COGS analysis (Cephelometrics for orthognathic surgery) / fixed orthodontics courses india

COGS ANALYSIS
www.indiandentalacademy.com

contents
• Introduction
• Development of COGS analysis
• Hard tissue analysis
• A) landmarks
• B ) analysis
• Soft tissue analysis
• A) landmarks
• B ) analysis

• Conclusion
• References

Introduction
• The introduction of radiographic cephalometrics in 1934 by Hofrath in
Germany and Broadbent in the United states provided both a research
and a clinical tool for the study of malocclusion and underlying
skeletal disproportions.
• Any malocclusion is the result of an interaction between jaw position
and the position the teeth assume as they erupt, which is affected by
the jaw relationship.

Cephalometric basics and errors
Classification of
cephalometric
analysis
Methodological
method
According to
area of analysis
Normative
classification

Methodological
Angular : Linear :
Dimensional: downs
Proportional: koski
Orthogonal
Proportional

Angular analysis :
Dimensional analysis: considers various angles in
isolation,comparing them with average figures.
Proportional anlaysis: comparison of various angles to
establish significant relations between separate parts of
the facial skeleton

Proportional linear analyses: based on relative rather than
absolute values, measurements compared to each other than to
norms

Normative
Multinormative

Mononormative : averages serve as norms for these. Can be
arthimetic or geometric . They are suitable for group studies
not for diagnostic purposes
Multinormative
: whole series of norms are used, along with age and sex
consideration
Correlative : they are used to assess individual variations of
facial structure
to establish their mutual relationship

Area of analysis
Dentoskeletal Functional
Soft tissue

• A cephalometric analysis especially designed for the patient who
requires maxillofacial surgery was developed to use landmarks and
measurements that can be altered by common surgical procedures.
• Because measurements are primarily linear, they may be readily
applied to prediction overlays and study cast mountings and may serve
as a basis for the evaluation of post treatment stability.

• The successful treatment of the orthognathic surgical patient is
dependant on careful diagnosis.
• Cephalometric analysis can be an aid in the diagnosis of skeletal and
dental problems and a tool for stimulating surgery and orthodontics by
the use of acetate overlays.
• The first step in the diagnosis of the orthognathic surgical patient is to
determine the nature of dental and skeletal defects.

• Patients who require orthognathic surgery usually have facial bones as
well as tooth positions that must be modified by a combined
orthodontic and surgical treatment.
• For this reason, a specialized cephalometric appraisal system, called
CEPHALOMETRICS FOR ORTHOGNATHIC SURGERY (COGS)
was developed at The University of Connecticut.

• The standards are based on a sample obtained from the child research
council of The University of Colorado school of medicine through 16
females and 14 males.

ADVANTAGES
• The chosen landmarks and measurements can be altered by various
surgical procedures.
• The comprehensive appraisal includes all the facial bones and a
cranial base reference.
• Rectilinear measurements can be readily transferred to a study cast for
mock surgery.

• Critical facial skeletal components are examined.
• A systematized approach to measurement that can be computerized is
used.

• The COGS appraisal describes
• Dental,
• Skeletal
• Soft tissue variations.

LAND MARKS
• SELLA (S) : Centre of pituitary
fossa.
• NASION (N) : Most anterior
point of nasofrontal suture in
the midsagittal plane.
• ARTICULARE (Ar):
Intersection of basisphenoid
and posterior border of the
condyle.

• PTERYGOMAXILLARY
FISSURE (PTM) : Most
posterior point on the anterior
contour of maxillary tuberosity.
• SUB SPINALE (A) : Deepest
point in midsagital plane
between ANS and Prosthion.

• POGONION (Pg) : Most
anterior point in midsagittal
plane of the contour of the chin.
• SUPRAMENTALE (B) :
Deepest point in the midsagittal
plane between Infradentale and
Pg.

• ANS : Most anterior point of
nasal floor.
• MENTON (Me) : Lowest point
of the contour of mandibular
symphysis.

• GNATHION (Gn) : Mid point
between Pg and Me.
• MANDIBULAR PLANE : Plane
constructed (MP) from Me to the
angle of Mandible (Go)
• NASAL FLOOR (NF) : Plane
constructed from PNS to ANS
• GONION (Go) : Located by
bisecting posterior ramal plane and
MPA

Plane of Reference ( H-P line )
• A constructed plane called
Horizontal Plane which is
surrogate Frankfort Horizontal
plane constructed by drawing a
line 70
from SN plane
• Most measurements will be
made from projections either
parallel or perpendicular to the
Horizontal Plane
7°

Cranial Base
1.Ar-N:length of the cranial base
(not an absolute value,
proportional,so that can be
correlated with
mandibular,maxillary lengths)

2.Ar-PTM :
measure horizontal distance b/t
poterior aspects of mandible &
maxilla.The greater the distance,the
more the mandible will lie posteriorly
to maxilla
Males=37.1 +/- 2 mm
Females = 32.8 +/- 1.9 mm
3. PTM –N :
Males = 52.8 +/- 4.1 mm
females= 50.9 +/- 3.0 mm

HORIZONTAL SKELETAL PROFILE
1. N-A-Pog=angle of skeletal facial
convexity
- indication of overall facial convexity
measurement doesn’t indicate if
due to maxilla or mandible
+ angle-convex face
- angle –concave face
Mean :
Males : 3.9 +/- 0.4 °
females: 2.6 +/- 5.1 °

2.N-A :
• A perpendicular from HP is dropped through N.
The horizontal position of A is measured to this
perpendicular line ( N-A).
• This measurement describes the apical base of
maxilla in relation to N and enables the clinician
to determine if the anterior part of maxilla is
protrusive or retrusive.
• Useful in planning treatment of anterior maxillary
horizontal advancement or reduction, and of total
maxillary horizontal advancement or reductions.
• M ean : males= 0.0 +/- 3.7mm ; females =
-2.0 +/- 3.7 mm www.indiandentalacademy.com

3.N-B :
• Also measured in a plane parallel to HP
from the perpendicular line dropped
from N.
• This measurement describes the
horizontal position of the apical base of
mandible in relation to N.
• Useful in planning the treatment of
anterior mandibular horizontal
advancement or reduction and the total
mandibular horizontal advancement or
reduction. www.indiandentalacademy.com

• N- POG
• Measured in the same manner as N-
A and N-B and indicates the
prominence of the chin.
• This measurement helps to
determine if there is a horizontal
genial hyperplasia or hypoplasia.
• Useful in the planning of treatment
augmentation or reduction
genioplasty, of anterior mandibular
horizontal advancement or
reduction, and of total mandibular
horizontal advancement orwww.indiandentalacademy.com

Horizontal Measurements

VERTICAL SKELETAL
ANALYSIS
• In this analysis all measurements are made
perpendicular to HP.
• Reflects the anterior, posterior or complex
dysplasia of face.
 N-ANS(Linear)
 ANS-GN(Linear)
 PNS-N(Linear)
 MP-HP(Angle)

Helps in Diagnosis of:
• anterior , posterior or total vertical
maxillary hyperplasia or hypoplasia.
• clockwise or counterclockwise rotations
of maxilla and the mandible.

N-ANS(LINEAR)
• It signifies the middle
third facial height.
• Male – 54.7 +/- 3.2
• Female – 50 +/- 2.4

Measurements of N-ANS

ANS-GN(LINEAR)
• It signifies the lower
third facial height.
• Male – 68.6 +/- 3.8
• Female – 61.3 +/- 3.3

PNS-N(LINEAR)
• It signifies the posterior
maxillary height
• Male – 53.9 +/- 1.7
• Female – 50.6 +/- 2.2

Measurements of PNS-N

MP-HP(ANGLE)
• It signifies the posterior
divergence of mandible
shown by MP angle.
• The angle relates the
posterior facial divergence
with respect to anterior
facial height
• Male - 23o
+/- 5.9o
• Female – 24.2o
+/- 5o

Construction of MP-HP

Vertical Measurements

MAXILLA AND MANDIBLE ANALYSIS
• This is analysed by following measures
PNS – ANS
AR – GO
GO - PG
AR-GO-GN
B - PG

PNS-ANS MEASUREMENTS
• Denotes the total
effective length of
maxilla.
• Male - 57.7 +/- 2.5
• Female – 52.6 +/- 3.5

Measurements of PNS-ANS

Ar-Go linear)
• Quantitates the length of
mandibular ramus
• Male - 52 +/- 4.2
• Female – 46.8 +/- 2.5

GO-PG(LINEAR)
• Aids in establishing the length of mandibular body
• Male – 83.7 +/- 4.6
• Female – 74.3 +/- 5.8

B-POG
• This measurements denotes prominence of chin related to mandibular denture
base
• Male - 8.9 +/- 1.7
• Female – 7.2 +/- 1.9

AR-GO-GN(ANGLE)
• This angle denotes relationship between ramal plane and MP.
• Aids in diagnosis of skeletal open/closed bite problems.
• Male – 119.1o
+/- 6.5o
Female – 122o
+/- 6.9o

Maxilla and Mandible

VERTICAL DENTAL ANALYSIS
• Measurements for this analysis
UI perpendicular to NF
LI perpendicular to MP
U6 perpendicular to NF
L6 perpendicular to MP

UI TO NF
• It denotes the anterior maxillary dental
height.
• Aids to evaluate the total vertical dimensions
of premaxilla from approximate piriform
aperture perpendicular to tip of maxillary
incisor crown.
• Signifance: indicates how far the incisor
have erupted in relation to nasal floor.
• Male - 30.5 +/- 2.1
• Female – 27.5 +/- 1.7 www.indiandentalacademy.com

LI TO MP
• This measures the anterior mandibular dental
height.
• Determines the total dmensions of anterior
mandible from MP perpendicular to tip of
mandibular incisor crown.
• Signifance: denotes how far the incisor have
erupted in relation to MP
• Male - 45 +/- 2.1
• Female – 40.8 +/- 1.8

U6 TO NF
• This measures the posterior
maxillary dental height.
• Aids to evaluate the posterior
dental mandibular vertical
height/molar eruption
• Male - 26.2 +/- 2
• Female – 23 +/- 1.3

L6 TO MP
• Measures the posterior
mandibular dental height
• Male - 35.8 +/- 2.6
• Female – 32.1 +/- 1.9

OP-HP(ANGLE)
• OP denotes its steepeness/flatness
• Increased angle: assess skeletal open bite,
lip incompetence,increased facial height,
retrognathia.
• Decreased angle: assess deep bite,
decreased facial height, lip redundancy.
• Male - 6.2o
+/- 5.1o
• Female – 7.1o
+/-2.5o

IN CASE OF ANTERIOR OPEN
BITE

Measurements of OP-HP ANGLE

A-B(LINEAR)
• This linear measurements represents the
relationship of maxillary and
mandibular apical base to OP
• Male - -1.1 +/- 2
• Female - -0.4 +/- 2.5
• Significance: if A-B distance is large
with point B projected posteriorly to
point A denotes class II occlusion and
vice versa

U1 – NF(ANGLE)
• Represents angulations of maxillary
central incisors to NF
• Male - 111o
+/- 4.7o
• Female – 112o
+/- 5.3o
• Signifance: aids to determine the
procumbency/recumbency of incisor
• Vitals in assessing long term stability pf
dentition

LI – MP(ANGLE)
• Denotes angulation of mandibular
incisors to MP
• Male - 95.9o
+/- 5.2o
• Female – 95.9o
+/-5.7o
• Significance: determines the
procumbency/recumbency of lower
incisor.

Dental Measurements

Soft tissue
analysis

TRACINGS AND LANDMARK

FACIAL FORMS ANALYSIS
This analysis describes overall horizontal soft tissue profile.
The following analysis is used:
 Facial convexity angle(G-Sn-Pg)
 Maxillary prognathism(G-Sn)
 Mandibular prognathism(G-Pg)
 Vertical height ratio(G-Sn/Sn-Me)
 Lower face throat angle(Sn-Gn-C)
 Lower vertical height depth ratio(Sn-Gn/C-Gn)

FACIAL CONTOUR ANGLE

FACIAL CONTOUR ANGLE
INFERENCE
• Mean value 12o
+/- 4o
• +ve value indicates a convex profile
• -ve value indicates concave profile

MAXILLARY PROGNATHISM(G-Sn)
• Describes the amount of
maxillary excess/deficiency
in AP
• +ve - maxillary retrusion
• -ve - maxillary
procumbency
• Mean value 6+/-3

MANDIBULAR
PROGNATHISM(G-Pg)
• Mean value 0 +/- 4
Inference :
• Indicates mandibular
prognathism/
retrognathism
• Increase –ve value
indicates mandibular
deficiency www.indiandentalacademy.com

Vertical Height Ratio (G-Sn/Sn-
Me I HP)
• In the vertical dimension, the
anterior facial proportionality
is assesed by taking the ratio of
middle-third facial height to
lower-third facial height
measured perpendicular to HP.
• The ratio must be
approximately 1:1

• A ratio of less than one would connote a
disproportionately larger lower third of the
face.
• A vertical maxillary excess, vertical
macrogenia, or a combination of these
deformities can be assesed.

Lower Face-Throat Angle (Sn-Gn’-C)
• It is formed by the intersection
of the lines Sn-Gn’ and Gn’-C.
• An application of this angle is
critical in planning treatment
to correct anteroposterior facial
dysplasias.
• Mean- 100+7

• Lower Vertical Height-
Depth Ratio
• Sn-Gn’/C-Gn’
• Is useful in determining
the feasibility of reducing
or increasing the
prominence of chin.
• Mean-1:2

• The ratio of the distances subnasale to
gnathion and cervical point to gnathion is
normally a little larger than 1.
• In other words, if this ratio becomes much
larger than 1, the patient has a relatively
short neck, and the anterior projection of
the chin should not be reduced.

• An obtuse angle should warn the clinician
not to use those procedures which will
reduce the chin prominence.
• Class III patients who have short, heavy
throats and an obtuse lower face-throat
angles should not have mandibular set
backs.

• Alternatives such as maxillary
advancement, a mandibular subapical
surgery, mandibular setback with
advancement genioplasty.
• Compromised tooth position can also be
attempted.

Lip Position and Form
• Nasolabial Angle (Cm-Sn-Ls)
• Is an important measurement in assessing
anteroposterior maxillary dysplasias.
• Although the angle takes into account the
inclination of the nose, it is useful in
evaluating the position of the upper lip.

• Mean- 102+8
• An acute nasolabial angle will often alow us to surgically retract the
maxilla or retract the maxillary incisors, or both.
• An obtuse angle suggests a degree of maxillary hypoplasia and calls
for a maxillary advancement or orthodontic proclination of maxillary
incisors.

• Anteroposterior Lip Position
• Is evaluated by drawing a line from
subnasale to soft tissue pogonion.
• The amount of lip protrusion or
retrusion is measured as a
perpendicular linear distance from
this line to the most prominent point
of both lips.

• Upper Lip Protrusion {Ls to (Sn-Pg’)}
• Mean - 3+1mm
• Lower Lip Protrusion {Li to (Sn-Pg’)}
• Mean – 2+1mm
• Retracting or protracting the incisors surgically or orthodontically or
advancing or reducing the prominence of chin, or both, can achieve
concordant lip position.

Mento-Labial Sulcus { Sl to (Li-pg’)}
• Measured from the depth of
sulcus perpendicular to the Li-
Pg’ line.
• A sulcus of 4mm is average in
providing a pleasing lower lip
to chin contour.
• Mean – 4+2mm

• Factors that can affect the lower lip
inclination and deepen the mentolabial
sulcus.
• Flared lower incisors.
• Extruded upper incisors.
• Flaccid lower lip tone.
• Abnormal morphology of the lip.

• To Reduce a deep Mentolabial Sulcus.
• Upright the lower incisors.
• Intrude the maxillary incisors.
• Cheiloplasty to retract the lower lip.
• Bony Chin. ( Can affect the depth of sulcus)
• Advancement Genioplasty will deepen and Reduction Genioplasty will
aid in reducing excessive sulcular depth.

• Vertical Lip-Chin ratio.
Sn-Stms/Stmi-Me’ (HP)
• The lower third of the face (Sn-
Me’) can be divided into thirds;
the length of the upper lip, or
Sn-Stms should be
approximately one third the
total.

• The distance Stmi-me’ should be about two thirds.
• In other words, the ratio should be 1:2.
• When this ratio becomes smaller than one half,
often a vertical reduction genioplasty should be
considered.

• Maxillary Incisor Exposure
(Stms-1)
• A Key factor in determining the vertical
position of maxilla.
• 2mm of maxillary incisor exposure with
the lips at rest is desirable.
• This will also correspond in general with
a pleasing smile.

• Patients with vertical maxillary excess tend to show a large
amount of upper incisor with lips in repose.
• The patients that show an excess exposure of tooth may
just have a short upper lip also. So, Treatment approach
should be accordingly planned.

• Treatment modalities orthodontically is to establish a large
curve of spee.
• Conversely, patients with a long face that also have open
bites may have an acceptable tooth-to-lip relationship but
may need superior repositioning of the posterior portion of
the maxilla.

• Patients with vertical maxillary deficiency tend not to
show maxillary teeth with lips relaxed and may have
incisors at a level superior to the upper lip, giving an
edentulous look.
• Orthodontically, extruding the maxillary teeth or
surgically positioning the maxilla inferiorly will be a
useful treatment approach.

• Interlabial Gap {Stms-stmi
(HP)}
• Vertical distance between the upper
lip to the lower lip in repose, has
been shown by Burstone to be fairly
ideal at a range of from just lightly
touching to approximately 3mm
apart.
• Mean – 2+2mm

CONCLUSION
• A thorough knowledge about Burstone analysis will
definitely help the orthodontist and the maxillofacial
surgeon in successfully treating orthognathic surgery
patients and in establishing an esthetic, harmonious and
stable relationship of the cranial base, jaws and teeth.

References
• RADIOGRAPHIC CEPHALOMETRY- ALEXANDER JACOBSON.
• ORTHODONTIC CEPHALOMETRY- ATHANASIOS E.
ATHANASIOU.
• FACIAL AND DENTAL PLANNING FOR ORTHODONTISTS
AND ORAL SURGEONS – ARNETTE – MCLAUGHLIN

• Charles J Burstone , cephalometrics for
orthognathic surgery ; Journal Of Oral
Surgery vol36, April 1978.
• Legan HL, Burstone CJ. Soft tissue
cephalometric analysis for orhtognathic
surgery. J Oral Surg 1980: 38 : 81-87.

Than Q

COGS analysis (Cephelometrics for orthognathic surgery) / fixed orthodontics courses india

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