Cephalometric analysis is the clinical application of cephalometry. It is analysis of the dental and skeletal relationships of a human skull. It is frequently used by dentists, orthodontists, and oral and maxillofacial surgeons as a treatment planning tool. Two of the more popular methods of analysis used in orthodontology are the Steiner analysis (named after Cecil C. Steiner) and the Downs analysis (named after William B. Downs). There are other methods as well which are listed below.
Cephalometric radiographs Cephalometric analysis depends on cephalometric radiography to study relationships between bony and soft tissue landmarks and can be used to diagnose facial growth abnormalities prior to treatment, in the middle of treatment to evaluate progress, or at the conclusion of treatment to ascertain that the goals of treatment have been met.Predoctoral Orthodontic Laboratory Manual 2008, Department of Undergraduate Orthodontics, New Jersey Dental School A Cephalometric radiograph is a radiograph of the head taken in a cephalometer (cephalostat) that is a head-holding device introduced in 1931 by Holly Broadbent Sr. in USA. The Cephalometer is used to obtain standardized and comparable craniofacial images on radiographic films.
Machine and dimensions To carry out cephalometry, the X-ray source is placed a steady five feet away from the mid sagittal plane, with film situated just 15 cm from there. This allows for accurate measurements to be taken and recorded. Distance has a direct impact on cephalometric image magnification. With an object-to-film interval of 15 cm and a source-to-object span of 5 feet, magnification of anatomical landmarks will be reduced in all three dimensions.When attempting to analyze a patient's anatomy through lateral and frontal cephalograms, the challenge arises due to these images being two-dimensional projections of three-dimensional structures. Magnification and distortion as an outcome of traditional radiography further complicates the process by blurring important details.
Lateral cephalometric radiographs
Lateral cephalometric radiograph is a radiograph of the head taken with the x-ray beam perpendicular to the patient's sagittal plane. Natural head position is a standardized orientation of the head that is reproducible for each individual and is used as a means of standardization during analysis of dentofacial morphology both for photos and radiographs. The concept of natural head position was introduced by Coenraad Moorrees and M. R Kean in 1958 and now is a common method of head orientation for cephalometric radiography.
Registration of the head in its natural position while obtaining a cephalogram has the advantage that an extracranial line (the true vertical or a line perpendicular to that) can be used as a reference line for cephalometric analysis, thus bypassing the difficulties imposed by the biologic variation of intracranial reference lines. True vertical is an external reference line, commonly provided by the image of a free-hanging metal chain on the cephalostat registering on the film or digital cassette during exposure. The true vertical line offers the advantage of no variation (since it is generated by gravity) and is used with radiographs obtained in natural head position.
Posteroanterior (P-A) cephalometric radiograph A radiograph of the head taken with the x-ray beam perpendicular to the patient's coronal plane with the x-ray source behind the head and the film cassette in front of the patient's face. PA ceph can be evaluated by following analyses that have been developed through the years: Grummon analysis MSR Hewitt analysis Svanholt-Solow analysis Grayson analysis
Cephalometric tracing A cephalometric tracing is an overlay drawing produced from a cephalometric radiograph by digital means and a computer program or by copying specific outlines from it with a lead pencil onto acetate paper, using an illuminated view-box. Tracings are used to facilitate cephalometric analysis, as well as in superimpositions, to evaluate treatment and growth changes. Historically, tracings of the cephalometric radiographs are done on an 0.003 inch thick matte acetate paper by using a #3 pencil. The process is started by marking three registration crosses on the radiograph which are then transferred to the acetate paper.
Anatomical structures are traced first and some structures are bilateral and have tendency to show up as two separate lines, should have an "average" line drawn which is represented as a broken line. These landmarks could include inferior border of mandible.
Cephalometric landmarks The following are important cephalometric landmarks, which are points of reference serving as datum references in measurement and analysis. (Sources: Proffit; others.)
Landmark points can be joined by lines to form axes, vectors, angles, and planes (a line between 2 points can define a plane by projection). For example, the sella (S) and the nasion (N) are points that together form the sella-nasion line (SN or S-N), which can be projected into the SN plane. A prime symbol () usually indicates the point on the skin's surface that corresponds to a given bony landmark (for example, nasion (N) versus skin nasion ().
Landmark name Landmark symbol Comments A point (subspinale) A Most concave point of anterior maxilla A point–nasion–B point angle ANB Average of 2° ± 2° B point (supramentale) B Most concave point on mandibular symphysis basion Ba Most anterior point on foramen magnum anterior nasal spine ANS Anterior point on maxillary bone articulare Ar Junction between inferior surface of the cranial base and the posterior border of the ascending rami of the mandible Bolton point Point at the intersection of the occipital condyle and Foramen Magnum at the highest notch posterior to the occipital condyle cheilion Ch Corner of oral cavity chresta philtri Chp Head of nasal filter condylion Most posterior/superior point on the condyle of mandible dacryon dac Point of junction of maxillary bone, lacrimal bone, and frontal bone endocanthion En Point at which inner ends of upper and lower eyelids meet (medial canthal point) exocanthion (synonym, ectocanthion) Ex Point at which outer ends of upper and lower eyelids meet (lateral canthal point) frontotemporal Ft Most medial point on the temporal crest glabella Most prominent point in the median sagittal plane between the supraorbital ridges gnathion Gn Point located perpendicular on mandibular symphysis midway between pogonion and menton gonion Go Most posterior inferior point on angle of mandible. Can also be constructed by bisecting the angle formed by intersection of mandibular plane and ramus of mandible key ridges Posterior vertical portion and inferior curvature of left and right zygomatic bones labial inferior Li Point denoting vermilion border of lower lip in midsagittal plane labialis superior Ls Point denoting vermilion border of upper lip lower incisor L1 Line connecting incisal edge and root apex of the most prominent mandibular incisor menton Me Lowest point on mandibular symphysis soft tissue menton M Lowest point on soft tissue over mandible nasion N Most anterior point on frontonasal suture soft tissue nasion Point on soft tissue over nasion odontale Highest point on second vertebra orbitale Or Most inferior point on margin of orbit opisthion Op Most posterior point of foramen magnum pogonion Pg Most anterior point of mandibular symphysis soft tissue pogonion P Soft tissue over pogonion porion Po Most superior point of outline of external auditory meatus machine porion Superior-most point of the image of the ear rod posterior nasal spine PNS Posterior limit of bony palate or maxilla pronasale (synonyms, pronasal or pronasion) Prn Soft tissue point on tip of nose prosthion (supradentale, superior prosthion) Pr The most inferior anterior point on the maxillary alveolar process between the central incisors PT point PT Point at junction between Ptm and foramen rotundum (at 11 o'clock from Ptm) pterygomaxillary fissure Ptm Point at base of fissure where anterior and posterior wall meet. Anterior wall represents posterior surface of maxillary tuberosity registration point A reference point for superimposition of ceph tracings sella (that is, sella turcica) S Midpoint of sella turcica sphenoethmoidal suture SE the cranial suture between the sphenoid bone and the ethmoid bone sella–nasion line SN or S–N Line from sella to nasion sella–nasion–A point angle SNA or S-N-A Average of 82 degrees with +/- of 2 degrees sella–nasion–B point angle SNB or S-N-B Average of 80 degrees with +/- of 2 degrees sublabialis Sl subnasale (synonyms, subnasal or subnasion) Sn In the midline, the junction where base of the columella of the nose meets the upper lip stomion inferius Sti Highest midline point of lower lip stomion superius Sts Highest midline point of upper lip throat point Junction of inferior border of mandible and throat tragion Notch above the tragus of the ear where the upper edge of the cartilage disappears into the skin of the face trichion Tr Midline of hairline upper incisor U1 A line connecting the incisal edge and root apex of the most prominent maxillary incisor xi point Xi An approximate point for inferior alveolar foramen
Cephalometric planes Cephalometric planes are commonly used in different cephalometric analyses. Cephalometric planePlane symbolDefinition palatal plane ANS-PNSThis plane is formed by connecting ANS to PNS and is used to measure the vertical tilt of maxilla SN plane SN planeThis plane represents the anterior cranial base and is formed by projecting a plane from the sella-nasion line Frankfort horizontal plane (Frankfurt horizontal plane)P-OrThis plane represents the habitual postural position of the head. condylar planeCo-OrThis plane can be used as an alternate to Frankfort horizontal plane. functional occlusal planeFOPThis plane passes is formed by drawing a line that touches the posterior premolars and molars. Downs occlusal planeDOPThis plane is formed by bisecting the anterior incisors and the distal cusps of the most posterior in occlusion. mandibular plane Go-GnThis plane is formed by connecting the point gonion to gnathion at the inferior border of the mandible. facial plane N-PgThis vertical plane is formed by connecting nasion to pogonion as described in the Schudy analysis. Bolton planeThis plane is formed by connecting the Bolton point to nasion. This plane includes the registration point and is part of the Bolton triangle.
Classification of analyses The basic elements of analysis are angles and distances. Measurements (in degrees or millimetres) may be treated as absolute or relative, or they may be related to each other to express proportional correlations. The various analyses may be grouped into the following:
Angular – dealing with angles Linear – dealing with distances and lengths Coordinate – involving the Cartesian (X, Y) or even 3-D planes Arcial – involving the construction of arcs to perform relational analyses These in turn may be grouped according to the following concepts on which normal values have been based: Mononormative analyses: averages serve as the norms for these and may be arithmetical (average figures) or geometrical (average tracings), e.g. Bolton Standards Multinormative: for these a whole series of norms are used, with age and sex taken into account, e.g. Bolton Standards Correlative: used to assess individual variations of facial structure to establish their mutual relationships, e.g. the Sassouni arcial analysis
Cephalometric angles According to the Steiner analysis:
ANB (A point, nasion, B point) indicates whether the skeletal relationship between the maxilla and mandible is a normal skeletal class I (+2 degrees), a skeletal Class II (+4 degrees or more), or skeletal class III (0 or negative) relationship.