Influence of Occlusal Plane on ANB & Wits Assessments

WITS APPRAISAL

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

Influence of occlusal plane
inclination on ANB & Wits
assessments of anteroposterior jaw
relationships


Introduction
 Angular

measurements are geometrically
sensitive & can give false results.
 ANB angle is used to determine the
anteroposterior maxillomandibular
relationships.
 It varies with the extension & inclination of
cranial base.
 Routinely, ANB angle & Wits appraisal are
the most common cephalometric tool for
assessing AP jaw discrepancies.

 ANB

& Wits are related to vertical
features.
 There is influence of the occlusal plane
angle & facial height on the ANB
assessment.


Aim
 The

primary purpose of this study were to
verify whether ANB & Wits assessments
show consistent results in patients with
high & low occlusal plane angles & to
determine whether specific cranial base
features have an important geometric
influence in the assessment.


Materials & Methods
 The

sample consisted of 122 patients, 44
males & 78 females.
 Their mean age at the initial records was
13.5 (+/- 5.3 yrs).
 The sample included the following types of
malocclusions
 29 Class I
 82 Class II div 1
 7 Class II div 2
 4 Class III

Criteria for selection of cases
 The

samples were selected based on
consecutive chronological orthodontic
patients started from 1995 to 2003, who
were treated & had standardized initial &
final records taken ( cephalo –lateral
radiographs).
 Patients with cranio-facial deformities
were rejected.










All patients received treatment from the
same orthodontist.
Patients were treated by straight wire
fixed appliance, 0.018” slot brackets &
molar bands.
Headgears and lip bumpers were used
when appropriate.
Pretreatment (T1) & pretreatment (T2)
lateral cephalograms were taken from
the same cepahalostat.

 Orthodontic

treatment was performed
a) Without extraction in 99 patients.
b) With maxillary & mandibular extraction in
11 patients.
c) With maxillary premolar extractions in 10
patients.
d) With mandibular premolar extractions in 2
patients.


 Cephalometric

landmarks were identified
and traced on acetate paper by the
orthodontist.
 All landmarks were digitized & all
measurements were computed by usind
DFPlus software.


Landmarks
 Basion,

Sella, Nasion, ANS, Point-A,
Point-B, Gonion, Gnathion, Menton
 The occlusal plane was formed by the
half-distance point between the incisal
edges of the maxillary incisors & the
mesial cuspid tips of the mandibular
bilateral first molars.


Cephalometric landmarks


Measurements

a.
b.
c.
d.
e.
f.
g.
h.
i.
j.

The following measurements were computed
S-N
NSB
ANB
Wits
S-Go
N-me
SNOP
Y-axis
AP proportion
Anterior proportion

 To

calculate for systemic & random errors,
a sub-sample of 5 randomly selected
radiographs was retraced & redigitzed.
 Systematic errors was not statistically not
significant.
 Random method errors, ranged from
0.5mm for S-Go to 1.0mm for Wits & from
0.3° for Y-axis to 1.2° for NSBa.

Cephalometric measurements

Wits appraisal


Statistical method
 All

data were computed with SPSS
software.
 Paired t-test were performed to evaluate
treatment changes.
 Pearson product moment correction
coefficients were calculated between T1 &
T2 variables.
 Based on the descriptive statistics of the
total sample, 2 occlusal plane angle
groups were constituted.

 The

median of 15.3° for SNOP angle
divided the patients into high & low occlusal
plane.
 The median of 73mm for the S-N distance
divided the patients into short and long
anterior cranial base sub groups.
 The median of 123.4° for NSBa angle
divided the patients into small & large
cranial base angle subgroups.

High occlusal plane angle
www.indiandentalacademy.com Normal occlusal plane

Short
www.indiandentalacademy.com anterior cranial base
Normal anterior cranial base

Results
Variable

n

Mean T1

SD

Mean T2

SD

Mean diff

SD

P

S-N

122

72.4

3.8

74.0

3.8

1.6

2.2

.01

SNBa

122

123.5

5.1

123.3

5.3

-0.2

2.3

.26

ANB

122

3.8

2.5

2.8

2.3

-1.1

1.8

.01

Wits

122

2.1

4.1

1.3

2.9

-0.8

2.7

.01

S-Go

122

73.9

6.8

79.2

5.9

5.3

5.0

.01

N-Me

122

118.5

8.4

124.2

7.8

5.8

6.2

.01

SNOP

122

14.9

4.2

14.1

4.0

-0.8

3.2

.01

Y-axis

122

85.0

3.8

85.4

3.8

0.4

1.7

.01

AP
proportion

122

0.62

0.04

0.63

0.04

0.01

0.02

.01

Ant
proportion

122

0.43

0.02

0.43

0.02

0.01

0.02

.30

Descriptive statistics for all patients at T1 & T2 are shown. Paired t test
showed Significant differences for variables, except SNBa & anterior
proportion

 There

was a
significant Pearson
product moment
correlation between
ANB & Wits for T1
& T2 data.
 The lowest were
found between
ANB & Wits when
comparing T1 & T2.

Variable

ANB T1

Wits T1

ANB T2

Wits
T2

ANB T1

-

-

-

-

Wits T1

0.76

-

-

-

ANB T2

0.72

-

-

-

Wits T2

0.65

0.74

0.71

-


Sub group

Variable

n

Difference

P

Short anterior cranial
base

ANB T1 & ANB T2

38

1.1

.01

Wits T1 & Wits T2

38

0.1

.95

ANB T1 & ANB T2

21

1.4

.01

Wits T1 & Wits T2

21

0.3

.64

ANB T1 & ANB T2

36

1.3

.01

Wits T1 & Wits T2

36

-0.2

.72

ANB T1 & ANB T2

23

1.1

.01

Wits T1 & Wits T2

23

0.6

.41

Long anterior cranial
base

Small cranial base
angle

Large cranial base
angle

Paired t test between ANB & Wits (T1 & T2) for high
occlusal plane angle group

Sub group

Variable

n

Difference

P

Short anterior cranial
base

ANB T1 & ANB T2

29

0.9

.05

Wits T1 & Wits T2

29

1.1

.07

ANB T1 & ANB T2

34

0.9

.01

Wits T1 & Wits T2

34

1.6

.01

ANB T1 & ANB T2

28

0.5

.23

Wits T1 & Wits T2

28

0.6

.31

ANB T1 & ANB T2

35

1.3

.01

Wits T1 & Wits T2

35

2.0

.01

Long anterior cranial
base

Small cranial base angle

Large cranial base angle

Paired t test between ANB & Wits (T1 & T2) for low
occlusal plane angle group

 Paired

t tests were applied between T1 & T2 data for
ANB & Wits assessment in the high occlusal plane
angle & low occlusal plane angle.
 In the high occlusal plane angle group, the
statistically significant differences between T1 & T2
by ANB assessment were not seen in the Wits
assessment foe all groups .
 In the low occlusal plane angle group, the statistically
significant difference between T1 & T2 shown by
ANB assessment were confirmed by the Wits
assessment for the long anterior cranial base & large
cranial base angle group.

A

statistically significant difference was
practically confirmed by ANB & Wits
assessment for short anterior cranial base
but not confirmed by both assessments for
the cranial base angle group .


Discussion
 The

most common doubts of the clinical
orthodontist revolve around 2 major questions
 Does the patient have a skeletal malocclusion?
 If so, to what degree?
 Although ANB & wits are cephalometric tools
widely applied to evaluate AP relationship, there
is a significant lack of certainty.
 Consequently, there is an intensive search for
new & better cephalometric & noncephalometric
diagnostic resource to assess jaw discrepancies.

 This

research is needed because vital
orthodontic decisions depend on correct
assessments.
 Literature provide new formulas to assess
skeletal discrepancies, but further research is
required on traditional measurements, such as
ANB & Wits is still necessary.
 The normal range of ANB angle is 2°+/- 3°.
 The wits distance should be 0mm in females
& -1mm in males with skeletal class I
relationship.

 Geometric

effects causes the occlusal plane
angle to modulate the ANB & Wits
assessments.
 This study attempted to identify agreement
or disagreement between ANB & Wits
assessments in high & low occlusal plane
angle groups, controlling for anterior cranial
base size & cranial base angulation
subgroups.
 The general view of treatment effects shows
growth effects on the anterior cranial base
but no significant change in the cranial base
angle.

 ANB

& Wits significantly decreased with
treatment because 3/4th of the patients had
class II malocclusion at T1, orthodontic
mechanics were intended to decrease the
initial ANB angle.
 Vertical growth occurs in posterior & anterior
facial heights, however, the AP proportion is
increased.
 ANB & Wits assesses the same problem but
have fair correlations.
 These results show at least 1 assessment
has a weakness per se.

 There

was clearly a lack of consistency
between them in the high occlusal plane
angle group.
 It is suggested that, in high occlusal plane
angle group, ANB might have overestimated
AP positioning of the jaws or Wits have
underestimated AP positioning of the jaws.
 In contrast, in the low occlusal group the
statistically significant difference between T1
& T2 of the ANB assessment were confirmed
by wits assessment for the long anterior
cranial base subgroup & large cranial base
angle subgroup.

Conclusion
 ANB

& Wits have important drawbacks
although they are routinely used in clinical
orthodontics.
 Our results show a tendency for lack of
consistency between ANB & Wits
assessment in high occlusal plane angle
patients & a lack of certainty in at least one
measurement.
 In the low occlusal plane angle patients, both
assessments were consistent.

Reference
 Longitudinal

changes in the ANB & Wits appraisal :
clinical implications –(AJODO 93 Aug) Samir E.
Bishara, Julie A. Fahl, Larry C. Peterson.
 This study suggests that the ANB angle changes
significantly with age , while Wits appraisal indicates
that the relationship between points A B does not
change significantly with age.
 Correlation coefficients shoed that the ANB angle &
Wits appraisal are significantly correlated.


 Relation

of Wits appraisal to ANB angle Järvinen AJODO 1988 Nov (432 - 435):
 In this study the hypothesis was that the
relationship between the ANB angle and the
Wits appraisal could be declared by
measuring individual variations in their
reference systems and by constructing a
model of regression between them and the
parameters describing the reference systems.


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Influence of Occlusal Plane on ANB & Wits Assessments

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