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Cone beam computed tomographic measurements of buccal alveolar bone widths overlying the maxillary premolars

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Cone beam computed tomographic measurements of buccal alveolar bone widths overlying the maxillary premolars

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CONE BEAM COMPUTED TOMOGRAPHIC MEASUREMENTS OF BUCCAL
ALVEOLAR BONE WIDTHS OVERLYING THE MAXILLARY PREMOLARS

by

Marwa B. Abulhasan

________________________________________________________________________

A Thesis Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(CRANIOFACIAL BIOLOGY)

December 2012

Copyright 2012 Marwa B. Abulhasan

ii

DEDICATION

This thesis is dedicated to my parents, brothers and friends for their constant
support, inspiration and love. A very special thanks to Dr Tamer Sabry for his morale-
boosting and inducement through out the journey. I am very grateful and thankful.

iii

ACKNOWLEDGEMENTS

I would like to first thank Dr Hessam Nowzari for his ideas, encouragement,
support and guidance throughout this project. I would also like to thank Dr Sandra Rich
for her advice, insightful criticism, morale support and constant motivation, which were
deeply needed and appreciated. I would also like to thank Dr Kian Kar for his ongoing
dedication to his residents (us). I would like to thank Dr Homa Zadeh for his valuable
advice. I would like to thank Dr Michael Paine and Dr Glenn Sameshima for being in my
committee and supporting this endeavor. I would like to thank Victoria Rodriguez (Dee
Dee) for her amazing personality, expertise and help. Last but not least, I would like to
thank Dr Faisal Alonaizan for his enthusiasm, support and assistance with the statistical
analysis.

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TABLE Of CONTENTS

Dedication ii
Acknowledgements iii
List of Tables v
List of Figures vii
Abstract viii
Chapter 1: Introduction 1
Chapter 2: Materials and Methods 10
Chapter 3: Results 15
Chapter 4: Discussion and Conclusions 26
References 31

v

LIST OF TABLES

Table 1: Gender Distribution 15
Table 2: Ethnic Distribution 15
Table 3: Age Distribution 16
Table 4: Width of the Buccal Bone Overlying Maxillary Right 17
First Premolar, Measured 1 to 10 mm from the Buccal
Bone Crest

Table 5: Width of the Buccal Bone Overlying Maxillary Left 17
First Premolar, Measured 1 to 10 mm from the Buccal
Bone Crest
Table 6: Width of the Buccal Bone Overlying Maxillary 18
Right Second Premolar, Measured 1 to 10 mm from
the Buccal Bone Crest

Table 7: Width of the Buccal Bone Overlying Maxillary 18
Left Second Premolar, Measured 1 to 10 mm
from the Buccal Bone Crest

Table 8: Mean Distance and Range (mm) from 20
the CEJ to the Buccal Bone Crest for Maxillary
Right First Premolar
Table 9: Mean Distance and Range (mm) from 20
the CEJ to the Buccal Bone Crest for Maxillary
Left First Premolar

Table 10: Mean Distance and Range (mm) from 20
the CEJ to the Buccal Bone Crest for Maxillary
Right Second Premolar

Table 11: Mean Distance and Range (mm) from the CEJ 20
to the Buccal Bone Crest for Maxillary
Left Second Premolar

Table 12: Maxillary Premolars’ CEJ to Alveolar Bone Crest Distance 22
and Age

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Table 13: Frequency of Maxillary Premolars with Buccal 23
Bone Width Measurement of ≥ 2 mm, ≥ 1 mm,
<1 mm, and = 0 (No Bone) at 1 to 10 mm Apically From
Alveolar Bone Crest

vii

LIST OF FIGURES

Figure 1: Sagittal View Locating the Respective Arch 11
Figure 2: Axial View 12
Figure 3: Axial View With Connected Point Locators Following 12
the Respective Arch
Figure 4: Axial View With 1mm Incremental Cuts 13
Figure 5: Incremental Cut Chosen For Taking Measurements 13
A: Measuring Bone Thickness 13
B: Measuring CEJ to Alveolar Bone Crest 14
Figure 6: The Mean Bone Thickness at Each mm 19
Figure 7: Mean CEJ to Bone Crest Distance 21
Figure 8: Percentage of Maxillary Premolars with (≥ 2 mm) of 24
Buccal Bone Thickness at Each mm

Figure 9: Percentage of Maxillary Premolars with (≥ 1 mm) of 25
Buccal Bone Thickness at Each mm

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ABSTRACT

Background: Maxillary buccal bone thickness is critical in determining bone and soft
tissue response after extraction. Two millimeters of buccal bone may be optimal for
proper hard and soft tissue healing for immediate implant placement.
Objective: The purpose of this study was to utilize cone beam computerized tomography
(CBCT) to (1) measure the horizontal width of buccal alveolar bone overlying healthy
maxillary first and second premolars, (2) measure the distance from the CEJ to the bone
crest, and (3) evaluate the impact of demographic factors in relation to the independent
variables.
Methods: Tomographic data from 65 (F=39, M= 26) consecutively selected patients (age
range: 10 - 64 y/o) were evaluated twice by one examiner. Buccal bone width was
assessed at levels 1.0 -10.0 mm apical to the alveolar bone crest. The distance from the
CEJ to alveolar bone crest was also measured.
Results: A total of 260 premolars were evaluated. The percent of teeth with buccal bone
≥ 2 mm at levels 1,2,3,4 and 5 mm from the bone crest was 6.3, 8.5, 17.7, 20 and 20%
respectively for first premolars, and 20.1, 32.3, 50.8, 51.5 and 46.2% respectively for
second premolars. The overall mean thickness of bone was 1.58 mm for the first
premolars and 1.94 mm for the second premolars. Percentage widths (≥ 2 mm) observed
at levels 1 to 5 mm were 14.48% (first premolars) and 40.2% (second premolars). The
overall (levels 1 to 10 mm) percentages were 22.35% and 43.81% for the first and second
premolars respectively. Fenestrations were found in 3% of the first premolars and in 1.5
% of the second premolars. The mean distance between the CEJ and bone crest was 1.96

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mm (range: 0.7 - 3.45 mm) for the first premolars and 1.71 mm (range: 0.4 - 2.9 mm) for
the second premolars. Statistical significance was evident when age and CEJ to bone
crest distance were correlated.
Conclusion: The study’s statistics suggested a generally greater (≥ 2 mm) alveolar
buccal bone thickness overlying the maxillary second premolars, when compared to the
first premolars at all levels (1- 10 mm from bone crest). The first premolar sites
exhibited an apical gradual increase in alveolar bone thickness. However, the second
premolar sites’ maximum buccal bone thickness (≥ 2 mm) was mostly at the 4 mm level
from the alveolar bone crest. The alveolar buccal bone thickness generally increased the
more posterior the tooth is in the arch. The distance between the CEJ to the bone crest is
a wide range, not a constant uniform measurement.
In order to achieve optimal soft and hard tissue healing, a minimum of 2 mm of
buccal bone may be required when placing implants immediately after extractions
(Qahash et al. 2008, Spray et al 2000, & Grunder et al. 2005). Immediately placed
implants are usually positioned 2 to 3 mm sub-crestally. The CBCT images in the present
study revealed that buccal alveolar bone width of maxillary premolars was mostly less
than 2 mm, but increased in the apical and posterior directions. These results indicate an
increased risk of buccal implant thread exposure at the coronal part of maxillary first
premolars compared to second premolars during an immediate implant placement
protocol.

1

CHAPTER 1: INTRODUCTION

Bone tissue present at the facial and palatal/lingual aspects of the root is made up
of two layers of cortical bone (the outer bone plate and the alveolar bone proper)
separated by a varying-thickness layer of trabecular bone. Shroeder (1986) estimated that
the width of the alveolar bone proper varies between 0.1 mm and 0.4 mm. In sites where
the facial bone is extremely thin, the trabecular bone may be missing resulting in direct
contact between the outer cortical bone plate and the alveolar bone proper.
The alveolar bone proper (histologically referred to as bundle bone) is a tooth-
dependent tissue that develops in conjunction with the eruption of teeth (Araujo &
Lindhe 2005). It is part of the alveolar process that surrounds teeth and into which the
collagen fibers of the periodontal ligaments are embedded. Therefore, after tooth loss in
adulthood, the bundle bone or the alveolar bone proper is lost together with the
periodontal ligament (Cardarpoli et al. 2005, Araujo & Lindhe 2005). This process
induces an acute inflammatory response, which disrupts the alveolar bone renewal
causing reduction in height and decrease in residual ridge width (Atwood 1957, Hedegard
1962, Tallgren 1972).
Hard tissue resorption affects the soft tissue condition, which may create
potential problems when placing immediate implants in fresh extraction sockets (Evans
& Chen 2008). Implant placement in fresh extraction sockets has been a topic of
controversy. Some researchers and clinicians used to think that placing implants in
extraction sockets will prevent bone loss and would actually preserve the existing ridge.
Studies have been done to investigate this topic and check its validity (Spray et al. 2000,

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Grunder et al. 2005, Besler 2007, Qahash et al. 2008). It was noted that histologically
when the teeth are extracted along with their corresponding bundle bone, the residual
ridge is bound to resorb. Therefore, the question was raised (Belser et al. 2007) that what
is the minimal amount of buccal bone needed to minimize buccal bone resorption and
adverse esthetic outcome when placing implants in fresh extraction sockets.
Studies and general consensus reports have indicated that two millimeters of
buccal bone may be optimal for proper hard and soft tissue healing when placing
implants immediately post extraction
(Spray et al. 2000, Grunder et al. 2005, Besler
2007, Qahash et al. 2008). Qahash et al. created bilateral, critical size, supra alveolar,
peri-implant defects in 12 male Hound Labrador mongrel dogs after reducing the alveolar
ridge. Implants were placed and primary flap closure achieved. Their study objective
was to evaluate healing dynamics at buccal peri-implant sites in relation to the
dimensions of the alveolar ridge. Their results, using fluorescent (specifically
Fluorochrome) light detected mean buccal bone loss was significantly greater when the
ridge width was less than 2 mm (Qahash et al. 2008).
Spray et al. (2000) also demonstrated the impact of buccal bone thickness on
implant survival in a clinical study. Facial bone thickness was measured immediately
after tooth extraction, before implant placement, using calipers. The measurement was
then repeated after the implant healing period of 3 – 6 months. Significant facial bone
loss was observed when the initial facial bone thickness was less than 2 mm. They
reported a tendency towards bone filling or no change when the remaining buccal bone
thickness approached 2mm.
Furthermore, Grunder et al. (2005) studied the 3-D bone-to-implant relationship

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in order to establish proper measures to allow for optimal soft tissue healing. His group
suggested that the buccal bone thickness is as important as the interproximal bone level
for longevity of the implant and for an optimal aesthetic result.
On the other hand, different studies were done in order to measure the normal
thickness of buccal bone in both dentate and edentulous individuals. As an example,
Katranji et al. (2007) used 28 cadaver jaws to determine the average buccal/facial cortical
thickness in the edentulous and dentate maxilla and mandible. They measured molar,
premolar and anterior sites and determined the following: The average buccal cortical
thickness ranged from 1.0 to 2.1 mm in the edentulous maxilla and mandible. The
thinnest sites were the anterior maxilla and thickest sites were the posterior mandible. In
dentate subjects, after extraction, buccal bone thickness was measured using using a
digital Boley gauge caliper at the alveolar crest level and 3 mm apical to that. The buccal
bone thickness varied from 1.6 to 2.2 mm. The thinnest sites were the anterior mandible
and the thickest buccal bone was found in the posterior maxilla.
Cone beam computed tomography scans were also used to measure buccal/facial
bone thickness. Braut et al. (2011) measured facial bone thickness of the maxillary
anterior teeth using the sagittal CBCT cuts. Measurements were taken 4 mm apical to the
CEJ (location 1) and also at the middle level of the root (location 2). They found bone
73.3% of the time in location 1 and 90% of the time in location 2. Seventy percent of the
location 1 had buccal bone that was less than 1 mm in thickness and 80 % of location 2
bone was also less than 1 mm. Statistical significance was noted when comparing the
buccal bone thickness difference between the teeth. There was a significant decrease in
thickness from the first premolar to the central incisors. The thickness of bone at the

4

crestal portion was noted to be very minimal or missing in almost 90% of the patients.
Nowzari et al. (2010) used CBCT scans to measure facial alveolar bone overlying
healthy maxillary central incisors in 101 randomly selected patients at levels 1 to 10 mm
apical to the bone crest. The overall thickness of bone was a mean of 1.05 mm for the
right and left central incisors. The bone thickness increased apically. On the whole, the
mean facial bone thickness was less than 2 mm at all levels.
The previous study was repeated at the Catholic University of Sacred Heart in
Rome, Italy by Ghassemian et al (2012). In this study however, the facial bone thickness
measured was overlying the six maxillary anterior teeth. The bone width (from 66 CBCT
scans) was measured at points 1 to 5 mm from the bone crest by two calibrated
examiners. The results indicated a generally high occurrence of thin facial bone (less
than 2 mm). The buccal bone thickness increased apically. The bone thickness overlying
the lateral incisors at all levels measured was more than that of the centrals and canines.
Januario et al. (2011) further measured the facial bone thickness (using CBCT
scans) at the following levels apical to the CEJ of the maxillary anterior teeth: 1,3,and 5
mm. His group reported thin facial bone that is also less than 2 mm at all levels and 50 %
of the sites were less than 0.5 mm.
A fifth similar study by Shen et al. (2012) measured facial bone wall thickness of
maxillary anterior and premolar teeth using 118 CBCT scans. They only measured the
thickness of the bone at 4 mm apical to CEJ (point 1) and at the middle of the root (point
2). They had similarly reported facial bone that is less than 2 mm for the maxillary
anterior teeth (range: 0.5 to 1.5 mm). As for the premolars, they reported a thickness of
more than 1 mm at both measured levels more than 68% of the time.

5

Most of the literature available focused on measuring buccal bone in the maxillary
anterior region. When the premolars were studied, the bone thickness measured was only
at certain locations from the CEJ. This current study focused on measuring buccal bone
thickness overlying the maxillary premolars at levels 1 to 10 mm apical to the bone crest.

BIOLOGIC WIDTH
One of the concepts in periodontology that is important in restorative dentistry is
biologic width especially when restoring a compromised tooth. A compromised tooth
can be one with subgingival caries, subgingival dental defect, subgingival crown fracture,
inadequate crown length and external perforation of a retentive pin (Kaldahl et al. 1984).
Biologic width is a range that varies between humans, between different teeth
belonging to one human and between the multiple surfaces of one tooth. Garguilo and
his co-researchers studied the biological width components of periodontally healthy
cadaver teeth and they depicted their mean averages and ranges. Connective tissue
attachment mean average was 1.07 mm and ranged between 0.75 mm and 1.53 mm. On
the other hand, epithelial attachment average was 0.97 mm and ranged between 0.71 mm
and 1.35 mm. They also measured biological parameters such as the depth of the sulcus
and the distance between the cementoenamel junction (CEJ) and the bone crest. The
depth of the sulcus averaged 0.69 mm and the distance between the CEJ and bone crest
averaged 1.8 mm with a range of 0.75 mm to 3.10 mm (Garguilo et al. 1961).
Nowzari et al. (2010) measured the CEJ to bone crest of healthy maxillary right
and left central incisors using CBCT scans of 101 patients. Their study also reported a
range in the CEJ to bone crest distance (0.5 mm to 4.9 mm) for both teeth and an average

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of 2.4 mm. When all the maxillary anterior teeth (CEJ to bone crest distances) were
measured in a different study also using CBCT scans, the range detected was 0.8 mm to
7.2 mm (Ghassemian et al. 2012). In a similar CBCT study as the above two, Januario et
al. (2011) published the range to be 1.6 mm to 3 mm after studying the maxillary anterior
teeth (CEJ to bone crest distance). The researchers studied 250 CBCT scans performed
by the iCAT unit.
This shows that even within the same contralateral teeth in the same patient, the
measurements obtained can be different. This particular parameter (CEJ to bone crest)
was also investigated in the current study.
Even though the biological parameters vary between patients, it is important to
acknowledge them and their vast range in order to maintain a healthy, non-violated
periodontium unique to each tooth.
Space between the CEJ (or the new restorative margin) and the bone crest has to
be provided in order for the epithelium and the CT to establish proper attachment.
Disregarding these biological parameters when restoring teeth may lead to poor soft and
hard tissue response such as gingival inflammation and alveolar bone loss (Inger et al.
1977).

COMPUTED TOMOGRAPHY
In this study CBCT scans were the main source of collecting data. Radiographs
are critical tools used in dentistry to evaluate hard tissues such as teeth, alveolar bone and
any suspicious radiolucencies or radiopacities related to both. The most common dental
radiographs currently used are two-dimensional (2D) representations of structures

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superimposed on each other. These include periapical radiographs, bitewing radiographs
and panoramic radiographs. Since these radiographs are two dimensional, detection of
specific structures is not precise and may be missed. Additionally, these radiographs may
have errors such as magnification because of the unparalleled x-ray beams reaching the
examined structure/s. This magnification can further lead to geometric distortion, which
impedes accurate visibility of the anatomical features.
In this research project, computed tomography, specifically cone beam computed
tomography (CBCT) was used. Computed tomography (CT) is a technology that uses
computers to assist in reconstructing and producing three-dimensional (3D)
representation of objects (ie. maxillofacial structures) from a series of 2D x-ray images
taken around a single axis of rotation. It makes cross sections of the body and its
different tissues visible in a radiographic form. Conventional medical CT was found to be
superior to periapical radiography in identifying various types of artificially created bone
defects (Fuhrmann et al. 1995 & 1997, Langen et al. 1995).
Originally, one of EMI’s (a British multifactorial music company) branches
developed the first CT scanner and called it EMI scan. This scanner was then developed
into what is currently called computed axial tomography (CAT) scanner or simply CT
scanner by Sir Godfrey Hounsfield in 1967 (Sukovic, 2003). This conventional large CT
scanner emits high radiation dose and is primarily used for full-body scanning at a high
speed. Continuous developments of the CT scan machines lead to the invention of the
first cone beam system in 1996 (Mozzo et al. 1998). Cone beam computed tomography
(CBCT) scanner is smaller than a conventional CT scan machine, less expensive and
dedicated only to the maxillofacial region. It also offers high diagnostic value with a

8

relatively low radiation dose (approximately 50 -70 times lower dose than a conventional
CT scanner) and is comparable to dental periapical full mouth series (Ludlow et al. 2003,
Mozzo et al. 1998).
Cone beam computed tomography (CBCT) can be used with different machines
such as NewTom 3G, which was used in this study. The Newtom 3G machine was
manufactured by QR s.r.l, Verona, Italy, and distributed in the United States by APF
Imaging. It has a fixed-anode cone beam volumetric scanner that takes 360 individual
images (one per each degree of rotation) and combines them to produce the 3D
reconstruction. Radiation is not continuous which means less exposure time.
Additionally, an image intensifier (part of the machine) also allows images to be
generated with less radiation and more accuracy. Stravropoulous and Wenzel in 2007
compared the accuracy of CBCT (NewTom 3G) with intra-oral periapical radiography
for detection of simulated periapical bone defects in dry pig jaws. The CBCT revealed
results that were statistically significantly better in terms of sensitivity, positive and
negative predictive values and diagnostic accuracy when compared to digital intra oral
radiographs.
After scan completion, computer softwares are utilized to reconstruct, view and
manipulate the 3D complete anatomical image. In this study, NewTom NNT software
was used. It allows viewing the examined area from an axial plane, sagittal plane,
coronal plane and a transverse plane. This software also allows one to take wanted
measurements and in this case, buccal bone thickness at different crestal heights.

9

OBJECTIVES
Cone bean computed tomographic (CBCT) scans are valuable tools to view,
pinpoint and measure specific anatomical landmarks. This information is necessary for
proper surgical treatment planning to minimize any unnecessary short- or long-term
complications. CBCT scans provide the surgeon with the ability to measure bone length
and width, and thus to decide what implant dimensions are proper for the case. Also, in
cases of immediate implant placement, CBCT scans are used to detect position of the
existing teeth to determine whether or not immediate implant placement is even possible.
Using CBCT, the purpose of this study was to (1) measure the horizontal width of
buccal alveolar bone overlying healthy maxillary first and second premolars, (2) measure
the distance from the CEJ to the bone crest, and (3) evaluate the impact of demographic
factors in relation to the independent variables.

10

CHAPTER 2: MATERIALS AND METHODS
The University of Southern California Institutional Review Board approved the
patient chart and database review protocol of this study (# UP-09-00379).
Eighty-five scans were consecutively selected from the Ostrow School of
Dentistry of USC active CBCT database (Redmond Imaging Center, Los Angeles, CA).
The scans chosen were initial scans of patients prior to undergoing orthodontic treatment.
The inclusion criteria required no indications of periodontal disease (bone loss), no
previous periodontal therapy, and that the maxillary right and left first and second
premolars be free of dental caries and restorations.
The cone beam computed tomography hardware used in this study was NewTom
3G. X-ray settings were at 110 kV and 1 to 15 mA and the effective dose was 60 MSV.
Total scan time was 36 seconds and X-ray emission time was approximately 5 seconds.
Three-dimensional resolution was voxel size 0.3 mm and signal grey scale was 12-bit.
All scans used in this study were with resolution volume 7.9 “ cm (12 FOV). The
computer software utilized here was the NewTom NNT, which allowed viewing the
examined area from an axial plane, sagittal plane, coronal plane and a transverse plane.
Precise 1:1 scale imaging (eliminating magnification errors) provided by NewTom
technology made taking the necessary measurements for this study possible.
Each scan consisted of the patient’s information (name, date of birth, and scan
date). The Newtom NNT software provided the following view options: axial view,
panoramic view, and a three dimensional view.
First, the sagittal view (figure 1) was used to choose the respective arch. Second,
the axial view was uploaded (figure 2). This view allowed for dividing the arch into four

11

quadrants. Third, a point locater was placed at the junction of the two axes to ensure
symmetric cross sectional cuts (Figure 3). Fourth, a line was drawn to connect each of
the point locators to allow following the proper arch pattern as accurately as possible
(Figure 3). This axial view then provided cross-sectional cuts in increments of 1mm each
(Figure 4). The cross-sectional view at exactly the mid-point of each of the maxillary
premolars was chosen and measurements were taken (Figure 5). The buccal bone width
was assessed at levels 1.0 - 10.0 mm apical to the bone crest. The distance from the CEJ
of each tooth to bone crest was also computed. The measurements were taken twice by
one examiner (MA), and the averages were documented.

Figure 1: Sagittal View Locating the Respective Arch

12

Figure 2: Axial View

Figure 3: Axial View with Connected Point Locators Following the Respective Arch

13

Figure 4: Axial View With 1mm Incremental Cuts

Figure 5: Incremental Cut Chosen for Taking Measurements
A: Measuring Alveolar Bone Thickness (1 to 10 mm from Bone Crest)

14

B: Measuring CEJ to Alveolar Bone Crest

STATISTICAL ANALYSIS
Descriptive statistics were calculated for relevant variables. Two-tailed
Independent t test was used to compare mean CEJ to bone crest distance between male
and female in each group (tooth type). A simple linear regression model was constructed
to detect potential impact of independent variables for each tooth type (group) at each
mm. Statistical significance level was set at α =0.05. All Statistical analyses were
performed using SAS version 9.1 software (SAS Institute Inc., Cary, North Carolina).

15

CHAPTER 3: RESULTS

DISTRIBUTION OF GENDER, ETHNICITY AND AGE
Eighty-five CBCT scans were selected and viewed. Sixty-five scans (a total of
260 premolars) were eligible and evaluated in this study. Twenty (20) scans were
eliminated due to scatter problems (unclear images). The demographic data of this study
included 39 females and 26 males (Table 1) with an age range of 10 to 64 years old
(Table 3). The ethnicities were African Americans, Asian American, Hispanic American
and Caucasians (Table 2).

Table 1: Gender Distribution
Gender Frequency Percent (%)
Female 39 60
Male 26 40
Total 65 100

Table 2: Ethnic Distribution
Ethnicity Frequency Percent (%)
African American 3 4.6
Asian American 7 10.7
Hispanic American 27 41.5
Caucasian 28 43.0
Total 65 100
Age: Mean= 18.8, Std. div.= 9.8, Range (10-64 y/o)

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Table 3: Age Distribution
Age
(y/o)
Frequency Percentage
10 - 20 48 73.8%
21 – 30 10 15.38%
31 - 40 4 6.2 %
41 - 50 2 3.1%
51 - 60 0 0
61 - 70 1 1.5 %

MEAN BONE THICKNESS AT EACH MM
The study’s statistics suggest a generally greater (≥ 2 mm) alveolar buccal bone
thickness overlying the maxillary second premolars when compared to the first premolars
at all levels (1- 10 mm from bone crest). The alveolar buccal bone thickness increases
the more apical the bone is in the first premolar sites. However, the buccal bone is at its
maximum thickness (≥ 2 mm) mostly at 4 mm from the bone crest in the second premolar
area. Descriptive statistics for buccal bone thickness overlying each maxillary premolar
are described in tables 4,5,6, and 7. Comparison of mean bone thickness for all four teeth
is illustrated in Figure 6.

17

Table 4:
Width of the Buccal Bone Overlying Maxillary Right First Premolar, Measured 1 to 10
mm from the Buccal Bone Crest

Distance from
Crest (mm)
Mean SD Min Max
1 1.18 0.47 0.4 2.4
2 1.42 0.51 0.4 2.6
3 1.60 0.59 0.5 3.7
4 1.67 0.61 0.7 3.6
5 1.71 0.70 0.7 4.1
6 1.68 0.73 0.4 4.2
7 1.69 0.74 0.0 4.7
8 1.75 0.83 0.0 4.8
9 1.72 0.83 0.0 5.0
10 1.91 0.95 0.0 5.2

Table 5:
Width of the Buccal Bone Overlying Maxillary Left First Premolar, Measured 1 to 10
mm from the Buccal Bone Crest

Distance from
Crest (mm)
Mean SD Min Max
1 1.12 0.44 0.40 2.40
2 1.26 0.44 0.40 2.40
3 1.36 0.49 0.50 2.60
4 1.41 0.56 0.40 2.80
5 1.43 0.57 0.40 3.10
6 1.47 0.61 0.40 3.60
7 1.51 0.64 0.40 2.90
8 1.60 0.59 0.50 3.10
9 1.63 0.65 0.40 3.30
10 1.76 0.79 0.40 3.60

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Table 6:
Width of the Buccal Bone Overlying Maxillary Right Second Premolar, Measured 1 to 10
mm from the Buccal Bone Crest

Distance from
Crest (mm)
Mean SD Min Max
1 1.45 0.70 0.40 5.20
2 1.86 0.72 0.70 5.40
3 2.09 0.87 0.60 6.00
4 2.10 0.82 0.60 6.00
5 2.05 0.79 0.80 5.50
6 2.00 0.78 0.60 5.50
7 1.91 0.72 0.50 4.70
8 1.97 0.82 0.70 5.00
9 2.15 1.01 0.40 6.10
10 2.23 1.17 0.40 6.90

Table 7:
Width of the Buccal Bone Overlying Maxillary Left Second Premolar, Measured 1 to 10
mm from the Buccal Bone Crest

Distance from
Crest (mm)
Mean SD Min Max
1 1.53 0.69 0.50 3.30
2 1.91 0.70 0.50 3.70
3 2.08 0.71 0.70 3.90
4 2.03 0.78 0.70 4.40
5 1.94 0.83 0.40 4.70
6 1.93 0.82 0.40 4.20
7 1.82 0.72 0.40 3.30
8 1.87 0.68 0.50 3.60
9 1.92 0.73 0 3.60
10 2.07 0.91 0 4.40

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Figure 6: Comparing Mean Bone Thickness of All Maxillary Premolars

BONE TO CEJ DISTANCE

The distance between the CEJ to the bone crest (according to this study) is a wide
range, not a constant uniform measurement. Mean, standard deviation, minimum and
maximum vales of CEJ to bone crest for each premolar are displayed in tables 8,9, 10,
and 11. The mean CEJ to bone crest distance is less in the second premolars when
compared to the first premolars. No statistical significant difference in alveolar bone to
CEJ distance was found between male and female subjects (p > 0.05).

20

Table 8:
Mean Distance and Range (mm) from the CEJ to the Buccal Bone Crest for Maxillary
Right First Premolar

Mean SD Min Max
1.95 0.46 0.9 2.9

Table 9:
Mean Distance and Range (mm) from the CEJ to the Buccal Bone Crest for Maxillary
Left First Premolar

Mean SD Min Max
1.98 0.59 0.7 3.45

Table 10:
Mean Distance and Range (mm) from the CEJ to the Buccal Bone Crest for Maxillary
Right Second Premolar

Mean SD Min Max
1.64 0.50 0.40 2.8

Table 11:
Mean Distance and Range (mm) from the CEJ to the Buccal Bone Crest for Maxillary
Left Second Premolar

Mean SD Min Max
1.64 0.51 0.40 2.80

COMPARING MEAN CEJ TO BONE DISTANCE OF ALL PREMOLARS
The mean CEJ to bone crest distance was comparable between the first right and
left premolars and also between the second right and left premolars. The mean CEJ to
bone crest distance was greater in the first premolars when compared to the second
premolars (Figure 7).

21

Figure 7: Comparing Mean CEJ to Alveolar Bone Crest Distance of All Maxillary
Premolars

COMPARING MEAN CEJ TO BONE DISTANCE BETWEEN MALES AND
FEMALES
When comparing the mean CEJ to bone crest distance between males and females
using a Student t-test, there were no significant differences noted between the genders.
The p values for the maxillary right first premolar, maxillary left first premolars,
maxillary right second premolars and the maxillary left second premolars were the
following respectively: 0.448, 0.160,0.115 and 0.103.

22

CEJ TO BONE DISTANCE AND AGE
The Pearson correlation coefficient test revealed statistically significant
correlation between age and CEJ to bone crest distance (Table 12). As age increased, the
distance between the CEJ and bone crest also increased.
Table 12: Maxillary Premolars’ CEJ to Bone Crest Distances and Age

Tooth Pearson correlation
coefficient
P value
Right First premolar 0.28 0.02
Left First Premolar 0.29 0.02
Right Second premolar 0.29 0.02
Left Second Premolar 0.38 0.002

FREQUENCY OF BONE THICKNESS AT DIFFERENT MEASUREMENTS

The percent of teeth with buccal bone ≥ 2 mm at levels 1, 2, 3, 4, 5, 6, 7, 8, 9, and
10 mm from the bone crest was 6.3, 8.5, 17.7, 20, 20, 23.9, 26.2, 29.3, 29.3, and 42.4%
respectively for first premolars, and 20.1, 32.3, 50.8, 51.5, 46.2, 43.1, 37.6, 41.4, 49.3,
and 47.7% respectively for second premolars. Detailed 1 mm incremental measurements
for each tooth are found in table 13 and figure 8 and 9. Age, gender and ethnicity had no
statistical significant effect on alveolar bone thickness (p>0.05).

23

Table 13:
Frequency of Maxillary Premolars with Buccal Bone Width Measurement of ≥ 2 mm, ≥ 1
mm, <1 mm, and = 0 (No Bone) at 1 to 10 mm Apically from Alveolar Bone Crest

1 mm 2 mm 3 mm 4 mm 5 mm 6 mm 7 mm 8 mm 9 mm 10 mm
Tooth # 4
(n=65)

n ≥ 2 mm
(%)
11
(17%)
18
(27.7%)
33
(50.8%)
35
(53.8%)
32
(49.2%)
25
(38.5%)
22
(33.8%)
25
(38.5%)
34
(52.3%)
31
(47.7%)
n ≥ 1 mm
(%)
56
(86%)
63
(96.9%)
61
(93.8%)
61
(93.8%)
62
(95.4%)
62
(95.4%)
63
(96.9%)
61
(93.8%)
60
(92.3%)
61
(93.8%)
n < 1 mm
(%)
10
(15.4%)
2
(3.1%)
4
(6.25%)
4
(6.25%)
3
(4.6%)
3
(4.6%)
2
(3.1%)
4
(6.25%)
5
(7.7%)
4
(6.25%)
n = 0 0 0 0 0 0 0 0 0 0 0
Tooth # 5
(n=65)

n ≥ 2 mm
(%)
4
(6.3%)
8
(12.3%)
16
(24.6%)
16
(24.6%)
16
(24.6%)
18
(27.7%)
19
(29.3%)
23
(35.4%)
21
(32.3%)
30
(46.2%)
n ≥ 1 mm
(%)
45
(69.2%)
56
(86.2%)

58
(89.2%)
61
(93.8%)
61
(93.8%)

57
(87.7%)
56
(86.2%)
57
(86.7%)
56
(86.2%)

59
(90.8%)

n < 1 mm
(%)
20
(30.8%)
9
(13.8%)
7
(10.8%)
4
(6.3%)
4
(6.3%)
8
(12.3%)
8
(12.3%)
6
(9.23%)
7
(10.8%)
4
(6.2%)
n = 0
(%)
0 0 0 0 0 0 1
(1.5%)
2
(3.1%)
2
(3.1%)
2
(3.1%)
Tooth # 12
(n=65)

n ≥ 2 mm
(%)
4
(6.2%)
3
(4.6%)
7
(10.8%)
10
(15.4%)
10
(15.4%)
13
(20%)
15
(23.1%)
15
(23.1%)
17
(26.2%)
25
(38.5%)

24

Table 13, Continued

n ≥ 1 mm
(%)
40
(61.5%)
50
(76.9%)
50
(76.9%)
52
(80.0%)
51
(78.5%)

53
(81.5%)
51
(78.5%)
57
(87.7%)
54
(83.1%)
53
(81.5%)
n < 1 mm
(%)
25
(38.5%)
15
(23.1%)
15
(23.1%)
13
(20.0%)
14
(21.5%)
12
(18.5%)
14
(21.5%)
8
(12.3%)
11
(16.9%)
12
(18.5%)
n = 0 0 0 0 0 0 0 0 0 0 0
Tooth # 13
(n=65)

n ≥ 2 mm
(%)
15
(23.1%)
24
(36.9%)
33
(50.8%)
32
(49.2%)
28
(43.1%)
31
(47.7%)
27
(41.5%)
29
(44.6%)

30
(46.2%)
31
(47.7%)
n ≥ 1 mm
(%)
52
(80%)
61
(93.8%)
63
(96.9%)
60
(92.3%)

57
(87.7%)
59
(90.8%)
57
(87.7%)
58
(89.2%)
61
(93.8%)
60
(92.3%)
n < 1 mm
(%)
13
(20%)
4
(6.2%)
2
(3.1%)
5
(7.7%)
8
(12.3%)
6
(9.2%)
8
(12.3%)
7
(10.8%)
3
(4.6%)
4
(6.2%)
n = 0
(%)
0 0 0 0 0 0 0 0 1
(1.54%)
1
(1.54%)

Figure 8: Percentage of Maxillary Premolars with (≥ 2 mm) of Buccal Bone Thickness at
Each mm

25

Figure 9: Percentage of Maxillary Premolars with (≥ 1 mm) of Buccal Bone Thickness at
Each mm

26

CHAPTER 4: DISCUSSION AND CONCLUSIONS

In this study cone beam computed tomography scans were utilized to collect the
data of concern. CBCT was originally developed at the Mayo clinic for angiography
procedures back in 1982 (Robb et al. 1982). Subsequently (1998), it was used for the
craniofacial region. CBCT use has become increasingly more popular and is
characterized by its low cost, reduced radiation dose compared to conventional computed
tomography, and high performance. The scans are available in the Ostrow School of
Dentistry of USC active CBCT database (Redmond Imaging Center, Los Angeles, CA).
They are normally taken prior or during orthodontic treatment, prior to implant placement
or, at appropriate times, to assess specific anatomy or pathology in a 3-D form. Having
these scans available as a database makes retrospective studies or data viewing and
collection easier. Eighty-five pre-orthodontic treatment scans were viewed for this study.
Twenty were discarded due to scatter or clarity problems, a limitation of the study. The
CBCT technology has advantages over investigator study of dry skulls and cadavers,
which can produce very accurate results. However, dry skulls are often not available and
are not as easy to use as CBCT scans.
Accuracy of CBCT has been questioned and studies investigating this matter
started in 2004. Patcas et al. in 2012 studied the accuracy of linear measurements of
CBCT on intact cadaver heads. They also compared different voxel size settings and
their impact on accuracy and examined the clinical relevance of the acquired data. They
measured the facial bone overlying the mandibular incisors using CBCT scans and
compared them to clinical measurements. They concluded that (1) CBCT (both high and
low resolutions) provided accurate data and depicted the anatomic truth reliably. This

27

feature makes CBCT an appropriate tool for linear intraoral measurements. They also
reported that voxel size affects the precision of the measurements agreeing that 0.4 mm
voxel resolution is adequate for measurements craniofacial structures. When comparing
different CBCT devices with identical voxel sizes, it was noted that accuracy level is
hardly distinguishable. These findings go hand in hand with our findings especially since
the voxel size used in our study was 0.4 mm and results are as accurate as can be.
Another study by Patcas et al. (2012) also investigated the image quality and
accuracy of CBCT was compared with anatomical reference standard measure. The
researchers stated that CBCT scans are reliable for linear measurements and are less
susceptible to metal artifacts. They also confirmed that CBCT accuracy of linear soft
tissue measurements is similar to the accuracy of linear bone measurements. This further
confirms the use of CBCT as a reliable diagnostic and measuring tool in dentistry.
When comparing the results of our study to the results of a study done on cadaver
heads by Katranji et al. (2007), results were similar. Katranji et al. (2007) reported a 1.62
mm average buccal bone thickness on the dentate maxilla premolar region, but they only
measured the most crestal bone thickness and 3 mm apical to the crest. Our study
reported the average buccal bone thickness to be 1.73 mm and this includes all 10 mm
apical to the bone crest. This minimal difference is an indication that CBCT is a reliable
and accurate tool for reflecting clinical reality.
The descriptive statistics of this study illustrate an increase in mean bone
thickness exponentially the more apical the bone level is buccal of the first premolars.
Both right and left first premolar buccal bone thickness was comparable. The right first
premolar mean increased from 1.18 mm to 1.91 mm, and the left first premolar mean

28

ranged from 1.11 mm to 1.76 mm. The thickness was still less than 2 mm at all levels. If
an immediate implant is placed in this site, it will be placed 2 to 3 mm subcrestal in order
to achieve proper emergence profile, which means the platform will be at a level where
the bone thickness is around 1.41 mm. According to the general consensus of having at
least 2 mm of buccal bone for optimal hard and soft tissue healing around implants,
complications may arise if an implant is placed immediately in this site. An increased
risk of buccal implant thread exposure and soft tissue recession may occur. This calls for
proper treatment planning and possible need for bone and site augmentation or even
delayed implant placement after complete socket healing.
The risk of coronal implant thread exposure mentioned above is not as extensive
with the second premolar as it is with the first premolar. The reason being is that the
alveolar bone is thicker buccal of the second premolars in comparison to the first
premolars. The trend noted in the results of this study is an increase in the mean bone
thickness from the first level measured (1 mm from bone crest) to 3 or 4 mm from the
crest. Then a decrease is noted and then an increase at level 8 mm from the crest to point
10 mm (last measurement). If an implant in this site is placed immediately, 2 mm of
buccal bone maybe available where the implant platform will reside. The decrease in
thickness to below 2 mm apical to that may cause some thread exposure (mid 1/3 or
apical 1/3 of implant) if the implant is placed too far buccally. The frequency (%) of the
first premolar bone thickness ≥ 2 mm increased with apically increased measurements.
The frequency for the second molar was highest (51.5%) at level 4 mm apical to the bone
crest. Caution should still be taken when treatment planning an immediate implant,
including consideration of the root size bucco-lingually and mesio-distally. Grafting

29

(osseous or soft tissue) or even delayed implant placement may be necessary, if all the
existing parameters could lead to compromised results when placed immediately. Figure
6 compares the mean buccal bone thickness of all 4 premolars.
Our study findings regarding CEJ to bone crest (mid-buccal) distance is a wide
range consistent with other studies’ findings (both cadaver and CBCT studies). Garguilo
et al. (1961) reported a range of 0.75 mm to 3.10 mm when measuring all periodontally
healthy cadaver teeth. This wide range is consistent with the wide range measured in our
study (0.4 mm to 3.45 mm) when combining only the 4 maxillary premolars. A similar
wide range (0.5 mm to 4.9 mm) was reported by Nowzari et al. (2010) when measuring
only the central incisors. It was also a wide range distance (0.8 mm to 7.2 mm) as noted
by Ghassemian et al. (2012) in her study focusing on all the maxillary anterior teeth. This
finding proves that each tooth can have its own CEJ to bone crest measure, which will
automatically affect the biologic width of each tooth. This fact is important because
when teeth need to be restored, biologic width satisfaction means healthy periodontal
environment. Each tooth has its own biological width, (since the range is wide as shown
by the different studies) which needs to be addressed uniquely. A correlation was
depicted between age of the patient and the distance between CEJ to bone crest (Table
12). Older age meant increased CEJ to bone distance according to our study findings.
This maybe due to the human normal anatomy as one grows and the facial structure
grows too.
Within the limits (small sample size, one examiner, uneven distribution of gender,
age and ethnicity) of the current study the following conclusions were made. The study’s
statistics suggest a generally greater (≥ 2 mm) alveolar buccal bone thickness overlying

30

the maxillary second premolars when compared to the first premolars at all levels (1- 10
mm from bone crest). The alveolar buccal bone thickness increases the more apical the
bone is in the first premolar sites. However, the buccal bone is at its maximum thickness
(≥ 2 mm) mostly at 4 mm from the bone crest in the second premolar region. The
alveolar buccal bone thickness generally increases the more posterior the tooth is in the
arch. The distance between the CEJ to the bone crest is a wide range, not a constant
uniform measurement.
In order to achieve optimal soft and hard tissue healing, a minimum of 2 mm of
buccal bone may be required when immediately placing implants after extractions
(Qahash et al. 2008, Spray et al 2000, & Grunder et al. 2005). Immediately placed
implants are usually positioned 2 to 3 mm sub-crestally. The CBCT images in the present
study revealed that alveolar bone width buccal of the maxillary premolars was mostly
less than 2 mm, but increases in the apical and posterior directions. These results indicate
an increased risk of buccal implant thread exposure at the coronal part of maxillary first
premolars compared to second premolars during an immediate implant placement
protocol. Proper treatment planning and data collection are needed prior to implant
placement in order to optimize the outcome of these procedures.

31

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