Advice needed on ceph / impaction / surgery plan

[kavan]

Thank you, yes i understand the geometric principles discussed.

I will ask the next surgeon since he offers 3D planning so will be easier to visualize.

Indeed, it's much easier when you can see the 'geometry' of the output vs. the input. You are doing your due diligence.

[TWGOAT]

I don't know how it's done, but since the jaw can move in any dimension, I'd imagine it's possible.

Maybe baking it into the posterior wedge cut/impaction so when it's reattached there's margin to swing it down. It's not up to me to answer that, though. He needs to ask the surgeon. I'm just saying what he needs. And if he doesn't get that, he'll be disappointed.

Take it to the extreme with a thought experiment and say they impact your maxilla so its height is only 1mm total. Then they CCW rotate it. You really think that would result in a posterior gummy smile? The starting point when it begins rotation matters. The impaction moves it up, and then it can be rotated it from a higher starting point.

Maybe I'm wrong or missing something that can't be done, but that's how I imagine it working out and getting the best of both worlds.

I don't think it would necessarily result in a posterior gummy smile. It's just that why would they reduce the maxilla height let's say to 1mm,  if at the end once the rotation is done, it needs to be 10mm height to have the bone connect, and i guess fill the gap with posterior downgraft, or it's just gonna be hanging loose.

Since i have an occlusal plane of around 20 degrees and optimal is 8, there needs to be big amount of rotation as you know.

I'll see with the 3D planning and update you on what the next surgeon says about what happens to the posterior maxilla if he doesn't downgraft and how to achieve the rotation needed.

[GJ]

I don't think it would necessarily result in a posterior gummy smile. It's just that why would they reduce the maxilla height let's say to 1mm,  if at the end once the rotation is done

To get a higher starting point, so when they rotate it's not a posterior gummy smile. Your posterior maxilla is too low to rotate right now (at first I didn't see this as a major problem, but after looking more, now I do). Impact posterior as high as possible, then rotate it. Again, I don't know if this is possible, but it's what I'd personally be trying to figure out. I would guess the limit would be enough bone to house the teeth, but I've never looked into this type of movement. You also need to factor in how to close that open bite - surgically or ortho. That could be another limiting factor.

Just to be clear: a 1mm maxilla is impossible and was just a thought experiment!

I'm done with the thread, but when you find out more info and go on more consults I'll come back and read it because it's an interesting case.

[thedude]

Thank you for your thoughts.

When you say chin reduction would make apnea worse, you take into account the 8mm advancement of the chin also ?

And from what he showed me, the CCW rotation will quadruple my airway width (which is currently like 3mm based on the CBCT) so i don't think sleep apnea would be a concern anymore.

It's not an exact science. Plenty of people with bad sleep apnea have had far more aggressive surgeries than you are having and still ended up with quite a bit of sleep apnea. Airway measurements are basically meaningless. It's just something they show you to make it look like they did their job. The size of your soft tissues, size of your tongue, the size of your nasal airway, width of your palate, all matter just as much or more than the big part of your airway they measure on a CT scan. No matter what you do sleep apnea will still be a concern, it's just a matter of how much of a concern. A well done sleep apnea double jaw surgery usually results in a 50% decrease in sleep apnea. A poorly done one can make it worse.

My concern with chin reduction is that if you look at an xray you will see the muscle that is part of the tongue literally attaches to the chin very close to the part they are shaving. I would suspect if you damage that attachment it could do more damage than 8mm of advancement will compensate for. It just seems like a strange thing to do unless you want to look more like a girl and have worse sleep apnea.

[kavan]

TWGOAT,

Here is how I would go about guesstimating the net rotation. But mostly, this is a demonstration of conceptual methodology rather than an exercise in mm or degree 'exactitude'.

I increased size of your ceph so that from the root of your nose to the base of it measured 60 mm on my screen (which is the average length of a nose). Although it might not be your exact nose length, I'm just showing how I would make a ballpark estimate of the net CCW. Also, 'round' numbers are just easier for me to deal with when I'm holding a transparent ruler and protractor up to the screen.

From there, I got a measure of about 50 mm of ANS-PNS (maxilla area) and marked a CUT OUT figure in red where the right side of the figure was about 5mm and left side about 3mm.

It's basically the SEGMENT being removed across the length of the maxilla.

Since the red figure is one where there is more vertical length to the right of it than the left of it, I knew I could draw 2 white lines bordering it and extrapolate them all the way back UNTIL they CONVERGED. I got about 3 degrees. Although subtracting 3mm from 5mm=2mm, the angle measure can differ.

So, the net CCW would be the bottom white line rotating about 3 degrees CCW to meet the top white line. That's the impaction.

Now, if you wanted to do it using the EXACT length of ANS-PNS, you could. I'm just showing the basic METHOD I would use from a geometric perspective.

Illustration included in this post.

[TWGOAT]

It's not an exact science. Plenty of people with bad sleep apnea have had far more aggressive surgeries than you are having and still ended up with quite a bit of sleep apnea. Airway measurements are basically meaningless. It's just something they show you to make it look like they did their job. The size of your soft tissues, size of your tongue, the size of your nasal airway, width of your palate, all matter just as much or more than the big part of your airway they measure on a CT scan. No matter what you do sleep apnea will still be a concern, it's just a matter of how much of a concern. A well done sleep apnea double jaw surgery usually results in a 50% decrease in sleep apnea. A poorly done one can make it worse.

My concern with chin reduction is that if you look at an xray you will see the muscle that is part of the tongue literally attaches to the chin very close to the part they are shaving. I would suspect if you damage that attachment it could do more damage than 8mm of advancement will compensate for. It just seems like a strange thing to do unless you want to look more like a girl and have worse sleep apnea.

Good thing i don't have sleep apnea yet, i want to do the procedure before i develop it.

But the reduction is just to reduce lower third length, correct? I have severe long face and don't think i'll look like a girl no matter what they do lmao.  I don't think they damage the hyoid muscles attachments, i hope lol

I see what you mean if the tendon or ligament is damaged it could lessen muscle strength

[kavan]

Good thing i don't have sleep apnea yet, i want to do the procedure before i develop it.

But the reduction is just to reduce lower third length, correct? I have severe long face and don't think i'll look like a girl no matter what they do lmao.  I don't think they damage the hyoid muscles attachments, i hope lol

I see what you mean if the tendon or ligament is damaged it could lessen muscle strength

Referring back to the basic ABC triangle figure I gave prior where A=ANS and C=pog point of chin and I told you the distance between points A and C were being reduced, so correct, it's just the linear distance from ANS to pog point of chin that is being reduced by about 5mm. Anterior facial height is being reduced.

[TWGOAT]

TWGOAT,

Here is how I would go about guesstimating the net rotation. But mostly, this is a demonstration of conceptual methodology rather than an exercise in mm or degree 'exactitude'.

I increased size of your ceph so that from the root of your nose to the base of it measured 60 mm on my screen (which is the average length of a nose). Although it might not be your exact nose length, I'm just showing how I would make a ballpark estimate of the net CCW. Also, 'round' numbers are just easier for me to deal with when I'm holding a transparent ruler and protractor up to the screen.

From there, I got a measure of about 50 mm of ANS-PNS (maxilla area) and marked a CUT OUT figure in red where the right side of the figure was about 5mm and left side about 3mm.

It's basically the SEGMENT being removed across the length of the maxilla.

Since the red figure is one where there is more vertical length to the right of it than the left of it, I knew I could draw 2 white lines bordering it and extrapolate them all the way back UNTIL they CONVERGED. I got about 3 degrees. Although subtracting 3mm from 5mm=2mm, the angle measure can differ.

So, the net CCW would be the bottom white line rotating about 3 degrees CCW to meet the top white line. That's the impaction.

Now, if you wanted to do it using the EXACT length of ANS-PNS, you could. I'm just showing the basic METHOD I would use from a geometric perspective.

Illustration included in this post.

Yes i see, thank you for the visual.

That would mean about the same degree of change for the occlusal plane ?

[TWGOAT]

Referring back to the basic ABC triangle figure I gave prior where A=ANS and C=pog point of chin and I told you the distance between points A and C were being reduced, so correct, it's just the linear distance from ANS to pog point of chin that is being reduced by about 5mm. Anterior facial height is being reduced.

I was replying to thedude about the genioplasty, which is 8mm advancement and 3-4mm reduction, which i think the 3-4mm is height reduction of the chin ?

[kavan]

Yes i see, thank you for the visual.

That would mean about the same degree of change for the occlusal plane ?

Well, technically with AOB there are 2 occlusal planes. I'm getting in the approx range of about 13 degrees for the singular maxillary OP. So, it would be the maxillary OP being reduced by about 3 deg. But consider, that's done for the lower jaw to go on the upswing to close the AOB.

[kavan]

I was replying to thedude about the genioplasty, which is 8mm advancement and 3-4mm reduction, which i think the 3-4mm is height reduction of the chin ?

Oh, OK. Genioplasty - 8mm advancement - 3 to 4mm reduction. That could refer to an upward diagonal sliding genio where they make a diagonal cut which has 2 displacement vectors; horizontally outward and vertically upward where 8 would be the horizontal outward displacement and 4 would be the upward vertical displacement which is type they do as add ons for sleep apnea reduction. It isn't something where they lop off or shave down the base of your chin to make it shorter or anything like that.

ETA. By 'add ons' for sleep apnea cases, the type of genio I described is to advance the genioglossus muscle which helps with breathing. But again, the base of the chin is not being 'shaved down'.

[thedude]

Oh, OK. Genioplasty - 8mm advancement - 3 to 4mm reduction. That could refer to an upward diagonal sliding genio where they make a diagonal cut which has 2 displacement vectors; horizontally outward and vertically upward where 8 would be the horizontal outward displacement and 4 would be the upward vertical displacement which is type they do as add ons for sleep apnea reduction. It isn't something where they lop off or shave down the base of your chin to make it shorter or anything like that.

ETA. By 'add ons' for sleep apnea cases, the type of genio I described is to advance the genioglossus muscle which helps with breathing. But again, the base of the chin is not being 'shaved down'.

I think if you did that and looked at impacting more like 3mm like GJ suggested you would have a nice outcome. There is no reason to go from one extreme to the other - a little maxillary excess looks normal and you’ll come out of the surgery still recognizable and won’t risk damaging sleep or nasal breathing so much either.

[kavan]

I think if you did that and looked at impacting more like 3mm like GJ suggested you would have a nice outcome. There is no reason to go from one extreme to the other - a little maxillary excess looks normal and you’ll come out of the surgery still recognizable and won’t risk damaging sleep or nasal breathing so much either.

Than that would give him 0 deg CCW r as in NO net CCW because both the anterior and posterior impaction would be 3.

[thedude]

Than that would give him 0 deg CCW r as in NO net CCW because both the anterior and posterior impaction would be 3.

Sorry I’m not really up on the complexities of rotation or how lowering the jaw unequally in the front and back works or looks for that matter I was just making a general observation that moving the teeth up around 3mm would be where I would see them looking nice aesthetically (however you get them there).

[kavan]

Sorry I’m not really up on the complexities of rotation or how lowering the jaw unequally in the front and back works or looks for that matter I was just making a general observation that moving the teeth up around 3mm would be where I would see them looking nice aesthetically (however you get them there).

no problem