Comparison of two bimax simulations

[VincentGT]

Thanks for the clear explanation, Kavan!

In the meantime I finally got the exact measurements for all the simulations that were made.
Here you find the three simulations with the exacte measurements.

1A: here I find the chin too pointy and the upper jaw advancement seems like not enough (3mm). No CCW..

1B: 6mm maxilla advancement could be a bit much, no? I do like the look of the profile. With a big(ger) maxilla movement like this, I fear unwanted side effects like nose deformities and a longer philtrum, chimp face, etc. Bizarre though: no maxilla rotation. Isn't some rotation necessary with moves like this? Won't pure linear advancement make my face (and philtrum) look longer? Is it even possible to move the maxilla 6mm forward and 2mm upwards without rotating? I think my occlusal plane is (pre-op) a bit too steep too. Genio of 2mm seems like hardly worth it.. He doesn't charge anything extra though.

=> A visual comparison between 1A en 1B.

2: again, the 3mm maxilla advancement seems a bit conservative. Maybe the sweet spot is 4 - 4,5mm? No genio, but maybe not necessary. I dislike the 1.4 CW rotation.. I feel like I'd want CCW rotation for my steep occlusal plane.

[kavan]

Thanks for the clear explanation, Kavan!

In the meantime I finally got the exact measurements for all the simulations that were made.
Here you find the three simulations with the exacte measurements.

1A: here I find the chin too pointy and the upper jaw advancement seems like not enough (3mm). No CCW..

1B: 6mm maxilla advancement could be a bit much, no? I do like the look of the profile. With a big(ger) maxilla movement like this, I fear unwanted side effects like nose deformities and a longer philtrum, chimp face, etc. Bizarre though: no maxilla rotation. Isn't some rotation necessary with moves like this? Won't pure linear advancement make my face (and philtrum) look longer? Is it even possible to move the maxilla 6mm forward and 2mm upwards without rotating? I think my occlusal plane is (pre-op) a bit too steep too. Genio of 2mm seems like hardly worth it.. He doesn't charge anything extra though.

=> A visual comparison between 1A en 1B.

2: again, the 3mm maxilla advancement seems a bit conservative. Maybe the sweet spot is 4 - 4,5mm? No genio, but maybe not necessary. I dislike the 1.4 CW rotation.. I feel like I'd want CCW rotation for my steep occlusal plane.

Notes:

1A: Max. No rotations to maxilla, 3mm translation, No autorotations to the mandible. Good line up with the TVL.

1B: Max. No rotations to maxilla, 6mm translation, No autorotations to mandible.
Good line up with TVL.

2: (other surgeon's) I don't know what to make of the surgeon's listings under rotations to the maxilla in the absence of any listings for 'auto rotations' of the mandible other than to tell you that with either CCW or CW, they effect an auto rotation to the mandible and there is no listing for that and it doesn't look like there is. From his visual, I can't confirm any rotation to the maxilla. However, his visual proposal shows a good line up with the TVL.

Comments:

1: Rotations are different operations (movements) than translations. CW or CCW rotations take place at the maxilla and effect an AUTO ROTATION to the mandible. ABSENCE of any rotations; CCW or CW are more straight forward to observe in both 1A and 1B because they are substantiated via the readouts which convey none to the maxilla and no subsequent autorotations to mandible. I can't confirm there is a rotation to the maxilla for the second surgeon's presentation other than to tell you that CCW isn't really indicated for your case.

2: Rotations to the maxilla (of which NONE are listed in proposal 1A and 1B and are unclear in proposal 2 if a rotation takes place but don't look to be) change the Mandibular Plane Angle (MPA) in addition to the occlusal plane angle (OP). Here, it doesn't matter if you think your OP is 'too steep'. What matters here as it relates to aesthetics (outward appearance) is that 'steep' OPs, more often than not are associated with steep Mandibular Plane Angles (MPA) and you DON'T have a steep MPA. The MPA is the angle of inclination the diagonal line to the border of the lower mandible has relative to a horizontal plane.

So CCW-r is indicated for someone having a high MPA. If someone has an overly 'flat' MPA (a LOW angle of inclination with reference to a horizontal plane), then CW is indicated to increase the MPA. Your MPA veers toward the LOW side of the spectrum but is within the aesthetic norms. So CCW-r isn't really indicated for you whether or not you think you have a steep OP. So MOOT POINT for me to get drawn into questions that express 'alarm' on the basis that proposal '2' doesn't have CWW but could have a bit of CW other (or that another proposal also doesn't have CCW than to tell you that your somewhat neurotic concern about having a 'steep OP' and not having it addressed via CCW precluded you from seeing/perceiving that the MPA was not steep.

3: Because there are NO rotations to the maxilla listed in 1A, 1B and I can't confirm whether there are any on '2' either (but it doesn't look like it) AND CCW-r isn't indicated for you anyway because your MPA leans toward 'low angle' side of spectrum for MPA norms, there is no need for me to discuss those further with regard to spin off questions revolving around want for one and/or fear of the other.

4: Because there are NO rotations to the maxilla in the proposals, the proposals look to be those of linear advancement, ALL of which have a good line up with reference to a TVL.
I gave sufficient information (and an illustration) in my prior post (#14 of this thread) as to how  to do a comparison of the visual proposals. One puts the visual proposals together ALL on one photo document like I did  in post #14 of this thread, draws a TVL through each which is sufficient to make a choice based on the STILL visuals. I did not suggest evaluation of proposals via moving morphs. However, if your moving morph allows YOU to decide which you like better, then by all means do so.

5: I've already gone over the relationships as to possible philtral changes in my prior post (#14 of this thread) to tell you that the more the maxilla is advanced (pushed out), the more it straightens out the 'curl' to the philtrum in profile and the philtrum could look longer to you in frontal for that reason and GJ already told you that maxillary advancements can bring about unwanted changes. So, any fears about unwanted changes due to maxillary advancement don't go away when you want more maxillary advancement. Again, the more the maxilla is pushed out, the more the curl/curve (seen in profile) of the philtrum will be straightened out and look longer to you in frontal. Those type of things are called TRADE-OFFS. So, probably best for you to discuss possible tradeoffs concerning your requests of maxillary advancements with your surgeon.

6: You have FEARS/concerns about proposal 1A. You have FEARS/concerns about 1B. You have FEARS/concerns about 2. So, you have fears/concerns with EACH proposal and what they all have in common is the prospect of getting maxillary advancement. I can't resolve all those FOR you other than giving you the info I've provided here.

7: If you CAN'T make a decision based on looking at each proposal relative to the TVL and deciding on which one you like best in addition to taking into account the info I've already given here aimed at trying to help you make one for YOURSELF, I can't make one for you, nor can I address every 'spin off' concern you may have with EACH proposal the surgeon/s give you, ALL of which ACCOMMODATE your request for maxillary advancement. It's getting too excessive and time intensive for me to be drawn into a 'perpetual motion' cycle of indecision that arises from EVERY proposal you are given that includes maxillary advancement.

8: In closing if you need every possible trade-off you don't want to go away along with the choice of maxillary advancement, then the option of NO maxillary advancement at all (lower jaw/chin only) is a VIABLE option to take and that option also has a very good line up with the TVL.

[kavan]

1A: here I find the chin too pointy and the upper jaw advancement seems like not enough (3mm). No CCW..

What I can confirm from this statement is that there is no CCW and the proposal is not to your satisfaction. When that's the case, they are grounds for ruling it out.

1B: 6mm maxilla advancement could be a bit much, no? I do like the look of the profile. With a big(ger) maxilla movement like this, I fear unwanted side effects like nose deformities and a longer philtrum, chimp face, etc. Bizarre though: no maxilla rotation. Isn't some rotation necessary with moves like this? Won't pure linear advancement make my face (and philtrum) look longer? Is it even possible to move the maxilla 6mm forward and 2mm upwards without rotating? I think my occlusal plane is (pre-op) a bit too steep too. Genio of 2mm seems like hardly worth it.. He doesn't charge anything extra though.

=> A visual comparison between 1A en 1B.

2: again, the 3mm maxilla advancement seems a bit conservative. Maybe the sweet spot is 4 - 4,5mm? No genio, but maybe not necessary. I dislike the 1.4 CW rotation.. I feel like I'd want CCW rotation for my steep occlusal plane.

What I can confirm about this statement is there is no CCW in this (6mm max advance) proposal either. It is linear advancement. By definition, linear advancement means NO rotations done to the maxilla. So there should be nothing 'bizarre' with the FACT that linear advancement involves NO CCW to the maxilla.  MOOT point to discuss CCW within the context of this proposal because no rotations are being done to the maxilla. Linear advancement means the maxilla (ANS-PNS) is being moved along it's native angle of inclination. Your NATIVE angle of inclination to ANS-PNS already has a CCW orientation relative to a horizontal plane because ANS-PNS is an upward diagonal. Concerns about possible unwanted side effects can increase with more maxillary advancement. It isn't a thing where liking the profile proposal of the one with 6mm advancement mitigates the chances of unwanted side effects with the frontal perspective. So, yes, your philtrum could look longer to you with the profile advancement you like. Your concerns about the OP being 'too steep' are unfounded because it isn't too steep.  If it were, your mandibular plane angle (MPA) would not be on the shorter side of the spectrum (low angle). It would be on the higher side of the spectrum as far as MPAs go, which it ISN'T which yet another reason CCW to the maxilla isn't being suggested or offered.

So, if this 6mm max proposal is NOT to your liking because it's linear advancement to the extent that could increase your risk of not liking the frontal perspective and you require your face to look shorter (from frontal), the genio doesn't look worth it to you, well on those grounds, you can rule it out 1B too.

Here you express NO grounds to rule in any of the options that include max. advancement . Only grounds to rule them out. You can't make a decision based on the offerings that include maxillary advancement. Some of the inability resolves to your thinking you need something you don't need ,like CCW to the maxilla 'because' you think your OP is 'steep' when it ISN'T or liking a profile associated with a 6mm max. advancement but being too risk averse to your face/philtrum looking longer to you in frontal which are self negating requirements to have.

Inability to make a decision based on option offered to you that includes maxillary advancement resolves to NO decision on your part to go forward with any of the proposals that involve maxillary advancement. So, to mitigate concerns or self negating expectations that arise from your desire to have maxillary advancement why not just go with the option of no maxillary advancement and single jaw/chin only option?
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[VincentGT]

Thank you again, Kevan, for your interesting insights.

Before I go over them one by one: you say that my MPA is not steep. What is this based on? I’ve noticed that under the Ceph Measurement “Upper Occlusal Plane - Lat. Incl.” both surgeons use different pre-op values: the first says it measures 9.41°, while the second states 7.09°. I thought I understood that an angle between 8 and 10 is considered ideal. So at 9.41, I’m still on the higher end of that range, no? And would a slight CCW rotation of 1 degree perhaps be useful?

Unscientifically speaking, I do have the feeling that when I hold my head as ‘correctly’ upright as possible (Frankfort Horizontal Plane), my occlusal plane seems to point quite strongly downward toward the ground.

From what I understood CCW - if a possibility - is a way to get some advancement, better lip support, etc. without much of the negatives (e.g. longer philtrum, nasal flaring, etc.). If CCW really isn't an option for me then I will opt for a smaller maxille advancement (e.g. 3mm) to find the middle ground between aesthetic advantages and possible disadvantages. Although 6mm still doesn't look like a lot on paper..

[kavan]

Thank you again, Kevan, for your interesting insights.

Before I go over them one by one: you say that my MPA is not steep. What is this based on? I’ve noticed that under the Ceph Measurement “Upper Occlusal Plane - Lat. Incl.” both surgeons use different pre-op values: the first says it measures 9.41°, while the second states 7.09°. I thought I understood that an angle between 8 and 10 is considered ideal. So at 9.41, I’m still on the higher end of that range, no? And would a slight CCW rotation of 1 degree perhaps be useful?

Unscientifically speaking, I do have the feeling that when I hold my head as ‘correctly’ upright as possible (Frankfort Horizontal Plane), my occlusal plane seems to point quite strongly downward toward the ground.

From what I understood CCW - if a possibility - is a way to get some advancement, better lip support, etc. without much of the negatives (e.g. longer philtrum, nasal flaring, etc.). If CCW really isn't an option for me then I will opt for a smaller maxille advancement (e.g. 3mm) to find the middle ground between aesthetic advantages and possible disadvantages. Although 6mm still doesn't look like a lot on paper..

The basis of an angle measurement in maxfax relates to basic geometrical relationships and measures thereof and not 'feelings'.

The first part of your question about the MPA (or any angle) is based on elementary geometry, for example a line can be drawn from 2 points and an angle can be formed from 2 lines. If one line is a diagonal one and the other line is a horizontal one, the angle of inclination that the diagonal line has with the horizont can be measured and the angle of inclination the diagonal line has with the horizont is the same thing as how many degrees it's rotated away from the horizont. Although a diagonal line is rotated away via the angle of inclination it has with (for example) the horizon, movement along the line is not a 'rotation'. Movement along it is a 'translation'; a combination of horizontal and vertical displacements like walking up a hill is which isn't a rotation.

The second part of your question as it applies to an angle called the MPA depends on it being intuitively obvious that the border of the mandible is oriented along a diagonal line AND a diagonal line is formed by connecting 2 points along the border of the mandible. From there, the angle of inclination with the horizontal can be measured. It's just a matter of knowing which points to use along the line of the mandible.

The 3rd part of your question as it applies to the spectrum or range of MPAs; whether or not the MPA is closer to the range of being 'steep' (high angle) or closer to the range of being 'flat' (low angle) is cross referenced with normative values of MPAs. An MPA can be within the range of the spectrum as far as normative ranges go but closer to either low or high angle. When an MPA is closer to the low angle spectrum, CCW-r (via posterior downgraft) would lower the angle.
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Maxfax relationships have quite a number of angle measures. As to the OP, doing a search for ranges of OPs calls up the following entry: [The normal angle of the occlusal plane, in relation to the Frankfort horizontal plane, is generally considered to be 8° ± 4°. This means that a normal occlusal plane typically forms an angle of between 4° and 12° with the Frankfort horizontal.] What can be concluded from that is that an OP within the range of 7.09 deg and 9.41 is also within the range of 4 deg and 12 deg. So, not steep enough to justify altering via CCW-r.

Although CCW-r via posterior downgraft is a way to get extra lower jaw advancement than one would otherwise get without it, it is also one aimed at MINIMIZING maxillary advancement so a request for extra maxillary advancement runs counter to that. As to the MPA and OP, it is the (extent of) DEVIATIONS from normative values for both the OP and the MPA that justify it. 

[VincentGT]

The normal angle of the occlusal plane, in relation to the Frankfort horizontal plane, is generally considered to be 8° ± 4°. This means that a normal occlusal plane typically forms an angle of between 4° and 12° with the Frankfort horizontal.] What can be concluded from that is that an OP within the range of 7.09 deg and 9.41 is also within the range of 4 deg and 12 deg. So, not steep enough to justify altering via CCW-r.

I understand that a CCW-r is indeed not clinically required given the 9.41° occlusal plane, but it can still be applied. The reason I would consider it is because, according to the literature, certain aesthetic drawbacks can be avoided by incorporating a slight CCW rotation instead of relying solely on linear advancement — specifically: a flatter and longer philtrum, less prominent upper lip, etc. So no, it’s not necessary, but perhaps still possible, even if it's just 1 to 1.5° combined with a slightly milder maxilla advancement of, for example, 4 mm. I undoubtedly don't understand it well enough, but I don’t see any downsides to preferring a slight CCW-r instead of a more aggressive maxillary advancement."

I’m not in favor of a posterior downgraft, because although it does produce rotation, it has no effect on the soft tissues. In that case, I might as well go with the BSSO-only proposal.

[kavan]

I understand that a CCW-r is indeed not clinically required given the 9.41° occlusal plane, but it can still be applied. The reason I would consider it is because, according to the literature, certain aesthetic drawbacks can be avoided by incorporating a slight CCW rotation instead of relying solely on linear advancement — specifically: a flatter and longer philtrum, less prominent upper lip, etc. So no, it’s not necessary, but perhaps still possible, even if it's just 1 to 1.5° combined with a slightly milder maxilla advancement of, for example, 4 mm. I undoubtedly don't understand it well enough, but I don’t see any downsides to preferring a slight CCW-r instead of a more aggressive maxillary advancement."

I’m not in favor of a posterior downgraft, because although it does produce rotation, it has no effect on the soft tissues. In that case, I might as well go with the BSSO-only proposal.

For all intents and purposes, the proposals you have to choose from here are those of linear advancement. If you want to pursue CCW with other surgeons for other proposals, look for one who can work with any uncertainties or misconceptions that might arise from the proposals. Just sayin' I don't anticipate volunteering to work out 'if this, then that' type of conceptual relationships, goals, fears, misconceptions etc.. that go along with yet more displacement proposals. The last misconception that I will address here is your assertion that a posterior downgraft 'has no effect on the soft tissues'. The assertion belies an assumption that moving bone has no effect on moving soft tissues and/or you haven't made the association that a posterior down graft is aimed at moving bone. Here I'm referring to 'connecting the dots' to make logical statements which is needed to make a logical conclusion.

[VincentGT]

Kavan, fair enough. I’ll first follow up with some surgeons and see what they think about a CCW rotation and whether they’re willing to simulate it. Once that’s the case, I’ll report back here!

And yes, of course you’re right about the posterior downgraft. What I actually meant is this: pure rotation — whether through anterior impaction or posterior downgraft — can indeed have (positive or negative) aesthetic effects on the lips, philtrum, and nose, but without any advancement, my maxilla will remain mildly recessiv (as shown in the CBCT report). And from what I understood an anterior impaction will have more of the soft tissue effects that I long for: a better 'slope' of the philtrum, more nose support and a fuller upper lip.

[kavan]

Kavan, fair enough. I’ll first follow up with some surgeons and see what they think about a CCW rotation and whether they’re willing to simulate it. Once that’s the case, I’ll report back here!

And yes, of course you’re right about the posterior downgraft. What I actually meant is this: pure rotation — whether through anterior impaction or posterior downgraft — can indeed have (positive or negative) aesthetic effects on the lips, philtrum, and nose, but without any advancement, my maxilla will remain mildly recessiv (as shown in the CBCT report). And from what I understood an anterior impaction will have more of the soft tissue effects that I long for: a better 'slope' of the philtrum, more nose support and a fuller upper lip.

Thanx for explaining. Initially it was hard to wrap my head around the assertion made prior.

[kavan]

....... And from what I understood an anterior impaction will have more of the soft tissue effects that I long for: a better 'slope' of the philtrum, more nose support and a fuller upper lip.

Can you explain HOW you 'understood' that anterior impaction; a procedure done for anterior  vertical maxillary excess (VME for gummy smile) that lops off part of the anterior maxilla including part of the anterior nasal spine (which SUPPORTS the nose base) is going to give better nose support? Also, appox how many FEWER millimeters of tooth show do you wish to not be visible anymore when the lips are at rest and the mouth slightly open? Like it's not something where you can request the doctor to give you 'X' degrees of CCW impaction. Instead you just tell him how much excess tooth show you want to reduce so he knows how many mm he needs to lop off from above and below the ANS because they use the amount of mm removal to calculate how many degrees the rotation is.

Also can you explain WHY you think coupling up maxillary advancement with part of the anterior nasal spine lopped off is going to give you the soft tissue effects you 'long for'. Like why do you think that you would be the EXCEPTION to the trade-offs other people do get when coupling up maxillary advancement with maxillary impaction which are unfavorable changes to the nose base?