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A cone beam-CT evaluation of the proximity of the maxillary sinus to commonly used TAD sites
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A cone beam-CT evaluation of the proximity of the maxillary sinus to commonly used TAD sites
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Content
A CONE BEAM-CT EVALUATION OF THE PROXIMITY OF THE MAXILLARY
SINUS TO COMMONLY USED TAD SITES
by
Jason Michael Pambrun, DDS
____________________________________________________________________
A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(CRANIOFACIAL BIOLOGY)
May 2007
Copyright 2007 Jason Michael Pambrun, DDS
ii
DEDICATION
To my Wife and Kids:
Stefanie Pambrun
Camille Pambrun
Harper Pambrun
Leland Pambrun
iii
ACKNOWLEDGEMENTS
A special thank you to:
Dr. Sameshima
Michelle Bailey
My Co-Residents
Brent Bethers
iv
TABLE OF CONTENTS
Dedication ii
Acknowledgements iii
List of Tables v
List of Figures vi
Abstract vii
Chapter 1: Introduction 1
Chapter 2: Review of Literature 3
Chapter 3: Hypothesis 23
Chapter 4: Materials and Methods 25
Chapter 5: Results 28
Chapter 6: Discussion 53
Chapter 7: Assumptions 58
Chapter 8: Limitations 59
Chapter 9: Summary 60
Chapter 10: Conclusions 61
Bibliography 62
v
LIST OF TABLES
TABLE 1: Sample Descriptives, Ethnicity 29
TABLE 2: Sample Descriptives, Sex 29
TABLE 3: Sample Descriptives, Ethnicity/Sex 29
TABLE 4: Descriptive Statistics, Sites Measured 29
TABLE 5: Descriptive Statistics, Left and Right Combined Sites Measured 29
TABLE 6: Descriptive Statistics, Caucasian and Hispanic 34
TABLE 7: Descriptive Statistics, Males and Females 37
TABLE 8: Group Statistics, Right and Left 41
TABLE 9: Independent Samples Test, Right vs Left 43
TABLE 10: Group Statistics, Caucasians and Hispanics 44
TABLE 11: Independent Samples Test, Caucasians vs Hispanics 46
TABLE 12: Group Statistics, Males vs Females 47
TABLE 13: Independent Samples Test, Males vs Females 49
TABLE 14: Group Statistics, 7/6 and 6/5 50
TABLE 15: Independent Samples Test, 7/6 vs 6/5 52
vi
LIST OF FIGURES
FIGURE 1: Horizontal cut of maxilla 25
FIGURE 2: Coronal cut through interproximal area 25
FIGURE 3: Graph of Means, Sites Measured 30
FIGURE 4: Box Plot of Means, Sites Measured 31
FIGURE 5: Graph of Means, Left and Right Combined Sites Measured 32
FIGURE 6: Box Plot of Means, Left and Right Combined Measurements 33
FIGURE 7: Graph of Means, Caucasians and Hispanics 35
FIGURE 8: Box Plot of Means, Caucasians and Hispanics 36
FIGURE 9: Graph of Means, Males and Females 37
FIGURE 10: Box Plot of Means, Males and Females 39
FIGURE 11: Selected crest measurement outliers as an example of extreme
Individual variation 40
FIGURE 12: Means - Right vs Left 42
FIGURE 13: Means - Caucasians vs Hispanics 45
FIGURE 14: Means - Males vs Females 48
FIGURE 15: Means - 7/6 vs 6/5 51
FIGURE 16: Location of maxillary sinus above level of palatal roof. 54
vii
ABSTRACT
Introduction: The purpose of this study was to characterize common TAD
placement sites in the posterior maxilla and their proximity to the maxillary sinus,
and to compare gender, ethnic, and insertion site groups. Methods: Pretreatment
CBCT images of 66 consecutively scanned orthodontic patients (34 females (17
Hispanic/17 Caucasian) D 16 years old and 32males (15 Hispanic/17 Causcasian) D
21years old) were rendered to provide vertical sections between the second and first
molar (7/6), and first molar and second premolar (6/5). The distances from the floor
of the maxillary sinus to the alveolar crest, buccal plate and alveolar plates were
measured. Results: Few significant differences were found between gender and
ethnic groups. Significant differences existed between the 7/6 and the 6/5 sites.
Conclusions: The palatal of the 6/5 site was considered the safest area for placement,
followed by buccal of 6/5, palatal of 7/6, and buccal of 7/6.
1
Chapter 1: INTRODUCTION
Mini screw type temporary anchorage devices (TADs) are rapidly gaining
popularity in orthodontics as a means of providing cost effective, compliance-free
anchorage. As the clinical acceptance and use of this type of TAD widens, knowing
where they can safely and effectively be placed is an important question. With
typical mini screw sizes ranging from 1.2-2mm in diameter and 4-14mm in length,
1-3
they have been posited as being ideally suited for interradicular placement.
4
Current research has provided important, initial guidelines for the effective
and safe placement of mini screws.
5-7
Previous research in this area has been
directed toward identifying areas with sufficient bone stock to sustain the screws,
seeking to avoid injury or damage to adjacent structures. These studies have
adequately characterized the amount of bone in interradicular sites; however, little
attention has been given with respect to the presence of the maxillary sinus in the
interradicular sites of the posterior region of the maxilla. While a few of these
studies warned of the possible presence of the sinus in these areas often selected for
screw placement, none specifically addressed this potential hazard.
6,7
Also lacking
from these studies are data detailing the differences amongst ethnic groups or
between males and females. By providing this data, this study will help clinicians
better avoid sinus damage during screw placement in the course of orthodontic
treatment.
2
Cone Beam Computed Tomography (CBCT) can provide highly accurate 1:1
images allowing for equally precise measurements of the craniofacial structure.
8,9
This study utilized imaging data acquired from the NewTom® (DVT9000) Volume
Scanner QRsr1 Verona CBCT to accurately detail interradicular areas of the maxilla,
thereby testing the hypotheses that the maxillary sinus-alveolar crest relationship
significantly differs amongst interradicular sites measured, ethnic backgrounds, and
gender groups.
.
Purpose of the Study
characterize interradicular sites in the posterior maxilla with respect to the
distance of the inferior sinus floor to the alveolar crest and the buccal and palatal
alveolar plates
compare the measured distances between ethnic (Hispanics and Caucasians) and
gender groups
3
Chapter 2: REVIEW OF THE LITERATURE
Orthodontic Anchorage and the Temporary Anchorage Device
While conceptually the idea of orthodontic anchorage was understood for
centuries, it was not until 1923 in the Standard Dental Dictionary that Louis Ottofy
offered the first clearly defined reference of the term “orthodontic anchorage” as “the
base against which orthodontic force or retraction of orthodontic force is
applied.”
10,11
Ottofy’s definition has since been through many permutations. In
perhaps its most recent form, Daskalogiannakis has attempted to simply the concept
and offered a definition of “orthodontic anchorage” as a “resistance to unwanted
tooth movement.”
10,12
Ottofy further summarized the anchorage categories that were initially
described by E.H. Angle and described them as: intraoral, extraoral, simple,
stationary, reciprocal, and intermaxillary.
10,11
Much like the definition of anchorage,
these categories have undergone modification or expansion throughout the years.
Giannelly and Goldman quantified the amount of movement of the active and
reactive units that should be expected and offered the descriptive terms “minimum”,
“moderate”, and “maximum” anchorage.
10,13
Both Marcotte and Burstone offered
their own interpretation of anchorage demands as defined by three categories – A, B,
and C referring to the contribution of the anchorage unit towards space closure.
10,14,15
Moyers contribution finds a further subdivision of Ottofy’s classifications. Most
notably he divided simple anchorage into single, compound, and reinforced.
10,16
In
4
what is perhaps the most well recognized restatement of this concept, Tweed gives
us the tent peg analogy to better describe his concept of distally tipping posterior
teeth in what he termed as “anchorage preparation.”
10,17
Clinically, orthodontic anchorage found perhaps its first relevance in the use
of expansion arches as noted by Fauchard in the 18
th
century.
10,18
Utilizing heavy
wire arches to move crowded teeth into more ideal arch forms, Fauchard realized the
limitations of utilizing teeth to move other teeth.
10,18
It wasn’t until the 19
th
century,
however, that anchorage needs precipitated the radical developments of the
Delabarre crib, occipital anchorage, as well as the concept of using tooth mass to
differentially move other teeth.
10,19
While E.H. Angle perfected the use of occipital
anchorage, he also contributed the ideas of stationary and occlusal anchorage late in
that century.
10,19
After decades of variations on these themes, many schemes and implements
have been derived to help supplement anchorage demands required in successful
although often compromised orthodontic treatment. In a search for an alternative
and effective means to provide all of the anchorage necessary to treat a case without
the typical constraints of moving teeth against other teeth, orthodontists looked to
skeletal anchorage to provide this “absolute anchorage”.
In the early 20
th
century, dentist soon realized the potential of implants as a
means of replacing teeth. Greenfield’s 1909 patent for a metal frame supported
prosthesis that was to be inserted into the jaw was perhaps the first legitimate attempt
5
at ossoeintegrated tooth replacement.
10,20
A few decades later Alvin Strock utilized
the newly developed less corrosive and more biocompatible alloy Vitalium, to
develop a screw type implant as a means of replacing teeth.
10,21
Even in 1940, nearly
10 years prior to Brånemark’s discovery of the biocompatibility and osseointegration
of titanium, Strock realized some of the important limitations of metal screws and
osseointegration.
With the advent of dental implants, orthodontists saw the potential of an
osseointegrated bony anchor that could to move teeth without any unwanted side
effects. In 1969, Linkow documented his use of an implant supported bridge as a
means to provide anchorage for orthodontically moving teeth.
10,22
This eventually
led to the successful implementation of dental implants as bony anchorage units,
unfortunately however, a minority of orthodontic patients are in concurrent need of
restorative dental implants. Orthodontists needed an alternative and oral surgeons
helped provide the answer with screws developed for orthognathic fixation. Early
orthognathic fixation consisted of the use of splints, bandages, or combinations of
intraoral and extraoral appliances.
10,23
It wasn’t until the 1970’s that Brons and
Boering introduced the use of lag screws for orthognathic fixation.
10,24
By 1984,
miniaturized titanium bone screws, 2.0 mm in diameter, were being used as the sole
source of fixation.
10,25
These small screws used in orthognathic fixation laid the
groundwork for the successful development of orthodontic mini screws as temporary
anchorage devices.
6
TADs have become the current focus in the search for absolute anchorage. As
a relatively new technology, terminology for what exactly constitutes a temporary
anchorage device is still under debate. Currently, they are classified as either
biocompatible or biological.
10
The biocompatible group can further be subdivided
into two groups: those which rely on osseous integration, including dental or palatal
implants and onplants, and those that utilize mechanical retention, such as mini
screws.
10
The biological group of TADs is also subdivided into an osseointegrated
and mechanical groups.
10
The osseointegrated subgroup includes ankylosed teeth
while the mechanical subgroup consists of dilacerated teeth.
10
Several osseointegrated implant type systems have been investigated and
used with success, however, few have proven to be as easy to implement or as cost
effective as the mini screw as a means of providing absolute orthodontic
anchorage.
25
In light of these advantages, mini screws are enjoying a substantial
popularity among the various absolute anchorage systems. Developed from the
miniature screws utilized in orthognathic fixation, orthodontic mini screws are
titanium screws ranging from 1.2-2mm in diameter and 4-14mm in length.
1-3
Because of their diminutive size, they have proven ideal for their placement in both
the maxilla and mandible, particularly in between tooth roots.
4
Unlike dental
implants, histologic studies have revealed that mini screws fail to completely
osseointegrate
25-28
leading to a mechanically sturdy anchorage unit that is easy to
remove once treatment is completed.
27,28
Since the mini screw relies almost entirely
7
on mechanical retention, the typical 4-6 month waiting period for osseointegrated
implants is not required, providing the potential for early loading.
10
Studies by
Creekmore and Eklund
29
, Melsen and Costa
30
, as well as Freudenthaler and
colleagues
31
found similar success with early and immediately loaded mini screws.
Clinical and histological reports have demonstrated the effectiveness of using
mini screws for a wide variety of orthodontic tooth movements, and their
applications are rapidly increasing.
3,4,28,33,34
Perhaps the most exciting use of mini
screws has been as a means of treating what are traditionally challenging vertical
cases. Whether intruding posterior teeth to treat anterior openbite or intruding
anterior teeth to treat deepbite and or VME, mini screws are offering clinicians an
alternative to possibly indicated surgery or relieving the clinician of having to
depend on patient compliance appliances like headgear and elastic wear.
32
Mini
screws find an obvious use in maximum anchorage retraction cases as well.
4
By
placing the screws laterally in the alveolus, en-masse retraction of the anterior teeth
following extraction is possible. They have further demonstrated the ability to
mesialize, distalize, upright, intrude, extrude individual teeth, groups of teeth, or
entire arches without the compromising side effects between the active and reactive
units.
3,4,28,33,34
8
Mini Screw Placement
Two general principles typically guide mini screw placement in the jaws.
First is the type of orthodontic movement to be attempted. Once this is determined, a
general idea of where the screw will have to be located to accomplish this movement
is established. Ideally, a screw should be placed in a location through the necessary
line of force action to provide direct anchorage. Adding to its overall versatility, if
the mini screw cannot be placed in a manner to allow for direct anchorage, it can also
be used as a means of indirect anchorage. Indirect anchorage allows the screw to
brace the reactive unit
46
as opposed to being the reactive unit itself. Once a surgical
site is selected, consideration should be given as to whether this area can physically
sustain the placement of the mini screw.
Even though the clinical consequences of root contact have been found to be
relatively minimal, care should still be taken to minimize complications related to
placement.
35-37
With the major goal for safe placement being avoidance of vital
structures (tooth roots, maxillary sinus, nerves, vessels, etc…), it is recommended
that for alveolar placement, a periapical radiograph of the selected placement site be
taken prior to insertion.
38
For extra-alveolar placements, standard panographic
radiographs have been reported to be adequate for safe placement.
38
Recent studies
investigating placement of mini screws have focused on the amount of bone
available in various locations of the jaws. In 2004, Schnelle et al
5
used panographic
films to measure available “bone-stock” between interradicular sites to derive
9
confidence intervals for safe placement locations. Using the commonly accepted
guideline of maintaining at least 1mm of bone around the screw, they considered
safe placement as the availability of 3-4mm of bone between adjacent tooth roots as
measured horizontally from the PDL. Their findings suggest that adequate bone
stock exists in the maxilla mesial to the first molars and in the mandible both mesial
and distal to the first molars. In 2006 Poggio et al
7
utilized CBCT images from 21
subjects in an effort to provide similar placement recommendations. Using the same
guideline (1mm of bone required to surrounding the implant) as used by Schnelle et
al,
5
their study looked at both the mesio-distal dimension and the bucco-lingual
dimension. They concluded that for their sample, the greatest amount of buccal bone
in the maxilla was between the canine/first premolar. They also issued a caution
against placement in the buccal area between the first molar and second bicuspid
area because of possible sinus impingement. Another similar study conducted by
Ishii et al
6
used highly detailed micro-CT to evaluate bone stock between the
maxillary first molar and second premolar using a sample of five cadaver specimens.
Their study found that the amount of bone in this area increased apically, with
adequate bone stock available 6-8mm apical of the alveolar crest. Similar to the
Poggio study, a caveat was issued with regard to buccal placement at this location.
They characterized this area as unsafe for potential TAD placement after noting the
presence of the maxillary sinus in the buccal region in some subjects as close as
10mm from the alveolar crest.
10
In regard to the maxillary sinus location with respect to the posterior teeth, a
CT study by Eberhardt et al
39
looked at 12 autopsy specimens and 38 human
subjects. Their results showed the apex of the second molar’s mesial buccal root was
closest to the floor of the sinus (mean 1.97mm) but also the farthest from the buccal
bony surface (mean 4.45mm). The buccal root of the maxillary first premolar was
farthest from the sinus floor (mean 7.05) but closest to the buccal bony surface
(1.63). Other studies have looked at the distance from the apex of the roots of the
teeth in the posterior maxilla to the floor of the sinus; however, very little data exists
detailing the distance from the alveolar crest.
40-41
Spyropoulus et al
42
looked at this
distance but limited their scope to edentulous regions of the maxilla.
Once a suitable site has been located and determined capable of successfully
sustaining a mini screw, the surgical procedure for placement is fairly
straightforward. Screw systems typically come in two variations – self tapping and
self drilling. Self tapping systems require an initial pilot channel to be drilled prior
to inserting the screw. While this technique can certainly be helpful in the dense
cortical bone of the mandible, it also increases risk for iatrogenic damage to tooth
structures as well as the potential for overheating the surrounding bone. While self
drilling systems can reduce those potential risks, iatrogenic damage is certainly still a
possibility. Additionally, self drill screws require careful and steady placement to
ensure good mechanical retention. Although they are technically self drilling, they
may still require a small pilot hole in areas of dense cortical bone to allow for proper
11
placement and to reduce the risk of fracturing the screw. Most protocols do not
require a soft tissue flap to be raised for placement, however some systems do
recommend a soft tissue punch or a small incision, especially when the screw is
being placed in unattached tissue.
32,38
Prior to placement, any antibiotic prophylactic
coverage as prescribed by the recommendations of the American Heart Association
should be administered. Some protocols call for the patient to rinse with
chlorhexidine prior to placement, while others call for the area to merely be
swabbed.
32,38
Local anesthesia is typically required to keep the patient comfortable
through the placement procedure; however, some protocols suggest topical may be
all that is required.
10,32,38
If a pilot hole is necessary, it should be made with a low
speed handpiece under saline irrigation.
38
A depth gauge should be used on the bur
to insure proper depth is achieved. For self drilling systems that do not require a
pilot hole, the screw is steadily placed, limiting any eccentric motions that could
cause the screw to lose mechanical retention. If the implant is not stable
immediately following placement, it should be removed and another site chosen for
placement.
10,32,38
Post-op instructions should be clearly discussed prior to placement
as well as following the procedure and should focus on the importance of the
extreme level of hygiene required to help insure the screw is successfully
maintained. Screws should be lightly brushed with a toothbrush and the
surrounding tissues must be kept free of any inflammation.
10,32,38
Dental floss dipped
in 2% chlorhexidine has been recommended to help control peri-screw soft tissue
12
inflammation.
38
While several studies have sought to determine specific causes of
screw failure, poor hygiene/tissue inflammation are commonly reported causes of
failure.
10,43
As reported earlier, loading can be done immediately and can continue
as long as the screw remains stable. Removal of the screw involves simply backing
out the screw and typically does not require application of local anesthesia.
10,32,38
Possible Complications
Complications during screw insertion are basically limited to two areas:
iatrogenic damage to dental or other vital structures and failure to achieve or
maintain stability of the screw. Because they are not left in for extended periods of
time it has been assumed the risk of irreversible damage is limited.
34
Multiple
studies looking at root contact by titanium screws surprisingly revealed that healthy
teeth can typically sustain even severe contact by sterile titanium with little
consequence.
35-37
Most studies available on complications of screw placement have
come from their extensive use in post surgical bony fixation. A study by Cogburn in
2002 on screws used in IMF following maxillofacial surgery reported a case that
resulted in multiple tooth loss as a consequence of burring into the apical region of
teeth.
44
In light of this problem, many systems are moving toward a self-drill design
which would help avoid this type of complication. Self drill screws may allow for
better tactile feel during placement allowing the operator the ability to redirect before
doing serious, irreversible damage to the tooth. While root contact can be easily
13
averted and is relatively well tolerated, tissues such and nerves, vessels, or sinus
membranes do not afford the same level of tactile feedback upon insertion and
ultimately would not fare as well upon encroachment. The risk for nerve or vascular
damage in the maxilla is somewhat limited; however, the maxillary sinus certainly
poses a risk when the posterior maxilla is chosen as a site for mini screw placement.
During treatment, common complications reported include loosening of the screw
due to local inflammation or local bone remodeling, and hypertrophy of the
surrounding tissues. Hypertrophy can be minimized with screw placement in
attached gingival tissues as well as the patient maintaining a high level of oral
hygiene.
38
A healing cap can be placed onto the head of the screw if the screw is
placed in an area prone to overgrowth.
32,38
If a soft tissue infection does develop,
appropriate antibiotic treatment is indicated.
10,32
Complications that can arise during
removal include difficulty removing the screw, in which case, a second attempt
should be made a few days following the initial attempt, or it can be trephined
out.
10,32,38
The screw may also fracture upon removal. In this case, the screw can be
trephined out or can be left in the patient indefinitely.
32
Function and Development of the Maxillary Sinus
The maxillary sinus (the antrum of Highmore) is part of the paranasal sinus
system. These sinuses, which include the maxillary, ethmoid, sphenoid, and frontal,
are composed of several air filled spaces in the skull that communicate with the nasal
14
cavity. The purpose of these sinuses has yet to be fully determined. Current theories
suggest their function may be to lighten the skull, absorb shock, or provide a means
of improved vocal resonance, while others maintain they are a crucial aspect of the
respiratory system, humidifying the incoming air while helping to control
environmental pollutants.
45-49
While extensive research of the paranasal sinuses of
both extinct and extant hominoids (including humans) has sought to elucidate the
evolution of the species, many have looked to the higher primates for answers
regarding the development and role of the paranasal sinuses in humans.
45- 52
Distinct
differences among humans and primates have led some researches to propose that
rather than the traditional notion that humans evolved from the arboreal apes,
humans may have had an aquatic relative somewhere along the evolutionary path.
50
This “aquatic ape” theory attributes the paranasal sinuses to an evolutionary
development that served to protect the airway via improved buoyancy of the head.
50
While more of an interesting side note, this theory demonstrates that the jury is
indeed still out regarding the purpose of the paranasal sinuses.
In humans, the maxillary sinus forms during the sixteenth week of fetal
development.
53,54
Beginning as a shallow groove on the nasal aspect of the
developing maxilla, by birth it is still only the size of a pea and is typically fluid
filled. The maxillary sinus growth parallels that of the maxilla.
53,54
By around age
13, the sinus will have expanded to the point at which its floor will be on the same
horizontal level as the floor of the nasal cavity. While the sinus is typically
15
observed to expand inferiorly to the level of the apices of the maxillary dentition, the
roots of posterior teeth often appear to perforate the sinus floor on the radiographs of
adults.
39-42
A study by Ariji et al
41
looked at the relationship of maxillary molar
roots and the maxillary sinus. CT analysis of one hundred twenty subjects found that
the floor of the maxillary sinus was most frequently observed at the level between
the bifurcation and apices of roots in both first and second molars. It is currently
unclear as to the mechanism that limits sinus expansion inferiorly. Studies in
primates have led to the idea that maxillary sinus size may simply be a function of
allometry.
46,48,49,52
Rae states that while the exact mechanism is undetermined,
“sinuses may be pneumatizing as much bone as they can within the limits imposed
by certain biomechanical loading regimes, perhaps in a completely opportunistic
manner” but the concludes the process is more likely under epigenetic control
48
Often a complication in dental implant site selection, the maxillary sinus will expand
inferiorly into the edentulous ridge, leaving only a thin shell of alveolar bone.
Anatomical Aspects of the Maxillary Sinus
Anatomically speaking, the adult maxillary sinus is best described as a
pyramid, the base of which is the nasal wall and the peak of the pyramid pointing
toward the zygomatic process.
42,55,57,58
The average volume of the adult maxillary
sinus is 15ml.
42,55,56
The roof is formed from the orbital floor, the posterior wall
backs up to the pterygomaxillary fossa, while the floor as previously mentioned,
16
moves inferiorly as the maxillary sinus develops. Blood supply to the sinus is via
branches of the internal maxillary artery including the infraorbital, the lateral
branches of the sphenopalatine, greater palatine, as well as the alveolar arteries.
Anterior venous drainage is via the facial vein, while the posterior drainage is
handled by the maxillary vein and the jugular venous system. Innervation of the
maxillary sinus is from the greater palatine nerve as well as branches of the
infraoribital nerves.
Microscopic examination of the maxillary sinus reveals a lining of
pseudostratified ciliated columnar epithelium including ciliated columnar epithelial
cells, nonciliated columnar cells, basal cells, and goblet cells. The ciliated cells
function to move mucus out of the sinuses, while the nonciliated cells are thought to
increase surface area and thus help to facilitate the conditioning of inspired air. The
goblet cells contribute to mucus production and are innervated both sympathetically,
leading to thinner mucus secretion, as well as parasympathetically, which leads to
thicker mucus production. The basal cell’s functions are as yet undetermined. This
epithelial layer is supported by a thin basement membrane, lamina propria, and
periosteum.
Gender and Ethnic Differences in the Maxillary Sinus
While individual variations in sinus size and shape have been well
documented, sexual dimorphism in the maxillary sinus has also been established.
59,60
17
In an effort to detail sinus development by age and by gender, Jun et al
56
conducted a
detailed CT analysis of one hundred seventy three people. They concluded that for
their sample population, development of the maxillary sinus continues until the 3
rd
decade for males and until the 2
nd
decade for females. In a study of thirty three hemi
sectioned Korean heads, Kim et al,
57
found all measurements of the maxillary sinus
were larger in males than in females. Ethnic variations have also been reported and
find support in a CT study by Fernandes
61
which observed differences between the
maxillary sinus structure of Europeans and those of Zulus, as well as in a study by
Shea et al
62
of native Eskimo populations. While these studies have allowed the
maxillary sinus to be used in successfully identifying the ethnicity and gender of
forensic remains,
63
it should be noted that none of these studies rule out the
possibility of the environmental impact on sinus development as a reason for the
observed differences as opposed to strictly ethnic differences. Indeed, the Shea
study
62
goes so far as to propose that environment may be the sole cause for these
noted differences and would validate previous anthropological studies of
Neanderthals suggesting the noted craniofacial trait of an enlarged nasal cavity
(smaller maxillary sinus volume) was a climate induced autapomorphy.
45
Many
other primate and monkey studies have in fact shown environmental variables such
as diet and climate can affect the maxillary sinus development.
46,48,49,51,52
18
Cone Beam Computed Tomography
Over thirty years ago, Sir Godfrey Hounsfield introduced the medical
community to computerized axial transverse scanning revolutionizing medical
imaging. Utilizing a computer to digitize and then analyze the analog signal
produced by the scan, a high contrast three dimensional image could be constructed.
Unlike traditional radiography, this technique offers complete elimination of
superimposition of over or underlying structures in the imaging field.
64
Another
unique advantage is multiplanar reformatting. A single scan can produce images in
any plane of space.
64
Since then, computed tomography (CT) has undergone
continuous improvement and transformation, increasing the speed of the scan and
decreasing the radiation dose to the patient while improving the image quality.
Until the relatively recent introduction of CBCT, three dimensional
volumetric imaging was the realm of large hospitals. With their high cost, high
radiation exposure and poor image quality of the maxillofacial structures the dental
applications for CT were few. CBCT has been able to offer dentistry a lower cost,
lower patient dose, and a highly detailed volumetric image. As such, CBCT
immediately found use in implant dentistry and continues to find new applications in
other aspects of dentistry.
19
CBCT versus Standard Radiographic Imaging
In a demonstration of its clinical superiority over older imaging techniques, a
study by Sharan et al
58
compared traditional radiographic techniques to CBCT
images. Looking specifically at the topography of the maxillary sinus floor with
respect to the apices of the posterior dentition, the differences between the panoramic
images and the CBCT volumetric images were, as expected, quite dramatic. They
found that only 39% of the panoramic radiographs demonstrating tooth root
projection into the maxillary sinus were also seen on the CT image. Additionally,
they reported that the panoramic images significantly overestimated the amount of
actual root projection into the maxillary sinus on an order of over 200%. Another
study by Peck et al
65
compared the accuracy of standard panoramic projections
versus CBCT images in assessing mesiodistal root angulations. They determined
that panoramic radiographs are sufficient as a screening tool, but proved they lacked
the precision and reliability that the CBCT images were able to offer when used to
evaluate mesiodistal root angulations. CBCT images did not suffer from the various
magnification and distortion problems common to the standard panoramic images
and were found to be the gold standard with regard to these specific measurements.
CBCT in Orthodontics
In orthodontics, this technology is rapidly replacing the traditional two-
dimensional radiography. Current orthodontic research has investigated the use of
20
CBCT in localizing impacted teeth
66
as well as the development of novel three-
dimensional cephalometric analyses.
67-69
In an early study of volumetric imaging by
Preda et al
70
compared spiral CT to traditional radiographic techniques in localizing
impacted canines. While determining CT to be superior in localizing the impacted
cuspid, CT was also able to determine the location and extent of root resorption. A
recent study by Walker et al,
66
also demonstrated the superior capability of CBCT in
the management of impacted maxillary canines. In an effort to improve upon the
shortcomings inherent in traditional 2-D cephalometrics, specifically problems with
analysis bias, Swennen et al
69
have proposed a new method of 3-D cephalometry
utilizing volumetric CBCT imaging. While still early in its implementation, they
have presented a system that has proven to be both accurate and reliable and will
likely see wider use as dental CBCT use increases.
Accuracy of CBCT Derived Measurements
With these new applications, the need to validate the accompanying
measurements became necessary and has subsequently been addressed by several
studies. In 2004 Lascalla et al determined measurements from the NewTom® CBCT
system were accurate with specific regard to linear measurements of the
dentomaxillofacial complex.
8
They used 8 dry skulls and recorded 13 linear
measurements with a digital caliper. These skulls were then scanned using a
NewTom 9000 CBCT and the measurements were repeated in three planes of space
21
utilizing the NewTom’s software. Through this study, they were able to deduce that
the NewTom image consistently underestimated the real distances. However, these
differences were significant only for structures of the skull base, measurements of
and around the dentomaxillofacial complex were established to be more reliable.
Marmulla et al conducted a similar study in 2005 addressing the geometric accuracy
of the NewTom® system and found that images were geometrically correct with
distortion below the resolution values of alternative tomographic techniques.
9
A
study by Togashi et al
71
to investigate the effect of head inclination on measurement
error found that these errors can be minimized by limiting slice thickness. Scanning
and measuring various landmarks of a dry skull, they found skull inclinations of 10
degrees from the reference position added measurement errors less than 5% of true
measurements as long as slice thickness was limited 3mm or less. With slices
greater than 5mm, some increase was noted. While these studies are valid only for
the particular systems they evaluated, they speak to the overall accuracy of a CBCT
image.
NewTom 9000 CBCT System
The NewTom 9000 is a volume imaging machine produced in Italy, and
received FDA approval in April 2001.
72
It was designed specifically for imaging the
maxillofacial region. In a single scan the x-ray source and a reciprocating x-ray
sensor rotate around the head and acquire 360 pictures (one image per degree of
22
rotation) in the span of the 17 seconds required for exposure time. With the entire
maxillofacial volume imaged, the patient receives an absorbed dose roughly
equivalent to a full mouth periapical series.
73
The 360 acquired images undergo
primary reconstruction into a single 3D volume that is comprised of voxels.
73
Each
voxel for the standard 9 inch sensor set for a large field scan is 0.29 mm for each of
the cube faces and therefore the image has a relatively high resolution.
73
Thickness
of the voxel is determined by the slice thickness as selected by the operator. Voxel
size will also vary slightly according the various sensor sizes as well as field size
used for scanning. For this study, both 9 and 12 inch sensors were used and scans
were taken in the small field setting. According to the manufacturer, these settings
yield voxel sizes of 0.25mm and 0.36mm respectively. The NewTom software
allows for reformatting and viewing the image data from any point of view in
straight or curved planes as well as in 3-D. Measurements made with the NewTom
software are also limited by the resolution of the scan.
23
Chapter 3: HYPOTHESES
The distance from the sinus floor to the alveolar crest, buccal plate and
palatal plate significantly differs between ethnic groups (Hispanics and
Caucasians).
The distance from the sinus floor to the alveolar crest, buccal plate and
palatal plate significantly differs between males and females.
The distance from the sinus floor to the alveolar crest, buccal plate and
palatal plate significantly differs between interradicular sites measured.
24
NULL HYPOTHESES
The distance from the sinus floor to the alveolar crest, buccal plate and
palatal plate does not significantly differ between ethnic groups (Hispanics
and Caucasians).
The distance from the sinus floor to the alveolar crest, buccal plate and
palatal plate does not significantly differ between males and females.
The distance from the sinus floor to the alveolar crest, buccal plate and
palatal plate does not significantly differ between interradicular sites
measured.
25
Chapter 4: MATERIALS AND METHODS
Pretreatment volumetric tomographic images of 66 consecutively scanned
orthodontic patients (34 females (17 Hispanic/17 Caucasian) D 16 years old, 32males
(15 Hispanic/17 Causcasian) D 21years old) from the University of Southern
California Department of Advanced Orthodontics were selected for evaluation.
Scans were selected from the archives of the department’s NewTom® (DVT9000)
Volume Scanner QRsr1 Verona CBCT unit. In addition to those previously
mentioned, all patients were selected using the following inclusion criteria: 1) fully
erupted 2
nd
molars, 2) complete dentition 3) no signs of sinus or periapical
pathology. Images were rendered with NewTom® software to provide vertical
sections between the following interradicular sites: 1) the second and first molar; 2)
first molar and second premolar. These were cut in 0.5mm thick slices from a
horizontal section parallel to the palatal plane (Fig.1).
The distance from the superior bony border of the most inferior point on the
floor of the maxillary sinus to the alveolar crest (Fig. 2, A) was measured with
NewTom® measurement software. The horizontal distance from the most inferior
point of the floor of the sinus to the medial border of the palatal (Fig. 2, B) and
lateral border of the buccal alveolar plates (Fig. 2, C) was also measured.
26
The measurements were statistically analyzed for means, standard deviations
and differences between ethnic groups, gender groups, and between sites measured.
The measurement error was calculated by statistically analyzing the difference
between duplicate measurements two weeks apart on ten images selected randomly
from the sample.
Figure 1- Horizontal cut of maxilla. In this example,
selected sites for coronal cuts are labeled 1-4.
Figure 2- Coronal cut through interproximal area
(slice P-3). A- distance from inferior most point on
the superior surface of sinus floor to base of
alveolar crest, B- distance from inferior most point
of sinus floor to medial border of palatal alveolar
plate, C- distance from inferior most point of sinus
floor to lateral border of buccal alveolar plate.
B
A
C
27
ANALYSIS OF DATA
Descriptive statistics including the means and standard deviations of all
continuous variables were calculated for each sample. Histograms and
Kolmorogov-Smirnov tests were used to check normality. Ethnic, gender, and
interradicular site differences were analyzed by independent t-tests and Levene’s test
for equality of variance. The level of significance was set at Q = 0.05.
All measurements were made by one examiner. The method error was
assessed by statistically analyzing the difference between duplicate measurements,
by the same examiner, that were taken 2 weeks apart on 10 randomly selected
members of the sample. The intraclass correlation coefficient was 0.96.
28
Chapter 5: RESULTS
In order to characterize the relationship of the maxillary sinus and the
alveolar crest of the posterior maxilla as well as clarify any morphological
differences between various interradicular sites, males and females, and Caucasians
and Hispanics, we analyzed 66 NewTom CBCT scans and a statistical analysis was
completed.
SAMPLE CHARACTERISTICS
The age of all male patients was 21 years old or older, while all female
patients were 16 years old or older. There were 66 total patients divided into ethnic
and sex groups. The Caucasian group consisted of 17 females and 17 males, while
the Hispanic group consisted of 17 females and 15 males. Table 1 illustrates the
ethnic distribution of the sample while the gender component of the sample is shown
in table 2. Table 3 describes the groups as broken down into gender/ethnic groups.
For each patient, four interradicular sites were selected for specific analysis: between
left and right maxillary second and first molars, and between left and right maxillary
first molars and second premolars. Three measurements were taken at each site for a
total of 12 measurements per patient, except in cases were no measurement was
possible (i.e. if sinus did not descend to a measurable point below hard palate).
Tables 4-7 outline the descriptive statistics for the sites measured. Figures 3, 5, 7, 9
are bar graph representations of the sample means. Outliers as noted in box plots of
29
the sample means are displayed in figures 4, 6, 8, 10 and all were verified as
examples of individual variation (figure 11).
Table 1 : Sample Descriptives, Ethnicity
Frequency Percent Valid Percent Cumulative Percent
Caucasian 34 51.5 51.5 51.5
Hispanic 32 48.5 48.5 100.0
Valid
Total 66 100.0 100.0
Table 2 : Sample Descriptives, Sex
Frequency Percent Valid Percent Cumulative Percent
Female 34 51.5 51.5 51.5
Male 32 48.5 48.5 100.0
Valid
Total 66 100.0 100.0
Table 3 : Sample Descriptives, Ethnicity/Sex
Frequency Percent Valid Percent Cumulative Percent
Female 17 53.0 53.0 26.0
Male 15 47.0 47.0 22.0
Hispanic
Total 32 100.0 100.0 48.0
Female 17 50.0 50.0 26.0
Male 17 50.0 50.0 26.0
Caucasian
Total 34 100.0 100.0 52
Table 4 : Descriptive Statistics, Sites Measured
N Minimum Maximum Mean Std. Deviation
R7/6 Crest
66 5.00 17.30 10.97 2.79
R7/6 Buccal
66 3.00 11.50 7.71 1.92
R7/6 Palatal
58 5.40 11.50 7.79 1.46
R6/5 Crest
65 3.60 19.50 12.41 3.28
R6/5 Buccal
66 2.20 11.20 6.38 1.90
R6/5 Palatal
54 4.00 13.30 7.62 2.11
L6/5 Crest
66 4.30 20.40 13.02 3.56
L6/5 Buccal
63 3.20 10.80 7.00 1.79
L6/5 Palatal
46 2.90 11.50 6.68 2.01
L7/6 Crest
66 6.50 18.00 11.21 2.57
L7/6 Buccal
64 3.20 12.60 8.11 2.29
L7/6 Palatal
59 3.20 14.40 7.55 2.51
30
Figure 3 : Bar Graph of Means, Sites Measured
L7/6
Palatal
L7/6
Buccal
L7/6
Crest
L6/5
Palatal
L6/5
Buccal
L6/5
Crest
R6/5
Palatal
R6/5
Buccal
R6/5
Crest
R7/6
Palatal
R7/6
Buccal
R7/6
Crest
12.50
10.00
7.50
5.00
2.50
0.00
Mean
Error bars: 95% CI
31
Figure 4 : Box Plot of Means, Sites Measured
L7/6
Palatal
L7/6
Buccal
L7/6
Crest
L6/5
Palatal
L6/5
Buccal
L6/5
Crest
R6/5
Palatal
R6/5
Buccal
R6/5
Crest
R7/6
Palatal
R7/6
Buccal
R7/6
Crest
20
15
10
5
0
45
32
Table 5:Descriptive Statistics, Left and Right Combined Sites Measured
N Range Mean
Std.
Deviation
Variance
Statistic Statistic Statistic Statistic Statistic
7/6 Crest
132 13.00 11.09 2.67 7.15
7/6 Buccal
130 9.60 7.91 2.11 4.46
7/6 Palatal
117 11.20 7.67 2.05 4.216
6/5 Crest
131 16.80 12.72 3.43 11.73
6/5 Buccal
129 9.00 6.68 1.86 3.47
6/5 Palatal
100 10.40 7.19 2.11 4.44
Figure 5: Graph of Means, Left and Right Combined Sites Measured
6/5 Palatal 6/5 Buccal 6/5 Crest 7/6 Palatal 7/6 Buccal 7/6 Crest
12.50
10.00
7.50
5.00
2.50
0.00
Mean
Error bars: 95% CI
33
Figure 6 : Box Plot of Means, Left and Right Combined Measurements
6/5 Palatal 6/5 Buccal 6/5 Crest 7/6 Palatal 7/6 Buccal 7/6 Crest
20
15
10
5
0
16
40
111
115
34
Table 6 : Descriptive Statistics, Caucasians and Hispanics
N Range Mean Std. Deviation Ethnicity Site
Statistic Statistic Statistic Statistic
R7/6 Crest 34 10.10 10.16 2.45
R7/6 Buccal 34 7.40 7.01 1.97
R7/6 Palatal 31 4.70 8.01 1.40
R6/5 Crest 34 15.90 12.32 3.49
R6/5 Buccal 34 6.90 6.26 1.75
R6/5 Palatal 27 7.30 7.69 1.81
L6/5 Crest 34 15.20 12.61 3.56
L6/5 Buccal 33 7.60 7.05 1.77
L6/5 Palatal 26 8.20 6.62 1.61
L7/6 Crest 34 8.00 10.31 2.37
L7/6 Buccal 34 9.40 8.47 2.39
C
L7/6 Palatal 32 7.50 6.89 1.96
R7/6 Crest 32 11.20 11.84 2.90
R7/6 Buccal 32 5.40 8.46 1.58
R7/6 Palatal 27 6.10 7.54 1.51
R6/5 Crest 31 12.70 12.52 3.10
R6/5 Buccal 32 9.00 6.51 2.06
R6/5 Palatal 27 9.00 7.55 2.40
L6/5 Crest 32 14.30 13.44 3.57
L6/5 Buccal 30 7.20 6.95 1.84
L6/5 Palatal 20 8.30 6.76 2.49
L7/6 Crest 32 10.10 12.17 2.47
L7/6 Buccal 30 8.70 7.70 2.12
H
L7/6 Palatal 27 11.20 8.34 2.88
35
Figure 7 : Graph of Means, Caucasians and Hispanics
L7/6
Palatal
L7/6
Buccal
L7/6
Crest
L6/5
Palatal
L6/5
Buccal
L6/5
Crest
R6/5
Palatal
R6/5
Buccal
R6/5
Crest
R7/6
Palatal
R7/6
Buccal
R7/6
Crest
14.00
12.00
10.00
8.00
6.00
4.00
2.00
0.00
Mean
14.00
12.00
10.00
8.00
6.00
4.00
2.00
0.00
c h
Ethnicity
Error bars: 95% CI
36
Figure 8 : Box Plot of Means, Caucasians and Hispanics
L7/6
Palatal
L7/6
Buccal
L7/6
Crest
L6/5
Palatal
L6/5
Buccal
L6/5
Crest
R6/5
Palatal
R6/5
Buccal
R6/5
Crest
R7/6
Palatal
R7/6
Buccal
R7/6
Crest
20
15
10
5
0
20
15
10
5
0
c h
Ethnicity
6
20
14
3
45
37
Table 7 : Descriptive Statistics, Males and Females
Sex Site
Measured N Range Mean
Std.
Deviation
Statistic Statistic Statistic Statistic
F R7/6 Crest 34 12.30 11.06 2.80
R7/6 Buccal 34 7.20 7.71 1.97
R7/6 Palatal 31 6.10 7.66 1.60
R6/5 Crest 34 14.00 12.26 3.16
R6/5 Buccal 34 7.90 6.12 1.98
R6/5 Palatal 30 9.30 7.64 2.31
L6/5 Crest 34 15.20 12.65 3.73
L6/5 Buccal 32 7.60 6.931 1.70
L6/5 Palatal 25 8.60 6.54 2.29
L7/6 Crest 34 11.50 11.64 2.71
L7/6 Buccal 33 9.40 7.30 2.50
L7/6 Palatal 30 10.40 8.24 2.84
M R7/6 Crest 32 10.20 10.86 2.82
R7/6 Buccal 32 8.50 7.71 1.90
R7/6 Palatal 27 5.10 7.93 1.29
R6/5 Crest 31 13.00 12.59 3.46
R6/5 Buccal 32 8.00 6.65 1.80
R6/5 Palatal 24 7.90 7.59 1.88
L6/5 Crest 32 14.30 13.40 3.38
L6/5 Buccal 31 6.80 7.08 1.90
L6/5 Palatal 21 7.00 6.85 1.67
L7/6 Crest 32 7.60 10.75 2.37
L7/6 Buccal 31 6.90 8.97 1.68
L7/6 Palatal 29 6.90 6.84 1.93
38
Figure 9 : Graph of Means, Males and Females
L7/6
Palatal
L7/6
Buccal
L7/6
Crest
L6/5
Palatal
L6/5
Buccal
L6/5
Crest
R6/5
Palatal
R6/5
Buccal
R6/5
Crest
R7/6
Palatal
R7/6
Buccal
R7/6
Crest
14.00
12.00
10.00
8.00
6.00
4.00
2.00
0.00
Mean
14.00
12.00
10.00
8.00
6.00
4.00
2.00
0.00
f m
Sex
Error bars: 95% CI
39
Figure 10 : Box Plot of Means, Males and Females
L7/6
Palatal
L7/6
Buccal
L7/6
Crest
L6/5
Palatal
L6/5
Buccal
L6/5
Crest
R6/5
Palatal
R6/5
Buccal
R6/5
Crest
R7/6
Palatal
R7/6
Buccal
R7/6
Crest
20
15
10
5
0
20
15
10
5
0
f m
Sex
38
19
52
40
Figure 11 : Selected crest measurement outliers as an example of extreme
individual variation
41
Comparison of Sites Measured: Right versus Left
Table 8 and figure 12 compare the means for contralateral sites measured.
The results of the independent t-test (table 9) showed that there were few significant
differences between the left and right sites measured. The only exception was noted
between the left and right 6/5 palatal measurements (P < 0.05). The results indicate
that for this sample, little difference exists between the left and right measurements.
Table 8 : Group Statistics, Right vs Left
Site
Measured Side R/L N Mean Std. Deviation
Std. Error
Mean
Right 66 10.97 2.79 .34 7/6 Crest
Left 66 11.21 2.57 .32
Right 66 7.71 1.92 .24 7/6 Buccal
Left 64 8.11 2.29 .29
Right 58 7.79 1.46 .19 7/6 Palatal
Left 59 7.55 2.51 .33
Right 65 12.41 3.28 .41 6/5 Crest
Left 66 13.02 3.56 .44
Right 66 6.38 1.90 .23 6/5 Buccal
Left 63 7.00 1.79 .23
Right 54 7.62 2.11 .29 6/5 Palatal
Left 46 6.69 2.01 .30
42
Figure 12: Means – Right vs Left
0
2
4
6
8
10
12
14
Millimeters
Means : R ig ht v s L eft
RIG H T 10.97 7.71 7.79 12.41 6.38 7.62
LE F T 11.21 8.11 7.55 13.02 7 6.68
7/ 6 C R E S T 7/ 6 B UC C AL 7/ 6 P AL AT AL 6/ 5 C R E S T 6/ 5 B UC C AL 6/ 5 P A L AT AL
43
Table 9 : Independent Samples Test, Right vs Left
t-test for Equality of Means
Site Measured t df Sig.(2-tailed) Mean Diff
7/6 Crest -.51 130 .61 -.24
7/6 Buccal -1.07 128 .29 -.40
7/6 Palatal .61 115 .54 .23
6/5 Crest -1.01 129 .32 -.60
6/5 Buccal -1.92 127 .06 -.62
6/5 Palatal 2.27 98 .03(*) .94
44
Comparison of Sites Measured: Caucasian versus Hispanic
Table 10 and figure 13 describe the means for measurements between the
Hispanic and Caucasian groups in this study. The results of the independent t-tests
(table 11) showed that for this sample, there was little significant difference between
Caucasians and Hispanics with regard to sites measured. The only site found to
significantly differ was the 7/6 crest measurement (P < 0.001). These results indicate
that while Hispanics displayed larger measurements at every site surveyed, little
significant difference was noted when compared to Caucasians.
Table 10 : Group Statistics, Caucasian vs Hispanic
Site
Measured
Ethnicity
C/H N Mean Std. Deviation
Std. Error
Mean
c 68 10.23 2.39 .29 7/6 Crest
h 64 12.00 2.68 .33
c 68 7.74 2.30 .28 7/6 Buccal
h 62 8.09 1.89 .24
c 63 7.44 1.78 .22 7/6 Palatal
h 54 7.94 2.32 .32
c 68 12.46 3.50 .42 6/5 Crest
h 63 12.99 3.35 .42
c 67 6.65 1.79 .22 6/5 Buccal
h 62 6.72 1.95 .25
c 53 7.16 1.78 .25 6/5 Palatal
h 47 7.21 2.44 .36
45
Figure 13: Means - Caucasians vs Hispanics
0
2
4
6
8
10
12
14
Millimeters
Means: C aucas ians v s His panics
Ca u c a s ia n 10.23 7.74 7.44 12.46 6.65 7.16
H is panic 12 8.09 7.94 12.99 6.72 7.21
7/ 6 CRE S T 7/ 6 B UCCAL 7/ 6 P AL AT AL 6/ 5 CRE S T 6/ 5 BUC CAL 6/ 5 P AL AT A L
46
Table 11 : Independent Samples Test, Caucasian vs Hispanic
t-test for Equality of Means
Site Measured t df Sig.(2-tailed) Mean Difference
-4.01 130 .00 (**) -1.77
-.95 128 .34 -.35
-1.32 115 .19 -.50
-.87 129 .38 -.52
-.22 127 .83 -.07
-.11 98 .91 -.05
7/6 Crest
7/6 Buccal
7/6 Palatal
6/5 Crest
6/5 Buccal
6/5 Palatal
47
Comparison of Sites Measured: Males versus Females
Table 12 and figure 14 describe the means for the gender groups analyzed in
this study. The sample was combined to evaluate any differences between males and
females. The results of the independent t-test (table 13) demonstrate very little
difference between the males and females of this sample. However, a significant
difference was found for the 7/6 buccal measurement (P = 0.026). These results
indicate that for this sample, little difference exists between males and females with
regard to the measurements compared.
Table 12 : Group Statistics, Males vs Females
Site
Measured
Sex
M/F N Mean Std. Deviation
Std. Error
Mean
m 64 10.81 2.59 .32 7/6 Crest
f 68 11.35 2.75 .33
m 63 8.33 1.89 .24 7/6 Buccal
f 67 7.51 2.24 .27
m 56 7.37 1.73 .23 7/6 Palatal
f 61 7.95 2.29 .29
m 63 13.00 3.42 .43 6/5 Crest
f 68 12.45 3.44 .42
m 63 6.86 1.85 .23 6/5 Buccal
f 66 6.51 1.88 .23
m 45 7.24 1.80 .27 6/5 Palatal
f 55 7.14 2.35 .32
48
Figure 14: Means - Males vs Females
0
2
4
6
8
10
12
14
Millimeters
Means : Males vs F emales
Males 10.81 8.33 7.37 13 6.86 7.24
Fe m ales 11.35 7.51 7.95 12.45 6.51 7.14
7/ 6 C R E S T 7/ 6 B UC C AL 7/ 6 PAL ATAL 6/ 5 C R E S T 6/ 5 B UC C AL 6/ 5 PAL ATAL
49
Table 13: Independent Samples Test, Males vs Females
t-test for Equality of Means
Site Measured t df Sig.(2-tailed) Mean Diff
7/6 Crest -1.16 130 .25 -.54
7/6 Buccal 2.25 128 .03 (*) .82
7/6 Palatal -1.53 115 .13 -.58
6/5 Crest .91 129 .36 .55
6/5 Buccal 1.06 127 .29 .35
6/5 Palatal .24 98 .81 .10
50
Comparison of Sites Measured: 7/6 versus 6/5
Since the previous analyses have demonstrated little difference between right
and left sides measured, Hispanics and Caucasians, as well as between male and
females, the samples were combined and compared for differences solely between
the 7/6 and 6/5 sites. Table 14 and image 15 display and compare the means for
these groups. Statistical analysis (table 15) showed that there were significant
differences between 7/6 and 6/5 for two of the three measurements. Specifically,
there were very highly significant differences (P < 0.001) for both crestal and buccal
measurements, while no significance was noted between 7/6 and 6/5 for palatal
measurements (P = 0.08). These differences indicate that the 6/5 site has
significantly more clearance from the floor of the maxillary sinus but that the sinus is
closer to the buccal cortical plate.
Table 14 : Group Statistics, 7/6 vs 6/5
Measurement Site N Mean Std. Deviation
Std. Error
Mean
Crest 7/6 132 11.09 2.67 .23
6/5 131 12.72 3.43 .30
Buccal 7/6 130 7.91 2.11 .19
6/5 129 6.68 1.86 .16
Palatal 7/6 117 7.67 2.05 .19
6/5 100 7.19 2.11 .211
51
Figure 15: Means – 7/6 vs 6/5
0
2
4
6
8
10
12
14
Millimeters
Means : 7/ 6 VS 6/ 5
'7/ 6' 11.09 7.91 7.67
'6/ 5' 12.72 6.68 7.19
CR E S T B U CCA L P A L A T A L
52
Table 15 : Independent Samples Test,7/6 vs 6/5
t-test for Equality of Means
Site Measured t df
Sig.(2-
tailed) Mean Diff
Crest
-4.29 261 .00 (**) -1.63
Buccal
4.95 257 .00 (**) 1.22
Palatal
1.71 215 .09 .48
53
Chapter 6: DISCUSSION
As the clinical acceptance and use of mini screw TADs widens, knowing
where they can safely and effectively be placed is an important question. This study
addressed the relationship between the maxillary sinus and commonly recommended
mini screw placement locations in the posterior maxilla, specifically in Caucasians
and Hispanics. Further analysis was done to determine if any significant differences
exist between sites selected for placement, between Caucasians and Hispanics, or
between males and females. CBCT images were formatted to allow measurement of
the distance from the floor of the maxillary sinus to the alveolar crest, buccal plate
and palatal plate in the left and right interradicular areas between the first and second
maxillary molars and between the maxillary first molar and second premolar. This
study resulted in significant findings that will help clinicians better avoid sinus
damage during screw placement in the course of orthodontic treatment.
Differences Between Contralateral Sites
While it is generally accepted that some degree of anatomic asymmetry is
widely displayed in the average or normal human craniofacial complex, this study
failed to find a generalized significant difference between the left and right sites
measured. This would support the findings of Fernandes
61
who found no significant
difference between left and right maxillary sinus volume or linear measurements in
his sample of 53 dried skulls. The only significant difference was found at the palatal
54
measurement between the first molar and second premolar. It should also be noted
that this particular measurement location was highly variable with many subjects not
yielding an actual measurement. The palatal measurements were the only
measurements which could fail to provide an actual measurement and in fact resulted
in a much smaller actual sample size than the other sites (figure 16). In light of this
finding, left and right measurements were combined in an effort to bolster the sample
size for all further analyses.
Figure 16: Location of maxillary sinus above level of
palatal roof. Palatal measurement unable to be made
in this situation.
Ethnic Differences
Significant differences were similarly noted between Hispanics and
Caucasians, at the alveolar crest to maxillary sinus distance at the second and first
molar location. These findings support the ethnic dimorphism reported in the
55
Fernandes
61,63
and Shea
62
studies, however, it should be noted that their studies
focused primarily on sinus volume differences. The Shea
62
study also utilized a
significantly larger sample size (N = 362), while the Fernandes
61,63
studies utilized a
similar sized sample (N = 53). Stronger differences were noted in their findings and
this may indicate a difference between the extent of sinus pneumatization and sinus
volume with regard to their correlation to ethnicity. While clear ethnic dimorphisms
have been well established between Hispanics and Caucasians, another possible
explanation may simply be that those differences are simply not as pronounced as
those between African Zulus, Eskimos, and European Caucasians as studied by
Fernandes and Shae; however both of these possibilities would require further
investigation to substantiate.
Gender Differences
Significant gender differences were found, specifically at the buccal
measurement of the first molar/second premolar area (P < 0.05). This finding
supports the findings of Fernandes
63
and Teke
60
whose studies established significant
gender differences with regard to maxillary sinus volume. A third study by Kim et
al
57
, also noted gender differences in sinus volume, but did not report the
significance of those findings. They found that for all measurements, male sinus
volume was greater than those of the females in their sample. This study’s findings
may also support those of Ariji et al
55
. Their study found a negative correlation
56
between sinus floor height and sinus volume, noting that the sinus floor rose with a
decrease in zygomatic buttress distance, and body height and weight. Interestingly,
many of the measurements in this study were larger for females than for males.
Site Differences
The highly significant differences (P < 0.001) found between the 7/6 site and
the 6/5 site suggest that the palatal of the 6/5 site generally provides more clearance
from possible interference with the maxillary sinus. This finding is supported by the
previous findings of Ishii
6
, Poggio
7
, and Carano
2
, who also specifically recommend
this site as the safest in the posterior maxillary alveolus. If a buccal placement site
is required, the maxillary sinus at the 7/6 site was significantly closer to the alveolar
ridge than the 6/5 site, however, the sinus was farther from the buccal plate at the 7/6
site. This study further supports Poggio’s
7
assertion that screw insertion above 8-
11mm from the alveolar crest should be avoided due to possible sinus damage. Ishii
6
was a bit more conservative, recommending placement no higher than 6-8mm from
the alveolar crest and advised against buccal placement altogether. Carano
2
also
advised against placement above 8mm, but doesn’t reject buccal placement.
Clinical Implications
In spite of the lack of significant differences between Hispanics and
Caucasians, and males and females in this sample, this study provides valuable
57
information to the clinician with regard to confirming previous studies regarding
preferable sites for mini screw placement. Utilizing high resolution CBCT scanning,
this study has helped to further characterize the alveolar ridge/maxillary sinus
relationship, specifically the wide range of individual variation that should lead the
prudent practitioner to carefully evaluate any potential placement site in the posterior
maxilla.
58
Chapter 7: ASSUMPTIONS
There were several assumptions made for this study. The patient pool at
USC is representative of the general population of Southern California. Last names
and photographs were used to assign patients to their respective sample groups. All
measurements were accurate and reproducible. The distortion and magnification of
NewTom® images is statistically insignificant.
59
Chapter 8: LIMITATIONS
There were several potential limitations to this study. There were a limited
number of NewTom® records in department archives that met study inclusion
criteria. The study only used orthodontic patients as opposed to the general
population. Measurements were subjected to human error. Finally, the criteria for
assignment into the separate ethnic groups are difficult to define elements of
personal history, surname and appearance are good indicators, however they are not
definitive.
60
Chapter 9: SUMMARY
Several previous studies have found both ethnic and gender differences with
regard to maxillary sinus volume. This study sought to find if those same differences
could be found when looking at the relationship of the maxillary sinus to the
posterior maxillary alveolus. This type of information is helpful to the orthodontic
practitioner in potentially helping to avoid damage to the maxillary sinus during mini
screw placement in the posterior maxillary alveolus. This study was able to
complement the significant results of the maxillary sinus volume studies, while
differences between gender, ethnic, and commonly chosen placement sites were
validated and support previous placement studies. The placement sites determined
“safest” in this study would potentially limit the likelihood of damage to the
maxillary sinus; however, in light of the wide range of variation possible in the shape
and extent of the maxillary sinus as well as the ethnic and gender differences
documented, it is recommended that all proposed TAD insertion sites in the posterior
maxillary alveolus undergo careful individualized assessment.
61
Chapter 10: CONCLUSIONS
1. Comparisons between contralateral sites, Caucasians and Hispanics, as well
as males and females demonstrated limited significant differences with regard
to the distance of maxillary sinus floor and the alveolar crest, buccal plate,
and palatal plate.
2. Comparisons between the 7/6 and 6/5 interradicular sites indicate significant
differences do exist with regard to the distance of maxillary sinus floor and
the alveolar crest and buccal plate.
3. The palatal area of the 6/5 site was considered the safest area for placement,
followed by buccal of 6/5, palatal of 7/6, and buccal of 7/6.
4. There is a wide range of individual variation with regard to the distance of
maxillary sinus floor and the alveolar crest, buccal plate, and palatal plate.
62
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Asset Metadata
Creator
Pambrun, Jason Michael
(author)
Core Title
A cone beam-CT evaluation of the proximity of the maxillary sinus to commonly used TAD sites
School
School of Dentistry
Degree
Master of Science
Degree Program
Craniofacial Biology
Publication Date
04/10/2007
Defense Date
03/12/2007
Publisher
University of Southern California
(original),
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(digital)
Tag
cone beam-CT,OAI-PMH Harvest
Language
English
Advisor
Sameshima, Glenn T. (
committee chair
), [illegible], James (
committee member
), Reyes, [illegible] (
committee member
)
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