Cephalometric Appraisal of Anteroposterior Skeletal Discrepancy : An Overview

Cephalometry is one of the important diagnostic tools for assessment of jaw relationship. Sagittal jaw relationship is of utmost concern to the patients and orthodontist. Many linear and angular parameters are used for measurement of sagittal jaw discrepancies. This article reviews various AP cephalometric parameters. II: Value above normal (negative sign), Class III: Value below normal (positive sign). Disadvantage: Data obtained from samples of growing age may differ from adults. Also the linear measurements are more prone to errors than angular. 2. AB plane angle and Angle of Convexity9 Introduced by: William B. Downs (1948) First angular measurement for antero-posterior discrepancies. Angle of convexity (Nasion-Point A-Pogonion) gives the measure of protrusion of maxillary part of the face to the total profile. Location of AB plane angle with facial plane is the measure of anterior limit of the denture bases with each other and facial profile. Sample: 20 subjects (mean age 12-17 years). Mean value: Angle of Convexity: Considered negative if Point A falls behind the facial plane and positive if it is ahead; normal range +10° to -8.5°. A-B plane angle: 0° to – 9°. Disadvantage: As the facial type is known to differ racially this study is limited to White race.


INTRODUCTION
There are various methods used in orthodontics for treatment planning which includes clinical examination, model analysis, various radiographs like OPG, lateral cephalogram, PA cephalogram.
Cephalometric is one of the important diagnostic tools for assessment of jaw relationship in all three planes: sagittal, vertical and transverse.There have been many parameters introduced for evaluation of sagittal and vertical discrepancies.Antero-posterior jaw relationship is of utmost concern in evaluating the type of skeletal pattern.
Angular and linear parameters along with the cranial reference planes such as Frankfort horizontal plane and Sella-Nasion plane have been used for the measurement of sagittal discrepancies.ANB angle, 1 Wits appraisal, 2 W angle, 3 Beta angle, 4 Yen angle, 5 HBN angle 6 and SAR angle 7 have been defined for sagittal jaw relationship.Each of these parameters has their own advantages and drawbacks.This review article briefly describes these parameters in chronological order of their discovery and their use in orthodontics. 8troduced by: Wendel L. Wylie (1947)   First parameter of antero-posterior discrepancies

Angle ANB
Introduced by: Richard A Riedel1 (1952), later Cecil C Steiner10 in 1953 used this analysis.[13] Sample: 52 (24 children, 28 adults) aged between 18-36 years in Washington population.incisors is measured for the identification of dysplasia.

Disadvantage: Difference found between the interpretation of this angle and actual discrepancy
Advantage: The resultants of all components of force in the masticatory area are expressed about the occlusal plane.Thus, its behavior reflects the sum of all influences acting on this area.Since the teeth form the occlusal plane, this is the only plane to which the teeth of each jaw are intimately related.The occlusal plane is the plane of reference of the Angle Classification1 and Baume Classification. 9 Disadvantage: Normally, it is not a plane, but a complex curve; which is very difficult to define.In any case, it cannot be reliably drawn and a tracing cannot be reliably repeated.

Taylor's AB' linear distance 12
Introduced by: CM Taylor (1969)   The linear distance between Point A and B'.Point B' is the perpendicular from Point B to Sella-Nasion plane.
There was 1mm change from Point B' to 'A' with each degree of change in ANB angle.

AXD angle and AD' 19
Introduced by: Edward Beatty (1975)   AXD angle is the interior angle formed by the intersection of lines extending from Point A and D to point X (X is the perpendicular line from Point A dropped on SN plane).
AD' linear measurement is from Point A to line DD' as A-D' (D' is the perpendicular from D to Sella-Nasion plane).
Advantage: Uses Point D which is not affected by the changes in incisor position and chin prominence.It also eliminates Nasion point.
Disadvantage: Point A is still used, which is affected by orthodontic tooth movement.

Wit's Appraisal of jaw disharmony 2
Introduced by: Alex Jacobson (1975)   Overcomes the shortcomings of ANB angle.Perpendiculars from Point A and B on the maxilla and mandible, respectively, are drawn onto the occlusal plane.The points of contact are labelled AO and BO, respectively.
Mean value: Class I: BO coincides with AO in females, BO is 1mm ahead of AO in males.Class II: BO positioned well behind point AO (positive reading), Class III: BO positioned ahead of point AO (negative reading).
Advantage: Samir Bishara et al 20 showed that Wits value does not change with age.
Disadvantage: It uses occlusal plane, which is a dental parameter to describe skeletal jaw discrepancies.][23] Accurate identification of occlusal plane is not easy or accurately reproducible. 24,25

Freeman's AXB angle (1981) 11
Introduced by: Robert S.  27 Introduced by: S. Jarvinen  Advantage: Analysis is not dependent on variation of Nasion point.Palatal plane is considered to be more stable.

FH to AB Plane Angle 32
Introduced by: Sang D.

Beta Angle 4
Introduced by: Chong Yo Baik and Maria Ververidou  Advantage: Rotation of the jaws does not affect this angle.
Disadvantage: It uses Point A which is affected by orthodontic treatment.

Overjet as a predictor of sagittal dysplasia 33
Introduced by: Sanja Zupancic et al (2008)   Determines correlation between overjet value measured on study casts and cephalometric parameters.
Advantage/Disadvantage: Overjet is a good predictor for Class II division 1 malocclusion in sagittal plane; how it is not useful in skeletal Class I and Class II malocclusions.
Overjet value permits a significant part of variability of ANB angle, Wits appraisal, and convexity at Point A. However, there is a relatively wide interval variability, which cannot be explained by overjet alone.

Yen angle 5
Introduced by: Praveen Kumar   angle, Nasion point is the head of the angle that any deviation in its position would directly and principally affect the ANB angle (Taylor, 196912).Compared to Wits appraisal, it depends on landmarks that are easy to identify.Any inclination in the functional occlusal plane will not affect the final reading.

W angle 3
Introduced by: Wasundra A. Bhad et al (2011)   W angle is measured between the perpendicular line from Point M to S-G line and M-G line.
Advantage: W angle reflects true sagittal dysplasia and is not affected by growth rotations.

Pi analysis 35
Introduced by: Santosh Kumar  Advantage: The Walkers point was found to be stable after the age of five.W-SE remains unchanged in all periods of pubertal growth. 36The SAR angle is not influenced by growth, jaw rotations, orthodontic treatment or any other factor previously associated with other angles.

HBN angle 6
Introduced by: Harsh Bhagvatiprasad Dave (2015)   It is the angle between line perpendicular from point M to CG and MG.
Mean value: Class I skeletal: 39°-46°; Class II: < 39°, Class III: > 46° measured quantitatively in millimeters.Mandibular length was measured by dropping the perpendicular from posterior point of condyle, and pogonion to lower border of the mandible.Sample: Subjects of growing age (11.5 years).Mean value of maxillary length: Class I: 52 mm, Class Dr Suchita Tarvade Daokar, 1 Dr Raksha Rajput 2 Introduced by: William B. Downs (1948) First angular measurement for antero-posterior discrepancies.Angle of convexity (Nasion-Point A-Pogonion) gives the measure of protrusion of maxillary part of the face to the total profile.Location of AB plane angle with facial plane is the measure of anterior limit of the denture bases with each other and facial profile.Sample: 20 subjects (mean age 12-17 years).Mean value: Angle of Convexity: Considered negative if Point A falls behind the facial plane and positive if it is ahead; normal range +10° to -8.5°.A-B plane angle: 0° to -9°.Disadvantage: As the facial type is known to differ racially this study is limited to White race.

Figure 10 :Figure 11 :Figure 12 :
Figure 10: McNamara Maxillo-mandibular Differential formed between A-B line and Point A perpendicular to C-B line.This angle indicates the severity and the type of skeletal dysplasia in sagittal dimension.Sample: 120 samples, Age group: 15-25 years Mean value: Skeletal Class I: 28°-35°, Class II: < 28°, and

22 . SAR Angle 7
et al (2012) It consists of two variables, Pi angle and Pi linear in the evaluation of antero-posterior skeletal discrepancy.Pi angle is a perpendicular line is drawn from G point to intersect with the true horizontal at G', with a further line constructed from G' to M point.Sample size -155 subjects, Mean age 19.7 years.Mean value: Pi angle for skeletal Class I: 3.40o (±2.04),Class II: 8.94 o (±3.16),Class III: 23.57o (±1.61)Pi linear in skeletal Class I: 3.40mm (±2.20),Class II: 8.90mm (±3.56),Class III: 23.30mm (±2.30)Introduced by: Sonahita Agrawal et al (2014) SAR angle is measured between the perpendicular line from point M to W-G line and the M-G line.Sample size: 60 North Indian individuals, Age group: 13-25 years.Mean value: Class I skeletal: 55.98° (SD 2.24), Class II: 50.18° (SD 2.70), Class III: 63.65° (SD 2.25).

Figure 18 :
Figure 18: Pi angle and Pi linear