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Dentomaxillofacial Radiology (2007) 36, 97–101
q 2007 The British Institute of Radiology
http://dmfr.birjournals.org
RESEARCH
Evaluation of optical density of the midpalatal suture 3 months
after surgically assisted rapid maxillary expansion
EK Sannomiya*,1,2, MMC Macedo2, DF Siqueira2, FC Goldenberg2 and S Bommarito2
1
Department of Oral and Maxillofacial Radiology, São Paulo Metodista Dental School, São Paulo, Brazil; 2Orthodontic Post Graduate
Program, São Paulo Metodista Dental School, São Paulo, Brazil
Objectives: This study evaluated new bone formation at the midpalatal suture after surgically
assisted rapid maxillary expansion (SARME) by optical density analysis.
Methods: The study population consisted of 18 patients, 10 males and 8 females. All patients
presented maxillary atresia with posterior crossbite and were submitted to SARME. Maxillary
occlusal radiographs were taken at three stages (before SARME, immediately after SARME and
after 3 months). Three patients did not attend the session at the 3-month period for achievement of
the occlusal radiography and thus were excluded, leading to a final sample of 15 patients. Two
regions were selected and analysed at each stage. Region A measured 8 £ 1 mm2 and was located
1.2 cm from the tangent to the maxillary central incisors at the region of the midpalatal suture.
Region B measured 5 £ 9 mm2 and was located 4.3 cm from the tangent to the maxillary central
incisors at the region of the midpalatal suture. An aluminium scale (step wedge) with eight steps
varying from 1 mm to 8 mm was adapted at the end of the films. Radiographs were taken on a
Spectro 70X machine (Dabi Atlante, Ribeirão Preto, Brazil) set at 70 kVp and 10 mA with an
exposure time of 1.0 s. Radiographs were scanned using a Power Look 1000 scanner (Umax,
Taiwan, China) and a computer Dimension E510 (Dell Computer, Taiwan, China). Optical density
analysis was performed after digitization of radiographs using the software Image Tool (UTHSCSA,
San Antonio, TX).
Results: Statistical analysis of region A revealed statistically significant differences between
Stages I and II (P ¼ 0.0001), Stages II and III (P ¼ 0.0001) and Stages I and III (P ¼ 0.0003). In
region B, statistically significant differences were observed between Stages I and II, I and III and II
and III (P ¼ 0.0018, P ¼ 0.0003 and P ¼ 0.0003, respectively).
Conclusions: Optical density analysis improves post-treatment control of SARME procedures by
surgeons and orthodontists. After 3 months, new bone formation at the midpalatal suture is not
complete.
Dentomaxillofacial Radiology (2007) 36, 97–101. doi: 10.1259/dmfr/39081238
Keywords: radiograph, optical density, new bone formation
Introduction
Maxillary atresia or transverse deficiency is a dentofacial
disturbance characterized by the presence of uni- or
bilateral posterior crossbite, deep or high-arched palate,
tooth crowding, dental tipping and difficult nasal breathing.
The surgically assisted rapid maxillary expansion
(SARME) is a clinical therapeutic procedure used to correct
*
Correspondence to: Eduardo Kazuo Sannomiya, Department of Oral and
Maxillofacial Radiology, São Paolo Metodista Dental School, Av. Lacerda Franco
1180-Aclimação, Brazil, CEP 01536-000;
E-mail: eduardosannomiya@hotmail.com; eduardosannomiya@ig.com.br
Received 27 November 2005; revised 6 February 2006; accepted 2 March 2006
this deficiency. In adult patients, who have already
completed ossification of the midpalatal suture, this
treatment allows subsequent separation of the midpalatal
suture by orthodontic devices fabricated and adapted for
that purpose.1 The midpalatal suture appears on occlusal
radiographs as a narrow radiolucent line image. Immediately after rapid maxillary expansion, the radiolucent line of
the suture becomes wider and separated. Cobo et al2
emphasized that investigations into changes of the maxilla
and midpalatal suture during rapid maxillary expansion are
important for orthodontists to predict the effects of
orthopaedic treatment. Analysis of new bone formation by
Optical density after SARME
EK Sannomiya et al
98
optical density analysis of digitized radiographs using an
aluminium scale is a great source of post-operative
treatment control. Using this measurement, it is possible
to quantify new bone formation in the reference area to
control the ossification process. Several studies3 – 5 have
been published in the literature using optical density
analysis. Scarparo et al3 presented a non-invasive method
for bone density analysis at the mandible on periapical
radiographs. An aluminium scale made with seven steps
varying from 4.0 mm to 10.0 mm thickness was used as
reference in the analysis. A specific software was developed
(Densw) for optical reading of bone densities. The sample
was composed of 34 pairs of radiographs with a view to
compare bone density at both right and left sides of the
mandible, considering the medium portion of the interradicular septum of mandibular first molars. The study
showed no statistically significant difference in bone
density between right and left sides of the mandible.
Simões4 performed a study with the objective of evaluating
bone maturity using optical density measurement at
the region of the midpalatal suture after SARME. In both
studies, the authors agree that evaluation of bone maturity
using optical density is a powerful tool for orthodontists and
surgeons to control the results during and after SARME.
This study investigated the bone density by optical
density analysis immediately after SARME and 3 months
after surgery.
Materials and methods
The present sample comprised 18 patients, 10 male
patients and 8 female patients, aged 20 – 45 years old,
assisted by graduate orthodontic students at São Paulo
Metodista Dental School. All patients presented maxillary
atresia with posterior crossbite and were submitted to
SARME. The study was submitted to and approved by the
Institutional Review Board of São Paulo Metodista
University (protocol no. 67151/05). Patients were notified
about the use of their data for research studies and signed
an authorization for surgical procedures and utilization of
data. The SARME standard procedure followed the same
protocol of osteotomy of Le Fort I surgery, but without
inclusion of the pterygopalatine suture and association
with midsagittal maxillary osteotomy. Maxillary occlusal
radiographs were taken of patients at three treatment stages
using a Spectro 70X machine (Dabi Atlante; Ribeirão
Preto, Brazil), set at 70 kVp and 10 mA with an exposure
time of 1.0 s on 51 £ 71 mm2 occlusal films (Insight Film,
Eastman Kodak, Rochester, NY). For standardized
achievement of occlusal radiographs from the region of
maxillary central incisors, a Rinn intraoral film holder
(Rinn, Elgin, IL) was used. The focus – film distance was
9 cm and was kept constant for achievement of all occlusal
radiographs during the study, with standardized vertical
and horizontal projections. An aluminium scale (step
wedge) with eight steps, varying from 1 mm to 8 mm, was
adapted at the end of the films for optical density analysis.
The first occlusal radiograph was taken before surgery and
placement of the Hyrax expander (Stage I; Figure 1). After
Dentomaxillofacial Radiology
Figure 1 Pre-surgical radiograph
SARME, the Hyrax expander was activated until achievement of the desired opening. After the completion of screw
activation, the second occlusal radiograph was taken
(Stage II; Figure 2). The third radiograph was taken after
3 months (Stage III; Figure 3). Three patients did not attend
Figure 2 Radiograph taken immediately after surgery
Optical density after SARME
EK Sannomiya et al
99
for multiple comparisons was used to evaluate at which
stages there were changes in optical bone density. Tests
were performed at a significance level of 5%. Assessing the
study variables, the Kolmogorov – Smirnov test was used to
present the normal distribution. The paired t-test was used
for analysis of regions “A” and “B”.
Results
Figure 3
Radiograph taken three months after surgery
this follow up visit and thus were excluded from the study.
All radiographs were processed in the automatic processor
Dent X (Del Grand; São Paulo, Brazil).
All radiographs were digitized using the Power Look
1000 scanner (Umax; Taiwan, China) and a computer
Dimension E510 (Dell Computer; Taiwan, China), and
saved in TIFF format at 300 dpi resolution. Each radiograph was analysed by histograms and compared with the
aluminium scale using the Image Tool software
(UTHSCSA; San Antonio, TX).
Optical density analysis was standardized by delineation
of areas and planes on the digitized occlusal radiographic
image. Two regions were selected for optical density
analysis. Region A radiographically measured 8 £ 1 mm2
and was located 1.2 cm from the tangent to the maxillary
central incisors at the region of the midpalatal suture.
Region B radiographically measured 5 £ 9 mm2 and was
located 4.3 cm from the tangent to the maxillary central
incisors at the region of the midpalatal suture. Optical
density analysis was performed at areas A and B and
compared with the aluminium edge with the aid of the
Image Tool software at all Stages I, II and III.
For the calculation of method error, the sample was remeasured at two moments, immediately after achieving
radiographs and 20 days after the first measurement. Casual
errors were calculated as suggested by Dahlberg,6 and
systematic errors were evaluated by utilization of BlandAltman graphs, characterized by tendency of increase or
decrease in a measurement. Optical density was assessed by
analysis of variance for repeated measurements, supposing
a zero matrix of non-structured correlations with a factor
stage for each measured region. The Bonferroni correction
Measurement errors at each stage and region, as calculated by
the Dahlberg formula, are shown in Table 1. Figures 4 and 5
present the distribution of measurement errors with utilization
of Bland-Altman graphs. Casual errors were only observed
after the third decimal place, i.e. they were very small errors.
There was no relationship between measurement errors that
could characterize a systematic error, thereby constituting
only small casual errors, as presented in Table 1, without
clinical relevance. Calculation of intraclass correlation, which
measures the agreement measurement for the systematic error,
did not reveal agreement lower than 98%. Thus, measurements were highly concordant.
Table 2 presents the measurements and standard
deviations of optical density at each region and treatment
stage. The optical density was reduced at Stages II and III
compared with Stage I, with observation of a larger
reduction for region B compared with region A. Analysis
of variance for repeated measurements revealed that both
regions A and B presented a difference in mean optical
density at Stages II and III compared with Stage I
(P ¼ 0.0001 for both).
Tables 3 and 4 present the results of the Bonferroni
correction for multiple comparisons to evaluate at which
stage there were changes in optical bone density at regions A
and B, respectively. Table 3 demonstrates that all stages are
different from each other in region A with regard to optical
density, with the highest mean optical density at Stage I and
the lowest at Stage II. There was an increase in optical density
between Stages II and III. Table 4 demonstrates that the mean
optical density at region B is different in nearly all stages,
when the mean optical density is immediately reduced after
surgery and is closer to the initial value with time.
Discussion
The orthopaedic – orthodontic treatment adopted for maxillary atresia when diagnosed and treated in young patients
cannot be used in adult patients. Many studies 1 – 3
Table 1
Calculation of casual errors by Dahlberg’s formula
Region
Stage
Casual error
(Dahlberg’s formula)
A
I
II
III
I
II
III
0.0053
0.0050
0.0066
0.0061
0.0061
0.0079
B
0.0057
0.0067
Dentomaxillofacial Radiology
Optical density after SARME
EK Sannomiya et al
100
Figure 4
Measurement errors at region A
emphasize that SARME is performed when there is enough
ossification of the midpalatal suture in adult patients.
According to Krebs,7 posteroanterior separation of the
maxilla after expansion is V-shaped, with wider separation at
the anterior area compared with the posterior. It was noted in
this study that in most cases, suture separation was V-shaped
with the largest diastema between the central incisors.
The retention period after maxillary expansion, i.e.
maintenance of the appliance in the mouth, is very
controversial, even though its need is unquestioned, since
the immediately expanded bone tissue presents highly
vascular disorganized connective tissue, which is later
replaced by immature bone tissue. This retention period to
assure stability should be at least 3 months, according to
authors Bell,8 Bishara and Staley9 to allow reorganization
and stability of maxillary sutures submitted to rapid
expansion.
Utilization of occlusal radiographs is adequate for
evaluation of new bone formation at the midpalatal suture
separation.5
Figure 5
Measurement errors at region B
Dentomaxillofacial Radiology
Optical density analysis with digitized occlusal radiographs and the aluminium step wedge were used as an
advantageous and highly accurate method for bone
formation and mineralization of the midpalatal suture
after SARME, as revealed by Cobo et al,2 Hildebolt,10
Scarparo et al3 and Vardimon et al.11
Selection of the size and location of region A between
the central incisors at the region of the midpalatal suture
was based on its importance for surgical stability,
according to Person and Thilander.12 Size and location of
region B more posteriorly were used to allow distance from
the expanding appliance, which would interfere with the
optical density outcome. Studies conducted by Vardimon
et al11 revealed increased optical density at the posterior
region after maxillary expansion.
Reports of optical density in rapid maxillary expansion
describe that the optical density values decrease after the
procedure, but there is a tendency of return to the initial
values before expansion.13,14 In the present study, a
decrease in optical density at the post-surgical stage
Optical density after SARME
EK Sannomiya et al
Table 2 Measurements and standard deviations of optical density at
regions A and B
Region
Stage
Mean
Standard deviation
N
A
I
II
III
I
II
III
1.80
0.66
0.89
2.97
1.17
1.88
0.54
0.14
0.17
0.71
0.44
0.67
15
15
15
15
15
15
B
Table 3 Result of the Bonferroni correction for multiple comparisons
for region A
Stages Mean difference
Standard deviation DF
t
I – II
I – III
II – III
0.15
0.15
0.04
7.76 ,0.0001
5.92 ,0.0001
25.45
0.0003
1.14
0.91
20.23
14
14
14
P
P , 0.05%; DF, degrees of freedom
Table 4 Result of the Bonferroni correction for multiple comparisons
for region B
Stages Mean difference
Standard deviation DF
t
I – II
I – III
II – III
0.18
0.18
0.13
9.73 ,0.0001
6.15 ,0.0001
25.44
0.0003
1.80
1.09
20.71
14
14
14
P
P , 0.05%; DF, degrees of freedom
(Stage II) was observed according to the mean values in
regions A and B, namely 0.66 mm and 1.17 mm aluminium
equivalent (Table 2), but after 3 months (Stage III) these
values in regions A and B increased, with mean values of
0.89 mm and 1.88 mm aluminium equivalent (Table 2), in
accordance with the aforementioned authors. The values at
Stages II and III at regions A and B may be employed as a
standard reference in SARME. The present authors will
continue the evaluation of patients with a 6-month and
101
1-year follow-up after SARME. According to Vardimon,11
the increase in optical density values was higher in the
posterior region than at the midpalatal suture, which
indicates that the pattern of remineralization of the
expanded suture is similar to a zip closing posteroanteriorly.
On the other hand, Simões4 investigated a sample of
subjects aged 6 – 11 years submitted to rapid maxillary
expansion by orthopaedic expanding appliances, who
presented earlier new bone formation at the anterior region
compared with the posterior region. These data disagree
with the present study, since according to Sandikciouglu
and Hazar15 the patient’s age and type of rapid maxillary
expansion may lead to earlier new bone formation at the
anterior region. The present study sample was composed of
adult patients submitted to SARME. The present study
revealed higher increase in optical density at the posterior
region (B) compared with the anterior (A) as demonstrated
in Tables 3 and 4, confirming the posteroanterior closing
pattern (like a “zip”) of the midpalatal suture.
One of the great problems of SARME is the retention
period to avoid relapse, which might impair the orthodontic treatment. Thus, the expander should be kept for
retention until there is new bone formation at the expanded
region. Few studies1,2 have been conducted to verify
whether the new bone would be sufficiently mature to
assure treatment stability. Utilization of optical density
analysis in this type of procedure might allow better
control in the retention period after rapid maxillary
expansion.13,14 The present study could help orthodontists
because there was an optical density pattern between onset
and immediately after SARME and after 3 months.
Moreover, this methodology may be applied in the daily
routine of orthodontists to control new bone formation
after SARME, since a simple methodology is used with aid
of an occlusal radiographic film, an aluminium step wedge
and a program for optical density analysis.
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Dentomaxillofacial Radiology