Role of cephalometry in orthdodontics /certified fixed orthodontic courses by Indian dental academy


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Role of cephalometry in orthdodontics /certified fixed orthodontic courses by Indian dental academy

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. INTRODUCTION The discovery of X-rays led to the measurement of the head from shadows of bony and soft tissue landmarks on the roentgenographic image that came to be known as the Roentgenographic Cephalometry. For many years since the 1930’s spawned by the classic work of Broadbent and Hofrath in the United States and Germany respectively, cephalometrics has enjoyed wide acceptance as an essential component of the diagnostic phase for the more traditional forms of orthodontic treatment. Innumerable research works and papers have been published in this field. In more recent times, the importance of sophisticated cephalometric methods, often computerized, has become clearly established as an indispensable diagnostic tool for the analysis and correction of a wide range of craniofacial orthopedic problems.
  3. 3. DEFINITION Origin: ‘Cephalo’ means head and ‘Metric’ is measurement. In oral surgery and orthodontics: 1. “The scientific measurement of the bones of the cranium and face, utilizing a fixed, reproducible position for lateral radiographic exposure of skull and facial bones”. 2. “ A scientific study of the measurements of the head with relation to specific reference points; used for evaluation of facial growth and development, including soft tissue profile”.
  4. 4. HISTORY OF CEPHALOMETRICS In 1780, Petrus Camper, probably the first to employ angles in measuring the face, oriented the skull on a horizontal from the middle of porus acusticus to a point below the nose. Craniostats were designed to hold the skull in an oriented position to give greater reliability to the measurements, and they were the forerunners of the cephalostat or headholder. The dry skull measurements, craniometry, was done from countless aspects. But these static and nonvital studies did not interest the orthodontists. With the application of these measurements to living subjects, their use in orthodontics was deemed important.
  5. 5. At the 1882 meeting of the International Congress of Anthropology in Frankfort, Germany, Von Ihering’s line (drawn from the upper margin of the external acoustic meatus to the lowest point of the infraorbital margin) was accepted as a standard plane of orientation. This line is the forerunner of the Frankfurt Horizontal plane, which is the basis of the roentgenographic cephalometric orientation. In 1895 Wilhelm Conrad Roentgen discovered X-rays. In the same time period Milo Hellman adopted techniques of physical anthropology to orthodontic research followed by which skull radiographs came into use. 1921, A.J. Pacini, presented the paper “Roentgen Ray Anthropometry of the Skull” which stated that the accuracy of roentgen ray anthropometry far surpassed ordinary anthropometry. He aligned the subjects head so that the mid-sagittal plane was parallel the film. A constant target-film distance of 2½ feet was employed and the central ray was directed one inch above and in front of the EAM. In
  6. 6. In the 1920’s, B. Holly Broadbent of the USA worked with the anatomist T. Wingate Todd, after his orthodontic training in the Angle school. His previous experience with profile roentgenography helped Broadbent design his roentgenographic craniostat. His success with this led him to the development of the cephalostat or head holder. In Feb 1931, Broadbent presented his paper under the title “A new X-ray technique and its applications to orthdodontics”, describing roentgenographic cephalometry at the mid winter meeting of the Chicago Dental Society. Further work produced the roentgenographic cephalometer. It is a head positioning device similar to a craniostat. Further more in 1931, Herbert Hofrath published in the German literature an article entitiled “Importance of teleroentgenograms for the diagnosis of Jaw Abnormalities”. A 2M target distance was used. The X-ray tube was placed at one end of a long tube and at the other end was a device carrying two pairs of crossed wires for the purpose of orienting the axis ray. Hofrath’s method differed from that of Broadbent’s in that there was littkle mention of a frontal view, the path of the central ray was not fixed in relation to the head, there was no plane for superimposition and considerable stress was laid on the recording of the soft tissue. His procedures had less refinement and precision than Broadbent.
  7. 7. The University of Illinois and the University of Colorado were a few early centers for cephalometric research. After the invention of cephalometric radiograph, Lucien de Costar of Belgium was the first to publish an analysis based on the proportional relationships of face. Korkhaus (Germany) developed a systematic diagnostic evaluation of cephalometric films, which resembles our present analytical tracing. After the advent of Cephalometrics in 1931 (Broadbent & Hofrath), aspects of these standardized methods were propagated into general clinical use during 1940-1950 [Brodie, 1941; Downs, 1948; Ricketts, 1950; Krogman & Sassouni, 1952; Wylie, 1952; Steiner, 1953; Schwartz, 1961]. By 1960’s it had become a routine component of treatment planning.
  8. 8. TECHNICAL ASPECTS The basic components for producing a lateral cephalogram are: X-ray apparatus: It comprises of an X-ray tube, transformers, filters, collimators, and a coolant system all encased in the machines housing. Image receptor system: An image receptor system records the final product of X-rays after they pass through the subject. It consists of an extra oral film, intensifying screens, cassette, grid, and a soft tissue shield.
  9. 9. Cephalostat: The use of a cephalostat, also called a head-holder or cephalometer, is based on the same principle as that described by Broadbent. The patient’s head is fixed by the two ear rods. The head which is centered in the cephalostat, is oriented with the Frankfort plane parallel to the floor and the midsagittal plane vertical and parallel to the cassette.
  10. 10. CHOICE OF A HORIZONTAL REFERENCE LINE At the International Congress of Anatomists and Physical Anthropologists held in Frankfort, Germany in 1882, the Frankfort plane [extending from the upper rim of the external auditory meatus (porion) to the inferior border of the orbital rim (orbitale) ], was adopted as the best representation of the natural orientation of the skull. For living patients, however, it is possible to use a “ true horizontal” line, established physiologically rather than anatomically, as the horizontal reference plane. This approach requires that the cephalometric radiographs be taken in Natural Head Position. FH Plane The inclination of SN to the true horizontal plane (or FH plane if THP is not known) should always be noted, and if the inclination of SN differs significantly from 6 degrees, any measurement based on SN should be corrected
  11. 11. NHP-Natural Head Position: Broca defined it in 1861 as “when a man is standing and when his visual axis is horizontal, his head is in the natural horizontal position”. The simplest procedure to obtain head radiographs in the NHP is to instruct the patient to sit upright and look straight ahead to a point at eye level so that the head level is determined by the internal physiological mechanism. Other devices such as fluid level device, inclinometer and the plumb line have been used to measure the head posture.
  12. 12. ANALYSIS Cephalometric analysis is used to assess, express and predict the spatial relations of soft tissues, craniofacial and dentofacial complexes at one point or over time. The analysis is either objective or subjective. Objective evaluation involves quantification of spatial relationships by angular or linear measurements. Subjective evaluation involves the visualization of changes in spatial relationships of areas or anatomical landmarks within the same face and relating to a common point or plane over time.
  13. 13. CLASSIFICATION OF ANALYSES ANALYSES Methodological Normative Acc. To Area of Analyses 1. Methodological: Angular: Dimensional Analysis, Proportional Analysis, Analysis to determine position. Linear : Orthogonal Analysis, Dimensional Linear Analysis, Proportional Linear Analysis.
  14. 14. 2. Normative: Mononormative Analyses: Arithmetical or Geometrical. Multinormative Analyses. Correlative Analyses. 3. Acc. to Area of Analysis: Dentoskeletal Analyses: Facial Skeleton, Maxillary and Mandibular Base. Dentoalveolar Analyses: Position and Angulation of Upper & Lower Incisors. Soft Tissues Analyses.
  15. 15. APPLICATIONS IN ORTHODONTICS Cephalometrics is used in three major areas: Morphological Analysis; by evaluating the sagittal and vertical relations of dentition, facial skeleton and soft tissue profile. Growth Analysis; by taking two or more cephalograms at different time intervals and comparing the changes. Treatment Analysis; by evaluating alterations during and after therapy.
  16. 16. VARIOUS ANALYSES STEINER ANALYSIS: [AJO-1960] was developed and promoted by Cecil Steiner in the 1950s. It can be considered the first of the modern cephalometric analyses for two reasons: it displayed measurements in a way that emphasized not just the individual measurements but their interrelationship into a pattern, and it offered specific guides for the use of cephalometric measurements in treatment planning.
  17. 17. SASSOUNI ANALYSIS: [AJO-1969] was the first cephalometric method to emphasize vertical as well as horizontal relationships and the interactions between vertical and horizontal proportions. Sassouni pointed out that the horizontal anatomic planes-the inclination of the anterior cranial base, Frankfort plane, Palatal plane, Occlusal plane and Mandibular plane-tend to converge toward a single point in a well-proportioned face. The inclination of these planes to each other reflects the vertical proportionality of the face. If the planes intersect relatively close to the face and diverge quickly as they pass anteriorly, the facial proportions are long anteriorly and short posteriorly which predisposes the individual to an openbite malocclusion. Sassouni coined the term Skeletal Open Bite for this anatomic relationship, the opposite of which is Skeletal Deep Bite.
  18. 18. RICKETTS ANALYSIS: is a 11 factor summary analysis that employs specific measurements to (1) locate the chin in space, (2) locate the maxilla trough the convexity of the face, (3) locate the denture in the face, and (4) evaluate the profile. The Ricketts approach emphasizes not only an analysis of the patients initial condition, but the prediction of future growth and treatment effects in a VTO.
  19. 19. HARVOLD ANALYSIS, WITS ANALYSIS: both analyses were aimed solely at describing the severity or degree of jaw disharmony. Harvold [1974] using data derived from the Burlington growth study, developed standards for the ‘unit length’ of the maxilla and mandible. The difference between these provides an indication of the size discrepancy between the jaws. The Wits analysis [AJO-1975] was conceived primarily as a way to overcome the limitations of ANB as an indicator of jaw discrepancy. The Wits in contrast to the Harvold analysis, is influenced by the teeth both horizontally and vertically.
  20. 20. McNAMARA ANALYSIS: [AJO-1984] was originally published in 1983, and still represents the state of the art in cephalometric measurement analysis reasonably well. It combines elements of previous approaches (Ricketts and Harvold) with original measurements to attempt a more precise definition of tooth and jaw positions. This analysis has two major strengths: (1) it relates the jaws via the nasion perpendicular, in essence projecting the difference in anteroposterior position of the jaws to an approximation of the true vertical line, (2) the normative data are based on well defined Bolton sample, which is also available in template form, meaning that the McNamara measurements are highly compatible with preliminary analysis by comparison with Bolton templates.
  21. 21. ENLOWS COUNTERPART ANALYSIS: [AJO-1969] The basic idea of interrelated dimensions leading to an ultimately balanced or unbalanced facial pattern was expressed well by Enlow in the 1960s, in his “counterpart analysis”. As Enlow et al pointed out, both the dimensions and alignment of craniofacial components are important in determining the overall facial balance. TWEED ANALYSIS: [AO-1954] originally included only three measurements. It is centered around two highly critical parameters: the position of the mandibular incisors (over the basal bone), and the angle FMA, which represents the (anterior) vertical dimension of the maxilla and the mandible.
  22. 22. DOWNS’ ANALYSIS: [AO-1956] when observing facial profiles, W B Downs noted that generally the position of the mandible could be used in determining whether or not faces were balanced. Downs reduced his observations to the following four basic facial types: Retrognathic, Mesognathic, Prognathic and True Prognathism (a pronounced protrusion of the lower face)
  23. 23. WYLIE ANALYSIS: [AO-1947] The terms “orthognathism” and “prognathism” were selected to categorize facial types, in preference to “Class II faces” and “Class III faces”. “Prognathism” and “orthognathism”, when used by others, may apply either to the maxilla or the mandible or both. As it is used here it applies mainly to the mandible in relation to the maxilla. A method is presented whereby discrepancies in size of facial bones occurring in the anteroposterior plane of space may be assessed quantitatively in terms of millimeters. The method of assessment presented makes possible a net score of anteroposterior dysplasia which is approximately zero where such dysplasia is either non-existent or compensated for by variation in different parts, and which is negative in the type of face where relative mandibular insufficiency exists, and positive in cases of mandibular prognathism.
  24. 24. BJORKS ANALYSIS: [1954] the mechanism for the control and modification of craniofacial growth had been discussed earlier by Bjork, who noted after a survey of cephalometric X-ray analyses that compensation was dominant during adolescence, while dysplastic changes appeared mainly at an early stage of development.
  25. 25. DI PAOLO’S QUADRILATERAL ANALYSIS: [AJO-1983] The quadrilateral analysis offers an individualized cephalometric diagnosis on patients with or without skeletal dysplasias. It includes Skeletal assessment, Dental assessment and Assessment of Facial Types (normodivergent, hypodivergent and hyperdivergent). It is a reliable and accurate method of assessing whether orthodontic treatment, surgical treatment, or a combination of both is required to achieve a satisfactory result. RIEDEL ANALYSIS: [AO-1952] was established on the basis of a study undertaken by Richard A Riedel to determine the constancy or variation in the relation of maxilla to cranium and the mandible.
  27. 27. SOFT TISSUE CEPHALOMETRIC ANALYSIS A good mechanical relationship between maxillary and mandibular dentures was formerly regarded as the sole aim of orthodontic treatment. In the course of time, however, orthodontists have become increasingly aware that facia esthetics must also be considered in planning. According to Wuerpel, a face is beautiful and shows harmonious featuresif the proportions of its individual components are right, ie, no individual structure is over emphasized in relation to the others - what he refers to as ‘balance’. For soft tissue analysis, distinction is made between: Profile Analysis. Lip Analysis. Tongue Analysis.
  28. 28. PROFILE ANALYSIS: Further divided into Proportional Analysis and Angular Profile Analysis. Proportional Analysis: were in the profile may be divided into three approximately equal parts, Frontal Third (tr-n), Nasal Third (n-sn), and Gnathic Third (sn-gn). Angular Profile Analysis: were in Subtelny makes the distinction between the convexity of, the skeletal profile, the soft tissue profile, and the full soft tissue profile (including the nose). Skeletal Convexity is represented by N-A-Pog mean=175° Soft Tissue convexity is determined as n-sn-pog mean=161° Full Soft Tissue Convexity is based on n-n-pog mean=137°M/133°F
  29. 29. Profile Analysis by A M Schwarz: were in three reference lines are constructed for profile analysis: to 1. The H line, corresponding to the FH plane, 2. The Pn line, and 3. The Po line (orbital perpendicular), a perpendicular from the orbital the H line. The Gnathic Profile Field (GPF) permits assessment of the profile. Depending on the position of the subnasale relative to the nasion perpendicular three types of faces are seen, 1. Average Face – sn on nasion perpendicular, 2. Retroface – sn behind the nasion perpendicular, and 3. Anteface – sn in front of the nasion perpendicular.
  30. 30. LIP ANALYSIS: Analysis of the lip plays a significant role in treatment planning. Ricketts: uses the E line drawn from the tip of the nose to skin pogonion. Steiners: uses the S line drawn from the centre of the S shaped curve between the tip of the nose and sn, to the pog. Holdaways Lip Analysis: this is a quantitative analysis to assess lip configuration. Holdaway determines the angle between a tangent to the upper lip and NB line, called the H angle. Holdaway defines the perfect profile as follows: -ANB angle 2°, H angle 7-8°. -Lower lip touching the soft tissue line, and with -The relative proportions of nose and upper lip well balanced.
  31. 31. TONGUE ANALYSIS: Contains two parameters 1) assessing tongue position, and 2) assessing tongue motility Tongue Position: in relation to the Root: a space is formed between the root of the tongue and soft palate in cases of mouth breathing (nasal obstruction) & Cl II malocclusion. Dorsum: of the tongue is high in Cl II malocclusion and in deepbite cases. In all others it is low. Tip: is retracted in Cl III and in Cl II with nasal breathing and in deepbite cases. In openbite, tip is forward.
  32. 32. Tongue Motility: the changes in the position of the tip relate closely to the different types of malocclusion. With Cl II the tip is back at rest position, and with Cl III the tip lies further forward. It may be assumed that the changes in position of the tip of the tongue relate to the tendency to mandibular malformation.
  33. 33. ARNETT & BERGMAN ANALYSIS: The analysis is a radiographic instrument that was developed directly from the philosophy expressed in Arnett and Bergman’s Facial keys to orthodontic diagnosis and treatment planning [AJO April / May 1993]. Many authors have suggested utilizing soft tissue analysis as a reliable guide for occlusal treatment and attendant soft tissue changes. Arnett and Bergman presented the Facial Keys to Orthodontic Diagnosis and Treatment Planning as a three-dimensional clinical blueprint for soft tissue analysis and treatment planning. In preparation for the cephalometric radiograph, metallic markers were placed on the right side of the face to mark key midface structures. These included the orbital rim marker, cheekbone marker, alar base marker, subpupil marker and neck-throat marker. The True Vertical Line (TVL) was then established. The line was placed through subnasale and was perpendicular to the natural horizontal head position. ...........contd.
  34. 34. CLINICAL IMPLICATIONS: Soft Tissue Cephalometric Analysis (STCA) provides dental and facial diagnosis. Data provided by the STCA can then be used for Cephalometric Treatment Planning (CTP). The STCA can be used to diagnose the patient in five different but interrelated areas; dentoskeletal factors, soft tissue components, facial lengths, TVL projections, and harmony of parts. ................contd.
  35. 35. CEPHALOMETRIC TREATMENT PLANNING (CTP): Diagnosis generated by STCA is used to guide cephalometric treatment planning. Seven steps are involved in CTP to optimize occlusal and facial results: 1. 2. 3. 4. 5. 6. 7. Proper angulation of lower incisor teeth, Proper angulation of upper incisors, Maxillary incisor positioning, Autorotation of mandible to 3mm of overbite, Mandible is moved anteriorly or posteriorly to correct the overjet with the maxillary arch, Maxillary occlusal plane is defined, and lastly Chin projection and height assessment. ...........contd.
  36. 36. Cephalometric Treatment Planning: There are a number of other soft tissue analysis such as Powell’s, Farka’s, Lehman’s, Burstone’s, Wolford’s, Bolton’s, Spradley’s, Bowker and Meredith’s and Holdaway’s soft tissue analysis. The Reed Holdaway’s analysis has 11 measurements including facial angle, upperlip curvature, skeletal convexity, upper and lower depth, thickness and strain, harmony line angle etc.
  37. 37. FUNCTIONAL ANALYSIS OF THE RADIOGRAPH Cephalometric radiography will also demonstrate the relationship between rest and occlusal positions. Relative to its occlusal position, the mandible may be further back or further forward than in rest position. If a radiograph is taken in rest position and another in occlusion, mutual relations between these two may be established. In every movement of the mandible we can differentiate between a rotatory and gliding component. The principle of comparative assessment consists in the determination of one angle for the rotational component and another for the gliding component.
  38. 38. ASSESSING HORIZONTAL RELATIONS ORTHO/RETRO/PROGNATHIC: Cephalometrics helps in finding out whether the fault is in the maxilla or mandible in the cases of Cl II or Cl III. Also in the maxilla whether the malocclusion is due to fault in the basal bone or dento-alveolar or purely dental proclination. The treatment for each differs, from a bodily movement required in the basal bone fault, to just an incisor tipping in case of pure dental proclination. For assessing this the angles SNA, SNB, upper incisor angulation and position relative to N-Pog line are important.
  39. 39. ASSESSING VERTICAL RELATIONS: If growth in the posterior face (condylar growth) is greater than that in the anterior face (growth in facial sutures and alveolar growth), it causes forward rotation; while growth of anterior face greater than posterior face causes backward rotation. Equal growth produces no rotation but only parallel displacement. Mandibular rotation not only produces retro/prognathism but also deep/open bite. Therefore by determining this rotation, it is helpful in treatment planning. With forward rotation, treatment of Cl III and deep bite are difficult. With backward rotation, treatment of Cl II and openbite are difficult. Maxillary rotation occurs in midface which is partly due to growth and rest due to occlusal forces and gravity. Rotation also develops during headgear therapy and specially developed activators. Therapeutic parallel displacements of the maxilla enforced by translation are less liable to relapse. Measuring the centre of such rotation is possible by superimposing cephalometric radiographs taken before and after treatment.
  40. 40. AIMS OF INTERPRETATION OF THE MEASUREMENTS  To determine the skeletal structure and facial type.  To establish relationship between max. and man. base and determine type of growth.  To assess dental relationships.  To analyse the soft tissues regarding aetiology and prognosis.  To establish location of malocclusion and in the facial skull and determine, the extent to which it is skeletal / dentoalveolar.  Treatment planning, and also to determine how far, the treatment can be causal and how far merely compensatory (for skeletal abnormalities).
  41. 41. GROWTH PREDICTION The site, direction, growth potential, growth timing and growth pattern have to be determined. Generally horizontal growth changes are easily predictable than vertical changes.  Forecast Grid: L E Johnston has produced a diagram on the assumption of regular annual changes and an average direction of growth. He feels accurate prediction can be made in 65% of the cases. In this forecast grid each point was advanced one grid per year.
  42. 42.  Rickett's short term prediction makes distinction between vertical and horizontal growth. Rickett's Computer Analysis considers individual growth curves for separate regions. The computer diagnosis requires the patient to be of a certain age. During growth noticeable increase in linear dimensions of N-Me, S-Gn, Ar-Gn occurs. There is an average increase in SN line. This is used for prediction of sagittal and vertical growth changes. Growth rate of different regional growth centres is different. Also age and function change the form of growth. In order to determine the stability of the results and length of retention period, growth following conclusion of treatment is determined .  Holdaway's Growth prediction: it is based on the average increase in SN line. We can assess the different possibilities of treatment, thus visualize certain treatment objectives. It has some 12 stages of superimposition and was found that horizontal growth was better predictable.
  43. 43. SUPERIMPOSITION Serial superimposition of cephalograms reveals the rate, amount and relative directions of the growth and treatment changes of facial structures, including the changes in maxillary mandibular relationships, and the relative changes in the soft tissue integument. It however does not reveal either the sites or mode of growth of bone. 2D information was interpreted of a 3D process. It demonstrates the sum total of apposition and resorption at that particular time without detailed intervening changes.
  44. 44. Maxillary Superimposition: A comparison of three methods for cephalometric evaluation of growth and treatment change was made by Neilson [AJO 1989 May]. Previous cephalometric studies have indicated an apparent stability of the growth patterns of both the maxilla and mandible. There is a parallel descent of the maxilla, in relation to the anterior cranial base, in which the nasal floor appeared to remain unchanged during growth. The technique most commonly used for evaluating growth and treatment changes has been to superimpose serial head films along the palatal plane from ANS to PNS with the films registered at ANS. Broadbent found that when superimposition was made on the palatal plane at ANS, the anterior surface of the maxilla and point A moved posteriorly. Brodie and Downs recommended the superimposition of the nasal floors and films registered at the anterior surface of the maxilla.
  45. 45. The superior and inferior surfaces of the hard palate have been recommended for maxillary superimposition to eliminate possible appositional growth at ANS. Moore suggested the superimposition along the palatal plane but registered at the pterygomaxillary fissure. Riedel coincided the infratemporal fossa and the posterior portion of the hard palate. Luder made superimposition on the anterior contour of the zygomatic process registered at the most inferior point of the process at key ridge. Studies of maxillary growth with metallic implants by Bjork and Skieller have demonstrated that the maxilla undergoes extensive differential remodeling- a resorptive lowering of the nasal floor, greater anteriorly than posteriorly. It showed that the zygomatic process of the maxilla does not undergo the same remodeling changes. In fact the anterior surface remains unchanged during growth with the exception of the most inferior part at key ridge and the most superior part at the orbital floor. There is appositional growth at the orbital foor.
  46. 46. On the basis of these findings, Bjork and Skieller have suggested a “structural method” for evaluating maxillary growth and treatment changes. The head films are superimposed on the anterior surface of the zygomatic processof the maxilla with the second head film oriented so that the resorptive lowering of the nasal floor is equal to the apposition at the orbital floor. In general the results of the comparitive study between the different methods of superimposition showed that the displacement of the dental landmarks was greater with the implant superimposition than with best fit. Comparison between the implant and the structural methods, showed no significant difference in the vertical plane. In the horizontal plane, overall less displacement was observed with the structural method.
  47. 47. Mandibular superimposition: In the workshop on cephalometry conducted in 1960 superimposition of radiographs along the lower border of the mandible was adopted. Superimposition of the inferior border, however, proved difficult because of the curving path of the radiographic outline; to overcome this problem, Downs suggested a single straight line from the lowest point on the external contour of the symphysis to the midpoint at the gonian angle. Bjork’s studies have shown, however, that the inferior border of the mandible undergoes extensive differential remodeling during growth. The anterosuperior border of the chin, inner cortical structure of the inferior border of the symphysis, lower contour of the developing molar tooth germ and mandibular canal could be used to analyze mandibular growth. This was Bjork's structural method of superimposition. Ricketts developed a four-position analysis to study growth and treatment changes in the craniofacial complex. Position four uses the reference line, the corpus axis, which is used for analysis of mandibular changes.
  48. 48.  Cranial Base superimposition: 1) Superimposition on the best fit of anterior cranial base anatomy: Based on de Coster's observation of a stable basocranial line from inner contour of frontal bone to the anterior aspect of sella turcica Bjork advocated superimposing the anterior wall of sella turcica, the anterior contours of middle cranial fossa, the contours of cribriform plate and fronto ethmoidal crests and cerebral surfaces of the orbital roof and cortical layers of the frontal bone. The cribriform plate stops growing in length antero posteriorly after 2 yrs of age.
  49. 49. 2) Superimposition on sella nasion: It is found to be relatively stable. Steiner used SN plane with registration at S to evaluate mandibular positions. And registration at N to evaluate position of maxilla (SNA changes). Bjork used sella as the registration point to assess changes in both jaws. It is especially suitable during adoloscence because of constancy in relation SN and the deepest median contour of the anterior cranial fossa. But SN plane can't be used for facial contour estimation because of displacement of Nasion with growth of fronto nasal suture. Stramrud used sella ethmoidale (SE) because of variations of nasion SE and SN plane vary little after 3 yrs of age. Rickett's used the FHplane. 3) Superimposition at registration point R with Bolton-Nasion planes parallel: This method was introducedby Broadbent. A perpendicular to sella from Bo- N plane is erected. The mid point of this line is registration point R. Superimposition is done with registration at R keeping Bo- N plane parallel over each film.
  50. 50. 4) Superimposition over basion nasion plane: Advocated by Ricketts. A point called pterygoid point is selected at the lower rim of foramen rotundurn as the highest and most posterior point of the pterygopalatine fossa. A line from Pt to Gnathion constitutes the central axis. Atr, the inter section of Ba- N and central axis is located at a point CC which is used as a reference centre. The angle between Ba-N and central axis indicates the position of the mandible relative to cranial base. The direction of mandibular growth is evaluated by changes in the direction of the central axis. Registration at nasion depicts changes in position of maxilla through movement of Pt. The best fit method of anterior cranial base is better than others because it takes into consideration the detailed individual anatomy of the cranial base, rather than simplifying this anatomy into lines and points.
  51. 51. FINITE ELEMENT ANALYSIS It was first used to analyse cephalograms by Moss et al and Bookstein et al in 1985. It is an engineering principle that uses partial differential equations to interpolate loading values for intermediate points in irregular structures by dividing the structure into sets of regular geometric shapes (usually into a triangle). A finite element is a small block that is a part of the whole object under consideration. For example if you consider mandible, as a whole it is difficult to predict the growth pattern of the mandible. However should the mandible be visualised as "broken into small regular geometric shapes" like a triangle the problem of mandibular growth has now broken into the problem of growth of the individual triangles. The exact growth can now be reproduced by reassembling the individual blocks. Recent advances in finite element allow irregular patterns for objects that are even non-homogeneous to be assessed (earlier only homogeneous materials were assessed by this method), and this allows for accurate reproduction of mandibular growth.
  52. 52. DISTINGUISHING BETWEEN NATURAL GROWTH FROM ORTHODONTIC CHANGES A Four-Step method to distinguish orthodontic changes from natural growth: (ROBERT MURRAY RICKETTS) [JCO 1975] Ricketts suggested a method of superimposition to accomplish this. Method of Superpositioning: The objective of the four position analysis is very simple- two skeletal and two dental. First, it attempts to analyze the skeleton in terms of the chin, and secondly the maxilla. This comes from Position One and Position Two, respectively. Position Three is for the maxillary teeth. Position Four is for the mandibular teeth.
  53. 53. Pitchfork Analysis: To evaluate growth and displacement of the maxilla and mandible and to register the movements of the upper and lower molars and incisors, Johnston developed his Pitchfork Analysis. Growth or displacement of maxilla and mandible are measured relative to the cranial base (SE registration). The changes in the upper and lower incisors are measured relative to basal bone. The dental and skeletal measurements were executed parallel to the mean functional occlusal plane (MFOP) and each was given a sign appropriate to its impact on molar or overjet correction. Positive- if it improved the relationship (as with forward growth of the mandible/distal movement of maxillary molars and incisors). Negative- if it made them worse (eg. forward growth of the maxilla or mesial movement of the maxillary dentition.)
  54. 54. Using the Bjork's method of superimposition the following were found: Mandibular symphyseal movement relative to maxilla, The displacement (as a result of growth, orthopedic changes, or functional shift) of maxillary and mandibular basal bone relative to cranial base. The movement of the first molars (measured at the mesial contact point and at a point midway between the apices) and central incisors (at the incisal edge) relative to basal bone.
  55. 55. CEPHALOMETRICS IN TREATMENT PLANNING: Effective treatment planning in depends on accurate diagnosis. *In cases of malocclusion due to muscular dysfunction some times inhibition therapy is suggested. Cephalometeric radiography makes its possible to judge whether after elimination of the dysfunction the growth trend is likely-to be normal . *Similarly the indication of activator therapy can be determined using cephalometrics: Three conditions are essential 1)SNB small -suggesting a small mandible 2)Growth pattern is horizontal 3)SNA normal - maxilla in normal position *Cervical headgear therapy is indicated when SNA is large with anteinclination of maxilla (large J angle.) *Discrepancy calculation is made to determine the amount of space available and that required. It is done models and radiographs. On radiographs, the distance from the lower incisor to N-Pog line is determined. This is the sagittal discrepancy.(SD). Total discrepancy (TD) is calculated from SD & DD (Dental Discrepancy which is calculated from a model. TD = SD + ½ DD Treatment is planned so that the lower incisors are not more than 4mm anterior to the N-Pog line.
  56. 56. *Planning Anchorage -three degrees of anchorage are found. Minimal Anchorage is needed when lower incisors are very upright and behind N-Pog line. Moderate Anchorage is needed when lower incisors after treatment will be 2-4mm anterior to N-Pog line. Maximum Anchorage is needed when lower incisors after treatment will be 4mm anterior to N-Pog line.
  57. 57. P-A View Frontal view is particularly important in cases of dentoalveolar & facial asymmetry, crossbites and functional mandibular displacements. There are different methods of analysis 1)Rickett ‘s- measures the nasal cavity width, maxillary, mandibular, intermolar & intercuspid widths by connecting bilateral identical points and measuring the distance between them. Symmetry is measured from the mid-sagittal plane and relating the points pogonion and ANS to it. 2)Svanholt and Solow analysis- it measures the relationships between the midlines of the jaws and dental arches. It measures the transverse maxillary and mandibular positions, transverse jaw relationship, position of upper and lower incisors and the compensation of upper and lower incisors. It incorporates variables that will be zero in symmetrical subjects. 3)Grayson analysis- it uses multiple planes at selected depths to analyse facial asymmetry. 4)Hewitt analysis- it is performed by dividing the craniofacial complex into constructed triangles-triangulation of face 5)Chierici analysis- focuses on asymmetry of upper face. 6)Grummon 's analysis
  58. 58. COGS (CEPHALOMETRIES FOR ORTHOGNATHIC SURGERY) It was developed by Burstone and Legan. Normally during orthodontic treatment, the alveolar base is stable. But during orthognathic surgery, the alveolar base also changes position. The COGS system describes the horizontal and vertical position of facial bones by use of a constant coordinate system. 1. The chosen landmarks and measurements can be altered by various surgical procedures. 2. The comprehensive appraisal includes all of the facial bones and a cranial base reference. 3. Rectilinear measurements can be readily transferred to a study cast for mock surgery. 4. Critical facial skeletal components are examined. 5. Standards and static's are available for variations in age and sex. 6. Systematised approach to measurements that can be computerised. 7. COGS appraisal describes dental, skeletal and soft tissue variations.
  59. 59. PHOTOCEPHALOMETRY It is an attempt to obtain a more accurate and detailed information of the soft tissues in head views by superimposing co-ordinated head films with photographs. !t was developed for patients requiring orthognathic surgery. The assumption behind this technique is that the photographic images can be enlarged so that metal markers placed on the patient's skin are accurately superimposed on the corresponding radio opaque images on the cephalogram. The benefits are ~ A more detailed visualisation of the soft tissues in the frontal and lateral views. ~ A more accurate analysis of soft and hard tissue relationships, particularly of soft tissue thickness. There are 2 errors inherent in this method ~ Magnification distortion errors in superimposition of photographic cephalometric image. ~ Landmark identification The photocephalometric apparatus is adaptation of the standard cephalometric set-up
  60. 60. DIGIGRAPH A software product Digigraph enables clinicians to perform non-invasive and non-radiographic cephalometric analysis. This device uses sonic digitizing electronics to record cephalometric landmarks by lightly touching the sonic digitising probe to the patient and pressing the probe button. The probe emits a sound and the corresponding landmark is recorded sonically by the microphone array. Using this cephalometric analysis and monitoring of the patient's treatment progress is performed as often as desired without radiation exposure. Also data collection is non-invasive and efficient. It is very useful in quatifying facial asymmetries.
  61. 61. DIGITAL COMPUTED RADIOGRAPHY SYSTEM (CR) CR system operates with a punctiform X-ray beam which stimulates a 2-D memory sensor, in the space of only 1/100 th of a second. This memorised data is converted into electrical signal and then to a numerical 2-D image consisting pixels. The image is then enhanced by multiplying the value of each pixel and modifying the relationships between values of the pixels making up a certain area. This helps in varying the type of response that can be obtained from the detector. The imaging plate (analogous to a film), temporarily stores the X-ray energy and then emits it when scanned with a He-Ne laser. The blue light emitted is converted to an electrical signal which is read by the image reader. These signals are amplified and logarithmically converted before being transmitted through an analogical-digital converter which converts them to digital signals. .........contd.
  62. 62. Advantages >- Surpass conventional analogical radiology. >- Reduces radiation exposure by 28.6% for PA view and 58.4% for lateral Cephalometry. >- Converts information to digital signals (digital imaging) and enhanced information. >- Provide more sensitive, higher definition images. >- Optimisation of processing of images in terms of contrast, gradation, sharpness and granulosity, enhancing the diagnostic significance of the information. >- Process images to enable establishment of databases. >- Remote image transmission >- Increased reliability and accuracy >- Wide latitude. >- Modulation of the images (enlarging/reducing/changing contrast) is possible.
  63. 63. COMPUTERISED CEPHALOMETRICS This has two components- data acquisition and data management. X-ray beam attenuation is recorded directly and converted to a digital image. Sonic technology is also used nowadays. A variety of soft ware programmes are available ( like Por Dios, Dentofacial planner, etc. ) which use one of the pre-programmed analysis. They also allow superimposition, estimation of growth, simulation of orthodontic tooth movement, etc. Advantages >it is very fast. >It is only necessary to digitise the points directly on the cephalogram and calculations are done in seconds. >It removes human error >Facilitates use of double digitisation of landmarks, thus increasing reliability. >Easy storage and retrieval of values.
  64. 64. Thank you For more details please visit