Can fixing an overbite help the appearance of a slightly weak chin or would surgery be required?

Dear hannahr123,it is hard to tell without an examination. I would suggest you to consult a board-certified plastic surgeon. Only after a thorough examination you will get more information and recommendations.Daniel Barrett, MD, MHA, MS 
Certified, American Board of Plastic Surgery  
Member, Am. Society of Plastic Surgery

"Weak" chins may be due to one or more common factors:1. Overbite (technically "overjet" in the medical lingo)2. Small chin prominence (microgenia)3. Retrusive lower jaw (retrognathia)4. Fat in the submental neck area with or without loose skinOnly exam in the office, including examining your teeth (dentition) can fully assess which of these factors contribute to your chin appearance. Some plastic surgeons and oral surgeons are more facile with reshaping the actual jaw (orthognathic surgery) if that is required. Straightforward chin implant placement, liposuction of the neck, and other more straightforward procedures are commonly done by most plastic surgeons.

A full set of facial photographs are required from the side profile to make a determination about being a candidate for a surgical chin implant. Orthodontic Treatment will only get the teeth straightened so they fit properly together. To increase the amount of projection of the bony mandible needs to be augmented with an implant. For many examples, please see the video and the link below

Most chin recessions are from small jaw and not chin. Jaw surgery would give a better volume to lower facial third. 

An in office examination would be necessary to determine the cause of the weak chin and then a surgical plan can be put into place. Whether this is orthodontics, chin augmentation, or genioplasty. See many examples of chin augmentations in the link below and video library as well. Best regards, Michael V. Elam, M.D.

 Hi, I have performed many facial shaping procedures, including Chin Augmentation with dermal fillers or silastic chin implants, for over 30 years.  Non smiling photos of your face from the front and side would help in the evaluation.   If you have a weak (receding chin) and an overbite, correction of the overbite will have no implant on the weak chin.  Correcting the weak chin requires forward projection of the chin itself. When the chin is weak, this creates an imbalance making the nose appear larger, the mid face top heavy, the lower face looks short, de-emphasizes the lips and allows early formation of a "double chin".  
 Proper placement of a silastic chin implant adds forward projection to the chin thereby creating harmony and balance to the lower face.  Using the same incision, liposuction can be performed to reduce the fat and further shape the neck.  Excess skin, from below the chin, can also be removed through the same incision.  
 I have found that placement of a silastic chin implant, through a small curved incision under the chin (also allows excess skin removal) to be very safe, quick, highly effective and far less invasive than a sliding genioplasty (requires extensive tissue dissection, bone cuts and placement of metal screws and plates to secure the cut segments of bone).  I perform chin implant surgery in 30 minutes or less, often using a local anesthetic alone.  
Hope this helps.