How much does tooth/gum show increase with maxillary advancement?

[secondtimearound]

I have been reading this article here:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4686745/

Which seems to do a good job of summarizing studies on how maxillary advancement proportionately increases tooth/gum exposure.

In their own study, an average of ~5 mm of advancement led to an average of ~1 mm of increased tooth show (if I'm reading correctly).

They quote other studies though that I'm having trouble interpreting exactly.

For example, they say:

"Van Butsele et al17 evaluated soft and hard tissue ratios in relation to maxillary advancement. The authors concluded that, for each millimeter of maxillary advancement, the upper lip moved upward in almost 30% the amount of advancement, in addition to having an elongation of 1.7 mm."

So for a 5 mm advancement, are they suggesting this study would suggest 5x0.3 + 1.7 mm = 3.2 mm increased tooth show? That seems excessive to me.

Is there any consensus on what to expect?

This plays a huge role in planning, because the degree of increased predicted show will also dictate the degree of potential impaction you can add on with any rotations you might like at the same time.

ie. If you're going to get another 2-3 mm of tooth show from a 5 mm anterior maxillary movement, you could impact the upper jaw another 2-3 mm at the front for some "safe" CCW without changing the lip-tooth relationship.

I am sure all of this varies from person to person and is largely difficult to predict. But it is important to at least try to predict.

Thoughts?

[kavan]

I have been reading this article here:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4686745/

Which seems to do a good job of summarizing studies on how maxillary advancement proportionately increases tooth/gum exposure.

In their own study, an average of ~5 mm of advancement led to an average of ~1 mm of increased tooth show (if I'm reading correctly).

They quote other studies though that I'm having trouble interpreting exactly.

For example, they say:

"Van Butsele et al17 evaluated soft and hard tissue ratios in relation to maxillary advancement. The authors concluded that, for each millimeter of maxillary advancement, the upper lip moved upward in almost 30% the amount of advancement, in addition to having an elongation of 1.7 mm."

So for a 5 mm advancement, are they suggesting this study would suggest 5x0.3 + 1.7 mm = 3.2 mm increased tooth show? That seems excessive to me.

Is there any consensus on what to expect?

This plays a huge role in planning, because the degree of increased predicted show will also dictate the degree of potential impaction you can add on with any rotations you might like at the same time.

ie. If you're going to get another 2-3 mm of tooth show from a 5 mm anterior maxillary movement, you could impact the upper jaw another 2-3 mm at the front for some "safe" CCW without changing the lip-tooth relationship.

I am sure all of this varies from person to person and is largely difficult to predict. But it is important to at least try to predict.

Thoughts?

Use geometry to estimate. Forward advancements take place over diagonal lines (or 'planes') inclined at different angles from the horizont. So the forward advancement takes place over the OP whether it's one they keep as is or construct where you get 2 vector displacements; the pure horizontal displacement and the pure vertical. The latter being the tooth show you will get; increased or decreased. There will be some co-efficient of tissue resistance such that it won't be just like a straight forward geometry displacement. But still that article spoke little or nothing of those types of things.