SUPERIMPOSITION TECHNIQUES
By Dr Tony Pious
Introduction • In 1931 Broadbent in USA and Hofrath in Germany
simultaneously presented a standardised cephalometric technique using a high powered X-ray source and a head holder called a cephalostat.• Orthodontic diagnosis by enabling the study of skeletal, dental
and soft tissue structures of the craniofacial region• Treatment planning.• Evaluation of treatment results by quantifying the changes
brought about by treatment• Predicting growth related changes
What is cephalometric superimposition ?• A cephalometric superimposition is an analysis
of lateral cephalograms of the same patient taken at different times.• Uses:• Evaluate a patients growth pattern at different ages• To evaluate changes in basal and dentoalveolar
relationships after treatment• To quantify growth and treatment changes in
dentoalveolar and basal relationships.
Method of superimposing radiographs
Superimposing on a stable plane or structure
Registration on a stable landmark
Validity and reproducibility• Validity: it is the extent to which the value obtained
represents the object of interest.• Planes and landmarks should be anatomically valid and should
agree with the anatomic structures they represent• Reproducibility: it is the closeness of successive
measurements of the same object.
Methods of assessing Dentofacial changes• Study of changes in dentofacial dimensions using
cephalometric superimposition have shown varying results• Brodie and broadbent have shown that dentofacial
growth patterns are established at a very early age and thereafter are subject to proportional changes.• Downs and Rickkets pointed out that several angles and
dimensions change with age but in an orderly and progressive manner• Hellman suggested that the infant face is transformed
into that of an adult face by increase in size by changes in proportion and by adjustment in position.
Methods of assessing Dentofacial changes
• Areas studied to assess changes due to growth or treatment or both include:• Changes in the overall face• Changes in the maxilla and it’s dentition• Changes in the mandible and its dentition• Amount and direction of condylar growth• Mandibular rotation
• Color coding of consecutive cephalograms suggested by ABO:
• Pretreatment – black• Progress – blue• End of treatment – red• Retention - green
Evaluation of overall changes in the face• Superimposition methods:• Broadbent triangle• Sella nasion line• Basion horizontal• Basion nasion plane• De costers anterior cranial base reference line• Viazis cranial base triangle• Frankl’s occipital reference base
• Objectives • Overall assessment of growth and treatment changes of
the facial structures • Amount of change in direction of displacement and
growth of maxilla and mandible.• Changes in soft tissue• Changes in maxillo mandibular relationship• Overall displacement of teeth.
• Broadbent triangle• Among the first structures used for
superimposition• Broadbent based this method on
observations of dried skulls and a comparative study of cranial base planes (Bolton-nasion, porion-nasion, sella-nasion) in persons 3 to 18 years of age.
• Bolton point maybe obscured by Mastoid
Superimposition at registration point R with Bolton-nasion planes parallel
Evaluation of overall changes in the face
• Sella nasion plane:
• SN is a frequently used reference line that has been reported to be relatively stable.
• Both points S and N are located in the midsagittal plane and are displaced a minimal degree by movement of the head.
• Steiner used SN with registration point at sella to evaluate sagittal changes in mandibular positions and at nasion to evaluate the position of the maxilla through changes in the angle SNA.
•
• Sella nasion plane:• Unlike Steiner, Björk used sella as
registration point to assess changes in position of both jaws.
• Later, Björk reported that errors of biologic origins of S and N may weaken the SN reference for estimation of facial changes. He stated that an upward or downward displacement of nasion may occur with growth at the frontonasal suture. Likewise, a posterior displacement of sella may be induced by the remodeling of dorsum sellae connected with the increased size of the pituitary gland.
• Basion horizontal• Coben presented the Basion
horizontal concept.• Basion is used as the
registration point.• The SN planes are made
parallel by the help of the Basion horizontal line and it’s constant relationship with SN.• A coordinate grid system is used
to superimpose the radiographs.
• Basion - Nasion plane:• Suggested by Ricketts• He considered Ba-N plane as a line of
separation of the face from the skull and hence a basic cranial axis for growth and structural reference.
• Based on studies of laminograph sections, Ricketts suggested that the cranial base angle, while constant on average, exhibits a change of 5° in either direction over a 3-year period
• Basion - Nasion plane:• one may doubt the reliability of this
axis because growth at nasion is subjected to individual variations. Moreover, the position of basion is influenced by remodeling processes on the clivus surface and on the anterior border of the foramen magnum, and by changes in the position of the pars basilaris ossis occipitalis associated with growth in the spheno-occipital synchondrosis.
• De Coster line• He advocated tracing
the inner contour of the frontal bone through the cerebral aspect of the ethmoid , the planum sphenoidale and the anterior aspect of the sella turcica.
• Viazis cranial base triangle• The anterior wall of sella
turcica and the cribriform plate (laminar cribrosa) remain unchanged after age 5.
• Superimposition on the anterior wall of sella turcica and the stable TC (cranial base) line, with registration on T point, provides a practical and reliable formation in both the anteroposterior and vertical planes.
• Viazis cranial base triangle• Superimposition on the anterior
wall of sella turcica and the stable TC (cranial base) line, with registration on T point, provides a practical and reliable formation in both the anteroposterior and vertical planes.
• First priority should be given to registering on T point, followed by superimposing on the inner structure of the triangle, and finally superimposing on the TC line. This "best-fit" approach meets the realistic expectations of any superimposition technique.
Evaluation of overall changes in the face – Viazis Triangle
Frankl’s occipital reference base• Among the basal structures of the neurocranium, the
occipital bone around the foramen magnum is the first to ossify (between the third and fourth year of life).• Phylogenetically and ontogenetically as the midbrain is
highly conserved minimal postnatal growth of this structure and surrounding tissues is seen.• It permits the study of craniofacial growth in relation to an
individual bone and its immediate structures
Frankl’s occipital reference base
• Reference plane – based on natural head posture and parallel to the ground
Frankl’s occipital reference base
Evaluation of overall changes in the face• Reliability of the various cranial base reference planes used.• For meaningful interpretations of superimpositions they have to be
registered on stable reference landmarks.• Cranial base superimpositions are subject to error due to the
continued growth of the sphenoccipital synchondrosis (Knott).• Bone remodelling at sella and Nasion are also responsible for
further errors.• Nasion position can change in a vertical direction (Nelson and
Knott).• Melsen’s study’s on human autopsy material has shown that the
position of sella may change in a downward or a downward and backward direction. She also showed that the position of Basion changed due to remodelling of the clivus.
• The Bolton point could be difficult to locate in children due to the shadow of the mastoid process
Growth changes in position of Nasion and sella
Reference structures for overall face superimpositions.• Nelson’s cephalometric study and Melsen’s
histological study on human autopsy materials have reveled a few stable structures in the anterior cranial base for use in superimposition.• Anterior wall of sella turcica• The contour of the cribriform plate of the ethmoid • Trabecular system of the ethmoid air cells• The median border of the orbital roof• Planum sphenoidale
Method of superimposition of radiographs to assess overall changes
Pretreatment tracing Progress tracing
Method of superimposition of radiographs to assess overall changes
Superimposition using ‘Best fit method’
Evaluation of changes in maxilla and its dentition in relation to the maxilla
• Superimposition along the palatal plane registered at ANS• Broadbent, Moore,
Salzman, Ricketts, McNamara• Compromised by
remodelling of the palatal shelves and ANS- Bjork and Skeiler
Evaluation of changes in maxilla and its dentition in relation to the maxilla
• Superimposition on the nasal floors with films registered at the anterior surface of the maxilla• Downs and Brodie.
Evaluation of changes in maxilla and its dentition in relation to the maxilla
• Superimposition along the palatal plane registered at the pterygomaxillary fissure• Moore
Evaluation of changes in maxilla and its dentition in relation to the maxilla
• Superimposition on the outline of the infratemporal fossa and the posterior margin of the hard palate.• Reidel
Evaluation of changes in maxilla and its dentition in relation to the maxilla• superimpostion
registered at the common Ptm cordinate maintaining the basion horizontal relationship.• Coben
Evaluation of changes in maxilla and its dentition in relation to the maxilla
• superimposition on the best fit of the internal palatal structures.• McNamara
Evaluation of changes in maxilla and its dentition in relation to the maxilla
• superimposition on metallic implants• Bjork and skeiller
Evaluation of changes in maxilla and its dentition in relation to the maxilla
• the structural superimposition on the anterior surface of the zygomatic process of the maxilla• Bjork and Skeiler
Evaluation of changes in maxilla and its dentition in relation to the maxilla• Neilsen on a study of various maxillary
superimposition techniques concluded that:• The best fit method significantly under estimates the
vertical displacement of skeletal and dental landmarks• With the implant method and the structural method
ANS showed twice as much vertical displacement as PNS• Structural method and implant methd did not show
any significant differences• The structural method is a valid method of assessing
maxillary growth and treatment changes
Structural method of superimposing maxillary structures
Pretreatment tracing
Structural method of superimposing maxillary structures
superimposition
Mandibular superimposition
• Stable areas for superimposition:
• Anterior contour of the chin• The inner contour of the
cortical plates at the inferior border of the symphysis
• Contours of the mandibular canal
• Lower contour of the mineralized molar tooth germ
Mandibular superimposition technique
Mandibular superimposition technique
Methods to assess growth vs treatment changes• Though the techniques described till now will assess the
amount of growth changes in a given duration of time or the overall changes of treatment and growth during a given treatment period they do not however differentiate between changes produced due to growth and changes produced due to treatment.• The following cephalometric analyses help us to assess
treatment changes against the background of natural growth of the individual
Methods to assess growth vs treatment changes
• Rickett’s eleven factor summary analysis• Four position analysis
• The analysis is based on Rickkets short term growth forecasting, data which was obtained on patients – both male and female of different ages and growth patterns undergoing orthodontic treatment.
Rickett’s Eleven factor summary analysis• Eleven factors of the basic facial and skeletal
structures are recorded from the cephalometric tracing to describe the chin, maxilla, teeth and soft tissue profile.• Five areas of superimposition within which are a
total of seven areas of evaluation are used to evaluate in amount and direction, change in normal growth and change due to treatment.
Rickett’s Eleven factor summary analysis
CHIN IN SPACE MEAN CHANGEFACIAL AXIS 90+/-3 No changeFACIAL DEPTH 87+/-3 +10 for 3 yrsMAND PLANE 26+/-4 -1o for 3 yrsFACIAL TAPER 68+/-3 No changeCONVEXITYCON AT A 2+/-2 -1mm / 3 yrsTEETHL1 TO APO 1+/-2 No changeL1 INCL 22+/-4 No changeU6 TO PTV Age+3+2 1mm / yearPROFILEL LIP TO E LINE -2+/-2 Less with age
Rickett’s Eleven factor summary analysis
SUPERIMPOSITION AREA 1 – EVALUATION AREA 1 • FACIAL AXIS OPENS 1o FOR
DOLICOFACIAL PATTERN•FACIAL AXIS CLOSES 1O FOR BRACHYFACIAL PATTERNS
•FACIAL AXIS OPENS 1O FOR 5mm CONVEXITY REDUCTION•FACIAL AXIS OPENS 1O FOR 3mm MOLAR CORRECTION
•FACIAL AXIS OPENS 1O OR 4mm OVERBITE CORRECTION•FACIAL AXIS OPENS 1 TO 1.5O FOR CROSS BITE CORRECTION AND RECOVERS ONE HALFBASION-NASION PLANE at CC
Rickett’s Eleven factor summary analysis
SUPERIMPOSITION AREA 2 – EVALUATION AREA 2
• THE BASION-NASION-POINT A ANGLE OF 66O DOES NOT CHANGE WITH GROWTH•SO ANY CHANGES PRODUCED MUST BE DUE TO TREATMENT
BASION NASION PLANE AT NASION
Rickett’s Eleven factor summary analysis
SUPERIMPOSITION AREA 3 – EVALUATION AREAS 3 AND 4 • LOWER DENTURE REMAINS
CONSTANT WITH THE A Pog LINE•Without treatment, the lower molar will erupt directly upward to the new occlusal plane. •The LOWER INCISAL angle is 22° at +1mm to the APo plane and + 1 mm to occlusal plane, but the angle increases 2° with each mm of forward compromise.•OCCLUSAL PLANE TO CORPUS AXIS DOES NOT CHANGE•LOWER MOLAR ERUPTS IN A DIRECTION PERPENDICULAR TO THE FH PLANE•OCCLUSAL PLANE ERUPTS 0.8mm UPWARDS FROM THE CORPUS AXIS.
CORPUS AXIS AT PM
Rickett’s Eleven factor summary analysis
SUPERIMPOSITION AREA 4 – EVALUATION AREAS 5 AND 6
• THE UPPER MOLAR AND INCISOR FOLLOW THEIR POLAR AXIS WITH GROWTH•CHANGES IN POSITION OF THE MOLAR OR INCISOR IS DUETO TREATMENT.•UPPER DENTAL ARCH ERUPTS DOWNWARD AND FORWARD 0.2 TO 0.3mm PER YEAR
PALATE AT ANS
Rickett’s Eleven factor summary analysis
SUPERIMPOSITION AREA 5 – EVALUATION AREA 7•
ESTHETIC PLANE AT INTERSECTION OF OCCLUSAL PLANES
Rickett’s four position analysis• Takes into consideration two superimposition areas to
evaluate orthopedic change and two superimposition areas to evaluate orthodontic change against growth.
Rickett’s four position analysis
• Position 1• Mandible or chin
Rickett’s four position analysis
• Position 2• maxilla
Rickett’s four position analysis
• Position 3• Upper teeth
Rickett’s four position analysis
• Position 4• Lower teeth
Superimposition methods to assess dentoalveolar and skeletal changes in Class II treatment.
• Johnstons Pitchfork analysis
Pitchfork analysis
• Johnston in 1985• Used to describe the
treatment effects of different treatment strategies used to correct Class II patients• Data recorded in the
form of a pitch fork
Pitchfork analysis
• Superimposition on D• Measurement of
molar and incisal changes
Pitchfork analysis
• Measurement of amount of molar correction
Pitchfork analysis
• Measurement of overjet correction
• For overall craniofacial growth/displacement and treatment effect, superimpose on sella-nasion, registering at sella.
• For maxillary complex growth and treatment effect, superimpose at the best fit on the palatal surface of the maxilla parallel to ANS-PNS.
• For mandibular growth and treatment effect, superimpose on the inferior cortical contour of the symphusis and on the inferior alveolar canal. If the inferior alveolar canal is not clearly visible, then align on the lower border of the mandible.
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