Cephalometric Tracing

Alan A. Curtis

Amy Gimlen

December 9, 2002

Cephalometric tracing

[1]

            The beginnings of cephalometrics did not begin in orthodontics, but in studying human growth and development of craniofacial anatomy.  As the technology advanced Hofrath in Germany and Broadbent[2] in the United States developed and presented a standardized method of taking cephalometric radiographs so they could be used to analyze craniofacial growth changes that lead to skeletal discrepancies therefore to study the cause of malocclusions. 

Orthodontists used this technology and further developed this technology to study the morphology of the major structures of the head, the cranium, the cranial base, the skeletal maxilla, the skeletal mandible, the maxillary dentition and alveolar process, and the mandibular dentition and process in a vertical and sagittal dimension.  Orthodontists further used this technology to evaluate the structures’ proportions, their relationship each other, and identify possible causes for malocclusions.  Analysis of growth and alteration of growth could also be evaluated by taking serial radiographs and comparing them to each other, e.g. before and after treatment.  Treatment planning in orthodontics took a huge leap in advancement now a dental malocclusion could be differentiated from a skeletal malocclusion. 

 

[3]

[4]           Cephalometric analysis is not usually carried out on the lateral cephalograph itself, but is traced out by choosing specific points that when connected aid in evaluating the proportions of the craniofacial growth as compared to “ideal” standards usually based on the ethnicity and age of the patient.  Three components of analysis are analysis of the skeletal features of the patient, the dental features and the profile of the patient.  Therefore the “goal of cephalometric analysis: to estimate the relationship, vertically and horizontally, of the jaws to the cranial base and to each other, and the relationships of the teeth to their supporting bone.”[5]

 

Measurement analysis

            Measurement analysis is the marking of specific anatomical landmarks whether it be soft or hard tissue and relating them linearly or angular to a set of norms.  This analysis is good for determining the patients' facial relationships as compared to a set of norms determined by growth studies.  Below are examples of different methods of measurement analysis. (Landmarks are described at the end of this paper)

 

Downs Analysis

            Downs Analysis was developed and based on a reference group of twenty-five white individuals that had ideal occlusions that had no previous orthodontic treatment.  The skeletal and facial proportions of these adolescents were the strict ideal for occlusion and facial proportion.  In the Downs analysis specific linear and angular measurements are chosen to be the basis for specific comparisons between an ideal profile, skeletal relationship and occlusion and a patient.  See the following outline for specifics about Downs’ analysis :[6]

 

I.                   Skeletal

A.     Facial Angle-This measures the magnitude of the angle between the Po-Na and the FH

B.     Angle of Convexity-This measures the angle between Pog-A and Na-A

C.     A-B Plane- This measures the angle between Pog-Na and A-B

D.     Mandibular Palne Angle MP- a line drawn fron M to the tangent to the lower border of the mandible

E.      Y-(Growth) Axis- This measures the angle between FH and S-Gn

II.                Dental

A.     Cant of Occlusal Plane- This measures the angle between Occlusal plane and FH

B.   Interincisal Angle- The angle formed by the intersection of lines drawn through the long axis of the Maxillary and Mandibular incisors

C.  Incisor- Occlusal Plane Angle- The angle formed by the intersection of the occlusal plane through the long axis of the mandibular incisors.

D.     Incisor-Mandibular Plane Angle- This measurement is formed by the mandibular plane and a line drawn down the long axis od the mandibular incisor

E.      Protrusion of the Maxillary incisors-This is measured as the distance from the incisal edge of the maxillary central incisor to a line drawn between the Pog and pt. A

[7]

Steiner Analysis[8]

            Dr. Steiner was an orthodontist in the 1950’s and the Steiner analysis it believed to be based upon a Hollywood star, which had ideal occlusion, skeletal relationship and profile.  Whether or not this is true Dr. Steiner can be credited with developing an analysis that provided an interrelationship of measurements from the lateral radiograph into a pattern and it provided a guide for treatment planning based on the cephlometric measurements. 

            The skeletal analysis is based on a series of angles that connect various defined hard and soft tissue landmarks.  The first is the SNA angle, this angle evaluates the anterior-posterior position of the maxilla to the anterior cranial base.  The average for this measurement was determined to be 82 +/- 2 degrees.  Therefore if the measurement is smaller than this value then the patient’s maxilla is skeletally either class III or in specific cleft palate patients.  If the measurement is greater than this value the patient has a protruded maxilla and skeletally class II.  The next angle is the SNB angle, which gives the anterior-posterior position of the mandible.  The average is 78 +/- 2 degrees, if the angle is smaller it indicates a retrognathic mandible and a larger angle indicates a prognathic mandible.  The difference between the SNA and SNB is the ANB angle.  The ANB angle indicated the discrepancy between the maxilla and mandible, in which the average is 2 degrees.  An angle greater than 2 degrees is indicative of a class II skeletal relationship, where as a smaller than 2 degree angle indicates a class III skeletal relationship.  This is a relative relationship of ANB is influenced by the anterior-posterior position in the difference between the jaw positions, the vertical position of the face, which can change the ANB angle, and the position of nasion, which can change the ANB angle.  Therefore using this angle as a part of treatment planning may only take in to account the magnitude of the discrepancy between the jaws not the absolute discrepancy.  If treatment is based on obtaining the ideal ANB angle 2 degrees it may not necessarily obtain the ideal position of either the maxilla or mandible, but Steiner believed the main interest in treatment should be alleviating the magnitude of the discrepancy.

            Dental analysis is an evaluation of tooth position.  The linear relationship of the upper central incisor edge to the NA line is established, this indicates the anterior-posterior relationship.  The average measurement is 4mm, but does not indicate the angulation of the incisor. The linear relationship lower incisor edge of the central to the NB line has an average of 4mm.  A measurement greater than 4mm may show a convex facial profile, common in class I bimaxillary protrusion or in a class I division 1 relationship.  Conversely if the measurement is less than 4mm the patient may show a concave facial profile, as in class II division II or class III relationship.  The linear relationship determines the prominence of the incisor is relative to its supporting bone.  The angular relationship is also determined for the upper incisor to NA, with an average of 22 degrees.  An angle grater than 22 degrees maybe seen a patient that is class II division 1 or in a class III relationship with dental compensation.  A smaller than 22 degree angle is indicative of a patient that is class II division 2.  The angular relationship of the lower central incisor to NB is determined, with an average of 25 degrees.  In a case with a larger angle the patient may present as a class II division 1 and in a smaller than 25 degree angle the patient may either be class II division 2 or class III.  The angular relationship determined the proclination/ retroclination of the central incisors.  The linear relationship of pogonion to NB this indicates the position of the bony chin, an average of 4mm.  If the bony chin is insufficient it may lead to a convex profile and retraction of the lower incisors maybe needed to improve esthetics, as seen in class II division1.  If the bony chin is sufficient then there is a greater allowance for protrusion of the lower incisors and an esthetic profile.  The inclination to the mandibular plane to SN is then measured to indicate the vertical measurement of the face, which is averaged, based on ethnic groupings. 

            Steiner in his analysis took into account that it may not be possible to reach ideal proportions and relationships in all cases, but there are ways to maximize the esthetics.  Steiner devised ways to alter incisor positions to achieve normal occlusions even when the ideal ANB angle could not be achieved, ie how much the teeth needed to be moved to compensate for a skeletal malocclusion.  For large skeletal discrepancies the Steiner method would not be effective for treatment, dental camouflaging may not be able to make up for the skeletal discrepancy. 

 

Sassouni Analysis

            Sassouni analysis focused on the vertical and the horizontal relationship of the craniofacial structures and how they related to each other.  Sassouni recognized there was an interrelationship between the horizontal anatomic planes, the mandibular plane, the occlusal plane, the palatal plane, the Frankfort plane, and the inclination anterior cranial base, that indicates a vertical proportionality of the face.  In a face that is well proportioned these planes converge towards a single point.  In a skeletal open bite pattern the lines intersect close to the face and diverge quickly as they pass anteriorly.  In a skeletal deep bite pattern the planes are nearly parallel and do not converge until far behind the face and diverge slowly anteriorly.  A divergence of one of the planes can also indicate a specific skeletal discrepancy.

            Sassouni also took into account the anterior-posterior position of the face and the dentition.  He related the arcs drawn by the area of intersection of the planes to specific points.  For example, the anterior nasal spine, the maxillary central incisor, and the bony chin should be on the same arc in a face that is well proportioned.  This analysis is not as widely used, as Sassouni’s vertical analysis due to the fact with increasing anterior-posterior discrepancies the analysis becomes more arbitrary and less reliable.[9]

 

Harvold Analysis

            Harvold analysis concentrates on the magnitude of jaw discrepancies.  Harvold calculated an average length of the maxilla and mandible based upon the Burlington growth study.  The maxilla is measured from the posterior border of the mandibular condyle to the anterior nasal spine, this is the maxilla’s “unit length.”  The mandibular “unit length” is describes as the posterior border of the mandibular condyle to the anterior point of the chin.  The difference between the unit length of the maxilla and the unit length of the mandible indicates the discrepancy between the jaws.  This does not take into account the vertical distance of the jaws, which if decreased places the mandible more anteriorly.

 

 

 

 

Wits Analysis

            Wits analysis also concentrates on the skeletal discrepancy between the jaws as does Harvold analysis, but also tries to overcome the limitations of the ANB measurement as determining the magnitude of the jaw discrepancy.  The linear difference is taken between points A, B and the occlusal plane.  The occlusal plane is determined by the maximum intercuspation of the posterior teeth, not the anterior teeth.  When the A and B lines are drawn to intersect the occlusal plane line they should be within a millimeter of each other.  If the A line intersects far anterior to the B line this indicates a class II relationship.  If the opposite occurs where B is anterior to A this indicates a class III relationship. 

            Wits analysis takes into account the horizontal and vertical relationship of the jaws, but is still flawed due to the fact that it is influenced by the dentition and therefore skews the analysis from indicating the true skeletal discrepancies between the jaws.

 

Ricketts Analysis

Similar to the above-mentioned analyses, Ricketts tries to determine the proper spatial relationship of the jaws for both esthetics and function.  To assess this relationship, Ricketts looks at the following measurements:  Facial depth, Maxillary depth, Convexity, Mandibular plane to Frankfort horizontal, Facial Axis, Maxillary incisor to A-Pog degrees and mm, Mandibular incisor to A-Pog, degrees and mm.  These measurements are compared to idealized norms based upon studies of a significant sample size.  Using these ‘norms’, a problem list is created in order to address the orthodontic needs of the patient.[10]

 

 

 

 

 

 

McNamara Analysis

            The McNamara analysis incorporates many of the above analysis with his own measurements to indicate tooth and jaw positions more specifically.  The nasion perpendicular indicates the anterior posterior position of the maxilla it projects a line vertically down from the nasion to the Frankfort plane, the maxilla should be on or slightly anterior to this line.  The maxillary and mandibular length is compared as in Harvold analysis.  The mandible position is determined by the ANS- menton, in the lower face height.  The upper incisor is related to the maxilla similar to Steiner analysis relating A to the Frankfort plane.  The lower incisor is related to the mandible using A to Pogonion, as in Rickets. 

            McNamara relates the jaws in an anterior-posterior position to the vertical line and it also the average measurements that are used are closely compliant with the Bolton templates.  As with all of the analyses, McNamara is not a completely accurate analysis of craniofacial relationships.  All parts of the face are interrelated and one may compensate for another this complicates the process of treatment planning and determining the exact dental and skeletal relationships independently from one another. 

 

Enlow's counterpart analysis

            Endlow's analysis focused on the interrelationships of the face and determined whether they lead to a balanced or unbalanced facial pattern, taking into account both the dimensions of the face as well as the alignment of the face.  For example if the mandible is long anterior-posteriorly and the maxilla is also long than malocclusion may not occur, but if the mandible is long and the maxilla is not a malocclusion will occur.

 

Template Analysis

This analysis provides a graphic analysis of data rather than measurements values to determine the craniofacial relationships.  Analysis that is depicted graphically as in template analysis allows for patterns of relationships to be observed without the need for specific measurements.  This method of analysis can give insight into the dental compensation that may occur in some of these cases, which is more difficult to determine from measurements alone.  Template analysis gives an idea of the overall picture by comparing the skeletal, dental and profile of the template versus the patient. 

 For reliable comparisons between the template and the patient craniofacial relationship specific parameters must be set up.  "1. the measurements should be useful clinically in differentiating patience with skeletal and dental characteristics of malocclusion; 2. the measurements should not be affected by the size of the patient.  This is meant an emphasis on angular rather than on linear measurements; and 3. the measurements[11] should be unaffected, or at least minimally affected, by the age of the patient.  Otherwise, a different table of standards for each age would be necessary to overcome the effects of growth."  All of these criteria are very difficult to fill, this lead to an increase in linear measurement that were used and well as a trend towards using different templates depending on age.

There are two main template analyses, the schematic and the anatomically complete.  The schematic template is on a single template that shows changing positions of anatomic landmarks with age.  The anatomic complete has individual templates for age.  The anatomic landmarks can then be visualized directly between the patient and the norm for their age.  The most commonly used template is the Bolton, which is an anatomic template. 

In template analysis the first step is to pick the correct template for comparison of the patient to his/her norm, for this the patient's age should not be the main determinant.  All patients are different therefore a more reliable criteria for comparison is the patients developmental age and his/her physical size.  In picking a template the size of the anterior cranial base is usually the most accurate indicator, while also approximating the patients sella to nasion distance. 

A template is used in a very methodical way by placing a tracing over the template and superimposing different anatomic landmarks in order to compare the patient to their norm.  The first superimposition is of the cranial base, this indicates the relationship between the maxilla, the mandible and the cranium.  Superimposition of nasion is indicated when the cranial base length is not equal rather than sella.  The horizontal and vertical dimensions of the maxilla and the mandible can be compared at this point.  This first superimposition is useful in determining the skeletal relationship between the different functional units and how they may have compensated, skeletally, for eachother.

The maximum maxillary contour is then superimposed to determine the maxillary dentition's relationship to the maxilla.  It is very easy to see how the teeth relate to the maxilla if they are retroclined from the normal position due to a dental malocclusion or a skeletal cause.  The last superimposition occurs over the mandibular symphysis, along the lower border.  This allows the mandibular dentition to be related to the mandible. 

Template analysis allows for the big picture to be seen in the relationship of the patient skeletal, dental and profile as compared to the norm for the patients' developmental age.  It is a compatible method with computer analysis and should be a part of the treatment planning of a patient.

Cephalometric analysis has revolutionized treatment planning for orthodontic cases. It analyses the skeletal, dental and profile of the patient, proper analysis can lead to an understanding of the causes of malocclusions.  Comprehensive cephalometric analysis should take into account not only measurements but also the pattern of interrelationships of the functional units of the craniofacial region as well as the soft tissue profile.

 

Computerized Cephalometric Analysis

            With the advent of modern imaging technology, cephalometric analysis has become more precise and easy.  This technology automatically measures and analyzes lateral cephalometric images once the landmarks have been identified.  Tracings can be made using any of the above analyses using drop down menus.  These programs also allow the orthodontist to make tracings that reflect post surgical goals.  This can be very useful in case presentation.  Tracings can be superposed over clinical photographs to analyze the soft tissue component of the post surgical treatment objective.  Two of the major software developers include Dolphin and Quickceph.  These are only two of the many imaging software packages available to orthodontists.  (For more information see http://www.dolphinimaging.com/new_site/index.html and http://www.quickceph.com/ )

 

 

Cephalometric landmarks

Bo- Bolton point: the highest point in the upward curvature of the retrocondylar fossa of the occipital bone

Ba- Basion: the lowest point on the anterior margin of the foramen magnum, at the base of the clivus

Ar-Articulare: the point of intersection between the shadow of the zygomatic arch and the posterior border of the mandibular ramus

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)

S- Sella: the midpoint of the cavity of sella turcica

Ptm- Pterygomaxillary fissure: the point at the base of the fissure where the anterior and posterior walls meet

Or-Orbitale: the lowest point on the inferior margin of the orbit

ANS-anterior nasal spine: the tip of the anterior nasal spine

Point A: the innermost point on the contour of the premaxilla between the anterior nasal spine and the incisor tooth

Point B: the innermost point on the contour of the mandible between the incisor tooth and the bony chin

Pog-Pogonion: the most anterior point on the contour of the chin

Me- Menton: the most inferior point on the mandibular symphysis at the bottom of the chin

Na-Nasion: the anterior point of the intersection between the nasal and frontal bones

Go- Gogion: the midpoint of the contour connecting the ramus to the body of the mandible

Gn-Gnathion: the center of the inferior point on the mandibular symphysis

PNS-Posterior nasal spine: the tip of the posterior nasal spine of the palatine bone, at the junction of the hard and soft palate

FH-Frankfort Plane: the horizontal reference plane in the heads natural position extending from the porion to orbitale,