Can Botox prevent my chin from elongating when smiling? (Photos)

Botox is useful in the chin when there is an active mentallis muscle. I don't see that when you smile. You might want to consider chin reduction surgery to make your chin less prominent and pointy. There are several ways that this can be accomplished. I recommend that you find someone with experience in reduction genioplasty. Good luck

Botox is most commonly used in the chin area to decrease dimpling or wrinkling that occurs with facial expression. For this, it works quite well. It may also help to decrease the elongation of the chin that occurs with smiling, but this overall benefit may vary from one patient to another. An in-person exam could be very helpful to watch the facial movements in action and determine how effective Botox might be.
Be sure to see an expert physician injector who specializes in facial aesthetics as any Botox injections near the mouth are advanced techniques with potential negative side effects.
All the best,

Thank you for sharing your photos and your concerns.  Neuromodulators (Botox, Dysport, Xeomin) are used to relax / soften muscles.  In the area of the chin, Botox can soften the contracture of the mentalis muscle.  Unfortunately, this would not help as it may slightly elongate your chin.  
Please see a board certified dermatologist or plastic surgeon who specializes in nonsurgical approaches to see if you may be a candidate for filler to the upper cutaneous lip and the “prejowl” sulcus to change the proportions of your upper cutaneous lip / lower cutaneous lip and chin ratio.  If surgery is an option, consult with a plastic surgeon or oromaxillofacial surgeon regarding reduction genioplasty. 
Best of luck,
Suneel Chilukuri, M.D.
Houston, Texas