What can be done for an over active chin muscle? It hangs like a witch chin when smiling (photo)

At your age, botox or dysport would be the way to go to relax the muscle. Another approach, usually employed for older patients with a "witch chin" would be a submental (under the chin) incision and partial removal or tightening of the muscle (which I would not recommend for you). 

This problem can be troublesome to treat often less is best. Botox can be used to diminish the activity of the mentalis muscle. Without a true profile photo  it is difficult to determine if a reduction genioplasty would be helpful. A small amount of the soft tissue pad can be removed from a submental approach. 

Thank you for sharing your question about your chin. Botox is an excellent solution for the problem you are describing. A small amount of Botox can be injected into the mentalis muscle, which will relax the muscle and offer a nice, smooth, chin when smiling. The effects of Botox last approximately 3-4 months, at which time the procedure can be repeated for sustained results. For more information about Botox to the mentalis, please schedule a consultation with a board-certified specialist. Best of luck, Dr. Kian.

The mentalis muscle can be quite strong in many individuals.  Botox or dysport is great to treat this muscle.  Recent studies have shown by treating this area you can even increase your chin profile and improve the appearance of your chin.  
Find a Board Certified Facial Plastic Surgeon in your area who you can trust and communicate with and who actually does the injecting to address your concerns.

Thanks for your question.Most often a combination of Botox/Dysport/Xeonim with dermal filler can reduce the prominence of the Witch's chin. I would suggest you see an expert injector in your area.Good luck. Dr. ALDO 

Yes, Botox is an option for improving this. Botox results will resolve in 3-4 months. I recommend getting a formal evaluation with a cosmetic dermatologist. Best, Dr. Emer

Dear gettinfit25:
Thanks for sharing your photo. Without the opportunity to see photos from the past and a in-person evaluation, it is difficult to offer a remedy for your concern. 
Based on the photo, I do not see a mentalis muscle problem. The mentalis muscle attaches from the bone under the bottom teeth to dome shaped chin fibers and skin. When the muscle contracts, it lifts  the chin and middle lower lip upward and at times creates a orange peel effect. A Botox injection to this muscle would only lengthen the chin by weakening the natural tone to pull up and in; this could cause a longer droopier chin. 
Proper evaluation and a side x-ray or CT scan will help identify whether it is bone or a fatty protrusion anterior to the mentum. If this is the problem, the challenge will be to support the skin redundancy once the volume of bone or fat are removed. A wide chin and jaw-bone implant may be an option. 
It is best to search for a most gifted, Board Certified Plastic Surgeon or Oral Surgeon with such orthognathic and cosmetic experience to offer you the best options. 

Hello--Botox is a great option to decrease the hyper active mentalis muscle you are concerned with!
Hopefully this helps you,
Ralph R. Reynolds, DMD, MD

Thanks for your question and photos. We always recommend that you have a consultation with a board certified dermatologist or plastic surgeon to learn the best treatment options for you.  Using a neurotoxin in this area – Botox, Dysport, or Xeomin, can really make a difference when given by skilled injectors.  Good luck.

It's a bit difficult to tell exactly what your condition is from the photographs you have provided. But it does not appear to be a hyperactive chin muscle. You may have either access fat or possibly even a hereditary condition where  the chin bone actually jets out more than it should. You should get an evaluation by a plastic surgeon like myself and find out if you need fatty reduction or bone shaving. Good luck from New York City