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University of Iowa
Iowa Research Online
Theses and Dissertations
2008
Cortical bone thickness in the maxilla and
mandible for mini-implant placement
Shawneen M. Gonzalez
University of Iowa
Copyright 2008 Shawneen M Gonzalez
This thesis is available at Iowa Research Online: http://ir.uiowa.edu/etd/36
Recommended Citation
Gonzalez, Shawneen M.. "Cortical bone thickness in the maxilla and mandible for mini-implant placement." MS (Master of Science)
thesis, University of Iowa, 2008.
http://ir.uiowa.edu/etd/36.
Follow this and additional works at: http://ir.uiowa.edu/etd
Part of the Oral Biology and Oral Pathology Commons
CORTICAL BONE THICKNESS OF THE MAXILLA AND MANDIBLE
FOR MINI-IMPLANT PLACEMENT
by
Shawneen M Gonzalez
A thesis submitted in partial fulfillment
of the requirements for the Master of
Science degree in Stomatology
in the Graduate College of
The University of Iowa
August 2008
Thesis Supervisor: Professor Axel Ruprecht
Graduate College
The University of Iowa
Iowa City, Iowa
CERTIFICATE OF APPROVAL
_______________________
MASTER'S THESIS
_______________
This is to certify that the Master's thesis of
Shawneen M Gonzalez
has been approved by the Examining Committee
for the thesis requirement for the Master of Science
degree in Stomatology at the August 2008 graduation.
Thesis Committee: __________________________________
Axel Ruprecht, Thesis Supervisor
__________________________________
Ali Fahkry
__________________________________
Zoya Kurago
__________________________________
Fang Qian
__________________________________
Tom Southard
To Max for being loyal and patient throughout this process.
ii
ACKNOWLEDGMENTS
I would like to express my gratitude to Dr. Axel Ruprecht for his guidance and
helpful reviews throughout this project. To Dr. Ali Fahkry for his continuous advice and
direction especially in the image analysis portion of my thesis. To Dr. Tom Southard, for
his guidance in displaying all the results. Dr. Zoya Kurago for her advice and
encouragement. Fang Qian for her help and efficiency in preparing the statistical analysis.
Rich Tack from the Educational Media department for his help creating a custom macro
in Photoshop. Pat Conrad for her help creating the diagrams for presentation of the data.
I would like to thank my co-residents for their friendship and encouragement and all the
faculty and staff in the department of Oral Pathology, Radiology and Medicine for their
continuous support.
Special thanks to my parents for supporting me throughout my schooling and
encouraging me to never settle. To my siblings for continuing to keep me grounded.
And finally to Max who has always had a smile, while he would wait patiently for me to
finish my work.
iii
TABLE OF CONTENTS
LIST OF FIGURES ................................................................................................................. v
LIST OF ABBREVIATIONS .......... ................................................................................viii
CHAPTER
I.
INTRODUCTION................................................................................................ 1
Orthodontics ......................................................................................................... 1
Definition ...................................................................................................... 1
History ........................................................................................................... 1
Skeletal anchorage ........................................................................................ 1
Temporary Anchorage Devices (TADs) ............................................................. 3
Mini-implant ......................................................................................................... 4
Definition ...................................................................................................... 4
Imaging .......................................................................................................... 4
Uses outside of orthodontics ........................................................................ 5
Types of mini-implants ................................................................................ 5
Loading of mini-implants ............................................................................. 6
Osseointegration ........................................................................................... 7
Current Research .................................................................................................. 7
Hypotheses............................................................................................................ 9
II.
MATERIALS AND METHODS ...................................................................... 12
Case Selection .................................................................................................... 12
Image Analysis ................................................................................................... 13
Measurements ..................................................................................................... 14
Overview of Statistical Methods ....................................................................... 16
III.
RESULTS ........................................................................................................... 28
Statistical Results ............................................................................................... 28
Descriptive results ...................................................................................... 28
Cortical bone thickness in the maxilla ............................................. 28
Cortical bone thickness in the mandible .......................................... 29
Inter-root distance in the maxilla ...................................................... 30
Inter-root distance in the mandible ................................................... 31
Measurement Reliability .................................................................................... 33
IV.
DISCUSSION..................................................................................................... 56
Conclusions ........................................................................................................ 59
REFERENCES ....................................................................................................................... 60
iv
LIST OF FIGURES
Figure 1. A traditional implant (left) and a mini-implant (right) ........................................ 10
Figure 2. Two different mini-implants.................................................................................. 11
Figure 3. A maxilla aligned with the nasal spine with the sagittal plane and the
occlusal plane with the axial plane before scanning................................................... 18
Figure 4. A mandible aligned with the occlusal plane oriented along the axial plane
before scanning ............................................................................................................. 19
Figure 5. Multiple mandibles stabilized in styrofoam to prevent movement while
scanning.. ....................................................................................................................... 20
Figure 6. An axial slice of the mandible with a line demarcating the parasagittal
plane through the root canals of the canine, first premolar and second
premolar......................................................................................................................... 21
Figure 7. An axial slice of the mandible with a line demarcating the parasagittal
plane through the root canal of the second premolar and the buccal root of the
first molar ...................................................................................................................... 22
Figure 8. An axial slice of the mandible with a line demarcating the parasagittal
plane through the pulp canals of the first molar and second molar ........................... 23
Figure 9. The custom macro created with Adobe Photoshop .............................................. 24
Figure 10. The custom grid demarcating 6 mm, 9 mm and 12 mm .................................... 24
Figure 11. A screenshot of a starting image in Adobe Photoshop ...................................... 25
Figure 12. A screenshot of the image after the custom macro has been applied ............... 26
Figure 13. A screenshot of the image after it is enlarged to 400% for better
visualization of the edges of the cortical bone ............................................................ 27
Figure 14. An axial slice at 6 mm from the cemento-enamel junction noting the
locations of cortical bone thickness measured in the maxilla ............................. 34
Figure 15. Cortical bone thickness minimum to maximum measurement ranges
between the posterior teeth in the maxilla at 6 mm from the CEJ on the
right side.................................................................................................................. 35
Figure 16. Cortical bone thickness minimum to maximum measurement ranges
between the posterior teeth in the maxilla at 6 mm from the CEJ on the
left side. ................................................................................................................... 35
Figure 17. An axial slice at 9 mm from the cemento-enamel junction noting the
locations of cortical bone thickness measured in the maxilla ............................. 36
v
Figure 18. Cortical bone thickness minimum to maximum measurement ranges
between the posterior teeth in the maxilla at 9 mm from the CEJ on the
right side.................................................................................................................. 37
Figure 19. Cortical bone thickness minimum to maximum measurement ranges
between the posterior teeth in the maxilla at 9 mm from the CEJ on the
left side. ................................................................................................................... 37
Figure 20. An axial slice at 12 mm from the cemento-enamel junction noting the
locations of cortical bone thickness measured in the maxilla ............................. 38
Figure 21. Cortical bone thickness minimum to maximum measurement ranges
between the posterior teeth in the maxilla at 12 mm from the CEJ on the
right side.................................................................................................................. 39
Figure 22. Cortical bone thickness minimum to maximum measurement ranges
between the posterior teeth in the maxilla at 12 mm from the CEJ on the
left side. ................................................................................................................... 39
Figure 23. An axial slice at 6 mm from the cemento-enamel junction noting the
locations of cortical bone thickness measured in the mandible. ......................... 40
Figure 24. Cortical bone thickness minimum to maximum measurement ranges
between the posterior teeth in the mandible at 6 mm from the CEJ on the
right side.................................................................................................................. 41
Figure 25. Cortical bone thickness minimum to maximum measurement ranges
between the posterior teeth in the mandible at 6 mm from the CEJ on the
left side .................................................................................................................... 41
Figure 26. An axial slice at 9 mm from the cemento-enamel junction noting the
locations of cortical bone thickness measured in the mandible .......................... 42
Figure 27. Cortical bone thickness minimum to maximum measurement ranges
between the posterior teeth in the mandible at 9 mm from the CEJ on the
right side.................................................................................................................. 43
Figure 28. Cortical bone thickness minimum to maximum measurement ranges
between the posterior teeth in the mandible at 9 mm from the CEJ on the
left side .................................................................................................................... 43
Figure 29. An axial slice at 12 mm from the cemento-enamel junction noting the
locations of cortical bone thickness measured in the mandible .......................... 44
Figure 30. Cortical bone thickness minimum to maximum measurement ranges
between the posterior teeth in the mandible at 12 mm from the CEJ on the
right side.................................................................................................................. 45
Figure 31. Cortical bone thickness minimum to maximum measurement ranges
between the posterior teeth in the mandible at 12 mm from the CEJ on the
left side .................................................................................................................... 45
Figure 32. A diagram noting the locations of inter-root distance measured in the
maxilla on the right side ......................................................................................... 46
vi
Figure 33. A diagram noting the locations of inter-root distance measured in the
maxilla on the left side ........................................................................................... 47
Figure 34. Inter-root distance minimum to maximum measurement ranges between
the posterior teeth in the maxilla at 6 mm from the CEJ on the right side ......... 48
Figure 35. Inter-root distance minimum to maximum measurement ranges between
the posterior teeth in the maxilla at 6 mm from the CEJ on the left side............ 48
Figure 36. Inter-root distance minimum to maximum measurement ranges between
the posterior teeth in the maxilla at 9 mm from the CEJ on the right side ......... 49
Figure 37. Inter-root distance minimum to maximum measurement ranges between
the posterior teeth in the maxilla at 9 mm from the CEJ on the left side. .......... 49
Figure 38. Inter-root distance minimum to maximum measurement ranges between
the posterior teeth in the maxilla at 12 mm from the CEJ on the right side ....... 50
Figure 39. Inter-root distance minimum to maximum measurement ranges between
the posterior teeth in the maxilla at 12 mm from the CEJ on the left side ......... 50
Figure 40. A diagram noting the locations of inter-root distance measured in the
mandible on the right side ...................................................................................... 51
Figure 41. A diagram noting the locations of inter-root distance measured in the
mandible on the left side ........................................................................................ 52
Figure 42. Inter-root distance minimum to maximum measurement ranges between
the posterior teeth in the mandible at 6 mm from the CEJ on the right side ...... 53
Figure 43. Inter-root distance minimum to maximum measurement ranges between
the posterior teeth in the mandible at 6 mm from the CEJ on the left side......... 53
Figure 44. Inter-root distance minimum to maximum measurement ranges between
the posterior teeth in the mandible at 9 mm from the CEJ on the right side ...... 54
Figure 45. Inter-root distance minimum to maximum measurement ranges between
the posterior teeth in the mandible at 9 mm from the CEJ on the left side......... 54
Figure 46. Inter-root distance minimum to maximum measurement ranges between
the posterior teeth in the mandible at 12 mm from the CEJ on the right
side .......................................................................................................................... 55
Figure 47. Inter-root distance minimum to maximum measurement ranges between
the posterior teeth in the mandible at 12 mm from the CEJ on the left side ...... 55
vii
LIST OF ABBREVIATIONS
CT:
Computed tomography
CBCT:
Cone beam computed tomography
TADs:
Temporary anchorage devices
UIHC:
The University of Iowa Hospitals and Clinics
FOV:
Field of view
viii
1
CHAPTER I
INTRODUCTION
Orthodontics
Definition
Orthodontics is the specialty of dentistry that involves “diagnosis, prevention,
interception, and correction of malocclusion, as well as neuromuscular and skeletal
abnormalities of the developing or mature orofacial structures”1. Orthodontics was the
first specialty organization formed in 19002.
History
Attempts to treat overcrowding and malalignment of teeth have been recorded as
early as 1000 BC3. Traditional orthodontic concepts are credited to Edward H. Angle,
also known as the father of modern orthodontics, in the late 1800s. Angle described
different classifications of malocclusion based on the location of the permanent maxillary
first molars in relation to the permanent mandibular first molars4. With this classification
system, orthodontics began to view proper occlusion as just as important as correcting
other problems including overcrowding and malalignment.
Skeletal anchorage
Skeletal anchorage using a headgear, was first introduced as a treatment option in
orthodontics in the late 1800s4. As a treatment option it was quickly discarded due to
notions that the same results could be achieved using intraoral elastics. Angle did not
emphasize esthetics or the use of extra-oral forces or skeletal anchorage, such as
headgear, when practicing orthodontics. In the 1930s, esthetics became an important
aspect of orthodontics due to patient demands. In 1936, Oppenheim5 suggested that
headgear as a treatment option was valuable. Kloen6 showed that headgear is effective at
correcting occlusion and esthetics. In the 1950s, with the advent of lateral cephalometric
2
skull radiographs, headgear was shown to be effective at hindering or stimulating
maxillary growth7.
There are three types of headgear; cervical headgear, high-pull headgear, and
reverse-pull headgear. High-pull headgear applies a superior and distal force on the
maxilla and teeth4. Cervical headgear applies an inferior and distal force on the maxilla
and teeth4 . Reverse-pull headgear applies an anterior force on the maxilla and teeth.
There are many other factors that play a role in exact direction of forces including the
length of the facebow and the amount of forces applied.
Cervical and high-pull headgear are made up of two extra-oral components and
one intraoral component. The intraoral component consists of a metallic tube attached to
the teeth via a band. These bands are commonly cemented to the maxillary permanent
first molars. The extra-oral components include a facebow and skeletal stabilization.
The facebow has an intra-oral and extra-oral component. The intra-oral component of the
facebow inserts into the metallic tubes bilaterally. The extra-oral component of the
facebow is stabilized to the head with either a headcap (high-pull) or neckstrap (cervical).
In the case of reverse-pull headgear, the intra-oral component consists of a metallic hook
that is attached to the teeth via brackets. The facebow is stabilized with a chin cup and
forehead rest. The facebow attaches to the metallic hook via the use of elastics.
The brackets and bands, although cemented to the teeth, still have the possibility
of shifting. Shifting will alter the direction of forces in stabilizing the teeth and can
change the treatment outcome. Shifting or displacement of the brackets or bands can
occur through normal everyday use, diet and/or physical trauma.
Headgear is a common treatment option in stabilizing the teeth during growth and
generating or stabilizing tooth movement8, 9. A disadvantage of headgear is the amount
of wear necessary. A headgear should be worn for a minimum of 10 to 12 hours a day.
However, it should be ideally worn for a large majority of the day and/or overnight, that
is 23 hours per day10. The preferred time to wear it is in the early evening during the
3
highest time of growth hormone release11, 12. Many factors including patient compliance
and normal everyday activities such as eating decrease the overall wear time. Patient
compliance has been a major issue13, 14. The external component of the headgear has
disadvantages, in that it is unsightly and can be uncomfortable, especially while sleeping.
The psychological, social and physical factors decrease patient compliance15, 16. Another
disadvantage is that the amount of force applied to the teeth is frequently greater than
desired. The recommended force application is 250gm – 450 gm per side of the
dentition10. A practitioner must be careful to take the desired outcome into account to
ensure adequate forces are applied. If care is not taken, inadequate or extreme forces
may be applied and undesired outcomes may occur. Headgear has limitations in that it is
only a valid treatment option during growth. This precludes many patients from this
treatment option, if they are past puberty and growth has stopped.
Trauma while wearing headgear during vigorous activities and while sleeping is
possible17 . These disadvantages have lead to research into alternative types of anchorage
for orthodontic treatment. Creekmore and Eklund18 first suggested implants as a
possibility for alternative treatment options of skeletal anchorage, yet due to the large size
of traditional implants there were limited uses. Since Creekmore and Eklund’s original
suggestion implants have decreased in size. Now mini-implants are being used19, 20.
Such implants have been advocated as anchors for stabilization, thereby replacing the
external component of headgears21 - 24.
Temporary Anchorage Devices (TADs)
Temporary anchorage devices are devices that are placed for a limited amount of
time in the oral cavity and have the ability to be immediately loaded. These are different
from permanently placed implants in the placement techniques and sizes of implants.
Mini-implants are the most commonly used TADs.
4
Mini-implant
Definition
A traditional dental implant typically has a diameter of 4 mm or more. One
millimeter of bone is desired around the edge of an implant when placing it25. The
resulting 6 mm is too large for implantation between teeth. A mini-implant, which ranges
in diameter from 1.5 mm to 3 mm (Figure 1) and in length from 6 mm to 11 mm (Figure
2), can be placed in the axial plane between teeth without causing damage to them. Miniimplants are increasingly popular due to the elimination of compliance issues22, 26.
Mini-implants are commonly used in the posterior regions of the mouth for tooth
uprighting27, retraction28, extrusion29, intrusion30 and stabilization. Anteriorly, miniimplants are typically used for retrusion, retraction31, 32 and stabilization of teeth33.
Carrillo and co-authors34, 35 have shown mini-implants to be effective for intruding both
anterior and posterior teeth. Headgear is only able to stabilize the posterior teeth, but is
ineffective in retraction or protraction of teeth.
Imaging
Although there are continual advances in the use of mini-implants, there are still
some concerns. One is the safe placement of mini-implants without damage to vital
structures, such as the teeth36, 37. Most orthodontic practices are limited in their
radiographic imaging to pantomographic, cephalometric and intraoral units.
Pantomographic and cephalometric skull radiographs are limited views of the dentition
and surrounding structures, and may not truly depict the anatomical relationship of
structures, inasmuch as they only provide two-dimensional views. Also, there is some
magnification even with a properly positioned patient38. Superimposition of the head and
neck structures seen on these views can make certain regions more difficult to interpret.
Periapical radiographs may reduce the amount of superimposition, but angulation of the
beam and projection geometry may distort the image39. In the posterior maxilla there is
5
superimposition of the zygomatic arch making it difficult to correctly depict the location
of the roots of the maxillary molars. This is important, as the exact location of the roots
needs to be known to avoid damage during mini-implant placement.
CT images can provide accurate measurements of small areas in bone to
determine where anchors can best be placed40 – 43. Traditional CT imaging is expensive,
has a relatively high radiation dose, and may not be readily accessible. The advent of
cone beam CT (CBCT) has decreased patient exposure and is increasing accessibility to
imaging. Suomalainen44 showed that measurements using data from CBCT are accurate.
Imaging of each orthodontic patient before treatment is excessive45. In special cases,
CBCT is advised for better visualization of impacted teeth and/or disease processes in the
jaws46 .
Uses outside of orthodontics
Whereas mini-implants are commonly used in orthodontics, they have also been
used in prosthodontics for both removable and fixed prostheses. They can be used in
areas of severe atrophy, where there is inadequate bone height or width for a traditional
implant47 – 53. The life span of these implants has shown to be up to 10 years50.
Types of mini-implants
There are two different designs of mini-implants, conical and cylindrical.
Likewise, there are two different surface characteristics for mini-implants, etched and
sandblasted54. Both designs and surface characteristics have been found to have close
approximation with bone after insertion55 – 57. Both systems have been shown to be
effective58 as there has been research showing that conical mini-implants have a slightly
higher failure rate than cylindrical54 due to increased torque during placement. Increased
torque when placing mini-implants leads to higher failure rates59 – 61. This increased
torque may lead to microdamage of the bone and surrounding tissues, including necrosis
and local ischemia62, 63.
6
There are two delivery systems for inserting the implants, self-drilling and selftapping. The self-drilling mini-implant has a pointed end to pierce the overlying tissues
and bone. It is attached to a handpiece and drilled directly through the soft tissues and
bone into its final and desired location. The self-tapping mini-implant has a flat end. A
surgical flap must first be laid to visualize the bone. A pilot hole, corresponding to the
entire length of the mini-implant, is drilled through the bone along the desired path of
insertion. The mini-implant is then placed into the pilot hole and screwed into its final
location.
Each of the different systems has its own advantages and disadvantages. An
advantage of the self-drilling system is that it is a less invasive procedure, as no surgical
flap need be laid. It has been suggested that this leads to faster healing and a decreased
risk for infection64 . Disadvantages of the self-drilling system are the increased pressure
and damage to the overlying tissues, as a clean flap is not laid and the tissues may move
during insertion.
Self-tapping systems require complete visualization of the bone so that a pilot
hole can be drilled. The laying of a flap may lead to a longer healing time. The main
advantage of this complete visualization is that the desired path is more likely to be
followed as there will be no overlying tissue which may move, causing the path to be off
course65 .
Loading of mini-implants
Mini-implants are classified similar to traditional implants for immediate or
delayed loading. There can be either immediate or delayed loading66 – 68. Traditional
implants commonly use delayed loading as osseointegration increases overall success
rates69. Differences in forces applied to mini-implants vary depending on the desired
outcome70. When a traditional implant is immediately loaded, the prosthesis is placed in
such a way that little to no pressure is put on the implant while it osseointegrates. When
7
a mini-implant is immediately loaded, forces of up to 250g may be applied71 . The
implants found to fail with immediate loading are those that have peri-implant
inflammation after insertion 72 – 74.
Osseointegration
Implants have been used since the mid 1970s75. Initially there was a very high
failure rate76, 77. As implant design, surface quality and surgical techniques have
improved and osseointegration become available, failure rates dropped vastly78, 79 .
Implants80, 81 have been shown to be effective over long periods of time when
osseointegrated. Osseointegration is the process of direct connection of the bone with an
endogenous material surface without intervening connective tissues82. Originally it was
thought that mini-implants do not osseointegrate allowing for ease of removal83 and
immediate loading.
New research is showing that there actually may be some osseointegration of
mini-implants84, 85. How much osseointegration occurs is not yet known. Even a small
amount of osseointegration will increase the stability of the mini-implants which, in turn
is valuable if one considers the findings shown by Liou86 who showed that there is minor
movement with mini-implants. That raises another problem, namely the amount of
morbidity and ease of removal of the mini-implant at the completion of the orthodontic
phase. With this discovery, another question arose. Is this osseointegration
advantageous, thus encouraging a delayed loading of the mini-implant. These answers
are not known at this time, but with future studies they will come to be known.
Current Research
Currently there is limited research in the literature of potential osseous sites for
intraoral anchorage. This has been partially due to the lack of imaging technology that
makes such investigations readily practical. Even if such information were known for a
population, the lack of imaging in orthodontic offices has made it difficult to determine if
8
these areas are usable for specific patients. Advances in imaging technology have
resulted in CT units that can provide sufficient detail of small areas in the jaws. This
allows for accurate measurements to be made, thereby permitting establishment of which
areas of the jaws are most likely to provide sufficient thickness of cortical bone for
anchorage. For use of such appliances as mini-implants, CT images of the head and jaws
are needed to carry out measurements in specific areas. There have been several studies
looking at the total (cortical and cancellous bone) interdentally and in the palate87 . One
recent study88 looked at the mandibles and maxillae of 25 subjects to determine “safe
zones” for mini-implant placement using cone beam technology.
Another recent study looked specifically at the correlation between cortical bone
thickness and success rates of mini-implants. The cortical bone thickness was measured
in limited areas, namely the maxillary tuberosities. A minimum of 1mm of cortical bone
was shown to be necessary for increasing success rates89 . This study showed that
knowledge of the thicknesses of cortical bone throughout the jaws is directly linked to the
success of mini-implants.
Another article recently evaluated the thickness of cortical bone, in 1mm
increments, apically from the crest of the alveolar process90. The only areas measured
were mesial and distal to the first molar in both the maxilla and the mandible. The
authors found that the area with the most cortical bone was in the mandible and suggested
that the increase in cortical bone thickness of the mandible would lead to higher success
rates. Conversely, Miyawaki and co-authors72 suggested that thin cortical bone is
associated with an increased failure of mini-implants.
Song and co-authors58 showed that the thickness of cortical bone was an
important factor in deciding which design of mini-implant should be used. Different
designs of mini-implants used in varying thicknesses of cortical bone showed a wide
range of torques upon insertion. Increased damage at the insertion site resulted with
increased torque.
9
Cortical bone thickness and soft tissue thickness was measured in limited areas in
the maxilla by Kim and co-authors using cadavers91 . A total of 23 skulls were measured.
The areas measured were between the posterior teeth at 2 mm increments from the
cemento-enamel junction. Measurements were carried out using images of scanned
specimens. Kim et al found that buccal cortical bone thickness was thickest at the 2 mm
and 10 mm levels from the cemento-enamel junction.
These studies show that cortical bone thickness plays a large part in the success of
mini-implants, and that it may vary from place to place in the jaws. This information is
helpful for practitioners and should be verified so that the practitioner is able to determine
the best possible site for inserting mini-implants.
Hypotheses
There are areas in the maxilla and mandible that have sufficient bone to provide
adequate anchorage of mini-implants but not all areas of the jaws have this sufficient
thickness.
10
Figure 1. A traditional implant (left) and a mini-implant (right).
11
Figure 2. Two different mini-implants.
12
CHAPTER II
MATERIALS AND METHODS
Case Selection
Seventy-eight dry skulls obtained from the departments of Anatomy and Cell
Biology, Periodontics, and Oral Pathology, Radiology and Medicine at The University of
Iowa were scanned using a Siemens SOMATOM Sensation 64 slice computed
tomography (CT) scanner at The University of Iowa Hospital and Clinics (UIHC).
Mandibles and maxillae with multiple teeth missing or severe periodontal bone loss were
eliminated. There were 66 mandibles and 53 maxillas included based on these criteria.
The ethnicities, ages and sexes of the dry skulls were not known. The skulls were
scanned with a field of view (FOV) of 135mm at a pitch of 0.75 at 120 kV and 300 mAs.
The slice thickness was 0.4 mm. The skulls were aligned so that the maxillae were
positioned with the nasal spine oriented on the sagittal plane and the occlusal plane
oriented on the axial plane (Figure 3). The mandibles were aligned with the occlusal
plane oriented on the axial plane (Figure 4). The sagittal plane was perpendicular to the
table of the scanner for both the maxillae and mandibles. Multiple skulls were placed on
the table of the scanner and stabilized with styrofoam to ensure no movement on the table
as each individual skull was being scanned and the table was moving (Figure 5). There
were never more than five skulls on the table at one time. A scout image made of each
skull was used to select the final area to be scanned. Each maxilla was scanned from the
superior border of the zygomatic arch to a point inferior to the plane of occlusion. Each
mandible was scanned from the sigmoid notch of the ramus caudally to include the
inferior border of the mandible.
13
Image Analysis
The cemento-enamel junction interproximally of each tooth was determined as the
reference point for making measurements as this can be readily identified clinically and
on radiographs. The distance between the distalmost surface of a root and the mesialmost
surface of the root of the tooth immediately distal/posterior to it was measured. The
midpoint of this distance was determined and a line was made between the roots. The
line was oriented such that it was perpendicular to the facial cortical bone. It was on this
line that measurements of cortical bone were made. The distance between the two roots
was also examined to determine the widths of possible mini-implant placement.
Measurements at 6, 9 and 12 mm apical (superior/inferior) to the cemento-enamel
junction were made. These measurements were selected as arbitrary points to make the
measurements. At these points the amount of cortical bone thickness and width of bone
between the roots were measured.
The slices were reconstructed with algorithms of 30, 70, and 80. It was
determined that the 70 reconstruction algorithm gave the best viewable information for
measurement analysis. The data was transferred to the Vitrea (Vital Images, Plymouth,
Minn) program in the Department of Radiology at the UIHC. The data were then
processed such that single images could be exported from the program to make
measurements on Adobe Photoshop. When making the single image views for
measurements between the roots, the axial view was set to a level 2mm below the crest of
the alveolar ridge. On the axial view, a parasagittal plane was centered through the root
canals of the canine, first premolar and second premolar (Figure 6). The corresponding
parasagittal image was then exported. For the second premolar and first molar, the
14
parasagittal plane was oriented in the center of the root canal of the second premolar and
the buccal root of the first molar (Figure 7). For the molars, the parasagittal plane was
oriented in the center of the root canals of the buccal roots of the first and second molars
(Figure 8). The corresponding parasagittal image was then exported. This was repeated
for the second and third molars, if there was a third molar present, and the image
exported. In cases where the teeth were not aligned in a straight line antero-posteriorly,
the parasagittal plane was oriented between two teeth at a time and the images then
exported. The images for the cortical bone thickness were initially made on the same
axial view. On this view the coronal plane was positioned between the canine and first
premolar. It was then oriented at ninety degrees to the buccal cortical bone. The
corresponding paracoronal image was exported. This was repeated between the first
premolar and second premolar, the second premolar and first molar, the first molar and
second molar, and the second molar and the third molar, if a third molar was present.
The images were exported as Portable Network Graphics (PNG) formatted image files
and transferred to a separate computer for measurements.
Measurements
The measurements were made using Adobe Photoshop CS2 (Adobe Systems Inc.,
San Jose, CA, USA). A custom macro was created that was applied to each image. The
custom macro included the following steps; image size, open, set selection, paste (Figure
9). The first step of image size was enlargement of the image by 203.4% to make the
image exactly 8 pixels per 1 mm. This percentage was calculated using a scale that was
on each image as it was exported out of Vitrea. The image was enlarged with scale
15
styles, with constrain properties and a selection of the interpolation as bicubic. The next
step of the macro was to open an 8 mm grid Photoshop image. The grid was named 8
mm because it had lines equally spaced 8 pixels apart to demarcate each millimeter and
specifically marked 0 mm, 6 mm, 9 mm, and 12 mm (Figure 10). The set selection was
set to all followed by a copy and closing of the image. The last step was paste of the
copied image with a setting of anti-alias to none (Figure 11 – 12).
The grid could be moved to the desired location for a measurement on the image.
When measuring the distance between the roots, note was made of how far the cementoenamel junction was from the crest of the alveolar process for accuracy and consistency
when also measuring the cortical bone. The image was then magnified 400% for easier
viewing while making the measurements (Figure 13). While making each measurement,
the shift key was held down to ensure a straight line was made. The pixels were then
recorded. The beginning point for each measurement was at the edge of the lamina dura
of the mesial tooth to the bony edge of the lamina dura of the distal tooth. Measurements
were not made at levels where the maxillary sinus or the inferior alveolar canal were
present. After all measurements were made for the distance between the roots, the
measurements for cortical bone thickness were made. Measuring the cortical bone
images, the custom macro was again applied to all images. The grid was positioned such
that it was set at the distance of the cemento-enamel junction to the alveolar crest, as was
recorded previously while measuring inter-root distance on the parasagittal plane. The
image was then enlarged 400% for making of the measurements. Again the shift key was
held down while making measurements to ensure a straight line was made. The pixels of
each measurement were then recorded. Measurements were not made in areas where the
16
maxillary sinus, the inferior alveolar canal or the mental foramen were present.
Measurements were all made in pixels and then converted into millimeters for statistical
analysis. A total of ten percent of the measurements were made two times to check for
intraobserver error.
There were many areas that needed to be excluded from the current study due to
trauma to the teeth or bone defects. Some of the teeth had a portion of the tooth missing.
It was not known whether this was due to trauma antemortem or postmortem. When the
portion was fractured off, the cemento-enamel junction was no longer present and thus it
was not possible to verify how far the cement-enamel junction would have been from the
crest of the alveolar ridge to ensure consistency and accuracy when measuring the
cortical bone in the same sites. There were also sites where the teeth had been avulsed.
Once again the cemento-enamel junction was not present and no measurements could be
made in these areas. There were areas with large vertical bone defects such that the
measurements at 6 mm and/or 9 mm could not be made of the inter-root distance and
cortical bone thickness. On some teeth there was loss of lamina dura at the apical
portions of the teeth. This was most likely due to an inflammatory process antemortem.
These areas had to be excluded as there was no lamina dura present and the exact location
of where it would have been could not be accurately ascertained.
Overview of Statistical Methods
Descriptive statistics were calculated. The intraclass correlation was computed as
a measure of agreement between the first and second measurements which were made by
a single-observer. The following is an approximate guide for interpreting an agreement
between two measurements that correspond to an intraclass correlation coefficient. i) 1=
17
perfect agreement, ii) 0.8 = strong agreement, iii) 0.5 = moderate agreement, iv) 0.2 =
weak agreement, and v) 0 = no agreement.
In addition, a paired-sample t-test was used to determine significant differences in
bone thickness between first and second measurements made by a single observer.
All tests had a 0.05 level of statistical significance. SAS for Windows (v9.1, SAS
Institute Inc, Cary, NC, USA) was used for the data analysis.
18
Figure 3. A maxilla aligned with the nasal spine with the sagittal plane and the occlusal
plane with the axial plane before scanning.
19
Figure 4. A mandible aligned with the occlusal plane oriented along the axial plane
before scanning.
20
Figure 5. Multiple mandibles stabilized in styrofoam to prevent movement while
scanning.
21
Figure 6. An axial slice of the mandible with a line demarcating the parasagittal plane
through the root canals of the canine, first premolar and second premolar.
22
Figure 7. An axial slice of the mandible with a line demarcating the parasagittal plane
through the root canal of the second premolar and the buccal root of the first molar.
23
Figure 8. An axial slice of the mandible with a line demarcating the parasagittal plane
through the pulp canals of the first molar and second molar.
24
Figure 9. The custom macro created with Adobe Photoshop.
Figure 10. The custom grid demarcating 6 mm, 9 mm and 12 mm.
25
Figure 11. A screenshot of a starting image in Adobe Photoshop.
26
Figure 12. A screenshot of the image after the custom macro has been applied. The
image is magnified and the custom grid marking lines 6mm, 9mm, and 12mm is applied
as another layer on top of the image.
27
Figure 13. A screenshot of the image after it is enlarged to 400% for better visualization
of the edges of the cortical bone. Shown with the custom grid.
28
CHAPTER III
RESULTS
Statistical Results
Descriptive results
Cortical bone thickness in the maxilla
At the level of 6 mm from the CEJ, a mean ranging from 0.66 mm between the
second molar and third molar to 0.78 mm between the second premolar and first molar
was seen on the right side (Figure 14). The left side showed a mean ranging from 0.75
mm between the second molar and third molar to 0.87 mm between second premolar and
first molar (Figure 14). The minimum measurement made on the right side was 0.00 mm
between the canine and first premolar, and the maximum was 1.38 mm between the first
molar and second molar (Figure 15). The minimum measurement made on the left side
was 0.25 mm between the canine and first premolar and first premolar and second
premolar, and the maximum was 2.25 mm between the canine and first premolar and
second premolar and first molar (Figure 16).
At the level of 9 mm from the CEJ, a mean ranging from 0.78 mm between the
second molar and third molar to 0.94 mm between the first molar and second molar was
seen on the right side (Figure 17). The left side showed a mean ranging from 0.93 mm
between the second molar and third molar to 1.12 mm between second premolar and first
molar (Figure 17). The minimum measurement made on the right side was 0.38 mm
between the second premolar and first molar and second molar and third molar, and the
maximum was 2.50 mm between the first molar and second molar (Figure 18). The
minimum measurement made on the left side was 0.25 mm between the second molar
and third molar, and the maximum was 2.38 mm between the first molar and second
molar (Figure 19).
29
At the level of 12 mm from the CEJ, a mean ranging from 0.97 mm between the
second molar and third molar to 1.21 mm between the first molar and second molar was
seen on the right side (Figure 20). The left side showed a mean ranging from 1.09 mm
between the second molar and third molar to 1.31 mm between second premolar and first
molar (Figure 20). The minimum measurement made on the right side was 0.38 mm
between the first premolar and second premolar, second premolar and first molar, and
second molar and third molar, and the maximum was 3.13 mm between the first molar
and second molar (Figure 21). The minimum measurement made on the left side was 0.50
mm between the second molar and third molar, and the maximum was 2.88 mm between
the second premolar and first molar (Figure 22).
Cortical bone thickness in the mandible
At the level of 6 mm from the CEJ, a mean ranging from 0.61 mm between the
canine and first premolar to 3.65 mm between the second molar and third molar was seen
on the right side (Figure 23). The left side showed a mean ranging from 0.74 mm
between the canine and first premolar to 3.63 mm between second molar and third molar
(Figure 23). The minimum measurement made on the right side was 0.13 mm between
the first premolar and second premolar, and the maximum was 9.00 mm between the
second molar and third molar (Figure 24). The minimum measurement made on the left
side was 0.38 mm between the second premolar and first molar, and the maximum was
8.88 mm between the second molar and third molar (Figure 25).
At the level of 9 mm from the CEJ, a mean ranging from 0.82 mm between the
canine and first premolar to 3.17 mm between the second molar and third molar was seen
on the right side (Figure 26). The left side showed a mean ranging from 0.95 mm
between the canine and first premolar to 3.01 mm between the second molar and third
molar (Figure 26). The minimum measurement made on the right side was 0.38 mm
between the canine and first premolar and first premolar and second premolar, and the
30
maximum was 5.60 mm between the second molar and third molar (Figure 27). The
minimum measurement made on the left side was 0.50 mm between the canine and first
premolar, and the maximum was 5.50 mm between the first molar and second molar
(Figure 28).
At the level of 12 mm from the CEJ, a mean ranging from 1.04 mm between the
canine and first premolar to 2.72 mm between the second molar and third molar was seen
on the right side (Figure 29). The left side showed a mean ranging from 1.13 mm
between the canine and first premolar to 2.63 mm between the second molar and third
molar (Figure 29). The minimum measurement made on the right side was 0.50 mm
between the canine and first premolar and first premolar and second premolar, and the
maximum was 4.13 mm between the second molar and third molar (Figure 30). The
minimum measurement made on the left side was 0.50 mm between the first premolar
and second premolar, and the maximum was 4.25 mm between the second molar and
third molar (Figure 31).
Inter-root distance in the maxilla
At the level of 6 mm from the CEJ, a mean ranging from 1.26 mm between the
second molar and third molar to 2.24 mm between the second premolar and first molar
was seen on the right side (Figure 32). The left side showed a mean ranging from 1.31
mm between the first molar and second molar to 2.24 mm between the second premolar
and first molar (Figure 33). The minimum measurement made on the right side was 0.00
mm between the second premolar and first molar and second molar and third molar, and
the maximum was 4.50 mm between the second premolar and first molar (Figure 34).
The minimum measurement made on the left side was 0.00 mm between the first molar
and second molar and second molar and third molar, and the maximum was 4.25 mm
between the second premolar and first molar (Figure 35).
31
At the level of 9 mm from the CEJ, a mean ranging from 1.82 mm between the
canine and first premolar to 2.78 mm between the second premolar and first molar was
seen on the right side (Figure 32). The left side showed a mean ranging from 1.75 mm
between the canine and first premolar to 2.87 mm between the second premolar and first
molar (Figure 33). The minimum measurement made on the right side was 0.00 mm
between the canine and first premolar, second premolar and first molar, first molar and
second molar, and second molar and third molar, and the maximum was 6.00 mm
between the second premolar and first molar (Figure 36). The minimum measurement
made on the left side was 0.00 mm between the second molar and third molar, and the
maximum was 5.63 mm between the second molar and third molar (Figure 37).
At the level of 12 mm from the CEJ, a mean ranging from 2.20 mm between the
canine and first premolar to 3.68 mm between the second premolar and first molar was
seen on the right side (Figure 32). The left side showed a mean ranging from 1.98 mm
between the canine and first premolar to 3.71 mm between the second premolar and first
molar (Figure 33). The minimum measurement made on the right side was 0.00 mm
between the canine and first premolar, first premolar and second premolar, and second
molar and third molar, and the maximum was 8.75 mm between the second premolar and
first molar (Figure 38). The minimum measurement made on the left side was 0.00 mm
between the canine and first premolar and second molar and third molar, and the
maximum was 6.75 mm between the second molar and third molar (Figure 39).
Inter-root distance in the mandible
At the level of 6 mm from the CEJ, a mean ranging from 1.04 mm between the
canine and first premolar to 3.08 mm between the first molar and second molar was seen
on the right side (Figure 40). The left side showed a mean ranging from 1.14 mm
between the canine and first premolar to 2.98 mm between the first molar and second
molar (Figure 41). The minimum measurement made on the right side was 0.00 mm
32
between the canine and first premolar and second molar and third molar, and the
maximum was 5.00 mm between the second molar and third molar (Figure 42). The
minimum measurement made on the left side was 0.00 mm between the canine and first
premolar and second molar and third molar, and the maximum of 4.75 mm between the
first molar and second molar (Figure 43).
At the level of 9 mm from the CEJ, a mean ranging from 1.25 mm between the
canine and first premolar to 3.89 mm between the first molar and second molar was seen
on the right side (Figure 40). The left side showed a mean ranging from 1.49 mm
between the canine and first premolar to 3.89 mm between the first molar and second
molar (Figure 41). The minimum measurement made on the right side was 0.00 mm
between the canine and first premolar and second premolar and first molar, and the
maximum was 7.13 mm between the first molar and second molar (Figure 44). The
minimum measurement made on the left side was 0.00 mm between the canine and first
premolar, first premolar and second premolar, and second molar and third molar, and the
maximum was 6.50 mm between the first molar and second molar and second molar and
third molar (Figure 45).
At the level of 12 mm from the CEJ, a mean ranging from 1.98 mm between the
canine and first premolar to 5.38 mm between the first molar and second molar was seen
on the right side (Figure40). The left side showed a mean ranging from 2.05 mm between
the canine and first premolar to 5.49 mm between the first molar and second molar
(Figure 41). The minimum measurement made on the right side was 0.00 mm between
the second premolar and first molar, and the maximum of 8.50 mm between the second
premolar and first molar (Figure 46). The minimum measurement made on the left side
was 0.00 mm between the canine and first premolar, and the maximum was 9.00 mm
between the first molar and second molar (Figure 47).
33
Measurement Reliability
Intraclass correlation was computed as a measure of intra-observer agreement
between the first and second measurements. Overall, there was very strong evidence that
the intraclass correlations differed from zero in each instance (p<0.0001), and all those
intraclass correlation coefficients indicated strong agreement between the duplicate
measurements with a single-observer at each measurement point. The intraclass
correlation coefficients were 0.98 for root6R, 0.99 for root9R, 0.99 for root12R, 0.99 for
bone6R, 0.99 for bone9R, 0.98 for bone12R, 0.99 for root6L, 0.99 for root9L, 0.99 for
root12L, 0.99 for bone6L, 0.99 for bone9L, and 0.98 for bone12L, respectively.
In addition, in order to evaluate the accuracy of duplicate measurements made by
a single observer, a new variable “diff12” (diff12=measurement1 –measurement2) was
created. A paired-sample t-test was used to determine if the mean bone thickness
difference between the two measurements was significantly equal to zero. The data
revealed that there was no statistically significant difference in mean bone thickness
between the first and second measurements at each measurement point (p>0.0.05 for each
instance).
34
Figure 14. An axial slice at 6 mm from the cemento-enamel junction noting the locations
of cortical bone thickness measured in the maxilla. The following descriptors are the side
(right or left) followed by the letter denoting the specific location. The number in
parenthesis following is the total number of measurements made at that specific location.
The numbers are the mean ± the standard deviation. All numbers are in millimeters.
RA (46): 0.67 ± 0.23
LA (45): 0.81 ± 0.34
RB (46): 0.70 ± 0.14
LB (48): 0.78 ± 0.24
RC (47): 0.78 ± 0.22
LC (48): 0.87 ± 0.29
RD (47): 0.74 ± 0.25
LD (44): 0.78 ± 0.23
RE (26): 0.66 ± 0.22
LE (28): 0.75 ± 0.25
35
Figure 15. Cortical bone thickness minimum to maximum measurement ranges between
the posterior teeth in the maxilla at 6 mm from the CEJ on the right side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
Figure 16. Cortical bone thickness minimum to maximum measurement ranges between
the posterior teeth in the maxilla at 6 mm from the CEJ on the left side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
36
Figure 17. An axial slice at 9 mm from the cemento-enamel junction noting the locations
of cortical bone thickness measured in the maxilla. The following descriptors are the side
(right or left) followed by the letter denoting the specific location. The number in
parenthesis following is the total number of measurements made at that specific location.
The numbers are the mean ± the standard deviation. All numbers are in millimeters.
RA (47): 0.86 ± 0.24
LA (49): 1.05 ± 0.27
RB (47): 0.89 ± 0.28
LB (49): 1.01 ± 0.27
RC (48): 0.89 ± 0.32
LC (49): 1.12 ± 0.35
RD (50): 0.94 ± 0.43
LD (46): 1.01 ± 0.36
RE (30): 0.78 ± 0.24
LE (30): 0.93 ± 0.30
37
Figure 18. Cortical bone thickness minimum to maximum measurement ranges between
the posterior teeth in the maxilla at 9 mm from the CEJ on the right side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
Figure 19. Cortical bone thickness minimum to maximum measurement ranges between
the posterior teeth in the maxilla at 9 mm from the CEJ on the left side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
38
Figure 20. An axial slice at 12 mm from the cemento-enamel junction noting the
locations of cortical bone thickness measured in the maxilla. The following descriptors
are the side (right or left) followed by the letter denoting the specific location. The
number in parenthesis following is the total number of measurements made at that
specific location. The numbers are the mean ± the standard deviation. All numbers are in
millimeters.
RA (47): 1.08 ± 0.35
LA (49): 1.23 ± 0.35
RB (47): 1.07 ± 0.42
LB (49): 1.21 ± 0.37
RC (48): 1.12 ± 0.43
LC (49): 1.31 ± 0.47
RD (50): 1.21 ± 0.58
LD (46): 1.28 ± 0.47
RE (31): 0.97 ± 0.33
LE (30): 1.09 ± 0.39
39
Figure 21. Cortical bone thickness minimum to maximum measurement ranges between
the posterior teeth in the maxilla at 12 mm from the CEJ on the right side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
Figure 22. Cortical bone thickness minimum to maximum measurement ranges between
the posterior teeth in the maxilla at 12 mm from the CEJ on the left side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
40
Figure 23. An axial slice at 6 mm from the cemento-enamel junction noting the locations
of cortical bone thickness measured in the mandible. The following descriptors are the
side (right or left) followed by the letter denoting the specific location. The number in
parenthesis following is the total number of measurements made at that specific location.
The numbers are the mean ± the standard deviation. All numbers are in millimeters.
RA (39): 0.61 ± 0.16
LA (43): 0.74 ± 0.17
RB (58): 0.92 ± 0.35
LB (58): 1.04 ± 0.28
RC (55): 1.19 ± 0.49
LC (52): 1.21 ± 0.38
RD (51): 2.03 ± 0.84
LD (53): 2.12 ± 0.68
RE (35): 3.65 ± 1.38
LE (35): 3.63 ± 1.22
41
Figure 24. Cortical bone thickness minimum to maximum measurement ranges between
the posterior teeth in the mandible at 6 mm from the CEJ on the right side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
Figure 25. Cortical bone thickness minimum to maximum measurement ranges between
the posterior teeth in the mandible at 6 mm from the CEJ on the left side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
42
Figure 26. An axial slice at 9 mm from the cemento-enamel junction noting the locations
of cortical bone thickness measured in the mandible. The following descriptors are the
side (right or left) followed by the letter denoting the specific location. The number in
parenthesis following is the total number of measurements made at that specific location.
The numbers are the mean ± the standard deviation. All numbers are in millimeters.
RA (48): 0.82 ± 0.26
LA (53): 0.95 ± 0.22
RB (61): 1.20 ± 0.43
LB (60): 1.38 ± 0.36
RC (57): 1.51 ± 0.47
LC (54): 1.54 ± 0.51
RD (53): 2.38 ± 0.71
LD (55): 2.53 ± 0.73
RE (36): 3.17 ± 0.87
LE (35): 3.01 ± 0.66
43
Figure 27. Cortical bone thickness minimum to maximum measurement ranges between
the posterior teeth in the mandible at 9 mm from the CEJ on the right side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
Figure 28. Cortical bone thickness minimum to maximum measurement ranges between
the posterior teeth in the mandible at 9 mm from the CEJ on the left side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
44
Figure 29. An axial slice at 12 mm from the cemento-enamel junction noting the
locations of cortical bone thickness measured in the mandible. The following descriptors
are the side (right or left) followed by the letter denoting the specific location. The
number in parenthesis following is the total number of measurements made at that
specific location. The numbers are the mean ± the standard deviation. All numbers are in
millimeters.
RA (50): 1.04 ± 0.36
LA (53): 1.13 ± 0.34
RB (61): 1.49 ± 0.48
LB (60): 1.61 ± 0.41
RC (57): 1.78 ± 0.58
LC (54): 1.73 ± 0.54
RD (53): 2.48 ± 0.56
LD (55): 2.52 ± 0.62
RE (36): 2.72 ± 0.64
LE (35): 2.63 ± 0.70
45
Figure 30. Cortical bone thickness minimum to maximum measurement ranges between
the posterior teeth in the mandible at 12 mm from the CEJ on the right side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
Figure 31. Cortical bone thickness minimum to maximum measurement ranges between
the posterior teeth in the mandible at 12 mm from the CEJ on the left side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
46
Figure 32. A diagram noting the locations of inter-root distance measured in the maxilla
on the right side. The following descriptors are the millimeter distance from the
cemento-enamel junction followed by the letter denoting the specific location. The
number in parenthesis following is the total number of measurements made at that
specific location. The numbers are the mean ± the standard deviation. All numbers are in
millimeters.
6A (45): 1.30 ± 0.78
9A (47): 1.82 ± 1.04
12A (47): 2.20 ± 1.10
6B (47): 2.13 ± 0.67
9B (47): 2.39 ± 0.99
12B (47): 3.14 ± 1.39
6C (47): 2.24 ± 0.95
9C (45): 2.78 ± 1.32
12C (38): 3.68 ± 1.56
6D (45): 1.54 ± 1.00
9D (48): 2.01 ± 1.31
12D (37): 3.29 ± 1.69
6E (18): 1.26 ± 1.05
9E (25): 2.09 ± 1.26
12E (18): 3.43 ± 2.13
47
Figure 33. A diagram noting the locations of inter-root distance measured in the maxilla
on the left side. The following descriptors are the millimeter distance from the cementoenamel junction followed by the letter denoting the specific location. The number in
parenthesis following is the total number of measurements made at that specific location.
The numbers are the mean ± the standard deviation. All numbers are in millimeters.
6A (49): 1.31 ± 0.68
9A (49): 1.75 ± 1.05
12A (48): 1.98 ± 1.10
6B (49): 1.99 ± 0.72
9B (49): 2.21 ± 0.88
12B (48): 2.81 ± 1.07
6C (48): 2.24 ± 0.96
9C (47): 2.87 ± 1.16
12C (39): 3.71 ± 1.30
6D (45): 1.33 ± 0.90
9D (43): 1.85 ± 1.20
12D (31): 3.17 ± 1.16
6E (27): 1.38 ± 1.01
9E (26): 2.20 ± 1.48
12E (14): 3.27 ± 2.01
48
Figure 34. Inter-root distance minimum to maximum measurement ranges between the
posterior teeth in the maxilla at 6 mm from the CEJ on the right side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
Figure 35. Inter-root distance minimum to maximum measurement ranges between the
posterior teeth in the maxilla at 6 mm from the CEJ on the left side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
49
Figure 36. Inter-root distance minimum to maximum measurement ranges between the
posterior teeth in the maxilla at 9 mm from the CEJ on the right side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
Figure 37. Inter-root distance minimum to maximum measurement ranges between the
posterior teeth in the maxilla at 9 mm from the CEJ on the left side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
50
Figure 38. Inter-root distance minimum to maximum measurement ranges between the
posterior teeth in the maxilla at 12 mm from the CEJ on the right side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
Figure 39. Inter-root distance minimum to maximum measurement ranges between the
posterior teeth in the maxilla at 12 mm from the CEJ on the left side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
51
Figure 40. A diagram noting the locations of inter-root distance measured in the
mandible on the right side. The following descriptors are the millimeter distance from
the cemento-enamel junction followed by the letter denoting the specific location. The
number in parenthesis following is the total number of measurements made at that
specific location. The numbers are the mean ± the standard deviation. All numbers are in
millimeters.
6A (44): 1.04 ± 0.58
9A (48): 1.25 ± 0.74
12A (46): 1.98 ± 0.96
6B (59): 2.15 ± 0.98
9B (60): 2.62 ± 1.16
12B (60): 3.21 ± 1.36
6C (53): 1.90 ± 0.93
9C (55): 2.28 ± 1.11
12C (56): 3.24 ± 1.43
6D (49): 3.08 ± 0.87
9D (51): 3.89 ± 1.13
12D (51): 5.38 ± 1.00
6E (33): 2.48 ± 1.26
9E (31): 3.59 ± 1.59
12E (25): 5.04 ± 1.42
52
Figure 41. A diagram noting the locations of inter-root distance measured in the
mandible on the left side. The following descriptors are the millimeter distance from the
cemento-enamel junction followed by the letter denoting the specific location. The
number in parenthesis following is the total number of measurements made at that
specific location. The numbers are the mean ± the standard deviation. All numbers are in
millimeters.
6A (52): 1.14 ± 0.66
9A (54): 1.49 ± 0.87
12A (54): 2.05 ± 1.11
6B (58): 2.13 ± 0.80
9B (60): 2.54 ± 1.07
12B (60): 3.00 ± 1.24
6C (53): 2.00 ± 0.81
9C (55): 2.46 ± 0.97
12C (56): 3.49 ± 1.19
6D (54): 2.98 ± 0.88
9D (55): 3.89 ± 1.12
12D (51): 5.49 ± 1.34
6E (29): 2.31 ± 1.19
9E (31): 3.29 ± 1.55
12E (25): 5.27 ± 1.50
53
Figure 42. Inter-root distance minimum to maximum measurement ranges between the
posterior teeth in the mandible at 6 mm from the CEJ on the right side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
Figure 43. Inter-root distance minimum to maximum measurement ranges between the
posterior teeth in the mandible at 6 mm from the CEJ on the left side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
54
Figure 44. Inter-root distance minimum to maximum measurement ranges between the
posterior teeth in the mandible at 9 mm from the CEJ on the right side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
Figure 45. Inter-root distance minimum to maximum measurement ranges between the
posterior teeth in the mandible at 9 mm from the CEJ on the left side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
55
Figure 46. Inter-root distance minimum to maximum measurement ranges between the
posterior teeth in the mandible at 12 mm from the CEJ on the right side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
Figure 47. Inter-root distance minimum to maximum measurement ranges between the
posterior teeth in the mandible at 12 mm from the CEJ on the left side.
C = canine, P1 = first premolar, P2 = second premolar, M1 = first molar, M2 = second
molar, M3 = third molar
56
CHAPTER IV
DISCUSSION
A reconstruction algorithm of 70 and 80 provide edge construction on axial scans.
This is better when making multiplanar reconstructions but does not provide as clean
lines when viewing in 3D. A reconstruction algorithm of 30 provides the best
information when viewing the data in 3D. This method smoothes the data and provides
clean lines when in 3D.
The implementation of mini-implants has resulted in many advances in the field
of orthodontics. Mini-implants have competed with headgears as stabilization devices.
Mini-implants are better for compliance, as with headgear compliance is difficult to
predict, and noncompliance can greatly affect the overall outcome. The use of miniimplants has many advances, but there are still major concerns. Two major concerns are
what is the best site for placement and which imaging modalities that should be used to
determine these sites. There is a limited number of research articles on areas of adequate
bone thickness in the literature and thus there is limited confirmation that implant
placement is feasible on a routine basis. This has resulted in the need for multiple skulls
to be scanned and measurements to be made in the maxilla and mandible in order to
establish a database of bone thickness.
The results of this study showed that adequate amounts of bone were identified in
the posterior maxilla and mandible. Adequate cortical bone thickness is described as 1
mm as was noted in the introduction. The posterior maxilla provided adequate bone
thickness at the level of 12 mm apical/superior to the cemento-enamel junction. This
57
level was of concern as the location of the maxillary sinus prevented making
measurements as any implantation of a mini-implant in these locations would have the
mini-implant being directly placed into the maxillary sinus. It was seen that on many of
the skulls the maxillary sinus invaginates between the teeth often. This shows the
importance of accurate radiographic evaluation of this area before the placement of a
mini-implant. Implantation into the sinus has many implications including failure of the
implant as it is only stabilized by the cortical bone, an increased chance of infection in
the maxillary sinus due to disruption of the border of the sinus, and the possibility of
introducing foreign objects into the sinus. To ensure that this does not happen a CT scan
of the area is highly recommended. The specific areas which showed an adequate
quantity of bone for mini-implant placement in the maxilla included those between the
maxillary second premolar and first molar at the 9 mm level and at all sites at the 12 mm
level.
The mandible showed adequate cortical bone thickness at the levels of 6 mm, 9
mm and 12 mm in the posterior region. At the 6 mm level the location between the
canine and first premolar was noticeably below 1 mm in thickness. At the 9 mm level the
location between the canine and first premolar was slightly below 1 mm.
There was a large range of inter-root distance between all the teeth in both the
maxilla and the mandible. The region with the highest inter-root distance was between
the first molar and second molar in the mandible at the 6 mm, 9 mm, and 12 mm levels.
The 12 mm location for placement of implants is less frequently used due to
mobility of the mucosa in these areas. The measurements are still valuable to know
should this be the only location with adequate cortical bone thickness for implantation.
58
A consideration is the direction of implantation of the mini-implant. Whereas the
most accepted insertion is at 90 degrees to the bone, some practitioners are attempting to
place implants with a more oblique angled approach to engage a larger thickness of
cortical bone in an attempt to gain more stability for the mini-implant.
CT imaging adds valuable information, such as the location of the maxillary sinus
or inferior alveolar canal and exact locations of the roots, for determining mini-implant
placement location. Scans provide accurate information for measurements, however use
of a scanner is not always possible for a practitioner. Limits include patient finances or
location of an adequate CT machine. The advent of CBCT scanners have helped in
increasing access to CT technology and decreasing costs for scans. In the future this will
contribute to more information available for a practitioner before placing mini-implants.
This additional information is helpful to a practitioner but there are still many
things to be done. One major disadvantage to the use of dry skulls was not having
knowledge of the race, age or sex of the skull. The age of the skulls scanned were most
likely those of adults. The results are accurate for an adult population, whereas an
orthodontics patient population is large majority children and teenagers. This study
provides information that is a good starting point when determining a location for
placement of a mini-implant.
Further research using CBCT data to evaluate cortical bone thickness including
variables such as age, race and sex would help. The same information acquired for this
research could be evaluated for cortical bone thickness at angles versus the straight
horizontal that was used in this study.
59
Conclusions
There are many sites with adequate amounts of cortical bone throughout the
mandible and maxilla. In the maxilla the mean cortical bone thickness was below 1 mm
at the 6 mm location while at 9 mm and 12 mm locations the mean cortical bone
thickness varied from 0.78 mm to 1.31 mm. There was a wide range of measurements in
the mandible from 0.62 mm to 3.65 mm with the majority of the means over 1mm. The
mandible overall had more thickness of the cortical bone than the maxilla.
This data show that in general there are several areas of adequate bone thickness
for implant placement. However, for each patient imaging is necessary, because, although
the mean values show that bone is of adequate thickness, the range of thicknesses is
considerable. CT imaging is necessary to provide the practitioner with the inter-root
distance and cortical bone thickness in different areas before determining mini-implant
placement.
60
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