Cephalometric Radiograph

A radiograph of the head taken in a Cephalometer (Cephalostat) that is a head-holding device introduced in 1931 by B. H. Broadbent in the USA and by H. Hofrath in Germany. The original design included two ear rods for insertion into the external auditory canals, an infraorbital pointer and a forehead clamp, to achieve parallelism of the Frankfort plane with the floor. The cephalometer is used to obtain standardized and comparable craniofacial images on radiographic film.

Lateral Cephalometric Radiograph

A radiograph of the head taken with the x-ray beam perpendicular to the patient’s sagittal plane. The beam most commonly enters on the patient’s right side, with the film cassette adjacent to the patient’s left side (so that the patient’s head is oriented to the right on the radiograph), but the reverse convention also is used.

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 C. F. A. Moorrees and M. R Kean in 1958 and now is a common method of head orientation for cephalometric radiography.

To accomplish natural head position, the patient is asked to look into a mirror placed in front of him/her at eye level (as if he/she were looking at the horizon), with the interpupillary line parallel to the floor. Advocates of this method maintain that 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. P-A cephalograms are usually taken for evaluation and treatment planning of patients with facial asymmetry.

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.

Computerized Cephalometrics

The process of entering cephalometric data in digital format into a computer for cephalometric analysis. Digitization (of radiographs) is the conversion of landmarks on a radiograph or tracing to numerical values on a two- (or three-) dimensional coordinate system, usually for the purpose of computerized cephalometric analysis. The process allows for automatic measurement of landmark relationships. Depending on the software and hardware available, the incorporation of data can be performed by digitizing points on a tracing, by scanning a tracing or a conventional radiograph, or by originally obtaining computerized radiographic images that are already in digital format, instead of conventional radiographs. Computerized cephalometrics offers the advantages of instant analysis; readily available race-, sex- and age-related norms for comparison; as well as ease of soft tissue change and surgical predictions.

Finite Element Analysis

Finite elemental analysis is used in digital imaging and is an engineering technique of stress analysis, the basic concept of which is the visualization of a structure as an assemblage of a finite number of discrete structural elements connected at a finite number of points. The finite elements are formed by figuratively "cutting the original structure into segments. " For two-dimensional applications, triangles of various sizes and shapes usually are the finite elements of choice. Each element retains the mechanical characteristics of the original structure. Some characteristics of the material have to be specified (depending on whether it is isotropic or not).

Additionally, a numbering system is required to identify the elements and their connecting points, called "nodes. " A coordinate system also must be established to identify uniquely the location of the nodal points. A large number of simultaneous linear equations are computer-generated, which establishes compatibility within each element.

The technique has some very distinct advantages as a research tool, among which is the ability to obtain an estimate of the stresses throughout the structure under consideration. Further, the inclusion of any type of anisotropy and inhomogeneity conceptually is possible by inserting the appropriate distribution of material properties at the nodes of the elements. However, when it is applied to structures such as a tooth, there are some practical limitations, as relatively little is known about the mechanical properties of dental and especially periodontal tissues.

Moire Diffraction

This is a technique with many applications in medicine, is used mainly to map three-dimensional contour. In orthodontics it has been used for evaluation of facial asymmetry. The technique uses a series of lines produced by a transparent grid. The grid is placed in front of the object that is to be contour-mapped. A light source is offset from the viewing angle. The light passes through the diffraction grading twice: firstly on its way from the source to the object and secondly after it has been reflected off the object. It then is recorded by a film or viewed by an investigator. An interference pattern of

light and dark lines or fringes is created; each fringe represents a set of equidistant points from the grid. The fringes appear superimposed on the object as a series of contour plots of similar elevation. The method is limited by the viewing angle of the system to the object. Areas of rapid elevation change on the object are difficult to characterize because of inability to distinguish the line separation. This requires evaluation of the object from different viewing angles.

Visual treatment objective (VTO)

A treatment planning and communication aid that may be used to define the tooth movements and/or surgical changes required to achieve the desired facial goals. Essentially it consists of the patient’s pretreatment lateral cephalometric tracing, modified to demonstrate the changes that are anticipated in the course of treatment. This can be accomplished with the help of a computer program. A VTO of a growing child is an estimate of the growth of a growing patient with the orthodontic treatment outcome, and is a very helpful tool in arriving at a final treatment plan. Visual treatment objectives performed for orthognathic surgical treatment planning are sometimes referred to as STOs (Surgical Treatment Objectives).

The construction of a VTO can be very helpful in exploring various treatment options, but it is important, once a plan is determined, that the clinician goes back and makes sure that it is the product of a logical and practical approach to the problem. The VTO can be linked directly to, and evaluated in conjunction with, the occlusogram.

Occlusogram

An occlusolgram is a graphic representation of the arches from the occlusal view. Occlusograms are mainly used as treatment planning aids to assist in defining the specific tooth movements required within and between arches (in the sagittal and transverse planes) to achieve treatment goals. An occlusogram is essentially a two-dimensional diagnostic setup and is directly correlated with the Visual Treatment Objective (VTO). It can be constructed from tracings of radiographs or photographic or photostatic copies of the occlusal aspects of the maxillary and mandibular study casts. The tracings of the

teeth of both arches are superimposed on each other to reproduce the existing occlusal relationship, using index points that are marked on the images or models and subsequently transferred to the tracings. Anticipated movements of individual teeth as well as the need for extractions then can be determined, to simulate the desired treatment goal.

Superimposition

Superimposition is the process of placing two images upon each other, registering on structures that remain relatively stable during the time period separating the two images, to evaluate the changes brought about by growth and/or treatment. In orthodontics, most commonly applies to cephalometric tracings or occlusograms.

Reference Lines

A reference line is a line that is used as a basis for superimposition, or for comparison when several measurements are performed. Reference lines ideally should be stable with time and should not be affected by treatment. Because the cant or inclination of all intracranial reference lines is subject to biologic variation, it often is claimed that they are unsuitable for meaningful cephalometric analysis. Registration of the head in its natural position has the advantage that an extracranial "true" vertical or horizontal line can be used as a reference line for cephalometric analysis.

Frontal plane (Coronal plane)

Any plane passing longitudinally through the body from side to side, at right angles to the median plane and dividing the body into front and back parts.

Transverse plane (Horizontal plane)

Any plane passing through the body at right angles to both the median and the frontal plane, dividing the body into upper and lower parts.

Median plane (Midsagittal plane)

The imaginary plane passing longitudinally through the middle of the body, dividing it into left and right halves.

Sagittal plane (Parasagittal plane)

Any vertical plane that passes through the body parallel to the median plane and divides the body into left and right parts.

Cephalometric landmarks

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 measurements.

In the definitions of the specific landmarks the following convention is used: "midsagittal" identifies landmarks lying on the midsagittal plane, "unilateral"

identifies landmarks corresponding to unilateral structures and "bilateral" applies to landmarks corresponding to bilateral structures.

SUBTERMS:

A-point (Point A, Subspinale, ss)Anterior nasal spine (ANS)Articulare (Ar)B-point (Point B, Supramentale, sm)Basion (Ba)Bolton (Bo)Condylion (Co)Crista galliDacryonGlabella (G)Gnathion (Gn)

Gonion (Go)Incision inferius (Ii)Incision superius (Is)Infradentale (Id, Inferior prosthion)L-pointMenton (Me)Nasion (N, Na)Opisthion (Op)Orbitale (Or)Pogonion (Pog, P, Pg)Porion (Po)Posterior nasal spine (PNS)Prosthion (Pr, Superior prosthion, Supradentale)Pterygomaxillary fissure (PTM, Pterygomaxillare)R-point (Registration point)Sella (S)Cervical point (C)Inferior labial sulcus (Ils)Labrale inferior (Li)Labrale superior (Ls)Pronasale (Pn)Soft tissue glabella (G’)Soft tissue menton (Me’)Soft tissue nasion (N’, Na’)Soft tissue pogonion (Pg’, Pog’)Stomion (St)Stomion inferius (Sti)Stomion superius (Sts)Subnasale (Sn)Superior labial sulcus (Sls)Trichion (Tr)Soft tissue gnathion (Gn’)

Ricketts Anatomical Tracing

Ricketts Points and Planes

Ricketts Frontal Anatomy

A-point (Point A, Subspinale, ss)

The deepest (most posterior) midline point on the curvature between the ANS and prosthion. Its vertical coordinate is unreliable and therefore this point is used

mainly for anteroposterior measurements. The location of A-point may change somewhat with root movement of the maxillary incisor teeth. (midsagittal)

Anterior nasal spine (ANS)

The tip of the bony anterior nasal spine at the inferior margin of the piriform aperture, in the midsagittal plane. It corresponds to the anthropological point acanthion and often is used to define the anterior end of the palatal plane (nasal floor). (midsagittal)

Articulare (Ar)

A constructed point representing the intersection of three radiographic images: the inferior surface of the cranial base and the posterior outlines of the ascending rami or mandibular condyles. It was meant to substitute condylion when the latter is not readily discernible. Any movement of the mandible (i.e. opening or closing) will change the location of articulare. (bilateral)

B-point (Point B, Supramentale, sm)

The deepest (most posterior) midline point on the bony curvature of the anterior mandible, between infradentale and pogonion. (midsagittal)

Basion (Ba)

The most anterior inferior point on the margin of the foramen magnum, in the midsagittal plane. It can be located by following the image of the slope of the inferior border of the basilar part of the occipital bone to its posterior limit, superior to the dens of the axis. (midsagittal)

Bolton (Bo)

The highest points on the outlines of the retrocondylar fossae of the occipital bone, approximating the center of the foramen magnum. Named after C. B. Bolton. (bilateral)

CC Point (CC) Ricketts

(Cranial Center) Crossing of the facial axis with the BaN plane

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. (midsagittal)

Condylion (Co)

The most superior posterior point on the head of the mandibular condyle. (bilateral)

Crista galli

A vertically elongated, diamond-shaped radiopacity, appearing between the orbital outlines on postero-anterior cephalometric radiographs. Its location is used to establish a midsagittal reference plane. (midsagittal)

Dacryon

The point of intersection of the frontomaxillary, lacrimomaxillary and frontolacrimal sutures. An anatomic reference point used to record interorbital distance. (bilateral) Orbital hypertelorism

The increased distance between the medial orbital walls, reflecting an increased distance between the orbits (greater than 2 standard deviations from the norm). The anatomic landmarks used commonly for the measure-ment of interorbital distance are the dacryon points (bilaterally). Hypertelorism is described on the basis of skeletal measurements, because the presence of epicanthal folds or strabismus (exotropia), or other soft-tissue variations such as increased distance between the medial canthi (telecanthus) clinically may give a false impression of hypertelorism. Orbital hypertelorism is common in a number of craniofacial malformations such as Crouzon syndrome and frontonasal dysplasia.

Compare with Telecanthus

DC Point (Ricketts)

Center of the neck of the condyle on the Basion Nasion line.

Glabella (G)

The most prominent point of the anterior contour of the frontal bone in the midsagittal plane. (midsagittal)

Gnathion (Gn)

The most anterior inferior point on the bony chin in the midsagittal plane. (midsagittal)

Gonion (Go)

The most posterior inferior point on the outline of the angle of the mandible. It may be determined by inspection or it can be constructed by bisecting the angle formed by the intersection of the mandibular plane and the ramal plane and by extending the bisector through the mandibular border. (bilateral)

Infradentale (Id) Inferior prosthion Pr

The most superior anterior point on the mandibular alveolar process, between the central incisors. (midsagittal)

Incision inferius (Ii) or B1 (Ricketts)

The incisal tip of the most labially placed mandibular incisor. (unilateral)

Incisian Inferius Root or BR (Ricketts)

Incision superius (Is) or A1 (Ricketts)

The incisal tip of the most labially placed maxillary central incisor. (unilateral)

Incision Superious Root or AR (Ricketts)

L-point

A point located in the anterior surface of the cortical plate, labial to the apices of the maxillary central incisors. Introduced by F. P. G. M. van der Linden, as a point representing the anterior border of the maxillary apical area. (midsagittal)

Labrale inferior (Li)

The point denoting the vermilion border of the lower lip, in the midsagittal plane. (midsagittal)

Labrale superior (Ls)

The point denoting the vermilion border of the upper lip, in the midsagittal plane. (midsagittal)

Menton (Me)

The most inferior point of the mandibular symphysis, in the midsagittal plane. (midsagittal)

Molar Upper First (Ricketts)

Point on the occlusal plane perpendicular to the distal surface of the crown of the upper first molar.

Molar Lower First (Ricketts)

Point on the occlusal plane perpendicular to the distal surface of the crown of the lower first molar.

Nasion (N, Na)

The intersection of the internasal and frontonasal sutures, in the midsagittal plane. (midsagittal

Opisthion (Op)

The most posterior inferior point on the margin of the foramen magnum, in the midsagittal plane. (midsagittal)

Orbitale (Or)

The lowest point on the inferior orbital margin. (bilateral)

Pogonion (Pog, P, Pg)

The most anterior point on the contour of the bony chin, in the midsagittal plane. Pogonion can be located by drawing a perpendicular to mandibular plane, tangent to the chin. (midsagittal)

Porion (Po)

The most superior point of the outline of the external auditory meatus ("anatomic porion"). When the anatomic porion cannot be located reliably, the superior-most point of the image of the ear rods ("machine porion") sometimes is used instead. (bilateral)

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 (nasal floor) at its posterior aspect. It can be located by extending the anterior wall of the pterygopalatine fossa inferiorly, until it intersects the floor of the nose. (midsagittal)

Pronasale (Pn)

The most prominent point of the tip of the nose, in the midsagittal plane. (midsagittal)

Prosthion (Pr, Superior prosthion, Supradentale)

The most inferior anterior point on the maxillary alveolar process, between the central incisors. (midsagittal)

Protruberance Menti (Pm) or Supra pogonion (Ricketts)

A point where the curvature of the anterior border of the symphysis changes from concave to convex,

Pterygoid Point (Pt) Ricketts

Lower lip of foramen rotundum (Represents the position of the sphenoid bone) posterior superior tangent of the pterygomaxillary fissure

Pterygoid Root (Pr) Ricketts

Most posterior point on the outlines of the pterygopalatine fossa

Pterygomaxillary fissure (PTM, Pterygomaxillare)

A bilateral, inverted teardrop-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. (bilateral)

R-point (Registration point)

A cephalometric reference point for registration of superimposed tracings,

introduced by B. H. Broadbent, Sr. , in his original presentation of the cephalometric technique. It is the midpoint on a perpendicular drawn from sella to the Bolton-nasion line. (midsagittal)

Sella (S)

The geometric center of the pituitary fossa (sella turcica), determined by inspectionóa constructed point in the midsagittal plane. (midsagittal)

Soft tissue glabella (Gí)

The most prominent point of the soft tissue drape of the forehead, in the midsagittal plane. (midsagittal)

Soft tissue menton (Meí)

The most inferior point of the soft tissue chin, in the midsagittal plane. (midsagittal)

Soft tissue nasion (Ní, Naí)

The deepest point of the concavity between the forehead and the soft tissue contour of the nose in the midsagittal plane. (midsagittal)

Soft tissue pogonion (Pgí, Pogí)

The most prominent point on the soft tissue contour of the chin, in the midsagittal plane. (midsagittal)

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. (midsagittal)

Stomion inferius (Sti)

The highest midline point of the lower lip. (midsagittal) if lips are apart

Stomion superius (Sts)

The lowest midline point of the upper lip. (midsagittal) if lips are apart

Subnasale (Sn)

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

Superior labial sulcus (Sls) Soft Tissue Point A

The point of greatest concavity on the contour of the upper lip between subnasale and labrale superius, in the midsagittal plane. (midsagittal)

Soft Tissue B or Inferior labial sulcus (Ils)

The point of greatest concavity on the contour of the lower lip between labrale inferius and menton, in the midsagittal plane. (midsagittal)

Trichion (Tr)

An anthropometric landmark, defined as the demarcation point of the hairline in the midline of the forehead. (midsagittal)

No Picture

Xi Point (Xi) approximate for Inferior alveolar foramen (Ricketts)

A constructed point located at the geographic center of the ramus as indicated

below.

Cephalometric lines (planes)

Most analyses utilize one or more cephalometric lines that are joining two landmarks, are tangent to an outline from a landmark, or are perpendicular to another line from a landmark.

SUBTERMS:

A-B planeBasion-Nasion line (Ba-N)Bolton planeCampers base planeDe Coster lineE-line (E-plane, Esthetic line of Ricketts)Facial axis of RickettsFacial plane (FP, Facial line)Frankfort horizontal plane (FH, Frankfort horizontal line, Auriculo-orbital plane, Eye-ear plane)H-line (Harmony line of Holdaway)Intergonial lineMandibular plane (MP, Mandibular line, ML)Nasion-perpendicularOcclusal plane (OP)Palatal plane (ANS-PNS, PP, Nasal line, Nasal floor, Spinal plane)Rees esthetic planeReference lineRiedel planeS-line (Esthetic plane of Steiner)Sella-Nasion line (SN, Nasion-Sella line, NSL)True horizontal lineTrue vertical lineY-axis (Growth axis)Z-line (Profile line of Merrifield)

A-B plane

A line joining points A and B. As part of the Downs analysis, the superior angle formed by the intersection of the A-B plane and the

facial line (N-Pog) is measured to evaluate the relation of the anterior limit of the apical bases to each other, relative to the facial line. This angle is negative in patients with skeletal Class II and positive in patients with skeletal Class III malocclusions.

Basion-Nasion line (Ba-N)

A line considered by some to represent the cranial base more accurately than the SN line or the Bolton plane.

Bolton plane

A line connecting points Bolton and nasion; an alternate representation of the cranial base.

Camper’s base plane

An anthropometric line connecting the center of the bony external auditory meatus and the anterior nasal spine. It was used as a

horizontal reference line for evaluation of prognathism on dry skulls, prior to establishment of the Frankfort horizontal plane.

No Picture

De Coster line

A reference line proposed by L. De Coster as a stable area for cephalometric superimposition. It extends from the image of the anterior clinoid process along the planum sphenoidale and the anterior cranial edge of the sphenoethmoidal synchondrosis to the cranial aspect of the cribriform plate, terminating at the internal osseous line of the frontal bone above the crista frontalis.

E-line (E-plane, Esthetic line of Ricketts)

A line tangent to the chin and nose, introduced by R. M. Ricketts for assessment of lip fullness. According to him, the lower lip should fall slightly ahead of the upper lip when related to this line.

Facial axis of Ricketts

A line connecting gnathion with cranial point "Pt," defined as the lower border of the foramen rotundum and approximated by the most posterosuperior point of the outline of the pterygomaxillary fissure.

Facial plane (FP, Facial line)

A line extending from nasion to pogonion.

Frankfort horizontal plane (FH, Frankfort horizontal line, Auriculo-orbital plane,

Eye-ear plane)

An anthropological horizontal plane described on dry skulls as passing through the lowest point in the floor of the left orbit and the highest point on the margins of the external auditory meati. The plane was adopted at the 13th General Congress ofGerman Anthropologists in Frankfort, Germany in 1882 and later was endorsed by the International Agreement for the Unification of Craniometric Measurements in Monaco (1906) as a plane approximating the true horizontal line when the head is in an upright position. On a lateral cephalometric radiograph, the Frankfort horizontal plane is represented by a line connecting the cephalometric landmarks porion and orbitale.

H-line (Harmony line of Holdaway)

A line tangent to the soft tissue chin and the upper lip, introduced by R. A. Holdaway for assessment of the soft tissue profile.

Intergonial line

A line on a P-A cephalogram or tracing, connecting the gonion points to each other.

Mandibular plane (MP, Mandibular line, ML)

A line representing the plane passing through the mandibular borders (bilaterally). It can be drawn in two different ways: by joining points gonion and gnathion, or by drawing a tangent to the posterior aspect of the lower mandibular border from menton.Cephalometric measurements

Nasion-perpendicular

A line drawn perpendicular to the Frankfort horizontal from nasion. A reference line for anteroposterior measurements in the McNamara analysis.

Occlusal plane (OP)

A line on the cephalometric radiograph representing an imaginary plane at the level of the occlusion. There are various different definitions:

1. Bisected occlusal plane

A line passing through the cusp tips of the maxillary and mandibular first permanent molars andmidway between the incisal edges of the maxillary and mandibular central incisors (bisecting the overbite).

2. Functional occlusal plane

A line drawn through the occlusal surfaces of the maxillary and mandibular first permanent molars and first and second premolars (or first and second deciduous molars).

3. Mandibular occlusal plane

A line joining the cusp tips of the mandibular first permanent molars to the incisal edge of the mandibular central incisors.

4. Maxillary occlusal plane

A line joining the cusp tips of the maxillary first permanent molars to the incisal edge of the maxillary central incisors.

Ricketts Occlusal Plane

Slavicek Occlusal Plane and DPO

Palatal plane (ANS-PNS, PP, Nasal line, Nasal floor, Spinal plane)

A line joining PNS and ANS.

Rees esthetic plane

A line tangent to the nasal tip and upper lip, introduced by T. D. Rees for assessment of the soft tissue profile. According to him, it should pass near the bony pogonion when the face is well balanced.

Riedel plane

A line on which the upper lip, lower lip and chin should fall in esthetic profiles, according to R. A. Riedel. A concept similar to the esthetic plane of Steiner, although not taking into account the nasal prominence.

S-line (Esthetic plane of Steiner)

A line connecting the midpoint of the columella of the nose to the soft tissue pogonion. According to C. C. Steiner, the lips should fall on this line and any deviation shows prominence or flatness of the lips.

Sella-Nasion line (SN, Nasion-Sella line, NSL)

A frequently used cephalometric reference line representing the anterior cranial base. A line joining points S and Na.

True vertical line

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.

No Picture

True horizontal line

An external reference line constructed by drawing a perpendicular to the true vertical.

No picture

Y-axis (Growth axis)

A line connecting points sella and gnathion. In the Downs analysis, the anteroinferior angle between the Y-axis and the Frankfort horizontal (FH) plane is measured as an indication of the direction of mandibular growth.

Z-line (Profile line of Merrifield)

A line tangent to pogonion from the most prominent of the lips, introduced by L. L. Merrifield for soft tissue profile assessment. According to him, in well-balanced faces the upper lip should fall on the line and the lower lip should be slightly behind.

Hard Tissue Measurements

SUBTERMS:

ANB angleAngle of convexity (NAPog)Bolton triangleCranial base angle (NSBa, Saddle angle, Angle of flexure)Facial angle (FH-NPog)Facial axis angle of Ricketts (Ba-Pt-Gn)Facial height, Anterior; Posterior; and TotalFrankfort-mandibular incisor angle (FMIA)Frankfort-mandibular plane angle (FMA)Gonial angle (Angle of the mandible, Condylar angle)Holdaway ratio (LI-NB/Pg-NB)Incisor-mandibular plane angle (IMPA)Interincisal angleLI-to-AP distanceMandibular plane angleSNA angleSNB angleUI-to-AP distanceWits appraisalAngle of facial convexity (GíSn-SnPgí)H-angle (of Holdaway)Interlabial gapLower face-throat angle (SnPg'-CMe')Lower lip lengthNasolabial angle (NLA)Upper lip lengthZ-angle (of Merrifield)

Angle of convexity (NAPog)

One of the measurements of the Downs cephalometric analysis, assessing the degree of convexity (or concavity) of the skeletal profile. The angle is formed by the lines NA and A-Pog and has a positive value in convex and negative value in concave profiles, whereas in patients with a straight profile the angle is approximately 0.

ANB angle

The difference between angles SNA and SNB, as introduced by R. A. Riedel, aiming at providing an evaluation of the anteroposterior relationship between the maxillary and mandibular apical bases. The measurement is not specific as to the location of the deformity.

SNA angle

A commonly used measurement (of the Steiner analysis) introduced by R. A. Riedel for assessment of the anteroposterior position of the maxilla with regards to the cranial base. The inferior posterior angle formed by the intersection of lines SN and NA is measured.

SNB angle

A measurement introduced by R. A. Riedel to evaluate the anteroposterior position of the mandible in relation to the cranial base

(also part of the Steiner analysis). The inferior posterior angle formed by the intersection of lines NA and NB is measured.

Bolton triangle

A triangle formed by connecting points Bolton, nasion and sella, representing the area of the cranial base to which the face is joined. It was believed by B. H. Broadbent, Sr. to be the most stable reference for superimposition of serial cephalograms.

Cranial base angle (NSBa, Saddle angle, Angle of flexure)

The angle between the anterior and posterior cranial base, recorded as the inferior angle formed by the intersection of the lines BaS and SN. A large cranial base angle is thought to signify a posterior condylar and glenoid fossa position and a mandible that is positioned posteriorly with respect to the cranial base and the maxilla, unless it is compensated by a larger gonial angle and an increased mandibular length.

Facial angle (FH-NPog)

The inferior posterior angle formed by the intersection of the Frankfort horizontal and the facial plane (N-Pog). Introduced by W. B. Downs to provide an assessment of the anteroposterior position of the chin in relation to the Frankfort horizontal plane.

Facial axis angle of Ricketts (Ba-Pt-Gn)

The inferior angle formed by the intersection of the facial axis of Ricketts and the Ba-N line. This angle on the average approximates 90∞. A value smaller than 90∞ indicates facial growth primarily in the vertical direction and/or a Class II pattern, whereas a value greater than 90 degrees indicates a horizontal growth pattern and/or a Class III tendency.

Facial height, Anterior; Posterior; and Total

An appraisal of the face in the vertical dimension. The anterior lower facial height is expressed by the linear millimetric distance between the ANS and menton, measured directly, or along the true vertical line. The percent ratio of the previous linear measurement (ANS-Me) over the total anterior facial height (N-Me)ómeasured in the same wayóprovides an assessment of the relative proportionality of the anterior face in the vertical dimension. The measurement is obviously not specific as to the location of the deformity. Similarly, the linear measurement from S to Go on the lateral cephalometric radiograph provides an assessment of posterior facial height. The ratio of posterior face height x 100/anterior face height, according to the recommendations of J. R. Jarabak and J. A. Fizzel, can give an estimate of growth direction.

Ricketts

Gonial angle (Angle of the mandible, Condylar angle)

The anterior angle formed by the intersection of a line tangent to the posterior border of the ramus and the mandibular plane. It determines the degree of inclination of the ramus to the mandibular plane and may give an indication about mandibular growth direction. (Alternatively measured as the angle between Ar-Go and Go-Gn. )

Holdaway ratio (LI-NB/Pg-NB)

A measurement introduced by R. A. Holdaway to evaluate the relative prominence of the mandibular incisors, as compared to the size of the bony chin. It is calculated as the ratio of the linear distance from the labial surface of the mandibular central incisor to the NB line, over the linear distance of the chin to the same line.

Interincisal angle

A measurement of the degree of procumbency of the incisor teeth, introduced by W. B. Downs as the (posterior) angle formed by the intersection of the long axes of the maxillary and mandibular central incisors.

LI-to-AP distance

The perpendicular distance (in mm) of the incisal edge of the mandibular central incisors to the A-Pog line. A measurement of the Downs analysis, expressing the degree of protrusion of the mandibular incisors.

Mandibular plane angle

A measurement introduced by C. C. Steiner for assessment of the steepness of the mandibular plane in relation to the cranial base. The anterior angle formed by the intersection of SN and GoGn is measured. W. B. Downs defined the mandibular plane angle as the anterior angle formed by the intersection of the Frankfort horizontal plane and a tangent to the lower border of the mandible and symphysis.

Interlabial gap

The vertical distance between the upper and lower lip, measured with the lips at rest.

Lower face-throat angle (SnPg'-CMe')

The posterior superior angle formed by the intersection of the subnasale-pogonion line and the menton-cervical line, as described by H. L. Legan. This measurement is used when mandibular surgery is contemplated to evaluate the potential esthetic impact of the procedure on the profile.

Lower lip length

A linear measurement from soft tissue menton to stomion inferius, measured along the true vertical line.

Upper lip length

A linear measurement (in mm) from subnasale to stomion superius, measured along the true vertical line.

Nasolabial angle (NLA)

The anterior inferior angle formed by the intersection of a line tangent to the columella of the nose and a line drawn from subnasale to the mucocutaneous border of the upper lip. It evaluates the degree of protrusion or retrusion of the upper lip, in reference to the columella of the nose. The nasolabial angle can influence the decision for extractions as part of the orthodontic treatment plan, as it is partially dependent on the anteroposterior position of the maxillary incisors.

UI-to-AP distance

The perpendicular distance (in mm) of the incisal edge of themaxillary central incisors to the A-Pog line. A measurement of the Downs analysis, expressing the degree of protrusion of the maxillary central incisors.

Z-angle (of Merrifield)

The inferior posterior angle formed by the intersection of the profile line of Merrifield (Z-line) and the Frankfort horizontal plane.

Tweed cephalometric analysis

A set of three angular measurements (which constitute what has come to be known as the Tweed triangle), introduced by C. H. Tweed in 1946. The three angles that were originally described are the FMA (Frankfort-mandibular plane angle), the IMPA (Incisor-mandibular plane angle) and the FMIA (Frankfort-mandibular incisor angle). Their norms, as advocated by Tweed, were based on a sample of 95 individuals (some of whom were orthodontically treated) who according to him had good balance of facial outline, rather than ideal. The reference plane for the analysis is the Frankfort horizontal plane. Tweed’s entire philosophy of diagnosis and treatment was built around the relationship of the mandibular incisors to the mandibular plane of 90 degrees (IMPA angle).

Wits appraisal

A measurement introduced by A. Jacobson, designed to avoid the shortcomings of the ANB angle in evaluating anteroposterior jaw disharmonies. The method entails drawing perpendicular lines on a tracing of a lateral cephalogram from points A and B, ontothe functional occlusal plane (which is drawn through the region of the overlapping cusps of the first premolars and molars) and subsequently measuring the distance between the two points of intersection of the two perpendicular lines with the functional occlusal plane, along the latter. The greater the deviation of this reading from 0 mm in females and 1.0 mm in males, the greater the degree of sagittal discrepancy between the maxilla and mandible. The Wits appraisal is a linear measurement and not an analysis, per se. It is simply an adjunctive diagnostic aid that can be useful in assessing the extent of anteroposterior skeletal dysplasia and in determining the reliability of the ANB angle. [The name is an abbreviation for "University of

Witwatersrand," in Johannesburg, South Africa, where this appraisal was developed.

Ricketts Anatomical Tracing

Ricketts Points and Planes

Ricketts Frontal Anatomy

Frontal Landmark Points