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Cephalometric analysis
Cephalometric analysis
Cephalometric analysis
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Cephalometric analysis is the clinical application of cephalometry. It is analysis of the dental and skeletal relationships of a human skull.[1] It is frequently used by dentists, orthodontists, and oral and maxillofacial surgeons as a treatment planning tool.[2] 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).[3] There are other methods as well which are listed below.[4]

Cephalometric radiographs

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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.[5] 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.[6] The Cephalometer is used to obtain standardized and comparable craniofacial images on radiographic films.

Machine and dimensions

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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.[7] 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.[8]

Lateral cephalometric radiographs

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Lateral cephalometric radiograph, used for skull analysis

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[9][10] and now is a common method of head orientation for cephalometric radiography.[11][12]

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

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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.[13] 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

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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

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The following are important cephalometric landmarks, which are points of reference serving as datum references in measurement and analysis. (Sources: Proffit;[14] 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 (N′).

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 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 (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 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

Cephalometric planes

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Cephalometric planes 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 (Frankfurt 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

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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:

  1. Angular – dealing with angles
  2. Linear – dealing with distances and lengths
  3. Coordinate – involving the Cartesian (X, Y) or even 3-D planes
  4. 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:

  1. Mononormative analyses: averages serve as the norms for these and may be arithmetical (average figures) or geometrical (average tracings), e.g. Bolton Standards
  2. Multinormative: for these a whole series of norms are used, with age and sex taken into account, e.g. Bolton Standards
  3. Correlative: used to assess individual variations of facial structure to establish their mutual relationships, e.g. the Sassouni arcial analysis

Cephalometric angles

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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.
  • SNA (sella, nasion, A point) indicates whether or not the maxilla is normal, prognathic, or retrognathic.
  • SNB (sella, nasion, B point) indicates whether or not the mandible is normal, prognathic, or retrognathic.

SNA and SNB is important to determine what type of intervention (on maxilla, mandible or both) is appropriate. These angles, however are influenced also by the vertical height of the face and a possible abnormal positioning of nasion.[14] 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.[15]

Analyses (analytic approaches) by various authors

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Steiner analysis

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Cecil C. Steiner 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 reflect 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 (degree) Angle between upper incisor to NA line 22 degrees
U1-NA (mm) Distance from upper incisor to NA line 4 mm
L1-NB (degree) Angle between lower incisor to NB line 25 degrees
L1-NB (mm) Distance from lower incisor to NB line 4 mm
U1-L1 (°) Upper incisor to lower incisor angle 130 degrees
L1-Chin (mm) 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

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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".[16] 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:

  1. Patient's age where ANB has tendency to reduce with age
  2. Change in position of nasion as pubertal growth takes place
  3. Rotational effect of jaws
  4. 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.[17]

In his study, Jacobsen mentioned that average jaw relationship is -1mm in Males (AO is behind BO by 1mm) and 0mm in Females (AO and BO coincide). 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:[18]

  • 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.

Delaire analysis

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Prof. Jean Delaire started developing his analysis along with Dr M. Salagnac back in the 70's. [citation needed] This analysis is still developed and improved by his pupils. This analysis is based on reciprocal proportion and balance and doesn't use standard deviation. It gives the ideal architecture the patient should have, based on his skull shape, posture and functions.[19]

Downs analysis

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Name Description Normal Standard Deviation
Skeletal
Facial Angle (°) Angle between Nasion-Pogonion and Frankfurt Horizontal Line 87.8 +/- 3.6
Angle of Convexity (°) Angle between Nasion – A point and A point – Pogonion Line 0 +/- 5.1
Mandibular Plane Angle (°) Angle between Frankfort horizontal line and the line intersecting Gonion-Menton 21.9 +/- 5
Y Axis (°) Sella Gnathion to Frankfurt Horizontal Plane 59.4 +/- 3.8
A-B Plane Angle (°) Point A-Point B to Nasion-Pogonion Angle −4.6 +/- 4.6
Dental
Cant of Occlusal Plane (°) Angle of cant of occlusal plane in relation to FH Plane 9.3 +/- 3.8
Inter-Incisal Angle (°) 135.4 +/- 5.8
Incisor Occlusal Plane Angle (°) Angle between line through long axis of Lower Incisor and occlusal Plane 14.5 +/- 3.5
Incisor Mandibular Plane Angle (°) Angle between line through long axis of Lower incisor and Mandibular Plane 1.4 +/- 3.8
U1 to A-Pog Line (mm) 2.7 +/- 1.8

Bjork analysis

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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.[20]

  • 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)

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Charles H. Tweed developed his analysis in the year 1966.[21] 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.[22][23]

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

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Analysis developed by Joseph Jarabak in 1972.[24] The analysis interprets how the craniofacial growth may affect the pre and post treatment dentition. The analysis is based on 5 points: Nasion (Na), Sella (S), Menton (Me), Go (Gonion) and Articulare (Ar). 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 (S-Go) to Anterior Height (N-Me) is 56% to 44%. Therefore, a tendency to open bite will occur and a downward, backward growth of mandible will be observed.[25]

Ricketts analysis

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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 (Pterygoid vertical) 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 (functional plane)
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

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This analysis, developed by Viken Sassouni in 1955,[26][27] 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:

  1. Supraorbital plane (anterior clinoid to roof of orbits)
  2. Palatal plane (ANS-PNS)
  3. Occlusal plane (Downs occlusal plane)
  4. Mandibular plane (Go-Me)

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

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This analysis was developed by Egil Peter Harvold in 1974.[28] 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 (Co) to ANS. The mandibular unit length is measured from posterior border of mandibular condyle (Co) to Pogonion. This analysis also looks at the lower facial height which is from upper ANS to Menton.[29]

McNamara analysis

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Landmark Name Landmark Symbol Description Normal
Maxilla to Cranial Base
Nasolabial Angle 14 degrees
Na Perpendicular to Point A 0-1mm
Maxilla to Mandible
AP
Mandibular Length (Co-Gn)
Mandible to Cranial Base
Pog-Na Perpendicular Small = -8 to −6mm

Medium = -4mm to 0mm

Large = -2mm to +2mm

Dentition
1 to A-Po 1-3mm
1 to Point A 4-6mm
Airway
Upper Pharynx 15-20mm
Lower Pharynx 11-14mm

COGS analysis (cephalometrics for orthognathic surgery)

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This analysis was developed by Charles J. Burstone when it was presented in 1978 in an issue of AJODO.[30] This was followed by Soft Tissue Cephalometric Analysis for Orthognathic Surgery in 1980 by Arnette et al.[31] 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

Computerised cephalometrics

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Computerised cephalometrics is 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. 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.[32]

Digitization

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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

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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

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According to American Board of Orthodontics, this method is based on series of study performed by Arne Bjork,[33][34] Birte Melsen[35] and Donald Enlow.[36] 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

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Mandibular superimposition

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  • 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

[edit]

See also

[edit]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Cephalometric analysis

View on Grokipedia
from Grokipedia
Cephalometric analysis is a fundamental diagnostic technique in that evaluates standardized lateral skull radiographs, known as cephalograms, to assess the relationships between skeletal, dental, and structures of the craniofacial complex. This method uses a cephalostat to position the patient's head precisely, typically with the Frankfort horizontal plane parallel to the floor and a source-to-film distance of 5 feet, enabling the measurement of angular and linear dimensions for identifying malocclusions and growth patterns. It plays a crucial role in determining the complexity of orthodontic treatments, particularly those involving anteroposterior skeletal discrepancies. The origins of cephalometric analysis trace back to the late 1800s, when radiographs were first employed to study head and neck anatomy, but it was formalized in the 1930s through the pioneering work of B. Holly Broadbent Sr. at the , who developed the cephalostat and introduced standardized cephalometric to . Concurrently, similar advancements occurred in with H. Hofrath in , marking the shift from anthropological to clinical orthodontic applications. A key milestone came in 1955 with Arne Björk's introduction of superimposition techniques on serial cephalograms, allowing for the longitudinal assessment of craniofacial growth and treatment changes using stable cranial base landmarks like the sella-nasion line. In modern , cephalometric analysis is indispensable for diagnosing skeletal and dental malocclusions, planning individualized treatments, and evaluating post-treatment stability and growth modifications. It quantifies relationships such as the maxillomandibular discrepancy via angles like SNA (average 81° ± 3°), SNB (78° ± 3°), and ANB (2°), which help classify sagittal skeletal patterns as Class I, II, or III. Vertical assessments, including the R angle or KP plane, address facial height discrepancies, while sagittal methods like the YEN or W angles refine anteroposterior evaluations beyond traditional metrics. Despite its reliance on two-dimensional imaging, which can introduce projection errors and operator variability, the technique remains essential due to its low radiation exposure compared to alternatives. Advancements have evolved cephalometric methods from manual tracings to digital software for automated identification and analysis. techniques, initially two-dimensional and prone to distortions, have progressed to three-dimensional approaches using cone-beam computed tomography (CBCT) since the 2000s, incorporating surface-based registration (SBR) via algorithms like or voxel-based registration (VBR) for enhanced accuracy in assessing asymmetries and complex cases. These developments underscore cephalometric analysis's ongoing adaptation to improve diagnostic precision and treatment outcomes in and maxillofacial surgery.

Cephalometric Radiography

Lateral Cephalometric Radiographs

Lateral cephalometric radiographs, also known as lateral cephalograms, represent a standardized two-dimensional projection of the head in the sagittal plane, essential for evaluating craniofacial structures. This technique was pioneered by B. Holly Broadbent in 1931 through the development of extracoral radiography using the Broadbent-Bolton cephalometer, which allowed for reproducible imaging of the skull to study growth and orthodontic needs. The method marked a significant advancement in orthodontics by enabling precise measurement of skeletal and dental relationships beyond clinical examination alone. To obtain a lateral cephalometric radiograph, the patient is positioned in a cephalostat device, which secures the head for consistency. Ear rods are inserted into the external auditory , and a nasion holder or orbital pointer is placed at the to align the Frankfort horizontal plane parallel to the floor, ensuring the midsagittal plane is perpendicular to the image receptor. The beam is directed perpendicular to the midsagittal plane, centered on the external auditory , with a source-to-film distance typically of 60 inches to minimize . This setup produces an image with inherent magnification of approximately 5-10%, arising from the divergence of the beam, which must be accounted for in measurements. Digital systems further require a of at least 12-15 line pairs per millimeter to accurately resolve fine anatomical details. These radiographs offer distinct advantages in clinical practice, particularly for assessing anteroposterior (sagittal) relationships between the , , and cranial base, which are critical in diagnosing skeletal discrepancies. In , they facilitate treatment planning by revealing growth patterns and etiologies, while in , they aid in simulating surgical outcomes and evaluating postoperative stability. Key cephalometric landmarks, such as sella, , and pogonion, are identified on these images to support subsequent analyses.

Posteroanterior Cephalometric Radiographs

Posteroanterior (PA) cephalometric radiographs are obtained by positioning the patient facing the image receptor, with the tip of the and in light contact with the cassette or to ensure the is parallel to the receptor. The source is placed behind the patient's head at a distance of 1.5 to 2 meters to minimize , and the central beam is directed to the , projecting the image from posterior to anterior. This setup captures bilateral facial structures, enabling evaluation of transverse relationships and midline alignment without superimposition of sagittal features. Equipment for PA views follows similar principles to lateral cephalometry, emphasizing precise alignment to maintain . The primary utility of PA cephalometric radiographs lies in assessing transverse and vertical facial asymmetries, particularly in cases involving unilateral mandibular , where deviations in chin point position or mandibular body length can be quantified. For instance, in patients with condylar , PA views reveal chin deviations of up to 11.5 mm, aiding in and treatment planning for corrective . These radiographs facilitate midline analysis by highlighting discrepancies between left and right sides, such as ramal height differences or orbital asymmetries, which are critical for orthodontic and surgical interventions. Radiation exposure from PA cephalometric radiographs is generally lower than that from lateral views, with effective doses typically ranging from 2 to 5 μSv, compared to 5 to 7 μSv for lateral cephalometrics, though both remain well below natural background levels. Adherence to the ALARA (As Low As Reasonably Achievable) principle is essential, involving collimation to the and use of digital sensors to further reduce dose while preserving . Standardization poses challenges in PA cephalometry, primarily due to patient rotation artifacts; even small head rotations of 5 degrees in the can introduce significant errors in linear and angular measurements, distorting assessments of . Vertical rotations of 10 degrees primarily affect linear dimensions, underscoring the need for rigid head positioning aids and verification of alignment to ensure accurate projection and reliable diagnostic outcomes.

Equipment and Standardization

Cephalometric analysis relies on specialized equipment to ensure precise and reproducible imaging of the craniofacial structures. The primary device is the cephalostat, a head-positioning apparatus that stabilizes the patient's head to minimize movement and maintain consistent orientation. Key components include ear rods inserted into the external auditory meatus to align the porion, an orbitale indicator or rest positioned at the infraorbital margin or bridge of the nose to establish the vertical plane. The used in cephalometric is typically configured with specific technical parameters to optimize quality while minimizing dose. Common settings include a tube voltage of 70-90 kVp, often around 72 kVp, and exposure of 10-15 mAs, with a small focal spot size of less than 1 mm to enhance sharpness and reduce geometric unsharpness. The source-to-object distance is standardized at 150-180 cm (approximately 5 feet) from the focal spot to the midsagittal plane, with the receptor positioned 10-15 cm from the midsagittal plane to limit magnification to about 8% and control distortion. Imaging receptors in cephalometric systems include traditional film cassettes or modern digital sensors. Film-based systems commonly use 18 × 24 cm extraoral cassettes with rare-earth intensifying screens for improved sensitivity and reduced exposure. An optional is incorporated in the cassette holder to attenuate scattered , thereby enhancing overall clarity. Standardization protocols are essential for inter- and intra-operator reproducibility, guided by international recommendations such as those from the International Association of Dento-Maxillo-Facial (IADMFR). The patient's head is oriented with the Frankfort horizontal plane—defined by the porion and orbitale—parallel to the floor, ensuring the midsagittal plane is perpendicular to the image receptor and beam. A calibrated or scale is routinely included in the image field to account for any residual magnification in measurements. Patient positioning in lateral projections, for instance, briefly references this setup to align the beam perpendicular to the receptor. Quality control metrics focus on achieving diagnostic images free from artifacts. Sharpness is maintained through the small focal spot and fixed distances to minimize blur, while contrast is optimized by selecting appropriate kVp to differentiate bone and soft tissues without excessive noise. Distortion is controlled by rigid cephalostat fixation and beam collimation to rectangular fields, reducing elongation or foreshortening; periodic checks, including annual assessments of alignment and exposure accuracy, ensure compliance with standards like those from the American Dental Association.

Cephalometric Tracing and Landmarks

Manual Tracing Process

The manual tracing process for cephalometric analysis originated with B. Holly Broadbent's introduction of standardized roentgenographic cephalometry in 1931, which enabled the overlay of serial radiographs on acetate paper to track craniofacial growth and treatment changes by aligning on stable cranial base structures. This method evolved from early superimposition techniques in the Bolton Study (1929–), where tracings corrected for radiographic enlargement using measured distances, to routine use of matte acetate overlays for precise outlining of skeletal and dental contours. Essential materials for manual tracing include 0.003-inch thick matte acetate paper (typically 210 mm × 160 mm), a 0.003-inch or HB lead pencil for fine lines, colored pencils for distinguishing structures (e.g., for cranial base, for ), a protractor for angular measurements, a 300 mm ruler for linear assessments, an eraser, , and a light box (viewing box) for illumination. The process begins by orienting the lateral cephalometric radiograph on the light box with the patient's right side facing the observer and the film side up, then securing a sheet of acetate paper aligned with reference crosses marked on the radiograph (spaced 3 cm apart) using at the top edge. Tracing proceeds systematically: first, outline the cranial base by drawing the sella-nasion (SN) line and extending to porion and orbitale for the Frankfort horizontal plane; next, trace the mandible's border from condyle to chin (gnathion), the maxilla including the anterior nasal spine and posterior borders, and the dentition contours for upper and lower incisors and first molars; key landmarks such as Sella, Nasion, A-point, and B-point are then marked as intersection points along these outlines. Finally, delineate the soft tissue profile from glabella through subnasale, pogonion, and soft tissue landmarks like pronasale, using lighter lines to avoid obscuring hard tissues. To minimize errors, operators use a brightly illuminated viewer to enhance visibility of faint structures like the cranial base sutures, and double-tracing—repeating the process on a duplicate overlay after a short interval—is recommended to verify consistency. The entire tracing typically requires 15–20 minutes per radiograph for an experienced orthodontist. Intra-operator variability studies report landmark identification errors of approximately 0.5–1 mm for linear positions, with angular errors around 1–2 degrees, though these can increase to 1.33–3.56 mm for more challenging points like dental apices due to radiographic .

Key Cephalometric Landmarks

Cephalometric landmarks are specific anatomical points on lateral cephalometric radiographs used as references to assess skeletal, dental, and relationships in orthodontic and maxillofacial evaluations. These points are either (bony) or structures, identified through precise criteria to ensure reproducibility across analyses. Typically, 18-20 landmarks are commonly employed in standard cephalometric evaluations, though the exact set may vary depending on the specific analysis method.

Hard Tissue Landmarks

Hard tissue landmarks are bony points visible on radiographs, serving as foundational references for skeletal morphology.
  • Sella (S): The geometric center of the pituitary fossa (sella turcica) in the midsagittal plane.
  • Nasion (N): The intersection of the internasal and frontonasal sutures in the midsagittal plane.
  • Porion (Po): The most superior point on the outline of the external auditory meatus (bilateral); often defined using the ear rod image from the cephalostat for standardization.
  • Orbitale (Or): The lowest point on the inferior border of the orbit (bilateral).
  • Basion (Ba): The most inferior point on the anterior margin of the foramen magnum in the midsagittal plane.
  • Gonion (Go): The most inferior and posterior point on the angle of the mandible (bilateral), often constructed as the intersection of the mandibular body and ramus tangents.
  • Gnathion (Gn): The most anterior and inferior point on the mandibular symphysis in the midsagittal plane, constructed as the midpoint between pogonion and menton if needed.
  • Pogonion (Pog): The most anterior point on the contour of the mandibular symphysis in the midsagittal plane.
  • Anterior Nasal Spine (ANS): The tip of the anterior projection of the maxilla in the midsagittal plane.
  • Posterior Nasal Spine (PNS): The tip of the posterior projection of the palatal bone in the midsagittal plane.
  • Point A (A or Subspinale): The deepest point on the maxillary anterior contour between the anterior nasal spine and the crest of the maxillary incisor root in the midsagittal plane.
  • Point B (B or Supramentale): The deepest point on the mandibular anterior contour between the chin and the crest of the lower incisor root in the midsagittal plane.
These points are identified primarily through intersections of anatomical lines or tangents to bony contours, with visualization aided by radiographic diagrams highlighting suture lines and structural outlines for accuracy.

Soft Tissue Landmarks

Soft tissue landmarks overlay the external facial profile, providing insights into aesthetic and functional harmony.
  • Pronasale (Prn): The most prominent point on the tip of the nose in the midsagittal plane.
  • Subnasale (Sn): The point at the base of the nasal where it meets the upper lip in the midsagittal plane.
  • Labiale superius (Ls): The () of the upper lip in the midsagittal plane.
  • Stomion (St): The point of contact between the upper and lower lips in the midsagittal plane when closed.
  • Menton (Me): The most inferior point on the chin in the midsagittal plane.
  • Glabella (G): The most prominent point on the in the midsagittal plane.
Like points, landmarks are located using tangential lines to surface contours, often requiring enhancement on radiographs for clear demarcation. Landmark positions show variability across populations, influenced by ethnic differences; for instance, the anterior nasal spine exhibits morphological variations between white and black South African groups, affecting related reference points. Reliability in identification is critical, with studies reporting mean errors of 0.5-1.5 mm due to factors like radiographic magnification and observer interpretation. These landmarks form the basis for constructing cephalometric planes, such as the nasion-sella line or mandibular plane.

Cephalometric Planes

Cephalometric planes are reference lines constructed on lateral cephalometric radiographs to orient the cranium, , and relative to one another, facilitating standardized assessment of craniofacial relationships. These planes are typically drawn as straight lines connecting specific anatomical landmarks, allowing for normalization of head position and of anteroposterior and vertical dimensions. By providing a geometric framework, they enable clinicians to quantify deviations from normative patterns without relying on absolute measurements alone. Cranial planes serve as stable intracranial references, primarily derived from the anterior and posterior cranial base. The Frankfort horizontal plane (FH), also known as the porion-orbitale plane, is constructed by connecting porion (the superior point on the outline of the external auditory meatus) to (the lowest point on the inferior margin of the ). This plane approximates the natural horizontal orientation of the and is used to standardize head positioning during , ensuring reproducibility across analyses. The sella-nasion (SN) plane is formed by joining sella (the midpoint of the pituitary fossa at the center of the sella turcica) to nasion (the most anterior midline point on the frontonasal suture). As an intracranial reference, the SN line is particularly valuable for anteroposterior assessment of jaw positions relative to the cranial base, given its relative stability during growth. The basion-nasion (BaN) plane extends from basion (the most anteroinferior point on the anterior margin of the foramen magnum) to nasion, representing the posterior cranial base and aiding in evaluations of overall cranial vault relationships, though it is less frequently employed than SN or FH due to variability in posterior structures. Maxillary planes focus on the orientation of the upper jaw. The maxillary plane, often synonymous with the palatal plane, is defined by a line from the anterior nasal spine (ANS, the tip of the anterior projection of the ) to the posterior nasal spine (PNS, the tip of the posterior projection of the palatal bone). This construction captures the inclination of the and is essential for normalizing maxillary position in vertical and rotational assessments. Mandibular planes delineate the lower jaw's form and posture. The Go-Gn plane, a common mandibular reference, connects gonion (the point at the angle of the constructed as the intersection of s to the body and ramus) to gnathion (the most inferior midline point on the ). It reflects mandibular divergence and is constructed to evaluate vertical growth patterns. The corpus axis approximates the mandibular body by drawing a along its inferior border, typically from a point near gonion to the symphysis, providing insight into the 's linear orientation and length without direct reliance on ramus height.

Cephalometric Measurements

Angular Measurements

Angular measurements in cephalometric analysis evaluate the angular relationships between skeletal structures and dental components, primarily using lines connecting key landmarks such as sella (S), (N), point A, point B, and incisor axes relative to reference planes like the sella- (SN) line and mandibular plane (GoGn). These angles provide insights into anteroposterior positions and incisor inclinations, aiding in the diagnosis of skeletal discrepancies and dentoalveolar compensations. Skeletal angular measurements focus on the maxillomandibular relationship relative to the cranial base. The SNA angle, formed by the intersection of the SN line and the line from to point A (the deepest point on the maxillary anterior contour), assesses maxillary position; its normative value in Caucasian adults is 82° ± 2°. An increased SNA indicates maxillary , while a decreased value suggests retrognathia. The SNB angle, defined similarly using the line from to point B (the deepest point on the mandibular anterior contour), evaluates mandibular position, with a norm of 80° ± 2° in Caucasian adults. Values greater than the norm denote mandibular , and lower values indicate retrognathia. The ANB angle, calculated as the difference between SNA and SNB (ANB = SNA - SNB), quantifies the relative anteroposterior discrepancy between the and ; its norm is 2° ± 2° for skeletal Class I in Caucasian adults. Dental angular measurements assess incisor positioning relative to skeletal references. The upper incisor to SN angle (U1-SN), formed between the SN line and the long axis of the , has a normative value of 102° ± 5° in Caucasian adults, reflecting normal labial inclination. Angles exceeding this suggest proclination, often compensatory in Class II patterns, while reduced values indicate retroclination. The lower incisor to mandibular plane angle (IMPA), measured between the long axis of the and the GoGn plane, norms at 90° ± 5° in Caucasian adults. Increased IMPA values denote proclined lower incisors, common in Class III compensations, and decreased values show uprighting. Normative values for these angles vary by age and sex in Caucasian samples, primarily derived from longitudinal studies of individuals with normal occlusion. SNA and SNB increase with growth, with males showing greater increments (e.g., SNA rises ~1.7° from ages 8-17 in males vs. 0.4° in females), stabilizing post-adolescence; no significant sex differences persist in adulthood. ANB tends to decrease slightly with age (~0.6° in males, 1° in females from 8-17 years), maintaining ~2° in adults without notable sex disparities. U1-SN and IMPA show minimal age-related changes post-mixed dentition but may exhibit slight sex differences, with males often displaying marginally larger angles during . Adaptations for other ethnicities are necessary, as non-Caucasian populations (e.g., Asian or African samples) often present smaller SNA and SNB values (e.g., SNA ~79° in some East Asian groups) and adjusted ANB norms to account for cranial base differences. Clinically, angular deviations guide malocclusion classification and treatment planning. For instance, an ANB greater than 4° typically indicates a Class II skeletal pattern due to relative mandibular retrognathia, while values less than 0° suggest Class III . Discrepancies in U1-SN or IMPA beyond 1-2 standard deviations often signal dentoalveolar compensation, influencing decisions on extractions or . These interpretations stem from foundational works establishing the angles, emphasizing their role in achieving balanced facial harmony.

Linear Measurements

Linear measurements in cephalometric analysis quantify the absolute distances between key landmarks to assess the size and proportions of the craniofacial structures, providing essential data for diagnosing skeletal discrepancies and planning orthodontic interventions. These measurements are typically taken along established planes, such as the Frankfort horizontal or mandibular plane, to ensure perpendicular or direct linear assessments. Unlike angular measurements, which evaluate relationships, linear ones focus on dimensional extents, often expressed in millimeters, and are critical for evaluating growth patterns and treatment outcomes. Vertical linear measurements primarily evaluate height balance, which influences harmony and occlusion. The anterior height is measured as the linear distance from (N) to (Me), typically ranging from 120 to 130 mm in adult males, reflecting the overall vertical dimension from the midface to the chin. The posterior height is the distance from sella (S) to gonion (Go), averaging 75 to 85 mm in adults, capturing the ramus height and posterior vertical development. For balanced proportions, the of posterior to anterior height (S-Go / N-Me) is ideally 0.65, as deviations indicate brachyfacial (higher ) or dolichofacial (lower ) patterns. The height index, calculated as anterior height divided by posterior height (N-Me / S-Go), complements this by providing a reciprocal measure, often around 1.54 in harmonious profiles. Horizontal linear measurements assess anteroposterior skeletal lengths, aiding in the evaluation of maxillary and mandibular discrepancies. In the Ricketts analysis, maxillary length is determined as the distance from the pterygomaxillary point (Pt') to point A on the subspinale, with norms of approximately 49 to 52 mm in adult males, serving as a proxy for midfacial development. Mandibular length is commonly measured as the distance from gonion (Go) to gnathion (Gn), typically 70 to 80 mm, representing the corpus dimension, while the total mandibular length from condylion (Co) to gnathion (Gn) ranges from 110 to 120 mm in adult males. These values allow for growth prediction adjustments, such as adding 1-2 mm annually during based on pubertal timing. Overjet and are key dental linear measurements derived from perpendicular projections between incisor edges, quantifying occlusal relationships. Overjet is the horizontal distance from the labial surface of the to the labial surface of the , with a norm of 2 to 3 mm indicating proper Class I alignment. is the vertical overlap of the maxillary over the mandibular , ideally 2 to 3 mm for functional occlusion, measured perpendicular to the occlusal plane. These projections are often referenced to the functional occlusal plane for accuracy in assessing protrusive or deep bite tendencies.

Classification of Analyses

Angular Analyses

Angular analyses in cephalometric radiography focus on measuring angles between key skeletal landmarks to classify malocclusions and assess craniofacial relationships, emphasizing relational orientations over absolute sizes. These methods evaluate skeletal patterns by quantifying angular deviations from norms, aiding in the of anteroposterior and vertical discrepancies without relying on linear dimensions. By prioritizing angles such as those formed by the cranial base, , and , angular analyses provide a streamlined approach to identifying skeletal disharmonies, such as Class II or III malocclusions, through their impact on facial convexity and growth direction. Norms may vary by ethnic group; ethnic-specific studies are recommended. Bjork's structural signs utilize six key angular criteria to predict mandibular growth patterns and classify skeletal types, including the saddle angle formed by the nasion-sella and sella-articulare lines (normal: 123° ± 5° for balanced growth). These criteria, such as the articular and gonial angles, assess rotational tendencies and vertical control, with deviations signaling forward or backward mandibular . For instance, an increased saddle angle correlates with posterior mandibular positioning, informing prognostic evaluations in orthodontic planning. Downs' angular yardstick employs 10 primary angles to evaluate facial harmony and skeletal balance, including the facial angle between the nasion-pogonion plane and Frankfort horizontal (normal: 87.8° ± 3°). This set assesses convexity, mandibular inclination, and occlusal relationships, where values outside norms indicate disharmony, such as reduced facial angle suggesting chin retrusion. The yardstick's angular focus allows for quick profiling of skeletal patterns in diagnostic workflows. Diagnostic thresholds in angular analyses provide benchmarks for severity; for example, a saddle angle exceeding 130° often signifies mandibular retrognathia, contributing to Class II skeletal patterns by accentuating posterior positioning. Such thresholds enable clinicians to differentiate between dental and skeletal etiologies rapidly. The primary advantages of angular analyses lie in their simplicity and efficiency for identifying skeletal patterns, as angles remain relatively stable against errors and growth changes compared to linear measures, facilitating straightforward clinical application without complex dimensional computations.

Linear Analyses

Linear analyses in cephalometric radiography emphasize straight-line distances between defined landmarks to quantify skeletal disproportions, growth patterns, and facial proportions, providing clinicians with objective metrics for diagnosing anteroposterior and vertical discrepancies without relying on angular interrelationships. These methods are particularly valuable for assessing jaw harmony and vertical balance, where deviations from normative linear values can signal the need for targeted interventions such as extractions or orthognathic surgery. By focusing on measurable segments, linear analyses facilitate precise treatment planning, enabling orthodontists to predict outcomes and monitor progress in correcting malocclusions. Norms may vary by ethnic group; ethnic-specific studies are recommended. The Wits appraisal, developed by Jacobson in 1975, offers a straightforward linear assessment of anteroposterior disharmony by projecting points A (deepest point on the maxillary anterior contour) and B (deepest point on the mandibular anterior contour) perpendicularly onto the occlusal plane, then measuring the horizontal distance between these projections (AO-BO). In individuals with Class I skeletal and dental relationships, the normal value is approximately 0 ± 1 mm, reflecting balanced positioning relative to the occlusal plane. Values exceeding 4 mm typically indicate a Class II discrepancy, characterized by mandibular retrognathia or maxillary , while negative values less than -2 mm suggest Class III tendencies with mandibular . This method's simplicity allows quick integration into routine cephalometric evaluations, using landmarks like points A and B as endpoints for the linear projections. Sassouni plus analysis, an adaptation of Sassouni's original 1955 framework, employs linear segments along anterior and posterior facial pillars to evaluate vertical disproportions and ratios between facial heights. The anterior pillar extends from the supramentale to the gnathion, while the posterior pillar runs from the center of the to the gnathion; key linear segments are measured to compute the ratio of anterior facial height (AFH, often from to ) to posterior facial height (PFH, from sella to gonion). Normative ratios approximate 1:1 or 54-58% AFH relative to total height in balanced profiles, with deviations indicating hyper- or hypodivergent patterns that affect occlusion and . This approach enhances diagnostic precision for vertical growth issues by quantifying segment lengths, aiding in decisions for vertical control appliances or surgical adjustments. Harvold's linear segments, outlined in his 1974 cephalometric framework, assess facial balance through targeted measurements such as T1-T2 (condylion to anterior nasal spine for maxillary position) and T4-T5 (condylion to pogonion for mandibular position), emphasizing anteroposterior harmony between upper and lower compartments. Balanced profiles exhibit appropriate lengths in these segments, with normative differences varying by age and gender (e.g., adults: T1-T2 ~98 mm males, ~93 mm females; T4-T5 ~122 mm males, ~116 mm females); excesses may denote disproportional development. Derived from skeletal landmarks, these measurements provide insights into anteroposterior growth, supporting evaluations of disproportional development. In orthodontic and surgical treatment planning, linear analyses like these identify discrepancies exceeding established thresholds—such as Wits values over 4 mm or imbalanced Sassouni/Harvold ratios—which often necessitate extractions to relieve crowding or orthognathic procedures to reposition jaws, thereby optimizing long-term stability and facial esthetics.

Combined Analyses

Combined analyses in cephalometric evaluation integrate angular and linear measurements to provide a holistic assessment of craniofacial structures, enabling clinicians to evaluate interrelationships among skeletal, dental, and components more effectively than isolated metrics. These hybrid approaches facilitate the identification of growth patterns and treatment needs by balancing dimensions, often through geometric constructs like triangles and ratios that incorporate both types of data. Norms may vary by ethnic group; ethnic-specific studies are recommended. McNamara's analysis integrates angular measures like SNA (normal: 82° ± 2°) and SNB (normal: 80° ± 2°) with linear assessments of effective midfacial length (e.g., Co-A) to diagnose maxillary and mandibular positions relative to the cranial base. The SNA and SNB angles help classify skeletal relationships, where differences exceeding 2° indicate discrepancies like mandibular retrognathia in Class II cases. This integration accounts for midfacial length variations to refine interpretations, ensuring accurate identification of skeletal imbalances in diagnosis. The Tweed-Merrifield triangle exemplifies a combined method, forming a diagnostic tool that relates the lower position to the and cranial base using key angular measurements. It comprises the Frankfort-mandibular angle (FMIA) at a normative 65°, the incisor-mandibular plane angle (IMPA) at 90° ± 5°, and the Frankfort-mandibular plane angle (FMA) around 25° ± 4°, which together assess dentofacial harmony relative to a linear mandibular base. This integration allows for adjustments in inclination based on mandibular morphology, promoting stable orthodontic outcomes by aligning dental positions with skeletal foundations. Another prominent hybrid technique is the Jarabak ratio within the Björk-Jarabak analysis, which quantifies vertical facial proportions by dividing the posterior facial height (linear measurement from sella to gonion, S-Go) by the anterior facial height (linear from to , N-Me), yielding a normative range of 62-65% for balanced growth. This ratio is complemented by angular components, including the saddle angle (N-S-Ar), articular angle (S-Ar-Go), and gonial angle (Ar-Go-Me), to form a posterior cranial base summing to approximately 396° ± 6° in neutral patterns, thus linking linear heights to angular divergences for predicting mandibular and facial type. Classifications derived from such combined metrics categorize facial morphology into types like Type A (high-angle, dolichofacial patterns with Jarabak ratios below 62%, indicating vertical growth excess) and Type B (low-angle, brachyfacial patterns with ratios above 65%, suggesting horizontal growth dominance). These distinctions guide treatment by highlighting tendencies toward open bites in dolichofacial cases or deep bites in brachyfacial ones, informed by the interplay of linear heights and angular inclinations. The primary benefit of these integrated approaches lies in their ability to balance skeletal architecture, dental alignment, and profile through mixed metrics, reducing diagnostic oversights and enhancing treatment predictability across diverse populations. For instance, by correlating linear discrepancies with angular deviations, clinicians can achieve improved facial aesthetics and functional stability without over-relying on one dimension. Normative cephalometric polygons further support visual combined assessment by plotting multiple angular and linear values against established standards, creating graphical representations that highlight deviations in a single diagram for intuitive interpretation. These polygons, often derived from analyses like Tweed-Merrifield or Jarabak, allow for rapid comparison of patient data to ethnic-specific norms, aiding in the synthesis of complex relationships without exhaustive numerical review.

Classic Analytic Methods

Downs Analysis

The Downs analysis, introduced in , represents one of the earliest systematic cephalometric approaches in , focusing primarily on angular measurements to evaluate facial harmony and skeletal relationships. Developed by William B. Downs, it utilizes ten key parameters—five skeletal and five dental—to assess the dentofacial profile, serving as a diagnostic tool for identifying deviations from ideal patterns and guiding orthodontic treatment planning. This method emphasizes the aesthetic balance of the face by relating skeletal structures to dental positions, with particular attention to convexity as a yardstick for profile harmony; for instance, the convexity angle, formed by the intersection of the nasion-point A line and the point A-pogonion line, indicates the degree of facial convexity, where values approaching zero suggest a balanced skeletal profile. The analysis derives its norms from a study of 20 Caucasian individuals (10 males and 10 females, aged 12-17 years) with untreated, excellent Class I occlusions, providing mean values and standard deviations for the parameters. These norms prioritize angular evaluations to quantify anteroposterior and vertical relationships, such as the facial (formed by the intersection of the nasion-pogonion line and the Frankfort horizontal plane) to measure chin protrusion relative to the cranial base. Key measurements include the mandibular plane for assessing lower facial height and the Y-axis for evaluating facial growth direction. Representative norms are summarized below:
MeasurementDescriptionNorm (Mean ± SD)
Facial angleAngle between Frankfort horizontal and nasion-pogonion line87.8° ± 3.6°
Convexity angleAngle at point A between nasion-A and A-pogonion lines0° ± 3°
A-B plane angleAngle between A-B plane and nasion-pogonion line-4.6° ± 3.7°
Mandibular plane angleAngle between mandibular plane and Frankfort horizontal21.9° ± 3.8°
Y-axis angleAngle between sella-gnathion line and Frankfort horizontal59° ± 3.7°
Occlusal plane angleAngle between occlusal plane and Frankfort horizontal9.3° ± 3.8°
Interincisal angleAngle between upper and lower axes135.4° ± 6°
Dental parameters, such as the lower incisor to mandibular plane distance (approximately 1.2 mm ± 2 mm), further integrate tooth positioning with skeletal bases to evaluate harmony. The convexity angle, in particular, serves as a primary indicator of skeletal profile aesthetics, with positive values denoting convexity and negative values indicating concavity. In clinical applications, the Downs analysis aids in assessing facial aesthetics by comparing patient measurements to these norms, facilitating decisions on orthodontic interventions such as extractions or camouflage treatments to improve profile balance. It is particularly useful for predicting soft tissue profile changes in growing patients, as angular deviations can forecast how skeletal corrections might influence lip and chin positions relative to the esthetic plane. For example, a reduced facial angle may signal mandibular retrusion, prompting growth modification strategies. Additionally, it briefly references basic angular measurements like the SN-GoGn angle to contextualize mandibular inclination. Despite its foundational role, the Downs analysis has limitations, including norms derived from a small, ethnically homogeneous sample that may not generalize to diverse populations, rendering it dated for contemporary multicultural practices. It places relatively less emphasis on vertical dimensions compared to anteroposterior assessments, potentially overlooking deep bite or open bite discrepancies in favor of profile-focused evaluations. These constraints highlight the need for supplementary analyses in comprehensive .

Steiner Analysis

The Steiner analysis, introduced by Cecil C. Steiner in , is a widely used cephalometric method that evaluates skeletal, dental, and relationships to facilitate orthodontic and treatment . It establishes normative values derived from a sample of 100 Caucasian individuals exhibiting normal occlusion and facial harmony, emphasizing the interplay between hard and soft tissues for achieving balanced profiles. This approach integrates angular and linear measurements relative to key cephalometric planes, such as the nasion-A (NA) and nasion-B (NB) lines, to identify discrepancies and guide corrections. In the skeletal assessment, the analysis measures anteroposterior jaw positions using the sella-nasion-A point angle (SNA) at 82°, the sella-nasion-B point angle (SNB) at 80°, and their difference, the A point-nasion-B point angle (ANB) at 2°. These values indicate maxillary protrusion if SNA exceeds 82°, mandibular retrognathia if SNB is less than 80°, and Class II skeletal patterns if ANB surpasses 2°, providing a framework for evaluating sagittal discrepancies relative to the cranial base. The dental component examines positioning to account for compensations in skeletal imbalances. Upper inclination to the NA line is 22° with a 4 mm linear distance from the incisor tip to NA, while the lower incisor to NB is 25° with a 4 mm distance; the interincisal angle between upper and lower measures 130°–131°. These metrics help predict treatment outcomes, such as proclination or retroclination, to harmonize occlusion without altering skeletal structure excessively. Soft tissue integration in the Steiner method uses the S-line (from soft tissue pogonion to pronasale) for profile esthetics, with the upper lip at 0 mm (touching the line) and the lower lip at +1 mm (1 mm behind the line). Additionally, the occlusal plane angle relative to the sella-nasion line, ranging from 8° to 14°, informs management of the curve of Spee by assessing cuspal interdigitation and guiding leveling during orthodontic mechanics to prevent excessive or open bites.

Tweed Analysis

Tweed cephalometric analysis, developed by Charles H. Tweed in the 1940s, provides a framework for orthodontic diagnosis and treatment planning, emphasizing compatibility with the edgewise appliance through evaluation of skeletal and dental relationships. This method utilizes the diagnostic facial triangle to guide anteroposterior control, extraction decisions, and mechanics, focusing on key angular measurements derived from lateral cephalograms. Central to the analysis is the Frankfort-mandibular plane angle (FMA), which measures the inclination of the mandibular plane relative to the Frankfort horizontal plane, with an ideal range of 25° to 30° indicating balanced vertical facial proportions. The -mandibular plane angle (IMPA) assesses lower position, ideally at 90° to the mandibular plane, while the Frankfort-mandibular angle (FMIA) evaluates angulation to the Frankfort plane, targeting 65° for optimal alignment. These three angles form the triangle, summing to 180°, enabling clinicians to predict treatment outcomes and adjust positions for facial harmony and stability. In borderline cases where FMA exceeds 30°, signifying a high-angle pattern, the analysis highlights risks of deep bite exacerbation, necessitating cautious mechanics to control vertical growth and avoid excessive extrusion. The 1940s norms established by Tweed, based on extensive clinical observations of successfully treated cases, prioritize maintaining these angular relationships to achieve predictable results with edgewise archwires. An extension by Levern Merrifield incorporates linear arch analysis into the framework, quantifying space requirements through measurements such as the lower anterior arch length, ideally around 46 mm from canine to canine, to integrate skeletal discrepancies with form. This addition enhances diagnostic precision by combining angular evaluations with linear dimensions for comprehensive space analysis in treatment planning.

Ricketts Analysis

The Ricketts analysis, developed by orthodontist Robert M. Ricketts in the 1950s, provides a cephalometric framework for evaluating craniofacial relationships with an emphasis on facial esthetics, skeletal harmony, and predictive growth modeling to guide orthodontic treatment planning. This method integrates angular and linear measurements derived from norms established through longitudinal studies of Caucasian populations, allowing clinicians to assess deviations from ideal patterns and forecast mandibular development. Unlike static analyses, it incorporates growth forecasting based on mandibular rotation, enabling projections of facial changes over time to inform interventions that align with natural developmental trajectories. A key component is the esthetic line (E-line), drawn from the tip of the (pronasale) to the soft tissue (pogonion), which serves as a reference for evaluating lip position relative to the facial profile. In esthetically balanced profiles, the upper lip is positioned approximately 4 mm behind the E-line, while the lower lip lies about 2 mm behind it, promoting harmony between the , lips, and . Deviations from these norms, such as excessive lip protrusion, can indicate skeletal discrepancies requiring adjustment. Vertical facial dimensions are assessed through measurements like the facial axis, formed by a line from pterygomaxillary fissure (PT) to gnathion, intersecting the basion-nasion line at a norm of 90° ± 3°, which reflects the overall direction of facial growth. The mandibular plane angle, measured between the mandibular plane and the Frankfort horizontal plane, averages 22° ± 4° and indicates the steepness of the relative to the cranial base, influencing lower facial height and bite stability. These 1950s-derived norms facilitate identification of hyper- or hypodivergent patterns, with growth forecasting relying on anticipated mandibular rotation to predict how rotations (clockwise or counterclockwise) alter occlusal and profile outcomes during . In Class II malocclusions, particularly division 2 subtypes, the analysis highlights a concave profile as an indicator of retrognathic and deep , often marked by a reduced convexity (negative value relative to nasion-point A to pogonion line) and straighter or inward-curving lower contours. This concave appearance underscores the need for growth modulation to enhance mandibular advancement and profile balance. The method integrates seamlessly with the visual treatment objective (VTO), a tool developed by Ricketts for overlaying predicted growth and treatment effects on cephalometric tracings to visualize long-term outcomes. By superimposing current tracings with forecasted mandibular positions and proposed tooth movements, VTO enables clinicians to simulate profile improvements and anchorage requirements, ensuring treatments align with esthetic and functional goals.

Bjork Analysis

The Björk analysis, developed by Swedish orthodontist Arne Björk, is a cephalometric method that emphasizes structural features of the craniofacial , particularly the cranial base, to predict mandibular growth patterns and rotations. It utilizes a polygon constructed from key angular measurements to assess the relationships between the cranial base, , and , enabling identification of growth direction and potential skeletal discrepancies. This approach prioritizes cranial base stability as a reference for evaluating development, distinguishing it from analyses focused on dental relationships. Central to the analysis are three primary angles forming the posterior cranial base and mandibular framework: the saddle angle (N-S-Ar) at approximately 123° ± 5°, the articular angle (S-Ar-Go) at 143° ± 6°, and the gonial angle (Ar-Go-Me) at 130° ± 7°, with their sum typically around 396° ± 5° indicating balanced growth. Deviations in these angles, especially an increased saddle angle, correlate with vertical facial growth patterns, while smaller values suggest horizontal development. To determine , identified seven structural signs observable on lateral cephalograms: (1) inclination of the condylar head, (2) curvature of the , (3) shape of the lower border of the near the gonial area, (4) inclination of the , (5) shape of the , (6) interincisal angle, and (7) lower inclination relative to the mandibular plane. These signs classify rotation as forward (Type A, associated with horizontal growth and brachyfacial types) or backward (Type B, linked to vertical growth and dolichofacial types). Björk's method was informed by a initiated in 1948 involving approximately 100 Swedish children, tracking facial growth through serial cephalograms. For enhanced accuracy in measuring changes over time, he pioneered the cephalometric implant technique, inserting small pins into bony landmarks to allow precise superimposition of radiographs, minimizing errors from or postural variations. This implant-based approach revealed that backward mandibular rotation often accompanies high angles and pronounced vertical growth, aiding in prognostic assessments for orthodontic planning. Cranial base landmarks such as (N), sella (S), and articulare (Ar) serve as stable references in this framework.

Modern and Specialized Analytic Methods

McNamara Analysis

The McNamara analysis, developed by James A. McNamara Jr. in 1984, is a linear cephalometric method designed to evaluate anteroposterior and vertical skeletal relationships, emphasizing effective lengths and positions relative to a constructed perpendicular line for balanced in orthodontic treatment planning. This approach divides the craniofacial complex into components such as the , , and dentoalveolar structures, using linear measurements to assess discrepancies rather than relying solely on angles, which allows for straightforward identification of skeletal imbalances. For the maxilla, the effective length is measured as the distance from condylion (the most posterior-superior point on the mandibular condyle outline) to point A (the deepest point on the anterior maxillary contour), with adult norms of 94 mm for females and 100 mm for males. The maxillary position is evaluated by the perpendicular distance from point A to the nasion perpendicular line (a vertical line through nasion parallel to the Frankfort horizontal plane), ideally 1 mm anterior for adults. These measurements help diagnose maxillary protrusion or retrusion by comparing to age-specific norms. The mandibular effective length is determined from condylion to gnathion (the most anteroinferior point on the ), with norms ranging from 120 to 123 mm for adult females and 130 to 133 mm for adult males. Mandibular position is assessed via the perpendicular distance from pogonion (the most anterior point on the bony chin) to the perpendicular line, typically -4 to 0 mm for medium-sized adult faces, indicating a balanced profile when within this range. Incisor positions are evaluated relative to the A-pogonion line (connecting point A to pogonion) to ensure proper dentoalveolar compensation; the upper tip should be 4 to 6 mm anterior to a vertical line through point A, while the lower tip is ideally 1 to 3 mm anterior to the A-pogonion line. Norms in the 1984 analysis are adjusted for age and growth stage, with mandibular pogonion position, for instance, advancing approximately 0.5 to 1 mm per year during . This method's reliance on linear measurements facilitates adaptation to diverse ethnic populations by allowing establishment of group-specific norms, reducing biases inherent in angular analyses derived primarily from Caucasian samples; for example, studies have derived adjusted norms for Chinese, Saudi, and Asian adults. Linear assessments like anterior facial height ( to ) provide additional vertical context without dominating the anteroposterior focus.

Delaire Analysis

The Delaire analysis, also known as the architectural and structural craniofacial analysis, is a functional cephalometric method developed by Jean Delaire to assess the equilibrium and harmony of craniofacial structures based on biomechanical principles. Introduced in a seminal publication, it shifts focus from isolated linear measurements to the interrelationships among skeletal components, emphasizing mutual balance between the cranial base and . This approach integrates skeletal and soft tissue profiles to evaluate overall facial aesthetics and function, making it particularly suited for planning interventions that respect natural growth vectors. Central to the method are functional planes that serve as lines for analyzing positional relationships. The (C1) is drawn tangent to the inferior border of the orbit, approximately parallel to the Frankfort horizontal, while the mandibular plane follows the inferior border of the from gonion to . These planes are measured relative to a vertical reference, such as the craniovertical line perpendicular to the horizontal C3 plane (connecting the midpoint of the lesser wing of the sphenoid to the posterior clinoid process). For example, the anterior maxillary plane (FM-CPA, from frontomaxillary contact to posterior alveolar point) ideally forms an of about 96° to the vertical, ensuring proper anteroposterior projection and vertical control of the . Norms derived from French populations in 1978 highlight gender-specific ideals, such as C3/FM-CPA angles of 90° for males and 85° for females, with deviations indicating retrusion or protrusion. integration is emphasized through evaluation of the nasolabial and lip competence relative to these skeletal planes, promoting aesthetically balanced outcomes. Vectors provide a dynamic assessment of balance in the Delaire system. The D1 vector, or craniovertical vector, quantifies the orientation of the cranial base relative to the vertical reference, reflecting overall head posture and foundational stability. The D2 vector, focused on the , measures its projection and rotation from the mandibular plane to the vertical, aiding in the of anteroposterior discrepancies. These vectors facilitate the identification of imbalances, such as excessive mandibular clockwise rotation in Class III patterns. Classifications within the analysis include hyperdivergent types, defined by a mandibular plane exceeding 10° inclination to the horizontal C3 plane, which signals vertical excess and guides compensatory treatment strategies. In functional orthopedics, the Delaire analysis is invaluable for growing patients, as it informs the use of appliances like the Delaire facemask to redirect skeletal growth toward equilibrium. By prioritizing functional planes and vectors, it enables early intervention to correct dysharmonies in developing craniofacial architecture, reducing the need for later surgical corrections while preserving harmony. This method's emphasis on holistic balance has influenced modern orthognathic planning, particularly in cases involving vertical discrepancies.

COGS Analysis

The Cephalometrics for Orthognathic Surgery (COGS) analysis, developed by J. Burstone and colleagues, is a specialized cephalometric method designed for planning maxillofacial surgical interventions in patients with significant skeletal discrepancies. Introduced in 1978, it emphasizes linear and angular measurements that directly inform planning, using the Frankfort horizontal plane as a stable reference to evaluate the size, shape, and position of the craniofacial bones relative to established norms. Unlike general orthodontic analyses, COGS prioritizes quantitative assessment of skeletal disproportions exceeding 4 mm, which are clinically significant for surgical correction, facilitating precise predictions of bone movements during procedures like Le Fort I or mandibular advancements. The system incorporates 10 primary linear measurements to quantify skeletal dimensions, focusing on the , , and their relationships to the cranial base. For instance, maxillary length is measured as the distance from condylion (Co) to point A (Co-A), while mandibular body length is assessed from gonion (Go) to pogonion (Go-Pog). These measurements, along with others such as the posterior maxillary height (from the posterior nasal spine to the horizontal plane) and anterior facial height (from to gnathion), enable surgeons to identify deviations from norms and simulate postoperative outcomes. Ratios are also integral, such as the posterior-to-anterior maxillary height ratio, which helps evaluate vertical discrepancies in the midface. Norms provide gender-specific standards primarily derived from Caucasian adults but adaptable for diverse populations through comparative studies. COGS integrates seamlessly with model surgery techniques, where physical or digital articulator-based simulations use the cephalometric data to predict positions and segment movements, ensuring alignment with functional and aesthetic goals. For soft tissue evaluation, the analysis incorporates complementary assessments from Legan and Burstone (1980), estimating that and soft tissues reflect 50-70% of underlying skeletal advancements or setbacks, aiding in holistic treatment planning. techniques may be applied briefly to compare pre- and postoperative tracings for validation. Overall, COGS remains a cornerstone for due to its surgeon-oriented metrics, promoting reproducible outcomes in correcting severe malocclusions.

Jarabak Analysis

The Jarabak analysis is a cephalometric method developed by orthodontist Joseph R. Jarabak to evaluate vertical craniofacial growth and proportions through ratios of facial heights, aiding in the of skeletal patterns and treatment . This approach emphasizes the relationship between posterior and anterior facial dimensions to assess mandibular and overall facial harmony, distinguishing it from horizontal-focused analyses by prioritizing vertical assessments. Norms for the analysis were established in Jarabak's 1972 textbook, providing benchmarks for growth evaluation in orthodontic patients. Central to the Jarabak analysis are key ratios derived from linear measurements of heights. The posterior height (measured from sella to gonion, S-Go) to anterior height (nasion to , N-Me) ratio is typically 65% in balanced growth patterns, reflecting proportional vertical development. The upper posterior height (sella to articulare, S-Ar) to total posterior height (S-Go) ratio is approximately 0.56, indicating the relative contribution of the upper ramus segment to posterior dimension stability. These ratios help classify growth vectors, with linear heights such as S-Go and N-Me serving as foundational measurements for vertical pattern identification. Angular measurements in the Jarabak analysis include the saddle angle (basion-sella-nasion, Ba-S-N) at 130° and the gonial angle (articulare-gonion-menton, Ar-Go-Me) at 130°, which together contribute to evaluating cranial base flexure and mandibular posture. A low Jarabak ratio of less than 59% signifies a hyperdivergent growth pattern, characterized by increased anterior facial height relative to posterior, often associated with open bite tendencies and clockwise mandibular rotation. The utility of the Jarabak analysis lies in its ability to predict the vertical effects of orthodontic appliances, such as potential or intrusion impacts on heights during treatment. By quantifying these proportions, clinicians can anticipate growth outcomes and adjust to control vertical discrepancies, enhancing long-term stability in diverse skeletal profiles.

Computer-Assisted Cephalometrics

Digitization Techniques

Digitization techniques in cephalometric analysis involve converting analog radiographs or tracings into digital formats to enable precise coordinate capture and subsequent computerized evaluation. Prior to widespread digital adoption, manual tracing on overlays served as the standard method, but it was labor-intensive and prone to inter-observer variability. The shift to digital workflows accelerated in the post-1990s era, driven by advancements in hardware and software that improved efficiency and reproducibility. Common hardware for digitizing analog cephalograms includes flatbed scanners, which capture images at a minimum resolution of 300 dpi to ensure sufficient detail for identification without excessive . These scanners offer versatility for scanning printed films or tracings in mode, typically at 8-bit depth, achieving resolutions comparable to traditional radiographs. In contrast, (CCD) cameras provide direct digital input by capturing radiographs via video acquisition systems, allowing real-time without intermediate , though they require consistent and controls to minimize . Specialized software facilitates the coordinate capture process by enabling users to import scanned images and manually select landmarks to record x,y coordinates. Examples include NemoCeph, which supports intuitive tracing wizards for rapid landmark placement and analysis integration, and Dolphin Imaging, a widely used platform for digitizing cephalograms and performing measurements with high reproducibility. Calibration is essential and typically involves pixel-to-mm conversion by digitizing known distances on a built-in radiograph scale, such as a 10 mm , to account for magnification factors and ensure metric accuracy. To reduce errors inherent in pixel-based selection, subpixel techniques refine positions beyond whole-pixel resolution, achieving accuracies of approximately 0.1 mm for linear dimensions. The typical entails importing the calibrated image into the software, manually digitizing 15-20 key landmarks by cursor placement, verifying coordinates against radiographic features, and exporting the data to dedicated analysis modules for angular and linear computations. This process enhances precision over manual methods while minimizing operator fatigue.

Automated Landmark Detection

Automated landmark detection represents a key advancement in computer-assisted cephalometrics, enabling software algorithms to identify anatomical s on digitized lateral cephalograms without requiring manual operator input. These systems typically process radiographic images to locate up to 19 standard points, such as (N), sella (S), and pogonion (Pog), by analyzing image features like edges and shapes. This automation addresses the subjectivity and time-intensive nature of manual tracing, which can vary by operator experience. Early automated approaches relied on techniques to extract contours from cephalometric images, identifying boundaries based on intensity gradients and changes. Such methods often employ operators like the Sobel filter to compute image gradients, highlighting potential locations along skeletal and outlines before refining positions through model fitting. Following edge extraction, active shape models (ASMs) are commonly applied; these statistical models, trained on annotated sets, deform to match detected contours while constraining shapes to plausible anatomical variations. A seminal evaluation of ASMs in cephalometrics demonstrated successful localization for 35% of landmarks within 2 mm error on a of 63 images. Machine learning methods have enhanced detection reliability, particularly through ensemble classifiers like random forests trained on annotated cephalometric datasets. These algorithms regress landmark coordinates by voting across decision trees, incorporating features such as gradient magnitudes and local textures. In the IEEE ISBI 2015 Grand Challenge, a random forest regression-voting system achieved a mean radial error of approximately 1.7 mm across 19 landmarks on a test set of 300 images, outperforming prior rule-based techniques. Early convolutional neural networks (CNNs), introduced around the same period, further improved accuracy by learning hierarchical image features, though they remained focused on supervised regression rather than end-to-end deep architectures. Commercial software has integrated these techniques for clinical use, with tools like WebCeph offering automated detection via cloud-based processing. Evaluations of WebCeph report mean landmark errors under 2 mm for key points and successful detection rates exceeding 85% within a 2 mm threshold compared to expert manual tracings, across analyses like Downs and Steiner. Similar performance is observed in other platforms, such as Imaging, which employs hybrid edge and model-based algorithms for 95% agreement on skeletal landmarks. These systems streamline workflows by processing images in under 10 seconds. Validation studies confirm the reproducibility of automated detection, with intra-class correlation coefficients (ICC) greater than 0.9 for landmark positions relative to manual methods, indicating minimal intra- and inter-session variability. For instance, repeated analyses on the same images yield ICC values of 0.99 for critical points like sella and gnathion. Post-2010 developments, including optimized pipelines and faster hardware integration, have reduced overall tracing time from 5-10 minutes manually to seconds per radiograph, enhancing clinical efficiency without compromising precision.

Artificial Intelligence Applications

Artificial intelligence has revolutionized cephalometric analysis by enabling automated interpretation and prediction beyond traditional detection, leveraging architectures to enhance diagnostic precision in . models such as have been widely adopted for cephalometric , allowing for accurate delineation of craniofacial structures in lateral radiographs. For instance, -based systems facilitate the segmentation of regions like the , achieving high fidelity in boundary detection that supports subsequent analytical measurements. Similarly, ResNet architectures are employed for regression, where convolutional layers regress coordinate positions directly from input images, demonstrating mean radial errors around 1-2 mm across clinical datasets. End-to-end AI systems further advance cephalometric interpretation by predicting classifications directly from raw radiographs, integrating feature extraction and diagnostic output in a single pipeline. These models, often built on convolutional neural networks, classify skeletal and dental discrepancies such as Class II or III with reported accuracies exceeding 90%. Recent 2025 reviews of applications in report average accuracies around 92% for class prediction. Such systems not only identify anomalies but also quantify severity, aiding orthodontists in decision-making for interventions like extractions or appliances. Commercial tools exemplify these AI applications, providing FDA-approved platforms for comprehensive cephalometric reports. CephX, cleared by the FDA in 2024, utilizes to automate landmark identification, tracing, and analysis generation, producing reports aligned with standards like Ricketts or McNamara in under a minute per image. Comparative evaluations of similar tools, including WebCeph and AudaxCeph, confirm their reliability, with inter-tool agreement rates above 95% for angular measurements in clinical validations conducted in 2024. These platforms integrate seamlessly into workflows, minimizing errors from human fatigue while supporting remote consultations. Recent advances in multimodal bridge 2D and 3D cephalometrics through hybrid models that fuse radiograph and CBCT data, reducing interpretive biases inherent in single-modality approaches. The DeepFuse framework, introduced in a 2025 study, combines lateral cephalograms with volumetric scans using attention mechanisms to predict treatment outcomes, achieving a mean radial error of 1.21 mm and up to 13% improvement in landmark localization over competing methods on datasets of around 300 cases. These models mitigate discrepancies in soft-tissue rendering and enhance prognostic reliability for complex cases like orthognathic planning. Ethical considerations remain paramount in AI-driven cephalometric applications, particularly regarding dataset diversity to prevent ethnic biases in model performance. Studies from 2025 emphasize that training data skewed toward specific demographics can lead to higher error rates in underrepresented groups. To address this, frameworks advocate for inclusive datasets reflecting global craniofacial variations, alongside transparent bias audits, ensuring equitable diagnostic outcomes across diverse patient populations.

Three-Dimensional Cephalometrics

CBCT Integration

Cone-beam computed tomography (CBCT) represents a significant advancement in cephalometric analysis by enabling the acquisition of three-dimensional volumetric data, marking a shift from traditional two-dimensional radiography. Introduced to orthodontics in the early 2000s, CBCT adoption accelerated by the mid-decade due to its compact design, lower cost compared to medical CT, and reduced radiation exposure, allowing for detailed visualization of dentofacial structures without the limitations of planar projections like superimposition of bilateral anatomy. CBCT systems for dentofacial cephalometric imaging typically feature voxel sizes of 0.3 to 0.5 mm, providing isotropic resolution suitable for orthodontic assessments, with field-of-view (FOV) settings around 8 × 8 cm to capture the craniofacial region while minimizing unnecessary exposure. Effective radiation doses range from 50 to 200 µSv for these protocols, significantly lower than conventional CT but higher than 2D cephalograms, necessitating judicious use. The raw data forms a 3D volume from which multiplanar reconstructions (MPR) are generated, yielding sagittal, coronal, and axial slices that facilitate precise orientation and measurement without geometric distortion. Key advantages of CBCT over 2D methods include the elimination of artifacts from overlapping structures and the ability to visualize soft tissues, such as airways, in three dimensions for comprehensive airway analysis in orthodontic planning. To ensure standardization, head positioning employs ear rods inserted into the external auditory meati to align the Frankfort horizontal plane parallel to the floor, with software-based corrections using fiducials or reference markers to mitigate tilt errors post-acquisition. By 2025, international guidelines from organizations like the European Academy of DentoMaxilloFacial Radiology recommend CBCT for orthodontic cephalometrics only when 2D imaging is insufficient, emphasizing dose optimization and evidence-based indications to balance diagnostic benefits with radiation risks.

3D Landmark Identification

In three-dimensional (3D) cephalometric analysis, landmark identification involves precisely locating anatomical points within cone-beam computed tomography (CBCT) volumes to enable quantitative assessment of craniofacial structures. This process typically utilizes multiplanar reconstruction views (MPRV) and 3D virtual reconstruction views to navigate the volumetric data, allowing clinicians to define points such as the , sella, and porion in all three spatial dimensions. Manual identification remains a foundational technique, where operators place cursors directly on CBCT images using specialized software such as Dolphin Imaging or InVivo Dental. For curved structures like the mandibular border, semi-landmarks are often employed to sample points along the contour, ensuring representation of complex geometries without excessive subjectivity. This approach demands expertise to minimize intra- and inter-observer variability, particularly for subtle features. Semi-automatic methods enhance efficiency by combining user input with algorithmic assistance, such as region-growing algorithms initiated from seed points. For instance, in identifying condyle centroids, an operator selects initial seeds every few slices, after which the algorithm propagates segmentation based on local thresholding and morphological operations to delineate the structure. Post-processing refines the output, separating adjacent anatomy like the , yielding reproducible 3D models suitable for landmark placement. Reported accuracy for 3D landmark identification typically ranges from 0.13 mm to 2.6 mm in mean error, with intra-examiner differences under 1.4 mm and inter-examiner up to 2.6 mm. Errors below 1 mm are considered clinically acceptable, while bilateral structures like condylion exhibit slightly higher variability (intraclass correlation coefficient [ICC] 0.28–0.66) compared to midsagittal points, though overall reliability remains high (ICC >0.9 for most landmarks). Key challenges include metal artifacts from dental restorations, which distort CBCT images and obscure landmarks, often necessitating manual or algorithmic correction to estimate positions. Such artifacts can elevate mean radial errors above 1 mm in affected regions, underscoring the need for robust validation in complex clinical cases. Derived norms adapt traditional 2D measurements to 3D, such as the 3D SNA angle equivalent at approximately 82° for maxillary position and 3D ANB at 2° for sagittal discrepancy. indices, assessing transverse deviations (e.g., upper incisal to midsagittal plane), ideally measure 0 mm, with values exceeding 2 mm indicating clinically significant imbalance.

Volumetric Analysis

Volumetric analysis in three-dimensional cephalometrics utilizes cone-beam computed tomography (CBCT) scans to quantify the volumes of structures, enabling precise assessment of asymmetries and spatial relationships beyond traditional two-dimensional projections. This approach involves segmenting regions of interest to compute volumes, which aids in diagnosing skeletal discrepancies and evaluating treatment outcomes in and maxillofacial . By focusing on volumetric metrics, clinicians can identify subtle imbalances that influence harmony and function. Segmentation techniques form the foundation of volumetric analysis, employing thresholding methods to differentiate from air or based on Hounsfield unit values in CBCT images. For instance, semi-automatic global thresholding is commonly applied to isolate the , yielding typical adult volumes of 15-20 cm³, which vary by gender and skeletal pattern. These segmented regions are then reconstructed into three-dimensional models for volume calculation, often using boundaries defined by 3D landmarks to ensure accuracy. To evaluate facial asymmetries, volumetric indices are derived by digitally the across the midsagittal plane and computing differences between the original and mirrored structures. This mirroring technique quantifies mandibular volume discrepancies, with differences exceeding 10% often indicating pathological requiring intervention. Such indices provide a comprehensive measure of skeletal imbalance, surpassing linear assessments in detecting volumetric distortions. Airway analysis represents a key application of volumetric methods, measuring pharyngeal volume and minimal cross-sectional area to assess respiratory patency. Normal pharyngeal airway volumes in adults range from 10-15 cm³ for the oropharyngeal segment, with minimal cross-sections typically above 100 mm² to avoid obstruction risks. These metrics are segmented via thresholding to exclude surrounding tissues, offering insights into conditions like (OSA). Recent studies from 2024-2025 have leveraged software such as ITK-SNAP for segmentation to predict OSA severity through pharyngeal volume reductions, demonstrating correlations between diminished airway volumes and apnea-hypopnea indices. In clinical practice, volumetric analysis tracks changes following , where post-operative CBCT evaluations often reveal 20-30% reductions in volumetric discrepancies, such as improved symmetry in mandibular segments or expanded airway spaces. These quantitative shifts confirm surgical efficacy in correcting asymmetries and enhancing functional outcomes.

Superimposition Methods

Structural Superimposition

Structural superimposition is a technique in cephalometric analysis used to evaluate craniofacial growth or orthodontic treatment changes by overlaying serial lateral cephalograms on biologically stable anatomical structures. This method allows for the isolation of true skeletal displacements from remodeling or positional shifts, providing a reliable assessment of longitudinal alterations in relationships and morphology. The foundational principles of structural superimposition were established through longitudinal studies employing metallic implants to validate stable reference areas. In the 1960s, Arne Björk utilized implants placed in the craniofacial bones of over 200 children to track growth patterns, demonstrating that certain cranial base structures remain unaltered after , thus serving as ideal registration points. These implant-based validations confirmed the stability of regions such as the inner contour of the and the anterior cranial fossae, minimizing superimposition errors compared to less precise anatomic alignments. For overall registration, the best-fit approach employs a method to align multiple stable points, minimizing the sum of squared Euclidean distances between corresponding landmarks on serial tracings. Reference areas typically include the stable cranial base, such as from the to the key ridge (anterior contour of the middle ), ensuring accurate transformation for , , and scaling. In software implementations for computer-aided cephalometrics, users select regions of on digitized tracings, after which algorithms apply matrices—often affine or Procrustes-based—to achieve precise overlay, with errors reduced to under 0.5 mm when using five or more cranial base landmarks like , , porion, orbitale, and basion.

Cranial Base Superimposition

Cranial base superimposition is a fundamental technique in cephalometric analysis for evaluating overall craniofacial growth and treatment changes by aligning serial radiographs on stable structures of the anterior cranial base. This method relies on the relative stability of the cranial base after , where approximately 90-95% of anterior cranial base growth is complete by age 7, allowing for reliable assessment of subsequent facial modifications. Key reference structures include the sella-nasion (SN) line extending to the pterygomaxillary fissure, which provide a consistent framework for registration in growing individuals post-7 years. The procedure begins by orienting the tracings along the SN line, with the sella point registered as the common origin, followed by fine adjustments through rotation and scaling to achieve the best fit along the contour of stable cranial base landmarks such as the inner cortical plate of the anterior sella wall and the . This approach, often building on the structural method framework introduced by , ensures that changes in the and can be isolated from cranial base remodeling. In clinical applications, cranial base superimposition enables precise quantification of skeletal growth patterns, such as condylar remodeling in the , which typically progresses at a rate of 2-3 mm per year during peak pubertal growth phases. It is particularly valuable for longitudinal studies tracking overall facial harmony and orthodontic outcomes, distinguishing true skeletal displacements from apparent shifts due to cranial base flexion. Potential errors in this method arise primarily from anatomical variations, such as an enlarged , which can introduce inaccuracies up to 0.5 mm in landmark registration. To mitigate such issues, alternatives like the basion-nasion (Ba-N) line are recommended for cases where SN stability is compromised, offering a more posterior reference with enhanced reliability. In adults, norms indicate minimal cranial base alteration, with structural changes typically less than 1 mm per year, underscoring the method's suitability for evaluating age-related or post-treatment stability. This low variability supports its use in forensic and long-term orthodontic evaluations, where precise differentiation of stable versus dynamic regions is essential.

Maxillary and Mandibular Superimposition

Maxillary and mandibular techniques in cephalometric analysis focus on aligning serial radiographs using stable bony landmarks within each to isolate regional growth, remodeling, and treatment-induced changes, distinct from broader cranial alignments. For the maxilla, is typically performed by registering on the anterior contour of the of the , a stable structure after early growth phases. The palatal vault outline serves as a reliable reference structure, exhibiting relative stability after approximately 12 years of age when major sutural growth subsides and remodeling predominates. This method allows precise of maxillary displacement, such as downward and forward during growth or orthopedic intervention. In the , relies on the lower border of the corpus from the to the antegonial notch, combined with the head of the condyle as the primary growth center, to capture the bone's remodeling patterns accurately. Stable references include the inner cortical plate along the lower border of the corpus, the , and the anterior contour, enabling differentiation between condylar growth contributions and corpus apposition or resorption. This regional approach highlights mandibular adaptations, including posterior ramal growth and anterior remodeling. The procedure often involves a double strategy, beginning with alignment on the cranial base to establish overall head positioning, followed by separate regional overlays on the and to reveal differential jaw movements relative to the stable cranial framework. This sequential method enhances the detection of localized changes, such as maxillary sutural expansion or mandibular , without confounding from whole-face shifts. Key measurements derived from these superimpositions include assessments of mandibular , contributing to increased height and overjet persistence in certain malocclusions. Such quantitative insights guide the evaluation of growth direction and treatment efficacy. Clinically, these techniques are invaluable for tracking orthopedic effects, such as those from rapid palatal expansion (RPE), which typically produces 3-5 mm of midpalatal suture widening and parallel maxillary expansion in growing patients, verifiable through post-treatment overlays showing increased interpremolar and intermolar widths.

Clinical Applications and Limitations

Diagnostic and Treatment Planning Uses

Cephalometric analysis plays a pivotal role in diagnosing malocclusions by quantifying skeletal and dental relationships, enabling clinicians to classify discrepancies such as skeletal Class III, characterized by an ANB angle less than 2°, which indicates mandibular relative to the . This classification aids in distinguishing between dentoalveolar and skeletal etiologies, as seen in analyses that differentiate growth patterns using measurements like the mandibular plane angle. For instance, a steep mandibular plane angle greater than 30° often signals a hyperdivergent pattern associated with open bite tendencies. In treatment planning, cephalometric analysis facilitates growth assessment and outcome simulation, particularly through methods like Björk's , which examines indicators of mandibular rotation to evaluate growth direction. Similarly, Ricketts' Visual Treatment Objective (VTO) overlays predicted skeletal profiles on current tracings to simulate post-treatment stability, aiding orthodontists in visualizing skeletal changes. These tools help tailor extraction versus non-extraction approaches by estimating space requirements and skeletal maturation. For , the Cephalometrics for Orthognathic Surgery (COGS) analysis provides norms for surgical planning, such as maxillary advancement in LeFort I osteotomies, where typical advancements of 3-5 mm correct Class III discrepancies while maintaining facial harmony, guided by reference lines like the Frankfort horizontal plane. This analysis integrates hard and soft tissue measurements to predict postoperative profiles, ensuring balanced anteroposterior relationships. Monitoring treatment progress involves serial cephalometric superimpositions on stable structures like the cranial base, which reveal changes such as 2-4 mm retraction of incisors in extraction cases, confirming alignment with planned tooth movements and growth modifications. These comparisons quantify progress, such as reductions in overjet, and adjust appliances accordingly to avoid deviations. In multidisciplinary contexts, cephalometric analysis integrates with cone-beam computed tomography (CBCT) for comprehensive TMJ assessment, correlating two-dimensional skeletal patterns with three-dimensional joint morphology to evaluate condylar position and disc integrity in patients with temporomandibular disorders. This combined approach enhances planning for cases involving , , and TMJ therapy by identifying asymmetries that may contribute to joint loading.

Sources of Error and Reliability

Cephalometric analysis is susceptible to various sources of error, primarily arising from the process and human interpretation. Projection errors occur due to the two-dimensional representation of three-dimensional structures, leading to and . Magnification in lateral cephalograms typically ranges from 5% to 8%, influenced by the source-to-object and object-to-film distances, which can alter linear measurements and affect diagnostic accuracy. Additionally, landmark projection overlap, where bilateral structures superimpose, introduces ambiguity in identifying points such as the gonion or condylion, potentially resulting in positional inaccuracies of up to several millimeters. Operator errors represent another major source of variability in traditional cephalometric analysis. Landmark identification errors, often quantified by standard deviation, commonly range from 1 to 2 mm, particularly for or dental landmarks like the lower apex, due to subjective interpretation of radiographic images. Tracing errors contribute further, with angular measurements showing deviations of approximately 0.5 degrees, stemming from inconsistencies in drawing lines between identified points. Reliability in cephalometric measurements is assessed using established statistical methods to quantify intra- and inter-observer variability. The Dahlberg formula, ∑d22n\sqrt{\frac{\sum d^2}{2n}}
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