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Continuing education
In search of improved skeletal transverse diagnosisPart 2: A new measurement technique used on 114
consecutive untreated patients
Dr. John L. Hayes continues his review of the important aspects of improving
skeletal transverse diagnosis and introduces a new method for taking
measurements
Abstract
This article proposes a new a lab method, using dental
casts, to determine the “center of the alveolar crest”
(CAC) at the molars, which is then measured bilaterally
to record a skeletal transverse dimension. A total of 114
consecutive untreated patients were then evaluated
for their transverse skeletal dimensions using the
CAC measurement. New criteria for determination of
skeletal transverse deficiency have also been proposed.
Using CAC measurement and the new diagnostic
criteria, 108 of the 114 patients were judged to be
maxillary deficient. The severity of deficiency varied;
some patients were judged to need more maxillary
expansion than others. Thirty-four patients out of the
114 presented with posterior crossbite.
I. Proposed CAC measurement technique–
using dental casts1
This article proposes a new lab method, using dental
casts, to estimate the CAC at the molars, which is then
measured bilaterally. The CAC features less variation
than measurements at the buccal aspects of the arches.
This technique avoids the need for posteroanterior (PA)
films or cone beam computed tomography (CBCT) in
an attempt to diagnose a patient’s transverse skeletal
situation. It is hoped that the ease of measurement and
less variation in landmark determination will lead to
more consistent skeletal transverse diagnosis.
Educational aims and objectives
The aims and objectives of this article are to: (1) illustrate a new measurement method, with easily identifiable landmarks, to approximate the skeletal transverse
of the maxillary and mandibular arches by measuring
from the center of the alveolar crests (CAC); (2) suggest a range of maxillary transverse values that would
be compatible for a given mandibular CAC based on
criteria found from old and prehistoric arches; (3)
more clearly define and diagnose a possible maxillary deficiency; and (4) show the CAC measurements
of 114 consecutive untreated patients to gain some
sense of maxillary deficiency prevalence in one private
practice.
Expected outcomes
Reading the article and correctly answering the questions on page XX,
worth 2 hours of verifiable CE, will demonstrate to you that:
• The skeletal measurement of dental casts using the CAC technique is a
skill that can be learned and mastered.
• The diagnosis of each patient could include a transverse skeletal assessment of maxillary deficiency or sufficiency based on CAC measurements and the newly suggested diagnostic criteria.
• Improved transverse skeletal diagnosis along with other diagnostic techniques can be used to develop an appropriate orthodontic and/or
orthopedic treatment plan.
• If and when agreed-upon skeletal transverse measurements and criteria
for maxillary deficiency can become well accepted, patients will tend to
be more consistently diagnosed and treated, and orthodontists should
find fewer differences of opinion for second opinions.
• Orthodontic research needs agreed-upon skeletal measurements and
criteria for improvement in the validity necessary for evidence-based care
(EBC).
Materials and methods
The centerline of the maxillary and mandibular bony
ridges can be approximated on dental casts using two
different methods:
Method 1
A caliper is used to capture the buccal and lingual aspects
of the ridges slightly apical to the cemento-enamel
junction (CEJ), which is the alveolar crest area (Figure
8). A caliper set at 14.5 mm is a good start (however,
the caliper may need to be adjusted between 11 mm
and 14.5 mm depending on the buccal-lingual width of
the molars). The caliper is then placed over the mesiallingual cusps of the maxillary molars, and a bisecting
mark is then made on the teeth representing the midpoint of the ridge (Figure 9). Bilateral measurements are
recorded. For the mandibular arch, the central fossa of
each mandibular molar is used, and a bisecting mark is
made (Figure 10). Bilateral measurements are recorded.
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Figure 8: Method 1: Measurement of maxillary arch with
caliper. Posterior teeth have been removed to level of CEJ for
demonstration purposes only. CAC shown with the dashed
lines
Method 2
A caliper is not used. Sighting along the maxillary bony
ridge, one draws a curved line to conform to the center
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Figure 9: Method 1: Caliper measurement at mesial-lingual
cusp of first molar. Location is bisected for CAC
Figure 10: Method 1: Caliper measurement at central fossa
of first molar. Location is bisected for CAC
Figure 11: Method 2: Maxillary arch. Sight along ridge while
ignoring teeth
Figure 12: Method 2: Mandibular arch. Sight along ridge
while ignoring teeth
of the curved alveolar ridge (Figure 11). During this
exercise, the locations of the teeth are ignored because
teeth are usually inclined and not well-centered on
the ridge. As with method 1, a second line is drawn
perpendicular to the center of the ridge line at the
mesial lingual cusp tips of teeth Nos. 3 and 14. Bilateral
measurements are recorded. For the mandibular arch,
as with method 1, a second line is drawn perpendicular
to the center of the ridge line at the central fossas of teeth
Nos. 19 and 30 (Figure 12). Bilateral measurements are
recorded.
For either method, the CAC measurement points
and the resulting transverse dimensions should be
identical.
Regarding the accuracy and repeatability of CAC
measurements: we will see later that there is, by
experience, a generous biologically stable range of
acceptable maxillary values for a given mandibular
CAC transverse dimension. Accordingly, exactness of
measurement by the CAC technique does not appear
to be requisite. However, given some experience, it is
reasonable to expect accuracy and repeatability to be
within 0.5 mm. Just as we do not need to use a highpowered microscope to see the writing on this page,
measuring the CAC of arches to the 0.25 mm would
likely be overkill. For several years, the author has found
that orthodontic residents, after a short course in CAC
measurement, easily find confidence in measurement
accuracy and repeatability. The CAC technique has
also been taught to orthodontic assistants with similar
results.
Discussion
Molars that are rotated or have drifted due to premature
loss of primary teeth or for any other reason will require
an approximation to record the location where the
molars should have been located. Additionally, with
older patients, one may have some difficulty locating
the center of an edentulous ridge due to resorption at
the buccal aspect. Approximation will also be necessary
if the first molars have not yet erupted on a very young
patient.
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Conclusions
1. “Center of alveolar crest” is a measurement that
can be used bilaterally for diagnosis of the skeletal
transverse dimension by way of either CBCT or the
proposed dental cast technique.
2. CAC is determined at or slightly apical to the CEJ
at the 6-year molars. This measurement technique is
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in the spirit of Lundstrom’s apical base hypothesis (see
Part 1 of 2).2
3. The maxillary skeletal transverse width is determined
from bilateral CAC points; the mandibular skeletal
transverse width is determined in a similar manner.
References
1. Hayes JL (March, 2003) A clinical approach to identify
transverse discrepancies. Presentation to the Pennsylvania
Association of Orthodontists, Philadelphia.
2. Lundstrom AF (1923). Malocclusion of the Teeth Regarded
as a Problem in the Connection with the Apical Base. Svensk
Tandlakare Tidskrift.
II. 114 consecutive patients measured with
the CAC measurement technique1
CAC measurements have not been used previously to
describe a population of patients. Accordingly, 114
consecutive, untreated patients were chosen to evaluate
their maxillomandibular skeletal situations.
Additionally, criteria for the diagnosis of skeletal
transverse deficiency, based on CAC, have not been
previously established. Criteria were derived from the
author’s previous studies.1-3 A narrow range of biologic
maxillary values (optimal to acceptable) is proposed to
correspond to each mandibular CAC value. Outside
of this range, the patient would be judged to have a
deficient maxilla.
Materials and methods
A total of 114 consecutive untreated patients were
evaluated using the model measurement technique
described previously. CAC measurements were taken
of both mandibular and maxillary arches. The patients
were stratified by sex, resulting in 58 male and 56
female subjects.1,2
All arch measurements were performed by the
same individual. Two measurements were taken for
each point. If the two measurements were not identical,
a third or fourth measurement was taken until the
measurement was confirmed. In many instances, the
re-measurements were due to indecision regarding
which way to round–up or down. Measurements in the
114 patient study were rounded to the nearest 1 mm.
Measurement fractions equal to or greater than 0.5 mm
were rounded up to the next whole number. Since this
study was performed, subsequent patients have been
recorded to the nearest 0.5 mm.
All measurements were performed on dental stone
casts made from alginate molds. A Miltex® caliper,
model 68-694, was used both for method 1 and
method 2, as described previously.
Figure 13: Ages of 114 consecutive patients
Figure 14: Mandibular CAC measurement of 114 consecutive patients
Results1
Age demographics graph (Figure 13)
Ages ranged from 5 to 17 years. The predominant age
group was in the 7-9-year segments.
Mandibular arch graph (Figure 14), Table 1
Average transverse width (male and female combined),
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Figure 15: Maxillary CAC measurement of 114 consecutive patients
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Continuing education
measured by CAC was 44 mm. The graph suggests a
bell-shaped curve, which would likely become more
bell-like with a larger population.
Maxillary arch graph (Figure 15), Table 2
As with the corresponding mandibular arch graph, a
bell-shaped curve is suggested. Average transverse
width (male and female combined), measured by CAC
was 40 mm.
Figure 16
Maxillary/mandibular combined graphs
(Figure 16)
It is interesting to graphically visualize the population
of all the maxillary dimensions superimposed on all
the values of the mandibular dimensions. One may
note that the CAC width of the maxilla lags behind
mandibular width for the population studied.
Mandible versus maxilla xy scatter charts
(Figures 17 and 18), Table 3
Individual male and female data are shown on scatter
charts to help illustrate the different arch widths as
well as the interarch measurements for this untreated
population. For males, the mandibular arch varied
from 41 mm to 50 mm. The maxillary arch varied from
33 mm to 46 mm in transverse width. The average
values were 45 mm and 40 mm mandible to maxilla,
respectively.
For females, the mandibular arch varied from 40
mm to 47 mm. The maxillary arch varied from 33 mm
to 47 mm in transverse width. The average was 43 mm
and 39 mm mandible to maxilla, respectively.
Figure 17
Figure 18
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Old skulls evaluated with CAC2
Old and prehistoric skulls usually reside in museums
around the world. The reader may recall from Part 1
of 2 that the skulls held arches that were considered to
be in harmony, and they revealed remarkable life-long
stability.4 In a previous study, the author measured old
and prehistoric skulls with the CAC method.1
Measuring old and prehistoric arches with the
CAC technique was revealing. It was quite evident
from the beginning that a hypothesis for harmony
was self evident considering their morphology: it was
found that the CAC of the old maxillas were, nearly
uniformly, 5 mm wider than the CAC of the mandibles.
In addition, the maxillas were most frequently “U”
shaped–no “V” shapes could be found. The old arches
were also without malocclusion–without crowding
long term–and they were in a word, beautiful. The
harmony that Lundstrom noted and proposed as
emanating somehow from the “apical base”4 could now
be measured and diagnosed with a CAC criterion in
mind. That same criterion could be and has been used
as the skeletal transverse goal for present-day patients.
That “5 mm wider than the CAC of the mandible”
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criterion is now referred to as “optimal harmony” for
the maxilla, and it is represented by the solid black
line in the scatter charts (Figures 17 and 18). No old
or prehistoric skulls were found to be above the solid
black line and no old or prehistoric skulls were found
to be more than 0.5 mm below the solid black line.
Application of that criterion to patients of today would
mean that, with a given mandibular CAC of 43 mm,
the “optimal harmony” would be a CAC of 48 mm for
the maxilla.
One may recall from the untreated sample of
114 patients that the average male maxilla was 5 mm
less than the width of the mandible. For females, the
maxilla was 4 mm less than the width of the mandible.
The disparity in skeletal morphology from the distant
past to present day is dramatic. Our so-called modern
arches are not what they used to be. And as far as arch
morphology goes, with old skulls as an ideal, we could
be considered deformed in a maxillary way.
It is interesting to note that the arches of the old
and prehistoric skulls feature posterior teeth that are
upright or only very slightly inclined, considering
the long axis of the teeth. It may be that the lack of
inclination (unlike the typical patients of today) has
something to due with the long-term stability and lack
of malocclusion.
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Discussion
Lines on the graphs (Figures 17 and 18) delineate
the proposed range of skeletal harmony. The upper
criterion limit (solid black line of “optimal harmony”)
was established, as previously mentioned, by CAC
measurement of old and prehistoric skulls.7 The
dashed black line represents the lower criterion limit–a
maxilla equal in width to the mandible. That line
was determined by measurement of several thousand
treated patients and is considered a working “acceptable
harmony.”3
The vertical distance between the solid black
line and the dashed line is 5 mm and, thus, there is
a “biologic” range of maxillary transverse CAC widths
for a given mandibular CAC measurement. Below
the dashed line, class II malocclusions become more
common. And 4 or 5 mm below the dashed line,
crossbites become more common.
Two males and two females had values precisely
on the dashed black line (Figures 17 and 18).
Although they were on the line, the four patients were
nevertheless treated with rapid palate expansion (RPE)
to move them closer to the solid black line because
of their history of asthma. Improvement in the nasal
airway has proven helpful for those patients. In another
departure from a proposed criterion, one may find that
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some class II patients will be aided in their growth
toward class I by improving the maxillary width to at
least within 4 mm of the solid black line representing
“optimal harmony.”
It is interesting to note that the widest maxilla
is not from a patient with the widest mandible, and
the narrowest maxilla is not from a patient with the
narrowest mandible. As one moves to the right along the
x-axis, towards mandibular values of 47 mm or more,
the likelihood of a class III growth pattern increases.
Accordingly, for young patients, a wider-than-average
mandible may be a predictor of future class III growth.
As revealed, there was variability among patients
in transverse CAC dimension. Using the new
diagnostic criteria for the skeletal transverse, 108 of
the 114 patients were judged to be maxillary deficient.
Maxillary skeletal transverse deficiency may be more
prevalent than previously thought, based on CAC
measurement and the new criteria.
The severity of deficiency varied; some patients
were judged to need more maxillary expansion than
others. For example, considering males, with “optimal
harmony” as the criterion, the CAC expansion
recommendation varied from 5 mm to 17 mm in the
sample of 58 subjects. For females, with the same
criterion, the CAC expansion recommendation varied
from 5 mm to 14 mm in the sample of 56 patients.
It was found that CAC measurements, post-RPE
did not change over time from measurements taken
immediately after RPE removal. Thus, the skeletal
changes remained stable.
On the other hand, the dental measurements did
change, as suspected, once the RPE was removed and
when the arches were not held in retention. Dental
relapse post-RPE could easily be determined when
the skeletal transverse dimension was measured by
CAC. The dental relapse phenomenon is not new
information.1,5,6 In some cases, the relapse was 30% of
that measured by turnbuckle (a modified Haas design);
in other cases, it was more than 50%. A study by the
author was accomplished by measurement of models
from unretained patients that were taken at least 6
weeks post-RPE removal compared to measurement of
the patient’s RPE turnbuckle expansion.1
Conclusions
1. There was variability in transverse dimensions for
patients that approaches a bell-shaped curve; there were
numerous interarch skeletal transverse combinations of
maxilla to mandible. Not all combinations appeared to
support class I occlusions, in the long term, especially
those far below the dashed line (Figures 17 and 18).
2. The author’s previous study of old and prehistoric
skulls suggested a criterion for the upper limit of
maxillary transverse skeletal width: a maxilla up to
5-mm wider than the mandible as determined by CAC
measurement for “optimal harmony.”
3. Another study by the author suggested a working
criterion for the lower limit of maxillary transverse
skeletal width: a maxilla should at least be equal
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in width to the mandible as determined by CAC
measurement for “acceptable harmony.”
4. Some of the 114 subjects needed CAC expansion
in excess of 10 mm; others needed CAC expansion
as little as 5 mm to reach “optimal” harmony. Most
patients were between these recommended expansion
goals.
5. Considering the 114 consecutive pretreatment
patients in the study, no arches of those patients
approached the interarch “ideal harmony” found from
a previous study of old and prehistoric skulls.
6. Using the CAC measurement technique and the new
diagnostic criteria for the skeletal transverse, 108 of
the 114 patients were judged to be maxillary deficient.
Thirty-four patients out of the 114 presented with
posterior crossbite.
7. Maxillary skeletal transverse deficiency may be more
prevalent than previously thought.
John L. Hayes, DMD, MBA, received
his dental degree from the Boston
University H.M. Goldman School of
Graduate Dentistry and his orthodontic
certificate from the University of
Pennsylvania School of Dental
Medicine Orthodontic Department
where he is a Clinical Associate. Dr.
Hayes is on the Editorial Review Board
of the American Journal of Orthodontics and Dentofacial
Orthopedics, as well as Orthodontic Practice US. He
continues to research and lecture on the advantages
of early interceptive treatment and on the etiology of
malocclusions. He is board certified by the ABO. He has
been the secretary of his local dental society since 1986.
Dr. Hayes is in private practice in Williamsport, PA, with
his wife, Sharon, who is also an orthodontist. He can be
reached at [email protected]
References
1. Hayes JL (March, 2003) A clinical approach to identify
transverse discrepancies. Presentation to the Pennsylvania
Association of Orthodontists, Philadelphia.
2. Hayes JL (November, 2007) Kennewick Man helps to Prove
a Premise. Unpublished Manuscript, Physical Anthropology,
National Museum of Natural History, Smithsonian Institution.
3. Hayes JL (October 9, 2009) On the Origin of Malocclusions
by Means of Skeletal Transverse Disharmony: “The Williamsport
Orthodontic Study” Presentation to the University of
Pennsylvania Department of Orthodontics, Annual Alumnae
Meeting, Philadelphia.
4. Lundstrom AF (1923) Malocclusion of the Teeth Regarded
as a Problem in the Connection with the Apical Base. Svensk
Tandlakare Tidskrift.
5. Haas AJ (1980) Long-term posttreatment evaluation of rapid
palatal expansion. Angle Ortho 50:189-217.
6. Vanarsdall RL Jr (1999) Transverse dimension and long-term
stability. Seminars in Orthodontics 5:171-180.
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