GITAM DENTAL COLLEGE & HOSPITAL
ORAL AND MAXILLOFACIAL SURGERY
SEMINAR ON CEPHALOMETRICS IN ORTHOGNATHIC SURGERY
Presente d By: Dr. DORCUS PRIYA EDWIN
AIM & OBJECTIVES
RADIOGRAPHIC CEPHALOMETRIC TECHNIQUE
TRACING TECHNIQUE AND IDENTIFICATION OF LANDMARKS
SOFT TISSUE ANALYSIS
HARD TISSUE ANALYSIS
CEPHALOMETRIC PREDICTION TRACING
LIMITATIONS & CONTROVERSIES IN CEPHALOMETRICS
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 â€œthe art of measuring skulls of animals so as to discover their specific differencesâ€?. 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.
Orthognathic surgery is routinely performed for patients with dentofacial deformity and has been conducted for more than 100 years. Orthognathic surgery has created new and exciting opportunities in the treatment of patients with dentofacial deformities. TREATMENT OBJECTIVES IN ORTHOGNATHIC SURGERY: 1. Function 2. Esthetics 3. Stability The success of orthognathic surgery depends on the effective communication between the orthodontist, patient and maxillofacial surgeon.
Treatment should commence only after both the orthodontist and surgeon have consulted with the patients and the treatment plan should be jointly prepared (records can be duplicated). A complete examination of the patient should include: 1. General patient evaluation a. Medical history b. Dental evaluation
i. History ii. General evaluation iii. Periodontal considerations iv. Occlusal-oral function evaluation
2. Sociopsychologic evaluation
3. Esthetic facial evaluation a. Frontal analysis b. Profile analysis 4. Radiographic evaluation a. Lateral cephalometric evaluation b. Antero-posterior cephalometric evaluation c. Full mouth periapical evaluation d. Panoramic evaluation 5. Occlusion and study cast evaluation a. Intra-arch relationship b. Interarch relationship 6. Temporomandibular joint evaluation
CEPHALOMETRICS is a technique employing oriented radiographs for the purpose of making head measurements. The term cephalometrics is used to describe the analysis and measurements made on a cephalometric radiograph. The use of cephalometrics for orthodontic diagnosis and treatment planning in modern times owes much to some of the early works laid down by certain pioneers of science, who carefully and meticulously studied the osteology of the cranium. Cephalometric normative values have been identified as guidelines to diagnosis and treatment planning. Cephalometric analysis has been used as a standard because of the ease of procuring, measuring and comparing hard tissue structures. The belief that treating to cephalometric hard tissue norms results in a pleasing face is far behind in the thoughts of the current trend of diagnosis and treatment planning. The information from lateral and posteroanterior cephalometric radiographs forms an important part of the database for orthognathic surgical treatment planning. Although clinical evaluation must be the primary treatment tool in determining surgical treatment of the orthognathic patient, cephalometric analysis is a helpful diagnostic guide. The primary objective of treatment is not to make the patientsâ€™s cephalometric measurements normal, but rather to make the facial appearance harmonious and occlusal function normal.
AIM & OBJECTIVES -
To understand the technical aspects, landmarks, lines and planes of cephalometrics
To help in orthodontic diagnosis by enabling the study of skeletal and soft tissue structures.
Describe the subjectâ€™s dento-facial morphology
Quantitative description of morphological deviations
Make diagnostic and treatment planing decisions
HISTORY PRIOR TO THE ADVENT OF RADIOGRAPHY The assessment of cranio-facial structures forms a part of orthodontic diagnosis -
Historically human form has been measured for many reasons:
1. self portrayal in sculpture, drawing and painting. 2.
relation of physique - health, temperament and behavioral traits.
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. 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 3000 BC. 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).
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.
Albrecht Durer (1471-1528 AC) was a brilliant, unusually productive and exuberant artist of great virtuosity. The sixteenth century saw the first truly scientific attempt at cranial measurement
introduction by Spigel (1578-1625AC) of the “lineae cephalometricae”. Spigel’s linear cephalometricae consisted of four lines: the facial, occipital, frontal, & sincipital lines. Craniometry can be said to be the forerunner of cephalometry. Craniometry involved the measurement of craniofacial dimensions of skulls of dead persons. This method was not practical in living individuals due to soft tissue envelop which made direct measurements difficult and far less reliable. The evolution of cephalometry in the twentieth century is universally linked to Edward Angle’s publication of classification of malocclusion. With various motives and methods, mathematics of measurement was applied to human form. The discovery of x-rays in 1985 by Roentgen revolutionized dentistry. It provided a method of obtaining the inner craniofacial measurements with quite a bit of accuracy and reproducibility. In 1922 paccini standardized the radiographic head images by positioning the subjects against a film cassette at a distance of 2 metres from the x-ray tube. In 1931 Broadbent in USA and Hofrath in Germany simultaneously presented a standardized cephalomertic technique using a high powered x-ray machine and a head holder called cephalostat.
RADIOGRAPHIC CEPHALOMETRIC TECHNIQUE The patient is positioned within the cephalostat using adjustable bilateral ear rods placed within each auditory meatus. The midsagittal plane of the patient is vertical and parallel to the film plane and perpendicular to the x-ray beam. The patient’s Frankfort plane (ie line connecting the superior border of the external auditory meatus and infraorbital rim) is oriented parallel to the floor. There is always a varying amount of magnification in any radiograph. The
amount of magnification is determined by the ratio of x-ray source-object distance and to source-to-film distance.
CEPHALOMETRIC LANDMARKS 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. Reliable evaluation of a cephalometric radiograph depends on accurate definition and localization of landmarks; there are certain soft t issue landmarks that are essential to the basic understanding of the various analyses used today in clinical dentistry.
HARD TISSUE LANDMARKS: •
A-point (Point A, Subspinale, ss) : the deepest point (most posterior) midline point on
the curvature between the ANS and prosthion •
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
Gonion (Go): the most posterior inferior point on the outline of the angle of the
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
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
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
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.
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 within 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.
TRACING TECHNIQUE AND IDENTIFICATION OF LANDMARKS Before any attempts are made to trace a cephalometric head film, one should be thoroughly familiar with gross anatomy of head, especislly the bony componenets of cranium and face. It
should be understood that a 2-dimentional cephalogram represents a 3-dimentional object and that the bilateral structures will be projected onto the film. Bilateral structures are traced independently. An average is then drawn by visual approximation, which is represented by a broken line. TRACING EQUIPMENT: 1. A lateral cephalogram with usual dimensions 8x10 inches 2. Acetate matte tracing paper (0.003 inches thick and 8x10 inches) 3. A sharp 3H drawing pencil or fine felt-tipped pen 4. Masking tape 5. Protractor 6. Viewbox 7. Pencil sharpener and eraser
GENERAL CONSIDERATIONS: 1. Start with placing the cephalogram on the view box with patientâ€™s image facing to right 2. Tape the four corners of the radiograh to the view box 3. With a fine felt tipped black pen draw 3 crosses on the radiograph, two on the cranium
and one on the cervical vertebrae. These registration crosses helps in reorienting the acetate sheet for later verification. 4. Place the matte acetate sheet on the radiograph and secure it to radiograph and
viewbox 5. After firmly affixing the acetate film trace the three registration crosses
6. Print the patient’s name, record number, age, the date the cephalogram was taken and
your name in the bottom left hand corner of the acetate tracing 7. Begin tracing by identifying the relevant landmarks 8. While tracing use smooth continuous pressure on the pencil. Whenever possible trace
image lines without stopping or lifting the pencil. Avoid erasures.
LINES AND PLANES OF LATERAL CEPHALOMETRICS A cephalometric evaluation of the craniofacial complex requires a plane of reference from which we can assess the location of various anatomic structures. Tradit ionally two planes have been used, namely the sella turcica-nasion (SN) plane and the Frankfort horizontal (FH). 1) Blumenbach’s plane (Resting horizontal plane) - It is the plane formed as the skull,
minus the mandible rest on a flat horizontal surface. Entails the skull resting anterior on maxillary teeth and posterior either on occipital condyles or on the mastoid process. 2) Broadbent’s line (S-N reference line) – From sella to nasion. 3) Broadbent Bolton line – Line from Bolton patient to nasion. 4) Broca’s line – Extends from true anatomic prosthion to the lower most point of the
occipital condyle. When skull is resting on horizontal surface. 5) Camper’s line – Line extending from tip of ANS to the centre of external auditory
meatus. Camper’s plane is a triangular plane formed by two lines from tip of ANS to each external auditory meatus. 6) Decoster’s line – This is the only line that is not linear connection of two points. It
represents an actual anatomical contour of the planoethmoidal line from internal plate
of frontal bone down through roof of cribriform plate to the anterior portion of sella turcica. 7) Frankfort horizontal plane) – Its origins date back to the international congress on
prehistoric anthropology and archaeology, held in Frankfort in 1882. The line runs from orbitale to porion. It is supposed to represent the ideal horizontal position of the head when the patient stands erect. 8) Palatal plane – Line running from ANS to PNS. 9) His plane – Runs from acanthion to opisthion. 10)
Hold way line – Also referred as harmony line was developed by R.A. Holdaway and is strictly a soft tissue profile assessment reference line. Runs from soft tissue pogonion to vermilion border of upper lip.
Huxley’s line – Runs from nasion to basion and referred as nasion – basion line. It would be the near perfect base reference line for research purposes on growth and development.
Mandibular plane – Four different mandibular planes. Steiner – Line joining Go and Gn Downs – Line joining Go and Me Tweed and Ricketts – Straight line tangent to the lower most border of mandible. Bimpler’s line – Line from menton to antigonial notch.
Margolis line – Line runs from nasion to spheno-occipital-synchondrosis.
Occlusal plane – 3 occlusal planes. First plane – Line joining midpoint of overlap of M-B cusps of upper and lower first molars with point bisecting overbite of incisions. Used by Downs and Steiner. Second plane – Used by Ricketts and in Wits analysis called as functional occlusal plane and is line joining the midpoint of the overlap of M-B cusp of I st molars and buccal cusps of premolars or deciduous molars. Third plane – Line joining midsection of molar cusps to the tip of upper incisors.
Orbital plane – Plane perpendicular to FH plane at orbitale.
Ramal plane – Line tangent to posterior border of ramus of mandibular.
Rickett’s esthetic line –Extends from soft tissue tip of nose to the most anterior portion o profile of soft tissue chin.
Von Ihering’s line – Orbitale to center of external auditory meatus.
Y-axis – Given by Downs and extends from sella to gnathion.
Constructed horizontal (cHP) plane - Legan and Burstone suggest using a constructed horizontal . This is a line drawn through nasion at an angle of 7 degrees to the SN line. This constructed horizontal tends to be parallel to true horizontal . However, in those cases in which SN is excessively angulated, even the constructed horizontal would not approximate true horizontal, in which case an alternative reference line must be sought.
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.
METHODS OF CEPHALOMETRIC ANALYSIS
Two basic approaches -
Metric approach - use of selected linear and angular measures
Graphic approach - “overlay” of individual’s tracing on a reference template and visual inspection of degree of variation
In 1946, Dr. Charles Tweed developed Tweeds diagnostic triangle. First true classic full scale cephalometric analysis developed by William B. Downs in 1948. In 1953, Dr. C.C. Steiner presented his famous Steiner’s analysis. Riedel in 1952 developed SNA and SNB angle. Sassouni (1995) described total archial analysis. Rickets (1960) give dynamic analysis to study morphology of a patient at different stages of development or treatment. Jacobson’s ‘Wits’ appraisal (1975) was used for assessing horizontal disharmony of the jaw. For surgical correction quadrilateral analysis Dipaolo (1970) and an analysis by McNamara (1984) developed. BURSTONE HARD TISSUE ANALYSIS: PLANES •
Constructed points like Gnathion & Gonion
CRANIAL BASE: Length of cranial base is measured from Articulare to nasion parallel to HP •
Ar-PTM is measured parallel to HP to determine the horizontal distance between the posterior aspects of mandible and maxilla.
– 37.1 +/- 2.8
Female – 32.8+/-1.9
Increase or decrease in these values indicates prognathism/retrognathism
PTM – N :MALE 52.8 +/- 4.1; FEMALE 50.9 +/- 3
HORIZONTAL SKELETAL PROFILE ANALYSIS In this analysis all measurements are made parallel to HP N-A-Pg(angle) - This measurement indicates the degree of skeletal convexity
– 3.9 +/- 6.4o Female – 2.6 +/- 5.1o ; + ve angle indicates convex face; -ve angle
indicates concave face
N-A (Linear) - Here apical base of maxilla is related to N. Used to determine if anterior
part of maxilla is protrusive/retrusive. Male
– 0.0 +/- 3.7 Female - -2 +/- 3.7; +ve
indicates prognathism ; -ve indicates retrognathism N-B (Linear) - Here apical base of mandible is related to N. Male
- -5.3 +/- 6.7;
Female - -6.9 +/- 4.3 ; This quantitates the AP position of mandible and degree of mandibular horizontal dysplasia N-Pg (Linear) - This indicates prominence of chin. Used to determine discrepancy in
alveolar process, chin or mandibular proper Also determines the discrepancy in genials Male
- -4.3 +/- 8.5; Female - -6.5 +/- 5.1
VERTICAL SKELETAL ANALYSIS •
In this analysis all measurements are made perpendicular to HP.
Reflects the anterior, posterior or complex dysplasia of face.
N-ANS(Linear) - It signifies the middle third facial height. Male
– 54.7 +/- 3.2
Female – 50 +/- 2.4
ANS-GN(Linear) - It signifies the lower third facial height. Male Female – 61.3 +/- 3.3
– 68.6 +/- 3.8;
PNS-N(Linear) - It signifies the posterior maxillary height Male
– 53.9 +/- 1.7
Female – 50.6 +/- 2.2
MP-HP(Angle)- It signifies the posterior divergence of mandible shown by MP angle. The angle relates the posterior facial divergence with respect to anterior facial height. Male - 23o +/- 5.9o ; Female – 24.2o +/- 5o
VERTICAL DENTAL ANALYSIS •
Measurements for this analysis -
UI perpendicular to NF - It denotes the anterior maxillary dental height. Aids to evaluate the total vertical dimensions of premaxilla from approximate piriform aperture perpendicular to tip of maxillary incisor crown. Signifance: indicates how far the incisor have erupted in relation to nasal floor. Male - 30.5 +/- 2.1; Female – 27.5 +/- 1.7
LI perpendicular to MP - This measures the anterior mandibular dental height. Determines the total dmensions of anterior mandible from MP perpendicular to tip of mandibular incisor crown. Signifance: denotes how far the incisor have erupted in relation to MP ; Male - 45 +/- 2.1; Female – 40.8 +/- 1.8
U6 perpendicular to NF - This measures the posterior maxillary dental height. Aids to evaluate the posterior dental mandibular vertical height/molar eruption Male - 26.2 +/- 2 ; Female – 23 +/- 1.3
L6 perpendicular to MP - Measures the posterior mandibular dental height; Male - 35.8 +/- 2.6; Female – 32.1 +/- 1.9
MAXILLA AND MANDIBLE ANALYSIS •
This is analysed by following measures -
PNS – ANS - Denotes the total effective length of maxilla. Male - 57.7 +/- 2.5 Female – 52.6 +/- 3.5
AR – GO - Quantitates the length of mandibular ramus Male - 52 +/- 4.2 ; Female – 46.8 +/- 2.5
GO - PG - Aids in establishing the length of mandibular body. Male – 83.7 +/4.6; Female – 74.3 +/- 5.8
AR-GO-GN - This angle denotes relationship between ramal plane and MP. Aids in diagnosis of skeletal open/closed bite problems. Male – 119.1 o +/- 6.5o ; Female – 122o +/- 6.9o
B – PG - This measurements denotes prominence of chin related to mandibular denture base. Male - 8.9 +/- 1.7; Female – 7.2 +/- 1.9
DENTAL ANALYSIS Measurements for this analysis -
OP – HP (Angle) - OP denotes its steepeness/flatness. Increased angle: assess skeletal open bite, lip incompetence,increased facial height, retrognathia. Decreased angle: assess deep bite, decreased facial height, lip redundancy. Male - 6.2 o+/- 5.1o ; Female – 7.1o+/-2.5o
A – B(Linear) - This linear measurements represents the relationship of maxillary and mandibular apical base to OP Male - -1.1 +/- 2 ; Female - -0.4 +/- 2.5 Significance: if A-B distance is large with point B projected posteriorly to point A denotes class II occlusion and vice versa
U1 – NF(Angle) - Represents angulations of maxillary central incisors to NF Male - 111 o +/- 4.7o Female – 112o +/- 5.3o Signifance: aids to determine the procumbency/recumbency of incisor . Vitals in assessing long term stability of dentition
L1 – MP(Angle) - Denotes angulation of mandibular incisors to MP; Male - 95.9 o+/- 5.2o Female – 95.9o+/-5.7o Significance: determines the procumbency/recumbency of lower incisor.
SOFT TISSUE ANALYSIS
The soft-tissue envelope of the face plays an important role in esthetics, functional balance and facial harmony. Today the soft t issue evaluation receives an awesome acknowledgement and is recognized by every cl inician that the success of orthodont ic treatment is closely related to the soft tissues changes of the face. VARIOUS SOFT TISSUE ANALYSIS HAVE BEEN PUT FORTH: Steiner Ricketts McNamara Merrifield’s Z angle Holdaway Burstone – COGS Arnett, Bergman et al - STCA Burstone CJ (1958) pointed out the importance of analyzing the soft t issues around the skeletal structures and out lined the procedure for taking the cephalograms used for analyzing the soft t issue. He pointed out that the average profile must be considered depending upon individual, ethnic, racial and imperial factors.
FACIAL FORMS ANALYSIS This analysis describes overall horizontal soft tissue profile. The following analysis is used:
Facial convexity angle(G-Sn-Pg) - Mean value 12o +/- 4o ; +ve value indicates a convex profile; -ve value indicates concave profile
Maxillary prognathism(G-Sn) - Describes the amount of maxillary excess/deficiency in AP ; +ve - maxillary retrusion; -ve - maxillary procumbency ; Mean value 6+/-3
Mandibular prognathism(G-Pg) - Mean value 0 +/- 4; Indicates mandibular prognathism/ retrognathism . Increase –ve value indicates mandibular deficiency
Vertical height ratio(G-Sn/Sn-Me) - Mean value 1:1 (G-Sn To Sn-Me) Inference : Ratio <1 denotes that disproportionality and there is large lower 3rd face height and vice-versa
Lower face throat angle(Sn-Gn-C) - Mean value - 100o +/- 7o
Lower vertical height depth ratio(Sn-Gn/C-Gn) - Mean value 1.2:1; Inference : Ratio>1 indicates short neck
LIP POSITION AND FORM ANALYSIS The following analysis is used -
Nasolabial angle(Cm-Sn-Ls) - Mean value 102o +/- 8o ; Inference : obtuse angle indicates maxillary hypoplasia and vice-versa
Upper lip protrution(Ls to Sn-Pg) - Mean value 3 +/- 1; Inference : Increased value indicates protrusion and vice-versa
Lower lip position(Li to Sn-PG) - Mean value 2 +/- 1; Inference: Denotes amount of lip protrusion
Mento labial sulcus(Si to Li-Pg) - Mean value 4 +/- 2; Inference: Assess prominence of the chin
Vertical lip chin ratio(Sn-Stms/Stmi-Me) - Aids to assess the lower 3 rd face. Lower 3rd face is divided into 3 parts: length of upper lip i.e distance from Sn-Stms shoule be approximately 1/3rd the total and distance from stmi to Me should be 2/3rd.
Maxillary incisor exposure(Stm-U1) - Distance from upper lip to maxillary incisor is the key factor in determining vertical position of maxilla. This corresponds to pleasing smile.
2mm of incisor exposure at rest is normal Inference: pt. with vertical maxillary excess tend to show a larger amount of upper incisor with lips in repose.
Interlabial gap(Stms-Stmi) - Mean value â€“ 2+/-2; Aids to measure the vertical distance between upper lip and lower lip with lips at rest. Inference: patient with vertical maxillary excess have increased interlabial gap and lip incompetence and vice-versa
SURGICAL-ORTHODONTIC CEPHALOMETRIC PREDICTION TRACING By Epker and Fish (1980 JCO) adopted in part from the mechanics developed by Ricketts for cephalometric analysis, growth prediction and visual treatment objective construction as presented by Bench, Gugino, and Hilgers. 1) To accurately assess the profile esthetic results which will result from the proposed
surgery, 2) To consider the desirability of simultaneous adjunctive procedures such as genioplasty,
suprahyoid myotomy, etc., 3) To help determine the sequencing of surgery and orthodontics (i.e., if the surgery is
done first will it be more difficult or easier to do the indicated orthodontics), 4) To help decide what type of orthodontics might best be employed (i.e., extraction
versus non-extraction) 5) To determine the anchorage requirements should extraction treatment be chosen -
The first step in producing a prediction tracing is to overlay a piece of acetate paper on the original cephalometric tracing and trace all structures which will not be significantly altered by the surgery and/or orthodontics
Determination of Ideal Vertical Position for the Upper Incisor.
Autorotation of the Mandible.
Placement of Teeth In Ideal Positions.
RECENT ADVANCES Although the time honoured process of hand tracing and analyzing cephalograms is still clinically useful, it has clear drawbacks. One major drawbacks is the amount of time required for tracing. Another is the difficulty of presenting the data in a form that the avarage patient can easily understand. In an effort to address these problems a process of digitalization made it possible to insert information on relative landmark positions into computer usable format. The various advances in cephalometrics are: Digital cephalometry Laser scanning Softwares - Dolphin - Vistadent - OPAL
LIMITATIONS OF VARIOUS CEPHALOMETRIC ANALYSIS COMMONLY USED
ANB angle as a measure of jaw Dysplasia •
According to Steiner, the SNA reading indicates whether face protrudes or retrudes bellow the skull. Although the ANB is a reliable indication of A-P jaw relationship in most instances, there are many situations in which this reading cannot be relied on.
The ANB angle in normal occlusions is generally 2 degrees. Angle greater than this mean value indicate tendency toward class II jaw disharmonies; smaller angles (negative readings) reflect class III jaw discrepancies. While this is an acceptable generalization, numerous instances exist in which this does not apply. Cephalometrics for you and me – Steiner – 1953 ;AJO
Porion and Orbitale are not accurate for our use as we are not dealing with dry skulls.
Points S and N are clearly visible in the X- ray pictures and can be located easily and accurately.
Emphasizes that points S and N are located in the mid sagittal plane of the head and therefore they are moved a minimum amount whenever the head deviates from the true profile position and that the points are located on hard non yielding tissue.
The same holds true for a rotation of the occlusal plane: backward (counterclockwise) rotation of the occlusal plane has a decreasing effect on the ANB angle, though sagittal basal relationships remain constant. Shortcomings of ANB angle
Taylor in 1969 pointed out that ANB angle did not always indicate true apical base relationship. Varied horizontal discrepancies of points A and B could give the same ANB measurement because variation in the vertical distance from nasion could compensate for other variation.
Beatty in 1975 reported that ANB angle is not always an accurate method of establishing the actual amount of apical base divergence.
As an alternative to ANB angle for measuring apical base discrepancy , he devised the AXD angle, where point- x is located by projecting point A on to a perpendicular to SN line. Point D is located in the bony sympyhsis as described by Steiner. The two variables, nasion and point B, were eliminated. He also introduced a linear measurement AD, to describe the A-P relationship of the jaws.
Cross evaluation with different reference planes is important and can be demonstrated with the ANB angle.
If one takes only the ANB angle to measure the relative position of maxilla and mandible to each other ,one must realize that any different horizontal or vertical position of point N and the location of the points A and B in the vertical plane will have an influence on the size of this angle and not on the actual sagittal relation of the two jaws. (Hussals and Nanda-1984) STEINERS ANALYSES - Acceptable compromises:
Steiner clearly recognized that cephalometric standards are merely gauges by which to determine more favorable compromises as a treatment goal. He developed a chart that reflects a number of average measurements of normal Dentofacial relationships.
Steiner recognized variations in antero -posterior jaw relations to each other.
The compromise describes the anticipated axial inclinations of the maxillary and mandibular incisors to the NA and NB lines at various ANB relationships.
Soft tissue analyses- Holdaway •
NASO LABIAL ANGLE – formed by two lines namely the columella tangent and an upper lip tangent. Arbitrary value is 90 to 110 degrees.
Legan and Burstone report a mean value of 102 +/- 4 degrees.
Scheidman et al drew a postural horizontal line through subnasale and further divided the nasolabial angle into columella tangent to postural horizontal ( 25 degrees) and upper lip tangent to postural horizontal ( 85 degrees).
They argue that each of these angles should be assessed individually in as much as they vary independently.
An apparently normal nasolabial angle may be oriented in an abnormal fashion, a fact that would be disclosed if the component angles were measured individually.
Although innumerable limitations exist in the field of cephalometrics. This is not to suggest that cephalometry is not a useful measurement tool for use by clinical orthodontist, it is still a very significant & effective diagnostic tool.
A combination of various cephalometric norms and variables should be compiled to arrive at a proper diagnosis.
REFERENCES: 1. Burstone CJ, Legan HL: Cephalometrics for orthognathic surgery, J Oral Surg
1978;36:269-277 2. Legan HL, Burstone CJ: Soft t issue cephalometric analysis for orthognathic surgery, J
Oral Surg 1980; 38:744-51 3. Text book of Radiographic Cephalometry by Alexander Jacobson. 4.
Text book of Orthodontic current principals & tech; 4th edn, by T.M.Graber & Robert .L. Vanarsadall
5. Textbook of Essentials of orthognathic surgery by Johan P Reyneke