Download prediction of transverse Mx dimension using Orth models

Prediction of Transverse Maxillary Dimension
Using Orthodontic Models
Melchiades Alves de Oliveira, Jr, DDS, PhD, Max Domingues Pereira, MD, PhD,
Claudia Toyama Hino, DDS, PhD, Anelisa Bittencourt Campaner, MD, PhD,
Marco Antonio Scanavini, DDS, PhD, Lydia Masako Ferreira, MD, PhD
São Paulo, Brazil
The main objective of this study was to quantify the
transverse maxillary dimensions using orthodontic
cast models of individuals with natural normal
occlusion. Sixty-eight pairs of orthodontic models
were evaluated with the respective posteroanterior
radiographies of white adults (38 women and 30
men; mean age, 17 years and 5 months). The models
were placed in Class I molar occlusion, and on each
pair, 4 points were marked on the alveolar buccal
ridge (2 on the premolar region and 2 on the molar),
determining the upper and lower transverse interpremolar and intermolar dimensions. The variables
analyzed in the 3 measurements, obtained from the
cephalometric radiographies and the cast models,
showed no statistical differences. The upper intermolar distance was 57.20 T 2.60 mm; the lower
intermolar, 55.16 T 2.40 mm; the upper interpremolar, 42.17 T 2.19 mm, and the lower interpremolar;
39.67 T 1.77 mm. On the posteroanterior cephalograms, the maxillary width was 65.97 T 3.42 mm and
the mandibular width was 87.92 T 4.60 mm. There
was intraresearcher and interresearcher correlation.
There was no sexual dimorphism. The method
proposed in this study can predict the transverse
maxillary dimension, applying the formula µm =
8.62 + 0.88xm (µm = expected upper intermolar
distance, xm = lower intermolar distance) for the
molar region, and µpm = 4.87 + 0.94xpm (µpm =
expected upper interpremolar distance, xpm = lower
interpremolar distance) for the premolar region.
Key Words: Palatal expansion technique, Natural
normal occlusion, Cephalometric
From the Plastic Surgery Division of Federal University of São
Paulo, Brazil.
Address correspondence and reprint requests to Dr. Max
Domingues Pereira, Rua Napoleão de Barros, 715-4- andar, CEP:
04024-002, São Paulo, SP, Brazil; E-mail: [email protected]
T
ransverse maxillary deficiency has been
studied in terms of its etiology, forms of
treatment, and devices used for its correction. However, the majority of these studies,
which are available in the scientific literature, do not
clearly demonstrate the method used to evaluate the
transverse maxillary prediction.
The methods of evaluating the transverse maxillary dimension can be classified into dental, radiographic, and clinical methods.
In the dental method, the transverse dimension
is obtained measuring the distance of the first molar
and first premolar regions and is determined by
mathematical equations. These equations have preestablished constants of the upper interpremolar and
intermolar distances, with variable being the sum of
the diameters of the upper incisors.1,2 On the other
hand, this method may lead to error because of
alterations in the form and size of some of the upper
anterior dental elements.
In the radiographic method, a specific radiographyVposteroanterior radiograph (PA)Vis used.
The dimension of the maxillary and mandibular
width is obtained based on values proposed by
Ricketts et al,3 whereas Betts et al4 established a
transverse maxillary index. Despite this method being
the most commonly used to predict the transverse
maxillary dimension, the lack of precision in the location of the points of the maxilla and the mandible
may lead to miscalculations of the maxillomandibular width.
The clinical method is based on visible observation of the palatal cusp tip of the upper molar, which
should be in contact with the buccal cusp tip of the
lower molar.5Y7 The clinical method should not be used
to determine the prediction of maxillary expansion
when surgically assisted rapid maxillary expansion
(SARME) is required, due to the dental compensation
that occurs in these cases.
The aim of this study was to determine the
prediction of the transverse maxillary dimension
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THE JOURNAL OF CRANIOFACIAL SURGERY / VOLUME 19, NUMBER 6
November 2008
38 (55.88%) females aged from 16 to 21 years (average
of 17.4 years). Their respective posteroanterior cephalometric radiographies were also evaluated. This
study was approved by the Ethics Committee of
the ‘‘Universidade Federal de São Paulo’’ Ethics
Committee.
Posteroanterior Radiographs
Posteroanterior radiographs were obtained using the
same radiographic device and standardized according to the technique described by Ricketts.8
To determine the transverse maxillary and mandibular dimensions, an anatomic outline was drawn
over each PA,9 with the width of the maxilla ( JD-JE)
and the mandibula (AG-GA) outlined according to
Ricketts et al.3 The PAs were used to determine if
the samples had values similar to those proposed
by Ricketts et al.3
Orthodontic Cast Models
Fig 1 Metal ruler positioned on the side of the orthodontic
models, parallel to the mesiobuccal sulcus of the first lower
molar.
using the buccal ridge of the alveolar process in
orthodontic cast models from patients with natural
normal occlusion.
MATERIALS AND METHODS
P
airs of upper and lower orthodontic cast models
were obtained from 68 white individuals with
natural normal occlusion, with 30 (44.12%) males and
The orthodontic cast models were built up using
white plaster stone.
The orthodontic cast models were placed in
Angle Class I occlusion and supported on a firm,
flat base to demarcate the points on the left and right
surfaces. A metal ruler was positioned touching the
lateral bases, perpendicularly to the occlusal surface,
and parallel to the buccal surface, demarcating a
small segment of vertical straight line, crossing the
horizontal lines on the upper and lower alveolar
bones, and giving the points to determine the transverse dimensions in the first molar and first premolar regions (Fig 1).
Fig 2 Orthodontic cast models in occlusion. A, Right side with points A1, B1, C1, and D1. B, Left side with points A2, B2, C2,
and D2.
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TRANSVERSE MAXILLARY DIMENSION / de Oliveira et al
Point D. Intersection of the horizontal line of the
alveolar buccal ridge of the mandibula, with
the segment of the vertical line passing through
the tip of the buccal cusp of the lower premolar (D1Vright side; D2Vleft side)
After determining the points on the upper and
lower orthodontic cast models, the distance between
the region of the upper and lower first molar and first
premolar were measured and denominated as follows (Fig 3):
Fig 3 Orthodontic cast models with the occlusal surfaces
turned up, indicating distances 1, 2, 3, and 4.
The reference used in the molar region was the
mesiobuccal sulcus of the first lower molar, and in
the premolar region, the reference was the center of
the buccal cusp of the lower first premolar.
The intersection with the horizontal line of the
buccal ridge of the alveolar process with the segments of vertical lines determined the points where
they intersect (Fig 2):
Point A. Intersection of the horizontal line of the
alveolar buccal ridge of the maxilla, with the
segment of the vertical line passing through
the mesiobuccal sulcus of the first lower molar
(A1Vright side; A2Vleft side)
Point B. Intersection of the horizontal line of the
alveolar buccal ridge of the mandibula, with
the segment of the vertical line passing through
the mesiobuccal sulcus of the first lower molar
(B1Vright side; B2Vleft side)
Point C. Intersection of the horizontal line of the
alveolar buccal ridge of the maxilla, with the
segment of the vertical line passing through
the tip of the buccal cusp of the lower premolar
(C1Vright side; C2Vleft side)
Upper intermolar distance (Dist1)Vdistance between points A1 to A2
Lower intermolar distance (Dist2)Vdistance between points B1 to B2
Upper interpremolar distance (Dist3)Vdistance
between points C1 to C2
Lower interpremolar distance (Dist4)Vdistance
between points D1 to D2
Three measurements were performed by 2
researchers. The first researcher performed 2 measurements with an interval of 15 days between
the first (M1P1) and the second (M2P1). The second
researcher performed a third measurement (M1P2). A
digital caliper was used to obtain all the measurements, for both the posteroanterior cephalometric
radiographs and orthodontic cast models. After each
measurement had been taken, the lines and points
were erased using a soft white eraser.
STATISTICAL METHOD
T
he variables for the PAs analyzed were the
maxillary and the mandibular width. For the
orthodontic cast models, the variables were as
follows: the upper intermolar distance (Dist1), the
lower intermolar distance (Dist2), the upper interpremolar distance (Dist3), and the lower interpremolar distance (Dist4).
Table 1. Mean, Median, Standard Deviation, Maximum, and Minimum, in Millimeters, for the Transverse Maxillary
and Mandibular Dimensions Measurements, Determined in the Posteroanterior Radiographs
Transverse
Transverse
Transverse
Transverse
Transverse
Transverse
maxillary dimensionVM1 P1
maxillary dimensionVM2 P1
maxillary dimensionVM1 P2
mandibular dimensionVM1 P2
mandibular dimensionVM2 P1
mandibular dimensionVM1 P2
Mean
Median
Standard Deviation
Minimum
Maximum
66.03
65.93
65.96
87.43
88.52
87.81
66.09
65.76
66.13
87.33
88.15
87.41
3.13
3.49
3.62
4.51
4.62
4.84
60.05
59.64
58.77
77.34
78.85
76.56
74.07
73.90
74.32
99.43
98.79
99.92
M1P1 indicates measurement 1 of the first researcher; M2P1, measurement 2 of the first researcher; M1P2, measurement 1 of the second researcher.
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THE JOURNAL OF CRANIOFACIAL SURGERY / VOLUME 19, NUMBER 6
November 2008
Table 2. Mean, Median, Standard Deviation, Maximum, and Minimum of the 3 Measurements, Values in Millimeters
for Upper Intermolar Distance (Dist1), Lower Intermolar Distance (Dist2), Upper Interpremolar Distance (Dist3), and
Lower Interpremolar Distance (Dist4), Calculated Using the Orthodontic Cast Models
Upper
Upper
Upper
Lower
Lower
Lower
Upper
Upper
Upper
Lower
Lower
Lower
intermolar distance (Dist1)VM1P1
intermolar distance (Dist1)VM2P1
intermolar distance (Dist1)VM1P2
intermolar distance (Dist1)VM1P1
intermolar distance (Dist1)VM2P1
intermolar distance (Dist1)VM1P2
interpremolar distance (Dist3)VM1P1
interpremolar distance (Dist3)VM2P1
interpremolar distance (Dist3)VM1P2
interpremolar distance (Dist4)VM1P1
interpremolar distance (Dist4)VM2P1
interpremolar distance (Dist4)VM1P2
Average
Median
Standard Deviation
Minimum
Maximum
57.28
57.20
57.13
55.23
55.19
55.05
42.31
42.12
42.07
39.81
39.63
39.57
57.32
57.26
56.99
54.88
54.79
54.65
42.15
42.17
42.16
39.62
39.26
39.14
2.61
2.56
2.63
2.41
2.41
2.38
2.15
2.23
2.19
1.78
1.79
1.73
52.57
52.19
52.21
50.71
50.74
50.64
37.81
37.96
37.75
36.07
35.97
36.22
64.03
63.66
63.73
61.30
61.56
61.24
48.31
47.89
47.90
43.65
43.50
43.39
M1P1 indicates measurement 1 of the first researcher; M2P1, measurement 2 of the first researcher; M1P2, measurement 1 of the second researcher.
The mean, median, and standard deviation were
calculated, and the Kolmogorov-Smirnov test was carried out for these variables, to determine any similarity in the distribution of the sample. Once confirmed,
we used the average values for the 3 measurements.
The intraresearcher and interresearcher reproducibility of the median values was calculated using
the interclass coefficient correlation method.
The Mann-Whitney test was used to verify any
sexual dimorphism differences in the variables for the
orthodontic cast models.
Analysis of variance was used to determine the
transverse maxillary dimensions in the orthodontic
cast models, to confirm the existence of the straight
line linear regression equation, to validate the simple
linear regression equation by the least squared
method.
The level of significance for rejection of the
null hypothesis was fixed at a value of equal to or
less than 0.05 (5%).
RESULTS
T
here was no observed statistical intraresearcher
or interresearcher difference ( P e 0.05), applied to
the variables from the posteroanterior cephalometric
radiographies and the orthodontic cast models.
In the posteroanterior cephalometric radiographies (PA), the maxillary width (JD-JE) and the mandibular width (AG-GA) were, respectively, 65.97 T
3.42 and 87.92 T 4.60 mm (Table 1).
In the orthodontic cast models, the mean upper
intermolar distance (Dist1) was 57.20 T 2.60 mm, the
mean lower intermolar distance (Dist2) was 55.16 T
Fig 4 Coefficients of the intraresearcher correlation (M1P1 M2P1) and intraresearcher correlation (M1P1 M2P1) and
(M2P1 M1P2) for the orthodontic cast models, and the posteroanterior cephalometric radiographies. M1P1 indicates
measurement 1 of the first researcher; M2P1, measurement 2 of the first researcher; M1P2, measurement 1 of the second
researcher; Dis1, upper intermolar distance; Dist2, lower intermolar distance; Dist3, upper interpremolar distance, Dist4,
lower interpremolar distance; Max. Width, maxillary width; Mand. Width, mandibular width.
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TRANSVERSE MAXILLARY DIMENSION / de Oliveira et al
Fig 5 Expected upper intermolar distance after applying the formula to predict the transverse maxillary dimension based
on the lower intermolar distance (Dist2).
2.40 mm, the mean upper interpremolar distance
(Dist3) was 42.17 T 2.19 mm, and the mean lower interpremolar distance (Dist4) was 39.67 T 1.77 mm
(Table 2).
As much for the orthodontic models as for the PA,
values above 0.8 were observed for all variables (Fig 4).
The variables for the orthodontic cast models
showed no sexual dimorphism.
The equation µm = 8.62 + 0.88xm was determined
in the molar region, where µm = the expected upper
intermolar distance and xm = lower intermolar
distance. The equation was only valid when the
lower intermolar distance (Dist2 = xm) was between
61.37 and 50.76 mm (Fig 5).
The equation µpm = 4.87 + 0.940xpm was
determined for the premolar region, where µpm =
the expected upper interpremolar distance and
xpm = lower interpremolar distance, but it was
valid only when the lower interpremolar distance
(Dist4 = xpm) was between 43.51 and 36.09 mm
(Fig 6).
DISCUSSION
A
ll the existing methods for predicting the
transverse maxillary dimensions have clinical
applicability, but with drawbacks.
In the dental method, cast models are used to
predict the transverse maxillary dimension based
on the teeth, whereas the new method enables the
selection of measuring site based on the bone
structure. The dental method is based on the sum
total of the mesiodistal dimensions of the upper
incisors, using the formula denominated indices,
which vary, according to studies by different authors,
to numerically determine the transverse dimension
and the correct form of the dental arch, without
taking into consideration the bone structure that
Fig 6 Expected upper interpremolar distance after applying the formula to predict the transverse maxillary dimension
based on the lower interpremolar distance (Dist4).
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THE JOURNAL OF CRANIOFACIAL SURGERY / VOLUME 19, NUMBER 6
was analyzed in this study. Thus, any alterations in
the form and size of the upper incisors could influence the results and cause them to be misleading.
These indices should be evaluated and validated for
each geographic region and ethnic group before being
adopted.1,2,10
The radiographic method is carried out using
PA, which is useful for evaluating the width-height
ratio of the surface. However, the interpretation of
these posteroanterior cephalometric radiographs has
never been an easy task.11 The use of posteroanterior cephalometric radiograph is important for the
diagnosis of cross bite and the evaluation of orthopedic modifications inherent to rapid disjunction of
the midpalatal suture according to Marshall, 11
Vanarsdall and White,12 and Sato et al.9 In this
study, the resulting values for the maxillary and
mandibular widths are compatible with those of
Ricketts et al,3 Sato et al,9 and Betts et al.4
The need for this complementary radiography
was a limiting factor for this method because its
analysis does not form part of the daily clinical
routine, unlike orthodontic cast models, which are
routinely used for assessment before treatment. The
study of Vanarsdall and White12 reports that posteroanterior cephalometric radiographs are widely
rejected by orthodontists. For Hixon13 and Yoon
et al,14 one of the reasons for this is the difficulty
in standardizing the cephalometric points that are
marked out, and as a result, there is a wide variation in the measurements. Another reason for the
rejection by orthodontists, according to Baumrind
and Frantz,15 is that the overlapping of images and
projections, caused by adjacent structures, makes it
difficult to identify some anatomic structures and
cephalometric points. Grummons and Van De
Coppello,16 on the other hand, argue that this reluctance is mainly due to the difficulty in identifying the reference points due to the poverty of the
radiographic technique and concerns over exposure
to radiation. Therefore, the width of the maxilla
and the mandibula may present dimensions with a
variation, which could lead to an inadequate diagnosis and, consequently, to a wrong treatment. In
relation to the present study, there was no error
in the markings of the points because of the extensive training of the researchers. However, the
points in the cast models showed intraresearcher
and interresearcher correlation indices that were
higher than those obtained in the posteroanterior
cephalometric radiographs.
Using the posteroanterior cephalometric radiograph, Betts et al4 created a transverse maxillary index, in which a maxillomandibular difference higher
November 2008
than 5.0 mm was established as a skeletal alteration,
with SARME being recommended for the patients
with complete bone maturity.
Compared with the new method, radiography
has another limitation: the fact that it is not possible to determine whether the transverse maxillary
deficiency molar and/or premolar region, because
the region of the measurement is posterior, leaving
the anterior region with no reference for the transverse dimension.
The clinical method is the most widely used
evaluation procedure for the correction of transverse
maxillomandibular deficiency in young patients.
The transverse correction will be complete when observed, through clinical visibilization, that the palatal
cusp of the upper molars was riding up on the buccal cusps of the lower molars.5,7,17Y21
Due to the fact that the method of clinical visibilization is based on the teeth, it becomes inadequate when there is a transverse deficiency of the
lower dental arch because the real upper deficiency
is camouflaged by the simultaneous deficiency of
the lower arch. If the lower posterior teeth have a
lingual axial inclination of more than 30 degrees,
which is considered not normal, according to
Andrews and Andrews,22 the amount of expansion
of the maxilla may be insufficient, compromising
the final result of the occlusion in the transverse
direction.
Therefore, the clinical method should not be
used for adult patients requiring SARME because
they present dentoalveolar compensation of the
lower dental arch in the transverse direction. Hence,
this method is inadequate because it uses the teeth
as a reference, like the dental method. The new
method proposed in this study does not have this
inadequacy once it uses the bone structure as a reference, and because it is transversely corrected, so
will the teeth be corrected.
After correction of the axial inclinations of the
lower molars, insufficiency of the transverse maxillary dimension is observed. For this method to be
used successfully, transversal treatment of the mandibula should be carried out before SARME.
The methodology proposed in this study for
adult patients with transverse maxillary deficiency
establishes the bone structure as the basis for
determining the desired transverse maxillary dimension. This results in a prediction with less risk of error
for palatal expansion, giving a transverse maxillomandibular balance. Furthermore, orthodontic cast
models are used, which can be produced in the
clinical use itself.
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TRANSVERSE MAXILLARY DIMENSION / de Oliveira et al
The measurement references of this method are
the bone bases of the maxilla and mandibula. The
points of reference showed to be easy to locate, which
can be evaluated by the high intraresearcher and interresearcher correlation index between the intermolar and interpremolar maxillary and mandibular
distances. Because the teeth are not used to analyze
the transverse maxillomandibular relation, the initial
morphology of the lower dental arch does not interfere in the amount of maxillary expansion, independent of the axial inclination of the posterior teeth.
It is also feasible for evaluating the maxillary
bone base in 2 regions: a more posterior region,
which is based on the first molar, and another anterior region, in the dental arch, located in the first
premolar. It is therefore possible to evaluate whether
the maxillary atresia occurs in the posterior and/
or anterior region, enabling the treatment to be directed according to the area of the maxilla that
requires expansion.
The possible benefits of this procedure include
the following: elimination of the need for complementary radiography (posteroanterior radiography),
its easy applicability, the possibility of its use independent of the correction method (SARME or surgical expansion), assistance in the diagnosis of the
type of transverse deficiency (skeletal or dentoalveolar), and its ability to determine whether the maxillary atresia is in the molar or premolar region.
The prediction of the transverse maxillary dimension can be obtained using the alveolar buccal ridge
of the orthodontic cast model of the maxilla and
mandibula, which clinical applicability consists on
those steps:
For first molar region, the expected upper intermolar distance (µm) is obtained by the equation:
µm = 8.62 + 0.88xm, with µm being the expected upper
intermolar distance and xm being the actual lower
intermolar distance. The prediction of the transverse
maxillary dimension for the first molar region is calculated by the difference between the expected upper
intermolar distance (µm) and the actual intermolar
distance (Dist1).
For the region of the first premolar, the expected
upper interpremolar distance (µpm) is obtained by
the equation: µpm = 4.87 + 0.94xpm, with µpm being
the expected upper interpremolar distance and xpm
being the actual lower interpremolar distance. The
prediction of the transverse maxillary dimension for
the first premolar region is calculated by the difference
between the expected upper interpremolar distance
(µpm) (Dist3) and the actual interpremolar distance.
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Copyright @ 2008 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.