Thank you for the response. From what I understand, the CCWr is being done to achieve enough mandible advancement to make bimax worthwhile as I am getting surgery-first despite my overbite being compensated so I cannot just get a linear advancement.
From the images I have seen, a posterior gummy smile is still aesthetically more pleasing than a short-face smile. Right now my issue is a lack of teeth show, pretty much like this: https://i.ytimg.com/vi/M3b-DxdWoNI/maxresdefault.jpg
My main concern is regarding the change in the occlusal plane that might be negative in the after. I don't think negative occlusal planes even naturally exist. Is this what might lead to a posterior gummy smile, and are there any other aesthetic downsides to this?
Assuming that the CCW-r is a via a POSTERIOR DOWNGRAFT, the fundamental relationship is that BOTH posterior tooth and/or gum show AND extent of lower jaw advancement are direct functions of the extent of the posterior down graft. So if one quantity increases the other one automatically increases also. Not necessarily by the 'same amount' though. CCW-r via posterior downgraft DROPS DOWN the posterior maxilla. So, the tooth/gum bearing part of the posterior maxilla is lowered in that process (and hence show more).
Rotations in maxfax planning/surgery are based on elementary and fundamental geometrical concepts, in particular, the rotation of a TRIANGLE, one formed by 3 bony landmarks to the upper and lower jaw complex and a selected rotation point. This triangle has 2 upper vertexes, an anterior one and a posterior one and a lower vertex below the upper ones. A rotation point either at the upper anterior vertex or slightly below it will rotate the triangle so that the (upper) posterior vertex goes downward and the lower vertex goes forward. To grasp this concept, construct a triangle, rotate it ccw-r around the fixed point mentioned here and observe the displacement of the lower vertex relative to where it was before you rotated it. The salient observation to be made is that the EXTENT of the ccw rotation (near the upper anterior vertex) is directly proportional to the extent of the upper posterior vertex being lowered and also directly proportional to the extent the lower vertex is advanced forward. Point here is that some basis is these fundamental relationships is needed to understand those in maxfax displacement planning that are based in these types of fundamental relationships.
Now to build on the above concept of a TRIANGLE is constructed by 3 bony landmarks as mentioned above, the occlusal plane will be within (inside) the triangle and will also rotate in accordance to the extent of the rotation taking place. Inside the triangle the OP has direction of downward and outward 'slope' and this slope will have an angle of inclination relative to say a horizontal line. So, the ccw-r will decrease its slope/angle of inclination. When inclination decreases to 0 deg from horizont, it's basically flat OP. (Any OP that is less than the norm of about 4 degrees can be considered a 'flat' one.) Any decrease that sets the slope in opposite direction of its original slope/angle of inclination will be a negative OP. Aside from whether or not a negative OP exists in nature, a rotation to the extent that would result in a negative OP would be 'pushing the envelope' in order to MAX OUT the advancement of the lower jaw. I've heard of one surgeon doing this. But concerns about having a negative OP are neither here or there in the absence of knowing what your OP actually is and how many degrees it will be disinclined.
So, as to your question of whether or not excess posterior gum show results from a negative OP, it doesn't mean that the surgeon is going to give you a negative OP. Like you can't assume the likelihood of excess posterior gum show is 'because' the OP is going to be negative. The excess and how much will be a function of the extent of ccw-r via posterior downgrafting used to maximize the extent the lower jaw can be advanced out. The more the ccw-r is, the more the lower jaw can be advanced and the more your jaw is advanced via the CCW-r, the more posterior gum show will follow. Maximizing lower jaw advancement is a FUNCTION of the extent of CCW-r. But so is excess posterior gum show. Hence the trade-off of maximizing jaw advancement via CCW-r can be excess posterior gum show. It is a matter of what thing you want to TRADE IN for the other. A decrease in the CCW-r will decrease the amount of lower jaw advancement you can get and also decrease the amount of potential excess gum show. Your surgeon is conveying this FUNCTIONAL relationship to you when he tells you he can maximize your lower jaw advancement via ccw-r but you would need to accept the excess posterior gum show in X-change.
Those are the basic concepts to grasp. The rest is a multi-factorial mathematical calculation based on quite a number of possible displacements relative to aesthetic norms and function which are done via a high tech displacement design program.
