The contour of your neck and jaw line are primarily determined by underlying facial bone structure.
When the mandible lacks forward projection platysma muscle drapes the neck in a more oblique angle. People who have a Mandible that is undersized compared to the Maxilla typically have a dental...
While a 10mm sliding genioplasty will provide some improvement it will still be very inadequate. You need the maximum forward chin movement as well as bringing it up as it comes forward. In essence you need what is known as a jumping genioplasty technique which can bring the chin forward up to...
With a 100% overbite you ideally need a combined orthodontic and lower jaw advancement surgery. But if you are to bypass that option and just deal with the chin issue the next best option becomes a vertical opening bony genioplasty to stretch down a vertically short chin. (which is why the soft...