Download cortical bone thickness of black and white

CORTICAL BONE THICKNESS OF BLACK AND
WHITE AMERICAN ADOLESCENTS
Ningning Zhang D.D.S.
An Abstract Presented to the Graduate Faculty of
Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2012
ABSTRACT
Purpose:
To assess the differences in maxillary and
mandibular cortical bone thickness between black and white
American adolescents using CBCT images. Methods:
Pre-
treatment cone-beam computed tomography (CBCT) images of 69
patients, including 34 black adolescents (17 females; 17
males) and 35 white adolescents (18 females; 17 males) were
studied. The Digital Imaging and Communication in Medicine
(DICOM) multifiles of each CBCT scan were imported into the
Dolpin Imaging 11 3D software. Standardized orientations
were used to measure the buccal and lingual cortical bone
thickness in both maxilla and mandible at 16 interradicular
sites. Total alveolar ridge thickness and medullary space
thickness were also measured at the same interradicular
sites. Results: Two-way analysis of variants showed (P‹0.05)
significant group differences at 3 of the 16 sites, with
black adolescents having thicker cortical bone. Alveolar
ridge thicknesses were significantly greater in black
adolescents, except at the distal of the first molar in the
mandible. Medullary thickness was also significantly
greater in black adolescents, except between the first and
second mandibular premolars. No statistically significant
gender differences in cortical thickness were found. Males
1
had significantly thicker alveolar ridge and medullary
space than females except for distal to the first molar in
the mandible. Conclusion: Black adolescents have thicker
cortical bone than whites but the difference is small.
There is no significant sex difference in cortical bone
thickness. There is a significant difference in alveolar
ridge thickness between blacks and whites. The difference
in alveolar ridge thickness is due to the difference in
medullary space.
2
CORTICAL BONE THICKNESS OF BLACK AND
WHITE AMERICAN ADOLESCENTS
Ningning Zhang D.D.S.
A Thesis Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2012
3
COMMITTEE IN CHARGE OF CANDIDACY:
Adjunct Professor Peter H. Buschang
Chairperson and Advisor
Professor Rolf G. Behrents
Associate Professor Ki Beom Kim
Associate Clinical Professor Donald R. Oliver
i
DEDICATION
This thesis is dedicated to my parents, my husband and
my teachers who have supported and guided me throughout my
life to achieve my dreams.
ii
ACKNOWLEDGEMENTS
The author would like to acknowledge:
Dr. Peter Buschang for the tremendous dedication and
time he put into this project, guiding me through every
step of the thesis process. My gratitude is beyond words;
Dr. Rolf Behrents for providing advice and direction
not only throughout the thesis process but throughout my
entire orthodontic education;
Dr. Donald Oliver and Dr. Ki Beom Kim for guidance
with this thesis and teaching me their knowledge during my
orthodontic education;
Dr. Derid Ure and Dr. Joe Mayes for use of their
records in this study.
iii
TABLE OF CONTENTS
List of Tables . . . . . . . . . . . . . . . . . . . . . .v
List of Figures . . . . . . . . . . . . . . . . . . . . .vi
CHAPTER 1: REVIEW OF THE LITERATURE . . . . . . . . . . . 1
Overview. . . . . . . . . . . . . . . . . .1
Bone development and adaptation to loads. .4
Recent studies on source of variation in
cortical bone thickness . . . . . . . . . 11
Differences between American white and
black population . . . . . . . . . . . . .21
Clinical implications. . . . . . . . . . .29
Summary and statement of thesis. . . . . .31
References . . . . . . . . . . . . . . . .33
CHAPTER 2: JOURNAL ARTICLE . . . . . . . . . . . . . . . 39
Abstract . . . . . . . . . . . . . . . . .39
Introduction . . . . . . . . . . . . . . .40
Materials and methods. . . . . . . . . . .42
Sample size and composition . . . . .42
Method of analysis . . . . . . . . . 43
Statistical analysis . . . . . . . . 47
Results. . . . . . . . . . . . . . . . . .47
Comparisons between black and
white adolescents . . . . . . . . . .47
Comparisons between female and
male adolescents . . . . . . . . . .48
Inter- and intra-arch comparisons. . 48
Discussion . . . . . . . . . . . . . . . .57
Cortical bones . . . . . . . . . . . 57
Alveolar ridge and medullary
thickness . . . . . . . . . . . . . .59
Conclusions. . . . . . . . . . . . . . . .61
References . . . . . . . . . . . . . . . .62
Appendix . . . . . . . . . . . . . . . . . . . . . . . . 67
Vita Auctoris . . . . . . . . . . . . . . . . . . . . . .71
iv
List of Tables
Table 1:
Summary of articles. . . . . . . . . . . .12
Table 2:
Difference in cortical bone thickness in
posterior region . . . . . . . . . . . . .14
Table 3:
Values for appendicular skeletal muscle and
regional bone mineral for black and white
females matched for age, height, weight and
menstrual status. . . . . . . . . . . . . 23
Table 4:
Body composition variables for the core
group by gender and race. . . . . . . . . 24
Table 5:
Bone mineral density in the core group by
gender and race . . . . . . . . . . . . . 25
Table 6:
Summary of the mean difference in cortical
bone thickness at the mandibular left 6mm
site. . . . . . . . . . . . . . . . . . . 28
Table 7:
Summary of the mean difference in cortical
bone thickness at the mandibular left 9mm
site. . . . . . . . . . . . . . . . . . . 28
Table 8:
Maxillary and mandibular cortical bone
thickness (mm) in black and white American
adolescents. . . . . . . . . . . . . . . .49
Table 9:
Maxillary and mandibular alveolar ridge and
medullary thickness (mm) in black and white
American adolescents. . . . . . . . . . . 50
Table 10:
Maxillary and mandibular cortical bone
thickness (mm) in female and male American
adolescents. . . . . . . . . . . . . . . .51
Table 11:
Maxillary and mandibular alveolar ridge and
medullary thickness (mm) in black and white
American adolescents. . . . . . . . . . . 52
v
List of Figures
Figure 1:
A diagram illustrating the relationship of
strains and adaptive responses . . . . . . 8
Figure 2:
Cortical bone thickness in sections mesial
and distal to the first molar. . . . . . .15
Figure 3A:
Means and ranges of cortical bone thickness
in various areas. . . . . . . . . . . . . 17
Figure 3B:
Means and ranges of cortical bone thickness
in various areas. . . . . . . . . . . . . 18
Figure 4:
Maxillary and mandibular cortical bone
thicknesses of hypodivergent and
hyperdivergent young adults measured 5mm
from the crest of the alveolar ridge . . .20
Figure 5:
Mean PMI of men and women by age group and
racial group . . . . . . . . . . . . . . .26
Figure 6A:
Axial slice showing the sagittal plane runs
through all posterior teeth on the side of
measurement. . . . . . . . . . . . . . . .45
Figure 6B:
Sagittal CBCT slice showing the axial plane
orientated parallel to the alveolar ridge
crest . . . . . . . . . . . . . . . . . . 45
Figure 6C:
Sagittal CBCT slice showing the axial plane
positioned 5mm from the crest of the
alveolar ridge. . . . . . . . . . . . . . 46
Figure 6D:
Axial CBCT slice showing buccal and lingual
cortical bone thickness measured. Alveolar
ridge thickness was measured at the same
level. . . . . . . . . . . . . . . . . . .46
Figure 7:
Means of buccal cortical bone thickness in
the maxilla. . . . . . . . . . . . . . . .53
Figure 8:
Means of lingual cortical bone thickness in
the maxilla. . . . . . . . . . . . . . . .53
Figure 9:
Means of buccal cortical bone thickness in
the mandible. . . . . . . . . . . . . . . 54
vi
Figure 10:
Means of lingual cortical bone thickness in
the mandible. . . . . . . . . . . . . . . 54
Figure 11:
Means of alveolar ridge thickness in the
maxilla. . . . . . . . . . . . . . . . . .55
Figure 12:
Means of medullary space thickness in the
maxilla. . . . . . . . . . . . . . . . . .55
Figure 13:
Means of alveolar ridge thickness in the
mandible. . . . . . . . . . . . . . . . . 56
Figure 14:
Means of medullary space thickness in the
mandible. . . . . . . . . . . . . . . . . 56
Figure 15:
Means of buccal cortical bone thickness in
the maxilla. . . . . . . . . . . . . . . .67
Figure 16:
Means of lingual cortical bone thickness in
the maxilla. . . . . . . . . . . . . . . .67
Figure 17:
Means of buccal cortical bone thickness in
the mandible. . . . . . . . . . . . . . . 68
Figure 18:
Means of lingual cortical bone thickness in
the mandible. . . . . . . . . . . . . . . 68
Figure 19:
Means of alveolar ridge thickness in the
maxilla. . . . . . . . . . . . . . . . . .69
Figure 20:
Means of medullary space thickness in the
maxilla. . . . . . . . . . . . . . . . . .69
Figure 21:
Means of alveolar ridge thickness in the
mandible. . . . . . . . . . . . . . . . . 70
Figure 22:
Means of medullary space thickness in the
mandible. . . . . . . . . . . . . . . . . 70
vii
CHAPTER 1: REVIEW OF THE LITERAURE
Overview
Bone is one of the most important biological tissues
affecting orthodontic treatment. In clinical practice,
mini-screw implants (MSIs) have been widely used for
anchorage in orthodontics. Their success depends on the
length and type of the MSI used, as well as the cortical
bone available at the placement site. It has been shown
that the quality and quantity of cortical bone is better at
predicting the stability of MSI than the length and type of
MSI.1 Understanding the variations in maxillary and
mandibular cortical bone may be beneficial for placing MSIs.
One potentially important source of variation in cortical
thickness is the ethnicity of the patient.
It is widely accepted that bone adapts to the
mechanical loads applied to it. The Frost mechanostat
theory outlines the process of bony adaptation by
osteoblasts and osteoclasts.2,3 Bone adaptation to strains
can also be explained by the fluid flow theory, which
states that osteocytes are excited by mechanical loading
influenced bone fluid to induce apposition while the
reduction of canalicular fluid flow causes apoptosis of
osteocytes.4 Applying these theories to the craniofacial
1
region, the cortical bone thickness might be expected to be
related to the stresses and strains applied to the maxilla
and mandible. For example, biting forces generated by the
muscles of mastication might be expected to influence the
modeling of the maxilla and mandible. The specific modeling
changes that occur depend on craniofacial morphology, age,
gender and presence of dental and temporomandibular joint
pathology.5 For example, adults have thicker cortical bone
than children,6 and they also have stronger biting forces.
Hypodivergent patients have thicker cortical bone than
hyperdivergent patients7,8 and they also have stronger
muscle of mastication.9,10 In contrast the gender difference
in cortical thickness has been found to be minimal6,7,11
while maximum bite forces are higher in males.5
Many studies have compared post cranial bone of black
and white populations.12–15 They all show that blacks have
thicker bones at all skeletal sites than their white
counterparts. Relatively few studies have been performed
that evaluate black and white differences in the
craniofacial region. Benson et al16 developed the panoramic
mandibular index (PMI) to relate cortical bone thickness
with the relative constant distance between mental foramen
and the inferior mandibular boarder measured on panoramic
2
radiograph. They found that black Americans have thicker
cortical bone than their white counterparts in both the
maxilla and the mandible, but the differences were not
significant.
A recent study by Humphries17 studied the cortical
bone thickness between second premolars and first molars
from cone-beam computed tomography (CBCT) slices at four
vertical sites. The results indicated that cortical bone
was thicker in blacks than whites at all mandibular sites
except for mandibular left 3mm away from the alveolar crest.
However, the differences between blacks and whites were not
statistically significant. The author suspected that the
distortion in the CBCTs may have masked the ethnic
differences.
The purpose of the present study was to measure the
thickness of cortical bone in the posterior regions of the
maxilla and mandible of black and white American
adolescents. The measurements were taken from pre-Phase II
treatment CBCT slices. The subjects were classified by
ethnicity and compared to determine whether there were
ethnic differences in alveolar cortical bone morphology. If
differences could be demonstrated between black and white
3
American adolescents, the patient’s ethnicity will have to
be considered when using MSIs as a modality of treatment.
The following will start with a review of the
literature pertaining to bone development and its
adaptation to function because mechanical loads produce
stress and strains in the bone affecting the modeling and
remodeling process. The masticatory force is the major load
to the craniofacial region. The second section will review
studies on how variables, such as age, gender, vertical
facial pattern, affect cortical bone thickness. The last
section will discuss the known post-craniofacial and
craniofacial bone differences in whites and blacks.
Bone’s development and adaptation to loads
Bone is an important tissue. It functions as support
and protection for the body and organs, while producing red
and white blood cells, and storing minerals. Bone is also a
specialized matrix composed of collagen and ground
substance. Osteoblasts form bone and partially mineralize
it. They are formed by perivascular connective tissue cells
surrounding venules and capillaries. Osteoclasts resorb
bone by a lytic process involving acid and enzymes. They
4
are formed by circulating preosteoclasts produced in bone
marrow.
Bones grow and adapt by surface apposition and
resorption.18
Bone can be classified as woven, lamellar, composite
and bundle bone according to its histology.18 Woven bone
varies considerably in structure. It serves a critical role
in wound healing and provides initial stability for
fractures. Lamellar bone is strong, highly organized and
well mineralized. It forms the majority of the adult human
skeleton. In orthodontic treatment, mature lamellar bone is
formed approximately one year after tooth movement.18 Both
compact and trabecular bone are lamellar bone. Composite
bone is formed by the deposition of lamellar within the
woven bone lattice. It is generally high-quality and loadbearing. It eventually is remodeled into secondary osteons.
Bundle bone is a functional adaption of lamellar bone with
attached ligaments and tendons.
Alveolar bone holds teeth for mastication and
withstands the masticatory force. It consists of buccal and
lingual cortical plates and medullary space in between.
Cortical bone consists of compact bones, made of osteons.
Each osteon has a central Haversian canal and peripheral
concentric layers of lamellae. Medullary bone is the
5
central cavity of a bone where bone marrow exists. It is
composed of trabecular bone.
It is generally accepted that bone adapts to
mechanical loads. Bone adapts through changes in bone mass,
geometric distribution, matrix organization and the
collagen orientation of the lamella. The two distinct
mechanisms in an adaptation process are modeling and
remodeling.18 The process is influenced by genetics,
biomechanical environment and force application. The
modeling and remodeling processes rely on the actions of
osteoblasts and osteoclasts. In cortical bone, they form a
unit called basic multicellular unit (BMU). The BMU forms a
cylindrical canal in cortical bone. Osteoclasts form a
circular tunnel in the loading direction while osteoblasts
follow them forming secondary osteons.19 BMUs provide the
main postnatal modifications affecting bone strength. When
the remodeling process starts, osteoclasts start to attach
to the bone tissue matrix and acidfy the microenvironment
dissolving the organic and inorganic matrices of the bone.
Osteoblasts then appear at the same surface depositing
osteoids and mineralizing them to form new bones.20 Global
modeling increases bone mass and strength. Global
remodeling by BMUs turns over bones in either the
6
conservation or disuse modes. In the conservation mode
resorption equals formation. In the disuse mode, the
remodeling BMUs make less bone than they resorb causing a
net loss of bone. Remodeling also repairs bone microdamage
by removing and replacing the damaged bone with new bone.21
The detailed mechanism by which the mechanical forces
influencing bone modeling and remodeling is a very complex
process and yet to be fully discovered. One widely accepted
theory is Frost’s mechanostat hypothesis. Frost stated that
there is a minimum effective strain (MES). Any external
mechanical load must exceed the MES to elicit an adaptive
response in bone. There is a range of MES strain values
that will not evoke any response. Strains above the range
will have a positive adaptive response causing bone gain
while strains below the MES range will have a negative
adaptive response, causing bone loss. The modelingdependent bone gain happens at strain values above 1500
microstrains, while the remodeling-dependent bone loss
occurs at strain values below 100 microstrains.2,3,21
Therefore modeling and remodeling are not stimulated at the
same time on the same surface (Figure 1). The mechanical
factors dominate the control of bone growth and development.
Nonmechanical agents could influence the mechanical factor
7
and thus influence the bone modeling and remodeling process
but would not replace the mechanical factors.21
Figure 1. A diagram illustrating the relationship of strains and
adaptive responses. MESr: minimum effective strain range at and above
which BMUs begin decreasing towards normal. MESm: minimum effective
strain range at and above which mechanically controlled lamellar
modeling drifts begins. MESp: minimum effective strain range above
which woven bone drifts turn on and suppresses local lamellar bone
drifts (Adapted from Jee21)
An alternative theory, the fluid flow theory describes
the cellular mechanisms by which bone adapts to mechanical
loads. The theory states that when mechanical load was
applied to the bone, strains were produced.4,19,22 The strains
alter the fluid flow in the cannaliculi in the bone
connecting osteocytes. The fluid produces shear stress on
the membranes of osteocytes.4 Osteocytes were activated
producing anabolic paracine factors, recruiting
8
osteoblasts.23 When fluid flow in the cannaliculi is reduced,
osteoclasts resorb bone.22,24 In vivo studies were done to
test this theory.
Tan et al24 studied the effect of
pulsating fluid flow on TNF-α induced apoptosis in chicken
osteocytes, osteoblasts and periosteal fibroblasts. TNF-α
is a pro-inflammatory cytokine with apoptotic potency. They
found that when fluid was static, TNF-α increased apoptosis
by more than two-folds in osteocytes and osteoblasts. One
hour of pulsating flow inhibited TNF-α induced apoptosis.
Owan et al25 studied the fluid forces and the expression of
osteopontin (OPN) mRNA expression. The expression of OPN
was used to measure the anabolic response of MC3TC-E1 cells,
mouse osteoblast-like cells. They found that high magnitude
fluid forces significantly increased OPN message level. It
indicated that fluid forces influence OPN expression in
osteoblasts and the fluid forces within the bone matrix may
play an important role in bone’s modeling response to
mechanical loading.
Examples of bone adapting to function can be found in
daily life such as tennis players with much stronger
racquet-holding arm than the other arm. Studies have shown
a positive correlation between the size the masseter and
medial pterygoid muscles and the remodeling process of the
9
bone at the gonial angle. When masseters are hypertrophied,
it causes the gonial angles to be hypertrophied as well26.
The atrophied or absence of the temporal muscle also
results in a smaller and modified coronoid process.27
Murray28 stated that bones, when separated from
function during growth, developed the general features of
that particular bone but the specific morphological details
were missing. Genetics determines the formation and general
morphology of a bone. However, the combination of genetics
and its mechanical environment can make the same bone
differ from each other.
Tsai29 et al studied the mandible after botulinum
neurotoxin type A (BoTx/A) injections into the temporalis
and masseter muscles of growing rats to induce masticatory
hypoactivity. One-way analysis of variance was used to
analyze muscle volume and bone mineral density (BMD). They
found reductions in cortical bone thickness and BMD in the
skull and mandible of rats injected with BoTx/A. The
volumes of the temporalis and masseter muscles injected
with BoTx/A were also smaller.
These findings are consistent with the notion that
both direct and indirect loadings, such as tension or
bending from the function of muscles, contribute to
10
alterations in skeletal development.30 With respect to the
craniofacial complex, weaker muscles might be expected to
produce weaker bite forces, leading to smaller functional
effects on the alveolar bone of maxilla and mandible,
causing less bony adaptation.
On the other hand it is
reasonable to propose that individuals with larger
mechanical load to the jaws and stronger masticatory force
will have thicker mandible and cortical bone.
Recent studies on sources of variations in cortical bone
thickness
Studies6–8,11,31,32 (Table 1) have been performed to
measure differences in maxillary and mandibular cortical
bone thickness.
Between individuals, age, sex, and vertical growth
patterns have been studied. It has been shown that adults
have thicker cortical bone than children.6 Such differences
can be explained by the fact that bone adapts to function.
During growth, individuals grow in body size, muscles size
and occlusal force.33–36 Higher occlusal forces in adults
cause alveolar bone to adapt, inducing formation of thicker
cortical bone. Hypodivergent individuals have also been
11
shown to have higher masticatory forces than hyperdivergent
individuals.9 Hypodivergent patients have shown to have
thicker cortical bone than hyperdivergent patients.7,8
However, there are no differences between males and females
in cortical bone thickness.
Within the same individual, no side differences in
cortical thickness have also been found.31,32 The posterior
aspect of the mandible has been shown to have thicker
cortical bone than the anterior aspect.6,11 Mandibular
cortical bone has also been shown to be thicker than
maxillary cortical bone.6,8,11
Table 1 Summary of articles comparing cortical bone thickness 1)
between individuals 2) within an individual
Adult vs.
adolescent
Male vs. Female
Hypodivergent vs.
hyperdivergent
Deguchi et
al31
no age
differences
no difference
―
Ono et al32
―
thinner in female in
the maxilla mesial to
the first molar
―
Farnsworth
et al6
thicker in
adults
no difference
―
Swasty et
al7
―
Wider mandible in
male, but no
difference in cortex
thicker in
hypodivergent
patients
Horner et
al8
―
―
thicker in
hypodivergent
patients
Variables
12
Table 1 Continued
Right vs. Left
Maxilla vs.
Mandible
Anterior vs.
Posterior
Mandible
―
―
Posterior is
thicker
Deguchi et
al31
no differences
Thicker in
mandible
―
Ono et al32
no differences
Thicker in
mandible
―
Farnsworth
et al6
―
Thicker in
mandible
thicker in the
posterior region
Horner et al8
―
Thicker in
mandible
thicker in the
posterior region
Variables
Carter et
al11
Carter et al11 studied human cadaver hemimandibles that
were subjected to sagittal split ramus osteotomies. They
found a difference between anterior and posterior mandible
in the cortical thickness in the proximal segment. The
areas of the mandible closest to the sagittal split, the
posterior segments were the areas exhibiting the thickest
cortical bone.
Deguchi et al31 quantitatively evaluated cortical bone
thickness in various common mini-screw implant (MSI)
placement locations in the maxilla and the mandible using
three-dimensional computed tomographic images reconstructed
from 10 adults. Cortical bone thicknesses were measured in
the buccal and lingual regions mesial and distal to the
first molar, distal to the second molar and in the
13
premaxillary region at two different vertical levels. It
was found that there were no significant differences in
either cortical bone thickness or root proximity due to sex,
age, or side. Significantly less cortical bone was found in
the maxillary buccal region at the occlusal level distal to
the second molar, than in other areas in the maxilla.
Significantly more cortical bone was observed on the
lingual side of the second molar compared with the buccal
side. In the mandible, mesial and distal to the second
molar, significantly more cortical bone was observed
compared with the maxilla. No significant differences
between vertical locations were noted within either the
mandible or the maxilla (Table 2). However, there was a
significant difference in cortical thickness between the
mandible and maxilla at the same vertical heights. There
was significantly thicker cortical bone in the mandibular
molar area than the same area of the maxilla.
Table 2.Difference in cortical bone thickness in posterior region
(Aapted from Deguchi et al31)
5-6 (O)
Maxilla
Mean
SD
5-6 (A)
Mean
SD
6-7 (O)
Mean
SD
6-7 (A)
Mean
SD
7 (O)
Mean
SD
Buccal
1.8
0.6
1.6
0.6
1.5
0.5
1.6
0.5
1.3
0.5
Lingual
1.7
0.9
—
—
1.7
0.7
—
—
1.7
0.6
Mandible
Buccal
1.9
0.6
1.8
0.5
2.0
0.6
1.8
0.5
1.9
0.7
Significant difference between 5-6, 6-7 and lingual (P‹0.05)
Significant difference between buccal (P‹0.05)
Significant difference between jaws (P‹0.05)
5 Second premolar; 6 first molar; 7 second moalr; O,occlusal level;A,
apical level
14
Ono et al32 evaluated cortical bone thickness in the
buccal posterior region mesial and distal to the first
molar in 43 patients. Computed tomography was used to
evaluate the sites. The average cortical bone thicknesses
ranged from 1.1 to 2.1 mm in the maxilla and 1.6 to 3.0 mm
in the mandible. The mandibular cortical bone sites were
significantly thicker than the corresponding maxillary
cortical bone sites. The further the distance away from the
alveolar crest, the thicker the cortical bone tended to be.
Cortical bone thickness did not differ significantly
between the right and left sides. However, it was thinner
in females than males in the region of attached gingival in
the maxilla mesial to the first molar (Figure 2).
Figure 2. Cortical bone thickness in sections mesial and distal to the
first molar; 5-6: mesial to the first molar; 6-7: distal to the first
molar; *: significant difference (P‹0.05)between 5-6 and 6-7 (Adapted
from Ono et al32)
15
Farnsworth et al6 studied age, sex, and regional
differences in cortical bone thickness at commonly used
maxillary and mandibular MSI placement sites. Cone-beam
computed tomography (CBCT) slices of 26 adolescents and 26
adults were evaluated. They found that there was no
significant difference in cortical bone thickness between
the sexes, but that there were significant differences
between adolescents and adults. Adult cortices were
significantly thicker in all areas except the
infrazygomatic crest, the mandibular buccal first molarsecond molar site, and the posterior palate site (Figure 3).
It was also found that there were differences in cortical
bone thickness between and within regions of the jaw.
Cortical bone was thicker in the posterior than the
anterior regions of both the maxilla and mandible. Thicker
cortical bone was also present in the mandible than in the
maxilla.
16
Means and ranges of cortical bone
thickness (mm)
Mandibular Buccal
3
2.5
2
1.5
Adolescents
1
Adults
0.5
0
2-3
4-5
5-6
6-7
Site
Means and ranges of cortical bone thickness
(mm)
Maxillary Buccal
2
1.8
1.6
1.4
1.2
1
Adolescents
0.8
Adults
0.6
0.4
0.2
0
2-3
4-5
5-6
6-7
Site
Figure 3A Means and ranges of cortical bone thickness in various areas
(Adapted from Farsworth6 et al)
17
Means and ranges of cortical bone
thickness (mm)
Maxillary Lingual
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Adolescents
Adults
2-3
4-5
5-6
6-7
Site
Means and ranges of cortical bone thickness
(mm)
Palatal and Infrazygomatic Crest
2.5
2
1.5
Adolescents
1
Adults
0.5
0
3 mm
6 mm
9 mm
IZ
Palatal Site
Figure 3B Means and ranges of cortical bone thickness in various areas
(Adapted from Farsworth6 et al)
Swasty et al7 studied CBCT slices to determine the
differences in cortical plate thicknesses in patients with
different vertical facial dimensions. Both the facial
height index (ratio of posterior facial height to anterior
facial height) and mandibular plane angle were used to
18
categorize patients. The long-face group was found to have
slightly thinner cortical bone than the other two groups.
The difference was statistically significant at some sites
in the mandible. The long-face group also had somewhat
thinner widths in the upper third of the mandible than the
other two facial groups. The mandible was wider and taller
in males than females. There were no statistically
significant differences in cortical plate thickness between
males and females.
Horner et al8 assessed differences in maxillary and
mandibular cortical bone thickness between hyperdivergent
and hypodivergent young adults. Pre-treatment CBCT from 57
patients were studied. Hypodivergent subjects were found to
have significantly thicker buccal cortices than the
hyperdivergent subjects except for the bone between the
maxillary first molars and second premolars, and the bone
between mandibular canines and first premolars (Figure 4).
Medullary thickness was largely unaffected by facial
divergence. A study by Proffit et al9 showed that adults
with long faces have weaker biting forces during swallowing,
simulated chewing and maximum biting. The results agree
with the previous discussion related to the function of
masticatory muscles and their influence on the bony shape
and structure of the maxilla and mandible.
19
Figure 4: Maxillary and mandibular cortical bone thicknesses (mean ±
1SD) of hypodivergent and hyperdivergent young adults measured 5mm from
the crest of the alveolar ridge.
(Adapted from Horner et al8)
The above studies demonstrate that the maxillary and
mandibular cortical bone thicknesses vary at different
sites and among different groups. These studies suggest
that the stress and strains of the masticatory muscular
apparatus may be a determinant of the amount and density of
20
the cortical and trabecular bone of the mandible and
maxilla.
The only exception to the relationship between muscle
force and cortical thickness pertains to sex differences.
It is reasonable to assume that males would have thicker
cortical bone in alveolus due to their larger masticatory
muscles and greater maximum biting forces than females33,36.
Maximum biting force, however, is rarely required during
daily mastication. Although sex differences in diet were
shown by studies,37,38 the force required to masticate modern
diet was far below the maximum biting force.39 The
similarity in cortical bone thickness of two sexes
indicates that the strains associated with daily
masticatory forces are more important in determining group
differences than maximum bite forces or muscle mass.
Differences between American white and black populations
American blacks comprised an increasingly larger
minority group in the U.S. In the 2000 census, black
American was the largest minority group, comprising of 12.0%
of the population. Black American held its largest minority
position in the 2010 census comprising 12.6% of the
population. As such, American black patients could comprise
21
a large part of the orthodontic patient base. Understanding
the differences and similarities between American black and
white population should help practitioners make appropriate
treatment decisions.
Studies12–14 have demonstrated that black Americans have
higher skeletal mass and denser skeletal bones than their
white counterparts in all skeletal sites. However,
relatively few studies have been performed evaluating
differences in the craniofacial region.
Cohn et al12 studied skeletal mass and radial bone
mineral content in black and white women. Twenty-six black
women were studied using total-body neuron activation
analysis. It was found that black women had a greater
skeletal mass and bone mineral content of the radius than
age-matched white female subjects, when controlling for
differences in statue. The mean absolute total-body calcium
of black females was 16.7% higher than that of age-matched
white women. Controlling for body size showed that more
than half of this differences was due to the larger muscle
mass. The larger muscle mass in black women was a
determinant of their increased skeletal mass.
Ortiz et al13 studied body composition difference
between black and white females. Twenty-eight matched pairs
were studied. Body composition was evaluated by means of
22
anthropometry, dual-photon-absorptiometry (DPA),
dilution, underwater weighting and whole-body
3
H2O
40
K counting.
The results of these procedures were used to calculate
compartmental masses and other relevant body-composition
indices. Total bone density of the black females was
1.18±0.14 g/cm2, which was significantly higher than the
bone density of white females (1.09±0.09 g/cm2). Black
females had greater skeletal muscle and bone mineral in the
upper and lower and combined extremities than the white
females (Table 3). The results confirmed that black and
white females of equivalent age, weight, height and
menstrual status differed significantly in body composition.
The black females had 10-15% more skeletal muscle and total
bone mineral mass than their white counterparts.
Table 3. Values for appendicular skeletal muscle (SM) and regional bone
mineral (bone) for black and white females matched for age, height,
weight and menstrual status (Adapted from Ortiz et al13)
Upper Extremities
SM
Black
6.1±1.3
(4.09.4)
White
4.8±1.2
(2.68.3)
Bone
0.31±0.06
(0.190.42)
0.25±0.04
(0.160.32)
Lower Extremities
SM
Bone
11.9±2.1
(8.117.0)
0.91±0.19
(0.501.31)
10.9±1.6
(8.514.6)
0.80±0.13
(0.521.01)
Total Appendicular
SM
18.0±3.0
(12.725.0)
15.7±2.2
(12.019.4)
Bone
1.22±0.25
(0.691.76)
1.05±0.17
(0.681.32)
Ettinger et al14 performed a cohort study of 402 black
and white men and women. Dual energy x-ray absorptiometry
(DXA) of total body, hip and lumbar spine were performed in
the array scanning mode. Mean hip and spine size,
23
determined by DXA, was smaller in black than in white women.
There were no statistically significant racial differences
between black and white men at these sites. Black men were
found to have 3% greater total skeletal area than their
white counterparts due to larger appendicular bone area.
Similar trends were observed between black and white women
(Table 4). Bone density at all skeletal sites were
significantly greater in blacks than in whites (Table 5).
Young, adult, black men and women had substantially greater
bone-mineral-density than whites at all skeletal sites.
Table 4. Body composition variables for group by gender and race
(Adapted from Ettinger et al14)
Men
Women
Black
White
Black
White
Spine, posterior anterior
65.3
65.7
55.2
57.6
hip, total
43.7
43.7
32.9
34.3
arms
47.4
441
388
356
legs
907
861
792
770
Skeletal area, cm²
2436
2355
2096
2075
L3 Volume, cm²
whole body
39.6
40.5
31.6
35
Lean mass, kg
64.2
60.2
43.7
42.6
16
18.6
27.9
23.5
Trunk: leg fat ratio
0.92
1.24
0.92
0.86
Waist:hip ratio
0.82
0.85
0.75
0.72
Sum of 4 skinfold measurements, mm
52.9
53.4
77
58.7
Fat mass, kg
24
Table 5. Bone mineral density (BMD) in the core group by gender and
race (Adapted from Ettinger et al14)
Men
Women
Black
White
Black
White
posterioranterior, g/cm²
1.148
lateral L3,g/cm²
0.909
1.03
1.13
1.045
0.8
0.862
0.812
volumtric, L3, g/cm²
0.246
0.223
0.256
0.241
neck, g/cm²
1.068
0.891
0.962
0.862
trochanter, g/cm²
0.903
0.783
0.778
0.728
Ward's triangle, g/cm²
0.961
0.769
0.894
0.789
total, g/cm²
1.187
1.034
1.036
0.955
1.295
1.177
1.163
1.09
Spine:
Femur
Total body, g/cm²
In one of the few studies evaluating ethnic
differences in the craniofacial complex, Benson16 developed
panoramic mandibular index to study mandibular cortical
bone thickness. The index was calculated as a ratio of the
cortical thickness to the distance between the mental
foramen and the inferior mandibular border on panoramic
radiograph. Greater index indicates a greater cortical bone
mass. The index was applied to 353 subjects, evenly
distributed among black, Hispanic, white and male and
females. All panoramic radiographs were obtained from the
same radiograph unit. It was found that blacks had greater
mean PMI than Hispanics or whites (Figure 5). However, the
differences in the index were only significantly different
among elderly men.
25
0.45
0.4
0.35
PMI
0.3
0.25
Black Male
0.2
Hispanic Male
0.15
White Male
0.1
0.05
0
30-39
40-49
50-59
60-69
70-79
Age Group (years)
0.45
0.4
0.35
PMI
0.3
0.25
Black Female
0.2
Hispanic Female
0.15
White Female
0.1
0.05
0
30-39
40-49
50-59
60-69
70-79
Age Group (years)
Figure 5. Mean panoramic mandibular index of men and women by age
group and racial group. Standard error of the mean are indicated.
Significant differences (p ‹0.05) were noted among black and Hispanic
in 60-69 age group.(Adapted from Benson et al16)
A recent master’s thesis evaluated ethnic differences
in the cortical bone of the craniofacial region.17 CBCT
scans of 154 consecutively scanned patients were studied.
26
There were 18 African Americans, including nine males and
nine females. The Caucasian sample included 21 females and
22 males. The age of the samples was not disclosed. The
cortical bone thickness between the second premolars and
first molars were measured at 3, 6, 9, and 12mm increments
from the crest of the alveolar ridge. At the mandibular
left quadrant at 6 mm (LL6), African-Americans had
significantly greater cortical bone thickness than Asians
and Hispanics. No significant differences were observed
between African-Americans and Caucasians at this site
(Table 6). At the mandibular left quadrant at 9 mm African
American cortical bone thickness was significantly greater
than all other ethnic groups (Table 7). Although not
statistically significant, the data indicated that cortical
bone thickness was greater in the African Americans than
Caucasians. Humphries stated that there was distortion in
the CBCT data which may have masked some of the ethnic
differences. He suggested that ethnicity of the patients
should be considered when planning orthodontic treatment
using MSIs. The theoretical basis for the speculated ethnic
difference in cortical bone thickness was not mentioned.
Age6 and vertical facial pattern7,8 have been proved to
affect cortical bone thickness. Neither variable was
controlled in this study.
27
Table 6: Summary of the mean difference in cortical bone thickness at
the mandibular left 6mm site. The mean difference is significant at the
0.05 level. (Adapted Humphries17)
Ethinicity
Ethinicity
(I)
(I)
Mean Differences (I-J)
A
AA
C
AA
-0.22*
C
-0.15*
H
-0.05
A
0.22*
C
0.08
H
0.17*
A
0.15*
AA
H
-0.08
H
0.09
A
0.05
AA
-0.17*
C
-0.09
Table 7: Summary of the mean difference in cortical bone thickness at
the mandibular left 9mm site. The mean difference is significant at the
0.05 level.(Adapted from Humphries17)
Ethinicity
Ethinicity
(I)
(I)
Mean Differences (I-J)
A
AA
C
H
AA
-0.25*
C
-0.03
H
-0.02
A
0.25*
C
0.21*
H
0.23*
A
0.03
AA
-0.21*
H
0.02
A
0.02
AA
-0.23*
C
-0.02
The thickness of alveolar ridge is often called
alveolar ridge width in literature. The width of alveolar
ridge is closely related to the tooth supported. The ridge
develops both vertically and horizontally as tooth erupts.40
28
Alveolar ridges resorb when a tooth is extracted41–43 or
periodontal disease is present.44,45 It is therefore an
important consideration factor in dental implants
placement.46,47 Studies have shown that males have wider
alveolar ridge than females at selected sites7 and
mandibular ridges are thicker than maxillary ridges.46 The
sex difference may be due to the larger tooth size in
males.48,49
No study has been published on the ethnic difference
in alveolar ridge thickness. It also has been demonstrated
blacks are larger than whites in most body composition.50,51
According to the allometric scaling, the larger alveolar
ridge may be expected in blacks.
Clinical implication
Multiple sites for MSIs have been utilized to obtain
desired stability including the basal bone below the roots
of the teeth,1,52 infrazygomatic crest of the maxilla53 and
palatal alveolar bone and paramedical plate.54,55 Cortical
bone thickness has been shown to affect both the primary
and secondary stability of MSIs and dental implants.
29
The strength of primary stability can be evaluated by
pull-out test. Huja et al56 studied the pull-out strength of
56 titanium screws in bone at various sites in the maxilla
and mandible of four beagle dogs. It was found that screws
placed in the anterior mandibular region had significantly
lower pull-out strength than those placed in the posterior
mandibular region. The cortical bone in the anterior
mandible was also thinner and less dense than the cortical
bone in the posterior region. Their regression analysis
showed a weak but significant correlation between the pullout force and cortical bone thickness.
Motoyoshi et al57 examined the relationship between
cortical bone thickness and the success rate of MSIs placed
for orthodontic anchorage. They studied 32 patients using
pre-treatment CT scans to measure the cortical bone
thickness around the proposed implant sites. The success of
the MSIs was defined as being able to withstand the force
application for at least six months. The results show that
the cortical bone thickness was significantly greater in
the successful MSI group than in the failure group.
The success rates of MSIs in different ethnic groups
are yet to be studied. If the results of this thesis show
that black Americans have thicker cortical bone than white
30
American, the patient’s ethnicity will have to be
considered when using MSIs as a modality of treatment. If
the results of this study indicate no differences, then the
patient’s ethnicity will play a less important role in
orthodontic MSIs treatment planning.
Summary and Statement of Thesis
It has been well established that that the function of
muscles of mastication influence the bony shape and
structure of the maxilla and mandible. Ethnic differences
in masticatory forces have yet to be established. Studies
suggest that black Americans have thicker cortical bone
than whites but the difference are usually not
significant16,17. A more comprehensive study of cortical bone
thickness is necessary to determine if ethnic differences
actually exist. It is also important to evaluate ethnic
differences in alveolar ridge thickness, which holds
important implications in implant and MSI placements.
Ethnic differences in alveolar ridge thickness have not
previously been evaluated. If current study shows there is
a significant difference between blacks and whites in
cortical bone thickness and alveolar ridge thickness,
patient’s ethnicity will have to be given consideration
31
while treatment planning for MSI and dental implants.
32
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38
CHAPTER 2: JOURNAL ARTICLE
Abstract:
Purpose:
To assess the differences in maxillary and
mandibular cortical bone thickness between black and white
American adolescents.
Methods:
Pre-treatment cone-beam
computed tomography (CBCT) images of 69 patients, including
34 black (17 females; 17 males) and 35 white (18 females;
17 males) adolescents were used to evaluate cortical bone
and alveolar ridge thickness 5 mm below the alveolar crest.
The shortest distances between the periosteal and endosteal
aspects of cortical bone were measured in both maxilla and
mandible at 16 interradicular sites. Total alveolar ridge
thickness was measured at the same interradicular sites.
Results: Two-way analysis of variance showed no significant
sex differences and significant (P‹0.05) group differences
at three of the 16 sites, with black adolescents having
thicker cortical bone. Alveolar ridges were significantly
greater in black adolescents, except distal to the first
molasr in the mandible. Medullary thickness was
significantly greater in black adolescents, except between
the first and second mandibular premolars. Males had
significantly thicker alveolar ridges and medullary spaces
than females, except distal to the first mandibular molars.
39
On the buccal surface, the more posterior cortical bone of
the mandible was thicker than the more anterior cortical
bone. The cortical bone was thicker in the maxilla than in
the mandible. Conclusion: There were only limited
differences in cortical bone thicknesses between black and
white adolescents, but there were significant differences
favoring blacks in alveolar ridge thickness. There was no
sex difference in cortical bone thickness but definite
differences favoring males in alveolar ridge and medullary
space.
Introduction
Mini-screw implants (MSIs) are widely used by
orthodontists, with approximately 80% of the AAO
orthodontists having used at least one MSI.1 The success of
MSIs depends on their stability. Cortical bone quality and
quantity are major factors associated with stability of
MSIs,2–4 with failures being linked to thin cortical bones.3–
5
It has even been suggested that the cortical bone
thickness is more important than the implant length in
determining MSIs stability.6
40
Differences in cortical bone thickness are thought to
be related to function; cortical plate thickness adapts to
masticatory forces.7–10 Hyperdivergent individuals have
thinner cortical bone,12,13
which could be due to lower
masticatory forces. It has also been shown that adults have
thicker cortical bone than children,11 which could be
explained by increases in body size, muscle size and
occlusal forces during growth.15–18
Differences in post-cranial bone indicate that there
could also be differences between blacks and whites in
cortical bone surrounding the teeth. Blacks have thicker
post-cranial cortical bones, stronger muscles and greater
muscle mass.20–22 Benson et al23 reported thicker cortical
bone among blacks than whites, but the differences were
only significantly different among elderly men. Humphries,24
who studied the cortical bone thickness at four vertical
sites between second premolar and first molars, found that
blacks have thicker mandibular cortical bone thickness at
two sites. This study had limited sample sizes and the ages
of the samples were not given.
The purpose of the present study was to measure the
thickness of cortical bone in the posterior regions of the
maxilla and mandible of black and white American
41
adolescents. If differences exist, patient’s ethnicity has
to be considered as a factor in using MSI as a treatment
modality.
Materials and Methods
Sample size and composition
Pre-treatment cone beam computed tomography (CBCT)
scans (i-CAT Classic, Imaging Science International,
Hatfield, PA) were taken with a single 360° rotational scan
time of 20 seconds, 120 kVp, and 0.4 mm voxel size. The
sample and the side of the mouth used for the measurements
were selected based on: 1) no missing or unerupted
permanent teeth in the areas being measured; 2) no
periapical or periradicular pathology; 3) no apparent
facial or dental asymmetries on photographs; 4) no vertical
or horizontal periodontal bone loss; 5) no medical or
dental diseases affecting bone metabolism. The side that
best met the inclusion criteria was measured; if both sides
met the criteria, the side was randomly chosen because
studies have shown no side differences in cortical bone
thicknesses in either the maxilla or mandible.25,26
42
The scans were selected based on sex, age (patients
had to be 10-17 year old), vertical growth pattern
(measured based on the Frankfort to mandibular plane or FMA
angle) and race (either white or black). The white subjects
were matched to the black subjects based on age, sex and
FMA. Samples were obtained from a private practice in
Lubbock Texas. The samples included 34 blacks and 35 whites.
The black group was 12.7 ±1.8 years of age and had an FMA
of 24.7 ±5.2°. The white group was 12.8 ±1.6 years old and
had a mean FMA of 24.2 ±5.8°.
Methods of analysis
The Digital Imaging and Communication in Medicine
(DICOM) multifiles of each CBCT scan were imported into
Dolphin Imaging 11 3D software (Dolphin Imaging Systems LLC,
Chatsworth, CA) for analysis. Each image as oriented in
three planes of place so that the buccal and lingual
cortical plates could be measured 5 mm apical to the
alveolar crest, approximately at the level of mucogingival
junction. The height of 5 mm was chosen because it has been
commonly used for MSI placement.27,28
The images were orientated so that the sagittal plane
in the axial slice went through all posterior teeth on the
side of measurement (Figure 6A). The alveolar crest was
43
then orientated parallel to the axial plane in the sagittal
slice (Figure 6B). The measurement site was selected 5 mm
from the alveolar ridge crest (Figure 6C). The cortical
bone thickness was measured on the axial slice. The slices
were oriented so that the shortest distance between the
buccal and lingual was measured (Figure 6D).
Cortical bone thickness was measured on the buccal and
lingual sides of maxilla and mandible 1) 1 mm distal to the
first molars (distal of 6); 2) between the second premolars
and first molars (5-6); 3) between the first premolars and
second premolars (4-5); and 4) 1 mm mesial to the first
premolars (mesial of 4). These are the sites commonly used
for MSI placement.1,2,28–30
Alveolar ridge thickness was measured at the same
sites as cortical bone thickness in both the maxilla and
mandible (Figure 6C). Alveolar ridge thickness was defined
as the distance between the buccal and lingual cortical
periosteal sites. Medullary thickness was calculated as the
differences between alveolar ridge thickness and the sum of
the buccal and lingual cortical bone thickness.
Twenty subjects were chosen randomly to be measured a
second time at all sites by the same operator. Method
44
Figure 6A. Axial CBCT slice showing the sagittal plane running through
all posterior teeth on the side of measurement.
Figure 6B. Sagittal slice showing the axial plane orientated parallel
to the alveolar ridge crest.
45
Figure 6C. Sagittal slice showing the axial plane positioned 5 mm from
the crest of the alveolar ridge.
Figure 6D. Axial slice showing buccal and lingual cortical bone
thickness measured. Alveolar ridge thickness was measured at the same
level.
46
errors (√(∑differences2/2n) of the replicate measures ranged
from 0.15-0.24 mm. There were no statistically significant
systematic errors.
Statistical analysis
Descriptive statistics indicated that the data were
normally distributed. Two-way ANOVA were used to evaluate
groups and sex differences in cortical bone, alveolar ridge
and medullary space thickness.
Results
Comparisons of blacks and whites
Cortical bone was generally thicker in black than in
white adolescents, but the differences were statistically
significant at only three sites: maxillary buccal between
first molar and second premolar, between the first premolar
and second premolar and maxillary lingual mesial of the
first premolar. No statistically significant differences
between blacks and whites were observed in the mandible
(Table 8; Figures 7-10).
Alveolar ridge thickness was greater in black than in
white adolescents at all sites. The differences were
47
statistically significant at all sites except distal to the
first mandibular molar (Table 9; Figures 11, 13). Medullary
thickness was also significantly greater in blacks than in
whites at all maxillary sites, and at the two most
posterior mandibular sites (Table 9; Figures 12, 14).
Comparison of females and males
While cortical bone tended to be thicker in males than
in females, none of the sex differences were statistically
significant (Table 10; Figures 15-18).
The alveolar ridges were consistently thicker in males
than females, with differences being statistically
significant at all sites except distal to the mandibular
first molar (Table 11; Figures 19, 21). Medullary thickness
was also significantly greater in males than females,
except distal to the first mandibular molars (Table 11;
Figures 20, 22).
Inter- and intra-arch comparisons
The cortical bone was significantly thicker in the
maxilla than in mandible, except on the buccal surface
mesial to the first premolars and between first and second
premolars in blacks. The alveolar ridges and medullary
thickness were also significantly thicker in the maxilla
48
than in the mandible, except mesial to first premolars and
distal to the first molars (Tables 8, 9).
The cortical bone thickness increased from posterior
to anterior on the buccal side of the mandible. The
thickest cortical bone on the lingual side was between
first and second premolar. There was no clear pattern of
differences observed for cortical bone thickness in the
maxilla. Alveolar ridge and medullary thickness were
greater at the more posterior sites than at the more
anterior sites of both jaws (Tables 8, 9).
Table 8. Maxillary and mandibular cortical bone thickness (mm) in black
and white American adolescents (* indicates statistically significant
group difference (p≤0.05)).
Jaw
Cortex
Maxilla
Buccal
Lingual
Mandible
Buccal
Lingual
Site
Black
White
Differences
Mean
SD
Mean
SD
Mean
Sig.
Distal of 6
1.85
0.34
1.78
0.36
0.07
0.44
5-6
1.85
0.36
1.67
0.26
0.18
0.02*
4-5
1.89
0.33
1.67
0.32
0.22
0.01*
Mesial of 4
1.77
0.40
1.63
0.29
0.14
0.11
Distal of 6
2.04
0.46
1.97
0.38
0.07
0.56
5-6
1.85
0.38
1.87
0.32
-0.02
0.82
4-5
1.96
0.46
1.81
0.42
0.15
0.17
Mesial of 4
2.14
0.47
1.87
0.33
0.27
0.01*
Distal of 6
3.23
0.81
3.25
0.59
-0.02
0.87
5-6
2.20
0.52
2.11
0.52
0.09
0.43
4-5
1.91
0.42
1.85
0.41
0.06
0.52
Mesial of 4
1.79
0.44
1.67
0.37
0.12
0.21
Distal of 6
2.75
0.46
2.86
0.53
-0.11
0.38
5-6
2.79
0.41
2.63
0.51
0.16
0.13
4-5
3.17
0.68
2.73
0.61
0.44
0.07
Mesial of 4
2.91
0.60
2.57
0.45
0.34
0.08
49
Table 9. Maxillary and mandibular alveolar ridge and medullary
thickness (mm) in black and white American adolescents (* indicates
statistically significant group difference (p≤0.05)).
Jaw
Maxilla
Site
Alveolar
Ridge
Medullary
Thickness
Mandible
Alveolar
Ridge
Medullary
Thickness
Black
White
Differences
Mean
SD
Mean
SD
Mean
Sig.
Distal of 6
17.31
2.00
15.88
1.22
1.43
<0.01*
5-6
15.30
1.62
13.72
1.34
1.58
<0.01*
4-5
13.35
1.83
11.66
1.42
1.69
<0.01*
Mesial of 4
12.10
2.13
10.48
1.53
1.62
<0.01*
Distal of 6
13.42
2.09
12.13
1.35
1.29
<0.01*
5-6
11.60
1.58
10.18
1.13
1.42
<0.01*
4-5
9.51
1.70
8.18
1.22
1.33
<0.01*
Mesial of 4
8.19
1.91
6.97
1.32
1.22
<0.01*
Distal of 6
15.98
1.92
15.33
1.98
0.65
0.17
5-6
13.39
1.78
12.48
1.60
0.91
0.03*
4-5
11.99
1.83
10.84
1.91
1.15
0.01*
Mesial of 4
11.13
1.97
10.14
1.75
0.99
0.02*
Distal of 6
10.00
1.26
9.22
1.68
0.78
0.03*
5-6
8.40
1.43
7.73
1.33
0.67
0.04*
4-5
6.91
1.30
6.32
1.37
0.59
0.06
Mesial of 4
6.43
1.60
5.92
1.54
0.51
0.14
50
Table 10. Maxillary and mandibular cortical bone thickness (mm) in
female and male American adolescents (* indicates statistically
significant group difference (p≤0.05)).
Jaw
Cortex
Maxilla
Buccal
Site
Female
Mean
Lingual
Mandible
Buccal
Lingual
SD
Male
Mean
SD
Differences
Mean
Sig
Distal of 6
1.78
0.38
1.86
0.28
-0.08
0.57
5-6
1.76
0.36
1.79
0.27
-0.03
0.97
4-5
1.74
0.35
1.81
0.33
-0.07
0.41
Mesial of 4
1.63
0.36
1.78
0.35
-0.15
0.10
Distal of 6
1.96
0.43
2.04
0.45
-0.08
0.17
5-6
1.84
0.35
1.85
0.36
-0.01
0.64
4-5
1.86
0.37
1.91
0.50
-0.05
0.66
Mesial of 4
1.97
0.46
2.04
0.37
-0.07
0.52
Distal of 6
3.18
0.76
3.31
0.63
-0.13
0.47
5-6
2.16
0.53
2.16
0.48
0.00
0.90
4-5
1.82
0.39
1.94
0.46
-0.12
0.25
Mesial of 4
1.67
0.35
1.77
0.47
-0.10
0.15
Distal of 6
2.85
0.48
2.75
0.51
0.10
0.40
5-6
2.40
0.40
2.70
0.52
-0.30
0.91
4-5
2.88
0.61
3.02
0.74
-0.14
0.38
Mesial of 4
2.66
0.58
2.81
0.50
-0.15
0.23
51
Table 11. Maxillary and mandibular alveolar ridge and medullary
thickness (mm) in female and male American adolescents (* indicates
statistically significant group difference (p≤0.05)).
Jaw
Maxilla
Site
Alveolar
Ridge
Medullary
Thickness
Mandible
Alveolar
Ridge
Medullary
Thickness
Female
Male
Differences
Mean
SD
Mean
SD
Mean
Sig
Distal of 6
15.79
1.22
17.40
1.95
-1.61
<0.01*
5-6
13.44
1.22
15.18
1.82
-1.74
<0.01*
4-5
11.92
1.14
13.15
2.18
-1.23
<0.01*
Mesial of 4
10.38
1.28
12.17
2.20
-1.79
<0.01*
Distal of 6
12.05
1.35
13.58
2.03
-1.53
<0.01*
5-6
10.24
1.11
11.54
1.67
-1.30
<0.01*
4-5
8.31
1.11
9.43
1.87
-1.12
<0.01*
Mesial of 4
6.78
1.00
8.36
1.95
-1.58
<0.01*
Distal of 6
15.31
1.91
16.00
1.91
-0.69
0.14
5-6
12.62
1.46
13.31
1.88
-0.69
0.02*
4-5
10.89
1.68
11.95
2.02
-1.06
0.01*
Mesial of 4
9.85
1.56
11.45
1.83
-1.60
<0.01*
Distal of 6
9.28
1.52
9.95
1.40
-0.67
0.06
5-6
7.73
1.30
8.44
1.39
-0.71
0.02*
4-5
6.25
1.24
7.02
1.31
-0.77
0.01*
Mesial of 4
5.53
1.37
6.86
1.44
-1.33
<0.01*
52
Black
White
2.50
2.00
mm
1.50
1.00
0.50
0.00
Distal of 6
5-6*
4-5*
Mesial of 4
Figure 7. Means of buccal cortical bone thickness in the maxilla.
(* indicates statistically significant sites(p≤0.05))
Black
White
3.00
2.50
mm
2.00
1.50
1.00
0.50
0.00
Distal of 6
5-6
4-5
Mesial of 4*
Figure 8. Means of lingual cortical bone thickness in the maxilla.
(* indicates statistically significant sites (p≤0.05))
53
Black
White
4.50
4.00
3.50
mm
3.00
2.50
2.00
1.50
1.00
0.50
0.00
Distal of 6
5-6
4-5
Mesial of 4
Figure 9. Means of buccal cortical bone thickness in the mandible.
(* indicates statistically significant sites(p≤0.05))
Black
White
4.50
4.00
3.50
mm
3.00
2.50
2.00
1.50
1.00
0.50
0.00
Distal of 6
5-6
4-5
Mesial of 4
Figure 10. Means of lingual cortical bone thickness in the mandible.
(* indicates statistically significant sites(p≤0.05))
54
Black
White
25.00
20.00
mm
15.00
10.00
5.00
0.00
Distal of 6*
5-6*
4-5*
Mesial of 4*
Figure 11. Means of alveolar ridge thickness in the maxilla.
(* indicates statistically significant sites (p≤0.05))
Black
White
18.00
16.00
14.00
mm
12.00
10.00
8.00
6.00
4.00
2.00
0.00
Distal of 6*
5-6*
4-5*
Mesial of 4*
Figure 12. Means of medullary space thickness in the maxilla.
(* indicates statistically significant sites (p≤0.05))
55
Black
White
20.00
18.00
16.00
14.00
mm
12.00
10.00
8.00
6.00
4.00
2.00
0.00
Distal of 6
5-6*
4-5*
Mesial of 4*
Figure 13. Means of alveolar ridge thickness in the mandible.
(* indicates statistically significant sites (p≤0.05))
Black
White
12.00
10.00
mm
8.00
6.00
4.00
2.00
0.00
Distal of 6*
5-6*
4-5
Mesial of 4
Figure 14. Means of medullary space thickness in the mandible.
(* indicates statistically significant sites (p≤0.05))
56
Discussion
Cortical bones
Only limited differences in cortical bone thickness
were observed between blacks and whites. The differences
were statistically significant at only three maxillary
sites. This is consistent with previous studies,23,24 showing
limited differences between blacks and whites. The CBCT
used in the study had a 0.4 mm voxel size, which was larger
or equivalent to some of the differences calculated. The
mean method error was 0.15-0.24 mm, which increased the
variability of the measurement. The present study may not
have enough power to detect all the differences. However,
the pattern was for blacks to have thicker (4-14%) cortical
bone than whites. Blacks are known to have larger postcranial muscle mass and strength than whites.20–22 There have
been no comparative craniofacial muscle forces studies
published. The similarity in cortical bone indicates
similar muscle force of blacks and whites. Future study for
craniofacial muscle force may be needed.
Males and females had similar cortical bone
thicknesses. Males had thicker cortical bone than females,
but the differences were even smaller than the black and
white differences, and not statistically significant. This
57
lack of sex difference in cortical bone thickness has been
previously demonstrated.11,25 Males have larger masticatory
muscles and greater maximum biting forces than females.14,15
Although sex differences in diet have been reported31,32
maximum biting forces rarely occur in daily mastication.
The forces required to masticate modern diets is far below
the maximum biting force.33 The similarity in cortical bone
thickness indicates that the strains associated with daily
masticatory forces are more important in determining group
differences than maximum bite forces or muscle mass.
The mandible has thicker buccal and lingual cortical
bone than the maxilla. The differences ranged from 0.03 mm
to 1.42 mm. Previous studies have also shown thicker
cortical bone in the mandible than maxilla.11,12,25,26 During
mastication more stress and strains are applied to the
mandible because it is a single bone. The maxilla is
connected to the midface and is able to dissipate any of
the force produced. Consequently, the mandible undergoes
greater bending than the maxilla during mastication. In
clinical practice, it is difficult to anesthetize
mandibular teeth through infiltration due to the thick
cortical plate preventing the diffusion of anesthetics into
the pulp.34
58
Cortical bone thickness increased from posterior to
anterior on the buccal side of the mandible. The thickest
cortical bone on the lingual side was found between first
and second premolar. These findings are consistent with
studies by Farnsworth et al11 and Horner et al.12 The pattern
can be explained by masticatory force distribution within
the mandible. The force developed during biting increases
from anterior teeth to molars.7,35 Therefore, bone in the
molar areas is subject to the higher levels of stress and
strains, necessitating more bony adaptation than in the
anterior region. The thicker cortical bone in the posterior
mandible makes it well suited for MSI placement.
Alveolar ridge and medullary thickness
Black adolescents have thicker alveolar ridges than
white adolescents, primarily due to increased medullary
thickness. The results indicated that medullary thickness
was approximately 8-17% greater in black than in white
adolescents, which is relatively only slightly greater than
the differences observed in cortical thickness. Alveolar
and medullary width might be expected to be related to
tooth size. Studies have demonstrated that blacks have
bigger teeth than whites.36,37,38,39 Differences in ridge and
59
medullary thickness may also be related to body size
because blacks are larger than whites in most body
composition.40,41 The body size difference may explain the
larger alveolar ridge and medullary thickness according the
allometric scaling.
Males have thicker alveolar ridge than females due to
greater medullary bone. The results indicated that the
difference was 4-19%. Males have larger teeth than females
in all dimensions.42,43 In addition, males are bigger than
females in most dimensions.44 The difference in tooth size
and body size may explain the differences in alveolar ridge
width. Swasty et al13 reported that males have thicker
ridges than females only in the premolar and canine regions
of the upper third of the mandible. However, their study
was based on a wide age-range (10-65 years old) and the
number of males and females were not indicated. Thicker
alveolar bone has important indications in dental implant
placement and denture prosthesis fabrication.
60
Conclusions
Based on pre-treatment CBCT images of 69 adolescent
patients, the following conclusions can be made about
interradibular bone 5 mm from the alveolar crest:
1) The thickness of cortical bone is similar or slightly
thicker in blacks than in whites.
2) Alveolar ridge thickness is thicker in blacks than in
whites due primarily to thicker medullary bone.
3) The cortical bone thickness is similar in males and
females.
4) Alveolar ridge thickness is thicker in male than in
females due to the differences in medullary thickness.
5) Buccal cortical bone in the mandible increases from
more anterior to the more posterior sites.
6) The cortical bone was thicker in the mandible than in
the maxilla.
61
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Appendix
Female
Male
2.50
2.00
mm
1.50
1.00
0.50
0.00
Distal of 6
5-6
4-5
Mesial of 4
Figure 15. Means of buccal cortical bone thickness in the maxilla.
(* indicates statistically significant sites(p≤0.05))
Female
Male
3.00
2.50
mm
2.00
1.50
1.00
0.50
0.00
Distal of 6
5-6
4-5
Mesial of 4
Figure 16. Means of lingual cortical bone thickness in the maxilla.
(* indicates statistically significant sites(p≤0.05))
67
Female
Male
4.50
4.00
3.50
mm
3.00
2.50
2.00
1.50
1.00
0.50
0.00
Distal of 6
5-6
4-5
Mesial of 4
Figure 17. Means of buccal cortical bone thickness in the mandible.
(* indicates statistically significant sites(p≤0.05))
Female
Male
4.00
3.50
3.00
mm
2.50
2.00
1.50
1.00
0.50
0.00
Distal of 6
5-6
4-5
Mesial of 4
Figure 18. Means of lingual cortical bone thickness in the mandible.
(* indicates statistically significant sites(p≤0.05))
68
Female
Male
25.00
20.00
mm
15.00
10.00
5.00
0.00
Distal of 6*
5-6*
4-5*
Mesial of 4*
Figure 19. Means of alveolar ridge thickness in the maxilla.
(* indicates statistically significant sites (p≤0.05))
Female
Male
18.00
16.00
14.00
mm
12.00
10.00
8.00
6.00
4.00
2.00
0.00
Distal of 6*
5-6*
4-5*
Mesial of 4*
Figure 20. Means of medullary space thickness in the maxilla.
(* indicates statistically significant sites (p≤0.05))
69
Female
Male
20.00
18.00
16.00
14.00
mm
12.00
10.00
8.00
6.00
4.00
2.00
0.00
Distal of 6
5-6*
4-5*
Mesial of 4*
Figure 21. Means of alveolar ridge thickness in the mandible.
(* indicates statistically significant sites (p≤0.05))
Female
Male
12.00
10.00
mm
8.00
6.00
4.00
2.00
0.00
Distal of 6
5-6*
4-5*
Mesial of 4*
Figure 22. Means of medullary space thickness in the mandible.
(* indicates statistically significant sites (p≤0.05))
70
VITA AUTORIS
Ningning Zhang was born to Mr. Feng Zhang and Mrs. Min
Li in SuZhou city, People’s Republic of China in 1983. She
moved to the United States in 2001 for education. She
received her undergraduate education at University of
Rochester in Rochester New York. She finished her dental
education at Columbia University in New York City in 2009
with a degree of Doctor of Dental Surgery. She then
completed one year residency in advanced education in
general dentistry at New York Presbyterian Hospital. She is
currently doing postgraduate education in Orthodontics at
Saint Louis University. She plans to graduate in December
2012 with Master of Science in Dentistry. She is married to
Dr. Somnang Lim.
71