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Application of the “Wits” appraisal
Application of the “Wits” appraisal A.
Jacobson,
M.D.S.,
Johannesburg,
M.S.,
Ph.D.
South Africa
T
he “Wits” appraisal2 is a diagnostic aid which enables the severity of degree of anteroposterior jaw disharmony to be measured from a lateral cephalometric head film. Briefly, the method entails drawing perpendiculars from points A and B on the maxilla and mandible, respectively, onto the occlusal plane. The points of contact of the perpendiculars onto the occlusal plane arc labeled A0 and BO, respectively (Fig. 1). On average, it was found that in female normal occlusions points A0 and BO coincided, whereas in males point BO was located approximately 1 mm. ahead of point AO. The “Wits” reading in females having a normal occlusion would thus be 0, whereas in males it would be -1.0 mm. The ANB angle (the difference between the SNA and SNB angles) is the most commonly used measurement in appraising horizontal jaw disharmony. The ANB reading, however, does not take into consideration the relative relationship of the denture bases to cranial reference planes. The singular advantage of the “Wits” appraisal is that it overcomes this shortcoming and concomitantly emphasizes an awareness of this relationship in the over-all interpretation of a cephalometric analysis. Various lateral cephalometric head film tracings have been selected to illustrate this point and to outline a method of application of the “Wits” appraisal. Application
of “Wits”
appraisal
Relating jaws to cranial reference planes introduces inherent inconsistencies because of variations in craniofacial physiognomy. Included among these craniofacial skeletal variations are (1) the anteroposterior spatial relationship of nasion relative to jaws and (2) the rotational effect of the jaws relative to cranial reference planes. A high.ANB angle frequently observed in persons with excellent occlusions2 may be attributed to anterior positioning of jaws relative to nasion and/or clockwise rotational effect (downward tipping of ANS) of the jaws relative From School.
the
Department
of
Orthodontics,
University
of
the
Witwatersrand,
Dental
179
180
Jacobson.
Fig. 1. Points A and
A0 and B, respectively,
A?% J. Orthod. August 1976
BO are the points of contact onto occlusal plane.
of
perpendiculars
dropped
from
points
to anterior cranial base (Figs. 2 and 3). Fig. 4 shows an example of a Lengua Indian with an excellent occlusion but in whom, because of retropositioning of nasion (short anterior cranial base) and clockwise rotation of the jaws (high palatal, occlusal, and mandibular plane angles), the ANB reading is 9 degrees. The “Wits” appraisal of -1.0 mm. indicates very mild mandibular prognathism (probably due to attrition, thereby permitting rotation of the mandible), which for this population group is norma1.3 In many instances, however, the ANB angle is suspect. The manifest question therefore is how to determine whether the ANB angle is reliable or suspect. In an endeavor to answer the question, it is necessary to ascertain (1) the relative anteroposterior position of the jaws to nasion and (2) the rotational relationship of the jaws relative to the anterior cranial base. Anteroposterior relationship of jaws to nasio,n. At the outset, it should be pointed out that all cranial reference planes are relative to each other and that no single plane may be used reliably as a baseline from which to measure all craniofacial relationships for diagnostic purposes. This was adequately demonstrated by Nanda and Sassouni,4 who reviewed various cranial reference planes and revealed the shortcomings of each in five different analyses.
Applica~tion
AV.
NORMAL
ANB ‘WITS’
CL.
2” Omm
Fig. 2. “Average” ANB
AV.
Fig. 3. Average tions
of
base (A). The in B and C.
cranial is illustrated
angle
jaws
NORMAL “normal” relative
III
AND ‘WITS’ effect
LONG BASE to
occlusion anterior
(A). The cranial
of “Wits”
ROTATION
CL.
--5” Omm of
ANT. (SN)
long
and
short
8” Omm
anterior
cranial
SHORT BASE is
181
11 ROTATION
ANB ‘WITS’
CRANIAL
effect of anticlockwise base on ANB angle
nppraisd
ANT. (SN)
bases
on
CRANIAL
and clockwise rotashown in B and C.
182
Ja#cobson
Fig. 4. Tracing occlusion. ANB
of lateral cephalometric angle is 9 degrees, “Wits”
Am. J. Orthod. August 1976
head film appraisal
of Lengua is -1 mm.
Indian
male
with
excellent
The SNA angle, however, offers a simple method of ascertaining whether the maxilla is forward or backward relative to nasion. An angle of higher than 82 degrees indicates forward positioning of the upper jaw relative to nasion, whereas an angle of less that 82 degrees indicates retropositioning of the maxi11a.5-7 This reading, however, tends to be reliable only when and if the mandibular plane angle to SN reading approximates 32 degrees. Mandibular plane angles considerably higher or lower than 32 degrees immediately cause the SNA angle to be suspect. (In a series of twenty-five male and twenty-three female Caucasians with excellent occlusions, the mean mandibular plane angles for the sexes were 30.3 degrees [S.D. 5.01 and 29.4 degrees [S.D. 6.41, respectively.3 For convenience, and since the Steiner analysis is so extensively used, a mean mandibular plane angle of 32 degrees is used.) A high mandibular-plane-angle reading generally suggests a divergent type of profile. In most of these eases the anterior cranial base is tipped superiorly in front. This, in effect, reduces the SNA angle reading, thereby providing specious information, The converse is true, a particularly low mandibular-plane-angle reading suggests a convergent type of profi1e.l The SNA angle in these cases would be larger than the average 82 degrees. Therefore, high or low mandibular-plane-angle readings,
f&&cation
of “Wits"
appraisal
183
q.&++c$
u ............ ...’
.. -=+t
..... 7
of the palate. differences are
*
. . ............ -==-+t ...... ........ .......
,,..,,....... ”
Q...... ..... “...., ... ‘....
.. .. T
-
Fig. 5. Palatal
.,... .,..,,,,......... .. .
plane drawn Stippled line evident.
3 . ........... .. AX 7
as a solid line passing through joins anterior nasal spine to
the most radiopaque posterior nasal spine.
portion Angular
usually in execess of 1 standard deviation (6 degrees), causes the SNA reading to be suspect. Rotational e#ect of jaws. To determine the extent of clockwise rotation (downward tipping of ANS) of the jaws relative to anterior cranial base, the mandibular plane angle is again noted. A high mandibular plane angle (above 37 degrees) would, in effect, be an indication of clockwise rotation of the jaws, thereby increasing the ANB angle (divergent facial type). Reduction of the mandibular plane angle (convergent facial type) will have the opposite effect, namely, reducing the ANB angle. In the sample of “normal” occlusions, the degrees of variability of palatal, occlusal, and mandibular planes relative to anterior cranial base (SN) were calculated (Table I). The plane exhibiting the greatest coefficient of variability was the palatal
104
Ja.cobson
Am. J. Orthod. Awust 1976
Fig. 6. Tracings
illustrating methods of drawing occlusal plane. Solid (concave upward) line is drawn through points of maximum contact of teeth. Stippled line is plane drawn joining mesiobuccal cusp of upper first molar to point midway between overlap of upper and lower incisors. (See text.)
Table
I.
Relationship
of
palatal,
occlusal, Males
Parameter
SN - Palatal plane SN - Occlusal plane SN - Mandibular plane
Mean 7.4 13.3 30.3
and
mandibular
planes
Females
(N=25) S.D. 3.9 3.9 5.0
to
1
SN (N=23)
C.V.
Mean
S.D.
c. v.
0.530 0.296 0.166
8.4 14.1 29.4
3.5
0.422 0.317 0.219
4.5 6.4
plane (C. V. males 0.530, females, 0.422), followed by the occlusal plane (C. V. males 0.296, females 0.317), the least variable being the mandibular plane (C. V. males 0.166, females 0.219). The greater degree of variability of palatal and occlusal planes may be attributed in part to difficulty or inaccuracy in identifying the respective planes. A line joining anterior nasal spine to posterior nasal spine is not necessarily representative of the palatal plane. A line passing through the most radiopaque portion of the palate in a lateral head film would probably more accurately reflect the plane of the palate. Fig. 5 shows a series of tracings in which a solid line is drawn through the most radiopaque section of the palate, whereas the stippled line joins ANS to PNS. The angular differences between these planes are immediately evident.
The occlusal plane is likewise difficult to measure accurately, particularly in adult dentitions in which third molars are present. The occlusal plane is not flat; rather, it is concave. In more mature dentitions, therefore, the plane oi maximum intercuspation cannot always be used in that this plane follows a turns (solid line in Fig. 6). A line joining the mesiobuccal cusp of the upp~ first molar to a point midway between the overlap of the upper and lower incisors is D satisfactory method of standardizing occlusal plane measurement in most normal occlusions (stippled line in Fig. 6, 8). In occlusions with a deep curve of Specl and in malocclusions with supra- or infra-erupted upper or lower incisors, the latter method is likewise unsuitable. Probably the most suitable and convenient method of standardizing the plane of occlusion is to join midpoints of overlalj of the mesiobuccal cusps of the first molars and the buccal cusps of the first premolars. SNA,
ANB,
reliable
or suspect?
In many instances the SNA, SNB, and ANB angles accurately reflect thr degree of anteroposterior positioning of the jaws in the relationship of the jaws to each other. There are other instances however in which these angles are in no way representative of jaw relationship or disharmony. It is here that the “Wits” appraisal could be conveniently applied and prove clinicall> useful . Should the mandibular plane be in excess of or less than 1 standard deviation of the mean of 32 degrees (+ 5 degrees), the interpretation of an SNA angle of 82 degrees becomes suspect. An angular reading of less than 82 degrees does not, necessa.rily mean a relatively (to anterior cranial base) recessive maxilla or ric*c versa. When the mandibular plane angle reading is in excess of or less than 1 standard deviation of the mean, the ANB angle is likewise suspect. A high mandibular plane angle reading generally suggests a divergent type of profile, whereas a low reading usually obtains in the convergent type of profile. The jaws in a divergent type of profile tend to rotate clockwise (lowering of anterior part of hard palate), thus increasing the ANB reading. The opposite condition prevails in the convergent. type of profile; that is, the ANB reading is lowered. Should the mandibular plane angular reading be within the range of normality-82 degrees (rt 5)-the SNA angle interpretation is usually reliable. However, this is not necessarily the case in the interpretation of the ANB angle. The “Wits” appraisal is a more reliable measure of anteroposterior jaw relationship. In sum, therefore, a high mandibular-plane reading causes SNA and ANB readings to be suspect. Mandibular-plane-angle readings within the range of normality are usually reliable reflections of maxillary position (anteropostrriorly) ; that is, SNA is reliable, but ANB is not necessarily so. Mandibular
plane angle high or low
Mandibular
plane “normal”
-
SNA ANB SNA ANB
suspect suspect reliable not necessarily reliahlr
186
Jacobson
Am. J. Orthod. August 1976
‘WITS’
lmm
fig. 7. “WITS” Parameter
1
Mandibular plane SNA ANB “Wits” Male Female
Ref.
32” 82” 2” -1
Norm
(-+ 5) (-+ 3.5) p 2)
mm. 0 mm.
1 /
Patient D. M. APPRAISAL Interpretation
Mearurement
1
46”
High
79” 10.5”
(? 2) (+ 2)
1 mm.
SNA
Eable
mandibular
SNA wise “Wits” mild high
SNA
plane
angle;
angle is suspect; ANB suspect appraisal of 1 mm. Class II jaw dysplasia ANB angle (10.5”)
qsuspect
therefore,
79”
of
like-
10.5”
indicates very in spite of
Fig. 8. Patient J. Y. “WITS” APPRAISAL Parameter
1
Ref.
Norm
Measurement
Interpretation SNA
reliable
El Mandibular plane SNA ANB “Wits” Male Female
32”
(+ 5)
82” 2”
(k 3.5) (+ 2)
-1
mm. 0 mm.
(2 2) (* 2)
34” 85.5” 8.5”
2.5
mm.
SNA
suspect
cl
Average mandibular plane angle, SNA probably reliable indicating relative forward positioning of iaws causing ANB reading (8.5”) to be high “Wits” appraisal of 2.5 mm. indicates mild jaw disharmony, but not as severe as ANB of 8.5” would indicate
of ‘Tits”
Application
fig.
9.
Patient
“WITS”
K.
187
appraisal
P.
APPRAISAL
-Parameter
1
Ref.
Norm
Measurement
Interpretation SNA
reliable
SNA
suspect
q Mandibular
32”
(+
5)
37”
Mandibular
plane
SNA
SNA
82”
(It
3.5)
90”
ANB
2”
(?
2)
10”
plane of
Female
mm.
(+ 2)
0 mm.
(* 2)
fairly
and
high;
ANB
probably
10”
forward
therefore, are
suspect;
and
relatively
rotated Wits”
-1
90”
maxilla
“Wits” Male
EJ
2
mm.
measurement
mild
Class
ANB
of
II,
10”
of but
not
would
2
mm.
nearly
indicates as
much
as
indicate -
Fig.
10.
“WITS”
Parameter
Ref.
Norm
Patient
A.
K.
APPRAISAL
Interpretation
Measurement
SNA
,
reliable
SNA
cl Mandibular
32”
(+ 5)
42”
High
plane SNA
angle 82”
ANB
2”
(+
3.5)
(5 2)
80”
wise
1”
“Wits”
“Wits” Male Female
Class -1
mm.
(? 2)
0 mm.
(t 2)
mm.
lzl
mandibular therefore
plane
angle;
suspect;
ANB
80”
SNA
1.0”
like-
of
suspect appraisal III
measurement -6.5
suspect
jaw
-6.5
mm.
dysplasia
of
in
of only
reflects spite
severe of
1’ __-
AN8
188
Jacobson
Am J. Orthod. Aumst 1976
Fig. 11. “WITS” Parameter
Ref.
Norm
Measuremerit
Patient I. K. APPRAISAL Interpretation SNA
reliable lxl
Mandibular plane SNA ANB “Wits” Male Female
Application
32”
(+ 5)
35”
82” 2”
(-c 3.5) (2 21
79” 2”
-1
of the
0 mm. mm.
“Wits”
(+ 2) (+ 2)
-4.5
mm.
SNA
suspect Cl
Maxilla possibly mildly retropositioned relative to nasion, viz. 79” instead of 82”; AN6 of 2” indicates “normal” jaw relationship “Wits” appraisal of -4.5 mm., however, suggests Class III tendency (more reliable-clinically observed)
cppraisal
The following cases show the usefulness of the “Wits” the reliability of the SNA and ANB angles.
appraisal in assessing
Summary
The “Wits” appraisal is intended as a diagnostic aid to be used in conjunction with other analyses. Whereas the popularly used ANB angular reading is a simple method of measuring degree of jaw disharmony, there are many instances in which this reading is suspect. The “Wits” appraisal permits easy identification of these
Volume
Number2
70
shortcomings and substitutes a reasonably reliable of anteroposterior jaw disharmony. My sincere thanks Mathematics for his
and appreciation invaluable aid
to and
Mr. Paul suggestions
means of measuring
Fatti of the in computing
Department of the statistical
extent Applies1 data.
REFERENCES
1. Jacobson A., Evans, W. G., Preston, C. R., and Sadowsky, P. L.: Mandibular prognxthisrn, AM. J. ORTHOD. 66: 140-171, 1974. 2. Jacobson, A.: The “Wits” appraisal of jaw disharmony, AM. J. ORTHOD. 67: 125-138, I97L 3. Jacobson, A., Preston, C. R., Roettner, V., and Perreira, C.: The crania-facial skeletal pattern of the Lengua Indians of Paraguay. (Submitted for publication in Am. J. Phys. Anthropol.) 4. Nanda, 8. K., and Sassouni, V.: Planes of reference in rocntgenographia cephalometry, Angle Orthod. 35: 311-319, 1965. 5. Steiner, Cecil C.: Cephalometrics for you and me, AM. J. ORTHOD. 39: 729-755, 1!)5:L 6. Steiner, Cecil C.: Cephalometrics in clinical practice, Angle Orthod. 29: 8-29, .1959. 7. Steiner, Cecil C.: The use of cephalometrics as an aid to planning and assessing otthodontic treatment, AM. J. ORTHOD. 46: 721.735, 1960.
Probably the community will be best served when every dentist has a working knowledge of orthodontics whereby he will be able to recognize in their early stages and so to prevent deformities before they arise, and to treat at any rate the simpler cases when circumstances make it desirable and when in every district there is available a specialist to whom the general practitioner may refer such patients as he may be unwilling or unable to deal with himself. It will be for the specialist to remain the pioneer and the expert, and he will be none the worse if his rank be recruited from those of the general practitioner. (Badcock, J .H.: Discussion of President’s Address, Transactions of the First [ 19261 International Orthodontic Congress, St. Louis, 1927, The C. V. Mosby Company, p. 11.)
Jacobson,
M.D.S.,
Johannesburg,
M.S.,
Ph.D.
South Africa
T
he “Wits” appraisal2 is a diagnostic aid which enables the severity of degree of anteroposterior jaw disharmony to be measured from a lateral cephalometric head film. Briefly, the method entails drawing perpendiculars from points A and B on the maxilla and mandible, respectively, onto the occlusal plane. The points of contact of the perpendiculars onto the occlusal plane arc labeled A0 and BO, respectively (Fig. 1). On average, it was found that in female normal occlusions points A0 and BO coincided, whereas in males point BO was located approximately 1 mm. ahead of point AO. The “Wits” reading in females having a normal occlusion would thus be 0, whereas in males it would be -1.0 mm. The ANB angle (the difference between the SNA and SNB angles) is the most commonly used measurement in appraising horizontal jaw disharmony. The ANB reading, however, does not take into consideration the relative relationship of the denture bases to cranial reference planes. The singular advantage of the “Wits” appraisal is that it overcomes this shortcoming and concomitantly emphasizes an awareness of this relationship in the over-all interpretation of a cephalometric analysis. Various lateral cephalometric head film tracings have been selected to illustrate this point and to outline a method of application of the “Wits” appraisal. Application
of “Wits”
appraisal
Relating jaws to cranial reference planes introduces inherent inconsistencies because of variations in craniofacial physiognomy. Included among these craniofacial skeletal variations are (1) the anteroposterior spatial relationship of nasion relative to jaws and (2) the rotational effect of the jaws relative to cranial reference planes. A high.ANB angle frequently observed in persons with excellent occlusions2 may be attributed to anterior positioning of jaws relative to nasion and/or clockwise rotational effect (downward tipping of ANS) of the jaws relative From School.
the
Department
of
Orthodontics,
University
of
the
Witwatersrand,
Dental
179
180
Jacobson.
Fig. 1. Points A and
A0 and B, respectively,
A?% J. Orthod. August 1976
BO are the points of contact onto occlusal plane.
of
perpendiculars
dropped
from
points
to anterior cranial base (Figs. 2 and 3). Fig. 4 shows an example of a Lengua Indian with an excellent occlusion but in whom, because of retropositioning of nasion (short anterior cranial base) and clockwise rotation of the jaws (high palatal, occlusal, and mandibular plane angles), the ANB reading is 9 degrees. The “Wits” appraisal of -1.0 mm. indicates very mild mandibular prognathism (probably due to attrition, thereby permitting rotation of the mandible), which for this population group is norma1.3 In many instances, however, the ANB angle is suspect. The manifest question therefore is how to determine whether the ANB angle is reliable or suspect. In an endeavor to answer the question, it is necessary to ascertain (1) the relative anteroposterior position of the jaws to nasion and (2) the rotational relationship of the jaws relative to the anterior cranial base. Anteroposterior relationship of jaws to nasio,n. At the outset, it should be pointed out that all cranial reference planes are relative to each other and that no single plane may be used reliably as a baseline from which to measure all craniofacial relationships for diagnostic purposes. This was adequately demonstrated by Nanda and Sassouni,4 who reviewed various cranial reference planes and revealed the shortcomings of each in five different analyses.
Applica~tion
AV.
NORMAL
ANB ‘WITS’
CL.
2” Omm
Fig. 2. “Average” ANB
AV.
Fig. 3. Average tions
of
base (A). The in B and C.
cranial is illustrated
angle
jaws
NORMAL “normal” relative
III
AND ‘WITS’ effect
LONG BASE to
occlusion anterior
(A). The cranial
of “Wits”
ROTATION
CL.
--5” Omm of
ANT. (SN)
long
and
short
8” Omm
anterior
cranial
SHORT BASE is
181
11 ROTATION
ANB ‘WITS’
CRANIAL
effect of anticlockwise base on ANB angle
nppraisd
ANT. (SN)
bases
on
CRANIAL
and clockwise rotashown in B and C.
182
Ja#cobson
Fig. 4. Tracing occlusion. ANB
of lateral cephalometric angle is 9 degrees, “Wits”
Am. J. Orthod. August 1976
head film appraisal
of Lengua is -1 mm.
Indian
male
with
excellent
The SNA angle, however, offers a simple method of ascertaining whether the maxilla is forward or backward relative to nasion. An angle of higher than 82 degrees indicates forward positioning of the upper jaw relative to nasion, whereas an angle of less that 82 degrees indicates retropositioning of the maxi11a.5-7 This reading, however, tends to be reliable only when and if the mandibular plane angle to SN reading approximates 32 degrees. Mandibular plane angles considerably higher or lower than 32 degrees immediately cause the SNA angle to be suspect. (In a series of twenty-five male and twenty-three female Caucasians with excellent occlusions, the mean mandibular plane angles for the sexes were 30.3 degrees [S.D. 5.01 and 29.4 degrees [S.D. 6.41, respectively.3 For convenience, and since the Steiner analysis is so extensively used, a mean mandibular plane angle of 32 degrees is used.) A high mandibular-plane-angle reading generally suggests a divergent type of profile. In most of these eases the anterior cranial base is tipped superiorly in front. This, in effect, reduces the SNA angle reading, thereby providing specious information, The converse is true, a particularly low mandibular-plane-angle reading suggests a convergent type of profi1e.l The SNA angle in these cases would be larger than the average 82 degrees. Therefore, high or low mandibular-plane-angle readings,
f&&cation
of “Wits"
appraisal
183
q.&++c$
u ............ ...’
.. -=+t
..... 7
of the palate. differences are
*
. . ............ -==-+t ...... ........ .......
,,..,,....... ”
Q...... ..... “...., ... ‘....
.. .. T
-
Fig. 5. Palatal
.,... .,..,,,,......... .. .
plane drawn Stippled line evident.
3 . ........... .. AX 7
as a solid line passing through joins anterior nasal spine to
the most radiopaque posterior nasal spine.
portion Angular
usually in execess of 1 standard deviation (6 degrees), causes the SNA reading to be suspect. Rotational e#ect of jaws. To determine the extent of clockwise rotation (downward tipping of ANS) of the jaws relative to anterior cranial base, the mandibular plane angle is again noted. A high mandibular plane angle (above 37 degrees) would, in effect, be an indication of clockwise rotation of the jaws, thereby increasing the ANB angle (divergent facial type). Reduction of the mandibular plane angle (convergent facial type) will have the opposite effect, namely, reducing the ANB angle. In the sample of “normal” occlusions, the degrees of variability of palatal, occlusal, and mandibular planes relative to anterior cranial base (SN) were calculated (Table I). The plane exhibiting the greatest coefficient of variability was the palatal
104
Ja.cobson
Am. J. Orthod. Awust 1976
Fig. 6. Tracings
illustrating methods of drawing occlusal plane. Solid (concave upward) line is drawn through points of maximum contact of teeth. Stippled line is plane drawn joining mesiobuccal cusp of upper first molar to point midway between overlap of upper and lower incisors. (See text.)
Table
I.
Relationship
of
palatal,
occlusal, Males
Parameter
SN - Palatal plane SN - Occlusal plane SN - Mandibular plane
Mean 7.4 13.3 30.3
and
mandibular
planes
Females
(N=25) S.D. 3.9 3.9 5.0
to
1
SN (N=23)
C.V.
Mean
S.D.
c. v.
0.530 0.296 0.166
8.4 14.1 29.4
3.5
0.422 0.317 0.219
4.5 6.4
plane (C. V. males 0.530, females, 0.422), followed by the occlusal plane (C. V. males 0.296, females 0.317), the least variable being the mandibular plane (C. V. males 0.166, females 0.219). The greater degree of variability of palatal and occlusal planes may be attributed in part to difficulty or inaccuracy in identifying the respective planes. A line joining anterior nasal spine to posterior nasal spine is not necessarily representative of the palatal plane. A line passing through the most radiopaque portion of the palate in a lateral head film would probably more accurately reflect the plane of the palate. Fig. 5 shows a series of tracings in which a solid line is drawn through the most radiopaque section of the palate, whereas the stippled line joins ANS to PNS. The angular differences between these planes are immediately evident.
The occlusal plane is likewise difficult to measure accurately, particularly in adult dentitions in which third molars are present. The occlusal plane is not flat; rather, it is concave. In more mature dentitions, therefore, the plane oi maximum intercuspation cannot always be used in that this plane follows a turns (solid line in Fig. 6). A line joining the mesiobuccal cusp of the upp~ first molar to a point midway between the overlap of the upper and lower incisors is D satisfactory method of standardizing occlusal plane measurement in most normal occlusions (stippled line in Fig. 6, 8). In occlusions with a deep curve of Specl and in malocclusions with supra- or infra-erupted upper or lower incisors, the latter method is likewise unsuitable. Probably the most suitable and convenient method of standardizing the plane of occlusion is to join midpoints of overlalj of the mesiobuccal cusps of the first molars and the buccal cusps of the first premolars. SNA,
ANB,
reliable
or suspect?
In many instances the SNA, SNB, and ANB angles accurately reflect thr degree of anteroposterior positioning of the jaws in the relationship of the jaws to each other. There are other instances however in which these angles are in no way representative of jaw relationship or disharmony. It is here that the “Wits” appraisal could be conveniently applied and prove clinicall> useful . Should the mandibular plane be in excess of or less than 1 standard deviation of the mean of 32 degrees (+ 5 degrees), the interpretation of an SNA angle of 82 degrees becomes suspect. An angular reading of less than 82 degrees does not, necessa.rily mean a relatively (to anterior cranial base) recessive maxilla or ric*c versa. When the mandibular plane angle reading is in excess of or less than 1 standard deviation of the mean, the ANB angle is likewise suspect. A high mandibular plane angle reading generally suggests a divergent type of profile, whereas a low reading usually obtains in the convergent type of profile. The jaws in a divergent type of profile tend to rotate clockwise (lowering of anterior part of hard palate), thus increasing the ANB reading. The opposite condition prevails in the convergent. type of profile; that is, the ANB reading is lowered. Should the mandibular plane angular reading be within the range of normality-82 degrees (rt 5)-the SNA angle interpretation is usually reliable. However, this is not necessarily the case in the interpretation of the ANB angle. The “Wits” appraisal is a more reliable measure of anteroposterior jaw relationship. In sum, therefore, a high mandibular-plane reading causes SNA and ANB readings to be suspect. Mandibular-plane-angle readings within the range of normality are usually reliable reflections of maxillary position (anteropostrriorly) ; that is, SNA is reliable, but ANB is not necessarily so. Mandibular
plane angle high or low
Mandibular
plane “normal”
-
SNA ANB SNA ANB
suspect suspect reliable not necessarily reliahlr
186
Jacobson
Am. J. Orthod. August 1976
‘WITS’
lmm
fig. 7. “WITS” Parameter
1
Mandibular plane SNA ANB “Wits” Male Female
Ref.
32” 82” 2” -1
Norm
(-+ 5) (-+ 3.5) p 2)
mm. 0 mm.
1 /
Patient D. M. APPRAISAL Interpretation
Mearurement
1
46”
High
79” 10.5”
(? 2) (+ 2)
1 mm.
SNA
Eable
mandibular
SNA wise “Wits” mild high
SNA
plane
angle;
angle is suspect; ANB suspect appraisal of 1 mm. Class II jaw dysplasia ANB angle (10.5”)
qsuspect
therefore,
79”
of
like-
10.5”
indicates very in spite of
Fig. 8. Patient J. Y. “WITS” APPRAISAL Parameter
1
Ref.
Norm
Measurement
Interpretation SNA
reliable
El Mandibular plane SNA ANB “Wits” Male Female
32”
(+ 5)
82” 2”
(k 3.5) (+ 2)
-1
mm. 0 mm.
(2 2) (* 2)
34” 85.5” 8.5”
2.5
mm.
SNA
suspect
cl
Average mandibular plane angle, SNA probably reliable indicating relative forward positioning of iaws causing ANB reading (8.5”) to be high “Wits” appraisal of 2.5 mm. indicates mild jaw disharmony, but not as severe as ANB of 8.5” would indicate
of ‘Tits”
Application
fig.
9.
Patient
“WITS”
K.
187
appraisal
P.
APPRAISAL
-Parameter
1
Ref.
Norm
Measurement
Interpretation SNA
reliable
SNA
suspect
q Mandibular
32”
(+
5)
37”
Mandibular
plane
SNA
SNA
82”
(It
3.5)
90”
ANB
2”
(?
2)
10”
plane of
Female
mm.
(+ 2)
0 mm.
(* 2)
fairly
and
high;
ANB
probably
10”
forward
therefore, are
suspect;
and
relatively
rotated Wits”
-1
90”
maxilla
“Wits” Male
EJ
2
mm.
measurement
mild
Class
ANB
of
II,
10”
of but
not
would
2
mm.
nearly
indicates as
much
as
indicate -
Fig.
10.
“WITS”
Parameter
Ref.
Norm
Patient
A.
K.
APPRAISAL
Interpretation
Measurement
SNA
,
reliable
SNA
cl Mandibular
32”
(+ 5)
42”
High
plane SNA
angle 82”
ANB
2”
(+
3.5)
(5 2)
80”
wise
1”
“Wits”
“Wits” Male Female
Class -1
mm.
(? 2)
0 mm.
(t 2)
mm.
lzl
mandibular therefore
plane
angle;
suspect;
ANB
80”
SNA
1.0”
like-
of
suspect appraisal III
measurement -6.5
suspect
jaw
-6.5
mm.
dysplasia
of
in
of only
reflects spite
severe of
1’ __-
AN8
188
Jacobson
Am J. Orthod. Aumst 1976
Fig. 11. “WITS” Parameter
Ref.
Norm
Measuremerit
Patient I. K. APPRAISAL Interpretation SNA
reliable lxl
Mandibular plane SNA ANB “Wits” Male Female
Application
32”
(+ 5)
35”
82” 2”
(-c 3.5) (2 21
79” 2”
-1
of the
0 mm. mm.
“Wits”
(+ 2) (+ 2)
-4.5
mm.
SNA
suspect Cl
Maxilla possibly mildly retropositioned relative to nasion, viz. 79” instead of 82”; AN6 of 2” indicates “normal” jaw relationship “Wits” appraisal of -4.5 mm., however, suggests Class III tendency (more reliable-clinically observed)
cppraisal
The following cases show the usefulness of the “Wits” the reliability of the SNA and ANB angles.
appraisal in assessing
Summary
The “Wits” appraisal is intended as a diagnostic aid to be used in conjunction with other analyses. Whereas the popularly used ANB angular reading is a simple method of measuring degree of jaw disharmony, there are many instances in which this reading is suspect. The “Wits” appraisal permits easy identification of these
Volume
Number2
70
shortcomings and substitutes a reasonably reliable of anteroposterior jaw disharmony. My sincere thanks Mathematics for his
and appreciation invaluable aid
to and
Mr. Paul suggestions
means of measuring
Fatti of the in computing
Department of the statistical
extent Applies1 data.
REFERENCES
1. Jacobson A., Evans, W. G., Preston, C. R., and Sadowsky, P. L.: Mandibular prognxthisrn, AM. J. ORTHOD. 66: 140-171, 1974. 2. Jacobson, A.: The “Wits” appraisal of jaw disharmony, AM. J. ORTHOD. 67: 125-138, I97L 3. Jacobson, A., Preston, C. R., Roettner, V., and Perreira, C.: The crania-facial skeletal pattern of the Lengua Indians of Paraguay. (Submitted for publication in Am. J. Phys. Anthropol.) 4. Nanda, 8. K., and Sassouni, V.: Planes of reference in rocntgenographia cephalometry, Angle Orthod. 35: 311-319, 1965. 5. Steiner, Cecil C.: Cephalometrics for you and me, AM. J. ORTHOD. 39: 729-755, 1!)5:L 6. Steiner, Cecil C.: Cephalometrics in clinical practice, Angle Orthod. 29: 8-29, .1959. 7. Steiner, Cecil C.: The use of cephalometrics as an aid to planning and assessing otthodontic treatment, AM. J. ORTHOD. 46: 721.735, 1960.
Probably the community will be best served when every dentist has a working knowledge of orthodontics whereby he will be able to recognize in their early stages and so to prevent deformities before they arise, and to treat at any rate the simpler cases when circumstances make it desirable and when in every district there is available a specialist to whom the general practitioner may refer such patients as he may be unwilling or unable to deal with himself. It will be for the specialist to remain the pioneer and the expert, and he will be none the worse if his rank be recruited from those of the general practitioner. (Badcock, J .H.: Discussion of President’s Address, Transactions of the First [ 19261 International Orthodontic Congress, St. Louis, 1927, The C. V. Mosby Company, p. 11.)