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Tagged: amy, Chad Carter

Sample Case and Cranial Base Flexure
Posted by Donna Nichols on January 14, 2023 at 10:54 amI looked at Case 2 for Module 3 and it seems as though SNA and SNB needed to be corrected because SNFH is greater than 7. I may be doing it wrong but doing so would make SNA larger and in the prognathic maxilla range. Also, A point looked protrusive to Nasion perpendicular. Can someone please explain what I’m doing wrong?
Chad Carter (Course Director) replied 1 year, 7 months ago 3 Members · 6 Replies 
6 Replies

Donna, Great question here!
So for Module 3, Case 2 we have SNMP of 27 and FMA of 15 so FHSN is 2715=12; Then 12 – 7 (avg cranial base) = 5 as our corrector for the steep cranial base. Then Ceph shows SNA of 78 and we add 5 to get SNA of 83 and do the same for SNB to get 78. Is that what you got for the cranial base adjustment?
So still definitely large ANB. Normal SNA of 82 +/ 2 so 83 is normal for me.
You bring up an EXCELLENT point about then looking at A point with NasionPerpendicular. I attached the image from McNamara’s article that shows when you have a steep cranial base (high C), that the A to N Perpendicular will be 1.57mm. So you are seeing the right things! This is a normal maxilla in the AP with a steep cranial base.
Keep up the good work!

I can’t seem to find the ABO norms with the St Dev for each of the measurements the ABO uses. SNA, SNB, ANB, MPA, FMA, U1s to EN, U1s to NA, IMPA, L1s to NB, lips to E line. Did you already post these somewhere?? The question arrises since I have on my notes SNA 82 StDev 3.5 Therefore I rather very all of the measurements I have on my notes. Can you please post all the norms w.the StDev if you have not already done so. I appreciate it!

I have on my notes SNA 82 StDev 3.5 Therefore I rather verify all of the measurements I have on my notes. Can you please post all the norms with the corresponding StDev if you have not already done so. I appreciate it!

Antonia, you express the same question I had! (I’m sure many others as well)
The ABO does not have an “endorsed” set of norms.
If you go up to the General Discussion Feed and the discussion “Board Test Taking Tips” you will see a study sheet we have created which includes the cephalometric norms.
The board recognizes there are dozens of analyses out there however rather than getting locked into our pet project areas just stick with the big picture.


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