Ceph history, evolution & landmarks/ dental implant courses by Indian dental academy

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CEPHALOMETRICS : HISTORY, EVOLUTION AND LANDMARKS S eeniya. C.K

INTRODUCTION Ever since God created man in His image, man has been trying to change man into his image. Attempts to change facial appearance are recounted throughout recorded history. The question of what is a normal face, as that of what constitutes beauty, will probably never be answered in a free society.

Orthodontists, in their attempts to change facio-oro-dental deviations from accepted norms, have adopted cephalometric measurement, a method long employed in physical anthropology. With the introduction of roentgenography, it was inevitable that this procedure should be employed as a medium for the purpose of roentgenographic cephalometrics.

Cephalometric radiography was introduced in to orthodontics during the 1930s.

Cephalometry had its beginnings in craniometry. Craniometry is defined in the Edinburgh encyclopedia of 1813 as “the art of measuring skulls of animals so as to discover their specific differences�. For many years anatomists and anthropologists were confined to measuring craniofacial dimensions using the skull of long dead individuals.

Although precise measurements were possible Craniometry has the disadvantage for growth studies.

Cephalometry is concerned with measuring the head inclusive of soft tissues, be it living or dead. However this procedure had its limitations owing to the inaccuracies that resulted from having to measure skulls through varying thickness of soft tissues.

With the discovery of X rays by Roentgen in 1895, radiographic Cephalometry came in to being. It was defined as the measurement of head from bony and soft tissue land marks on the radiographic image (Krogman & Sassouni 1957). This approach combines the advantages of Craniometry and anthropometry. The disadvantage is that it produces two dimensional image of a three dimensional structure.

HISTORY PRIOR TO THE ADVENT OF RADIGRAPHY CLASSIFYING PHYSIQUES

History prior to the advent of radiography should begin with the mention of the attempts of the scientists to classify the human physiques. In 500 BC, the Greek physician & Father of medicine, Hippocrates, designated two physical types – habitus phithicus with a long thin body subject to tuberculosis, & the habitus applecticus – a short thick individual susceptible to vascular diseases & apoplexy. The search was continued by Aristotle (400 BC), Galen (200AD), & Rostan (1828), who was the first to include muscle mass as a component of physique. Viola’s (1909) morphological index recognizes three morphological types. Kretschmer (1921) adhered to the three Greek terms: the pyknic (compact), asthenic (without strength), & athletic. Kretshmer also included dysplastic physique which was taken up by Sheldon again in 1940.

The long historic thread extended into the twentieth century when Sheldon introduced his method of somatotyping, based on three components of physiques, each rated on a seven pt. scale& expressed as a three digit no. called as somatotype. It also included a rating of dysplasia in the five regions of the body. “Dysplasia is literally bad shape or form. In somatotyping it refers to disharmony or uneven distribution of a component or components in diff. parts of the body,” acc. to Carter & Heath.

Morever their definition of a somatotype quantifies relative fatness or endomorphy, relative musculoskeletal robustness, or mesomorphy,& relative linearity, or ectomorphy. The somatotype then stands as a “quantitative overall appraisal of bodyshape & composition, an anthropological identification tag & a useful descriptionof human physique.” Heath & Carter also rigorously studied Sheldon’s instructions for somatotyping & introduced modifications to method, designed to avoid some of the limitation of Sheldon’s system.

Sheldon’s temperamental components, viscerotonia, somatotonia, & cerebrotonia, convey behavioral traits commonly associated with physique. With a 7 pt. scale for each somatotype component, there is a wide distribution in the dense midrange around the 4-44 type ;a close relation between somatotype & temperament becomes tenuous.

Nonetheless common knowledge suffices to recognize dominant behavioral trait in many instances, & that information can be revealing about the people in general. It may also give some clues relating to the orthodontic treatment by providing an insight into the character of the patients- their expectations concerning the treatment’s contribution to

their wellbeing, & even their understanding of & willingness to accept the discipline of cooperation needed for successful conclusion of therapy.

MEASUREMENTS AND PROPORTIONS Early history – The Canons Portrayal of human form demands not only artistic talent & technical ability but a disciplined & consistent style. To ensure these stipulations when images of royalty & deity were commissioned & executed, the ancient Egyptians developed an intricate quantitative system that defined the proportions of the human body. It became known as the Canon. The theory of proportions acc. to Panofsky, is a System of establishing the mathematical relations between the various members of the living creature, in particular of the human being, in so far as these beings are thought of as a subjects for artistic representation. The mathematical relation can be expressed by the division of a whole as well as by the multiplication of the unit ; the effort to determine them could be guided by the desire for beauty as well as interest in the norms, or finally by the need for establishing a convention ; and above all, the proportions can be investigated with reference to the object of representations well as with reference to the representation of the object.

The proportions of the human body were determined with an ell measuring ruler, established in 3000BC. Its length corresponded to the distance from the elbow to the outstretched thumb.

Initially the canons were enclosed in a grid system of equalized squares with 18 horizontal lines line 18 drawn through hairline. Later it was included in a grid system of 22 horizontal lines, line 21 drawn through the upper eyelid.

After the outline of the human figure was drafted on papyrus leaves the iconographic norms or canon, served to insert the figure into a network of equal squares.

The image could be transferred to any required size by first drawing a coordinate system to proper size ; into this system the image can then be drawn readily & accurately for

display in a tomb or on a wall. This procedure is still universally used to enlarge or reduce any kind of illustration (MISE AU CARREAU).

The classical art of Greeks rejected the rigid Egyptian system for creating human images. The Greeks needed the freedom to account for the shifting dimension of organic movement, and the foreshortening of the upper part of a stature relative to the lower part.

Indian iconometry studied extensively by the Ruelius, was transmitted through Sanskrit literature & extensively reviewed in Indian texts of architecture. The proportional canons of that system were already detailed in older sources & did not materially change with time. Face height was used as the module of both the sariputra & alekhyalakshana proportional system, which closely reflected the natural relation of the parts of the body to each other. The sariputra system , dated 1200 AD is known for the sculptures honoring the God Buddha.

In the Byzantine empire, the rectangular grid of the canon was replaced by a scheme of three concentric circles with nose length as the radius of drawing the two successive circles.

RENAISSANCE TO THE TWENTIETH CENTURY Fifteenth century saw the advent of specific measurements being made to compare the features of different skulls and head. Leonardo da vinci (1452-1519 AD) was probably one of the earliest people of note to apply the theory of head measurement to good effect in practice.

He used a variety of lines related to specific structures in the head to assist in his study of the human form (Fig-1). His drawings included a study of facial proportions in natural head position. According to the notes the profile was divided in to seven parts by eight horizontal lines. Sub division is made with vertical lines. In his study of horse & horse men he used a scheme of facial measurement with in a grid system with five horizontal and six vertical lines and the subject in natural head position (Fig-2). The joining of the lower lip and chin and the tip of the jaw and the upper tip of the ear with the temple forms a perfect square; and each face is half a head.

Albrecht Durer (1471-1528 AC) was a brilliant, unusually productive and exuberant artist of great virtuosity. He published a treatise in 1528 on cranial measurements which comprised “Vier Bucher von menschlischer Proportion” dealing with the proper proportion of human form in the first two books, the proportions according to mathematical rules in third book, the human figure in motion in the fourth book. Durer’s four books mark a climax which the theory of proportions had never reached before or was to reach ever after.

Using strictly geometrical methods he provided a proportionate analysis of the leptoprosopic (long ) face and euryprosopic (broad) face in coordinate system, where the horizontal and the vertical lines were drawn through the same land marks or facial features (Fig-3). His drawings attest to continuous efforts to define variations in the facial morphology. One of this is significant as the key to cephalometric analysis. In (Fig-4) the difference between the retroclined and the proclined facial profile is shown by a change of angle between the vertical and the horizontal axes of a rectangular coordinate system to characterize the facial configuration of each subject.

The sixteenth century saw the first truly scientific attempt at cranial measurement & the introduction by Spigel (1578-1625AC) of the “lineae cephalometricae”. Spigel’s linear cephalometricae consisted of four lines: the facial, occipital, frontal, & sincipital lines. He described these lines as follows: •

Facial: from the most inferior point of the chin to the most superior point on the forehead.

•

Occipital: from the crown of the head to the atlas.

•

Frontal: from one temple to the other.

•

Sincipital: from the lowest part of the ear, in the region of the mastoid process, to the highest part of the sinciput, sinciput being the anterior part of the head or skull from forehead to the crown.

According to him in a well proportioned skull, these lines should all be equal to one another. In reporting this Aitken-Meiges writes “although these lines are evidently not sufficient for the comparative ethnography, in ascending zoological scale, these lines approximate just in proportion as the head measured approaches the human form. To Spigel a skull was either well proportioned or it was not.

In 1699, a Cambridge physician, Edward Tyson (1650-1708 AD) under took some measurements on the chimpanzee skull & proposed that there was an intermediate animal between man and monkey. He described this animal as a form of ‘pigmy’ but this pigmy was later shown to be another chimpanzee there by negating his findings.

In the eighteenth century most of the workers in the field of craniometry were interested in relating intelligence to certain measurements. They not infrequently found that their native race demonstrated a higher level of intelligence, according to their measures than did others.

The Dutchman Pieter Camper (1722- 1789 AD) was credited with the introduction of facial angle & for famous publication “Dissertation sur les varietes naturelles de la physionomie” which appeared posthumously in 1791. The key to his methodology was to orient crania in space on a horizontal from the middle of the porus acusticus to a point below the nose. Camper’s horizontal became the reference line for the angular measurements used to characterize evolutionary trends in studies of facial morphology and aging.

The facial angle as he described it was formed by the intersection of a facial line and a horizontal plane (Fig-5). The facial line was a line tangential to the most prominent part of the frontal bone and to the slight convexity anterior to the upper teeth. The horizontal plane passes through the lower part of the nasal aperture, backwards along the line of the zygomatic arch, and through the centre of the external auditory meatus.

Camper’s facial angle was readily accepted as a standard measurement in craniology. The terms prognathic and orthognathic introduced by Retzius are tied to Camper’s illustrations of facial form in man and primates. As a result the angle between a horizontal line and the line nasion – prosthion became the time-honored anthropological method to determine the facial type. The term prognathism refers to the prominence of the face, or jaws, relative to the fore head, and a straight facial profile became labeled as orthognathous.

Camper also provided a variety of other differences in facial form by comparing the skull morphology of tailed simian, an orangutan, a young native African, and a Kalmuck. Age changes in human physiognomy are also described by him. Frontal views were also studied by Camper in a young orangutan, Kalmuck, native African, and the face of Apollo Pythius. The most interesting proportional difference was the long face height of native African.

The drawbacks of Camper’s facial angle were: •

It ignores the contribution made by he lower jaw to facial forms.

•

He did not adhere strictly to his location of posterior reference point for the horizontal plane.

•

The direct comparison of skull of different ages was not possible because the locating point might alter is position relevant to other bony structures with advancing age.

Shortly after this Deschamps (1740- 1824 AC) introduced the cephalic triangle made up of facial, occipital, & coronal angles. The facial angle was the lesser angle formed by the intersection of a horizontal line that passed from the external auditory meatus to the base of the nose, which crossed a profile line. This is similar to Camper’s facial angle. Fortunately the use of external auditory meatus as a reference point enabled a rough comparison to be made between different skulls.

The desire to learn how men differ from each other and from animals and why, motivated several other craniologists like Doornick, Spix, Oken and many others to put forward their individual methods of analyzing human and animal skulls.

In the same period as Camper, there was a French man; Daubenton (1716-1799 AC) was very concerned with the relative position of the foramen magnum in man and lower animals. He made use of new angles, including the occipital angle to make measurements. Although his measurements were not very reliable, a similar angle was later used by another craniologist, Pierre Broca.

Daubentons occipital angle is formed by 2 lines (Fig-6): the first line passes along the level of opening of the foramen magnum, from the inial edge of the foramen along the surface of the occipital condyles & anteriorily for short distance. The second line passes from the posterior margin of the foramen magnum to the tip of the nasal spine. Broca’s occipital angle was formed by two different lines giving alternative angles, originating from the posterior and anterior margins of the foramen magnum& passing anteriorly through the junction of frontal and nasal bones (Fig-7). The magnitude of occipital angle decreases as the habitual posture of the animal tends more towards upright.

Daubenton’s interest in the position of the foramen magnum was shared by Sir Charles Bell (1744 -1842 AC). According to him, since the head is movable on a pivot joint, it must always be balanced. Therefore the Negro skull being heavier in front & thus falling forward naturally is thrown backward to poise it and relieve the muscles which support it behind.

This hypothesis was tested by a medical student, William Gibson (1788-1868 AC) in 1809 by placing in front of him Negroid &European skulls resting on their occipital condyles. Contrary to expectation the European head fell forward and the

Negroid skull fell backward. Earlier Samuel Soemmering (1758-1826) had noted the same point in 1785.

An antagonist of Camper, Johann Friedrich Blumenbach (1752- 1840 AC) rejected the method of lines & angles as a test of national characteristics & proposed a minute survey of the skull particularly the frontal and maxillary bones. In 1795 he described a method of positioning the cranium to be measured in a standard reproducible manner. His method was simple consisting of resting the skull on its base and looking down vertically up on its vault. The points to be noted were the projection of the maxillae anterior to the frontal arch, the directions of the jaws & cheek bones (outward, forward, etc) & the proportional breadth or narrowness of the head. He completely rejected the idea of viewing the skull in Norma lateralis.

Anders Retzius (1796-1860 AC) correlated the two schemes, i.e., of Camper and Blumenbach, thereby providing a basis for the methods of craniology used today. He is also credited with the introduction of cephalic index, the ratio of breadth to length of the skull expressed as a percentage.

John Barclay (1758-1826 AC) proposed two new angles, the superior and the inferior basifacial angles& for the first time, incorporated the mandible in to his measurements. These angles were formed by the intersection of the basifacial lines with a profile line. The superior basifacial line was drawn along the basilar surface of the superior maxillary bone & the inferior basifacial line was drawn along the base of the lower jaw. The superior basifacial angle was not dissimilar to Camper’s facial angle & was measured by a custom made goniometer (supplied by Dr Leach.).

The nineteenth century produced three great men in the history of craniology: Huxley, Broca& Topinard.

Thomas Huxley (1825-1895 AC) wrote in 1876 “the so called facial angle, in the fact, does not simply express the development of the jaws in relation to the face, but is

the product of two factors, a facial& a cranial, which vary independently. The face remaining the same, prognathism may be indefinitely increased, or diminished, by rotation of the frontal region of the skull, backwards or forwards, upon the anterior end of the basicranial axes”. He also introduced two new angles, the spheno maxillary and spheno ethmoidal angles. He preferred the spheno maxillary angle to Camper’s angle when comparing the degree of prognathism in different skulls. This angle is formed by the two lines drawn from basion and prosthion to prosphenion. The other angle, spheno ethmoidal tends to be less than 180° in man.

Broca (1824-1880 AC) who is the founder of the Paris Society of Anthropology believed that the great variability of the cranial form constituted a principal difficulty for the craniologist. He was the first craniologist to institute a precise and accurate technique which could be used to compare crania so that it was made possible to discriminate between the variations in racial types among human skulls. He introduced a base line “plan alveolo- condylien” which passes through the alveolar point & tangential to the inferior surfaces of the two occipital condyles. He also developed a craniostat, mainly constructed of wood for positioning the skull (Fig-8).

It was generally accepted at this time that the angles were best determined on projected drawings of the skull. Broca devised a simple method to trace the out line of the skull on to a piece of paper by fixing the skull in the craniostat& positioning a drawing board with paper attached to it parallel to the mid sagittal plane& a pencil held in a frame perpendicular to the paper. The resultant tracing was equivalent to a tracing of the peripheral as depicted on a lateral skull radiograph.

Paul Topinard (1830- 1912 AC) used a similar criniostat with some additional modifications (Fig-9). Topinard wrote in 1890 “the craniometer substitutes the mathematical data for the uncertain data founded on judgment and opinion. Moreover it studies the skeleton of the ensemble, the cranium and the face separately and each of the plates as well.

During nineteenth century the need for standardization of methods used in craniometry became an important issue, and since then many bodies have met to better define those points and planes in use. The most important meeting as far as the dental profession is concerned was held in Frankfurt-am-Maine in August 1882. This was the 13th General Congress of the German Anthropological Society and it is to this Congress that the Frankfurt Horizontal Plane owes its name.

J.G.Garson (19th century) translated the agreement and published it in the Journal of Anthropological Institute 1885 Earlier in 1859 a horizontal plane following the zygomatic arches was suggested by a Russian craniologist, Von Baer. Later the plane was defined more precisely as line drawn from the centre of each auditory meatus to the lower point on the inferior margin of each orbit by Von Ihering (1850-1930). The Frankfurt agreement modified Von Ihesing’s definition so that the plane passes through the upper border of the bony meatus vertically above their centres. However the reproducibility of this plane on an intact skull is less than Broca’s condyloalveolar plane. Subsequent to the agreement the definition of the horizontal plane has been altered so that it is now taken as passing through the right and left porion &left orbitale. Thereby reducing the problems incurred by asymmetrical skulls.

Following the Frankfurt Agreement very little change of note has occurred in the definition of points and planes. In 1914 Rudolph Martin (1864-1925) published the “Lehrbuch

der

Anthropologie

in

Systematischer

Darstellung

mit

besonderer

Berucksichtigung der anthropologischen Methodoen” & this is still renowned as a fine reference book on physical anthropology.

CEPHALOMETRIC RADIOGRAPHY In 1895, Professor William Conrad Roentgen made a remarkable contribution to the field of science with the discovery of x-rays. On December 28 1895 he submitted a

paper “On A New Kind of Rays, A Preliminary Communication” to the Wurzburg Physical Medical Society for publication in its journal.

Prof. Wilhem Koening & Dr. Otto Walkhoff simultaneously made the first dental radiograph in 1896.

It was clear that the use of x-rays provided the means of obtaining a different perspective on the arrangement and relation of bones thus expanding the horizons of craniometry& cephalometry. The evolution of cephalometry in the twentieth century is universally linked to Edward angle’s publication of his classification of malocclusion.

But the dogmatic inferences of the new school were criticized for failing to include differential diagnosis of facial profile in patients with class iii& class ii malocclusion.

Van Loon was probability the first to introduce cepalometrics to orthodontics when he applied anthropometric procedures in analyzing facial growth by making plaster casts of face in to which he inserted oriented casts of the dentition. Hellman used cephalometric techniques and described their value beginning with 1920s.

The first x- ray pictures of skull in the standard lateral view were taken by A.J.Pacini & Carrera in 1922.Pacini received a research award from the American Roentgen Ray Society for a thesis entitled “Roentgen Ray Anthropometry of the Skull”. Pacini introduced a teleroentgenographic technique for standardized lateral head radiography and thereby opened, what proved to become a tremendous advance in cephalometry, as well as in measuring the growth and development of face. His method, which was rather primitive, involved a large fixed distance from the x ray source to the cassette. The head of the subject, placed adjacent to a standard holding the cassette, was immobilized with a gauze bandage wrapped around both the face and the cassette after the patient’s midsagittal plane was carefully oriented parallel to the cassette.

He identified the following anthropometric landmarks on the roentgenogram: gonion, pogonion, nasion, and anterior nasal spine. He also located the centre of the sella

turcica and the external auditory meatus.he measured the gonion angle and the degree of maxillary protrusion.

Atkinson in 1922 advocated the use of roentgenograms in locating the ‘key ridge’ and the soft tissue relations to the face and the jaws.

In 1923 Mc Cowen reported on profile roentgenograms that he used for orthodontic purposes to visualize the relationship between the hard and soft tissues and to note changes in profile which occur during treatment.

Simpson presented a method for obtaining profile roentgenograms in 1923 before the American society of orthodontists.

In 1927 Ralph Waldron of Newark, N.J. made mention of measuring the gonion angle from a roentgenogram taken at 90 to the facial profile. Waldron was the first to construct a cephalometer, which differed little from those used today.

In 1928 Dewey and Riesner published an article, “A Radiographic Study of Facial Deformity”. Dewey and Riesner immobilized the patients head in a head clamp and placed the cassette against the patient’s face. They took profile roentgenograms by aligning the eye- ear plane by a right angle leveling technique. They used a target distance of three feet.

In 1931 the methodology of cephalometric radiography came to full function when B. Holly Broadbent in USA and H. Hofrath in Germany simultaneously published methods to obtain standardized head radiographs in the Angle Orthodontist (A new X ray technique and its application to orthodontia) and in Fortschritte der Orthodontie (Bedeutung der Rontgen fern und Abstands Aufnahme fur die Diagnostik der kieferanomalien), respectively.

This development enabled orthodontists to capture the field of cephalometry from the anatomists and anthropologists who had monopolized craniometric studies, particularly in nineteenth century.

HOLLY B BROADBENT’S CONTRIBUTION Broadbent’s interest in craniofacial growth began with his orthodontic education under E.H. Angle in 1920. He continued to pursue that interest along with his orthodontic practice, working with a leading anatomist J. Wingate Todd The idea of diagnosing dental deformities by means of planes and angles was first proposed in 1922 by Paul Simon of Germany in his book, “Fundamental Principles of a Systematic Diagnosis of Dental Anomalies”. Although his “Law of the Canines” was later disproved by Broadbent, his theories stimulated the latter to apply the principles of craniometry to living subjects.

The uncertainty of locating land marks in the skull of the living child by approaching through skin and soft tissues led hi to search for a means of recording craniometric landmarks on the living child as accurately as done with a craniostat in measuring the dead skull.

During 1920’s Broadbent refined the craniostat in to craniometer by the addition of metric scales. That proved to be the first step in the evolution of craniostat in to a radiographic cephalostat. It did not take him much longer to convert the direct measuring instrument in to a radiographic craniometer.

Meanwhile the course of Broadbent’s orthodontic practice he corrected the malocclusion of Charles Bingham Bolton, son of Chester and Francis P Bolton. His discussions of facial growth with Congress woman Bolton led to the addition of Bolton study of facial growth to the long list of Bolton philanthropies. As Charles grew to adult hood this study became a major personal as well as financial commitment.

Cephalometrics was neither developed as a technique looking for an application nor was it developed as a diagnostic tool. Broadbent’s single goal was the study of craniofacial growth. The Broadbent technique for cephalometric radiography was one of the tools that he developed for the implementation of that study.

The technique and apparatus perfected for the Bolton Fund study of the normal developmental growth of the face, eliminated practically all of the technical difficulties encountered in previous methods of recording dento-facial changes, and proved to be a convenient as well as scientific method of measuring orthodontic procedures.

According to Broadbent the patient’s head was centered in the cephalostat with the superior borders of the external auditory meatus resting on the upper parts the two ear rods. The lowest point on the inferior bony border of the left orbit, indicated by the orbital marker, was at the level of the upper parts of the ear rods. The nose clamp was fixed at the root of the nose to support the upper part of the face. The focus film distance was set a t 5 feet (152.4 cm) and the subject film distance could be measured to calculate image magnification. With the two X ray tubes at right angles to each other in the same horizontal plane, two images (lateral & postero anterior) could be simultaneously produced. (A new x-ray technique and its application to orthodontia, By B. Holly Broadbent D.D.S., Angle Orthodontist, April, 1931) While Germany’s Hofrath’s technique differed from Broadbent’s in that the path of the central ray was not fixed in relation to the head and no plan was suggested for super positioning subsequent x-rays.

OTHER IMPORTANT CONTRIBUTIONS MADE BY BROADBENT. In 1937, using serial records of twins; he showed how growth – or its lack – was the greatest limiting factor in clinical success. In 1943 he stipulated that eruption of the third molars had no ill effect on the denture, particularly the lower incisors.

 In 1938, a group under Allan G. Brodie at the University of Illinois presented material based on a cephalometric appraisal of orthodontic results: 1)

The use of elastics causes a disturbance in the Bolton plane-occlusal plane angle;

2)

Axial inclinations of orthodontically-moved teeth tend to return to their original

inclinations; 3)

Bone changes during treatment are restricted to the alveolar process.  Brodie, in a landmark study (1941) used for his PhD in anatomy, corroborated Broadbent’s contention that the growth pattern of the normal child’s face develops in an orderly fashion downward and forward and that the pattern, once attained at an early age, did not change.  Thompson and Brodie (1942) in a report on the rest position of the mandible, concluded that:

1)

The morphogenetic pattern of the head was established at a very early age and did

not change; 2)

The presence or absence of teeth has little, if any, bearing on the form or the rest

position of the mandible; and 3)

Vertical facial proportions are constant throughout life.  Margolis (1943) wrote on the relationship between the inclination of the lower incisor and the incisor-mandibular plane angle and was the first to corroborate Tweed’s clinical observation that, in normal occlusions, the lower incisors are 90° to the mandibular basal bone.  In 1947, Wylie produced a method of assessing anteroposterior dysplasias, and, that same year, Margolis contributed his maxillo-facial triangle.

(Lewis, A.B.: The impact of cephalometry on orthodontic concepts. Angle Orthodontist, 1950) CEPHALOMETRIC ANALYSIS

The major use of radiographic cephalometry is in characterizing the patient’s dental and skeletal relationships. This led to the development of a number of cephalometric analyses to compare a patient to his or her peers, using population standards. William. B. Downs in 1948 developed the first cephalometric analysis. Its significance was that it presented an objective method of portraying many factors underlying malocclusion and there could be a variety of causes of malocclusion exclusive to teeth. This was followed by other analyses by Cecil. C. Steiner (1953), C.H.Tweed (1953) , R.M. Ricketts (1958), V.Sassouni (1969), H.D. Enlow (1969), J.R. Jaraback(1970), & Alex Jacobson (1975) etc.

EVOLUTION OF CEPHALOMETRICS The thoroughness of Broadbent’s approach to the design of the cephalometric method is evident from the fact that the basic technique has survived almost unchanged for over seventy years.

In about two decades times the instrumentation had evolved to a form more suitable for the individual practitioner through the pioneering efforts of Margolis, Higley & others.

PATIENT ORIENTATION: The ears were established as the basis for orientation& fixation in the beam axis.

Frankfurt plane was adopted for horizontal orientation with nasion for stabilization. The FH plane was chosen because this was approximate the natural head position (NHP). But the FHP also had its drawbacks & these were: 1. Some individuals show a variation of their FH plane to the true horizontal to an extent of ± 10°.

2. The landmarks to locate the FH plane, orbitale& porion, especially the latter are difficult to identify on a cephalogram.

An alternative to overcome this problem was to use a functionally derived NHP. According to Morrees &Kean, it was obtained by asking the subject to look at the image of their eyes in the mirror located at eye level. A frame of reference was originally intended as a reliable procedure for orienting facial profiles so that same orientation could be established on different occasion by different investigators. Although the functionally derived NHP was more accurate its reproducibility was less than FHP (anatomic approximation of NHP). Lateral and posterio- anterior views perpendicular to each other in the horizontal plane were specified for three dimensional analyses.

Bjork’s studies of facial prognathism illustrated the unreliability of intra cranial reference lines in cephalograms (Some biological aspects of prognathism and occlusion of teeth, Angle Orthodontist, 1951) Kroagman and Sassouni (1957) conducted an exhaustive survey of roentgenographic cephalometry in which the FH Plane coincided with the physiologic or true horizontal.

Sassouni made an attempt to standardize the orientation of cephalograms by means of an optical plane advocated in 1862 by Broca, who stated that “when a man is standing and when his visual axis is horizontal, he(his head) is I natural position.”

X-RAY SOURCE POSITION The x-ray source is positioned 5 feet (152.4) from the subject’s midsagittal plane.

A change to 150 cm has been adopted by some as a conveniently round metric number, but the difference is negligible. A major improvement in lateral cephalostats is the capability of taking lateral& postero-antrior views with a single x-ray source instead of two.

FILM POSITION & ENLARGEMENT

The other significant change from the original technique is adjustability of film position. The original cephalostat was based on the design of the anthropometric craniometer &cassettes were attached to these mechanisms. The disadvantage of this very efficient mechanical design is that it makes cassette position and resultant enlargement depended on head size. Evaluation of serial changes by direct superimposition is made unreliable by this variable enlargement.

The relative immunity of angular measurements to enlargement distortions led many researchers to opt for angular over linear values whenever possible. Also newer instruments have been developed that can over come this drawback of variable enlargement by providing independent adjustments for head holding mechanisms and cassette.

POSTERO-ANTERIOR (FRONTAL) CEPHALOMETRY Since the introduction of a standardized method for obtaining skull radiographs, cephalometrics has become one of the major diagnostic tools in orthodontics. The posterior anterior cephalogram contains diagnostic information not readily available from other sources. This information allows the practitioner to evaluate the width and angulation of the dental arches in relation to their osseous bases in the transverse plane; evaluate the width and transverse positions of the maxilla and mandible; evaluate the relative vertical dimensions of bilateral osseous and dental structures; assess nasal cavity width; and analyze vertical and/or transverse facial asymmetries.

Malocclusions &dentofacial deformities constitute three dimensional conditions or pathologies. Although all orthodontic patients deserve an equally comprehensive three dimensional diagnostic examinations, assessment of postero- anterior cephalometric views are of particular importance in cases of: 1. Dento alveolar & facial asymmetries

2. Dental & skeletal cross bites.

3. Functional mandibular displacements The same equipment that is used for the lateral cephalometric projections is utilized. The initial unit described by Broadbent consisted of a set up in which two X ray sources with two cassettes were simultaneously used, so that lateral and frontal cephalograms were taken at the same time.

Although precise three dimensional

evaluations are possible using this technique, it has now been almost abandoned since it requires rather large equipment with two x ray sources.

Modern equipment uses one x-ray source. Therefore following lateral cephalometric registration, the patient must be repositioned if a postero anterior cephalogram has to be produced. A head holder or cephalostat that can be rotated 90° is used, so that the central X ray beam penetrates the skull of the patient in a postero anterior direction and bisects the transmeatal axis perpendicularly. Maintaining the identical horizontal orientation from lateral to the postero- anterior projection is critical when comparative measurements are made on each other. (Moyers et al, 1988) In using natural head position for postero anterior cephalometric registrations, some practical problems are encountered. The patient’s head is facing the cassette; which makes it difficult for the patient to look in to a mirror to register natural head position (Solow &Tallgren, (1977). Furthermore, space problems make it impossible to place a nose piece in front of nasion to establish support in a vertical plane.

For better evaluation of patients with craniofacial anomalies that require special attention to the upper face, the patient head should be positioned with the tip of the nose and forehead lightly touching the cassette holder. (Chierci, 1981) In cases of suspected significant mandibular displacement, the PA cephalogram should be taken with the mouth of the patient slightly open in order to differentiate between functional mandibular displacements & dentoskeletal facial asymmetry (Faber,

1985). As far as exposure conditions and considerations are considered, more exposure is needed for PAcephalograms than lateral views (Enlow, 1982) CEPHALOMETRIC LAND MARKS Cephalometric landmarks are readily recognizable points on a cephalometric radiograph or tracing, representing certain hard or soft tissue anatomical structures (anatomical landmarks) or intersections of lines (constructed landmarks).landmarks are used as reference points for the construction of various cephalometric lines or planes and for subsequent numerical determination of cephalometric measurement.

Measure points and land marks used in anthropometrics were formulated at a series of international congress on “Prehistoric Anthropology and Archeology.” three of the more important ones were held at Frankfort (1882), Monaco (1906), and Geneva (1912). The agreements reached at Monaco and Geneva state that “A land mark in anthropometry is as near as possible a definite point from or to which to measure.”

Landmarks show a fairly definite range of normal variation or oscillation about mean. It is important for the orthodontist to determine whether facial dimensions and relationship of facial components fall with in the range of normal variation or whether the deviations are to be classified as abnormalities.

REQUIREMENTS OF LANDMARKS AND MEASURE POINTS 1. Landmarks should be easily seen on the roentgenogram, be uniform in out line, and easily reproducible.

2. Lines and planes should have significant relationship to the vectors of growth of specific Ares.

3. Landmarks should permit valid quantitative measurements of lines and angles projected from them.

4. Measure points and measurements should have significant relation to the information sought.

5. Measurements should be amenable to statistical analyses but should preferably not require extensive specialized training, in statistical methods.

Garn (1961) pointed out that there are no ‘fixed points’ in the skull of living person. Variability of the landmarks depends on age, sex, maturation rate, ethnic background, and other factors.

Following is a list of the most commonly used cephalometric landmarks. In these definitions, the following convention is used: midsagittal identifies landmarks lying on the midsagittal plane, unilateral identifies land marks corresponding to unilateral structures and bilateral applies to landmarks corresponding to bilateral structures.

LATERAL CEPHALOGRAM HARD TISSUE LANDMARKS •

A-point (Point A, Subspinale, ss) : the deepest point (most posterior) midline point on the curvature between the ANS and prosthioin

•

Anterior nasal spine (ANS): the tip of the bony anterior nasal spine at the inferior margin of the piriform aperture in the midsagittal plane.

•

Articulare (Ar) : a constructed point representing the intersection of three radiographic images: the inferior surface of the cranial base and the posterior out line of the ascending rami or mandibular condyles

•

B-point (Point B, Supramentale, sm): the deepest (most posterior) midline point on the bony curvature of the anterior mandible, between infradenale and pogonion.

•

Basion (Ba): the most anterior inferior point on the margin of the foramen magnum in the midsagittal plane.

•

Bolton (Bo) : the highest points on the outlines of the retrocondylar fossae on the occipital bone, approximating the centre of the foramen magnum

•

Condylion (Co) : the most superior point on the head of the mandibular condyle

•

Glabella (G): the most prominent point of the anterior contour of the frontal bone in the midsagittal plane.

•

Gnathion (Gn) : the most anterior inferior point on the bony chin in the midsagittal plane

•

Gonion (Go): the most posterior inferior point on the outline of the angle of the mandible.

•

Incision inferius (Ii) : the incisal tip of the most labially placed mandibular incisor

•

Incision superius (Is) : the incisal tip of the most labially placed maxillary central incisor

•

Infradentale (Id, Inferior prosthion) : the most superior anterior point on the mandibular alveolar process between the central incisors

•

Menton (Me): the most inferior point of the mandibular symphysis in the midsagittal plane.

•

Nasion (N,Na) : the intersection of the internasal and frontonasal sutures in the midsagittal plane

•

Opisthion (Op) : the most posterior inferior point on the margin of the foramen magnum in the midsagittal plane

•

Orbitale (Or) : the lowest point on the inferior orbital margin

•

Pogonion (pog, P, Pg) : the most anterior point on the contour of the bony chin in the midsagittal plane

•

Porion (Po): the most superior point of the outline of the external auditory meatus (anatomic porion). When the anatomic porion cannot be located readily the superior most point of the image of the ear rods (machine porion) sometimes is used instead.

•

Posterior nasal spine (PNS) : the most posterior point on the bony hard palate in the midsagittal plane, the meeting point between the inferior and the superior surfaces of the bony hard palate at its posterior aspect

•

Prosthion (Pr, Superior prosthion, Supradentale): the most inferior anterior point on the maxillary alveolar process between the central incisors.

•

Pterygomaxillary fissure (PTM, Pterygomaxillare): a bilateral inverted tear drop shaped radiolucency whose anterior border represents the posterior surfaces of the tuberosities of the maxilla. The landmark is taken at the most inferior point of the fissure, where the anterior and the posterior outline of the inverted teardrop merge with each other.

•

R- Point (Registration point): a cephalometric reference point for registration of superimposed tracings.

•

Sella (S): the geometric centre of the pituitary fossa (sella turcica), determined by inspection – a constructed point in the midsagittal plane.

SOFT TISSUE LANDMARKS •

Cervical point (C): the innermost point between the submental area and the neck in the midsagittal plane. Located at the intersection of lines drawn tangent to the neck and submental areas.

•

Inferior labial sulcus (Ils): the point of the greatest concavity on the contour of the lower lip between the labrale inferius and menton in the midsagittal plane.

•

Labrale inferior (Li): the point denoting the vermillion border of the lower lip in the midsagittal plane.

•

Labrale superior (Ls): the point denoting the vermillion border of the upper lip in the midsagittal plane.

•

Pronasale (Pn): the most prominent point of the tip of the nose, in the midsagittal plane.

•

Soft tissue glabella (G’): the most prominent point of soft tissue drape of the fore head in the midsagittal plane.

•

Soft tissue menton (Me’): the most inferior point of the soft tissue chin in the midsagittal plane.

•

Soft tissue nasion (N’, Na’): the deepest point of the concavity between the forehead and the soft tissue contour of the nose in the midsagittal plane.

•

Soft tissue pogonion (Pg’, Pog’): the most prominent point on the soft tissue contour of the chin in the midsagittal plane.

•

Stomion (St): the most anterior point of contact between the upper and lower lip in the midsagittal plane. When the lips are apart at rest, a superior and an inferior stomion point can be distinguished.

•

Stomion inferius (Sti): the highest midline point of the lower lip.

•

Stomin superius (Sts) : the lowest midline point of the upper lip

•

Subnasale (Sn): the point in the midsagittal plane where the base of the columella of the nose meets the upper lip.

•

Superior labial sulcus (Sls): the point of greatest concavity on the contour of the upper lip between subnasale and labrale superius in the midsagittal plane.

•

Trichion (Tr): an anthropometric landmark, defined as the demarcation point of the hair line in the midline of the forehead.

POSTERO- ANTEROIR CEPHALOGRAMS A. BILATERAL SKELETAL LANDMARKS •

Greater Wing Superior Orbit (GWSO) - the intersection of the superior border of the greater wing of the sphenoid bone and lateral orbital margin.

•

Greater Wing Inferior Orbit (GWI0) - the intersection of the inferior border of the greater wing of the sphenoid bone and the lateral orbital margin.

•

Lesser Wing Orbit (LWO) - the intersection of the superior border of the lesser wing of the sphenoid bone and medial aspect of the orbital margin.

•

Orbitale (O) - the midpoint of the inferior orbital margin.

•

Lateral Orbit (LO) - the midpoint of the lateral orbital margin.

•

Medial Orbit (MO) - the midpoint of the medial orbital margin.

•

Superior Orbit (SO) - the midpoint of the superior orbital margin.

•

Zygomatic Frontal (ZF) - the intersection of the zygomaticofrontal suture and the lateral orbital margin.

•

Zygomatic (Z) - the most lateral aspect of the zygomatic arch.

•

Foramen Rotundum (FR) - the center of foramen rotundum.

•

Condyle Superior (CS) - the most superior aspect of the condyle.

•

Center Condyle (CC) - the center of the condylar head of the condyle.

•

Mastoid Process (MP) - the most inferior point on the mastoid process.

•

Malar (M) - the deepest point on the curvature of the malar process of the maxilla.

•

Nasal Cavity (NC) - the most lateral point on the nasal cavity.

•

Mandible/Occiput (MBO) - the intersection of the mandibular ramus and the base of the occiput.

•

Gonion (G) - the midpoint on the curvature at the angle of the mandible (gonion).

•

Antegonial (AG) - the deepest point on the curvature of the antegonial notch.

B. MIDLINE SKELETAL LANDMARKS •

Crista Galli (CG) - the geometric center of the crista galli.

•

Sella Turcica (ST) - the most inferior point on the floor of sella turcica.

•

Nasal Septum (NSM) - the approximated midpoint on the nasal septum between crista galli and the anterior nasal spine.

•

Anterior Nasal Spine (ANS) - the center of the intersection of the nasal septum and the palate.

•

Incisor Point (IPU) - the crest of the alveolus between the maxillary central incisors.

•

Incisor Point (IPL) - the crest of the alveolus between the mandibular central incisors.

•

Genial Tubercles (GT) - the center of the genial tubercles of the mandible.

•

Menton (ME) - the midpoint on the inferior border of the mental protuberance.

C. BILATERAL DENTAL LANDMARKS •

Maxillary Cuspid (MX3) - the incisal tip of the maxillary cuspid.

•

Maxillary Molar (MX6) - the midpoint on the buccal surface of the maxillary first molar.

•

Mandibular Cuspid (MD3) - the incisal tip of the mandibular cuspid.

•

Mandibular Molar (MD6) - the midpoint on the buccal surface of the mandibular first molar.

IDENTIFICATION AND REPRODUCIBILITY OF CEPHALOMETRIC LANDMARKS: It is essential to evaluate the validity of information obtained from the lateral head film. Cephalometric measurements on radiographic images are subject to errors that may be caused by radiographic projection errors with in the measuring system & errors in landmark identification.

Landmark identification errors are considered as the major source of cephalometric error. Many factors are involved uncertainty. They are: •

Density & sharpness of the image

•

Anatomic complexity & superimposition of hard and soft tissues

•

Observer’s experience in locating a landmark and defining the location of the landmark.

A Meta analysis was carried out by B. Tipkova, P. Major, N. Prasad&B. Hebbe in 1997 AJO To determine the reproducibility of some commonly used 15 landmarks. Meta analysis is a quantitative review technique described as the statistical analysis of a large collection of results from individual studies for the purpose of integrated finding.

The 15 landmarks were N, S,Or, Ba, P, ANS, PNA, Pt. A, Ptm, Go, Co, Ar, Pog, Me, Pt.B. It was concluded from the study that some landmarks are more reproducible in a horizontal direction and others in a vertical direction. B, A, Ptm,Go, & S, exhibited acceptable levels of accuracy along the horizontal axis. A, S, Ptm exhibited acceptable levels of along the vertical axis as well.

LANDMARK

IDENTIFICATION

ERROR

IN

POSTERIOR

ANTERIOR

CEPHALOMETRICS Paul W. Major, Donald E. Johnson and Karen L. Hesse conducted a study which was designed to quantify the intraexaminer and interexaminer reliability of 52 commonly used posterior anterior cephalometric landmarks. The horizontal and vertical identification errors were determined for a sample of 33 skulls and 25 patients. The results show that there is a considerable range in the magnitude of error with different horizontal and vertical values.

Interexaminer landmark identification error was significantly larger than intraexaminer error for many landmarks. The identification error was different for the skull sample compared to the patient sample for a number of landmarks. The relevance of knowing the identification error for each landmark being considered in a particular application was discussed.

Regardless of the clinical or research application, it is critical to know the reliability of the reference landmarks. Baumrind and Frantz point out that there are two general classes of error associated with cephalometric measurements. The first class of errors is “projection� errors which arise from the geometry of the radiographic setup.

The fact that the x-ray beam originates from a source which has a finite size leads to a penumbra effect or optical blurring. The x-ray beam diverges as it moves away from the source, which results in an overall magnification of the object being radiographed and a radial displacement of all points which are not on the principal axis (central ray). The

radiographic image is distorted as points closer to the film are magnified less than points farther from the film.

The second general class of landmark errors may be termed “errors of identification,� and arise due to uncertainty involved in locating specific anatomic landmarks on the radiograph. The precision with which any landmark may be identified depends on a number of factors.

Landmarks lying on a sharp curve or at the intersection of two curves are generally easier to identify than points located on flat or broad curves.

Points located in areas of high contrast are easier to identify than points located in areas of low contrast. Superimposition of other structures, including soft tissue over the area of the landmark in question, reduces the ease of identification.

Precise written definitions describing the landmark reduces the chance of interpretation error. Operator experience is an important factor since increased knowledge of anatomy and familiarity with the radiographic appearance of the subject reduces interpretive errors.

A literature review concerning the reliability of landmark identification in posterior anterior cephalometrics revealed only one article, by El-Mangoury et al., which determined the horizontal, vertical and radial variability of 13 landmarks.

They found that each landmark had its own characteristic noncircular envelope of error, and that the variability is different in the horizontal and vertical directions.

Unfortunately, the majority of posterior anterior cephalometric analyses use landmarks whose identification error has not been independently reported.

CONCLUSION Broadbent did not present the profession with a premature infant in the need of artificial; life support and careful nurture. He gave us a gangling but vigorous adolescent ready to enter the work force.

Clinical orthodontics is yet to fully utilize Broadbent’s contribution. He gave us a three dimensional analysis, but orthodontics has remained preoccupied with the lateral view. The lateral view is easy to work with and the patient is also much more recognizable than in the frontal (P-A) view, especially with soft tissue enhancement. But it is not enough.

We treat in three dimensions and the width dimensions that are visualized on the frontal view are crucial in many cases. In these days of increasing awareness of the contribution of muscular and respiratory function, we can no more afford to continue to close our eyes to the information in the frontal view than we could afford to ignore the lateral view up to now.

REFERENCES 1. Craniometry and Cephalometry: A History Prior to the Advent of Radiography – Laetitia. M. Finlay ; Angle Orthodontist 1980 2. Fifty Years of Cephalometric Radiography – Editorial ; Angle Orthodontist 1981 3. A New X Ray Technique and its Application in Orthodontia – B. Holly Broadbent ; Angle Orthodontist 1931 4. Radiographic cephalometry – Alexander Jacobson 5. Practice of Orthodontics – J.A. Salzmann 6. Orthodontic Cephalometry – Athanasios. E. Athanasiou 7. Oral Radiology – Paul .W. Goaz, Stuart. C. White

8. Cephalometric Radiography – Thomas Rakosi 9. Glossary of Orthodontic terms – John Daskalogiannakis 10. Contemporary Orthodontics – William R. Proffit 11. Lewis, A.B.: The impact of cephalometry on orthodontic concepts. Angle Orthodontist, 1950 12. Some biological aspects of prognathism and occlusion of teeth, Angle Orthodontist, 1951 13. Cephalometric Landmarks Identification & Reproducibility – A Meta analysis – American journal of orthodontics 1997 14. Landmark identification error in posterior anterior cephalometrics Paul W. Major, Donald E. Johnson, Karen L. Hesse- Angle Orthodontist, 1994 15. Résumé of the workshop and limitations of the technique – Salzmann, AJODO 1958