cephalometric lnadmarks and down's analysis

The radiographic cephalometry was
introduced as a research and clinical tool
for the study of malocclusion and
underlying skeletal disproportions.
The most important clinical use of
radiographic cephalometrics is in
recognizing and evaluating changes
brought about by orthodontic treatment.
Superimpositions taken from serial
cephalometric radiographs before, during
and after treatment can be superimposed
to study changes in jaw and tooth position
• The head is in natural relaxed position. Patient gets it by
looking at a distant horizont.
• We have to keep these standard conditions to take standard
and comparable cephalometric radiographs.
• The distance of the X-ray tube from mid sagittal plane of the
patient 5 feet ( 152.4 cm).
Cephalometric landmarks
• Anatomic landmarks: these
landmarks represent actual
anatomic structures of the
• Derived landmarks: these
are landmarks that have
been obtained secondarily
from anatomic structures in a
• Hard tissue landmarks
• Soft tissue landmarks
1. Bo ( Bolton point)- the highest point in the
upward curvature of the retrocondylar
fossa of the occipital bone
2. Ba ( basion)- the lowest point on the anterior
margin of the foramen magnum. at the base of
3. Ar ( articulare)- the point of intersection
between the shadow of the zygomatic arch and
the posterior border of the mandibular ramus.
4. Po( porion)- the midpoint of the upper
contour of the external auditory canal
(anatomic porion) ; or the midpoint of the
upper contour of the metal ear rod of the
cephalometer ( machine porion).
5. SO ( spheno- occipital synchondrosis)- the
junction between the occipital and the
basisphenoid bone( if wide, the upper margin)
• 6. S( sella)- the midpoint of the cavity of
sella turcica.
• 7. Ptm( pterygomaxillary fissure)- the point
at the base of the fissure where the anterior
and posterior walls meet.
• 8. Or( orbitale)- the lowest point on the
inferior margin of the orbit.
• 9. ANS( anterior nasal spine)- the tip of the
anterior nasal spine (sometimes modified as
the point on the upper or lower contour of
the spine where it is 3 mm thick)
• 10. Point A(subspinale)- the innermost point
on the contour of the premaxilla between
posterior anterior nasal spine and the
prosthion ( the most inferior point on
the alveolar bone overlying the
maxilary incisors)
11. Point B( supramentale)- the innermost
point on the Contour of the mandible
between the incisor tooth (the most superior
point on the alvelar bone overlying the
lower incisors -( infradentale) and the bony chin.
12. Pog( pogonoin)- the most anterior point on
the contour of the bony chin.
13. Me( menton)- the most inferior point on the mandibular symphysis (i.e. the bottom of
the chin)
14. Go( gonion)- a point on the curvature of the angle of the mandible located by bisecting
the angle formed by lines tangent to the posterior ramus and the inferior border of the
N(nasion)- the most anterior point on the
frontonasal suture in the midsagittal
Gn (gnathion)- a point located by taking the
mid point between the anterior (pogonoin)
and inferior (menton) points of the bony chin.
PNS( posterior nasal spine)- the posterior spine of the palatine bone constituting the hard
• Horizontal planes
• S.N. Plane- sella to nasion. It
represents anterior cranial base.
• Frankfort horizontal plane (Po Or) –
• Mandibular plane –
• Based on analysis different types• Tweed- tangent to lower border of
• Steiner- - gonion to gnathion.
• Down’s analysis- gonion to menton.
• Maxillary plane – this is line through
the anterior and posterior nasal spine.
• Functional occlusal plane – the line
following the occlusion of the molar
and premolar teeth.
Vertical planes
A-Pog line- from point A to pogonion.
Facial plane (N Pog) – nasion to
It indicates the general orientation of
the facial profile.
E. Plane- esthetic plane- a line
between the most anterior point of the
soft tissue nose and soft tissue chin.
• It consists of 10 parameters- 5 skeletal
and 5 dental.
• Skeletal parameters1. Facial angle- nasion – pogonion
plane and the F.H. plne.
• Average value- 87.80
• Increased – skeletal class III with
prominent chin.
• Decreased- skeletal class II cases
• 2. Angle of convexity- nasion to point
A and to point A to pogonion.
• Average value- 00
• Increased –prognathic maxilla
relative to mandible
• Decreased- prognathic mandible
• Facial angle
• Angle of Convexity
• A –B Plane angle
• Mandibular plane angle
• A-B plane angle- line
connecting point A and
point B to nasion –
pogonion(facial plane).
• Average value- -4.60 ( -9
to 00)
• Increased –skeletal class
III malocclusion
• Mandibular plane anglemandibular plane ( GoMe) to Frankfort
horizontal plane( Pom-Or)
• Average value- 21.90 ( 17
to 280)
• Increased –vertically
• Decreased –Horizontally
• Y- axis ( growth axis)- sella –
gnathion to Frankfort
horizontal plane.
• Average value-59 0 ( 53 to
• Increased –class II facial
pattern- greater vertical
growth of mandible.
• Decreased –class III facial
pattern – greater horizontal
growth of mandible.
Cant of occlusal plane- angle between F.H.
Plne and Occlusal plane
Average value- 9.3 0 ( 1.5 to140)
Interincisal angle- between long axis of
upper and lower incisors.
Average value- 135.4 0 ( 130 to150.50)
Increased – angle’s class II division 2
Decreased – angle’s class II division 1
Incisor - occlusal plane angle- inside inferior
angle formed by the intersection between
the long axis of lower central incisor and
occlusal plane.
The inferior inside angle is read as positive or
negative deviation from a right angle.
The positive angle increases as the teeth
incline forward.
Average value- 14.50
The minimal angle is 3.50 and maximal 200
Cant of occlusal plane
Interincisal angle
Incisor - occlusal plane angle
Incisor mandibular plane angleintersection between the long axis of
lower central incisor and mandibular
The mandibular plane angle is read as
positive or negative deviation from a right
Average value- 1.4 0 ( -8.5 to 70)
Increased – angle’s class II division 2
Decreased – angle’s class II division 1
Upper incisor to A- pog line- linear
measurement between the incisal edge
of the maxillary central incisor and the
line joining point A to pogonion.
Average value- 2.7 mm ( n-1 to 5 mm)
Increased –upper incisor proclination.
Decreased – upper incisor retroclination.
Incisor mandibular plane angle
Upper incisor to A- pog line
• Radiographic cephalometry: from basics to video
imaging. Alexander Jacobson.
• Contemporary orthodontics. 5th edition. William R
• Orthodontics : the art and science. 4th edition. S I