N: The most anterior point of the frontonasal suture.Ba (Basion) point:Most inferior posterior point of the occipital bone, at the anterior margin of foramenMagnum.
Frankfurt plane drawback: Difficult to accurately locate position of porion thus affect orientation of frankfurt plane.S and N points advantages: 1.) S and N points easily located on ceph. 2.) S and N points located in the mid sagittal plane of head 3.) 2.) S and N points move minimally with any deviation of head from true profile position.
Mandibular plane disadvantage: curved plane & highly variable.
Down’s Mandibular plane: tangent to lower border of mandible and menton.
In analyzing the difference between maxillary and mandibular unit lengths, it must be kept in mind that the shorter the vertical distance betweenthe maxilla and mandible, the more anteriorly the chin will be placed for any given unit difference, and vice versa.Harvold did quantify the lower face height to account for this factor.
For eg. If BO is ahead of AO, Wits analysis say mandible is prognthic?, BUT WHY PROGNATHIC (1. maxillae is short and mandible is normal. 2. maxillae is normal but mandible is large) It doesn’t specifies which jaw is at fault.
Its greatest weakness was that the normative data for many of the measurements were based on unspecified samples collected by Rickets.The method therefore had limited scientific validity.
Represents the centre of the ramus, approximately equal to the location of the lingual.It is located by constructing a rectangle of four planes:Two prependicular planes from frankfort horizontal passing through points R1 & R2,and two horizontal planes parallel to Ptv through points R3 & R4,Xi is the centre of this rectangle.R1: the deepest point on the curve of the anterior border of the ramus.R2: a point located on the posterior the anterior border of the ramus opposite R1.R3: a point located at the centre and most inferior aspect of the sigmoid notch of the ramus.R4: a point on the lower border of mandible directly inferior to the centre of sigmoid notch.
Introduced by W. B. Downs to provide an assessment of the anteroposterior position of the chin in relation to the Frankfort horizontal plane.
This angle tends to decrease 1° every 3 years until maturity, as a result of growth and adaptive changes that occur to the mandible during normal development.
Lower facial height angle does not usually change significantly with age. However, this angle would be affected by treatment mechanics, i.e. it may open or close the bite. Any attempts at opening the facial axis will also open lower facial height & Vice versa.
The norm for a 9-yearold child is 26° + or - 4°. It increases approximately 0.5° per year with growth. This increase is due to slight changes in the morphology of the mandible as a result of arcial growth.
1.) owing to abnormal growth of chin brachyfacial patients show a decrease in convexity + 0.2mm per year.2.) Dolichofacial patients show -0.2mm decrease in convexity per year due to a vertical growth pattern of symphysis. This allows severlydolichofacial patterns to remain unaltered until maturity.
A high convexity indicates a Class II skeletal pattern; negative convexity, a skeletal Class III.
This measurement also determines the cause of overjet; i.e whether an increased or decreased overjet is due to malpositioning of the lower or upper incisor or both.
This is a critical measurement for planning purposes since for every 1mm forward or backward movement of incisors, the angle varies 2degree positive or negative. This is mainly due to type of movement of the incisor either forward or backward.
The McNamara Analysis has two major strengths.
1. It depends primarily on linear measurements rather than angles.This facilitates the orthopedic study and its basic principles can be easily communicatedto patients and parents.
The position of maxillae in the skull first should be assessed clinicallyby observing soft tissue profile & then evaluated by comparing various lateral cephalometric measurements to normative standards.Acute nasolabial angle may be reflection of the dentoalveolar protrusion, but it can also occur because of the orientation of base of nose.
owing to mandibular growth, this measurement doesn’t accept a constant norm since its yearly increase doesn’t correspond to increase at the cranial base.
There is a geometric relationship between maxillary and mandibular lengths.Any given maxillary length corresponds to a given mandibular length.The condylion is often difficult to locate, as it overlaps the petrous part of the temporalbones, and one may need to use a soft tissue filter or enhancing screens to find it.A slight error will not affect the relationship between maxillary and mandibular lengthbecause the condylion is a reference point for both.
Position of ramus is affected during growth and development by the muscular environment and dentoaleveolar growth.This is one of the two polygon angles that can be modified by treatment.
Transcript
1.
Cephalometric Analysis
Dr Abbas Naseem
B.D.S
2.
Goal Of Cephalometric Analysis
To evaluate the relationships, both horizontally & vertically, of the five major components of
face:
1. the cranium & cranial base
2. the skeletal maxillae
3. the skeletal mandible
4. the maxillary dentition and alveolar process
5. the mandibular dentition and alveolar process
i.e to estimate the relationships, vertically & horizontally, of the jaws to the cranial base & to each other
& the relationship of the teeth to their surrounding bone.
3.
Two basic approaches
Metric approach - use of selected linear and angular measures
Graphic approach - “overlay” of individual’s tracing on a reference template and visual
inspection of degree of variation
The analysis is usually given in tabular form
with data expressed either as a linear measurement (in mm or a proportion (%) )
or as an angle (degrees).
The advantage of angular measurements is that they are not inﬂuenced by image
magniﬁcation or patient size.
Standard deviation for each measurement allows the clinician to easily see where their
patient differs most signiﬁcantly from the norm.
4.
An alternative presentation of normative data is to express it graphically in the form of a
template.
This is superimposed on the patient’ s cephalogram to see where the patient varies from
the norm.
An example is the Proportionate Template, which is useful in determining the degree of
anteroposterior (AP) and vertical skeletal dysplasia present in adult patients.
This can then be used as a guide for planning for orthognathic (jaw) surgery.
7.
William Down’s Analysis (1948)
Considered Skeletal & Dental Pattern to measure facial form on a cephalogram.
Down felt that there are four types of faces as viewed on lateral profile.
1.
2.
3.
4.
Mesognathic with staight profile normal chin.
Retrognathic with recessive chin.
Prognathic where chin is prominent.
Prognathism when mandible is large.
Orignal sample and main reference plane
Down’s norms were based on 20 Caucasian subjects of range 17-21 years
of both sexes.
All individuals posses had ideal occlusions & no previous orthodontic treatment.
The frankfurt horizontal plane was used as a reference plane because of its clinical
visibility & its familiarity to clinicians.
8.
Retrognathic facial type
(recessive chin)
Orthognathic facial type
(staight profile normal chin)
9.
Prognathic facial type
(where chin is prominent)
True Prognathism
(when mandible is large)
10.
Basis of Down’s Analysis:
Down considered Sagittal position of ‘chin’ of greater importance in determining
the four basic facial types.
He felt that the subjects, whose malocclusion skeletal pattern variation was within range
of his norms, could be treated to norms.
However subjects whose skeletal and dental pattern were severely beyond the range
couldn’t be treated to hormonious balanced face within Down’s range of deviation.
Although facial pattern varied from orthognathic to a mild state of prognathism,
the face was still considered hormonious & balanced.
Down’s analysis provides information by which we can determine whether the
individual’s pattern shows comparatively hormonious relations or not,
& whether dysplasia present in the individual is in the facial skeleton, the dentition
or in both.
His analysis was not presented as the basis for a treatment goal rather it is a method for
examining & quantifying the relationships of the skeletal components of the face,
i.e maxillae & mandible & its dentition essentially the molars.
11.
Down’s Analysis (1948)
Reference planes
Facial plane
A line drawn from nasion through pogonion.
Mandibular plane
It is drawn tangent to the lower border of mandible and Me.
Occlusal plane
It is drawn by bisecting the overlapping cusps o f first molars and the incisal overbite.
In cases in which the incisors are grossly malposed, Downs recommended drawing
the occlusal plane through overlapping cusps of the premolars and the molars.
FH plane
It is drawn using superior border of machine porion and orbitale.
Y-axis plane
It is formed by drawing a line from sella turcica to gnathion.
Dental
Cant of occlusal plane
measures the angle between occlusal plane and FH.
Interincisal angle
angle formed by the intersection of lines drawn through the long
axis of the maxillary and mandibular incisors.
Incisor – occlusal plane the angle formed by the intersection of the occlusal plane
angle
through the long axis of the mandibular incisors.
IMPA
formed by the mandibular plane and a line drawn down the long
axis of the mandibular incisor.
Protrusion of maxillary
incisors
measured as the distance from the incisal edge of the maxillary
central incisal to a line drawn between the pog and point A.
12.
Down’s Analysis (1948)
Skeletal
Facial angle
measures the magnitude of the angle between the N-Pog
(facial) plane and the FH plane.
Angle of Convexity
measures the angle between N - point A and Pog - point A.
A-B plane angle
measures the angle between N-Pog and A-B line.
MP (mandibular plane)
angle
a line drawn from Me (menton) to the tangent to the lower
border of the mandible.
Y-axis (growth axis angle)
this measures the angle between FH & S – Gn.
17.
Skeletal: Facial Angle
The facial angle is used to measure the degree of protrusion or retrusion of the lower jaw.
• Increase facial angle = Prominent chin which may or may not be related with mandibular
prognathism.
• Decrease facial angle = Retrusive chin which may or may not be related with mandibular
retrognathism.
18.
Skeletal: Angle of Convexity
The angle of convexity is formed by the intersection of line from N to point A, to point A to
pogonion.
This angle measures the degree of the maxillary basal arch at its anterior limit (point A)
relative to total facial profile ( N – Pog ).
Positive angle suggests prominence of maxillary teeth relative to the mandible.
Negative angle is associated with prognathic profile.
Range extends from a minimal of -8.5: to a maximal of 10:, with mean reading of 0:.
20.
A-B plane: A line joining points A and B.
A-B angle: the superior angle formed by the intersection of the A-B plane and the facial line
(N-Pog) .
A-B plane is a measure of the relation of the anterior limit of the apical bases to each
other, relative to the facial line.
It represents an estimate of the difficulty in obtaining the correct axial inclination and incisor
relationship when using orthodontic therapy.
Because point B is positioned behind point A, this angle is usually negative in value except in
class III malocclusions or Class I occlusions with prominence of mandible.
A large negative value suggests a classII facial pattern.
This angle is negative in patients with skeletal Class II
and positive in patients with skeletal Class III malocclusions.
22.
Skeletal: Mandibular plane & Y-axis
• High mandibular plane angles occur in
both protrusive and retrusive faces AND
are suggestive of unfavourable
hyperdivergent facial patterns.
• Mandibular plane: tangent to lower
border of mandible and menton.
• Y axis indicates the degree of the downward, rearward or forward position of the chin in
relation to the upper face.
• Large Y-Axis ange indicates Class II facial patterns.
• Decrease of Y-Axis in serial radiographs may be interpreted as greater horizontal growth
pattern.
• Increase of Y-Axis is suggestive of greater vertical growth of the mandible.
23.
Dental: Cant of occlusal plane
A parallel relation of planes would provide a 0: reading.
Positive angle: when anterior part of the plane is lower than posterior. (large positive angles
are found in Class II patients)
Long rami tend to decrease this angle.
25.
Dental: Interincisal angle
This angle is relatively small in individuals whose incisors are tipped forward.
A measurement of the degree of procumbency of the incisor teeth, introduced by W. B.
Downs as the (posterior) angle formed by the intersection of the long axes of the maxillary
and mandibular central incisors.
• Highly variable according to the positions of these teeth in different biotypes.
• Dolichofacial patients will have vertical upper incisors & high interincisal angles eg. Deep
overbite
• Brachycephalic patients have more horizontal incisors and lower angles eg. The most
biprotrusions are accompanied by a lower IIA.
26.
Dental: Incisor – occlusal plane angle
Incisor – occlusal plane angle relates the lower incisors to their functioning surface at the
occlusal plane.
The positive angle increases as these teeth incline forward, Le. become proclined.
The values are least in class II div. 2 cases where the incisors are retroclined.
27.
Dental: IMPA (incisor mandibular plane angle)
The angle is positive when incisors are tipped forward. i.e, they are proclined forward.
The value increases as the proclination increases.
28.
Dental: Protrusion of maxillary incisors
The reading is positive if the incisal edge is ahead of the point A – pogonion line and
indicates the amount of maxillary dental prostrusion.
The reading is negative if the incisal edge lies behind the point A – pogonion line and
suggests a retruded position of maxillary incisors.
29.
Steiner Analysis
Cecil C. Steiner (1896-1989)
one of Edward H. Angle's first students in 1921.
He developed a form of cephalometric
analysis, presented in 1953, referred to as
the Steiner method of analysis.
He used the Ribbon Arch, as taught by
Angle, for many years, and he helped Angle file
out
some of the first Edgewise Brackets.
Cecil C. Steiner
30.
Steiner Analysis
Steiner approached and propagated cephalometrics
for effective use in treatment planning and not merely a diagnostic tool.
Steiner selected parameters from various analysis developed by several authors,
critically evaluated, modified and included them in his analysis.
Steiner proposed the appraisal of various parts of the skull separately as:
1. Skeletal analysis
2. Dental analysis
3. Soft tissue analysis
32.
Steiner in his analysis took into account that it may not be possible to reach ideal
Proportions and relationships in all cases, but there are ways to maximize esthetics.
Steiner devised ways to alter incisor positions to achieve normal occlusions even when
the ideal ANB angle couldn’t be achieved.
i.e how much the teeth needed to be moved to compensate for a skeletal malocclusion.
For larger skeletal discrpancies, the steiner method would not be effective for treatment.
Dental Camouflaging may be able to make up for the skeletal discrepancy.
38.
Skeletal: ANB angle
ANB angle indicates magnitude of the discrepancy between the maxilla and mandible.
ANB is affected by following factors other than anteroposterior discrepancy of jaws:
• Anteroposterior position of Nasion
• Vertical position of Nasion
• Jaw rotations
• Facial height
• ANB angle tell us only about “magnitude of the discrepancy between the jaws (maxilla and
mandible) ” not the absolute discrepancy.
• If treatment is based on obtaining the ideal ANB angle of 2: it may not necessarily obtain
the ideal position of either the maxilla or mandible.
• Steiner believed the main interest in treatment should be alleviating the magnitude of
discrepancy.
40.
Skeletal: occlusal plane angle (SN-Occlusal plane)
The mean reading for normal occlusions is 14°.
The angle is increased in long face or vertically growing individuals and also skeletal open
bite cases.
It may be decreased in horizontally growing individuals or cases with a skeletal deep bite.
41.
Skeletal: mandibular plane angle (SN-mandibular plane)
Excessively high (vertical growers) or low (horizontal growers) mandibular plane angles are
suggestive of unfavorable growth patterns
and these may complicate treatment results.
42.
Quiz
Mandibular plane Angle in Down’s Analysis
Vs.
Mandibular plane Angle in Steiner’s Analysis
44.
Dental: UI-NA distance
Dental: UI-NA angle
• Maxillary Incisors Position: The relative location and axial inclination of the upper incisors
are determined by relating the teeth to N-A line.
• To precisely determine the relative anteroposterior position of the incisors, it is necessary to
measure the distance of the most labial surface of the incisor to the NA line.
45.
Dental: UI-NA distance
Dental: UI-NA angle
• A measurement greater than 4mm show convex facial profile, common in class I bimaxillary protrusion or in class II div
1 relationship.
• A measurement less than 4mm show concave facial profile, as in class II div 2 or
• Angle greater than 22: may be seen in class II div 1 OR in class III relationship with dental compensation.
• Angle less than 22: may be seen in class II div II.
46.
Dental: LI-NB distance
Dental: LI-NB angle
• Angle greater than 25: may be seen in class II
div 1.
• Angle less than 25: may be seen in class II div
II OR class III.
Mandibular Incisors Position: The relative location and axial inclination of the lower incisors
are determined by relating the teeth to N-B line.
• To precisely determine the relative anteroposterior position of the incisors, it is necessary
to measure the distance of the most labial surface of the incisor to the N-B line.
47.
Dental: interincisal angle
A measurement of the degree of procumbency of the incisor teeth, introduced by W. B. Downs as the (posterior) angle
formed by the intersection of the long axes of the maxillary and mandibular central incisors.
• Highly variable according to the positions of these teeth in different biotypes.
• Dolichofacial patients will have vertical upper incisors & high interincisal angles eg. Deep overbite
• Brachycephalic patients have more horizontal incisors and lower angles eg. The most biprotrusions are accompanied
by a lower IIA.
48.
Dental: Holdaway ratio (LI-NB/Pg-NB)
A measurement introduced by R. A. Holdaway;
to evaluate the relative prominence of the mandibular
incisors, as compared to the size of the bony chin.
It is calculated as the ratio of the linear distance from the
labial surface of the mandibular central incisor to the NB
line, over the linear distance of the chin to the same line.
If ratio is 2:1 it means that lower incisors are more proclined
as compared to chin prominence.
If discrepancy is
2mm=acceptable
3mm=less desirable
4mm=correction indicated
Its importance lies in teeth extraction & genioplasty of the chin.
• Any discrepancy in the ratio indicates either dental proclination or chin protrusiveness /
retrusiveness.
• If extraction is indicated thick lips move half the value of teeth (50:100) , while thin lips move
the same value as teeth (100:100)
56.
Tweed’s Analysis (1954)
• Charles H Tweed (1895-1970)
• Tweed’s diploma from the Angle School.
• Angle and Tweed worked closely together
for the last two years of Angle's life.
• He devoted all 42 years of his professional
life to the use and refinement of Angle's
invention, the edgewise appliance.
Charles H. Tweed
57.
Tweed’s Analysis (1954)
Tweed’s analysis is based on:
inclination of mandibular incisors to the basal bone
& its association with the vertical relation of the mandible to the cranium.
58.
Cephalometric values effect decision to treat Extraction VS. Non Extraction
59.
When FMA<25 indicates Horizontal Growth Pattern
When FMA>25 indicates Vertical Growth Pattern
61.
FMA (Frankfurt mandibular plane angle)
Indicates the direction of lower facial Growth,
both horizontally and vertically
• Mean: 25 degrees
When FMA<25 indicates Horizontal Growth Pattern
When FMA>25 indicates Vertical Growth Pattern
62.
IMPA (incisor mandibular plane angle)
• Indicates that the upright position of the
mandibular incisor is normal
• Balance and harmony of the lower facial
• Mean: 87 degrees
profile
63.
FMIA (Frankfurt mandibular incisal angle)
Indicates the degree of balance and Harmony
between the lower face and the anterior limit of the dentition
• Mean: 68 degrees
64.
Variable
Mean Value
Range
Frankfort Mandibular plane Angle (FMA)
250
160-350
Incisor Mandibular Plane Angle (IMPA)
870
850-950
Frankfort Mandibular Incisor Angle (FMIA)
680
600-750
Mean %
Range%
Norms
used by
Dr. Tweed
FMA
24.57
16-35
25
26
Vertical growth pattern
IMPA
86.93
85-95
87
92
Proclined Lower Incisors
FMIA
68.2
60-75
68
62
Normal
Parameter
s
TOTAL
Patient
Value
Inference
180
179.7
180
65.
Viken Sassouni Analysis (1955)
Although several authors worked towards understanding the role and importance of the
vertical dimension, and its effect on the anteroposterior dimensions of the face, Viken
Sassouni’s work (1955) greatly emphasised it in orthodontic treatment planning.
Sassouni’s analysis was the first cephalometric method to categorize vertical as well as
horizontal relationships, and the interaction between vertical and horizontal proportions
of face.
Sassouni constructed a series of planes, arcs and axes on the profile cephalostatic
roentgenogram in order to study the structural configuration of the skull for the
purpose of growth analysis, diagnosis and treatment.
66.
Sassouni‘ contributed the idea that if a series of horizontal planes are drawn from the SN line
at the top to the mandibular plane below they will project toward a common meeting
point in a well-proportioned face.
67.
Inspection of the horizontal planes for this patient makes it clear that
the maxilla is rotated downward posteriorly and the mandible rotated downward Anteriorly.
These rotations of the jaws contribute to an open bite tendency, so the skeletal pattern
revealed here is often referred to as "skeletal open bite."
68.
Sassouni analysis
In a well-proportioned face, the under mentioned four planes meet at point O:
1. Tangent to sella and parallel with anterior cranial base (Os)
2. Palatal plane (On)
3. Occlusal plane (Op)
4. Mandibular plane (Og).
Sassouni considered the face to be well proportioned when axis of these four planes,
prolonged posteriorly meet at a common intersection which is posterior to the occipital
contour ‘O’.
71.
The relation of the four planes to the common point O permits of the classification of 4
facial types:
Type I: Anterior cranial base plane does not pass through O.
Type II: Palatal plane does not pass through O.
Type III: Occlusal plane does not pass through O.
Type IV: Mandibular base plane does not pass through O.
72.
Using O as the centre, Sassouni constructed the following two arcs:
Anterior arc: It is the arc of a circle, between anterior cranial base and the mandibular plane,
with O as the centre and O-ANS as radius.
Posterior arc: It is the arc of a circle, between anterior cranial base and mandibular base
plane, with O as centre and OSp as radius ( Sp the most posterior point on the rear
margin of sella turcica).
Sassouni’s approach was popularized as archial analysis.
Based on his observations and research, he classified all the malocclusions into 9 types of
craniofacial pattern.
These are:
1. Class I: neutral, open bite and deep bite
2. Class II: neutral, open bite and deep bite
3. Class III: neutral, open bite and deep bite
Essentially, the neutral or skeletal open bite (vertical pattern) and deep bite (horizontal
pattern) can exist in any all the three types of anteroposterior dysplasia of jaws.
73.
A well-proportioned face as defined by Sassouni is expected to possess normal occlusion.
To the contrary, of 50 persons with normal occlusion examined, only 16 were
found to have a well-proportioned face. Since the norm concept cannot be accepted as
absolute for the individual, Sassouni advocates the measurement of proportionality in
the individual as a basis of growth diagnosis and treatment planning.
74.
Sassouni evaluated the anteroposterior position of the face and dentition by noting the
relationship of various points to arcs drawn from the area of intersection of the planes.
In a well-proportioned face, the anterior nasal spine (representing the anterior extent of
the maxilla), the maxillary incisor, and the bony chin should be located along the same arc.
As with vertical proportions, it could be seen visually if a single point deviated from the
expected position, and in what direction.
Unfortunately, as a face becomes more disproportionate, it is more and more difficult to
establish the center for the arc, and the anteroposterior evaluation becomes more and
more arbitrary. (i.e increasing anterior-posterior discrepancies the analysis becomes more
arbitrary and less reliable.)
Although the total arcial analysis described by Sassouni is no longer widely used,
his analysis of vertical facial proportions has become an integral part of the overall analysis
of a patient.
In addition to any other measurements that might be made, it is valuable in any patient to
analyze the divergence of the horizontal planes and to examine whether one
of the planes is clearly disproportionate to the others.
75.
Harvold Analysis (1974)
Both the Harvold and Wits analyses are aimed solely at describing the severity or
degree of jaw disharmony.
Harvold, developed standards for the "unit length" of the maxilla and mandible.
• The maxillary unit length is measured from the posterior border of the mandibular
condyle to the anterior nasal spine. (TMJ to lower ANS)
( It measures the distance from condylion to point A. ) ?
• The mandibular unit length is measured from the posterior border of the mandibular
condyle to the anterior point of the chin. (TMJ to Prognathion)
(It measures the distance from condylion to Gnathion.) ?
• The difference between the unit length of maxilla and the unit length of mandible
indicates the size discrepancy between the jaws.
• This doesn’t take into account the vertical distance of the jaws, which if decreased places
the mandible more anteriorly.
• The position of the teeth has no influence on the Harvold figures.
76.
Measurements used in the Harvold analysis
• Maxillary length (TMJ to lower ANS) is measured from TMJ, the posterior wall of the
glenoid fossa, to lower ANS, defined as the point on the lower shadow of the anterior
nasal spine where the projecting Spine is 3mm thick.
• Mandibular length (TMJ to Prognathion) is measured from TMJ to prognathion, the point
on the bony chin contour giving the maximum length from the temporomandibular joint
(close to pogonion).
• Lower face height (upper ANS to Menton) is measured from upper ANS, the similar point
on the upper contour of the spine where it is 3mm thick, to menton.
77.
Wits Analysis (1975)
The Wits appraisal is a measure of the extent
to which the maxillae and mandible are
related to each other in the anterioposterior
(saggital) plane.
Wits analysis is used in the cases
where the ANB Angle is considered not so
reliable due to factors such as position of
nasion and rotation of the jaws.
A functional occlusal plane is drawn through
the overlapping cusps of first premolars and
molars.
Prependiculars are drawn to the occlusal plane from points A and B.
The points of contact of these prependiculars on the occlusal plane is termed AO & BO.
The distance between points AO and BO gives the anteroposterior relation between the
two jaws.
78.
In case of males BO is ahead of AO by 1mm
while in case of females AO & BO coincide.
In case of skeletal class II pattern BO is usually behind AO
while in case of skeletal class III pattern BO is located ahead of AO.
79.
Wits analysis; Considerations & Limitations
• The Wits analysis in contrast to the Harvold analysis, is influenced by the teeth
both horizontally and vertically.
Horizontally because points A and B are somewhat influenced by the dentition and
Vertically because the occlusal plane is determined by the vertical position of the teeth.
• It is important for Wits analysis that the functional occlusal plane,
drawn along the maximum intercuspation of the posterior teeth, be used rather than an
occlusal plane influenced by the vertical position of the incisors.
• Even so, this approach fails to distinguish skeletal discrepancies from problems caused
by displacement of the dentition or specify which jaw is at fault if there is a skeletal
problem.
If the Wits analysis is used, these limitations must be kept in mind.
The Wits analysis takes into account the horizontal and vertical relationship of the jaws,
but is still flawed due to fact that it is influenced by the dentition and therefore skews
analysis from indicating the true skeletal discrepancies between the jaws.
80.
Ricketts Analysis (1960s)
Ricketts analysis essentialy tries to orient
face and mandible to the cranium.
Ricketts tries to determine the proper spatial
relationship of the jaws for both esthetic and
function.
He gave great emphasis to the growth and
facial growth pattern.
The ultimate objective was to integrate growth
to work out best possible treatment plan.
Ricketts approach in selection of landmarks
and parameters was essentially based
on the pattern of facial growth.
Rickets Cephalometric analysis allows a detailed study of:
1.) the patient’s craniofacial morphology to determine the facial type.
2.) the positions and interrelations of the different components of the dento-maxillo-facial
structures in several fields.
82.
Landmarks:
C1
Condyle
A point on the condyle head in contact with & tangent to the ramus
plane
CC
Center of
cranium
The point of intersection of the basion nasion plane and the facial
axis
CF
Center of
face
The point of intersection of the pterygoid vertical to the Frankfort
horizontal plane.
PT
PT point
The junction of the pterygomaxillary fissure and
the foramen rotundum
DC
Dead centre
of Condyle
The point in the center of condyle neck along
the Ba-N plane
83.
Landmarks:
Gn
Gnathion
A point at the intersection of the facial and the
mandibular planes (cephalometric Gn as a
opposed to anatomic Go)
PM
Suprapogonio
n
(Protuberanc
e menti)
The point at which the shape of the symphysis mentalis changes
from concave to convex also know as protuberance menti.
Pog
Pogonion
The point on the bony symphysis tangent to the
facial plane.
PO
Cephalometri The intersection of the facial plane and the corpus axis
c
TI
TI point
(A point selected at the anterior border of the symphysis between point B
and pogonion where the curvature changes from concave to convex.)
The point of intersection of the occlusal and the
facial planes.
84.
Dental:
A1 incisor
Incisal edge of the upper incisor.
Ar incisor
Root apex of the lower incisor.
B1 incisor
Incisal edge of the upper incisor.
Br incisor
Root apex of the lower incisor.
A6
Upper
molar
A point on the occlusal plane located perpendicular to the distal
surface of the crown of the upper first molar.
B6
Lower
molar
A point on the occlusal plane located perpendicular to the distal
surface of the crown of the lower first molar.
85.
Soft tissue:
En
Nose
The anteriormost point of the soft tissue nose.
Dt
Chin
The anteriormost point of the soft tissue chin.
UL
Upper lip
The anteriormost point of the upper lip.
LL
Lower lip
The anteriormost point of the lower lip.
Em
Embrassure Where the upper and lower lips meet in the midline.
88.
Facial axis of Ricketts (Pt-Gn) :
A line connecting "gnathion" with cranial point pterygoid "Pt".
89.
Facial axis angle of Ricketts (Ba-N - Pt-Gn)
The inferior angle formed by the intersection of the facial axis of Ricketts and the Ba-N line.
This angle on the average approximates 90.
A value smaller than 90 indicates facial growth primarily in the vertical direction and/or a
Class II pattern,
whereas a value greater than 90 degrees indicates a horizontal growth pattern and/or a
Class III tendency
90.
Don’t Confuse facial axis with facial plane !!
Facial Axis is: Pt to Gn
Facial Plane is: N to Pog
91.
CC Point (Centre of cranium) :
formed at the intersection of the Ba-N & Pt-Gn(facial axis) lines.
92.
CF Point (Centre of face) :
Formed by the intersection of frankfort plane (Pr-Or) and the prependicular line tangent
to the posterior surface of the pterygomaxillary fissure
[i.e prependicular through (pterygoid) PT line (PTV) ]
93.
Dead Centre (of the condyle) Point (Ricketts)
Center of the neck of the condyle on the Ba-N(Basion Nasion) plane.
94.
Xi-point
A point located at the geometric centre of the ramus. Location of Xi is keyed geometrically to
porion-orbitale (FH) and perpendicular through PT (PTV) in the following steps:
• By construction of planes perpendicular to FH and PTV.
These constructed planes are tangent to points (Rl, R2, R3, R4) on the borders of the ramus.
• The constructed planes form a rectangle enclosing the ramus.
• Xi is located in the centre of the rectangle at the intersection of diagonals.
Steps in the construction of the Xi-point
Rl. Mandible.
The deepest point on the curve of the anterior border of the ramus, one-half the distance
between the inferior and superior curves.
R2. Mandible.
A point located on the posterior border of the ramus of the mandible.
R3. Mandible.
A point located at the centre and most inferior aspect of the sigmoid notch of the ramus of
the mandible.
R4. Mandible.
A point on the border of the mandible directly inferior.
98.
Condylar axis (Dc-Xi):
This plane is used to describe mandibular morphology.
In its relation to the axis of the corpous of the mandible it forms an angle, the mandibular
Arc.
99.
Axis of the corpous of the mandible/Corpous Axis (Xi – Pm) :
It is defined by tracing a line from Xi to Pm which will serve to define changes in the
lower dentition and in mandibular size & morphology.
100.
Ricketts Basic Cephalometric Analysis
It provides an overview of the patient’s craniofacial and dental growth direction.
Measurements to locate the chin in space
1. Facial axis angle
2. Facial depth angle
3. Mandibular plane angle
4. Lower facial height
5. Mandibular arc
Measurements to determine convexity
6. Convexity of point A
Measurements to locate denture in face
7. Lower incisor protrusion
8 . Lower incisor inclination
9. Upper molar position
10. Interincisal angle
Measurements to determine the profile
11. Lower lip to E-plane
12. Maxillary depth
101.
Ricketts Measurements to locate the chin in space
1. Facial axis angle of Ricketts (Ba-N - Pt-Gn):
The angle describes the direction of growth of mandible at chin.
The inferior angle formed by the intersection of the facial axis of Ricketts and the Ba-N line.
This angle on the average approximates 90:.
Facial axis angle remains stable in a normally growing child or reduce a little.
A value smaller than 90 indicates (smaller angle) facial growth primarily in the vertical
direction and/or a Class II pattern,
whereas a value greater than 90 degrees indicates (larger angle) a horizontal growth pattern
and/or a Class III tendency.
102.
2. Facial depth angle:
The inferior posterior angle formed by the intersection of the Frankfort horizontal and the
facial plane (N-Pog).
This angle gives the clinician an indication mandible (pogonion) in sagittal direction.
Increase in facial depth angle suggests a forward position of pog (brachyfacial type)
while decrease implies a retrusion, as in dolichofacial patterns,
• This facial depth angle increases 1° every 3 years as the mandible grows forward and
downward. This change with age is mainly due to a differential growth magnitude of the
anterior cranial base with respect to mandibular corpous.
• In adulthood, the mean measurement is 90°.
103.
3. Mandibular plane angle:
The mandibular plane angle is formed by the intersection of mandibular plane and the
Frankfort horizontal plane.
This angle gives the clinician an indication of the cant of the mandibular corpous
and its value depends on the shape & position of the mandible within the craniofacial
complex.
High mandibular plane angle is seen in dolichofacial patients with weak musculature and
prone to open bite or vertical growth problems.
Low mandibular plane angle is found in brachyfacial types with strong musculature
and deep bites who tend to have square jaws.
104.
4. Lower facial height:
This is the angle formed by the intersection of a line from anterior nasal spine (ANS)
to Xi-point and the corpus axis (Xi-Pm).
A larger angle indicates a divergence of mandible and maxilla or vertical growth trend.
(Dolichofacial pattern with weak musculature & prone to skeletal open bite)
Low values of angle are suggestive of horizontal facial pattern.
(Brachyfacial pattern with strong musculature & a deep overbite)
Ans
Xi
Pm
105.
5. Mandibular arc:
The mandibular arc is the angle formed by the intersection of the condylar axis (DC-Xi) and the
distal extrapolation of the corpus axis.
It describes the configuration of the mandible;
A large angle is indicative of a ‘strong’ and ‘square’ mandible; (brachyfacial pattern)
Smaller angles suggest a short ramus, obtuse-shaped mandible and vertical growth pattern.
(dolichofacial)
Dc
106.
Ricketts Measurements to determine convexity
6. Convexity of point A :
Facial convexity is the distance in millimeters from A point to the facial plane, when
measured perpendicular to that plane. The normal growth trend shows more anterior
growth of the mandible than the maxilla. Thereby a decreases in its measurement
with age. At maturity, the norm is 9 mm, indicating that A point lies along the facial plane.
A high convexity indicates a Class II skeletal pattern; negative convexity, a skeletal Class III.
107.
Ricketts Measurements to determine convexity
6. Convexity of point A :
108.
Ricketts Measurements to locate teeth in face
7. Lower incisor protrusion.
This linear measurement relates the position of the tip of the lower central incisor
to the maxillomandibular relationship. (it indicates the position of L.I in sagittal plane).
The plane used to describe this relationship intersects both A point and pogonion (A-PO).
The distance from the tip of the incisor is measured perpendicular to this plane.
The position of the lower incisor has been associated both with aesthetics and stability as
suggested by Tweed. Labial or lingual movement of lower incisors affects arch length.
109.
8. Lower incisor inclination:
The angular measurement formed by the intersection of the long axis of the lower central
incisor and the A-Pog plane is called the lower incisor inclination.
The measurement also relates the lower incisor to the maxillomandibular relationship.
110.
9. Upper molar position:
Upper molar position is the linear distance between the most distal point of the maxillary first
permanent molar, and the pterygoid vertical (PTV) measured parallel to the occlusal plane.
• Indicates protrusion or retrusion of the upper dental arch (i.e This measurement indicates
mesial or distal position of the upper teeth. )
• It is also indicative of whether or not the upper molar can be moved distally without
impacting the maxillary second and third molars.
• Norm is the patient’s age (in years) plus 3 mm.
At least 21 mm of maxilla (+/- 3 mm) is generally needed in later years for proper eruption of
the second and third molars. (lower values predict the impaction of 2nd and 3rd molars)
111.
10. Interincisal angle:
A measurement of the degree of procumbency of the incisor teeth, introduced by W. B. Downs
as the (posterior) angle formed by the intersection of the long axes of the maxillary and
mandibular central incisors.
• Highly variable according to the positions of these teeth in different biotypes.
• Dolichofacial patients will have vertical upper incisors & high interincisal angles eg. Deep
overbite
• Brachycephalic patients have more horizontal incisors and lower angles eg. The most
biprotrusions are accompanied by a lower IIA.
112.
Ricketts Measurements to determine the profile
11. Lower lip to E-plane:
The lower lip protrusion is evaluated by measuring the lower lip from an aesthetic
line constructed by joining the tip of the nose and the tip of the chin.
Esthetic plane: tip of nose to tip of chin
Lower lip protrusion: lower lip to E-plane
113.
12. Maxillary depth:
This angle is formed by intersection of FHP to a line from Nasion to A point.
The maxillary depth angle relates horizontal position of maxilla at point A to cranium (NA).
(i.e shows anteroposterior position of maxillae)
A high angle indicates protrusion of maxillae.
Low angle indicates retrusion of maxillae
Norm: 90± 3
Value doesn’t change with age.
114.
Two maxillae related measurements
1. Facial Convexity
2. Maxillary depth
115.
McNamara Analysis (1983)
• Dr. McNamara is considered an
innovator in orthodontic diagnosis and
treatment.
•
He developed a form of cephalometric
analysis referred to as the McNamara
method of analysis.
• His research focuses extensively on the
clinical modification of the growth of the
face and jaws.
James A. McNamara
DDS, MS, PhD
For more:
http://mcnamaraorthodontics.com
http://en.wikipedia.org/wiki/James_A._McNamara
116.
McNamara Analysis relate:
1. teeth to teeth
2. teeth to jaws
3. each jaw to the other
4. jaws to the cranial base
The McNamara analysis combines elements of previous approaches (Ricketts and
Harvold) with original measurements to attempt a more precise definition of jaw and
tooth positions.
In this method, both the anatomic Frankfort plane and the basion-nasion line are used as
reference planes.
117.
McNamara Analysis Method advantages:
1. It depends primarily on linear measurements rather than angles.
2. It analyses the interarch relationship in the vertical plane as well as sagittal,
integrating them into a single unit.
3. It helps in diagnosing the external condition of the airway.
118.
Planes & Measurements used for Skeletal study
1.
2.
3.
4.
5.
6.
Nasion prependicular ( also called McNamara’s line or vertical )
Linear distance from point A to Nasion prependicular.
Linear distance from point Pog to Nasion prependicular.
Maxillary length
Mandibular length
Lower anterior facial height
Planes & Measurements used for Analysis of the Airways
1. Upper pharynx diameter.
2. Lower pharynx diameter.
120.
Maxillae to the Cranial Base
Soft tissue evaluation by:
1. Nasolabial angle
2. Cant of the upper lip
Hard tissue evaluation by:
1. Point A to nasion prependicular
Nasolabial angle
Cant of the upper lip
121.
1. McNamara analysis; Skeletal study; McNamara’s line or vertical (Nasion Prependicular)
Constructed from nasion to chin, prependicular to the frankfort plane.
122.
2 . McNamara analysis; Skeletal study; Point A to Nasion Prependicular
It relates the maxillae to the cranial base.
The maxillae should be on or slightly ahead of this line.
If point A is ahead of the vertical line, the measurement will be positive.
If point A is behind of the vertical line, the measurement will be negative.
Norm for mixed dentition: 0 mm (vertical line intersects point A)
Norm for adults : 1 mm
123.
2 . McNamara analysis; Skeletal study; Point A to Nasion Prependicular
The norm for point to nasion prependicular for adults : 1mm
124.
3 . McNamara analysis; Skeletal study; Point Pognion to Nasion Prependicular
It relates the mandible symphysis to the cranial base.
If point Pognion lies anterior to Nasion prependicular, the measurement will be positive.
If point Pognion lies behind to Nasion prependicular, the measurement will be negative.
Norm for mixed dentition: -8 to -6 mm
Norm for adults women : -4 to 0 mm
Norm for adults men: -2 to +2 mm
125.
4 . McNamara analysis; Skeletal study; Maxillary Length (also called midfacial length)
It measures the distance from condylion to point A.
( Condylion: the most posterosuperior point on the outline of the mandibular condyle. )
126.
5 . McNamara analysis; Skeletal study; Mandibular Length
It measures the distance from condylion to gnathion.
( Condylion: the most posterosuperior point on the outline of the mandibular condyle. )
127.
Maxillae to Mandible
• Any given effective midfacial (maxillary) length corresponds to an effective mandibular
length within a given range (ref to table 9.1)
128.
6 . McNamara analysis; Skeletal study; Lower Anterior facial height
It measures from ANS to menton.
An increase or decrease in this measure can have a profound effect on the horizontal
relationship of the maxillae and mandible.
This measurement increases with age & corelates with the maxillary length.
130.
Vertical Relationship
2. Facial axis angle
Norm: 90:
negative value suggests excessive vertical development of face.
positive value suggests deficient vertical development of face.
131.
7 . McNamara analysis; Airway analysis; Upper pharyngeal width
the smallest distance from the posterior pharyngeal wall to anterior half of the soft palate
outline.
Norm for adult: 17±4
A marked decrease of this measurement is used only as an indicator of possible
upper airway impairment.
a more accurate diagnosis will be made by an otorhinolaryngologist during clinical exam.
132.
8 . McNamara analysis; Airway analysis; Lower pharyngeal width
measured on the mandibular plane from posterior tongue to posterior pharyngeal wall.
Norm for adult women: 11.3±4
Norm for adult: 13.5±4
Values >15 mm suggest anterior positioning of the tongue
either postural or enlargement of the tonsils.
a.) Postural anterior positioning of the tongue is associated with certain anomalies such as
mandibular prognathism, dentoalveolar anterior crossbite, or dentoalveolar biprotrusion
of the teeth.
b.) Anterior positioning of the tongue due to enlargement of the tonsils ( such as among
mouth breathers ) often accompanied by
a dolichofacial pattern, with open facial axis and a very steep mandibular plane.
135.
Enlow’s Counterpart Analysis
Enlow pointed out, both the dimensions and alignment of craniofacial components are
important in determining the overall facial balance.
Enlow's counterpart analysis emphasizes the way changes in proportions in one part of the
head and face can either add to increase a jaw discrepancy or compensate so that
the jaws fit correctly even though there are skeletal discrepancies
Vertical dimensions:
• If anterior face height is long,
facial balance and proper proportions are preserved
if posterior face height and mandibular ramus height also are relatively large.
Short posterior height can lead to a skeletal open bite tendency
even if anterior face height is normal because the proportionality is disturbed.
Horizontal dimensions:
• If both maxillary and mandibular lengths are normal but the cranial base is long,
the maxilla will be carried forward relative to the mandible and maxillary protrusion
will result.
Similarly short maxilla will compensate perfectly for a long cranial base.
136.
Alignment
would affect both the vertical and a-p position of the various skeletal units and
could compensate for or worsen a tendency towards imbalance.
If maxilla rotated down posteriorly, a long ramus, acute gonial angle would compensate
and allow normal facial proportions and normal occlusion.
but even a slightly short ramus would produce downward-backward
mandibular rotation and a long face-open bite tendency.
137.
Enlow’s Counterpart Analysis
lf anterior and posterior vertical dimensions
dimensions match each other, there is no
problem,
but if they do not, whether short or long,
malocclusion will result.
If the maxillae is long (measurement 6) ,
there is no problem if the mandible (7) also
is long,
but malocclusion will result if the
mandibular body length is merely normal.
138.
Template Analysis
• Compensatory skeletal and dental deviations within an individual can be observed
directly.
• Allows easy use of age-related standards.
• Quickly provides an overall impression of the way in which the patients dentofacial
structures are related.
139.
Template Analysis
Types of Templates:
1. Schematic (michigan,burlington)
2. Anatomically complete (broadbent-bolton,alabama)
The schematic templates show changing positions of selected landmarks with age on a single
template.
The anatomically complete templates, a different one for each age, are particularly
convenient for direct visual comparison of a patient with a reference group while accounting
for age
Bolton templates are most often used for template analysis
140.
Template Analysis
• The first step in template analysis is to pick the correct template
from the set of age-different ones that represent the reference data.
Two things to be kept in mind:
1. the patients physical age
2. his or her developemental age
The best plan usually is to select the reference template initially so that the length of the
anterior cranial base( of which the SN distance is a good approximation) is approximately
the same for the patient and the template.
and then to consider developmental age, moving forward or backward in the template age
if the patient is developmentally quite advanced or retarded.
141.
Template Analysis
• Analysis using a template is based on:
series of super impositions of the template, over a tracing of the patient being analyzed.
The sequence of superimpositions follows:
1. Cranial base superimposition
2. Maxillary superimposition
3. Mandibular superimposition
142.
1. Cranial base superimposition
• Allows evaluation of relationship of maxilla and mandible to the cranial base.
• For analysis with templates, registering SN at N is usually preferable.
(with cranial base registered, the anteroposterior and vertical position of maxilla and mandible
can be observed and described.)
• It is important to look, not at the position of the teeth,
but at the position of the landmarks that indicate the skeletal units.
The object is to evaluate the position of the skeletal units.
• The template is being used to see directly how the patient's jaw positions differ from
the norm.
• Compensations with in the individual's skeletal pattern are observed directly.
143.
Cranial base super imposition of the standard Bolton template for age 14 (red) on the
tracing of a 13-year-old boy.
*The age 14 template was chosen because it matches cranial base length.
In the figure, Comparison of the patient’s tracing
with the template shows:
1. increase in the lower face height.
2. downward rotation of the mandible.
3. maxilla is rotated down posteriorly.
Comparison of a patient's tracing to a template is a direct approach toward describing the
relationship of functional facial units.
144.
2. Maxillary superimposition
• The Maxillary superimposition is on the maximum contour of the maxilla
• To evaluate the relationship of the maxillary dentition to the maxilla.
• Evaluate the position of the teeth both vertically and anteroposteriorly.
The template makes it easy to see whether teeth are displaced vertically,
information not often obtained in measurement analysis techniques.
145.
Superimposition of the Bolton template on the maxilla (primarily, the anterior palatal
contour) of the patient.
This superimposition clearly reveals the forward protrusion of the maxillary incisors but
shows that the vertical relationship of the maxillary teeth to the maxilla for this patient is
nearly ideal.
146.
3. Mandibular superimposition
• The Mandibular superimposition is on the symphysis of mandible along the lower
border.
• To evaluate the relationship of mandibular dentition to mandible.
• lf the shadow of the mandibular canal is shown on the templates a, more accurate
orientation can be obtained by registering along this, rather than the lower border
posteriorly.
• Both the vertical and the anteroposterior positions of the anterior and posterior teeth
should be noted.
147.
Superimposition of the Bolton template on the mandible of the patient
This superimposition indicates that the patient's mandible is longer than the ideal,
but the ramus is shorter and inclined posteriorly.
All the mandibular teeth have erupted more than normal, especially the incisors.
148.
Bjork-Jarabak’s Analysis (1972)
Bjork-jarabak’s Polygon is very useful to predict growth patterns
both from qualitative and quantitative point of view (i.e direction and amount).
It also contributes to better defination of facial type.
Early prediction of the patients abnormal growth potential.
Bjork studied the behavior of craniofacial structures during growth.
His observations are based on a study of approximately 300 children aged 12and a simmilar
number of soldiers whose ages ranged from 21 – 23 in whom almost 90 measurements
were determined.
Bjork’s polygon:
1. Direction and amount of growth potential.
2. Supplement to the study of the facial type.
149.
Tracing the polygon
Planes of the polygon:
1.
2.
3.
4.
5.
6.
Anterior cranial base
Posterior cranial base
Ramus height
Mandibular plane
Anterior facial height
Posterior facial height
S
N
Ar
Go
Me
150.
Tracing the polygon
Angles of the polygon:
1.
2.
3.
4.
5.
Saddle angle
Articulare angle
Gonial angle
Upper gonial angle
Lower gonial angle
151.
Norms for Bjork-Jarabak’s
1.
Saddle angle
123: ± 5
2.
Articulare angle
143: ± 6
3.
Gonial angle
130: ± 7
4.
Sum of S+Ar+Go angles
396: ± 6
5.
Upper half gonial angle
52: to 55:
6.
Lower half gonial angle
70: to 75:
7.
Posterior cranial base
32 ± 3mm
8.
Ramus height
44 ± 5mm
9.
Anterior cranial base
71 ±3mm
10.
Length of the body of mandible
71 ± 5mm
11.
Posterior facial height
70 – 85 mm
12.
Anterior facial height
105 – 120mm
13.
Posterior/Anterior facial height
62 – 62 %
152.
Recall: Concepts of growth & developement
Cranial base synchondroses
Growth Site OR Growth Center ?
153.
Recall: Anatomy
1. the posterior cranial base is completed laterally with the temporal bones
2. glenoid cavities(fossae) are located in the squamous portion of the temporal bone
154.
1. Bjork-Jarabak’s Analysis: Saddle Angle (N-S-Ar) / Seat angle
Formed by union of Anterior cranial base (N-S) with the Posterior Cranial base (S-Ar).
To interpret measurements of saddle/seat angle;
It is necessary to consider the existence of a centre of endochondral growth formed by
the spheno occipital synchondrosis.
Since glenoid cavities(fossae) are located in the squamous portion of the temporal bone
(the posterior cranial base is completed laterally with the temporal bones )
they will be influenced by spheno occipital synchondrosis (center of growth)
The other bones that form up this portion of cranial base will be influenced as well.
The sphenooccipial synchondrosis stops growing at about age of 15,
and fusion is completed around age 20.
155.
Relationship between the saddle angle & the location of glenoid cavity and condyle.
Lower saddle angle
S
The norm for saddle angle is: 120:
Anterior
Cranial
Base
Posterior
Cranial
Base
Ar
low angle indicates S-Ar is vertical
Higher saddle angle
S
Posterior
Cranial
Base
Anterior
Cranial
Base
Ar
high angle indicates S-Ar is horizontal
This Variation in S-Ar line (posterior cranial base) results in different location of the
glenoid cavity thus influencing the mandible position anteroposteriorly.
Low angle: downwards and slightly backwards displacement of the joint cavity resulting
in more forward implantation of mandible. (this might cause, even with normal growth
of mandible a Class III skeletal profile)
High angle: downward and backward displacement of the joint cavity resulting
in distal implantation of mandible. (mandible has to grow more to reach orthognathic
profile)
156.
Saddle angle might be larger or lower than the norm in the three facial types.
In general,
1. Large(open) saddle/seat angles are frequent in Dolichofacial patients.
2. Low(closed) angles are usually seen in brachyfacial and mesofacial patients.
Although the saddle angle cannot be modified by an orthodontic
treatment,
it is structural factor that should be taken into account in growth forecast,
because mandibular projection might result in different angulation.
157.
2. Bjork-Jarabak’s Analysis: Articulare Angle (S-Ar-Go)
The norm for articulare angle is: 143:
Higher(open) angle: favour mandibular retrognathism
Lower(close) angle: favour mandibular prognathism
158.
Higher(open) angle:
• favour mandibular retrognathism
• Dolichofacial patterns with vertical rami
that will not project the symphysis forwardly
with growth.
Lower(close) angle:
• favour mandibular prognathism
• more the sagittal projection of the symphysis
during growth.
• suggests a strong muscular type.
Effect of the articulare angle on the
facial profile.
159.
3. Bjork-Jarabak’s Analysis: Gonial Angle (Ar-Go-Me)
Gonial angle can be analyzed in terms of
1. Total gonial angle
2. Or it two parts upper gonial angle and
lower gonial angle
Go
• Total gonial angle describes the shape of mandible.
• This structure can be considered as the center around which the rest of the face will
adapt its growth;
• it also determines the direction of growth of the lower half of the face.
160.
Closed (low) Gonial angle
Vs.
Square mandible.
High mandibular arch.
Orthognathic profile.
Brachyfacial pattern.
Subtle (Shallow) antegonial notch
The norm for gonial angle is: 130:
Open(high) Gonial angle
Low mandibular arch.
Retrognathic profile.
Dolichofacial pattern.
Marked antegonial notch
161.
Antegonial Notch
The antegonial notch depth is the deepest point of the mandibular inferior border
notch concavity.
163.
Am J Orthod Dentofacial Orthop. 1987 Feb;91(2):117-24.
The depth of the mandibular antegonial notch as an indicator of
mandibular growth potential.
Singer CP, Mamandras AH, Hunter WS.
Abstract
The craniofacial characteristics and growth potential of 25 orthodontically treated patients
with deep mandibular antegonial notch were compared with a similar group of 25 shallow
notch subjects by the use of longitudinal lateral cephalometric radiographs. Deep notch
cases had more retrusive mandibles with a shorter corpus, smaller ramus height, and a
greater gonial angle than did shallow notch cases. The lower facial height in the subjects with
a deep mandibular notch was found to be longer, and both the mandibular plane angle and
facial axis were more vertically directed. During the average 4-year period examined, the
deep notch sample experienced less mandibular growth as evidenced by a smaller increase
in total mandibular length, corpus length, and less displacement of the chin in a horizontal
direction than did the shallow notch sample. The
results of this study suggest
that the clinical presence of a deep mandibular antegonial notch is
indicative of a diminished mandibular growth potential and a
vertically directed mandibular growth pattern.
Ref: http://www.ncbi.nlm.nih.gov/pubmed/3468794
164.
4. Bjork-Jarabak’s Analysis: Upper half gonial angle ( Ar-Go-N)
Upper half gonial angle describes:
how oblique the ramus is.
High angle indicates:
a more forward projection of the symphysis.
Low angle indicates:
limited advancement of the chin.
The norm for upper gonial angle is: 52-55:
165.
5. Bjork-Jarabak’s Analysis: Lower half gonial angle ( N-Go-Me)
Lower half gonial angle describes:
the slant of mandibular body.
high angle indicates:
downward inclination & tendency for an open bite.
lower angle indicates:
horizontal mandibular body & tendency for an
overbite.
The norm for gonial angle is: 70-75:
166.
6. Bjork-Jarabak’s Analysis: Sum of posterior angles ( S-Ar-Go)
Adding the values of all three angles (S, Ar, Go) eliminates the compensations
& the “result” will show growth direction.
Lower angle suggests:
anterior growth of the symphysis
Sum less than 396:
High angle predicts:
vertical growth and limited chin advancement
Sum more than 396:
The norm for sum of S+Ar+Go angle is: 396:
167.
Linear measurements & their relationships
They are the measurements of the lines that form the 5 sides of the polygon:
1.
2.
3.
4.
5.
6.
Anterior cranial base
Posterior cranial base
Ramus height
Length of the body of mandible
Anterior facial height
Posterior facial height
168.
Anterior Cranial Base : Mandibular body length
• The normal ratio is 1:1.
• For every 1mm of growth of the anterior cranial base, the mandibular body will grow
1-1.5mm.
• Where the mandibular body is longer than the anterior cranial base by 3-5mm,
the mandible growth will be accelerated (higher than 1:1 ratio) and tends towards
Class III.
169.
Posterior Cranial base - Ramus height
According to Jarabak, a ratio of 3:4+ indicates a good vertical growth of the face.
170.
Dated: Nov, 2013
R E F E R E N C E S:
1. Orthodontics and Orthognathic Surgery; diagnosis and treatment planning; Jorge
Gregoret
2. Radiographic Cephalometry by Alexander Jacobson
3. Contemporary Orthodontics by William R. Proffit; 4th edition
4. Orthodontics Diagnosis and Management of Malocclusion and Dentofacial Deformities
by Om Prakash Kharbanda
Dr.Abbas Naseem