Cranial base flexure application

Synapse Orthodontics: Module 3

Cranial base flexure application

Posted by Joti Kaler on January 13, 2023 at 10:53 pm

I tried applying the cranial base flexure to this case. We have a flat cranial base with a difference between FMA and SN of 3 so we subtract 4 from SNA and SNB. giving us 81 and 71. From the numbers we are WNL for maxilla and we have a retrognathic mandible. However, the answer has protrusive maxilla? Did I do the calculations incorrectly? Can you explain why for this case and when to not follow numbers. If I just look at the ceph without the tracing or even the profile- I see relative to nasion the maxilla does look protrusive.

Adedolapo Ayediran replied 8 months ago 3 Members · 9 Replies
9 Replies

Chad Carter (Course Director)

Member
January 17, 2023 at 10:26 pm

Excellent question!

So you did the math correct. And yes the number may say “normal” SNA. But you then excellently applied the next step which is look at it and realize that A to N perpendicular is more predictive in this case of low cranial base (McNamara) and so you identify the protrusive maxilla.
Chad Carter (Course Director)

Member
January 17, 2023 at 10:29 pm
Here are the reference points from the McNamara article for your review.
McNamara-Low-Med-High-FH-SN.png 57 KB Image File - Click to view

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- Adedolapo Ayediran
  
  Member
  January 17, 2024 at 5:23 am
  
  Could you please explain how to properly utilize these standard deviations?
  - Chad Carter (Course Director)
    
    Member
    January 17, 2024 at 10:15 pm
    
    The standard deviations are the +/- range of the normative value relating to the observation of the cranial base angle. So a steep cranial base patient would be considered normal maxilla with an SNA of 79 degress (give or take 2 degrees from that). We don’t work in decimal places at the hundredths but this table is from a research article so it’s point is to help us understand what values are impacted by a steep or flat cranial base.
    
    Does that help?
    - Adedolapo Ayediran
      
      Member
      January 18, 2024 at 3:55 am
      
      Ok, is it worth memorizing the SD?
      - Chad Carter (Course Director)
        
        Member
        January 18, 2024 at 9:15 am
        
        Personally, I would not other than a general idea of +/- 2 for most. The more cases I see the more I get the feel of normal. The timing and quick analysis will help in actual test taking
      - Adedolapo Ayediran
        
        Member
        January 19, 2024 at 2:38 am
        
        Thanks, just to be sure on the application.
        
        So if it’s steep +2, flat -2 ???
        
        This reply was modified 8 months, 3 weeks ago by Adedolapo Ayediran.
        
        Chad Carter (Course Director)
        
        Member
        January 22, 2024 at 9:26 pm
        
        It is the range that is + 2 for most. So if 85 is norm then the range is 83-87 (the + or – of 2 for the standard deviation around the norm). That clear?
        
        Adedolapo Ayediran
        
        Member
        February 3, 2024 at 10:10 am
        
        Yes, that is clear. Thanks

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