Lets get critical 2
SNA SNB SN What
It was seen that S is mobile in time and that N is not a facial point.
If these two points vary, it seems obvious that defining a reference line with these points makes no sense. The use of SNA to follow a patient or to establish a diagnosis lacks any physiological basis.
It has already been seen the main reasons of variation of B. Once again, B is an alveolar point which which mainly depends on the situation and orientation of the lower incisors, on the mandibular rotations, and on the development of the mandible.
... If everything is variable, in relation to itself, in relation to others, in time, in space, according to the point of view and the way of seeing things, it becomes difficult to be ... rigorous.
Conclusion of section
Current cephalometric conventions have little biological or biometric Basis.
There is no Cephalometric Theory, only conventions that apply exclusively to points and lines linking point which don't know each other. This does not allow to measure exactly the size of the craniofacial structures or their growth disorders.
Conventional cephalometric procedures give wrong informations by :
- creation of "false geometric values",
- camouflage, especially of remodeling,
- confusion about what is really going on (analysis of the rotations, separate treatment of shape and size, recording of angles on superficial/ surface points),
- subtraction, as a representation of the growth processes.
These approaches actually offer little hope of meeting the intellectual needs for craniofacial growth study as they might not represent (the) reality :