Cephalometric analysis

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 and the Downs analysis. There are other methods as well which are listed below.

Cephalometric radiographs

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. A Cephalometric radiograph is a radiograph of the head taken in a Cephalometer 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.

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 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 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 datums in measurement and analysis.
Landmark points can be joined by lines to form axes, vectors, angles, and planes. For example, the [|sella] and the nasion are points that together form the sella-nasion line, 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 versus skin nasion.

Landmark name	Landmark symbol	Comments
A point	A	Most concave point of anterior maxilla
A point–nasion–B point angle	ANB	Average of 2° ± 2°
B point	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
exocanthion	Ex	Point at which outer ends of upper and lower eyelids meet
frontotemporal	Ft	Most medial point on the temporal crest
glabella	G'	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	Me′	Lowest point on soft tissue over mandible
nasion	N	Most anterior point on frontonasal suture
soft tissue nasion	N′	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	Pg′	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	Prn	Soft tissue point on tip of nose
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
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	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	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	T′	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

Below is a list of cephalometric planes that are commonly used in different cephalometric analyses.

Cephalometric plane	Plane symbol	Definition
palatal plane	ANS-PNS	This plane is formed by connecting ANS to PNS and is used to measure the vertical tilt of maxilla
SN plane	SN plane	This plane represents the anterior cranial base and is formed by projecting a plane from the sella-nasion line
Frankfort horizontal plane	P-Or	This plane represents the habitual postural position of the head.
condylar plane	Co-Or	This plane can be used as an alternate to Frankfort horizontal plane.
functional occlusal plane	FOP	This plane passes is formed by drawing a line that touches the posterior premolars and molars.
Downs occlusal plane	DOP	This plane is formed by bisecting the anterior incisors and the distal cusps of the most posterior in occlusion.
mandibular plane	Go-Gn	This plane is formed by connecting the point gonion to gnathion at the inferior border of the mandible.
facial plane	N-Pg	This vertical plane is formed by connecting nasion to pogonion as described in the Schudy analysis.
Bolton plane	This 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 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 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 or geometrical. 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 indicates whether the skeletal relationship between the maxilla and mandible is a normal skeletal class I, a skeletal Class II, or skeletal class III relationship.
SNA indicates whether or not the maxilla is normal, prognathic, or retrognathic.
SNB indicates whether or not the mandible is normal, prognathic, or retrognathic.

SNA and SNB is important to determine what type of intervention is appropriate. These angles, however are influenced also by the vertical height of the face and a possible abnormal positioning of nasion. By using a comparative set of angles and distances, measurements can be related to one another and to normative values to determine variations in a patient's facial structure.

Analyses (analytic approaches) by various authors

Steiner analysis

developed Steiner Analysis in 1953. He used S–N plane as his reference line in comparison to FH plane due to difficulty in identifying the orbitale and porion. Some of the drawbacks of the Steiner analysis includes its reliability on the point nasion. Nasion as a point is known not to be stable due to its growth early in life. Therefore, a posteriorly positioned nasion will increase ANB and more anterior positioned nasion can decrease ANB. In addition, short S–N plane or steeper S–N plane can also lead to greater numbers of SNA, SNB and ANB which may not reflex the true position of the jaws compare to the cranial base. In addition, clockwise rotation of both jaws can increase ANB and counter-clockwise rotation of jaws can decrease ANB.

Name	Description	Normal	Standard Deviation
Skeletal			-
SNA	Sella-Nasion to A Point Angle	82 degrees	+/- 2
SNB	Sella-Nasion to B Point Angle	80 degrees	+/- 2
ANB	A point to B Point Angle	2 degrees	+/- 2
Occlusal Plane to SN	SN to Occlusal Plane Angle	14 degrees
Mandibular Plane	SN to Mandibular Plane Angle	32 degrees
Dental			-
U1-NA	Angle between upper incisor to NA line	22 degrees
U1-NA	Distance from upper incisor to NA line	4 mm
L1-NB	Angle between lower incisor to NB line	25 degrees
L1-NB	Distance from lower incisor to NB line	4 mm
U1-L1	Upper incisor to lower incisor angle	130 degrees
L1-Chin	Also known as Holdaway Ratio. It states that chin prominence should be as far away as the farthest point of the lower incisor should be. An ideal distance is 2mm from Pogonion to NB line and L1 to NB line.	4mm
Soft tissue
S Line	Line formed by connecting Soft Tissue Pogonion and middle of an S formed by lower border of the nose	Ideally, both lips should touch the S line

Wits analysis

The name Wits is short for Witwatersrand, which is a University in South Africa. Jacobsen in 1975 published an article called "The Wits appraisal of jaw disharmony". This analysis was created as a diagnostic aid to measure the disharmony between the AP degree. The ANB angle can be affected by multitude of environmental factors such as:

Patient's age where ANB has tendency to reduced with age
Change in position of nasion as pubertal growth takes place
Rotational effect of jaws
Degree of facial Prognathism

Therefore, it measured the AP positions of the jaw to each other. This analysis calls for 1. Drawing an Occlusal Plane through the overlapping cusps of Molars and Premolars. 2. Draw perpendicular lines connecting A point and B Point to the Occlusal Plane 3. Label the points as AO and BO.
In his study, Jacobsen mentioned that average jaw relationship is -1mm in Males and 0mm in Females . Its clinical significance is that in a Class 2 skeletal patient, AO is located ahead of BO. In skeletal Class 3 patient, BO is located ahead of AO. Therefore, the greater the wits reading, the greater the jaw discrepancy.
Drawbacks to Wits analysis includes:

Left and Right molar outlines may not always coincide
Occlusal plane may differ in mixed vs permanent dentition
If curve of spee is deep then it may be difficult to create a straight occlusal plane
Angulation of functional occlusal plane to pterygomaxillary vertical plane was shown to decrease from age 4 to 24.
Downs analysis

Bjork analysis

This analysis by Arne Bjork was developed in 1947 based on 322 Swedish boys and 281 conscripts. He introduced a facial polygon which was based on 5 angles and is listed below. Bjork also developed the 7 structural signs which indicates the mandibular rotator type.

Nasion Angle - Formed by line connecting ANS to Nasion to Sella
Saddle or Cranial Base Angle - Formed by line connecting Nasion to Sella to Articulare
Articular Angle - Formed by line connecting Sella to Articulare to Gonion
Gonial Angle – Formed by line connecting Articulare to Gonion to Gnathion
Chin Angle – Formed by line connecting Infradentale to Pogonion to the Mandibular Plane.
Tweed analysis (triangle)

developed his analysis in the year 1966. In this analysis, he tried describing the lower incisor position in relation to the basal bone and the face. This is described by 3 planes. He used Frankfurt Horizontal plane as a reference line.

Name	Description	Normal
Tweed facial triangle
IMPA	Angle between long axis of lower incisor and mandibular plane angle	90 +/- 5
FMIA	Frankfort mandibular incisor angle	65
FMA	Frankfort mandibular plane angle	25
Total	180	-

Jarabak analysis

Analysis developed by Joseph Jarabak in 1972. The analysis interprets how the craniofacial growth may affect the pre and post treatment dentition. The analysis is based on 5 points: Nasion, Sella, Menton, Go and Articulare . They together make a Polygon on a face when connected with lines. These points are used to study the anterior/posterior facial height relationships and predict the growth pattern in the lower half of the face. Three important angles used in his analysis are: 1. Saddle Angle - Na, S, Ar 2. Articular Angle - S-Ar-Go, 3. Gonial Angle - Ar-Go-Me.
In a patient who has a clockwise growth pattern, the sum of 3 angles will be higher than 396 degrees. The ratio of posterior height to Anterior Height is 56% to 44%. Therefore, a tendency to open bite will occur and a downward, backward growth of mandible will be observed.

Ricketts analysis

Landmark Name	Landmark Symbol	Description
Upper Molar	A6	Point on the occlusal plane located perpendicular to the distal surface of the crown of the upper first molar
Lower Molar	B6	Point on the occlusal plane located perpendicular to the distal surface of the crown of the lower first molar
Condyle	CI	A point on the condyle head in contact with and tangent to the ramus plane
Soft Tissue	DT	Point on the anterior curve of the soft tissue chin tangent to the esthetic plane or E line
Center of Cranium	CC	Point of intersection of the basion-nasion plane and the facial axis
Points from Plane at Pterygoid	CF	The point of intersection of the pterygoid root vertical to the Frankfort horizontal plane
PT Point	PT	Junction of Pterygomaxillary fissure and the foramen rotundum.
Condyle	DC	Point in the center of the condyle neck along the Ba–N plane
Nose	En	Point on the soft tissue nose tangent to the esthetic plane
Gnathion	Gn	Point of intersection between the line between pogonion and menton
Gonion	Go	Point of intersection between ramus plane and mandibular plane
Suprapogonion	PM	Point at which shape of symphysis mentalis changes from convex to concave
Pogonion	Pog	Most anterior point of the mandibular symphysis
Cephalometric	PO	Intersection of facial plane and corpus axis
T1 Point	TI	Point of intersection of the occlusal and facial planes
Xi Point	Xi
Name of Planes	Symbol
Frankfort Horizontal	FH Plane	This plane extends from porion to orbitale
Facial Plane		This plane extends from nasion to pogonion
Mandibular Plane		Plane extending from gonion to gnathion
PtV		This line is drawn through PTM and is perpendicular to the FH plane
Basion-Nasion Plane		Plane extending from basion to nasion
Occlusal Plane		Occlusal plane through molars and premolars contact
A-Pog Line		A line extending from Point A to pogonion
E-Line		This line extends from the tip of soft tissue nose to soft tissue Pogonion

The Rickett analysis also consists of following measurements

Name	Description	Normal	Standard Deviation
Facial Axis	Angle between Pt/Gn and the line N/Ba	90	+/- 3.5
Facial Angle	Angle between the line FL and FH	89	+/- 3
ML/FH	Angle between the line FH and the line ML	24	+/- 4.5
Convexity	Distance between Pog/N and A	0	+/- 2
Li-A-Pog	Distance between Pog/A and Li	1	+/- 2
Ms-PtV	Projection on the line FH of the distance between the markers PT/Ms-d	18
ILi-/A-Pog	Distance between the line Pog/A and the line Lia/Li	22	+/- 4
Li-EL	Distance between the line EL and Li	−2	+/- 2

Sassouni analysis

This analysis, developed by Viken Sassouni in 1955, states that in a well proportioned face, the following four planes meet at the point O. The point O is located in the posterior cranial base.This method categorized the vertical and the horizontal relationship and the interaction between the vertical proportions of the face.The planes he created are:

Supraorbital plane
Palatal plane
Occlusal plane
Mandibular plane

The more parallel the planes, the greater the tendency for deep bite and the more non-parallel they are the greater the tendency for open bite. Using the O as the centre, Sassouni created the following arcs

Anterior Arc – Arc of a circle between the anterior cranial base and the mandibular plane, with O as the center and O-ANS as the radius.
Posterior Arc – Arc of a circle between anterior cranial base and mandibular base with O as centre and OSp as radius.
Basal Arc – From A point should pass through B point
Midfacial Arc – From Te and should pass tangent to the mesial surface of the maxillary first molar
Harvold analysis

This analysis was developed by Egil Peter Harvold in 1974. This analysis developed standards for the unit length of the maxilla and mandible. The difference between the unit length describes the disharmony between the jaws. It is important to know that location of teeth is not taken into account in this analysis.
The maxillary unit length is measured from posterior border of mandibular condyle to ANS. The mandibular unit length is measured from posterior border of mandibular condyle to Pogonion. This analysis also looks at the lower facial height which is from upper ANS to Menton.

McNamara analysis

COGS analysis (cephalometrics for orthognathic surgery)

This analysis was developed by Charles J. Burstone when it was presented in 1978 in an issue of AJODO. This was followed by Soft Tissue Cephalometric Analysis for Orthognathic Surgery in 1980 by Arnette et al. In this analysis, Burstone et al. used a plane called horizontal plane, which was a constructed of Frankfurt Horizontal Plane.

Landmark Name	Landmark Symbol	Description	Normal
Cranial Base
Posterior Cranial Base	AR-PTM
Anterior Cranial BAse	PTM-N
Vertical Skeletal and Dental
Upper Anterior Facial Height	N-ANS
Lower Anterior Facial Height	ANS-GN
Upper Posterior Facial Height	PNS-N
Mandibular Plane Angle	MP-HP
Upper Anterior Dental Height	U1-NF
Lower Anterior Dental Height	L1-MP
Upper Posterior Dental Height	UM-NF
Lower Posterior Dental Height	LM-MP
Maxilla and Mandible
Maxillary Length	PNS-ANS
Mandibular Ramus Length
Mandibular Body Length
Chin Depth	B-PG
Gonial Angle	AR-GO-GN
Dental Relationships
Occlusal Plane	OP-HP
Upper incisors inclination	U1-NF
Lower incisors inclination	L1/GO-ME
Wits Analysis	A-B/OP

Counterpart Analysis
Template Analysis
Computerised cephalometrics

Computerised cephalometrics is the process of entering cephalometric data in digital format into a computer for cephalometric analysis. Digitization is the conversion of landmarks on a radiograph or tracing to numerical values on a two- 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. Computerized cephalometrics has also helped in eliminating any surgeon inadequacies as well as making the process less time consuming.
The first medically certified automated cephalometric analysis of 2D lateral cephalometric radiographs by Artificial intelligence was brought to market in November 2019.

Digitization

Computer processing of cephalometric radiographs uses a digitizer. Digitization refers to the process of expressing analog information in a digital form. A digitizer is a computer input device which converts analog information into an electronic equivalent in the computer's memory. In this treatise and its application to computerized cephalometrics, digitization refers to the resolving of headfilm landmarks into two numeric or digital entities – the X and Y coordinate. 3D analysis would have third quantity – Z coordinate.

Superimposition

Cephalometric radiographs can be superimposed on each other to see the amount of growth that has taken place in an individual or to visualize the amount of movement of teeth that has happened in the orthodontic treatment. It is important to superimpose the radiograph on a stable anatomical structures. Traditionally, this process has been done by tracing and superimposing on cranial landmarks. One of the most common used methods of superimposing is called the Structural Method.

Structural method

According to American Board of Orthodontics, this method is based on series of study performed by Arne Bjork, Birte Melsen and Donald Enlow. This method divides superimposition in three categories: Cranial base superimposition, maxillary superimposition and mandibular superimposition. Some of the important landmarks in each category is listed below as per the structural method.

Cranial base superimposition

The inner contour of the anterior wall of sella turcica
Walker point
The anterior contour of the middle cranial fossa
The contour of the cribriform plate
Details in the trabecular system in the anterior cranial fossa.
The contours of the bilateral fronto-ethmoidal crests.
The cerebral surfaces of the orbital roofs
Mandibular superimposition
The anterior contour of the chin
The inner cortical structure at the inferior border of the mandibular symphysis.
Trabecular structures in the mandibular symphysis.
Trabecular structures related to the mandibular canal.
The lower contour of a molar germ
Maxillary superimposition
The anterior contour of the zygomatic process

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