Cephalometrics EVALUATION AND INTERPRETATION

CEPHALOMETRICEVALUATION AND INTERPRETATION

Contents

• Introduction• Cephalometrics for orthognathic surgery

(COGS)• Soft tissue cephalometric analysis by burstone• Downs Analysis• Steiner Analysis• Tweed Analysis• Wits Appraisal

Introduction• Origin: ‘Cephalo’ means head and ‘Metric’ is measurement

• Discovery of X-rays measurement of the head from shadows of bony and soft tissue landmarks on the roentgenographic image ,known as the Roentgenographic Cephalometry.

• Spawned by the classic work of Broadbent in United States and Hofrath in Germany, cephalometrics has enjoyed wide acceptance

Definitions

• “The scientific measurement of the bones of the cranium and face, utilizing a fixed, reproducible position for lateral radiographic exposure of skull and facial bones” -- Moyers

• “ A scientific study of the measurements of the head with relation to specific reference points; used for evaluation of facial growth and development, including soft tissue profile” -- Grabers

o The focus film distance was set at 5 feet (152.4 cm) and the subject film distance could be measured to calculate image magnification.

o With the two X ray tubes at right angles to each other in the same horizontal plane, two images (lateral & PA) could be simultaneously produced.

CEPHALOGRAM CAN BE OF TWO TYPES:a) LATERAL CEPHALOGRAM: this provides a lateral

view of the skull. It is taken with the head in a standardized reproducible position at a specified distance from the source of the X ray.

b) FRONTAL CEPHALOGRAM: this provides an antero-posterior view of the skull.

CEPHALOMETRIC LANDMARKSo Cephalometric landmarks are readily recognizable

points on a cephalometric radiograph or tracing, representing certain hard or soft tissue anatomical structures (anatomical landmarks) & (derived landmarks).

o Anatomic landmarks represent actual anatomic structures of the skull.

o Derived landmarks are the landmarks obtained secondarily from anatomic structures in the cephalogram.

Requirements o Should be easily seen on the roentgenogram, o Be uniform in out line, and easily reproducible.o Should have significant relationship to the vectors of growth.o Should permit valid quantitative measurements of lines and

angles projected from them. o Measurements should be amenable to statistical analyses.

HARD TISSUE LANDMARKS

Hard tissue landmarks

Lateral cephalometric landmarks• Nasion (N,Na) : the most anterior on the frontonasal sutures

in the midsagittal plane

• Orbitale (Or) : the lowest point on the inferior margin of the orbit.

• Porion (Po): the most superior point on the outline of the external auditory meatus (anatomic). The superior most point of the ear rods (machine porion) sometimes is used.

• Gonion (Go): the most posterior inferior point on the outline of the angle of the mandible.

• Pogonion(pog): its is the most anterior point of the boney cin in the median plane.

• Gnathion (Gn) : the most anterior inferior point on the bony chin in the midsagittal plane.

• Menton (Me) : the most inferior point of the mandibular symphysis in the midsagittal plane.

•

• A-point (Point A, Subspinale, SS) : the most posterior midline point on the concavity between the ANS and prosthion.

• Anterior nasal spine (ANS): the anterior tip of the sharp bony process of maxilla at he lower margin anterior nasal opening.

• Articulare (Ar) a point at the junction of the posterior border of ramus of mandible and inferior border of posterior cranial base (occipital bone).

• B-point (Point B, Supramentale, sm): the most posterior midline point in the concavity of the mandible between the most superior point on the alveolar bone overlying the mandibular incisors (infradental) and Pog.

• Basion (Ba): the lowest point on the anterior rim of the foramen magnum.

• Bolton (Bo): the intersection of the outline of the occipital condyle and the foramen magnum at the highest point on the notch posterior to the occipital condyle.

• Pterygo-maxillary fissure (PTM) : bilateral inverted tear drop shaped radiolucency whose anterior border represents the posterior surfaces of the tuberosities of the maxilla.

• Sella (S) : the geometric centre of the pituitary fossa (sella turcica), determined by inspection – a constructed point in the midsagittal plane.

• Posterior nasal spine (PNS) : the most posterior point on the bony hard palate in the midsagittal plane, the meeting point between inferior & superior surfaces of the hard palate at its posterior aspect.

When a jaw discrepancy accompanies a severe malocclusion, only 3 possible treatment options exist:

1. Modification of growth

2. Camouflage (displacing the teeth to obtain proper function despite the jaw deformity), which produces a dental compensation for skeletal discrepancy.

3. Surgical repositioning of jaws and dentoalveolar segments to obtain proper positioning

Analysis to help diagnose and plan for orthognathic surgeries came in late seventies and early eighties.

CEPHALOMETRIC ANALYSIS

COGS by Burstone(1978)

SOFT TISSUE ANALYSIS by Burstone

(1980)

CEPHALOMETRICS FOR ORTHOGNATHIC SURGERY (COGS) – BURSTONE

• Developed by Charles Burstone et al. at University of Connecticut.

• Presented first in Journal of Oral Surgery. 1978: April

• Followed by Soft Tissue Cephalometric Analysis for Orthognathic Surgery in Journal of Oral Surgery in 1980.

BURSTONE ANALYSIS

COGS system describes the horizontal and vertical positions of the facial bones by the use of constant coordinate systems as follows:

• Size of the bone are represented by direct linear measurements.

• Shape of the bones are represented by the angular measurements.

REFERENCE PLANE USED:• The base line used for

comparison of most of the data in this analysis is a constructed plane called as Horizontal Plane (HP)

• Most measurements in this analysis will be made either parallel to or perpendicular to this Horizontal Plane.

• It is constructed by drawing a line 70 from SN, intersecting at N

HP

PARAMETERS

CRANIAL BASE LENGTH

HORIZONTAL SKELETAL PROFILE

VERTICAL PROFILE

VERTICAL DENTAL

MAXILLA AND MANDIBLE

DENTAL

CRANIAL BASE LENGTH

• Cranial base length is measured by measuring the distance between Ar and N

• It is measured parallel to HP

• The measurement Ar to N is a relatively stable anatomical plane, however it can be changed by cranial surgeryLe Forte II and Le Forte III surgery changes position of NAutorotation of Mandible changes position of Ar

• Two measurements are considered in Cranial Base length –

• Ar-Ptm and Ptm-N

• Ar-Ptm is the distance between Ar and Ptm which is measured parallel to HP

• Standard Value MALES 37.1 + 2.8 mmFEMALES 32.8 + 1.9 mm

Ar-Ptm indicates the position of mandible in relation to posterior surface of maxilla

• Ptm-N is the distance between Ptm and N which is measured parallel to HP

• Standard Value MALES 52.8 + 4.1 mmFEMALES 50.9 + 3 mm

• Ptm-N indicates the position of posterior border of maxilla in relation to Nasion

• If this value increases it indicates more posterior position of maxilla in relation to N

• If it decreases it indicates anterior position of maxilla in relation to N

HORIZONTAL SKELETAL PROFILE ANALYSIS

Used to assess the amount of discrepancy in anteroposterior direction

All the measurements in this set of analysis are made parallel to HP--- hence it is called horizontal skeletal profile analysis

1. N Perpendicular to A, parallel to HP

• A perpendicular to HP is dropped from N (N perpendicular) and horizontal distance parallel to HP is measured from point A

• Standard Value MALES 0 + 3.7 mmFEMALES -2 + 3.7 mm

This measurement describes the position of apical base of maxilla in relation to nasion

2. N perpendicular to B, parallel to HP

• It is obtained by measuring the distance between Point B and Nasion perpendicular (N perpendicular)

• Standard Value MALES -5.3 + 6.7 mmFEMALES -6.9 + 4.3 mm

This measurement describes the position of apical base of mandible in relation to nasion

3. N perpendicular to Pg, parallel to HP

• It is obtained by measuring the distance between Pogonion and Nasion perpendicular (N perpendicular)

• Standard Value MALES -4.3 + 8.5 mmFEMALES -6.5 + 5.1 mm

This measurement describes the position of mandibular chin in relation to nasion

4. ANGLE OF CONVEXITY

• It is the angle formed between N-A and A-Pg

• Standard ValueMALES 3.90 + 6.40

FEMALES 2.60 + 5.10

A positive angle indicates convex profile while negative angle indicates concave profile

VERTICAL SKELETAL PROFILE ANALYSIS

• A Vertical skeletal discrepancy may reflect an anterior, posterior or complex dysplasia of the face

• It is divided into two components: Anterior component Posterior component

1. N - ANS perpendicular to HP

• Distance between N and ANS measured perpendicular to HP gives us the Middle third facial height.

• Standard Value MALES 54.7 + 3.2 mmFEMALES 50 + 2.4 mm

Any increase or decrease in this value indicates increased or decreased middle third facial height respectively

2. ANS – Gn perpendicular to HP

• Distance between ANS and Gn measured perpendicular to HP gives us the Lower third facial height.


Any increase or decrease in this value indicates increased or decreased lower third facial height respectively

3. PNS – N, perpendicular to HP

• Distance between PNS and HP gives us the posterior maxillary height.


Any increase or decrease in this value indicates increased or decreased posterior maxillary height respectively

HP

4. MP – HP angle

• Mandibular plane angle in relation to Horizontal plane intersecting at Gn gives us posterior divergence of mandible

• Standard Value MALES 230 + 5.90 FEMALES 24.20 + 50

• This angle relates posterior facial divergence with respect to anterior facial height

Any increase or decrease in value suggests increased or decreased posterior facial divergence

MAXILLA AND MANDIBLE1. ANS to PNS• ANS and PNS are projected

on HP

• Distance between these two points on HP gives us total effective maxillary length

• Standard Value MALES 57.7 + 2.5 mm FEMALES 52.6 + 3.5 mm

2. Ar to Go

• Mandibular ramal length is the linear distance between Articulare and Gonion

• Standard Value MALES 52 + 4.2 mm FEMALES 46.8 + 2.5 mm

Variation in Ramal length can be a causative factor for skeletal open bite or deep bite

3. Go to Pg

• Mandibular body length is the linear distance between Gonion and Pogonion


4. Point B to Pg

• This measurment describes the prominence of chin in relation to mandibular apical base

• It is obtained by measuring the distance between point B and a perpendicular to MP passing through Pg


5. Ar-Go-Gn Angle (gonial angle)

• This measurment represents the relationship between the ramal plane and mandibular plane

• Standard Value MALES 119.10 + 6.50 FEMALES 1220 + 6.90

Gonial angle also contributes to skeletal open bite or deep bite

VERTICAL DENTAL ANALYSIS

• To obtain upper anterior dental height, perpendicular distance from incisal edge of upper incisor to NF is measured


Any increase or decrease in this value indicates increased or decreased upper anterior dental height respectively

1. Upper 1 to NF

2. Lower 1 to MP

• To obtain lower anterior dental height, perpendicular distance between incisal edge of lower incisor to MP is measured

• Standard Value MALES 45 + 2.1 mm FEMALES 40.8 + 1.8 mm

Any increase or decrease in this value indicates increased or decreased lower anterior dental height respectively

3. Upper 6 to NF• To measure upper posterior dental

height a perpendicular line is dropped from the tip of mesiobuccal cusp of upper first molar to NF

• Standard Value MALES 26.2 + 2.0 mm FEMALES 23 + 1.3 mm

Any increase or decrease in this value indicates increased or decreased upper posterior dental height respectively

4. Lower 6 to MP

• To measure lower posterior dental height a perpendicular line is dropped from the mesiobuccal cusp of lower first molar to MP


Any increase or decrease in this value indicates increased or decreased lower posterior dental height respectively

DENTAL ANALYSIS1. OP – HP (angle)• OP is Occlusal Plane constructed

from buccal groove of first permanent molars through a point 1 mm apical to the incisal edge of the central incisors

• When incisors are not in proper overbite relation, two OP are to be constructed, upper and lower.

• Standard Value MALES 6.20 + 5.10 FEMALES 7.10 + 2.50

HPOP

• An increased OP-HP may be associated with skeletal open bite, lip incompetence and increased anterior facial height

• A decreased OP-HP may be associated with skeletal deep bite, decreased anterior facial height and lip redundancy

OP – HP (angle)

2. A – B parallel to OP

• This distance is obtained by measuring the distance between projection of Point A and Point B on OP

• Standard ValueMALES -1.1 + 2.0 mmFEMALES -0.4 + 2.5 mm

This distance gives us relationship between maxillary and mandibular apical bases in relation to OP

3. Upper 1 to NF (angle)• This angle is constructed by

intersecting a line passing through the tip of incisal edge through the root tip of upper incisor and NF line

• Standard Value MALES 1110 + 4.70 FEMALES 112.50 + 5.30

This angle gives us the inclination of upper incisors in relation to nasal floor (NF)

4. Lower 1 to MP (angle)

• This angle is constructed by intersecting a line joining the incisal edge of lower incisor passing through its root tip and MP

• Standard Value MALES 95.90 + 5.20 FEMALES 95.90 + 5.70

This angle gives inclination of lower incisors in relation to MP

SOFT TISSUE ANALYSIS--- BURSTONE

FACIAL FORM

FACIAL CONVEXITY ANGLE

MAXILLARY PROGNATHISM

MANDIBULAR PROGNATHISM

VERTICAL HEIGHT RATIO

LOWER FACE THROAT ANGLE

LOWER VERTICAL HEIGHT DEPTH RATIO

LIP POSITION AND FORM

NASOLABIAL ANGLE

UPPER LIP PROTRUSION

LOWER LIP PROTRUSION

MENTOLABIAL SULCUS

DEPTH

VERTICAL LIP CHIN

RATIO

MAXILLARY INCISOR EXPOSURE

INTERLABIAL

GAP

FACIAL FORM

1. FACIAL CONVEXITY ANGLE

• This angle is formed by intersecting G-Sn line and Sn-Pg’ line

• Standard Value 120 + 40

Any increase or decrease in this value indicates Convex or Concave Profile respectively.

2. MAXILLARY PROGNATHISM

• Distance between Sn and a line perpendicular to HP passing through glabella gives maxillary prognathism

• Standard Value 6 + 3 mm

A negative number suggests Retrognathism while a large positive value suggests Prognathism

3. MANDIBULAR PROGNATHISM

• Distance between Pg and a line perpendicular to HP passing through G gives Mandibular prognathism


A negative number suggests Retrognathism while a large positive value suggests Prognathism

4. VERTICAL HEIGHT RATIO• It is the ratio between G-Sn

(Middle Facial third) and Sn-Me’ (Lower Facial third) measured perpendicular to HP

• Standard Value 1 : 1

Increased ratio suggests increased middle third height and vice versa

5. LOWER FACE THROAT ANGLE

• It is the angle formed by intersection of Sn-Gn’ and Gn’-C


This angle affects treatment planning to correct anteroposterior facial dysplasia

6. Lower Face Vertical Height Depth Ratio

It is obtained by dividing Sn-Gn’ distance with C-Gn’ distance

Standard Value 1.2 : 1

A much larger than 1 value indicates that patient has a relatively short neck

LIP POSITION AND FORM

1. Nasolabial angle• It is the angle formed by intersection

of Cm-Sn line and Sn-Ls


• Lower than normal Nasolabial angle suggests proclination of upper incisors or anterior maxillary base protrusion or both

• Higher than normal Nasolabial angle suggests retroclination of upper incisors or maxillary base retrusion or both

2. Upper lip protrusion

• It is perpendicular distance between Ls to Sn-Pg’ line


• It is perpendicular distance between Li to Sn-Pg’ line


3. Lower lip protrusion

4. Mentolabial Sulcus depth

• It is perpendicular distance between deepest point on the mentolabial sulcus to Li-Pg’ line


The depth of sulcus is affected by various factors which are – flared lower incisors, flaccid lower lip tone, extruded upper incisors causing rolling of lower lip, and prominence of chin

5. Vertical lip:chin ratio

• It is ratio between Sn-Stms and Stmi-Me’

• Standard Value 0.5 or 1:2

Whenever the value decreases vertical reduction genioplasty should be considered

6. Maxillary incisor exposure• It is obtained by measuring the

distance between tip of upper central incisor and Stms


Increased incisor exposure may be due to vertical maxillary excess or short upper lip

Decreased incisor exposure may be due to vertical maxillary deficiency or larger upper lip

7. Interlabial Gap

• It is the distance between Stms and Stmi


Patients with vertical maxillary excess tend to have large interlabial gap and lip incompetence

Patients with vertical maxillary deficiency tend to have no Inter labial gap and Lip redundancy

This cephalometric analysis is one step in diagnosis and treatment planning for a surgical case. It gives the clinician an insight into the quantitative nature of the skeleto-dental and also soft tissue dysplasia.

COGS analysis uses linear dimensions to describe the size and positions of facial bones and this is practical because surgeon thinks more in millimeters than in angles for planning and accomplishing procedures.

• Types LATERAL CEPHALOGRAM FRONTAL CEPHALOGRAM• USES

Helps in orthodontic diagnosis. Helps in classification of skeletal and dental

abnormalities. Helps in planning treatment of an individual. Helps in evaluation of treatment results. Helps in predicting growth related changes.

LANDMARKS

Horizontal Planes in Cephalometry

Downs Analysis

• It is one of the most frequently used cephalometric analysis.

• Downs analysis consists of ten parameters of which five are skeletal and five are dental.

Skeletal ParametersFACIAL ANGLE

• It is the inside inferior angle formed by intersection of nasion - pogonion line and F.H. plane.

• Average value- 87.8’ ( 82 – 95’)

• Significance - Indicates antero - posterior positioning of mandible in relation to upper face. Angle is increased in skeletal class III with prominent chin while decreased in skeletal class II.

ANGLE OF CONVEXITY

• Angle formed at the inersection nasion-point A to point A – pogonion.

• Average value; 0’ ( -8.5 to 10’).

• Significance- A positive angle suggest a prominent maxillary denture base in relation to mandible.

• Negative angle is indicative of prognathic profile.

A-B PLANE ANGLE

• Angle formed at the intersection of point A – point B line to nasion – pogonion line.

• Average value- -4.6’ ( -9 to 0’)

• Significance- indicative of maxillo mandibular relationship in relation to facial plane.

• Negative since point B is positioned behind point A.

• Positive in class III malocclusion.

MANDIBULAR PLANE ANGLE

• Angle formed at the intersection of mandibular plane with F.H. Plane.

• Average value- 21.9’ ( 17 to 28’)

Y-AXIS

• Angle formed b/w sella gnathion to F.H. plane.

• Average value; 59’ ( 53’ to 66’)

• Angle is larger in class II facial patterns. Indicates growth pattern of a individual.

CANT OF OCCLUSAL PLANE

• Angle formed b/w occlusal plane to F.H. Plane

• Average value- 9.3 ( 1.5 to 14’)

• Gives a measure of slope of occlusal plane relative to F.H. Plane.

INTER INCISAL ANGLE

• Angle between long axes of upper and lower incisors.

• Average value: 135.4’ ( 130 to 150.5’)

• Decreased in case of bidental protrusion

INCISOR OCCLUSAL PLANE ANGLE

• This is the inside inferior angle formed by the intersection between the long axis of lover central incisor and the occlusal plane and is read as a plus or minus deviation from a right angle

• Average value: 14.5” ( 3.5 to 20’)

• An increase in this angle is suggestive of increased lower incisor proclination.

INCISOR MANDIBULAR PLANE ANGLE

• This angel is formed by intersection of the long axis of the lower incisor and the mandibular plane.

• Average value: 1.4’(-8.2 to 7’)

• An increase in this angle is suggestive of increased lower incisor proclination.

UPPER INCISOR TO A-POG LINE

• This is a linear measurement between the incisal edge of the maxillary central incisor and the line joining point A to pogonion. This distance is on an average 4mm mm(rang-1 to 5 mm)

• The measurement is more in patients presenting with upper incisor proclination.

STEINER ANALYSIS

• SKELETAL PARAMETERS

SNA ANGLE SNB ANGLE ANB ANGLE MANDIBULAR PLANE ANGLE OCCLUSAL PLANE ANGLE

• DENTAL PARAMETERS

UPPER INCISOR TO N-A ANGLE UPPER INCISOR TO N-A LINEAR LOWER INCISOR TO N-B ANGLE LOWER INCISOR TO N-B LINEAR INTER INCISOR ANGLE• SOFT TISSUE ANALYSIS S LINE

SNA (Maxillary position) 82.0

SNB (Mandibular position) 80

ANB (Maxillary/Mandibular relation) 2lncisor to NA (Upper incisors to NA mm) 4mmlncisor to NA (Upper incisors to NA degree) 22lncisor to NB (Lower incisors to NB mm) 4mmlncisor to NB (Lower incisors to NB degree) 25lnter-incisal angle 131Mandibular plane angle 32SN to occlusal plane 14

TWEED ANALYSIS

Makes use of three planes1. Frankfort horizontal plane 2. Mandibular plane3. Long axis of lower incisors

FMA (Frankfurt plane to mandibular plane) 16-35

FMIA (Frankfurt plane to lower incisor angulation)

85-95

IMPA (Lower incisor to mandibular plane) 60-75

WITS APPRAISAL

• Measures the relationship of maxilla and mandible to each other and to the sagital plane

• Used where ANB are not realiable• Perpendicular are drawn from point A and

point B to the functional occlusal plane to form AO and BO

Education

Cephalometrics EVALUATION AND INTERPRETATION