CEPHALOMETRICS AS A DIAGNOSTIC AID Introduction Definition Types of cephalogram Uses Anatomic landmarks Lines and planes of lateral cephalometrics Cephalostat Steiner analysis Downs analysis Tweed’s analysis Wits appraisal Sassouni analysis McNamara analysis Ricketts analysis
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INTRODUCTION ‘Beauty is the finest expression of human emotion. The art that was produced in the past has survived because it was expressed in the highest, finest and most sensitive manner possible. The beauty that survives knows no limits either of time or place’. - Wuerpel Ever since God created man in his image, man has been trying to change man into his image. Orthodontists, in their attempts to treatment planning with brought various analysis into being. In 1922, Pacini introduced a method for standardized head radiography and failed due to large fixed distance from X-ray source to the cassette. Dr. Herbert Hofrath of Germany and Dr. B. Holly Broadbent of U.S. published a new X-ray technique and its application in orthodontia. In 1946, Dr. Charles Tweed developed Tweeds diagnostic triangle. First true classic full scale cephalometric analysis developed by William B. Downs in 1948. In 1953, Dr. C.C. Steiner presented his famous Steiner’s analysis. Riedel in 1952 developed SNA and SNB angle. Sassouni (1995) described total archial analysis. Rickets (1960) give dynamic analysis to study morphology of a patient at different stages of development or treatment. Jacobson’s ‘Wits’ appraisal (1975) was used for assessing horizontal disharmony of the jaw. For surgical correction quadrilateral analysis Dipaolo (1970) and an analysis by McNamara (1984) developed.
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DEFINITION Cephalometrics includes measurements, description and appraisal of the morphologic configuration and growth changes in the skull by ascertaining the dimensions of lines, angles and planes between anthropometric landmarks established by physical anthropologists and point selected by orthodontists. TYPES OF CEPHALOGRAM 1) Lateral cephalogram 2) Frontal cephalogram USES 1) Helps in orthodontic diagnosis, by enabling study of skeletal, dental and soft tissue structures of the craniofacial region. 2) Helps in classification of malocclusion. 3) Helps in treatment planning. 4) Evaluation of treatment results. 5) Helps in predicting growth related change. 6) It is also valuable aid in research work. ANATOMIC LANDMARKS 1)
Nasion – Most anterior patient on naso frontal suture.
2)
Sella – Midpoint of hypophyseal fossa.
3)
Si – Most inferior patient of lower contour of sella turcica.
4)
SP – Most posterior patient on posterior contour of sella turcica.
5)
Se – Midpoint of the entrance of sella. At the same level of jugum sphenoidal.
3
6)
Point A (subspinale) – Deepest midline patient in the curved bony outline from the base of alveolar proceeds of the maxilla. i.e. between ANS and Prosthion. Donovan - Junction of maxillary basal bone and alveolar bone. Higley – Deepest midline point between ANS and Prosthion on the premaxilla. Jacobson – Anterior limit of maxillary denture base.
7)
Prosthion – Alveolar rim of maxilla or the lower most anterior point on the alveolar portion of the premaxilla in the median plane between upper central incisors.
8)
Is (Incisor spurious) – Tip of crown of most anterior maxillary central incisor.
9)
AP 1 (Apicale 1) - Root apex of the most anterior mandibular central incisor.
10) Ii (Incisor inferius) - Tip of crown of most anterior mandibular incisor. 11) AP 1 – Root apex of most anterior maxillary incisor. 12) Intradental – Alveolar rim of mandibular. 13) Point B (Supramentale) – Most anterior part of mandibular base or it is the most posterior point in the outer contour of the mandibular alveolar process, in the median plane. Donovan – Junction of mandibular basal bone and alveolar process. Jacobson – Anterior limit of mandible 14) Pog - Most anterior point on bony chin in median plane. 15) Gn Brodie – Located by taking the midpoint between most anterior and inferior points on the bony chin. Craig – Patient of intersection of facial and mandibular plane. 4
16) Go – Constructed point at the intersect of lines tangent to posterior margin of ascending ramus and mandibular base. Hingley – Intersection of posterior ramal and mandibular plane. 17) Me – Sassouni - Most caudal point in the outline of the symphysis or the inferior most point on mandible. 18) Ar (Articulare) Bjork – Point of intersection of the posterior margin of ascending ramus and outer margin of cranial base. 19) Cd (Condylion) – Most superior point on the head of the condyle. 20) Or (Orbitale) – Lower most point of the orbit in radiograph. 21) ANS – Tip of bony anterior nasal spine in the median plane. 22) PNS – The intersection of continuation of anterior wall of pterygopalatine fossa and the floor of nose. 23) Basion – Lowest point on the anterior margin of foramen magnum in the median plane. 24) Ptm (Pterygomaxillary fissure) – Anterior wall represents maxillary tuberosity outline, posterior wall represents anterior curve of pterygoid process. 25) Po (Porion) – Tweed – 4.5mm above geometric center of ear rod. Craig – Uppermost point on the soft tissues overlying the external auditory meatus. Ricketts – True Porion, located directly over that of basion and downward and forward from internal auditory canal. Moorrees – Center of ear rods. Higley – Highest point on the root of the left external auditory meatus.
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26) BO (Bolton point) – Broadbent – Highest point in the upward curvature of the retrocondylar fossa. Higley – Highest point in the concavity behind the occipital bone. 27) D point – Center of symphysis given by Steiner. 28) Op (Opisthion) – Most posterior point of the bony margin of the foramen magnum. 29) AC (Acanthion) – Tip of ANS. 30) J point – Located at the junction of the anterior border of ramus and the corpus of mandible. 31) DS (Dorsam selae) – Square bone forms posterior boundary of sella turcica. 32) Broadbent registration patient (R) – Perpendicular from sella on Nasion – Bolton plane.
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LINES AND PLANES OF LATERAL CEPHALOMETRICS 1) Blumenbach’s plane (Resting horizontal plane) - It is the plane formed as the skull, minus the mandible rest on a flat horizontal surface. Entails the skull resting anterior on maxillary teeth and posterior either on occipital condyles or on the mastoid process. 2) Broadbent’s line (S-N reference line) – From sella to nasion. 3) Broadbent Bolton line – Line from Bolton patient to nasion. 4) Broca’s line – Extends from true anatomic prosthion to the lower most point of the occipital condyle. When skull is resting on horizontal surface. 5) Camper’s line – Line extending from tip of ANS to the centre of external auditory meatus. Camper’s plane is a triangular plane formed by two lines from tip of ANS to each external auditory meatus. 6) Decoster’s line – This is the only line that is not linear connection of two points. It represents an actual anatomical contour of the planoethmoidal line from internal plate of frontal bone down through roof of cribriform plate to the anterior portion of sella turcica. 7) Frankfort horizontal plane) – Its origins date back to the international
congress
on
prehistoric
anthropology
and
archaeology, held in Frankfort in 1882. The line runs from orbitale to porion. It is supposed to represent the ideal horizontal position of the head when the patient stands erect. 8) Palatal plane – Line running from ANS to PNS. 9) His plane – Runs from acanthion to opisthion. 10) Hold way line – Also referred as harmony line was developed by R.A. Holdaway and is strictly a soft tissue profile assessment
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reference line. Runs from soft tissue pogonion to vermilion border of upper lip. 11) Huxley’s line – Runs from nasion to basion and referred as nasion – basion line. It would be the near perfect base reference line for research purposes on growth and development. 12) Mandibular plane – Four different mandibular planes. Steiner – Line joining Go and Gn Downs – Line joining Go and Me Tweed and Ricketts – Straight line tangent to the lower most border of mandible. Bimpler’s line – Line from menton to antigonial notch. 13) Margolis line – Line runs from nasion to spheno-occipitalsynchondrosis. 14) Occlusal plane – 3 occlusal planes. First plane – Line joining midpoint of overlap of M-B cusps of upper and lower first molars with point bisecting overbite of incisions. Used by Downs and Steiner. Second plane – Used by Ricketts and in Wits analysis called as functional occlusal plane and is line joining the midpoint of the overlap of M-B cusp of Ist molars and buccal cusps of premolars or deciduous molars. Third plane – Line joining midsection of molar cusps to the tip of upper incisors. 15) Orbital plane – Plane perpendicular to FH plane at orbitale. 16) Ramal plane – Line tangent to posterior border of ramus of mandibular. 17) Rickett’s esthetic line –Extends from soft tissue tip of nose to the most anterior portion o profile of soft tissue chin.
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18) Von Ihering’s line – Orbitale to center of external auditory meatus. 19) Y-axis – Given by Downs and extends from sella to gnathion. CEPHALOSTAT An 8 × 10 inches film cassette equipped with approximate film and intensifying screen is placed either horizontally or vertically in the cephalostat cassette holder. A distance of 15 cm from midsagittal plane of the cephalostat to the film cassette is often used. The patients head is fixed by two ear-rods that are inserted into ear holes so that upper border of ear holes rest on upper part of ear rods. The head is oriented with the FH plane parallel to the floor and midsagittal plane vertical and parallel to the cassette. The standardized FH plane is achieved by placing the infra-orbital pointer at the patients orbit and adjusting the head vertically until the infra-orbital pointer and two ear rods are at same level. The upper part of face is supported by forehead clamp positioned at nasion. Projection is taken when teeth are in centric occlusion and the lips relaxed. The focus film distance is usually 5 feet i.e. 152.4cm. Milliamperage should be 10MA, KVP is about 60-90Kv and exposure time is not longer than 3 seconds. STEINER ANALYSIS (1953) C. C. Steiner selected what he considered to be the most meaningful parameters and evolved a composite analysis. He proposed a appraisal of skeletal, dental and soft tissue analysis. He considered SN plane as a reference plane. L – Project the most anterior point of the body of the mandible to the line SN. 9
E – Erect the line from the most distal point of head of condyle, perpendicular to the line SN. Skeletal analysis 1) SNA angle
- 820
2) SNB angle
- 800
3) ANB angle
- 20
a. Class- I
– ANB
- 0-50
b. Class-II
– ANB
- ≥ 60
c. Class-III
– ANB
- < 00
4) SND angle
- 760
5) Mandibular plane to SN
- 320
6) Occlusal plane to SN
- 14.50
Dental analysis 1) UI to NA (angle)
- 220
2) UI to NA (linear)
- 4mm
3) LI to NB (angle)
- 250
4) LI to NB (linear)
- 4mm
5) Interincisal angle
- 1300
6) Holdaway ratio
- 1:1
SL
- 51mm
SE
- 22mm
Steiner analysis for Indian population Sidhu S.S. in 1970 gave the Indian (Maharashtrian) norms. Sample size was 25 and all were male with the age group of 13-16 years. 1) SNA
- 82.7 ± 7.42
2) SNB
- 79.4 ± 7.84 10
3) ANB
- 3.3 ± 3.64
4) UI to NA
- 25 ± 9.42
5) LI to NB
- 32 ± 7.22
6) SL (mm)
- 53 ± 11.78
7) UI to NA (mm)
- 6.7 ± 3.74
8) LI to NB (mm)
- 7.6 ± 2.68
9) FH to SN
- 6 ± 5.86
10) Distance of U6 to NA
- 23.3 ± 2.56
11) Distance of L6 to NB
- 17.9 ± 2.96
Gamm and Gianelly in 1970 gave S.D. to the values of Steiners analysis. Parameters
Mean
S.D.
SNA
80.60
3.3
SNB
780
3.1
ANB
2.50
1.7
SND
75.20
2.8
Pg to NB
2.5mm
1.5mm
I/I
125.40
OP
17.30
4.1
MP
32.80
3.5
UI/NA
5.2mm
1.2mm
UI/NA
230
6.1
LI/NB
4.7mm
1.5mm
LI/NB
27.50
4.5
7.9
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Comparison of Steiners values with Gamm and Gianelly’s value and Maharashtrian norms (Indian) Parameters
Steiner’s
Gamm &
Maharashtrian
values 820 800 20 760 320 14.50 220 4mm 250 4mm 1300 1:1 51mm 22mm
Gianelly 80.60 ± 3.3 780 ± 3.1 2.50 ± 1.7 75.20 ± 2.8 32.80 ± 3.5 17.30 ± 4.1 230 ± 6.1 5.2 ± 1.2mm 27.50±4.5mm 4.7 ± 1.5mm 125.40±7.9 -
norms 82.70± 7.42 79.40± 7.84 3.30±3.64 0 25 ±9.42 6.7 ± 3.74mm 32 ± 7.22 7.6 ± 2.68 53 ± 11.78 -
SNA SNB ANB SND MP OP UI to NA UI to NA LI to NB LI to NB I/I Holdaways ratio SL SE
DOWN ANALYSIS (1948) Downs observed following four basic facial types. 1) Retrognathic – A recessive lower jaw 2) Mesognathic – An ideal o average lower jaw 3) Prognathic – A protrusive lower jaw 4) True prognathism – Pronounced protrusion of lower face. Downs elected to use FH plane as a reference base from which to determine the degree of retrognathism, prognathism or orthognathism. Sample – 20 children, 12 to 17 years of age with excellent occlusion with a mean age of 14.5 ± 2.5 years were taken. Measurements A) Skeletal measurements 1) Facial angle
Range
Mean
820±920
87.80
2)
Angle of convexity
100±-8.50
00
3)
A-B plane angle
-90±0
-4.60
12
4)
Mandibular
plane
angle 5) Y-axis B) Dental measurements 1) Cant of occlusal plane
280 to 170
21.90
660 to 530
59.40
1.5-140
9.30
130-150.50
135.40
2)
Interincisal angle
-8.5-70
1.40
3)
LI to mandibular
3.50-200
14.50
-1mm to 5mm
2.7mm
plane 4)
LI to occlusal plane
5)
Distance UI to APog Vorrhies and Adams (1951) made a graphic portryal of 10 values
calculated by Downs. But later on in 1952 it was modified by Wylie and his polygon shows not only mean but the maximum and minimum range for each measurement. Downs analysis for Maharashtrian This study was done by Kotak V.B. (1960) Not mentioned any sample size.
Measurements 1) Facial angle 2) Angle of convexity 3) A-B plane angle 4) Mandibular plane
Mean 84.980 3.75 -4.85 22.73 13
Range 79-91 -14 to 13 -10 to 3.5 11-34
5) Y-axis 6) Cant of occlusal plane 7) Interincisal angle 8) LI to mandibular plane 9) LI to occlusal plane 10) UI to A-Pog (mm)
61.85 11.55 119.6 17.13 29.22 7.5
54.5-68.5 0-18 105.5-134.5 5-29 21-41 3.5-11
TWEED’S ANALYSIS – 1946 Tweed has focused on how cephalometrics might be applied in diagnosis and treatment planning for daily clinical orthodontics. It consists of a triangle formed by FH plane, mandibular plane and axis of lower incisor. A sample of 95 was taken and average values seen were FMPA
– 24.570
IMPA
– 86.930
FMIA
– 68.200
Hence FMPA of 240, IMPA of 900 and FMIA of 650 were workable figures ad still used. Tweeds projected scale (FMIA formula) 1) When FMPA is 300 or more – FMIA should be 650 or more upto 700. 2) If FMPA is 250±40 – FMIA should be 680 or 700. 3) If FMPA is 200 or less – IMPA should not exceed 940. Tweeds head plate correction If FMPA ore than 250 then IMPA should not be 900 or more. e.g. If FMPA showed 280, then IMPA would have to be positioned at 870. This is termed as Tweed’s head plate correct. Cephalogram correction To achieve the FMIA requirements of 650 we require tipping of mandibular incisors lingually and will require shortening both the side of dental arch. 14
According to Tweed’s head plate correction for every 20 correction 1mm of space is required. For both side of arch it will become 2mm. The measurement taken from cephalogram combined with actual arch length discrepancy and this is the total discrepancy in millimeters. WIT APPRAISAL (1975) Wits appraisal of jaw disharmony given by Jacobson is measure of the extent to which the jaws or related to each other anteroposteriorly. As a measurement from the cranial base do not necessarily provide are liable expression of A-P Jaw relationship in the dentofacial complex. Reference plane common is both dentures is that of occlusion, hence the effects of rotation of jaw are not affecting the overall assessment of the jaw. Sample of 46 adults with excellent occlusion were taken. (21 M & 25 F) Construction - Draw perpendicular from point A & B on the maxilla and mandible on to the occlusal plane. The points of contacts of the perpendicular onto the occlusal plane are labeled AO and BO respectively. Wits reading Males
– 1 mm
Females
– 0 mm
The more the wits reading deviates from -1 mm in males and 0 mm in females the greater the horizontal jaw disharmony Class-II - Positive wits reading Class-III - Negative wits reading If AO ahead of BO then wits appraisal positive SASSOUNI ANALYSIS (1955)
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Sassouni wanted a system based on relationships of anatomical structures to each other with in the frame work of the individual patients i.e. he wanted to let the patients own amatory serve as the clue to what is none al of abnormal to himself. Thus he developed a system that utilizes a series of portions of circles in the form of arcs, that have a common center formed by intersection of composite of anatomical planes to form what has become known as the Sassouni archial analysis. This analysis is 3-dimensional and inclusive of all the important structures of facial skeletal. Sample – 50 children with normal occlusion Point O – It is the center of the focal area where the four horizontal planes of the face i.e. cranial base, palatal, occlusal and mandibular converge. Planes Draw a plane parallel to supraorbital plane tangent to Si. Four planes converge toward focal area called center or point O. Generally 3 of the 4 planes meet, while the fourth is divergent. This shows the plane, which is not integrated in the facial balance. Occasionally only two planes meet at the same point two others are parallel or meeting in front or beyond point O. In these cases the junction of the cranial base & mandible planes should be taken as the center O. Arcs- From O as of center, draw arcs from N, ANS, A, Te & Sp. Norms 1. Planes – Four planes are converging toward a focal center O. 2. Facial angles – Cranial base plane to palatal plane angle is equal to the palato-mandibular angle. 3. Arcs16
a. The arc â&#x20AC;&#x201C; from N should pass through ANS, tip of UI, pogonion. If whole lower face is anterior or posterior to the arc from N, draw a second are from ANS down. This should pass through tip of UI and pogonion. b. The arc from point A down should pass through point B. c. The arc from Sp (Dorsam Sella) should pass through gonion. d. The arc from Te (Temporale) should be tangent to the mesial contour of U6. Vertical proportions 1) Anterior vertical proportions Put the point of compass on ANS & open compass to supraorbitale, then transfer this dimension by rotating the compass until it intersects anterior arc at the menton. Distance from ANS to supraorbitale should be equal to that from ANS to Me. 2) Post vertical proportions From PNS to cranial base plane & then from PNS to Go. Both distances should be equal.
Anteroposterior evaluation of profile In normal profile ANS, IS, and Pog should be located on anterior arc It ANS & Pog both posterior to anterior arc then the profile is retroarchial which essentially is normal. This situation may be due to the fact that nasion is to far anterior. It ANS is on anterior arc Pog is not there are two possibilities. 1. Pog is anterior to arc 2. Pog is post to arc 17
It Pog is on anterior arc & ANS is not, there are also two possibilities 1. ANS is anterior to arc 2.ANS is posterior to arc Any combination of maxillary protrusion and/or mandibular retrusion called as skeletal Class II. Any combination of maxillary retrusion and/or mandibular protrusion called as skeletal Class II. Size of corpus of mandible It Go located on posterior arc and Pog is on anterior arc then corpus length is equal to the cranial base (Sp to N). This is for 12 year of age. Before 12 years corpus of mandibular is small and after 12 year corpus is larger than cranial base. Vertical balance The anterior upper and lower face heights should be equal. The posterior upper and lower face heights should be equal. ANS to cranial base = ANS to mandibular plane and PNS to cranial base = ANS to mandibular plane The tip of UI is situated at the midpoint between ANS and Pog. The tip of LI is situated at the midpoint between A and B. Interpretation Skeletal deep bile cases â&#x20AC;˘
4 bony planes of face are not steep to each other and center O is away from profile.
â&#x20AC;˘
Cranial base angle (supraorbital to clivus angle) is small.
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•
Upper and lower incisors have long axis nearly parallel and are vertically extruded while molars are intruded.
•
Total post height is nearly equal to ant facial height
Skeletal open bile cases •
4 bony planes are steep to each other bringing the center O close to the profile.
•
Cranial base angle and genial angle are obtuse. PFH half the AFH.
Skeletal Class II cases •
Large cranial base angle, small gonial angle with short ramus.
•
Palate is tipped down word and backward
Skeletal Class III cases •
Small cranial base angle
•
Large genial angle and palate is tipped upward at PNS and downward at ANS.
SASSOUNI PLUS After Sassouni’s death in 1983, a new champion of archial analysis, Dr. Richard Beistle arose to continue work of teaching and promoting this great analysis. Beistle represents 11 points now called as Sassouni plus.
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The first eight components are from original Sassouni, the last three which form the plus form of the last three which form the plus form of the analysis. 1. Skeletal AP alignment 2. Skeletal vertical dimension 3. Maxillary incisor position 4. Maxillary AP length 5. Maxillary AP position 6. Maxillary 6 position 7. Mandibular AP length 8. Mandibular AP position 9. Mandibular incisor position 10.Growth direction indicator 11.Upper lip angle 1. Skeletal AP length It ANS and Pog both post to anterior arc profile is retroarchial It may be due to - N too for anteriorly - Entire lower face too far posteriorly. - Combination of both. If ANS to Pog both anterior to anterior arc profile considered prearchial. It may be due to - N positioned too far posteriorly - Entire lower face too far anteriorly - Combination of both. A point and B point ideally showed be on basal arc. 20
2) Skeletal vertical dimension At age 4 years AUFH = ALFH At age 12 years ALFH is more by 6mm and At adulthood ALFH is more by 10mm 3) Maxillary incisor position Tip of UI should be on anterior arc or within range of 0 to 3 mm ahead of anterior arc. 4) Maxillary AP length Drop cribriform perpendicular on PNS It PNS is on cribriform perpendicular and ANS on anterior arc then maxilla is normal. 5) Maxillary AP position If ANS and PNS both back of anterior arc and cr perpendicular by the same amount – maxillary retruded. If ANS and PNS ahead of there respective reference line – maxilla is protruded. 6) U6 position Mesial surface should be tangent to midfacial arc. 7) Mandibular AP length Measured from anterior and posterior arc at Go and Pog. 8) Mandibular AP position If Go and Pog displaced in opposite direction an abnormally large mandible or abnormally small mandible is indicated. 9) LI position IMPA angle is seen in this. It is 950 ± 50. 10) Growth direction indicator
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Beistle split the gonial angle and uses the upper and lower portions of it to evaluate growth direction. The upper position of split gonial angle represents slant of ramus. Lower portion of angle represents slant of the body of mandibular corpus. Total gonial angle 120-1320 Upper gonial
-
52-550
Lower gonial
-
70-750
If upper gonial angle is large and lower is small indicating strong horizontal growth pattern. If upper gonial angle is small and lower is large indicating strong downward and backward grower. 11) Upper lip angle Constructed by drawing a line tangent to anterior most tip of upper lip i.e. soft tissue subnasale and extending it upward to intersect the optic plane, which is parallel to FH. Angle is measured inferiorly and posterior at the intersection If
900 or less
Retruded
91-990
Flat
100-1150-
Normal
116 or more
Protruded
McNAMARA’S ANALYSIS (1984) The analysis proposed by McNamara is an effort to relate teeth to teeth, teeth to jaws, each jaw to the other and the jaws to the cranial base. Sample - 277 children 8 to 10 years of age with Class II malocclusion were selected. Effective maxillary length – Condylion to point A Effective mandibular length – Condylion to Gn Lower face height – ANS to Me 22
Anatomic portion is used Measurements a) Relating maxilla to cranial base – Determine by measuring distance of point A to Nasion perpendicular. b) Relating mandible to cranial base – Determined by measuring distance from Pog to Nasion perpendicular. Age
Point A-NP
Pog – NP
9 years
0mm
-8mm to –6mm
Adult
1mm in front
-2 to +2mm
c) Relating maxillary and mandibular height 9 years
Adult male Adult Female
Effective maxillary length-
85mm
100mm
94mm
Effective mandibular length-
105mm
130mm
120mm
LFH -
60mm
70mm
66mm
d) Mandibular plane angle FH to Go – M = 230 Low mandibular plane angle – Adequate ramus height High mandibular plane angle – Short vertical height e) Relating upper incisors to maxilla Horizontal position - Distance between point A perpendicular to the facial surface of upper incisors = 4 mm Vertical position - Incisal edge of upper incisors lies 2-3 mm below the upper lip at rest. f) Relating the lower incisor to mandible Horizontal position 23
- Distance between A-Pog line and facial surface of lower incisor = 2 mm Vertical position - Vertical position of lower incisors is evaluated on the basis of existing anterior facial height. RICKETS ANALYSIS (1960) In this analysis mean value are given that change with growth and those that remain stable. Points Pt- Located at lower border of foramen rotendum. CC – Intersection of facial axis and cranial axis i.e. N to Ba. Xi – Centroid of ramus Pm – Protrubrance menti between point B and Pog. Variables
norms
S.D.
For 9 years old+age adjust
1) Facial axis
900
±3
No adjustment
2) Facial angle
870
±3
+10 Every 3 years
3) Mandibular plane
260
±4
–10 every 3 years
4) Lower facial height
470
±4
No adjustment
5) Palatal plane to PH
00
(1-2.5)0
6) Convexity of point A 2
± 2mm
7) LI to Apog
1mm
±2
8) U6 to Ptv
Age± 3
increase 1mm/year upto maturity
9) Interincisal
1220
± 50
10) Lower lip to E line
–2
± 2mm
Interpretation
24
–1mm for every 3 years No adjustment
Less protrusive with growth
1. Facial axis Indicate chin is upward and forward or down ward and backward. 2. Facial angle Indicate mandibular prognathism or retrognathism. 3. Mandibular plane angle Low mandibular plane angle â&#x20AC;&#x201C; Adequate ramus height High mandibular plane angle â&#x20AC;&#x201C; Short vertical height of ramus 4. Palatal plane to FH Indicate position of nasal floor and it is a objective in orthodontic treatment to bring palatal plane parallel to the FH plane. 5. Maxillary convexity or convexity of point A Helps in locating the position of maxilla with relation to cranial base and it can be change with age and with mandibular growth. 6. Denture height Angle made by connecting ANS, Xi and Pm points. Its effectiveness represents the denture heights or lower facial height or vertical relation between maxillary and chin. 7. LI to A Pog line Helps in assessing lower incisor position in relation to existing skeleton. 8. Upper molar to PTV It is the indicator of upper denture position in the arch anteroposteriorly. 9. Interincisal angle Helps in assessing degree of proclination or retroclination of maxillary and mandibular incisors. 10. Lower lip and E line Protrusion or retrusion of lower lip. 25
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