Bimax: Pivot Points

[Deleted member 19766]

This is barely talked about and I can't find any information online about this. Can anyone explain this shit to me?

 

[Deleted member 19766]

@longjohnmong @tinderhacker @user47283 @dakchuh @Silver

 

[longjohnmong]

When they do rotation they can choose different points on the maxilla as the axis of rotation. Different points have different consequences. @tinderhacker seems to know the most about this. Everything I know is the product of my own thought, so it could be wrong. But say they chose the PNS (posterior nasal spine) as the axis, that means the CCW rotation will move the front of the maxilla, including the teeth, upwards (impaction), causing less tooth show. Presumably that would be a good choice for people with gummy smile and a bad choice for people with normal tooth show. If they choose the tip of the incisor as the axis it seems to me like that would necessitate everything above that moving backwards, and it also seems like it would result in less forward movement of the mandible per degree of rotation than if the pivot point were the ANS (anterior nasal spine) because the distance of the mandible from the axis is less in the case where the axis is the incisor tip. So I don't know why that would be more aesthetic, like @tinderhacker says, but he knows more than I do.

 

[dakchuh]

makes not much difference in your average lefort 1 tbh. thats why itsnot talked about. becuz they're always gonna cut around the same place more or less.

 

[longjohnmong]

makes not much difference in your average lefort 1 tbh. thats why itsnot talked about. becuz they're always gonna cut around the same place more or less.

He's asking about the axis of rotation, not the Lefort cut. Think about it, if the axis of rotation is the ANS (anterior nasal spine) then everything below it is going to swing forward, whereas if the axis is the incisor tip then that same stuff and also the ANS is going to swing backwards. Seems like there would be a big difference between these two choices of pivot points.

 

[dakchuh]

He's asking about the axis of rotation, not the Lefort cut. Think about it, if the axis of rotation is the ANS (anterior nasal spine) then everything below it is going to swing forward, whereas if the axis is the incisor tip then that same stuff and also the ANS is going to swing backwards. Seems like there would be a big difference between these two choices of pivot points.

yeah but the cut itself is still gonna be at the lefort 1 location. even if the axis is at incisor tip they're still gonna bring the jaws forward most likely, which in essence is just axis at the ANS even if there are minor up-down differences, which the surgeon is gonna correct anyway. point is theres no point autisming out over this because the surgeon's gonna do what hes gonna do. not like you'll be able to debate on him over the location of the axis.

 

[Silver]

You draw a triangle between the PNS, ANS and the pogonion. Along the lines of the triangle you choose a rotation point, this is a point which is made to act as an achor which the maxillomandibular complex (MMC) as a whole will rotate around. The cephalometric point that is chosen as the rotation point will maintain its place while the MMC is being rotated. For example, most commonly I see the maxillary incisor (mx1) being used as the rotation point. If they chose this point and do CCWr, you avoid overly flared incisors. You can use other points, as long as they are on the triangle, for example ANS, PNS and pogonion are the obvious rotation points but you can also use the zygomatic buttress, anterior maxilla and incisor tip.

 

[Deleted member 19766]

He's asking about the axis of rotation, not the Lefort cut. Think about it, if the axis of rotation is the ANS (anterior nasal spine) then everything below it is going to swing forward, whereas if the axis is the incisor tip then that same stuff and also the ANS is going to swing backwards. Seems like there would be a big difference between these two choices of pivot points.

You draw a triangle between the PNS, ANS and the pogonion. Along the lines of the triangle you choose a rotation point, this is a point which is made to act as an achor which the maxillomandibular complex (MMC) as a whole will rotate around. The cephalometric point that is chosen as the rotation point will maintain its place while the MMC is being rotated. For example, most commonly I see the maxillary incisor (mx1) being used as the rotation point. If they chose this point and do CCWr, you avoid overly flared incisors. You can use other points, as long as they are on the triangle, for example ANS, PNS and pogonion are the obvious rotation points but you can also use the zygomatic buttress, anterior maxilla and incisor tip.

What would you guys recommend for blackpilled people? I heard that rotating around some places is more functional vs cosmetic. I am a downgrown steep gonial angle LFS case w/gummy smile btw.

 

[longjohnmong]

What would you guys recommend for blackpilled people? I heard that rotating around some places is more functional vs cosmetic. I am a downgrown steep gonial angle LFS case w/gummy smile btw.

I don't know. I'd have to see multiple examples of each. My rotation was about the ANS and I'm happy with the results so far, but I also had 3mm linear advancement, and I didn't need any impaction.

It makes sense that if you chose a point closer to the pogonion that you would get less advancement of the pogonion per degree of rotation, right? Like if the point of rotation is the pogonion then it wouldn't advance at all regardless of the amount of rotation. So it seems like the choice would have to factor in how much advancement you need, how much rotation you can actually get due to your starting occlusal angle, as well as other considerations. I don't think there's a generic answer for what is better for aesthestics.