Wits appraisal

the presentation deals with the cephalometric wits appraisal .

1. Wits appraisal Prepared by:- Mona G hannam . . Supervisor:- Prof.dr Maher Fouda

2. Various cranial reference planes have been used as baselines from which to determine the degree of jaw dysplasia .. T hese reference planes deal with cranial architecture and so are useful in relating the jaws to the cranium .

3. Measurements from the cranial base, however do not always provide a reliable expression of anteroposterior jaw relationships in the dentoalveolar complex .

4. The ANB angle (the difference between SNA and SNB angles) is the most commonly used measurement for evaluating the anteroposterior disharmony of the jaws. The average ANB angle is 2 degrees. Angles greater than this mean indicate tendencies toward class II jaw disharmonies while smaller angles ( extending to – ve readings) reflect class III jaw discrepancies .

5. Although the ANB angle is a reliable indication of anteroposterior jaw relationship, there are many situations in which this reading cannot be relied on .

6. These situations are due to craniofacial skeletal variations such as : The anteroposterior spatial relationship of the jaws relative to the cranium ( nasion ). For example, Standard ANB=2 Long cranial base( retropositioned jaw) ANB= -2 Short cranial base(jaws positioned forward to nasion ) ANB=5

7. in prognathous faces, the ANB angle increases, whereas in jaws that are relatively retrusive , this angle is reduced while in both conditions, the relationship of the jaws to each other remains unchanged. Long cranial base( retropositioned jaw) ANB= -2 Short cranial base(jaws positioned forward to nasion ) ANB=5 Standard ANB=2

8. Binder recognized the geometric effects at work in the ANB angle. He showed that for every 5-mm anterior displacement of nasion horizontally , the ANB angle changed 2.5 degrees. Vertical positioning of nasion results in these ANB angles: 1 = 2 degrees , 2 = 1 degree, 3 = 0 degrees .

9. A 5-mm upward displacement of nasion altered the ANB angle 0.5 degrees; a downward displacement of nasion changed the ANB angle 1 degree Horizontal positioning of nasion results in these ANB angles: 1 = 2 degrees, 2 = 8.5 degrees 3 = - 4 . 5 degrees .

10. 2. The rotational effect of the jaws relative to the anterior cranial base . A clockwise rotation of the jaws relative to S-N plane(in a patient facing right) would cause the ANB angle to increase in size producing Class II and vice versa while the relationship of the jaws to each other is still unchanged. Counterclockwise rotation of the jaws ANB = -5 Clockwise rotation of the jaws ANB= 8 Standard ANB =2

11. The rotational effect of the S-N line virtually has no anteroposterior position effect on the nasion point; therefore, the ANB angle reading is minimally affected by angular deviations of S-N from the horizontal

12. . The Wits appraisal was developed in an effort to reduce these inconsistencies found within the ANB angle. The wits appraisal is a measure of the extent to which the jaws are related to each other. This appraisal relates point A and point B to the occlusal plane, providing a measurement of the anteroposterior relationship of the jaws nearer the teeth than is provided by the ANB angle.

13. The Wits appraisal is a linear measurement and not an analysis in itself.

14. The Wits appraisal uses a functional occlusal plane, which is the plane of maximum intercuspation of posteriors (drawn on lateral cehalometric tracing through the region of the overlapping cusps of the first premolars and first molars). In the mixed dentition, a horizontal plane can usually be drawn through the overlap of the cusps of both deciduous molars and the permanent first molars .

15. correct location or representation of the occlusal plane in Wits appraisal is very important, sometimes the left and right sides of the posterior teeth do not coincide or superimpose correctly. The latter problem may be due to true dentofacial asymmetry, a symmetric location of the external auditory meatus, and /or in correct positioning of the head in the cephalostat .

16. To overcome this discrepancy, a plane is drawn midway between the two posterior segments . Perpendicular lines are drawn from points A and B to this occlusal plane. The points on the occlusal plane is named AO and BO respectively.

17. Positive values occur when point AO is ahead of (anterior to) point BO, and negative values occur when point BO is anterior to point AO

18. The average jaw relationship according to wits reading is -1.0mm for men and 0 mm for women. In skeletal class II, point BO would be located well behind point AO(positive reading), whereas in skeletal class III, the wits reading would be negative(point BO is ahead of point AO).

19. . The severity of anteroposterior disharmony depends on the amount of deviation of wits reading from the mean.. Therefore, the Wits appraisal is intended not as a single diagnostic criterion but as an additional measurement, which may be included in the existing cephalometric analysis to aid in the assessment of the degree of anteroposterior jaw disharmony . Moreover, its usefulness in orthognathic surgery is self-evident.

20. Both ANB angle = 7 Class II Normal class I

21. Both ANB angle = 9 (suggesting sever class II) but Wits application indicate A ----- < major discrepancy class II B ----- < mild discrepancy class II

22. Mild class III Sever class III

23. These observations quite naturally lead one to ask the question, “ Can one determine whether or not the ANB angle is reliable ?”

24. Subsequent investigations have indicated that if the mandibular plane angle (Go- Gn to S-N) reading is considerably higher or lower than the mean of 32 degrees (plus or minus 1 SD of 5 degrees), the ANB reading as a reliable indication of anteroposterior jaw discrepancy is suspected. Simply stated, this means that ANB readings are suspected in patients having mandibular plane angles of greater than 37 degrees or less than 27 degrees .

25. CONCLUSION: The Wits appraisal is a linear measurement and not an analysis perse . It is simply an adjunctive diagnostic aid that may prove useful in assessing the extent of anteroposterior skeletal dysplasia and in determining the reliability of the ANB angle. Identification of landmarks and interpretation of findings of a three dimensional object on a two-dimensional image cannot be regarded as truly stable. No single parameter in cephalometry should be relied on entirely and interpreted as an absolute value , Correlation between the linear and angular measurements is a must for interpretation.