I saw a 2nd surgeon, he mentioned maybe more than 5mm anterior impaction based on my current tooth show (around 8mm), and also some posterior impaction.
He was vague about the amount of CCW achievable with the differential impaction, but he said i would need a big advancement and autologous bone graft on the BSSO sites to favor healing
Well, it's hard for them to be precise until an actual pre-surgical plan is charted out. With combined CCW anterior impaction + CW posterior impaction, anterior impaction , the rotation is net CCW if there is more anterior impaction than posterior impaction. If your maxilla was uniformly long both anteriorly and posteriorly and they removed a uniform segment from it, net rotation would be zero.
If the surgery is DJS where the maxilla is advanced after the combined impaction, there will be some gain in tooth show which was 'lost' from the anterior impaction. For example, if tooth show after anterior impaction was reduced by 5mm but the excess was 8mm, you wouldn't be left with 3, you would gain more than 3 as a function of the maxillary advancement. For every X mm of maxillary advancement, you gain Y mm of tooth show. There is no specific Y with each X because it's a function of the inclination of the maxilla (or Occlusal Plane) which is being advanced.
