Weak Chin - Jaw Surgery Vs. Chin Implant?

The first thing is you need a correct Diagnosis, do you indeed have a weak chin from a small lower jaw or do you have an isolated weak/small chin. Considering you acknowledge your underbite, you likely have a small/retrognathic mandible. So your best option would be to see a plastic surgeon whom is familiar with tooth/skeletal relationships to discuss your options. Not all plastic surgeons are the same with regards to this topic, do your research and find one who can and routinely performs either corrective jaw surgery or placement of chin implants. In regards to your TMJ pain, your malocclusion (underbite) is likely contributing to this, correcting your occlusion orthodontically would be a good place to start so having a consultation with an orthodontist would be another valuable consult for you to help you decide what your best options would be.good luck

It's best to begin by consulting with a surgeon in-person to discuss your options. During your initial examination, your #chin will be evaluated along with the neck and jawline. A weak #chin implies a lack of chin support for the skin along the neck line. In younger individuals a chin implant alone is usually all that is needed to improve the appearance of the neck. Subsequently, it will also improve the overall #balance of the face and can create the illusion of a smaller nose. As a stand-alone procedure, chin augmentation can be performed in the office under local #anesthesia. For individuals with signs of #aging in the neck, a chin implant added to one of the recommended procedures above, will provide optimal results.
If you are not a candidate at the time of your #consultation, your board certified plastic surgeon can recommend alternatives to address your concern. Consulting with a board-certified plastic surgeon who specializes in #face, #neck and #chin procedures is important to ensure you are receiving the best advice, care, and surgical experience possible.

You seem to be an ideal candidate for Chin Implant Surgery. You would have improvement in the appearance of your chin and jawline. This would also have the added benefit of making your nose look smaller. Chin Implant surgery is relatively inexpensive, and takes less than 30 minutes. Downtime is about a week, and your results are permanent.
I'm not a big fan of sliding genioplasty surgery (surgically advancing your chin-bone forward).
I've attached a link to my Chin Implant photos for your perusal.
I hope this is helpful for you.

While I perform both bony surgery to improve the chin, as well as implants, I generally favor implant surgery. A chin implant is a short, out-patient surgical procedure with few complications. Cutting the chin bone itself is a much bigger operation which I would hesitate to recommend, unless there was no alternative.
As a plastic surgeon with both a medical and dental degree, I have performed many operations on the jaws to move the bones, including the jaws and chin, but surgery on your jaw may not improve your TMJ problems and you should consider that fact in your decision. My gut reaction in looking at your photo would be to opt for a chin implant. If you did a chin implant, you are not burning any bridges, and could still do jaw/chin surgery at a later date.
To simulate what it might look like, I frequently inject sterile water into the patient's chin and you can immediately look at it in the mirror.

In many instances jaw surgery can accomplish both goals. However, traditionally these are different surgical proceduress. TMj surgery typically does not improve chin projection whereas a SSO for malocclusion or sliding genioplasty can definitively achieve chin enlargement. The use of submental liposuction can enhance the result as well.