Mod 4; Case 2

[Chad Carter (Course Director)]

Good question, Alice!

This is referring to the Sassouini Analysis. The Sassouini lines are anatomic planes including the anterior cranial base plane, Frankfort horizontal(plane), palatal plane (ANS to PNS), occlusal plane and mandibular plane. These lines or planes should all converge posteriorly at a single point in well-proportioned faces. If the point of convergence is further back (beyond the skull) then it’s indicative of a low vertical pattern / bracyfacial growth. If the lines all converge more anteriorly then it shows a vertical / hyperdivergent growth.

In this particular case, notice how the palatal plan tips down (ANS is higher than PNS; the palatal plane does not generally follow Frankfort horizontal as we see in normal growth cases. This posterior tip of the palatal plane indicates more vertical growth in the posterior than in the anterior.

This is especially helpful when diagnosing open bites that are skeletal in nature versus dental or habit in nature.

Is that helpful?

Good luck!

Carter

[Pegah Kamrani]

Hey Chad, looking more into the case and adjusting for a steep cranial base, I have the adjustment being 11 (18 from 44-26, then subtract 7). Should we add this number to the maxilla and mandible? Kind of confused on how to properly adjust for the steep cranial base and diagnose her Mx/Md skeletally. Thank you!!

[Chad Carter (Course Director)]

I’ll work on explanation here. There is a video covering this with Dan under Module 2 as well if that helps “Cranial Base Flexure”

1) You are correct on the math for the adjustment (SNMP – FMA = Cranial Base Angle). For this case 18. Then adjusting for “normal” by subtracting 7 because you see it is steep. Giving an adjustment of 11.

2) Because this is steep, the steep SN line has made SNA and SNB smaller (more acute angles). So you add the 11 to SNA and SNB to get the adjusted.

3) Now look at how this interprets. The SNA as measured on the ceph is 82 but that maxilla does not look “normal”, it definitely looks protrusive. When adjusting for cranial base the SNA is 93 which makes sense and now our “made up numbers” make sense and we can all agree it’s a protrusive maxilla. Similar for SNB.

4) Notice this does not change ANB. So this is where severe OCCLUSAL plane rotations some folks like the Wits (Witswatersrand) Analysis.

Bottom line: Cranial base adjustment helps put together the skeletal picture. Trust your gut. Don’t let numbers tell you lies! (For example seeing the number 82 for SNA and saying the maxilla is normal even though in your heart you know it’s protrusive)

Great discussion!

CBC

[Pegah Kamrani]

Ah, this makes more sense. So even though we also add 11 to SNB which would make her mandible SNB “normal”, ANB is still the same (large, so skeletal Cl II) so we need to consider the surgical correction to correct the vertical and AP, and that would mean a BSSO advancement.

[Chad Carter (Course Director)]

I like the thought process!