Superimposition techniques

transcript

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

• Superimposition on the nasal floors with films registered at the anterior surface of the maxilla• Downs and Brodie.

• Superimposition along the palatal plane registered at the pterygomaxillary fissure• Moore

• 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

• superimposition on the best fit of the internal palatal structures.• McNamara

• superimposition on metallic implants• Bjork and skeiller

• 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

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

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

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

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

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

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

• Position 2• maxilla

• Position 3• Upper teeth

• 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.

Superimposition techniques

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