د. محمد رافد Cephalometric landmarks, planes & angles



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د. محمد رافد



Cephalometric landmarks, planes & angles

The accurate picture of skeletal relationship between teeth , jaw and base of skull to each other can be taken by cephalometric radiograph and especially the lateral view .

The ceph. X-ray is a tow dimensional figures i.e. it gives us the picture of 2 planes. The lateral one, which is commonly used, clears the anteroposterior and vertical planes. in the lateral ceph. X-ray an actual size of the head is produced with the help of special machine in which there an equal and standardized distance from the tube – object – film as seen in this diagram.( go to any textbook).

There is 5 feet “150 cm” distance from tube to object and the film is near to the head as much as possible in order to minimize magnification, the head is fixed by the cephalostat, the cephalostat is an apparatus that contain 3 adjusted rods that can fix the head , the lateral rod are called the ear rods and the frontal one is applied on the N point


CEPH POINTS:
S {sella}: the center of sella tursica, pituitary gland fossa

N {nasion}: the junction of nasal and frontal bones “Frontonasal Suture”

P{Porion} :the highest point on the margin of external auditory meatus

OR{orbitale}: the lowest point in the infra orbital margin

ANS{ant. Nasal spine}: the most anterior projection of the premaxilla in the midline below the nasal cavity

PNS{ post. Nasal spine}: the most posterior projection of the hard palate in the midline

A: the deepest point in the anterior concavity of the premaxilla below ANS

B: the deepest point in the anterior concavity of anterior surface of the mandible

Pog[pogion] : the most anterior point of anterior surface of the bonny chin

Me[menton]: the most inferior point of the inferior surface of the bonny chin]

Gn [ginathion] :the most ant. & inf. Point of the bony chin midway between Pog & Me

Go [gonion] : the most post. &inferior point at the angle of mandible
There are hundreds of other point that was involved in hundreds of cephalometric analysis but the aboved are the most important

CEPHALOMETRIC PLANES


S-N plane: represents the base of the skull

Frankfort plane : line joins Or & Pog can represent the base of the skull

Max. plane: line joins ANS to PNS represents the level of maxilla could be parallel to Frankfort plane

Man. Plane: line joins Me to Go represents the level of the lower border of the mandible

Occlusal plane: a line bisects the incisor overbite and occlusal contact between upper 6 & lower 6

At centric occlusion



Common Ceph. Angles



SNA: represents the relative position of the maxilla to the base of the skull

SNB: represents the relative position of the mandible to the base of the skull

ANB: SNA, SNB difference , represents the relative position of the maxilla to the mandible

The aboved angles measure the saggital “ant. Post.” Relation of jaws to each other and to the base of the skull


FM: Frankfort mandibular plane angle represent the relative vertical position of the mandible to the frankfort plane

MM: Max-Man. Angle represents the relative vertical position or height of the Max to the mand.

  • the aboved tow vertical angles measures the vertical “ hight “ of the jaws & if increase means that there is increase facial hight and vice versa if decrease

  • 1/max: represents the axial inclination of upper incisors to max plane

  • 1/man: represents the axial inclination of the lower incisors to the mandibular plane

  • 1/1 : Interincisal Angle” represents the relative axial inclination of upper and lower incisors to each other

  • the last three angles measures the relative position & inclination of incisors to their opposing jaws if 1/max increase then there is proclination of upper incisors and e.g. if 1/man decrease then there is a retroclination of lower incisors

as shown in the figure if any angle lies within normal range then the condition is normal but if decrease or increase then we can say that there is abnormality.

For instance if FM increase then there is increase in lower facial height commonly associated with Cl III

Malocclusion & cases of skeletal open bite , but if FM angle is decreased its associated with short faces especially in cases of Cl II div 2 malocclusion or with patient that exhibit a deep complete overbite
When we gather all the informations taken from the history , clinical examinations “ including sk , st and dental” , radiographic examinations the cephalometric findings in addition to the observations taken from study models and combine it with the chief complain of the patient , we may proceed in our treatment plan which should be in harmony with our aims in orthodontics ,as much as possible i.e. we should not treat patient CC alone .

For example : we may have two cases of Cl II div1 malocclusion , both of them are with equal amount of overjet , same canine inclination ,same age & sex, same overbite…etc., but there is a difference in incisors inclination , the 1st is with normal 1 to max plane & 2nd with increase 1/max plane angle. So the treatment in the 1st case should go with bodily type of teeth movement to reduce the increased overjet & the 2nd should go with tipping type of tooth movement .both can be performed by fixed appliance & the 2nd could be performed by a removable appliance also.



This example is an absolute one . We take in consideration only the increased OJ for a studying purpose. But the real story is something different
So far, we orthodontists regard an orthodontic diagnosis is one of the most difficult and hard to reach it!!!!!!!


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