Sassouni's analysis
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Dr. Viken Sassouni developed a cephalometric analysis method based on craniofacial x-rays of 100 children. He identified planes, arcs, and points to analyze facial proportions and classify facial patterns. A well-proportioned face has four planes intersecting at point O and equal upper/lower anterior and posterior facial heights. Sassouni found most faces were Type II patterns. His analysis considered vertical and horizontal relationships and classified occlusions, palates, profiles, and dental axes. He concluded that "normal" is relative and proportions are more important than absolute measurements.
Sassouni's analysis
- 2. Introduction • Dr. Viken Sassouni, an American, was born in Iran in 1922. • He studied dentistry in the University of Paris, France and graduated in 1951. • He received his doctorate in dentistry from University of Pennslyvania in 1958 and doctorate in dental surgery in 1960. • He became professor and chairman of orthodontic department in West Virginia University. • In 1964 he joined the orthodontic department in University of Pittsburg which he retained till his death. • He wrote seven books and numerous papers. • He developed a system of identification based on cranio-facial x-rays for the U.S. Dept of Defense. • He was a pioneer in computerized orthodontic diagnosis and treatment planning. 1922-1983
- 3. The skull: A battleground of forces The architecture of the skull is a result of many forces on the adaptable bony substance Eg. Genetic forces in racial of familial patterns, growth forces, muscular forces at rest(static), functional muscle forces(dynamic), and environmental forces(health, diet). At each period of life the skull is the end result of the interaction of theses forces.
- 4. Sassouni based his analysis on a study conducted on tracings of 100 lateral head x-ray films. The sample included 51 girls and 49 boys. They were White children, primarily of Mediterranean origin. The chronological age ranges from 7 to 15 years. The aim of the study was to find some acceptable constant relationships in architecture of the face and use it for
- 5. Terminology He constructed a series of planes, arcs and axes on a profile/ lateral cephalostat. PLANES Mandibular base plane- OG Occlusal plane- OP Palatal plane –ON Anterior cranial base plane or Basal plane –OS’ Ramal plane –RX’
- 6. POINT O The relationship between 1. Mandibular base plane 2. Occlusal plane 3. Palatal plane 4. Anterior cranial base plane In a well-proportioned face, if these planes are prolonged, they all meet posteriorly at the same point i.e O
- 7. ARCS Anterior arc: the arc of a circle, between anterior cranial base plane and mandibular plane, with O as the center and O-ANS as radius. Posterior arc: the arc of a circle, between anterior cranial base plane and mandibular plane with O as center and OSp
- 8. The relationship between point O and bony profile of a well- proportioned face The anterior arc passes through:- pogonion, incisal edge of upper central incisor, anterior nasal spine,nasion & fronto- ethmoidal junction All these points are equidistant from point O
- 9. The posterior relationship well- proportioned face The posterior arc should also pass through the gonion. Thus: the gonion and Sp are equidistant from O
- 10. AXES 1. Axis of 6 2. Axis of 1 3. Axis of 6 4. Axis of 1
- 11. Relationship between anterior arc and posterior arc The face is limited: Above- by anterior cranial base plane Below- by mandibular base plane Anteriorly- by arc passing through ANS Posteriorly- by arc passing through Sp Proportion given by 1. Angle S’OG 2. Ratio of Radii- Ra / Rp 3. Combination gives
- 12. Analysis Sassouni’s analysis was the first cephalometric method to categorise vertical as well as horizontal relationships, and also the interaction between vertical and horizontal proportions of the face. He examined, in sequence, the mandible, the palate and the anterior cranial base.
- 13. THE MANDIBLE Three main types: 1. Curved: traction forces at Go & pulling forces at Me are in equilibrium 2. Oblique: traction & pulling forces are so strong that there is a notch anterior to gonial insertion of masseter 3. Horizontal: traction is greater
- 14. THE PALATE 1. Horizontal: line connecting ANS & PNS passes through bony structure 2. Convex: line passes above the bony structure 3. Concave: line passes below the bony structure
- 15. Relationship between palate and mandible Generally Curved mandible → horizontal palate Oblique mandible→convex palate Horizontal mandible→concave palate
- 16. Classification of facial types Type I: OS does not pass through point O Type II: ON does not pass through point O Type III: OP does not pass through Point O Type IV: OG does not pass through point O Subdivision: A- passes above point O B- passes below point O (Eg: Patient X shows facial pattern Type IIB)
- 18. Sassouni found( in 100 subject sample): 16 with well proportioned faces Type II as most frequent A well-proportioned face has normal occlusion; but normal occlusion is necessary but not sufficient for a well-proportioned face.
- 19. Vertical proportions Comparing lower face to upper face: Equal: distance from ANS to OG = distance from ANS to OS Minus: lower face is smaller than upper face Plus: lower face is larger than upper face Use PNS for posterior face
- 20. Classification of profile Based on anterior arc and reference points: Na, ANS, upper incisor & pogonion 1. Archial: anterior arc passes through all points 2. Prearchial: arc passes through Na. ANS, uppper incisor & Pog are anterior to it 3. Postarchial: same points posterior to arc 4. Convex: ANS & upper incisor anterior to arc passing through Na & Pog 5. Concave: Same
- 22. Dental axes Maxilla Axes of U6 & U1 intersect at level of bony orbital contour- point X Form a triangle with palatal plane Angle M’= angle I’ + 10˚ Mandible Ramal plane & axis of L1 form a triangle with occlusal plane Angle R= angle i
- 23. Thus : Complete, well-proportioned face, as seen on lateral ceph, is one in which 1. Four planes meet at point O 2. Upper anterior & lower anterior faces are equal 3. Upper posterior & lower posterior faces are equal 4. Profile is archial 5. Posterior arc passes through gonion
- 24. Diagnosis • Occlusion: class II, div 1 • Facial pattern: type IIB (ON) • Anterior arc: is in front of Pog, posterior to upper incisor & Na. thus major malposition is in pogonion • Posterior arc: intersects OG anterior to gonion • Vertical balance: At ANS: upper is shorter than lower At PNS: upper equal to lower • Palatal shape: convex So, Horizontally- class II malocclusion due to posterior position of mandible
- 25. Skeletal deep bite & open bite
- 27. Conclusion There is no norm that can be applied indiscrminately to everybody. The concept of “normal” is not absolute but is relative to individuality. Thus “absolute measurements, averages and mean values are less significant than proportions”.
- 28. References Orthodontics- diagnosis and management of malocclusion and dentofacial deformities- O P Kharbanda Viken Sassouni -- A roentgenographic cephalometric analysis of cephalo-facio-dental relationships - American Journal of Orthodontics Volume 41 issue 10 1955