A third chin implant and bone erosion.

Placing a third chin implant will not impact the skin/scar though you have the option of having the implant placed via an intraoral incision. Depending upon age, occasionally there is bone resorption beneath a chin implant. I would recommend a pre-surgical CT to evaluate the existing bone. Have you considered a genioplasty? This procedure is performed in the office through an intraoral incision. Your chin itself is re-positioned and there is no risk of bone resorption. I think that this procedure gives the most natural results. Good luck

 Hi, I have performed many facial shaping procedures, including Chin Augmentation with dermal fillers or silastic chin implants, for over 30 years.  Honestly, after three previous chin augmentation surgeries you should be examined and evaluated in person to see if you are even a candidate for another (the fourth chin implant surgery).  If there was true and significant "bone erosion" (I have only seen this a couple of times over the past 30 years) and not slight bone stimulation below the implant....you would not be a candidate for chin implant surgery as the new implant might cause bone resorption once again.  In these rare cases, I suggest and use a dermal filler to shape the chin.  Permanent fillers and fat injections (far less reliable and predictable) should be avoided.   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".  
 The 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.  I perform chin implant surgery in 30 minutes or less, often using a local anesthetic alone.  Hope this helps.