Cephalometric analyses Basal measurements – Direction of facial and mandibular growth
Cephalometric analyses
Basal measurements – Direction of facial and mandibular growth
1-FMA angle or Tweed angle:
It is the angle formed by the Frankfurt plane and the mandibular plane.
It objectifies the vertical and even antero-posterior relationships of the mandible in relation to the base of the skull.
Its average value : 27+-4°
- If FMA is greater than 31°: there is a vertical mandibular growth tendency, the lower level is increased, the mandible descends and moves back.
- If FMA is less than 23° : Mandibular growth tends to be horizontal. The mandible moves up and forward, the lower level is reduced.
2- The Y axis (Downs):
It objectifies the result of the different growth centers of the face as well as the general trend of the growth of the face.
It is the angle formed by the S-Gn axis and the Frankfurt plane
-Its average value = 59+-3°
- If the angle is less than 56°: Facial growth directed forward, with a horizontal tendency.
- If the angle is greater than 62°: Facial growth is of a vertical tendency directed forward but especially downward.
3-Goniac Angle (Schudy):
It is formed by the tangent to the condyle, and the tangent to the lower edge of the mandible .
Its average value = 128 +- 6 °
The opening or closing of the goniac angle influences the degree of posterior or anterior rotation of the mandible, and therefore the vertical position of the latter by causing the increase or decrease of the lower level of the face.
AG between 122° -134°: Normodivergent
AG greater than 134°: Hyperdivergent
AG less than 122°: Hypodivergent
4-Analysis by Wendell Wylie:
The measurement of the total height of the face at the profile level is made between points Na and Me
The lowered perpendicular of the anterior nasal spine on the Na – Me line, divides this height into two levels:
-Upper or nasal floor
– Lower or dental floor
- The ideal proportion of each floor is:
45.5% +-2% of the total height for the upper floor
54.5% +-2% of the total height for the lower floor
The proportion of the upper floor is given by the following formula:
Height of upper floor x 100
Total face height
The % of the lower floor is then obtained by subtraction.
Cephalometric analyses Basal measurements – Direction of facial and mandibular growth
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