The ABO Discrepancy Index D'I':

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The ABO Discrepancy Index (D.I.) A Measure of
Case Complexity
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Target Disorder
1) Overjet 2) Overbite 3) Anterior Open
Bite 4) Lateral Open Bite 5) Crowding 6)
Occlusion
7) Lingual Posterior Crossbite 8) Buccal
Posterior Crossbite 9) ANB Angle 10) SN-MP
Angle 11) 1 to MP 12) Other
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Occlusal Relationship Position of the Models
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Overjet
0 mm (edge to edge) 1 pt. 1-3 mm 0 pt. 3.1-5
mm 2 pts. 5.1-7 mm 3 pts.
7.1-9 mm 4 pts. gt 9 mm 5 pts. Negative OJ
(x-bite) 1 pt. per mm. per tooth
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Overbite
0-3 mm 0 pt. 3.1-5 mm 2 pts.
5.1-7 mm 3 pts. Impinging (100) 5 pts.
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Anterior Open Bite
0 mm (edge to edge) 1 pt. per tooth then 1
pt. per additional full mm. per tooth
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Lateral Open Bite
2 pts. per mm. per tooth
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Crowding
1 - 3 mm 1 pt. 3.1 - 5 mm 2 pts.
5.1 - 7 mm 4 pts. gt 7 mm 7 pts.
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Occlusion
Class I to end on 0 pt. End on Class II or
III 2 pts. per side
Full Class II or III 4 pts. per side Beyond
Class II or III 1 pt. per
each additional mm.
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Lingual Posterior Crossbite
1 pt. per tooth
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Buccal Posterior Crossbite
2 pts. per tooth
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Cephalometrics
ANB 6 or -2 4 pts.
Each degree gt 6 1 pt. Each degree
lt -2 1 pt. SN-MP 38
2 pts. Each degree gt 38 2 pts.
26 1 pt.
Each degree lt 26 1 pt. 1 to MP
99 1 pt. Each
degree gt 99 1 pt.
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Other Supernumerary teeth - 1 point each
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Other Ankylosis of permanent teeth 2 points
per tooth
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Other Anomalous Morphologyof tooth size and
shape (e.g. peg lateral incisor)2 points per
occurrence
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Other Impaction2 points for each occurrence
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Other Midline Discrepancy 2 pts. if midline
3 mm
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Other Missing teeth (except 3rd molars) are 1
point per tooth Congenital missing teeth are 2
points per tooth
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Other Spacing
Mx central diastema gt 2 mm 2
pts. AND/OR Generalized spacing (4 teeth or more)
2 pts. per arch
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Other Tooth Transposition 2 points for each
event
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Other Skeletal Asymmetry (treated
nonsurgically)3 pts.
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OtherAddl. treatment complexities 2 pts.
for each occurrence(identify on lines provided
on DI form)
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Example 2Addl. treatment complexitiesEctopic
Eruption2 points
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Discrepancy Index Measurement Form
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Presenter ScriptThe following four slides
contain the combined NOTES from each slide above
- for use by presenters who wish to print the
notes for their oral remarks.To print, choose
File-Print Print-Range 26-29 Print What Slides
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Slide 1. One of the criteria for evaluating the
acceptability of cases for The American Board of
Orthodontics Clinical Examination is the degree
of complexity, which may be related to case
difficulty measured by a Discrepancy index
derived from accepted norms. In 1998, the Board
devised a Discrepancy Index which was
field-tested and modified at the subsequent four
yearly clinical examinations. The Board now
requires that cases selected for clinical
examination meet exam specifications for
Discrepancy Index. Slide 2. Points are scored
on pre-treatment dental casts according to a
measurement discrepancy from accepted norms in
eleven target disorders. These are linear
measurements of overjet, overbite, anterior open
bite, lateral open bite, crowding, occlusion,
lingual posterior crossbite, buccal posterior
crossbite, and the angular measurements ANB,
Sella-Nasion to Mandibular Plane, and Lower
incisor to MP. An additional category designated
Other has been added so that other conditions
which may affect or add to complexity of
treatment may be scored. The total points scored
produce a value of Discrepancy Index, or case
complexity. The DI form and instruction sheet
can be found on the ABO website at the Clinical
Examination - Download and Print area. The
following illustrations will serve to demonstrate
the Discrepancy Index Target Disorders, as well
as the final category labeled Other which will
be used to complete your Discrepancy Index
scoring. Slide 3. Occlusion is determined by
placing the backs of the pre-treatment dental
casts on a flat surface after they have been
pushed together into centric occlusion. All
measurements must be made from this
position. Slide 4. The first target disorder is
Overjet. Overjet is a measurement between two
antagonistic incisor teeth comprising the
greatest overjet. It is measured from the facial
surface of the most lingual tooth (Mx to Mn) to
the middle of the incisal edge of the more
facially positioned tooth (Mx or Mn). For
overjet of 0 millimeters, that is, edge to edge,
1 point is scored for overjet of 1 to 3
millimeters, no points are scored for 3.1 to 5
millimeters, 2 points are scored for 5.1 to 7
millimeters, 3 points are scored for 7.1 to 9
millimeters, 4 points are scored if over 9
millimeters, 5 points are scored. If there is a
negative overjet, that is, anterior crossbite,
the score is recorded as 1 point per millimeter
per anterior tooth in crossbite. The example
shown has 10.38 millimeters of overjet
therefore, 5 points are scored. Slide 5.
Overbite is scored as the amount of overlap of
the maxillary and mandibular incisors. For
overbites of up to 3 millimeters, no points are
scored. If the overbite is between 3.1 to 5
millimeters, 2 points are scored from 5.1 to 7
millimeters, 3 points are scored. If the lower
incisors are impinging on the palatal tissue, or
100 overbite, then 5 points are scored. For the
example seen here, the overlap of the incisors is
measured as 1.76 millimeters, and therefore no
points are scored.
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Slide 6. When scoring anterior open bite, for
each anterior tooth (canine to canine) that is in
an edge-to-edge relationship as illustrated in
the figure on the right, with an overbite of 0
millimeters, then 1 point is scored per tooth.
For each additional full millimeter of open bite,
1 point is scored for each maxillary tooth
involved. No points are scored for any anterior
tooth that is simply blocked-out of the arch or
not fully erupted. Slide 7. Lateral open bite is
scored as follows for each maxillary tooth
spanning the first premolar to the third molar in
an open bite relationship with respect to the
mandibular arch, 2 points are scored for each
millimeter of open bite for each tooth. Both
sides of the arches should be observed and
scored. Slide 8. When scoring crowding, measure
the most crowded arch circumference between the
first molars. For 1 to 3 millimeters of
crowding, 1 point is scored for 3.1 to 5
millimeters, 2 points are scored from 5.1 to 7
millimeters, 4 points are scored and if the
crowding is greater than 7 millimeters, 7 points
are scored. For this illustration, the maxillary
arch has the greatest amount of crowding and is
measured as 3 millimeters therefore, score 1
point. Slide 9. When scoring occlusion, the
Angle Classification is used. If the mesiobuccal
cusp of the maxillary first molar occludes with
the buccal groove of the mandibular first molar
or anywhere between the buccal groove and the
mesiobuccal cusp (cusp-to-cusp or end on), no
points are scored. If the occlusal relationship
is end on (cusp-to-cusp) Class II or Class III,
then 2 points are scored per side in this
relationship. If the relationship is a full
Class II or Class III, then 4 points are scored
per side. If the relationship is greater or
beyond Class II or Class III, then 1 additional
point per millimeter is scored. Each side should
be scored individually and included in the point
accumulation for this category. With this
example, the right molar relationship is a full
step Class II so it is scored as 4 points. The
left side shows a full step Class II first molar
relationship so the left occlusal is scored as 4
points for a total of 8 points for both right and
left sides. Slide 10. For each maxillary
posterior tooth which is in lingual crossbite,
spanning the first premolar to the third molar, 1
point is scored. Here we see the left posterior
occlusal relationships which show the maxillary
left second premolars and the maxillary left
second molars in a crossbite relationship.
Therefore, score 1 point for each lingual
posterior crossbite for the left side, totaling 2
points. Slide 11. For each maxillary posterior
tooth, spanning the first premolar to the third
molar which is in complete buccal crossbite, 2
points are scored.
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Slide 12. If the ANB angle is (6 or greater)
OR (-2 or less), then 4 points are scored. An
additional point is scored for each degree above
6 or below -2. If the Sella-Nasion to
Mandibular Plane (SN-MP) angle is between 27
and 37 , zero points are scored. If the SN-MP
angle is 38 or greater, then 2 points are
scored for degree above 37. If the SN-MP angle
is 26 or less, then 1 point is scored for each
degree below 27. If the lower incisor to MP
angle is 99 or greater, then 1 point is scored
for each degree above 98. In this example
cephalometric tracing, ANB equals 7. One extra
point is scored because the ANB is 1 greater
than 6. The total ANB score is, therefore, 5
points. The SN-MP is 37 and therefore is
scored 0 points. The Lower 1 TO MP is measured
as 105 degrees and is scored as 7 points. Slide
13. Because it is not possible to include every
clinical entity in an index, an additional
category, Other is included to permit scoring
of other commonly occurring conditions which may
add to treatment complexity. One point is
scored for each occurrence of supernumerary
teeth. The x-ray in this example shows two
supernumerary teeth yielding a total of 2
points. Slide 14. This example illustrates
ankylosis of the maxillary left second molar.
Where there is ankylosis of permanent teeth, 2
points are scored for each tooth. This example
would be scored 2 points. Slide 15. Anomalous
morphology of tooth size and shape (e.g. peg
lateral incisor) is scored 2 points per tooth
occurrence. This example illustrates a maxillary
right lateral incisor with an anomaly of tooth
size AND tooth shape and would be scored 2 points
for one tooth occurrence. Slide 16. This
example illustrates an impacted tooth, the
maxillary right canine. This example would be
scored 2 points for the impaction. Slide 17.
This example illustrates a maxillomandibular
midline discrepancy of at least 3 millimeters.
This disorder will be scored 2 points for midline
discrepancy. Slide 18. Two points are scored for
each occurrence of Missing Teeth, except third
molars. The example, a panoramic x-ray,
illustrates 2 congenitally missing premolar teeth
in each quadrant which would yield a total of 16
points for missing teeth.
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Slide 19. Two conditions in spacing can be
scored. Two points are scored for Mx central
diastema of 2 mm. or more. Two points per arch
are scored for instances of generalized spacing
of 4 spaces or more. This example illustrates an
exceptional case which contains both conditions
in Spacing on the maxillary arch and generalized
spacing on the mandibular arch and would yield a
total of 6 points. Slide 20. This example
illustrates transposition of teeth which is
scored 2 points for each event. The maxillary
occlusal view shows the right canine and first
premolar in transposition yielding 2
points. Slide 21. This example illustrates a
significant skeletal discrepancy which requires
dental compensation. This disorder yields a
score of 3 points. Slide 22. The examinee may
identify Additional Treatment Complexities and
score 2 points for each occurrence. The following
are examples of additional treatment
complexities. Slide 23. As an Additional
Treatment Complexity, this example illustrates
ectopic eruption of the maxillary left second
premolar yielding 2 points. Slide 24. This is
the Discrepancy Index measurement form. You are
required to score each of the target disorders
and record the score in the appropriate place on
the form. Each of the Other conditions scored
must be recorded on the DI form in the lower
right hand corner and totaled.  Add the scores
for all ten items and record the Total D.I. Score
in the appropriate box at the top left of form.
The DI form and instruction sheet can be found on
the ABO website at the Clinical Examination -
Download and Print area.