Posterior maxillary impaction

[kavan]

I think this is a really interesting topic. Is there any way this relation can be understood? When I look at different animations of jaw surgeries, it doesn't make it clear that there's an automatic response to the other jaw when one of the jaws are having surgery.

I understand that I can't base my education on youtube clips, but these videos basically sums up what understanding I can have so far. Videos below displays posterior impaction, and the mandible seems to stay in the same position. How can I understand what happens to the mandible that is not shown in this video?
https://www.youtube.com/watch?v=IDURPY1TCBM
https://www.youtube.com/watch?v=VzUmMOCyBTA

In terms of what I told the OP (or 'OD'), I told him they take a wedge from the back of the (upper) jaw and the jaw rotates CW up. The video SHOWS the wedge shape removal at 0:21 and the subsequent CW rotation of the upper jaw and of course, the lower jaw will rotate in same direction to meet it.  Not clear on what you need to understand other than to tell you, the video shows what I was telling him at the time frame of the video I gave. So, we assume his excess face length is coming from the BACK of his upper jaw, (assumed because he says his face is long and he's getting posterior impaction). Hence, this will shorten where his EXCESS is.
 A lot of this stuff, conceptually is just grammar school geometry concepts and I think I told you sometime before that the lower jaw will swing in the direction of rotation the upper jaw has been displaced in.

[ODog]

What’s confusing are the posts on here that talk about CW rotation or posterior impaction lengthening the face. Clearly this is wrong... unless there is some other CW procedure I’m unaware of

[kavan]

What’s confusing are the posts on here that talk about CW rotation or posterior impaction lengthening the face. Clearly this is wrong... unless there is some other CW procedure I’m unaware of

Confusion abates when you think in terms of geometry concepts and observing relationships which is basically what is needed to conceptualize some very basic maxfax relationships.

For example, ROTATIONS: clockwise or counterclockwise (which are in reference to the profile facing to the right). Clockwise is in the 'downward' direction when the big hand on the clock rotates from 12 oclock to 6 oclock. But from 6 oclock back to 12 oclock, clockwise rotation is in the 'upward' direction. So, if someone gets an ANTERIOR downgraft (a wedge added to front maxilla), that is CW with reference to going in direction from 12 oc to 6 oc which is downwards (some elongation). But if someone gets a posterior impaction (a wedge removed from posterior maxilla), it's also CW but with reference to going in direction from 6oc to 12 oc which is upwards (some shortening). Same concept for CCW but in reverse.

[kavan]

The maxilla is cut and actually moved. The mandible is positioned differently because the support level it has to reach for occlusion has moved away and the after picture is at the new support level.
It's like if you would put your finger on the molars of the maxilla before and after, and say that the surgery affects and move your fingers.

Actually, it's more like you observe there has been a change in angle orientation of the mandible OR just take out your protractor and measure the change in angle of inclination of the mandibular plane.

[ODog]

Confusion abates when you think in terms of geometry concepts and observing relationships which is basically what is needed to conceptualize some very basic maxfax relationships.

For example, ROTATIONS: clockwise or counterclockwise (which are in reference to the profile facing to the right). Clockwise is in the 'downward' direction when the big hand on the clock rotates from 12 oclock to 6 oclock. But from 6 oclock back to 12 oclock, clockwise rotation is in the 'upward' direction. So, if someone gets an ANTERIOR downgraft (a wedge added to front maxilla), that is CW with reference to going in direction from 12 oc to 6 oc which is downwards (some elongation). But if someone gets a posterior impaction (a wedge removed from posterior maxilla), it's also CW but with reference to going in direction from 6oc to 12 oc which is upwards (some shortening). Same concept for CCW but in reverse.

Oh yes I forgot to say the front of my maxilla will also be brought down as I have 0 tooth show at rest (back maxilla is long, front is short); so I was wondering if THAT CW rotation would elongate the face or would the impaction balance it out ?

[kavan]

Oh yes I forgot to say the front of my maxilla will also be brought down as I have 0 tooth show at rest (back maxilla is long, front is short); so I was wondering if THAT CW rotation would elongate the face or would the impaction balance it out ?

Depends on the net CW rotation. If more is removed from the back than 'dropped down' in the front, then mandible plane angle should be LESS than what you started with.

[ODog]

Thank you Kavan.

[jawguy123]

Depends on the net CW rotation. If more is removed from the back than 'dropped down' in the front, then mandible plane angle should be LESS than what you started with.

Kavan and ODog, this isn't true at all.

Assuming solely autorotation of the mandible (and that occlusion will be satisfactory after surgery), the change of the mandibular plane angle can be explained by the following:

(CW rotation of mandibular plane) = (CW rotation of the maxilla) - (degrees of anterior open bite)

All terms are in degrees, and the last terms measures the discrepancy between the maxillary and mandibular occlusal planes (where an anterior open bite is positive). Negative CW rotations are positive CCW rotations.

QUIZ:

Derive the above "formula," using simple geometric concepts.

[ODog]

No idea what you are talking about.

[kavan]

Kavan and ODog, this isn't true at all.

Assuming solely autorotation of the mandible (and that occlusion will be satisfactory after surgery), the change of the mandibular plane angle can be explained by the following:

(CW rotation of mandibular plane) = (CW rotation of the maxilla) - (degrees of anterior open bite)

All terms are in degrees, and the last terms measures the discrepancy between the maxillary and mandibular occlusal planes (where an anterior open bite is positive). Negative CW rotations are positive CCW rotations.

QUIZ:

Derive the above "formula," using simple geometric concepts.

The videos shown on this thread titled 'Anterior Open bite' were introduced by neither me nor the OP. But from the videos we were looking at POSTERIOR IMPACTION.


The OP did NOT say he had an anterior open bite.


The OP also did not mention the NET number of degrees his maxilla was to be rotated.

What numbers do you propose be plugged into your equation given neither any mention of an anterior open bite NOR any mention of the proposed CW rotation of the maxilla???

PLEASE ANSWER the OP'S question:

["Oh yes I forgot to say the front of my maxilla will also be brought down as I have 0 tooth show at rest (back maxilla is long, front is short); so I was wondering if THAT CW rotation would elongate the face or would the impaction balance it out ?"]

In terms of only his question and in the ABSENCE of ANY mention of his having an anterior open bite and also in the absence of any quantitative degree measures.

I would like to see the correct answer relative to how he asked the question in the absence of any quantitative measures and mention of having any anterior open bite.

[jawguy123]

What numbers do you propose be plugged into your equation given neither any mention of an anterior open bite NOR any mention of the proposed CW rotation of the maxilla???

If OP doesn't have an anterior open bite, then the number to plug into the last term (I specified the last term as "the discrepancy between the maxillary and mandibular occlusal planes") would be zero.

Thus, in cases where the maxillary and mandibular occlusal planes are parallel, the formula simplifies to:

(CW rotation of mandibular plane) = (CW rotation of the maxilla)

OP mentioned that he is getting CW rotation, which implies the term on the right side of the equation is positive, which in turn implies that there will be "positive" CW rotation of the mandibular plane (assuming OP doesn't have an anterior open bite).

You said,

Depends on the net CW rotation. If more is removed from the back than 'dropped down' in the front, then mandible plane angle should be LESS than what you started with.

This is false. Consider a case when there is both a posterior impaction and an anterior disimpaction (downgrafting) where the magnitude of the posterior impaction is greater than the magnitude of the anterior disimpaction. Also assume OP doesn't have an anterior open bite. Since both the posterior impaction and anterior disimpaction contribute to CW, there must be a positive net CW rotation of the maxilla, which would yield a positive net CW rotation of the mandibular plane from the formula.

CW rotation of the mandibular plane is a steepening of the mandibular plane, or an increase in the mandibular plane angle. But you said that "If more is removed from the back than 'dropped down' in the front, then mandible plane angle should be LESS than what you started with." Thus, this case contradicts your statement.

@ODog, I was basically pointing out that if you don't have an anterior openbite, clockwise rotation of the maxilla will result in an INCREASE in mandibular plane angle, not a reduction like kavan said.

[kavan]

If OP doesn't have an anterior open bite, then the number to plug into the last term (I specified the last term as "the discrepancy between the maxillary and mandibular occlusal planes") would be zero.

Thus, in cases where the maxillary and mandibular occlusal planes are parallel, the formula simplifies to:

(CW rotation of mandibular plane) = (CW rotation of the maxilla)

OP mentioned that he is getting CW rotation, which implies the term on the right side of the equation is positive, which in turn implies that there will be "positive" CW rotation of the mandibular plane (assuming OP doesn't have an anterior open bite).

You said,

This is false. Consider a case when there is both a posterior impaction and an anterior disimpaction (downgrafting) where the magnitude of the posterior impaction is greater than the magnitude of the anterior disimpaction. Also assume OP doesn't have an anterior open bite. Since both the posterior impaction and anterior disimpaction contribute to CW, there must be a positive net CW rotation of the maxilla, which would yield a positive net CW rotation of the mandibular plane from the formula.

CW rotation of the mandibular plane is a steepening of the mandibular plane, or an increase in the mandibular plane angle. But you said that "If more is removed from the back than 'dropped down' in the front, then mandible plane angle should be LESS than what you started with." Thus, this case contradicts your statement.

@ODog, I was basically pointing out that if you don't have an anterior openbite, clockwise rotation of the maxilla will result in an INCREASE in mandibular plane angle, not a reduction like kavan said.

OK. I see what you are saying and how I went wrong on this one. I was looking at video only in terms of posterior impaction and disregarded the Title of 'Anterior Open Bite'. I erroneously attributed the decrease in MPA to posterior impaction when a screen shot of the video was entered from which I measured a decrease in the angle. Hence the decrease in MPA from the screen shot pulled from the video was attributable to the significant open bite.

Thanks for catching that. I gave you a Karma point.

[jawguy123]

OK. I see what you are saying and how I went wrong on this one. I was looking at video only in terms of posterior impaction and disregarded the Title of 'Anterior Open Bite'. I erroneously attributed the decrease in MPA to posterior impaction when a screen shot of the video was entered from which I measured a decrease in the angle. Hence the decrease in MPA from the screen shot pulled from the video was attributable to the significant open bite.

Thanks for catching that. I gave you a Karma point.

No problem, happy to help. Interesting that you used screenshots from the video simulation to try to see if the MPA steepened, since it would be way easier just to use basic geometric intuition (since you seem to often comment about that lol). If you were assuming OP didn't have an open bite pre-surgery, then obviously rotation of the maxilla would force an equal autorotation of the mandible, or else OP would be left with an open bite post-surgery.

[kavan]

I didn't take the screen shots though. Just measured the angle. The OP did not say he had an open bite. Again, got caught up in in just the posterior wedge cut of the video and disregarded the actual title of it.

[ODog]

I think my braces are decomensating my teeth and revealing a bit of an open bite actually. However I assumed having a long posterior maxilla and a short anterior maxilla basically = an anterior open bite. Or else why would you impact the posterior ?