jacobson ajo 1975-2003 - the wits appraisal of jaw disharmony

CLASSIC ARTICLE

The “Wits” appraisal of jaw disharmonyA. Jacobson, MDS, MS, PhDJohannesburg, South Africa

Alex Jacobson was born in South Africa and completed his dental education there in 1941. He received anMS degree in orthodontics from the University of Illinois in Chicago in 1953 and then returned to South Africato private practice. He was head of the orthodontic department at the University of Witwatersrand (known asWits, hence the name “Wits” analysis). He received an MDS degree in 1961 and a PhD in physicalanthropology in 1978 and was named chair of the orthodontic department at the University of Alabama atBirmingham in 1976. He returned to private practice and part-time teaching again in 1989. He has written oredited 3 textbooks and about 100 articles in refereed journals, and is editor of the Reviews and Abstractssection of the Journal.

Many analyses tend to be cumbersome and fartoo complex for routine clinical use. Numer-ous measurements are employed which do

not differentiate between meaningful information andinconsequential details. Others at the opposite end ofthe scale employ too few measurements to yield ade-quate information for appraisal of the orthodonticproblem. An analysis of choice is one which employsthe least possible number of measurements to beadequate.

The “Wits”* appraisal of jaw disharmony, however,is not an analysis per se; rather, it is intended as adiagnostic aid whereby the severity or degree of an-teroposterior jaw disharmony can be measured on alateral cephalometric head film.

Cranial and denture landmarks

Nasion is related functionally to the ectocranialtable of the calvaria, in which case growth may alter itsvertical and horizontal position in space.15 However,for practical purposes, nasion may be convenientlyregarded as the anteriormost point on the anteriorcranial base from which to relate the dentures.

Point A is located at the deepest point on thecontour of the maxilla between the anterior nasalspine and the alveolus. The anterior nasal spine is aprocess, as is the alveolar process, and between thesetwo lies the most basic part of the denture base at theanterior limit. All bone in the anterior part of themaxilla is thin and laminated and subject to change

when upper incisor teeth are moved. Since point Awas originally defined, clinicians and investigatorshave sought a better reference point but have some-how continued to revert to the basic point firstdescribed.17 From a practical standpoint, therefore,point A must be regarded as the anterior limit of themaxillary denture base.

Point B was described by Downs5 in 1948 as apoint at the deepest curvature of the outline of thesymphysis of the chin. This point is located at thejunction of basal and alveolar bone. A deepening ofthe body of the symphysis occurs with eruption ofthe teeth. The bony tissue that is alveolar in theyoung is incorporated in the body and becomesbasilar in the adult, so that point B moves horizon-tally and vertically. Point B was referred to earlier byBjork1 as supramentale, the anthropometric term.11

This point which, like point A, is subject to mildchange with lower incisor movement may be re-garded as the anterior limit of the lower denture base.

In appraising the horizontal disharmony of the face,the ANB angle (the difference between the SNA andSNB angles) is the most commonly used measurement.The SNA reading, Steiner reports, is of little concernbecause it merely shows whether the face protrudes orretrudes below the skull.23-25 However, rather thanignore or discount the relative relationship of thedenture bases to cranial reference planes, this articleendeavors to emphasize an awareness of this relation-ship in the overall interpretation and assessment ofcephalometric analyses.

ANB angle as a measure of jaw dysplasia

The ANB angle in normal occlusions is generally2 degrees.18 Angles greater than this indicate tenden-cies toward Class II jaw disharmonies; smaller an-gles (extending to negative readings) reflect Class III

First published February 1975;67:125-38.From the Department of Orthodontics, Dental School, University of theWitwatersrand, Johannesburg, South Africa.*Abbreviation for University of the Witwatersrand.Am J Orthod Dentofacial Orthop 2003;124:470-9Copyright © 2003 by the American Association of Orthodontists.0889-5406/2003/$30.00� 0doi:10.1067/S0889-5406(03)00540-7

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anteroposterior jaw discrepancies. The foregoing isan acceptable generality. However, there are numer-ous instances in which the contention does notobtain. Figure 1, A, for instance, shows a lateralcephalometric head film tracing of a Class II maloc-clusion. The ANB angle is 7 degrees, which isregarded as being high and typical of a Class II jawdysplasia. Figure 1, B, on the other hand, shows alateral head film tracing of a patient with a perfectlynormal occlusion. Paradoxically, here too the ANBangle measures 7 degrees. The tracing in the latterinstance was that of the male student adjudged by the

department of Conservative Dentistry as having thebest occlusion in the school. Figure 2, A and B,shows a further example of a Class II malocclusionand an excellent normal occlusion with identicalANB angle readings of 6 degrees. The anteroposte-rior relationship of the jaws in these examples is notsatisfactorily reflected by the ANB angle readings.These general variants, therefore, assume importancewhen one endeavors to appraise degree of craniofa-cial skeletal disharmony in orthodontics.

Relating jaws to cranial reference planes presentsinherent inconsistencies because of variations in cranio-

Fig 1. Lateral cephalometric head film tracing of a Class II malocclusion (A) and normal occlusion(B), each having an ANB angle of 7 degrees.

Fig 2. Further example of a Class II malocclusion (A) and a normal occlusion (B) having identicalANB angles readings (6 degrees).

American Journal of Orthodontics and Dentofacial OrthopedicsVolume 124, Number 5

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facial physiognomy. Included among the craniofacialskeletal variations are (1) the anteroposterior spatialrelationship of nasion relative to jaws and (2) therotational effect of the jaws relative to cranial referenceplanes.

The anteroposterior position of nasion. The relativeforward or backward positioning of nasion by virtue ofan excessively long or short anterior cranial base(represented by line SN) or a relative posterior oranterior positioning of both jaws within the skeletal

craniofacial complex will directly influence the ANBreading.

Figure 3 shows a lateral cephalometric head filmtracing of a normal occlusion with all ANB reading of2 degrees. Figure 4 is a diagrammatic representation ofthe same tracing with the landmarks, nasion and pointA and B identified.

Figure 5, A, shows a diagrammatic representationof a tracing of a normal occlusion with an ANB angleof 2 degrees. In Figure 5, B, the relationship of thejaws to each other remains unchanged. Nasion,however, is positioned farther forward in that theanterior cranial base length has been increased. Thishas the effect of reducing the ANB reading, in thisinstance from 2 degrees to �2 degrees. A similarreduction in the ANB reading is effected by the jaws(bearing the same relationship to each other) beingretropositioned in the craniofacial complex. Figure 5,C, shows an unchanged relationship of the jaws toeach other, only now nasion is retropositioned (re-duced anterior cranial base length). This has theeffect of increasing the ANB angle, in this instancefrom 2 degrees to no less than 5 degrees. Forwardpositioning of the jaws in the craniofacial complexwould have the same effect of increasing the ANBangle reading.

Rotational effect of jaws. Clockwise or counter-clockwise rotation of the jaws relative to cranial refer-ence planes (SN in the examples cited) likewise radi-cally affects the ANB angle reading.

Figure 6, A, is a diagrammatic representation of alateral head film tracing of a normal occlusion with anANB reading of 2 degrees.

In Figure 6, B, the relationship of the jaws to eachother is unchanged, but the jaws are now rotated in acounterclockwise direction relative to the SN plane.The rotation has had the effect of producing a Class IIItype of jaw relationship. The ANB angle had beenreduced from 2 degrees to �5 degrees.

A clockwise rotation of the jaws relative to thecranium or the SN reference plane produces the oppo-site effect; that is, a Class II type of jaw relationship. InFigure 6, C, the relative clockwise positioning of thejaws has increased the ANB angle reading from 2 to 8degrees in spite of the jaws maintaining an identicalrelationship to each other.

Clockwise or counterclockwise rotation of theSN line (due to nasion or sella turcica being posi-tioned relatively superiorly or inferiorly to eachother) either increases or decreases the SNA reading.Conventional analyses would suggest that the max-illa is positioned either forward or backward in thecraniofacial complex. This is a specious interpreta-

Fig 3. Lateral cephalometric head film tracing of “aver-age” normal occlusion with ANB angle of 2 degrees.

Fig 4. Diagrammatic representation of lateral cephalo-metric head film tracing with nasion and points A and Bidentified.

American Journal of Orthodontics and Dentofacial OrthopedicsNovember 2003

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Fig 5. A, Diagrammatic representation of an “average normal occlusion.” B, Nasion located fartherforward. This has the effect of reducing the ANB angle reading in this instance from 2 degrees to �2degrees. C, Nasion positioned farther back has the effect of increasing the ANB angle, in thisexample, from 2 degrees to 5 degrees.

Fig 6. A, Diagrammatic representation of an “average” normal occlusion. B, Counterclockwiserotation of the jaws has the effect of reducing the ANB angle (in this instance from 2 degrees to �5degrees). C, Clockwise rotation of the jaws has the effect of increasing the ANB angle (from 2degrees to 8 degrees).


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tion, as is evident in Figure 7. The SNA reading inthis instance is 69 degrees instead of an averagenormal of 82 degrees, which would suggest maxil-lary (and mandibular) retropositioning. It is obviousfrom the cephalometric head film tracing that this isnot the case; it is evident that it is the anterior part ofSN plane which is superiorly tipped. The rotationaleffect of the SN line virtually has no anteroposteriorpositioning effect on nasion point, in which case theANB angle reading is hardly affected by any angulardeviation of SN from the horizontal.

The “Wits” appraisal of jaw disharmonyThe “Wits” appraisal of jaw disharmony is a mea-

sure of the extent to which the jaws are related to eachother anteroposteriorly. The method of assessing thedegree or extent of the jaw disharmony entails drawingperpendiculars on a lateral cephalometric head filmtracing from points A and B on the maxilla andmandible, respectively, onto the occlusal plane which isdrawn through the region of maximum cuspal interdig-itation. The points of contact on the occlusal plane frompoints A and B are labeled AO and BO, respectively(Fig 8).

In a sample series of twenty-one adult males se-lected on the basis of excellence of occlusion, it wasfound that point BO was approximately 1 mm ahead ofpoint AO. The calculated mean reading was 1.17, S.D.1.9 (range, �2 to 4 mm). In twenty-five adult femalesselected on the same basis, points AO and BO generallycoincided. The calculated mean reading was �0.10mm, SD 1.77 (range, �4.5 to 1.5).

In sum, therefore, the average jaw relationship

according to the “Wits” reading is 1 mm in males and0 in females. In skeletal Class II jaw dyplasias, pointBO would be located well behind point AO (a positivereading) whereas in skeletal Class III jaw disharmonies,the “Wits” reading would be negative, namely, pointBO being forward of point AO. The more the “Wits”readings deviate from 1 mm in males and 0 in females,the greater the horizontal jaw disharmony.

Application of the “Wits” appraisal

Figure 9, A and B, shows the head film tracings ofthe Class II malocclusion and the normal occlusionillustrated in Figure 1, A and B. The ANB in eachinstance is 7 degrees. According to the “Wits” ap-praisal, however, the Class II reading is 10 mm (mark-edly Class II), whereas the reading for the normalocclusion (Fig 9, B) is 0 mm (normal).

Figure 10, A and B, shows repeat tracings of Figure2, A and B. Here again, the ANB angle readings in bothis 6 degrees, whereas the “Wits” appraisal clearlyreflects the difference between the Class II and thenormal occlusion. The “Wits” reading for the Class IImalocclusion is 6 mm, whereas the normal occlusionreading is 0 mm.

Figure 11, A and B, shows lateral head film tracingsof two Class III malocclusions. The ANB readingsdiffer only slightly, namely, �1 degree and �1.5degrees, respectively. The “Wits” appraisal, however,places a completely different complexion on the scene.According to the “Wits” reading, Figure 11, A, is �1.5mm, reflecting a mild discrepancy in the relationship ofthe jaws to each other, whereas the “Wits” reading inFigure 11, B, is no less than �12 mm, a major jawdisharmony. In fact, the latter patient is scheduled toundergo a bilateral mandibular osteotomy. The severityof the jaw disharmony is clearly reflected in the “Wits”appraisal but not so in the conventional ANB anglereading.

Figure 12, A and B, shows further examples ofClass II malocclusion tracings. The ANB angle in eachinstance was 9 degrees. The “Wits” readings in A andB, however, were 8 and 2.5 mm, respectively. Inter-preted, this means that the anteroposterior jaw discrep-ancy in A was severe, whereas that of B was mild (inspite of the identical ANB angle measurements). Be-cause of this, the high mandibular plane angle and thedivergent type of profile, A proved most difficult totreat. By contrast, B proved easily treatable, the antero-posterior discrepancy being mild and the vertical profiledimensions favorable.

Figure 13 shows the lateral cephalometric headfilm tracing of a patient with an ANB angle measure-ment of no less than 10 degrees. In spite of the high

Fig 7. Tipped anterior cranial base effecting reductionof SNA and SNB angle readings.


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ANB angle, the “Wits” reading was only 2 mm andeasily treatable.

Figure 14, A and B, shows similar tracings of ClassII malocclusions with ANB angle measurements of 7degrees. The anteroposterior disharmony, according tothe “Wits” appraisal in A, was severe (9 mm), whereasthat in B was minimal (1 mm). The anteroposterior jawcorrection in A entailed considerable therapy in spite of

what appeared to be a favorable convergent type9 ofcraniofacial skeletal pattern. The biggest problem incorrection of B was not the anteroposterior jaw dishar-mony (which, according to the “Wits” appraisal, wasminimal) but that of vertical dimension and its associ-ated orofacial muscular disharmonies.

A 2 degree ANB angle, by conventional assessmentof jaw disharmony, is normal. In Figure 15, the ANB

Fig 8. Perpendicular lines dropped from points A and B onto the occlusal plane. “Wits” reading(enlarged in right-hand block) is measured form AO to BO.

Fig 9. Repeat tracings of Fig 1 incorporating “Wits” reading. A, Class II malocclusion: ANB angle,7 degrees; “Wits” reading, 10 mm. B, Normal occlusion: ANB angle, 7 degrees; “Wits” reading, 0mm.


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angle measures 2 degrees; the “Wits” measurement,however, is �4.5 mm., indicating a Class III jaw,which is the type of malocclusion presented by thepatient.

A final example of discrepancy in interpretationbetween the conventional ANB angle and “Wits” read-ings is manifest in Figure 16. The ANB angle is 0degrees, suggesting a tendency toward Class III mal-occlusion. The “Wits” measurement, however, is noless than �9.5 mm., indicating severe anteroposteriorjaw disharmony. This particular Class III malocclusionrequired surgical correction.

Discussion

Various cranial reference planes have been usedas base lines from which to determine degrees of jawdysplasia. De Coster4 superimposed on outlines ofthe floor of the brain case from planum sphenoidaleforward into the anterior cranial edge of the spheno-occipital synchondrosis over sella, drawing a refer-ence line from there to nasion. Broadbent2 developedthe Bolton triangle, and the same triangle wasmodified by the substitution of basion for the Boltonpoint.3

All of the above reference planes deal with

Fig 10. Repeat tracings of Fig 2 incorporating “Wits” reading. A, Class II malocclusion: ANB angle,6 degrees; “Wits” reading, 6 mm. B, Normal occlusion: ANB angle, 6 degrees; “Wits” reading, 0 mm.

Fig 11. Class III malocclusion tracings with approximately same ANB angle readings. A, Mild ClassIII jaw disharmony: ANB angle, �1.5 degree; “Wits” reading, �1.5 mm. B, Severe Class III jawdisharmony: ANB angle, 1.0 degree; “Wits” reading, �12 mm.


476 Jacobson

cranial morphology and, as such, are most useful inrelating the jaws to the cranium. Measurements fromthe cranial base, however, do not necessarily providea reliable expression of anteroposterior jaw relation-ship in the dentofacial complex.13,14 The line ofreference from which anteroposterior jaw relation-ships should be assessed must, of necessity, beextracranial and relate to true vertical or a horizontalperpendicular to it.

Relating the jaws to an extracranial perpendicularmay provide an expression of anteroposterior jaw

relationship which is important from an estheticstandpoint. However, when one is endeavoring toappraise severity of anteroposterior jaw disharmonyor dysplasia, the jaws must of necessity be related toeach other and to neither cranial nor extracraniallandmarks. A reference plane, common to bothdentures and one most suitable from which to relateboth jaws, is that of the occlusion, namely, theocclusal plane. When relating the jaws to this com-mon plane, clockwise or counterclockwise rotationof the jaws relative to cranial or extracranial refer-ence planes will in no way affect the overall assess-ment of severity of jaw disharmony.

The “Wits” appraisal thus provides a reliableindication of extent or severity of anteroposteriorskeletal disharmony of the jaws. It does not neces-sarily relate to degree of difficulty in treatment. Alow “Wits” reading should not always be interpretedas being a malocclusion that is easily corrected.Factors such as posterior vertical dimension, ramuswidth, symphyseal thickness,7,16,19-22 etc, must betaken into account in predicting growth trends. Thelatter, in effect, still remains educated guesswork.Whereas a low mandibular plane angle in Class IImalocclusions usually indicates favorable mandibu-lar growth,6,12 investigators have shown how readilythis forward growth of the mandible can be counter-acted by backward movement of the condyle due toposterior cranial base growth.

The limitations of treatment must be recognized,not only from a mechanical standpoint but alsobiologically, since we are unable with any degree ofcertainty to predict, in the face of random environ-

Fig 12. Class II malocclusion tracings with identical ANB angles (9 degrees). A, “Wits” reading of�8 mm reflects a severe Class III jaw disharmony. B, “Wits” reading of �2.5 mm indicates a mildClass III jaw disharmony.

Fig 13. The ANB angle measures 10 degrees. By con-ventional assessment, this is a severe Class II jawdisharmony. According to “Wits” appraisal (2 mm), themalocclusion is that of a mild Class II skeletal pattern.


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mental influences, the final manifestations of thegrowth pattern or the severity of the malocclusion.8

The “Wits” appraisal is thus intended not as a singlediagnostic criterion but as an additional measurementwhich may be included in existing cephalometricanalysis to aid in the assessment of degree ofanteroposterior jaw disharmony.

Summary

The “Wits” appraisal of jaw disharmony is a simplemethod whereby the severity or degree of anteroposte-rior jaw dysplasia may be measured on a lateralcephalometric head film.

The method entails drawing perpendiculars from

Fig 14. Class II malocclusion tracings with identical ANB angle readings (7 degrees). A, “Wits”appraisal (9 mm) indicating severe Class II jaw disharmony. B, “Wits” appraisal (1 mm) indicatingmild Class II jaw disharmony.

Fig 15. Cephalometric tracing of a Class III malocclu-sion with ANB angle of 2 degrees. According to con-ventional assessment, this would appear to be an“average” normal occlusion. “Wits” reading of �4.5 mmsuggests a definite Class III skeletal disharmony.

Fig 16. The ANB angle of 0 degrees suggests a Class IIItendency by conventional assessment. According tothe “Wits” appraisal (�9.5 mm), the malocclusion is thatof a severe Class III.


478 Jacobson

points A and B on the maxilla and mandible, respec-tively, onto the occlusal plane. The points of contact ofthe perpendiculars onto the occlusal plane are labeledAO and BO, respectively.

In a sample of twenty-one male and twenty-fivefemale adults selected on the basis of excellence ofocclusion, it was found, on the average, that in femalespoints AO and BO coincided and in males point BOwas located 1 mm ahead of point AO.

In skeletal Class II jaw dysplasias, point BO wouldbe positioned well behind point AO (positive reading),whereas in Class III skeletal jaw disharmonies, the“Wits” reading would be negative, that is, with pointBO ahead of point AO.

The advantages of the “Wits” appraisal over that ofthe conventional ANB angle reading are illustrated anddiscussed.

REFERENCES

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3. Coben SE. The investigation of facial skeletal variants; a serialcephalometric roentgenographic analysis of craniofacial formand growth. Am J Orthod 1955;41:407-34.

4. De Coster L. A new line of reference for the study of lateral andfacial teleradiographs. Am J Orthod 1953;39:304.

5. Downs WB. Variations in facial relationship; their significance intreatment and prognosis. Am J Orthod 1948;29:8-29.

6. Enlow DH, Takayuki K, Lewis AB. Intrinsic craniofacial com-pensations. Angle Orthod 1971;41:271-85.

7. Isaacson JR, Isaacson RJ, Speidel TM, Worms FW. Extremevariation in vertical facial growth and associated skeletal anddental relations. Angle Orthod 1971;41:219-29.

8. Jacobson A. Orthodontics—mechanical or biologic objectives?Am J Orthod 1973;64:1-16.

9. Jacobson A, Evans WB, Preston CB, Sadowsky PL. Mandibularprognathism. Am J Orthod 1974;66:140-71.

10. Margolis HI. A basic facial pattern and its application in clinicalorthodontics, craniofacial skeletal analyses and dento-cranio-facial orientation. Am J Orthod 1953;39:425-43.

11. Martin R. Lehrbuch der Antropologie. Part II, ed. 2, Jena, 1928,Gustav Fischer.

12. McIver LW. Growth formulas in Class II treatment. Am J Orthod1973;43:1-17.

13. Moore AW. In: Salzmann JA, editor. Roentgenographic cepha-lometrics. Philadelphia: J. B. Lippincott; 1959. p. 85.

14. Moorrees CFA. Normal variation and its bearing on the use ofcephalometric radiographs in orthodontic diagnosis. Am JOrthod 1953;39:942.

15. Moss ML. In: Salzmann JA, editor. Roentgenographic cephalo-metrics. Philadelphia: J. B. Lippincott; 1961. p. 57.

16. Ricketts RM. The influence of orthodontic treatment on facialgrowth and development. Angle Orthod 1060;30:103-33.

17. Ricketts RM. The keystone triad. Am J Orthod 1964;50:244-64,728-50.

18. Riedel RA. An analysis of dentofacial relationships. Am JOrthod 1957;43:103-19.

19. Root TL. Anchorage concepts based on vertical dimension.Personal communication, 1973.

20. Sassouni V, Nanda S. Analysis of dentofacial vertical propor-tions. Am J Orthod 1964;50:801-23.

21. Schudy FF. The rotation of the mandible resulting from growth.Angle Orthod 1965;35:36-50.

22. Schudy FF. The control of vertical overbite in clinical orthodon-tics. Angle Orthod 1968;38:19-39.

23. Steiner CC. Cephalometrics for you and me. Am J Orthod1953;39:729-55.

24. Steiner CC. Cephalometrics in clinical practice. Angle Orthod1959;29:8-29.

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jacobson ajo 1975-2003 - the wits appraisal of jaw disharmony

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