat this at home in a couple weeks time to
compare so they can see the effects of the masseter reduction.  This also allows them to distinguish whether the square face is due to the jaw bone or also the masseter muscles.
Facial contouring goals may change the injection sites themselves to
affect different portions of the masseter as well as the dose. The
strength of the masseters can be felt by palpation and also helps me to
determine dosing. In general, I start with 15- 25 units of Botox (OR
50-75 units of Dysport) per side for most patients. If they have very
strong masseters, then I may increase the dose, but more commonly ask
them to return in three weeks for a touch up. Once you get the desired
result, I let patients know that future treatments may require less to
maintain the look or the jaw clenching symptoms, especially if they get
treated as soon as they notice the symptoms return. This can be as soon
as three to four months, but in some cases, patients report that it
lasts six months or more. I find it depends on the dose we use and how
many times we have done the procedure as the duration may lengthen for
patients that repeat it regularly.

Botox is injected directly into the jaw muscle, known as the masseter, to relax it, softening your jawline and giving you a thinner appearance. However, this is only effective if your jaw is affected by prominent masseter muscles. If the aesthetic concern is caused by the actual bone, then Botox will not help. Please see an experienced and certified medical injector for a physical examination to obtain a better assessment of your concern.

I have used Botox many times to treat an overly prominent jawline in women. It is not uncommon in Asian faces for the face to be more square in shape, and many women prefer, as you say, a more heart-shaped face.  One can inject the same muscles as well as the muscles of the temples in patients who grind their teeth. These patients can have severe chronic headaches and a painful jaw, as well as problems with their teeth. The muscles of their jaw and temples enlarge.  Some don't respond to teeth guards. Botox helps them to relax the involved muscles a bit so that their symptoms are relieved.Dysport should have a similar effect.