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A comparison of ANB, WITS, AF-BF, and APDI measurements
A comparison of ANB, WITS, AF-BF, and APDI measurements HOsamettin Oktay, DDS, PhD* Erzurum, Turkey In the present study, the relationships among ANB, Wits, AF-BF, and APDI measurements used in the assessment of the anteroposterior jaw disorders were examined on the cephalometric radiographs of 63 male and 82 female subjects, and high correlations were found among them. Furthermore, relationships were explored between these parameters and some measurements that were thought to have influenced them. The results of the geometric studies could not be proved on the basis of statistical evaluation. (AMJ ORTHOODENTOFACORTHOP 1991 ;99:122-8,)
F r e e m a n t stated that, even before Angle introduced his classification of malocclusion to the profession in the early 1900s, the anteroposterior relationship of mandible to maxilla was the most important diagnostic criterion. This relationship was subject to clinical observation for quite some time. With Broadbent's introduction of his cephalometer in 1931, 2 a new period began in orthodontics. More stable relationships among teeth, jaws, face, and head structures and more successful treatment were deemed possible) For the determination of sagittal denture base relationship, Downs 4 introduced the A-B plane angle. A few years later, Riedel s had recommended using the SNA, SNB, and ANB angles. The ANB angle (Fig. 1) has been recognized as a skeletal sagittal discrepancy indicator and has become the most commonly used measurement since that time. More recently, it has been claimed that the ANB angle is affected by several environmental factors and thus a diagnosis based on this angle may give false results.~.62t By arbitrarily varying the position of points, lines, and angles on cephalometric drawings, some authors have demonstrated geometrically that the ANB angle can be changed, although the intermaxillary relationships were unchanged. The following factors have been reported to affect the ANB angle: I. The patient's age. 6.~7.2' The ANB angle has a definite tendency to decrease with increasing age. 2. The change of the spatial position of the na-
sion either in the vertical or anteroposterior direction or both. ~s:°~6.~s'2° 3. The upward or downward rotation of the SN line.7.sa m2.,s.2o 4. The upward or downward rotation of the jaws.tH3.ts.16.tS.t9
*Associate Professor, Department of Orthodontics Faculty of Dentistry, AtatSrk University, Erzurum, Turkey. This study was presented at the International Congress of Dentistry, Izmir, Turkey, April, 25-27, 1988. 8/1/18055
5. The change in the angle SN to the occlusal plane./° 6. The degree of facial prognathism, t.9.~3 Because of the doubts mentioned above about the accuracy of ANB angle measurements, a number of
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Fig. 1. The ANB angle.
Volume 99 Number 2
Comparison of ANB, WITS, AF-BF, and APDI 123
L; Po
Fig. 2. The Wits appraisal in a skeletal Class III case. Perpendicular lines are dropped from points A and B onto the occlusal plane. The Wits reading is measured from AO to BO.
~BF
Or i
Fig. 3. The AF-BF distance is established by erecting perpendiculars from points A and B to the Frankfort horizontal plane, with the intersections identified as AF and BF.
different, new measurements have been developed to determine the actual relationships of the denture bases. 1.8-13.16.17.22 Jacobson "'~2 (and Harvey Jenkins) drew perpendiculars on a lateral cephalometric head film tracing from points A and B on the maxilla and mandible, respectively, to the occlusal plane to obtain a measurement that was less affected by variations in craniofacial physiognomy (Fig. 2). The distance between the points of contact of the perpendiculars on the occlusal plane, AO and BO, served as an indicator of skeletal sagittal jaw relationship• It has come to be known as the Wits (Witwatersrand University, Johannesburg, South Africa) Appraisal• To eliminate the great variations in the occlusal plane, Chang s reported a linear measurement of the distance between points A and B projected onto the Frankfort horizontal plane (Fig. 3). The points of contact of the perpendiculars on the Frankfort horizontal plane from points A and B were labeled AF and BF, respectively, and this measurement was called the AFBF distance. According to Kim and Vietas, Z6 deviations in the dentofacial complex are not affected by a singular factor; thus a combination of several different measure-
d Po
/
V
APDI =1"-2-'3
Fig. 4. The antero-posterior displasia indicator (APDI) is a resultant reading obtained from the facial angle (1) plus or minus the A-B plane angle (2) and again plus or minus the palatal plane angle (3).
124
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Po i)-
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G
Fig. 5. The measurements that are thought to affect the ANB angle: 1, SN length; 2, SN-GoGn angle; 3, FMA measurement; 4, OP-SN angle, 5, OP-GoGn (OM) angle.
ments may be more reliable for diagnosis. They suggested a formulary measurement, the anteroposterior displasia indicator (APDI), which is a resultant reading obtained from the facial angle plus or minus the A-B plane angle and again plus or minus the palatal plane angle (Fig. 4). Successful planning of treatment and treatment resuits depends on reliable diagnostic criteria. The aim of this study has been to determine which of the aforementioned criteria are more reliable for clinicians. For this purpose statistical comparisons were made among ANB, Wits, AF-BF, and APDI measurements, along with some measurements that are thought to influence them. MATERIALS AND METHODS
In this investigation, 145 cephalometric head films from 63 male subjects and 82 female subjects were used. These films were obtained from the files of the Department of Orthodontics of the Faculty of Dentistry at Atatiirk University. All of the subjects had, to varying degrees, either skeletal or dentoalveolar malocclusions or both, and their ages ranged from 9 to 14 years. The cephalometric film tracings were made by the usual methods. The traditional occlusal plane extending from the cuspal image overlap of the first molars to the middle of the incisor overlap was used. In addition to the sagittal parameters mentioned above (Figs. 1 to 4),
some measurements such as the SN-GoGn angle, OPSN angle, OP-GoGn (OM) angle, FMA measurement, and SN length, which were thought to influence the sagittal parameters, were also recorded (Fig. 5). To determine the errors associated with radiographic measurements, 20 radiographs were selected at random from the observation group. Their tracings and measurements were repeated 3 weeks after the first measurement. No statistically significant relationship (p > 0.05) was found between the first and second measurements. To check whether the male and female groups were homogeneous with regard to age, the Student's t test was applied to these two groups; this test was also used to determine whether there were any differences between the measurements of male and female subjects. In all of the measurements except SN distance, there were no statistically significant differences between sexes. Therefore, all measurements belonging to both sexes, except SN, were pooled, and a correlation analysis was made among them. FINDINGS
The mean age in both sexes was l l years 10 months. No statistically significant relationship was found between the ages of male and female subjects (t = - 0 . 0 4 , p > 0.05). All statistical data relating to measurements, such
Volume 99 Number 2
Comparison of ANB, WITS, AF-BF, and APDl
125
T a b l e I. T h e range o f m e a s u r e m e n t s o f m a l e and f e m a l e subjects and t values b e t w e e n the sexes (male, n = 63; female, n = 82) Variable ANB Male Female WITS Male Female AF-BF Male Female APDI Male Female SN-GoGn Male Female FMA Male Female OP-SN Male Female OP-GoGn Male Female SN MaIe Female
]
Standard deviation
Minimum
MaMmum
Mean
- 6.00 - 7.25
8.50 7.25
2.79 2.36
2.93 2.82
0.88
10.25 - 12.75
8.75 8.50
- 0.30 - 0.59
4.03 4.4 I
0.41
- 4.75 - 2.00
17.00 17.50
8.62 7.30
4.72 4.37
1.72
67.75 67.75
95.50 104.50
79.18 80.60
5.80 6.39
1.39
27.00 16.25
44.00 54.25
36.42 36.42
4.61 5.56
0.00
19.75 2.75
41.00 43.50
29.24 28.45
4.96 6.38
0.84
10.00 9.25
26.00 27.00
19.42 18.67
3.76 4.18
1.15
9.50 5.50
26.50 29.25
i 6.96 17.68
3.81 3.96
- 1.11
63.00 60.50
79.00 75.00
69.75 67.96
3.42 3.45
t ~'ahtes
3.11 ***
***p~O.O01.
T a b l e II, T h e range o f m e a s u r e m e n t s o f pooled g r o u p
] M,.mum I M ; um I ANB WITS AF-BF APDI SN-GoGn FMA OP-SN OP-GoGn
-7.25 12.75 -4.75 67.75 16.25 2.75 9.25 5.50
8.50 8.75 17.50 104.50 54.25 43.50 27.00 29.25
as m e a n s , standard deviations, ranges, coefficients o f variability, and the values o f the S t u d e n t ' s t test and correlation coefficients are presented in Tables I, lI, and III. T h e coefficients o f variability o f the four parameters used in the assessment o f anteroposterior j a w relationship are quite different f r o m each other (Table II). A c c o r d i n g to these coefficients, the m e a s u r e m e n t with the
Mean
Standard deviation
Coefficient variability
2.575 0.445 7.960 79.890 36.420 28.845 19.045 17.320
2.87 4.24 4.56 5.16 5.15 5.80 4.01 3.90
111.46 952.81 57.29 6.46 14.14 20.11 21.06 22.25
most h o m o g e n e o u s distribution was A P D I , f o l l o w e d by A F - B F and A N B ; the least h o m o g e n e o u s was the Wits appraisal. Statistically significant and highly correlated relationships w e r e found a m o n g four sagittal parameters and also a m o n g vertical m e a s u r e m e n t s (Table III). M a r k e d l y different correlations w e r e found b e t w e e n the sagittal parameters and the m e a s u r e m e n t s that are
126
Am. J. Orthod.Dentofac.Orthop. February1991
Oktay
Table IlL The correlation coefficients among the measurements
I ANB WITS AF-BF APDI SN-.GoGn OP-SN OP-GoGn FMA
I 0.758**
0.760** 0.662**
I s o°ol 0.802** -0.812"* 0.754**
0.142 0.080 0.309** -0.236**
i 0.271"* 0.170" 0.379** -0.302** 0.661"*
I -0.088 0.067 0.027 -0.004 0.648** - 0.142
FMA 0.042 -0.215"* 0.482** -0.059 0.753** 0.476** 0.514"*
[ SN male [ SN female 0.070 0.380** 0.193 -0.278* -0.149 -0.251" 0.051 -0.135
0.086 0.270* 0.165 -0.203 -0.301"* -0.248* -0.158 -0.190
*p --< 0.05. **p -< 0.01.
thought to affect the ANB angle. As can be seen from Table III, the measurement least affected by environmental factors is the ANB angle. DISCUSSION
Many papers have been published on the ANB angle. t6 A smaller number of papers has been devoted to the Wits appraisal, but none exists on the AF-BF and APDI measurements. Therefore, we could compare only our findings on ANB and Wits appraisal with those of other authors. The greatest coefficient of variability of the Wits appraisal may be attributed in part to difficulties or inaccuracies in identifying the occlusal plane and/or variations in it. 7's'1°'na3,ls-2° The result of this study, in which the Wits appraisal showed much more variation than the ANB angle, is similar to data contained in Gazilerli's unpublished study and literature. 6'~3a6 In Chang's sample, s as opposed to ours, the coefficient of variability of the ANB angle was higher than that of the AF-BF measurement. The high correlation coefficients among four sagittal parameters denote that these parameters are closely related to each other and may be used interchangeably. The correlation coefficient between the ANB angle and the Wits appraisal in this investigation is higher than that found by other authors. 6a3.tS'2° Most of the criticisms about the ANB angle have been based on geometric studies. Lsaz In these, the length and inclination of the SN plane, the anteroposterior position of the jaws, and the rotation of the jaws with respect to the SN plane have been arbitrarily changed on cephalometric drawings, while the anteroposterior relationship of the jaws has not. With respect to the conditions mentioned above, it has been suggested that although the apical base relationships were constant in all conditions, the ANB angle became either small or large, and thus such a measurement was not
reliable. L8~2 Statistical studies carried out on this subject are fewer, and their results do not provide perfect support for those of the geometrical studies. When the geometric studies are assessed, one must consider Bjrrk's opinion: "The human body constitutes a functional entity, no part of which can be varied without entailing some changes in other parts. Similarly, the facial skeleton and the dentition are functional parts of the skull as a whole. It follows, therefore, that variations in the bite will be largely related to the facial and cranial structure. ''z~ In the present study, the high correlation coefficients among the measurements of SN-GoGn, OP-SN, OPGoGn, and FMA (Table III) support Bjrrk's opinion. 23 Our finding is also similar to the findings of Gazilerli's unpublished study and those of Richardson. ~8 According to these statistical results, the SN plane, Frankfort horizontal plane, occlusal plane, and mandibular plane tend to move in the same direction. In this respect, it does not seem logical to attempt to change the inclination of some planes such as the SN line or occlusal plane on cephalometric drawings in different directions. It has been claimed that any change in the length of the SN plane would affect the ANB angle. 7,8,ll't2,tSA8-2° It has been known that nasion usually moves in an anterior and slightly superior direction because of the growth increments on the cranial base plane passing through sella and nasion. ~°'2° However, one must not forget that growth is a total process, and the face also grows in a forward and downward direction) T M In a longitudinal study, Nanda ~7demonstrated that the forward growth of the maxilla was, on the average, equivalent to the forward growth of nasion. The opinion admitting that only the nasion area of the face overgrows or undergrows contradicts our knowledge about complete facial growth. In the present study, the fact that no statistical relationship was found between the length of the SN plane and the ANB angle
Volume 99 Number 2
confirms the aforementioned opinions and contradicts the claims about the ANB angle in relation to SN length. Gazilerli carried out an investigation, which has not yet been published, on Turkish children with excellent occlusion and found a low correlation (r = - 0 . 1 6 7 in boys and r = - 0 . 2 5 9 in girls) between the length of SN and the ANB angle. Richardson ~8 also studied the correlation between the same measurements and found no relationship (r = - 0 . 0 2 ) . J~irvinen t5 determined by his multiple regression equation that the effect of SN length on the ANB angle was very weak, and thus he excluded the SN distance from his equation. Jacobson tt.t2 proposed that the mandibular plane angle (SN-GoGn) be considered in determinations of the rotation of the jaws relative to the anterior cranial base. The increase or decrease of this angle is a sign of downward and backward or upward and forward rotation of the jaws, respectively. The mandibular plane angle (SNGoGn) provides some indications of the rotation of the mandible, but it also indicates a mutual rotation between the cranial base and the jaws. t4 This angle is also used to determine the facial height. ~2 In the present study, no statistical relationship was found between SN-GoGn and ANB angles, and this result contradicted the claims that the ANB angle is affected by the Sn-GoGn angle. The correlation coefficient between anterior face height and the ANB angle computed by Richardson t~ is very low (r = 0.03), and it is similar to our finding. Gazilerli, in his unpublished study, has found a low relationship (r = 0.370 for male subjects and r = 0.277 for female subjects) between these two angles. A low but statistically significant relationship has also been observed between the angle of the occlusal plane with SN and the ANB angle. This finding agrees with the geometric relationship posited by Hussels and Nanda '° regarding this angle. In this study, it has been observed that the Wits appraisal, suggested as an alternative to the ANB angle measurement, was affected more by the environmental factors than was the ANB angle. On the basis of our results, there is a low and negative correlation (r = - 0 . 1 7 ) between the occlusal plane to SN and the Wits appraisal. The most important problem of the Wits analysis is that accurate identification of the occlusal plane is not always easy. 7'19It must be remembered that the inclination of the occlusal plane easily could be changed by the vertical movement of incisors, molar teeth, or both.~°'~5.2° The correlation between the Wits appraisal and the SN-GoGn angle was found to be insignificant. The findings of Gazilerli's unpublished study and those of
Comparison of ANB, WITS, AF-BF, and APDI 127 Richardson t8 are also similar to this. These agree with Jacobson's claim tl't2 that the Wits appraisal does not change with the rotation of the jaws. A low but statistically significant and negative correlation was observed between the Wits appraisal and the FMA measurement. Although it has been suggested that there is a correlation between SN length and the ANB angle, a statistically significant correlation was found in the present study between SN length and the Wits appraisal. Richardson ~8and Gazilerli did not find any correlation between these two factors. Chang s has claimed that the Wits appraisal easily could be affected by the changes in the inclination of the occlusal plane and the variations in the vertical positions of point A, point B or both, and he offered an alternative measurement, AF-BF. In this study, however, the correlation coefficients between AF-BF measurement and the measurements of OP-SN and FMA were found to be greater than the correlation coefficients between the Wits appraisal and the two measurements. On the basis of this result, AF-BF measurement has been affected by the inclinations of the Frankfort horizontal plane and the occlusal plane more than the Wits appraisal. Furthermore, this measurement has been affected by the SN-GoGn measurement, whereas the ANB angle and the Wits appraisal have not been affected. Low but statistically significant and negative correlations were found between the APDI measurement and the measurements of SN length (in male subjects), in the SN-GoGn angle, and in the OP-SN angle. CONCLUSION
High correlations were found among the ANB, Wits, AF-BF, and APDI measurements and among vertical parameters. In the light of these findings, it seems feasible that the sagittal parameters could be used interchangeably, and that the occlusal plane, the SN line, the Frankfort horizontal plane, and the mandibular plane tend to move in the same direction. The claims about the ANB angle, based upon the geometrical studies, could not be substantiated from the statistical analysis. On the other hand, measurements such as the Wits, AF-BF, and APDI, suggested as alternatives to the ANB angle, were affected more by the measurements of SN-GoGn, OP-SN, FMA, and SN length. As a resuit, it appears that the Wits, AF-BF, and APDI apical base assessment criteria are not more reliable in clinical diagnosis than the ANB angle. I express my gratitude to Dr. Omit Gazilerli, Director of the Orthodontic Department, for his valuable assistance in
128
Am. J. Orthod. Dentofac. Orthop. February 1991
Oktay
carrying out this study, and to Dr. Necati Yildiz for assistance with the statistical evaluation. 14. REFERENCES 1. Freeman RS. Adjusting A-N-B angles to reflect the effect of maxillary position. Angle Orthod 1981;51:162-71. 2. Broadbent BH. A new x-ray technique and its application to orthodontia. Angle Orthod 1931;1:45-66. (Reprinted in Angle Ortbod 1981;51:93-114.) 3. Gazilerli O. Tiirk (jocuklari i~in Downs ve Tweed ~lqiimleri. AU Di~ Hek Derg 1981;8:115-36. 4. Downs WB. Variations in facial relationships: their significance in treatment and prognosis. AM J ORTHOD 1948;34:812-40. 5. Riedel RA. Esthetics and its relation to orthodontic therapy. Angle Orthod 1950;20;168-78. 6. Bishara SE, Fahl JA, Peterson LC. Longitudinal changes in the ANB angle and Wits appraisal: clinical implications. AM J OR~toD 1983;84:133-9. 7. BrownM. Eight methodsofanalysingacephalogramtoestablish anteroposterior skeletal discrepancy, Br J Orthod 1981;8:13946. 8. Chang HP. Assessment of anteroposterior jaw relationship. AM J ORTHODDENTOFACORTHOP 1987;92:117-22. 9. Ferrazini G. Critical evaluation of the ANB angle. AM J ORTtIOD 1976;69:620-6. 10. Hussels W, Nanda RS. Analysis of factors affecting angle ANB. AM J ORTHOD 1984;85:411-23. l 1. Jacobson A. The "Wits" appraisal of jaw disharmony. AM J ORTHOD 1975;67:125-38. 12. Jacobson A. Application of the "Wits" appraisal. AM J OR'mOt) 1976;70:179-89. 13. J~irvinen S. A comparison of two angular and two linear mea-
15.
16.
17.
18. 19. 20. 21. 22. 23. 24.
surements used to establish sagittal apical base relationship. Eur J Orthod 1981;3:131-4. J~rvinen S. An analysis of the variation of the ANB angle: a statistical appraisal. AM J OP.'mOD 1985;87:144-6, Jarvinen S. Floating norms for the ANB angle as guidance for clinical considerations. AM J ORTHODDEN'I'OFACORI'HOP 1986; 90:383-7. Kim YH, Vietas JJ. Anteroposterior dysplasia indicator: an adjunt to cepbalometric differential diagnosis. Ar,t J OR'mOB 1978;73:619-33. Nanda RS. Growth changes in skeletal-facial profile and their significance in orthodontic diagnosis. AM J ORTttOD 1971; 59:501-13. Richardson M. Measurement of dental base relationship. Eur J Orthod 1982;4:251-6. Robertson NRE, Pearson CJ. The Wits appraisal of a sample of the south wales population. Br J Orthod 1980;7:183-4. Rotberg S, Fried N, Kane J, Shapiro E. Predicting the "'Wits'" appraisal from the ANB angle. AM J OR'roOD 1980;77:636-42. Walker GF, Kowalski C. The distribution of the ANB angle in "normal" individuals. Angle Orthod 1971;41:332-5. McNamara JA Jr. A method of cephalometric evaluation. AM J ORTHOD 1984;86:449-69. Bjrrk A. Some biological aspects of prognathism and occlusion of the teeth. Angle Orthod 1951;21:3-27. Perkfin F. Cene ortopedisi (ortodonti). istanbul: Gen~likbasimevi, 1973:159-79.
Reprint requests to: Dr. Hiisamettin Oktay Atafiirk Universitesi: Dis Hekimli/~i Fakiiltesi Ortodonti Anabilim Dali Er-zurum, Turkey
AAO MEETING CALENDAR
1991--Seattle, Wash., May 11 to 15, Seattle Convention Center. 1992--St. Louis, Mo., May 10 to 13, St. Louis Convention Center 1993--Toronto, Canada, May 16 to 19, Metropolitan Toronto Convention Center 1994--Orlando, Fla., May 1 to 4, Orange County Convention and Civic Center 1995--San Francisco, Calif., May 7 to 10, Moscone Convention Center 1996--Denver, Colo., May 12-15, Colorado Convention Center
F r e e m a n t stated that, even before Angle introduced his classification of malocclusion to the profession in the early 1900s, the anteroposterior relationship of mandible to maxilla was the most important diagnostic criterion. This relationship was subject to clinical observation for quite some time. With Broadbent's introduction of his cephalometer in 1931, 2 a new period began in orthodontics. More stable relationships among teeth, jaws, face, and head structures and more successful treatment were deemed possible) For the determination of sagittal denture base relationship, Downs 4 introduced the A-B plane angle. A few years later, Riedel s had recommended using the SNA, SNB, and ANB angles. The ANB angle (Fig. 1) has been recognized as a skeletal sagittal discrepancy indicator and has become the most commonly used measurement since that time. More recently, it has been claimed that the ANB angle is affected by several environmental factors and thus a diagnosis based on this angle may give false results.~.62t By arbitrarily varying the position of points, lines, and angles on cephalometric drawings, some authors have demonstrated geometrically that the ANB angle can be changed, although the intermaxillary relationships were unchanged. The following factors have been reported to affect the ANB angle: I. The patient's age. 6.~7.2' The ANB angle has a definite tendency to decrease with increasing age. 2. The change of the spatial position of the na-
sion either in the vertical or anteroposterior direction or both. ~s:°~6.~s'2° 3. The upward or downward rotation of the SN line.7.sa m2.,s.2o 4. The upward or downward rotation of the jaws.tH3.ts.16.tS.t9
*Associate Professor, Department of Orthodontics Faculty of Dentistry, AtatSrk University, Erzurum, Turkey. This study was presented at the International Congress of Dentistry, Izmir, Turkey, April, 25-27, 1988. 8/1/18055
5. The change in the angle SN to the occlusal plane./° 6. The degree of facial prognathism, t.9.~3 Because of the doubts mentioned above about the accuracy of ANB angle measurements, a number of
122
Tj /
Fig. 1. The ANB angle.
Volume 99 Number 2
Comparison of ANB, WITS, AF-BF, and APDI 123
L; Po
Fig. 2. The Wits appraisal in a skeletal Class III case. Perpendicular lines are dropped from points A and B onto the occlusal plane. The Wits reading is measured from AO to BO.
~BF
Or i
Fig. 3. The AF-BF distance is established by erecting perpendiculars from points A and B to the Frankfort horizontal plane, with the intersections identified as AF and BF.
different, new measurements have been developed to determine the actual relationships of the denture bases. 1.8-13.16.17.22 Jacobson "'~2 (and Harvey Jenkins) drew perpendiculars on a lateral cephalometric head film tracing from points A and B on the maxilla and mandible, respectively, to the occlusal plane to obtain a measurement that was less affected by variations in craniofacial physiognomy (Fig. 2). The distance between the points of contact of the perpendiculars on the occlusal plane, AO and BO, served as an indicator of skeletal sagittal jaw relationship• It has come to be known as the Wits (Witwatersrand University, Johannesburg, South Africa) Appraisal• To eliminate the great variations in the occlusal plane, Chang s reported a linear measurement of the distance between points A and B projected onto the Frankfort horizontal plane (Fig. 3). The points of contact of the perpendiculars on the Frankfort horizontal plane from points A and B were labeled AF and BF, respectively, and this measurement was called the AFBF distance. According to Kim and Vietas, Z6 deviations in the dentofacial complex are not affected by a singular factor; thus a combination of several different measure-
d Po
/
V
APDI =1"-2-'3
Fig. 4. The antero-posterior displasia indicator (APDI) is a resultant reading obtained from the facial angle (1) plus or minus the A-B plane angle (2) and again plus or minus the palatal plane angle (3).
124
Am. J.
Oktay
Po i)-
Orthod. Dentofac. Orthop. Februa,'-)' 1991
~j Or
G
Fig. 5. The measurements that are thought to affect the ANB angle: 1, SN length; 2, SN-GoGn angle; 3, FMA measurement; 4, OP-SN angle, 5, OP-GoGn (OM) angle.
ments may be more reliable for diagnosis. They suggested a formulary measurement, the anteroposterior displasia indicator (APDI), which is a resultant reading obtained from the facial angle plus or minus the A-B plane angle and again plus or minus the palatal plane angle (Fig. 4). Successful planning of treatment and treatment resuits depends on reliable diagnostic criteria. The aim of this study has been to determine which of the aforementioned criteria are more reliable for clinicians. For this purpose statistical comparisons were made among ANB, Wits, AF-BF, and APDI measurements, along with some measurements that are thought to influence them. MATERIALS AND METHODS
In this investigation, 145 cephalometric head films from 63 male subjects and 82 female subjects were used. These films were obtained from the files of the Department of Orthodontics of the Faculty of Dentistry at Atatiirk University. All of the subjects had, to varying degrees, either skeletal or dentoalveolar malocclusions or both, and their ages ranged from 9 to 14 years. The cephalometric film tracings were made by the usual methods. The traditional occlusal plane extending from the cuspal image overlap of the first molars to the middle of the incisor overlap was used. In addition to the sagittal parameters mentioned above (Figs. 1 to 4),
some measurements such as the SN-GoGn angle, OPSN angle, OP-GoGn (OM) angle, FMA measurement, and SN length, which were thought to influence the sagittal parameters, were also recorded (Fig. 5). To determine the errors associated with radiographic measurements, 20 radiographs were selected at random from the observation group. Their tracings and measurements were repeated 3 weeks after the first measurement. No statistically significant relationship (p > 0.05) was found between the first and second measurements. To check whether the male and female groups were homogeneous with regard to age, the Student's t test was applied to these two groups; this test was also used to determine whether there were any differences between the measurements of male and female subjects. In all of the measurements except SN distance, there were no statistically significant differences between sexes. Therefore, all measurements belonging to both sexes, except SN, were pooled, and a correlation analysis was made among them. FINDINGS
The mean age in both sexes was l l years 10 months. No statistically significant relationship was found between the ages of male and female subjects (t = - 0 . 0 4 , p > 0.05). All statistical data relating to measurements, such
Volume 99 Number 2
Comparison of ANB, WITS, AF-BF, and APDl
125
T a b l e I. T h e range o f m e a s u r e m e n t s o f m a l e and f e m a l e subjects and t values b e t w e e n the sexes (male, n = 63; female, n = 82) Variable ANB Male Female WITS Male Female AF-BF Male Female APDI Male Female SN-GoGn Male Female FMA Male Female OP-SN Male Female OP-GoGn Male Female SN MaIe Female
]
Standard deviation
Minimum
MaMmum
Mean
- 6.00 - 7.25
8.50 7.25
2.79 2.36
2.93 2.82
0.88
10.25 - 12.75
8.75 8.50
- 0.30 - 0.59
4.03 4.4 I
0.41
- 4.75 - 2.00
17.00 17.50
8.62 7.30
4.72 4.37
1.72
67.75 67.75
95.50 104.50
79.18 80.60
5.80 6.39
1.39
27.00 16.25
44.00 54.25
36.42 36.42
4.61 5.56
0.00
19.75 2.75
41.00 43.50
29.24 28.45
4.96 6.38
0.84
10.00 9.25
26.00 27.00
19.42 18.67
3.76 4.18
1.15
9.50 5.50
26.50 29.25
i 6.96 17.68
3.81 3.96
- 1.11
63.00 60.50
79.00 75.00
69.75 67.96
3.42 3.45
t ~'ahtes
3.11 ***
***p~O.O01.
T a b l e II, T h e range o f m e a s u r e m e n t s o f pooled g r o u p
] M,.mum I M ; um I ANB WITS AF-BF APDI SN-GoGn FMA OP-SN OP-GoGn
-7.25 12.75 -4.75 67.75 16.25 2.75 9.25 5.50
8.50 8.75 17.50 104.50 54.25 43.50 27.00 29.25
as m e a n s , standard deviations, ranges, coefficients o f variability, and the values o f the S t u d e n t ' s t test and correlation coefficients are presented in Tables I, lI, and III. T h e coefficients o f variability o f the four parameters used in the assessment o f anteroposterior j a w relationship are quite different f r o m each other (Table II). A c c o r d i n g to these coefficients, the m e a s u r e m e n t with the
Mean
Standard deviation
Coefficient variability
2.575 0.445 7.960 79.890 36.420 28.845 19.045 17.320
2.87 4.24 4.56 5.16 5.15 5.80 4.01 3.90
111.46 952.81 57.29 6.46 14.14 20.11 21.06 22.25
most h o m o g e n e o u s distribution was A P D I , f o l l o w e d by A F - B F and A N B ; the least h o m o g e n e o u s was the Wits appraisal. Statistically significant and highly correlated relationships w e r e found a m o n g four sagittal parameters and also a m o n g vertical m e a s u r e m e n t s (Table III). M a r k e d l y different correlations w e r e found b e t w e e n the sagittal parameters and the m e a s u r e m e n t s that are
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Am. J. Orthod.Dentofac.Orthop. February1991
Oktay
Table IlL The correlation coefficients among the measurements
I ANB WITS AF-BF APDI SN-.GoGn OP-SN OP-GoGn FMA
I 0.758**
0.760** 0.662**
I s o°ol 0.802** -0.812"* 0.754**
0.142 0.080 0.309** -0.236**
i 0.271"* 0.170" 0.379** -0.302** 0.661"*
I -0.088 0.067 0.027 -0.004 0.648** - 0.142
FMA 0.042 -0.215"* 0.482** -0.059 0.753** 0.476** 0.514"*
[ SN male [ SN female 0.070 0.380** 0.193 -0.278* -0.149 -0.251" 0.051 -0.135
0.086 0.270* 0.165 -0.203 -0.301"* -0.248* -0.158 -0.190
*p --< 0.05. **p -< 0.01.
thought to affect the ANB angle. As can be seen from Table III, the measurement least affected by environmental factors is the ANB angle. DISCUSSION
Many papers have been published on the ANB angle. t6 A smaller number of papers has been devoted to the Wits appraisal, but none exists on the AF-BF and APDI measurements. Therefore, we could compare only our findings on ANB and Wits appraisal with those of other authors. The greatest coefficient of variability of the Wits appraisal may be attributed in part to difficulties or inaccuracies in identifying the occlusal plane and/or variations in it. 7's'1°'na3,ls-2° The result of this study, in which the Wits appraisal showed much more variation than the ANB angle, is similar to data contained in Gazilerli's unpublished study and literature. 6'~3a6 In Chang's sample, s as opposed to ours, the coefficient of variability of the ANB angle was higher than that of the AF-BF measurement. The high correlation coefficients among four sagittal parameters denote that these parameters are closely related to each other and may be used interchangeably. The correlation coefficient between the ANB angle and the Wits appraisal in this investigation is higher than that found by other authors. 6a3.tS'2° Most of the criticisms about the ANB angle have been based on geometric studies. Lsaz In these, the length and inclination of the SN plane, the anteroposterior position of the jaws, and the rotation of the jaws with respect to the SN plane have been arbitrarily changed on cephalometric drawings, while the anteroposterior relationship of the jaws has not. With respect to the conditions mentioned above, it has been suggested that although the apical base relationships were constant in all conditions, the ANB angle became either small or large, and thus such a measurement was not
reliable. L8~2 Statistical studies carried out on this subject are fewer, and their results do not provide perfect support for those of the geometrical studies. When the geometric studies are assessed, one must consider Bjrrk's opinion: "The human body constitutes a functional entity, no part of which can be varied without entailing some changes in other parts. Similarly, the facial skeleton and the dentition are functional parts of the skull as a whole. It follows, therefore, that variations in the bite will be largely related to the facial and cranial structure. ''z~ In the present study, the high correlation coefficients among the measurements of SN-GoGn, OP-SN, OPGoGn, and FMA (Table III) support Bjrrk's opinion. 23 Our finding is also similar to the findings of Gazilerli's unpublished study and those of Richardson. ~8 According to these statistical results, the SN plane, Frankfort horizontal plane, occlusal plane, and mandibular plane tend to move in the same direction. In this respect, it does not seem logical to attempt to change the inclination of some planes such as the SN line or occlusal plane on cephalometric drawings in different directions. It has been claimed that any change in the length of the SN plane would affect the ANB angle. 7,8,ll't2,tSA8-2° It has been known that nasion usually moves in an anterior and slightly superior direction because of the growth increments on the cranial base plane passing through sella and nasion. ~°'2° However, one must not forget that growth is a total process, and the face also grows in a forward and downward direction) T M In a longitudinal study, Nanda ~7demonstrated that the forward growth of the maxilla was, on the average, equivalent to the forward growth of nasion. The opinion admitting that only the nasion area of the face overgrows or undergrows contradicts our knowledge about complete facial growth. In the present study, the fact that no statistical relationship was found between the length of the SN plane and the ANB angle
Volume 99 Number 2
confirms the aforementioned opinions and contradicts the claims about the ANB angle in relation to SN length. Gazilerli carried out an investigation, which has not yet been published, on Turkish children with excellent occlusion and found a low correlation (r = - 0 . 1 6 7 in boys and r = - 0 . 2 5 9 in girls) between the length of SN and the ANB angle. Richardson ~8 also studied the correlation between the same measurements and found no relationship (r = - 0 . 0 2 ) . J~irvinen t5 determined by his multiple regression equation that the effect of SN length on the ANB angle was very weak, and thus he excluded the SN distance from his equation. Jacobson tt.t2 proposed that the mandibular plane angle (SN-GoGn) be considered in determinations of the rotation of the jaws relative to the anterior cranial base. The increase or decrease of this angle is a sign of downward and backward or upward and forward rotation of the jaws, respectively. The mandibular plane angle (SNGoGn) provides some indications of the rotation of the mandible, but it also indicates a mutual rotation between the cranial base and the jaws. t4 This angle is also used to determine the facial height. ~2 In the present study, no statistical relationship was found between SN-GoGn and ANB angles, and this result contradicted the claims that the ANB angle is affected by the Sn-GoGn angle. The correlation coefficient between anterior face height and the ANB angle computed by Richardson t~ is very low (r = 0.03), and it is similar to our finding. Gazilerli, in his unpublished study, has found a low relationship (r = 0.370 for male subjects and r = 0.277 for female subjects) between these two angles. A low but statistically significant relationship has also been observed between the angle of the occlusal plane with SN and the ANB angle. This finding agrees with the geometric relationship posited by Hussels and Nanda '° regarding this angle. In this study, it has been observed that the Wits appraisal, suggested as an alternative to the ANB angle measurement, was affected more by the environmental factors than was the ANB angle. On the basis of our results, there is a low and negative correlation (r = - 0 . 1 7 ) between the occlusal plane to SN and the Wits appraisal. The most important problem of the Wits analysis is that accurate identification of the occlusal plane is not always easy. 7'19It must be remembered that the inclination of the occlusal plane easily could be changed by the vertical movement of incisors, molar teeth, or both.~°'~5.2° The correlation between the Wits appraisal and the SN-GoGn angle was found to be insignificant. The findings of Gazilerli's unpublished study and those of
Comparison of ANB, WITS, AF-BF, and APDI 127 Richardson t8 are also similar to this. These agree with Jacobson's claim tl't2 that the Wits appraisal does not change with the rotation of the jaws. A low but statistically significant and negative correlation was observed between the Wits appraisal and the FMA measurement. Although it has been suggested that there is a correlation between SN length and the ANB angle, a statistically significant correlation was found in the present study between SN length and the Wits appraisal. Richardson ~8and Gazilerli did not find any correlation between these two factors. Chang s has claimed that the Wits appraisal easily could be affected by the changes in the inclination of the occlusal plane and the variations in the vertical positions of point A, point B or both, and he offered an alternative measurement, AF-BF. In this study, however, the correlation coefficients between AF-BF measurement and the measurements of OP-SN and FMA were found to be greater than the correlation coefficients between the Wits appraisal and the two measurements. On the basis of this result, AF-BF measurement has been affected by the inclinations of the Frankfort horizontal plane and the occlusal plane more than the Wits appraisal. Furthermore, this measurement has been affected by the SN-GoGn measurement, whereas the ANB angle and the Wits appraisal have not been affected. Low but statistically significant and negative correlations were found between the APDI measurement and the measurements of SN length (in male subjects), in the SN-GoGn angle, and in the OP-SN angle. CONCLUSION
High correlations were found among the ANB, Wits, AF-BF, and APDI measurements and among vertical parameters. In the light of these findings, it seems feasible that the sagittal parameters could be used interchangeably, and that the occlusal plane, the SN line, the Frankfort horizontal plane, and the mandibular plane tend to move in the same direction. The claims about the ANB angle, based upon the geometrical studies, could not be substantiated from the statistical analysis. On the other hand, measurements such as the Wits, AF-BF, and APDI, suggested as alternatives to the ANB angle, were affected more by the measurements of SN-GoGn, OP-SN, FMA, and SN length. As a resuit, it appears that the Wits, AF-BF, and APDI apical base assessment criteria are not more reliable in clinical diagnosis than the ANB angle. I express my gratitude to Dr. Omit Gazilerli, Director of the Orthodontic Department, for his valuable assistance in
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Am. J. Orthod. Dentofac. Orthop. February 1991
Oktay
carrying out this study, and to Dr. Necati Yildiz for assistance with the statistical evaluation. 14. REFERENCES 1. Freeman RS. Adjusting A-N-B angles to reflect the effect of maxillary position. Angle Orthod 1981;51:162-71. 2. Broadbent BH. A new x-ray technique and its application to orthodontia. Angle Orthod 1931;1:45-66. (Reprinted in Angle Ortbod 1981;51:93-114.) 3. Gazilerli O. Tiirk (jocuklari i~in Downs ve Tweed ~lqiimleri. AU Di~ Hek Derg 1981;8:115-36. 4. Downs WB. Variations in facial relationships: their significance in treatment and prognosis. AM J ORTHOD 1948;34:812-40. 5. Riedel RA. Esthetics and its relation to orthodontic therapy. Angle Orthod 1950;20;168-78. 6. Bishara SE, Fahl JA, Peterson LC. Longitudinal changes in the ANB angle and Wits appraisal: clinical implications. AM J OR~toD 1983;84:133-9. 7. BrownM. Eight methodsofanalysingacephalogramtoestablish anteroposterior skeletal discrepancy, Br J Orthod 1981;8:13946. 8. Chang HP. Assessment of anteroposterior jaw relationship. AM J ORTHODDENTOFACORTHOP 1987;92:117-22. 9. Ferrazini G. Critical evaluation of the ANB angle. AM J ORTtIOD 1976;69:620-6. 10. Hussels W, Nanda RS. Analysis of factors affecting angle ANB. AM J ORTHOD 1984;85:411-23. l 1. Jacobson A. The "Wits" appraisal of jaw disharmony. AM J ORTHOD 1975;67:125-38. 12. Jacobson A. Application of the "Wits" appraisal. AM J OR'mOt) 1976;70:179-89. 13. J~irvinen S. A comparison of two angular and two linear mea-
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