Bone Mapping of the Mandibular Buccal Shelf: A CBCT study

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BONE MAPPING OF THE MANDIBULAR

BUCCAL SHELF – A CBCT STUDY

Dissertation submitted to

THE TAMILNADU Dr. M.G.R. MEDICAL UNIVERSITY

In partial fulfillment for the degree of

MASTER OF DENTAL SURGERY

BRANCH V

ORTHODONTICS AND DENTOFACIAL ORTHOPAEDICS

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ACKNOWLEDGEMENTS

I would like to acknowledge and thank my beloved Professor and Head, Dr. N. R. Krishnaswamy, M.D.S., M. Ortho (RCS, Edin), D.N.B. (Ortho), Diplomate of Indian board of Orthodontics, Department of Orthodontics, Ragas Dental College and Hospital, Chennai. I consider myself extremely fortunate to have had the opportunity to train under him. His enthusiasm, integral view on research, tireless pursuit for perfection and mission for providing ‘high quality work’, has made a deep impression on me. He has always been a source of inspiration to strive for the better not only in academics but also in life. His patience and technical expertise that he has shared throughout the duration of the course has encouraged me in many ways.

I am privileged to express my extreme gratefulness to my respected guide, Professor Dr. M. K. Anand, M.D.S., for his guidance which helped me complete this study. His everlasting inspiration, encouragement, constructive criticism and valuable suggestions conferred upon me have encouraged me.

My sincere thanks to Professor A. Kanakaraj, Chairman,

Dr. N.S. Azhagarasan, Principal, Ragas Dental College for providing me with an opportunity to utilize the facilities available in this institution in order to conduct this study.

I would also like to acknowledge Dr. G. Jayakumar (Professor),

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(Reader), Dr. Shobbana Devi (Reader), Dr. Premalatha (Reader),

Dr. Kavitha (Lecturer), Dr. Dhivya Lakshmi (Lecturer) and Dr. Bharath Ramesh (Lecturer) for their support, enthusiasm & professional assistance throughout my post graduate course.

I would also like to thank Dr. Madan Kumar (Professor) and

Dr. Brinda (Lecturer) Department of Community Dentistry for thier valuable suggestions during my statistical work.

I would also like to thank my friend Dr. John Nesan, M.D.S., for his fervent personal interest and selfless guidance and also the CTARS team for helping me with 3D reconstruction.

My heartfelt thanks to my wonderful batch mates, Dr. B. N. Vineesha, Dr. R. Preeti, Dr. Evan. A. Clement, Dr. G. Preethi, Dr. Veerasankar. S, Dr. Dhanalakshmi, Dr. Vidhu. S, who were cheerfully available at all times to help me. Their support and friendship was constant during these last years, and I deeply appreciate it.

I also extend my gratitude to my juniors Dr. Aparna, Dr. Mathew, Dr. Charles, Dr. Harish, Dr. Gopinath, Dr. Sam Prasanth, Dr. Rishi, and

Dr. Swathy for their support.

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and the Scribbles team for their co-operation and help during my course of study.

I would like to thank my seniors Dr. Arpitha Rao, Dr. Ravi Teja, Dr. Revathi. N, and Dr. Sharanya Devi for their constant encouragement and

support.

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1. INTRODUCTION 1

2. REVIEW OF LITERATURE 5

3. MATERIALS & METHODS 27

4. RESULTS 34

5. DISCUSSION 50

6. SUMMARY & CONCLUSION 67

7. BIBLIOGRAPHY 69

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Introduction

1

INTRODUCTION

One of the difficult malocclusions to diagnose and treat is the Class III

malocclusion which is believed to be hereditary, although environmental

factors also plays a major role. The prevalence of Class III malocclusion

varies among different ethnic groups, Southeast Asian populations have the

highest prevalence of Class III malocclusion (13% to 27%). Individuals with

Class III malocclusion may have combinations of skeletal and dentoalveolar

components.94

Various treatment modalities are available for class III individuals, like

early timely treatment, camouflage and orthognathic surgery. In severe

Class-III adult patients, surgical repositioning of the maxilla and/or mandible is often

the preferred choice of treatment. If patients consent to orthognathic surgery,

subsequent orthodontic treatment becomes simple with superior functional and

esthetic results. However, several patients refuse surgery. In such situations,

orthodontic camouflage treatment may be an alternative, particularly if

discrepancy is slight or moderate.25

With the advent of temporary anchorage devices (TADs) the envelope

of discrepancy has changed and the treatment methods have expanded with

more predictable tooth movements with empowered anchorage. Camouflage

treatment with TADs have recently proved to be effective for class III patients

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Introduction

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mild-to-moderate Class III malocclusions, TADs allow en masse distalization

of the mandibular arch without any anchorage loss.

Placement site and stability of TADs play an important role in

providing absolute anchorage during en masse retraction of the mandibular

dentition in class III patients. TADs are placed in the interradicular and

extraradicular areas of the mandible for en masse distalization. The common

failure that occurs with the interradicular TADs is the root contact and lack of

cortical bone thickness. Extraradicularly TADs are commonly placed in the

mandibular retromolar area and buccal shelf.

Among all the factors that determine TAD stability and success rate,

the most important is the thickness of the cortical bone in which it is being

placed.126,77 Researchers reported that even as small as 0.5 mm differences in

cortical bone thickness can have a major impact on success rates.91 By

understanding cortical bone trends vertically and horizontally, orthodontists

will be able to maximize the chances for success.

Buccal shelf is the extension of external oblique ridge of the mandible,

anatomically it is a very safe site for extraradicular TADs because of the

density of the cortical bone present. The slope of the mandibular buccal shelf

lateral to the first molar is often quite steep, compared to a flatter area lateral

to second molar, which is more appropriate for TAD placement. The area

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Introduction

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inadequate. It is always best assess the anatomical bone morphology of buccal

shelf three dimensionally before TAD placement.70

CBCT allows clinically accurate and reliable 3-dimensional linear

measurements of the cortical bone thickness in the mandibular buccal shelf.

Cone-beam computed tomography (CBCT) has become a popular modality in

the evaluation of orthodontic diagnoses and outcomes. It offers high

diagnostic value with a relatively low radiation dose.86 Measurements made

with CBCT have been shown to be accurate to within 0.1 to 0.2 mm.46 CBCT

helps to quantify the skeletal anatomy of the buccal shelf, placement angle of

the TADs, and amount of cortical and cancellous bone engagement at the

TAD interface lateral to the molar root.70

In recent past there has been an increase in the number of adult class

III cases seeking camouflage treatment, so an intense knowledge about the

bone morphology in various areas can guide the clinicians in selecting the

placement site and the proper placement protocol. A very scant literature is

available regarding the mandibular buccal shelf region in relation to TAD

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Introduction

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Hence the objective of this study is to assess the cortical and

cancellous bone thickness in the mandibular buccal shelf region using CBCT.

Aim of the Study

:

The aim of this study is to evaluate the cortical and cancellous bone

thickness in the mandibular buccal shelf region in class I and class III skeletal

malocclusion subjects by bone mapping using cone beam computed

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Review of Literature

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REVIEW OF LITERATURE

 Cone beam computed Tomography

 Temporary Anchorage Devices

 Alveolar bone thickness and different vertical face types

 Buccal Shelf and cortical bone thickness

CONE BEAM COMPUTED TOMOGRAPHY (CBCT)

Scarfe et al. 2006,115 described that CBCT for the maxillofacial region

enables multiplanar imaging and provides 3-dimensional (3D) information,

allowing measurement of axial inclinations of the dentition and changes in the

transverse dimensions free from distortion, magnification, and

superimposition. CBCT imaging provides submillimetre resolution images

(isotropic resolution, 0.4-0.125 mm) with relatively short scanning times

(10-70 seconds) and a reduced radiation dose (equivalent to that needed for

4-15 panoramic radiographs).

Maria et al. 2008,76 compared the radiation doses for conventional

panoramic and cephalometric imaging with the doses for 2 different CBCT

units and a multi-slice CT unit in orthodontic practice. The effective dose was

lower for the panoramic and lateral cephalometric device (10.4 µSv), and

highest for the multi-slice CT (429.7 µSv). It was concluded from

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doses to patients. However, when 3-dimensional imaging is required in

orthodontic practice, a CBCT should be preferred over a CT image.

De Vos W et al. 2009,32 reported that Cone beam Computed

Tomography systems offer many benefits over medical CT for orthodontic

treatment and planning. These benefits included a lower radiation dose to the

patient, shorter acquisition times for the resolution desired in orthodontics, and

significantly lower cost than medical CT. The limitations associated with

CBCT scanners are increased scatter radiation, limited dynamic range of

X-ray area detectors, and beam hardening artefacts.

Ribeiro et al, 2010,112 analyzed the rapid maxillary expansion using

CBCT and reported that the lateral repositioning of the maxilla and increased

basal bone can be accurately observed which confirms the marked

morphological changes that occur in the upper arch and nasomaxillary

structure. They concluded that CBCT is a ground-breaking diagnostic method

in dentistry as it provides high dimensional accuracy of the facial structures

and a reliable method for quantifying the behaviour of the maxillary halves,

dental tipping, bone formation at the suture in the three planes of space, as

well as alveolar bone resorption and other consequences of palatal expansion.

Mah et al, 2011,73 CBCT allows for visualization within the alveolar

bone volume for sclerotic phenomenon that produce local intra-alveolar bone

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high proportion of the lesions, between 88% and 100%, are found in the

mandible. Within the mandible, most of the lesions are noted in the premolar

and molar region. An orthodontist may use this valuable information to

preclude certain types of biomechanics, such as torqueing or protraction or

retraction of teeth through the affected area. For placement of TADs, CBCT

allows for visualization of the interproximal root space, palatal cortical bone

thickness, sinus morphology, and other critical structures for proper selection

of TAD length. In addition, assessment of bone density is possible from the

volumetric data which allows selection of an ideal site for placement of TADs.

In recent trends a number of orthodontic diagnosis and treatment plan

changes varied widely by patient characteristics. The most frequently reported

diagnosis and treatment plan changes were in patients with unerupted teeth,

severe root resorption, or severe skeletal discrepancies. Hodges et al, 2013,48

supported that obtaining a CBCT scan before orthodontic diagnosis and

treatment planning is necessary when a patient has an unerupted tooth with

delayed eruption or a questionable location, severe root resorption as

diagnosed with a periapical or panoramic radiograph, or a severe skeletal

discrepancy. He proposed that CBCT scans should be ordered only when there

is clear, specific, individual clinical justification.

Fernanda et al. 2013,40 presented a novel classification method for

individual assessment of midpalatal suture morphology using CBCT. They

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A, straight high-density sutural line, with no or little interdigitation; Stage B,

scalloped appearance of the high-density sutural line; Stage C, 2 parallel,

scalloped, high-density lines that were close to each other, separated in some

areas by small low-density spaces; Stage D, fusion completed in the palatine

bone, with no evidence of a suture; and Stage E, fusion anteriorly in the

maxilla. They concluded that this new classification method has the potential

to avoid the side effects of rapid maxillary expansion failure or unnecessary

surgically assisted rapid maxillary expansion for late adolescents and young

adults.

The heightened use of cone-beam computed tomography in

orthodontics has been coupled with increasing concern about the long-term

risks of x-ray exposure in orthodontic patients. Ludlow et al. 2013,71

calculated the effective doses in various combinations of field of view size and

field location comparing child and adult anthropomorphic phantoms. Scan

protocols used were high resolution (360 degrees rotation, 600 image frames,

120 kV[p], 5 mA, 7.4 seconds), standard (360 degrees, 300 frames, 120 kV[p],

5 mA, 3.7 seconds), QuickScan (180 degrees, 160 frames, 120 kV[p], 5 mA,

2 seconds), and QuickScan+ (180 degrees, 160 frames, 90 kV[p], 3 mA,

2 seconds). Contrast-to-noise ratio was calculated as a quantitative measure of

image quality for the various exposure options using the QUART DVT

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panoramic examinations. Significant dose reductions are accompanied by

significant reductions in image quality.

In a randomized block study design (left and right MSI interradicular

sites in the same arch in a patient). All the MSIs were then randomly allocated

by using split mouth system into two groups such that MSI placement guided

by CBCT on one side and RVG (digital intraoral periapical radiograph) on the

other side in all the patients, Kalra 2016,59 proposed that considering the high

cost and radiation dose compared to 2-D radiographs, routine use of CBCT is

not recommended for orthodontic mini-implant placement. However, if MSI

placement is difficult because of complex anatomy, the use of CBCT data for

planning may be considered.

TEMPORARY ANCHORAGE DEVICES (TADs)

Cope 2005,26 temporary anchorage device (TAD) is a device that is

temporarily fixed to bone for the purpose of enhancing orthodontic anchorage

either by supporting the teeth of the reactive unit or by obviating the need for

the reactive unit altogether, and which is subsequently removed after use.

Anchorage

Freudenthaler 200126 Anchorage in orthodontics is defined as the

amount of allowed movement of the reactive unit in a force system. Another

definition of anchorage as given by Daskalogiannakis & Ammann 2000,30

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situations, movement of the reactive unit is desirable, but quite frequently it is

critical for the reactive unit in the orthodontic system to remain absolutely

stationary while the active unit is moved in its desired direction.

Papadopoulos & Tarawneh 2007;101 Cope JB26 Miniscrew implants

or MSIs, have also been referred to as: microimplant, microscrew implant,

mini-implant, mini dental implant, miniscrew, temporary anchorage device

(TAD), and OrthoImplant.

According to Cope JB,26 Micro- is an inappropriate term, since it is

derived from microscopic or something so small that it can only be visualized

with a microscope. Sung et al. 2006,119 disagrees saying that micro- can be

used to emphasize small size such as in the terms microsomia, micrognathia,

microdontia and that “micro” should be used for implants smaller than 1.9 mm

and “mini” for implants greater than 1.9 mm, but still much smaller than

traditional dental implants.

Misch, 1988,83 classified the density of bone present in the maxilla and

mandible as D1, a dense cortical bone mostly seen in the anterior mandible at

less than 1250 Hounsfield units, then D2, a porous cortical and coarse

trabecular bone quality present commonly in the anterior and posterior

mandible and anterior maxilla which can be viewed at 850 to 1250 Hounsfield

units, then D3, a thin porous cortical and coarse trabecular bone seen in the

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units, and D4, a fine trabecular bone seen in the posterior maxilla viewed at

150-350 Hounsfield units.

Retention

Retention of MSIs in bone depends on different influencing factors

such as a) the miniscrew implant type, the miniscrew implant dimensions b)

the implant surface characteristics Kim et al. 2009,62 c) the insertion angle

Wilmes, Su & Drescher 2008,127 d) the drilling hole size e) the insertion

torque Motoyoshi et al. 2006,91 f) the force magnitude Cheng et al.22 23

g) the anatomic location Wiechmann et al.11quality and quantity of the bone,

the soft tissue characteristics Cheng et al.22 and inflammation of the

periimplant area Miyawaki et al. 2003.85

Stability of Mini-Implant

Marquezan et al. 2011,124 Meredith et al.82 When discussing MSI

stability and retention, it is important to define and understand the influence of

both primary and secondary stability separately. Primary stability is a function

of the mechanical retention between the MSI threads and the bone, and

expresses the initial stability of a recently placed MSI. It is most often

indirectly measured by the moment of force required to screw the MSI into the bone. This force is most commonly referred to as “insertion torque” Meredith

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Chen et al. 2009,20 performed a systematic review of the literature,

which identified primary stability, measured by insertion torque, as the most

critical factor for the success of MSI. If primary stability is not adequate

following implantation, the implant-bone interface is weakened and resulting

MSI micro-motion can cause failure Chen, Kyung, et al. 2009;20 Javed et al.

2011.54 The primary stability, which is important for MSI survival, is

measured in most studies by means of the insertion torque or pull out strength.

Meredith; Baumgaertel 2010,82116 Secondary stability is a

consequence of bony remodeling at the MSI bone interface and refers to the MSI’s stability after the placement site has healed. It represents the

maintenance of stability as a result of localized healing and bony remodeling,

with the possibility of new bone formation at the interface. Secondary stability is mainly dependent on the host’s response to the MSI and is influenced by

several factors.

The success rates of orthodontic microimplants have been reported

differently because of several variables. In addition, many studies have

recently been performed to determine factors affecting their success rates.

Among them, root proximity to the orthodontic implant, cortical bone

thickness, and placement angle have been reported frequently. Yi-Ra Jung et

al. 2011,131 examined microimplants implanted into the maxillary buccal

alveolar bone at the midpoint between the roots of the adjacent teeth, and

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chains, Vertical and horizontal placement angles were determined by

measuring the occlusal and mesial angles between the bone surface and the orthodontic microimplant’s long axis on the reoriented coronal and axial views

of the CBCT images, respectively. Vertical and horizontal placement angles

and cortical bone thickness are not significantly related to the success rate of

orthodontic microimplants, but root proximity is significantly related to their

success. Cortical bone thickness is significantly related to the vertical and

horizontal placement angles, but root proximity is not significantly related to

the vertical and horizontal placement angles.

Factors Affecting Mini-Implant Failure Rates

Primary stability has been shown to be the most critical factor for the

success of orthodontic MSI Chen, Kyung, et al. 2009.20 A review of the

literature identifies several factors that affect the insertion torques reached and

resulting primary stability of MSI. It has been well established that when

comparing screws of varying size, an increase in MSI diameter has a very

strong influence on peak insertion torques reached Lim et al. 2008,66 while

MSI length influences insertion torque to a lesser degree Kim et al. 2009.62

Wilmes, Su & Drescher 2008,127 Numerous studies have shown that

tapered screws reach significantly higher insertion torques, explained by the

gradual increase in diameter on insertion. Wilmes & Drescher 2011,127

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thicker layers of compact bone cause increased placement resistance. Uemura

et al. 2012,122 also well documented is the effect of MSI site preparation on

insertion torques reached. The presence of a pilot hole decreases insertion

torques due to decreased bone-to-metal contact, while the size of the pilot hole

is inversely proportional to the implant primary stability. Devlin et al. 1998,35

of all factors studied, it is generally agreed that the alveolar bone quality,

cortical bone thickness and insertion torque are among the most important

factors for achieving good primary stability. Regional differences in jaw

anatomy and bone structure may explain some of the variation in clinical

success rate between the maxilla and mandible.

Additional factors discussed in the literature affecting implant primary

stability include: thread design, MSI surface area, insertion depth, insertion

angle and bone quality related to age of the patient Motoyoshi et al. 2010.92

ALVEOLAR BONE THICKNESS AND DIFFERENT VERTICAL

FACE TYPES

While investigating the mandibular structures, it is vital to include the

teeth to comprehend the occlusal stability and determine the orthodontic tooth

positioning. Masahiro Tsunori, et al. 1998,78 illustrated that the long-face

pattern includes a narrow dental arch mainly because of the narrow mandible,

while short face pattern is wide. Mandibular molars erupt lingually but then

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tongue pressure. The dental arch width of the long-faced pattern is smaller

than the short-faced pattern. The molars will be more vertical as the equal

sized tongue exert excess pressure on the molars. The buccal cortical bone of

the short-faced pattern is thicker than the long-face pattern and the bone

inclination is more lingual than the long-faced pattern.

Beckmann et al, 1998,113 performed multiple stepwise regression

analysis to investigate the contribution of alveolar housing measurements,

proportions and their size and basal bone to the lower face height. It was

observed that in long-faced patients, the mandibular midsagittal alveolar bone

in the incisal region has limited anteroposterior dimensions. The shape of the

symphysis and the lower face height may be determined by genetic factors and

thus the shape of the symphysis can give some information for the prediction

of the adult lower face height in growing subjects.

Masumoto et al. 2001,79 provided evidence that the buccal cortical

bone thickness is associated with facial type. A thicker buccal cortical bone is

related with a smaller gonial angle and mandibular plane angle. In relation to

tooth inclination, patients with smaller gonial angle and mandibular plane

angle were found to have more vertically positioned molars. The cortical bone

thickness of the molar sections seemed to be influenced by the masticatory

functions. The mandibular body of the molar region had a structure resistant to

torsional movements. The width of the cortical bone in the buccal-alveolar

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cortical and cancellous bone on the buccal side were relatively thicker than the

lingual side.

Sadek et al. 2015,74 There is a statistically significant relationship

between facial type and alveolar height and thickness. Dentoalveolar

compensation mechanism acts in both high-angle and low-angle subjects by

vertical lengthening of the maxillary and mandibular frontal alveolar process.

Measurements of alveolar height in the posterior region in both arches showed

statistically no significant differences. High-angle cases had a thin alveolar

region in the anterior maxilla and almost at all sites in the mandible. With

marked anteroposterior incisor movement in high-angle subjects there seems

to be an increased risk of moving the incisors beyond alveolar bone support.

BUCCAL SHELF AND CORTICAL BONE THICKNESS

Lekholm and Zarb1 2 classified bone quality into 4 types: Type I, II,

III and IV, where Type I is the densest consisting mainly of cortical bone and

Type IV is the least dense bone that is loosely packed trabecular bone with

thin cortical bone.

Brunski 1999,9 in biomechanics, trabecular bone is often modeled as a

cellular solid, or, in other words, a porous version of dense (compact or

cortical) bone. The working hypothesis is that the fully mineralized solid

matrix of bone, regardless of whether this matrix exists in trabecular or

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bone, the term “density” by itself is ambiguous, since the mineralized portion

of this type of bone should always have the same density of 1.85 g/mL. To

clear up this ambiguity, researchers developed the concept of apparent density, which is defined as the “mass of bone tissue divided by the bulk volume of the

test specimen, including mineralized bone and marrow spaces”. This

definition accounts for the effects of porosity of trabecular bone, e.g., bone

with a small value of apparent density has a large porosity. Moreover, it has been found that key mechanical properties such as compressive Young’s

modulus and ultimate compressive strength depend on the apparent density

raised to the 3rd and 2nd power, respectively. Apparent density has therefore

become a standard part of the characterization of trabecular bone.

In an evaluation to determine the safe location for microimplants it was

found that the average thickness of the cortical bone at the mandibular first

and second molar region was 2.48 mm and 3.17 mm respectively and the

minimal thickness were 0.71 and 0.93 mm respectively, Park et al. 2002,103

stated that the clinician must examine the relationships between micro-implant

and the adjacent rots carefully.

In a study to quantify the treatment effects of distalization of the

mandibular molars using microscrew implants, Park et al. 2005,104 proved the

success rate and clinical considerations with the use of the microscrew

implants 90%. Miniscrews placed in the mandibular retromolar area provided

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moving posterior teeth simultaneously, the treatment time may be shortened

and round tripping of the anterior teeth can be avoided.

On a quantitative evaluation the cortical bone thickness averaged from

1.9 ± 0.6 mm, 2.0 ± 0.6 mm, and 1.9 ± 0.7 mm, mesial and distal to the first molar, and distal to the second molar, respectively at the occlusal level and 1.8 ± 0.5 mm mesial to the first molar and 1.8 ± 0.5 mm distal to the first molar at the apical level. Deguchi 2006,33 concluded that the best available location for a miniscrew is mesial or distal to the first molar, and the best angulation is 30° from the long axis of the tooth.

Motoyoshi, et al. 2007,90 in the cross sections mesial to the first molar,

the average cortical bone thickness ranged from 1.09 to 1.62 mm in the

maxilla and 1.59 to 2.66 mm in the mandible and inclined to increase with

height. In cross sections distal to the first molar, the average cortical bone

thickness ranged from 1.14 to 2.12 mm in the maxilla and 2.10 to 3.03 mm in

the mandible. The cortical bone thickness of the mandible in adolescents was

thinner than in adults at heights of 3–8 mm. No significant difference in

cortical bone thickness was observed in the mandible according to gender.

Thus the morphometric analysis revealed that the cortical bone of the

mandible was significantly thicker than that of the maxilla at any location in

the buccal posterior region, and the mandible suffices as a preparation site for

mini-implants. Bone quality is known to be one of the major factors in the

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cortical bone than mandibular third molar region so could show a lower

success rate. Cheol-Hyun Moon 2008.24

Baumgaertel et al. 2009,116 measured the cortical cortical bone

thickness at 2, 4, and 6 mm from the alveolar crest and they found the

mandible had a greater buccal cortical bone thickness than the maxilla. They

inferred that this thickness increase with increasing distance from the alveolar

crest in the mandible and in the maxillary anterior sextant. When the mean

measurements were compared, the maxillary buccal sextants, cortical bone

thickness was thickest at the 6-mm level and thinnest at the 4-mm level. At the

6-mm level in the maxillary anterior sextant, there was an increase in the

thickness progressively (thickest region) with increasing distance to the

alveolar crest. The same trend was observed in the mandibular sextant.

Cortical bone thickness increased in both jaws with increasing distance from

the midsagittal plane except distally to the maxillary second molars, where it

decreased.

Lim et al. 2009,65 regarding mandible cortical bone thickness, there

was no statistically significant difference in the anterior area while a

significant difference was found in the posterior area. The cortical bone

thickness in the mandibular posterior area was significantly greater compared

to that in the maxillary posterior area. In the mandible, cortical bone thickness

showed a gradual increase from the anterior to posterior areas. The maxilla

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different thickness. Cortical bone thickness in the mandible was greatest at 4

mm from the alveolar crest.

In the adult mandible, buccal cortex bone thickness and interradicular

space increase from anterior to posterior and from the cervical to the apical

areas. The safest implant site is between the first and second molar; and

placing the implant with an inclination almost parallel to the tooth axis (10 to

degrees) allows for maximum contact with bone cortex and minimum

penetration, Monnerat 2009.87

On determining he optimal sites for mini-implant placement in the

maxilla and the mandible based on dimensional mapping of the interradicular

spaces and cortical bone thickness, Fayed 2010,121 found in the posterior

region of the mandible the highest buccolingual thickness and buccal cortical

thickness were between the first and second molars (13.79 ± 2.03, 3.05 ± 2.22, respectively). The highest mesiodistal distance from the buccal side was found

between the second premolar and the first molar (5.61 ± 1.99), and the highest mesiodistal distance from the lingual side was between the first and second

molar. In comparison between the sexes, the males had significant higher

buccolingual thickness than the females at 2 mm level from the CEJ

posteriorly.

John Lin, 2010,69 stated that the slope of the buccal shelf around the

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molar is flatter, which makes it easier for direct mini-screw placement. The

slope around the 3rd molar has the flattest buccal shelf, but usually very

limited zone of attached gingiva. He also stated that in flatter buccal shelf,

with enough attached gingiva, direct self-drilling is possible, but cases steeper

buccal shelf, due to a narrow zone of attached gingiva and steeper cortical

bone surface, flap surgery is often needed. He suggested the following

parameters for placing buccal shelf miniscrew, the distance between the

mesial sites of the upper 1st molar to the one of the lower 1st molar should be

within one lower molar width. An orthognathic or retrognathic CR (Centric

Relation) profile at the beginning of treatment. The patient to have a little

prognathic profile and prefers nonsurgical treatment.

Timock et al. 2011,120 with the invention of 3-dimensional imaging

modality cone-beam CT (CBCT), orthodontist can now envisage and measure

the true 3-dimensional anatomy and quantitatively assess the buccal bone

height and buccal bone thickness with high precision and accuracy. The

reliability and accuracy of measurements of alveolar buccal bone height and

thickness were recorded from CBCT scans of cadaver heads relative to direct

measurements acquired after dissection by using multiple measures of

reliability and agreement. It was proved that CBCT measurements had good

reproducibility, with greater interrater agreement of buccal bone height (0.98)

than for buccal bone thickness (0.90). There were no statistically significant

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submillimeter range observed for both buccal bone height and buccal bone

thickness (between -0.77 and 0.81 mm, and between -0.32 and 0.38 mm,

respectively) were at 95% limits of agreement.

Kim, 2012,57 observed that the buccal cortical bone was thicker in men

than in women, but not statistically significant. The lingual cortical bone was

thicker in men than in women, except between left 1st and 2nd molars.

Mandibular lingual cortical bone thickness was the thickest between the 1st

and 2nd premolar region and the thickness gradually decreased posterior to

this region. On the other hand, the mandibular buccal cortical bone thickness

increased between the anterior and posterior regions. There was more than

2 mm of cortical bone in all areas, except between the canine and 1st premolar

on the buccal side of the mandible. The cortical bone on both mandibular

buccal and lingual sides is thick enough for TAD applications.

Placement of a TAD in the mandibular buccal shelf is

technique-sensitive. The mandibular second molar mesiobuccal area is the best location

for placement. At this place, the slope of the buccal shelf is less steep and

often has a better chance of placement into keratinized tissue. Avoiding a

more distal location on the buccal shelf limits the formation of mucosal

inflammation surrounding the TAD head that can lead to failure. The mandible

at this area has a relatively thick and dense cortical bone thickness. Pobanz,

2012,109 showed controlling insertion torque to within 5 and 10 N-cm has been

(32)

Review of Literature

23

Orthonia Tad Insertion Driver (RMO) allows for controlled insertion within

this torque range. A force application of 250-450 grams has been shown to be

successful in distalizing mandibular molars as well as the mandibular arch en

masse.

Ozdemir 2013,99 investigated the cortical bone thicknesses of the

maxilla and the mandible alveolar processes from adults with low, normal, and

increased facial heights with cone-beam computed tomography (CBCT)

images. He did a retrospective screening of the consecutive 3-dimensional

CBCT images with the following criteria: no periodontal disease with alveolar

bone loss, age between 20 and 45 years, no facial asymmetries, no cleft lip or

palate, no impacted or missing teeth in the measurement site, no diagnosed

systemic diseases, and no craniofacial dysmorphology. He found that cortical

bone thickness of the jaws is closely related to vertical facial type. His study

confirmed that the cortical bone thickness is low in the high angle case than

average angle and low angle cases.

Cassetta et al. 2013,12 examined the alveolar cortical bone thickness

and density for insertion of temporary anchorage device and also the

differences between age, sex, site and side of implantation using CT. He

measured the cortical bone thickness and density at 2, 4, 6 and 8 mm intervals

apical to the alveolar crest at thirteen interradicular sites form the right 2nd

molar to the left 2nd molar in both maxilla and mandible from the 48

(33)

Review of Literature

24

thicker and higher density alveolar cortical bone than females; Adults show a

thicker alveolar cortical bone than adolescents; In the mandible the alveolar

cortical bone is more compact and thicker than in the maxilla; High values of

thickness and density characterize posterior regions of both jaws; The alveolar

oral cortical bone is thicker than the buccal; There is a significant linear

increasing of thickness and density from crest to base of alveolar crest.

It was advocated that contingent on the sites between and within the

jaws, and vertical skeletal pattern the buccal cortical bone thickness fluctuates.

IIKnur Veli et al. 2014,53 evaluated the buccal cortical bone thickness using

cone-beam computed tomography (CBCT) in adolescent subjects with

different vertical skeletal patterns. In the mandible, at heights of 5 and 7 mm

in the canine–first premolar regions, and at 7 mm height from CEJ in the

second premolar–first molar region, there was statistically significant

differences between high-angle and low-angle groups. Significant differences

were also present between the first and second premolars at heights of 7 and 9

mm. Average cortical bone thickness observed ranged from 1.10–1.37 mm in

the maxilla and 1.20–3.28 mm in the mandible for all groups. As the buccal

cortical bone is thinner in high-angle patients, difficulties may be encountered

in achieving primary stability during miniscrew treatment.

Holmes et al. 2015,49 provided a road map of buccal cortical bone

thickness from the proximal surface of two teeth in areas where miniscrews

(34)

Review of Literature

25

and 50 mandibular) those were randomly selected from 50 CBCT scans with

the inclusion and exclusion criteria; the entire maxilla and mandible were present in that quadrant’s scan, all teeth were fully erupted, no teeth were

missing or impacted in areas of inspection and no pathology (including

periodontal bone loss) was observed in the areas of inspection. He concluded

that the cortical bone thickness is significantly thinner centrally between two

teeth than the areas adjacent to the roots. Of all the jaw locations studied, the

average thinnest cortical bone was between the mandibular canine and the first

premolar, whereas the thickest cortical bone was measured distal to the

midpoint of the second premolar and first molar.

Chang 2015,17 Miniscrews in the mandibular buccal shelf are

proposed as a reliable source of extra-alveolar anchorage for retracting the

entire mandibular arch to correct severe crowding, protrusion, and skeletal

malocclusion, without extractions or orthognathic surgery. Failure is common

in the posterior mandible, typically occurring in the first few weeks, so

primary stability is the critical factor for clinical success. Attempts to improve

primary stability include smaller diameter pilot holes, sites with increased

cortical bone thickness and density, and a self-drilling protocol. Bone quality

is particularly important for orthodontic miniscrews because they are retained

by mechanical locking rather than osseointegration. The average age of the

121 failure patients was 14 ± 3 years, which is considerably lower than the

(35)

Review of Literature

26

were more common among the younger patients who tended to have less

dense cortical bone in the MBS. Regarding side of patient, 78/121 (64.5%) of

the failures were on the left side and 43/121 (35.5%) were on the right. The

121 failed screws involved only 105 patients: 89 patients had single-screw

failure and the other 16 lost screws on both sides. The bilateral failures suggest

a predisposition to failure in a small portion of the patients.

Chen 2015,19 treated scissor bite with 2 x 12 mm miniscrews placed at the mandibular buccal shelves lateral to the second molars as was less invasive

and do not require much patient cooperation as intermaxillary elastics. Miniscrews placed in the buccal shelf is more efficient for molar intrusion than interradicular miniscrews because they are not placed between the roots

of teeth.

Failure of temporary anchorage devices (TADs) is a serious limitation

when treating complex problems like uprighting horizontally impacted

mandibular molars, as there are few other viable options. Chang et al. 2016,16

developed 2 mm diameter stainless steel bone screw for dense cortical

mandibular buccal shelf. This miniscrew is placed lateral to the first and second molars, so it did not interfere with the retromolar location of horizontal

impactions, or the path of tooth movement within the alveolar process. Failure of miniscrews also occurs because of hypertrophied soft tissue coverage over the implants. As commonly the 12 mm screw length is used in the ramal area

(36)

(37)

Materials and Methods

27

MATERIALS AND METHODS

The present in-vitro study was carried out in the Department of

Orthodontics and Dentofacial Orthopedics, Ragas Dental College and

Hospitals, Chennai.

All the CBCTs taken were from the patients who reported seeking

treatment to the Department of Orthodontics and Dentofacial Orthopedics at

Ragas Dental College and Hospital, Uthandi, Chennai, India, between January

and June 2016.

Inclusion criteria

 The CBCTs were taken as a pretreatment record for subjects who was

diagnosed with temporomandibular joint problems, facial asymmetry,

and moderate-to-severe skeletal class III malocclusion with reverse

overjet.

Exclusion criteria

 Subjects who had already undergone orthodontic treatment or

undergoing current orthodontic treatment.

 Subjects with noticeable periodontal disease.

(38)

Materials and Methods

28

 Subjects with severely ectopic teeth (such as buccally erupted canines

or premolars).

 Subjects with previous history of trauma

Based on the inclusion criteria subjects were majorly classified into

two groups based on their skeletal malocclusion:

o 10 subjects as class I (5 low-angle subjects and 5 high-angle subjects).

o 10 subjects as class III (5 low-angle subjects and 5 high-angle subjects).

The cone beam computed tomography (Digital Kodak 9500 cone

beam tomography scan, France) images of 20 subjects were analyzed.

Subjects were scanned standing with the head oriented in the natural head

position. For all scans, the minimum field of view used was 11 cm, and scan

time ranged from 8.9 to 20 seconds with a resolution of 0.25 to 0.30 mm.

(Figure 1)

Skeletal malocclusion categories were determined from lateral

cephalograms synthesized from the CBCT scans using the maximum intensity

projection technique. The CBCT-synthesized cephalogram of each subject was

saved as JPEG image and imported into Dolphin imaging software

(39)

Materials and Methods

29

Skeletal malocclusion were determined from the following

cephalometric measurements,

 Jarabak ratio [the ratio of posterior face height to anterior face

height using the measurements of the distance from sella (S) to

gonion (Go) divided by the distance of nasion (N) to menton

(Me)]. Average value 62% to 65%.

 Mandibular plane angle [the angle between the anterior

cranial base (sella to nasion SN) and the mandibular plane

(formed from menton to gonion Me–Go)]. Average value

32° ± 2°.

The CBCT images were stored in DICOM format and were analyzed

using Materialise Mimics Care Suite (Version 19.0) 3D software

(Materialize NV, Leuven, Belgium). (Figure 2)

A fully reconstructed three-dimensional image with sagittal, coronal,

and axial planes of the mandible was generated and the following

(40)

Materials and Methods

30

Reference Planes

 All the 3D CBCT slices selected for measurements were aligned

perpendicular to the sagittal plane (Figure 3). In the sagittal view the

axial plane was aligned at the mean mandibular alveolar crest level.

 In the axial view the sagittal plane was aligned by bisecting the

mandibular first and second molars symmetrically. An additional

sagittal reference plane was aligned at the linguala at the opening of

mandibular foremen perpendicular to the axial plane and in parallel

with the present sagittal plane. (Figure 4)

 Measurements were performed on slices in the frontal plane below the

alveolar crest level. (Figure 5)

 The axial reference plane aligned along the mean mandibular alveolar

crest level on the frontal view is correlated to be parallel with the

transverse/horizontal hinge axis (an imaginary line around which the

mandible may rotate within the sagittal plane).

The planes selected for cortical and cancellous bone measurements

from the mandibular first molar to second molar region were:

 Mesial of mandibular first molar (6M), (Figure 6).

 Middle of the crown through the furcation area of the mandibular first

(41)

Materials and Methods

31

 Interradicular bone/interdental region between the mandibular first and

second molars (6-7IR), (Figure 8).

 Middle of the crown through the furcation area of the mandibular

second molar (7Middle), (Figure 9).

 Distal of the mandibular second molar (7D) (Figure 10).

The cortical and cancellous bone thickness was measured

perpendicular along the surface of the mandibular buccal shelf at 3 mm, 5 mm

(42)

Materials and Methods

32

STATISTICAL ANALYSIS

The following statistical procedures were carried out:-

1. Data compilation and presentation

2. Statistical analyses

I. Data compilation and presentation:

Data obtained were compiled systematically in Microsoft Excel spread

sheet. The dataset was subdivided and distributed meaningfully and presented

as graphs and tables.

II. Statistical analyses:

Statistical analyses were performed using Statistical Package for Social

Sciences software (SPSS version 19, USA). Data comparison was done by

applying specific statistical tests to find out the statistical significance of the

obtained results. Depending upon the nature of the data, the statistical tests

were chosen. p value of 0.05 was considered to be significant.

Normality was checked using Shapiro-Wilk test. All the data were

found to not normal in distribution. Hence, non-parametric test was used. All

the inter group comparison was done using Mann-Whitney U test (two

(43)

Materials and Methods

33

Intergroup comparison between the 5 different mandibular sites was

done using Kruskal-Wallis test. All the significant values were taken and

Bonferroni correction was done to individually calculate the significance

(44)

Class III Class I

Left Right

Mesial of 1st molar

Middle of 1st molar

Interdental area of 1st and 2nd

molar

Middle of 2nd molar

Distal of 2nd molar 3 mm

Cortical

Cancellous

5 mm Cortical

Cancellous

7 mm Cortical

Cancellous

3 mm

5 mm

7 mm

Cortical

Cancellous

Cortical

Cancellous

Cortical

Cancellous Low

Angle

High Angle

Low Angle

High Angle

Left Right

(45)

(46)

[image:46.595.201.396.178.765.2]

Figures

(47)

[image:47.595.202.393.174.768.2]

Figures

(48)

Figures

FIGURE 3: – SAGITAL VEIW CBCT SLICE

FIGURE 4: – CORONAL VEIW CBCT SLICE

(49)

Figures

[image:49.595.73.533.228.470.2]

FIGURE 6: MESIAL OF MANDIBULAR FIRST MOLAR

(50)

[image:50.595.72.541.241.463.2]

Figures

FIGURE 7: MIDDLE OF MANDIBULAR FIRST MOLAR

(51)

[image:51.595.70.533.244.469.2]

Figures

(52)

[image:52.595.70.534.231.429.2]

Figures

FIGURE 9: MIDDLE OF MANDIBULAR SECOND MOLAR

(53)

Figures

[image:53.595.70.532.222.430.2]

FIGURE 10: DISTAL OF MANDIBULAR SECOND MOLAR

(54)

(55)

Results

34

RESULTS

This in-vitro study was performed to evaluate the thickness of cortical and cancellous bone present in the mandibular buccal shelf region in skeletal

class I and class III malocclusion individuals using bone mapping - a cone

beam computed tomography study. The results are based on the bone mapping

done on 20 CBCTs which were divided into two experimental groups; Class I,

(N = 10, low angle = 5 and high angle = 5) and Class III, (N = 10, low angle =

5 and high angle = 5) in the age range of 20 years ± 5 years.

All the CBCTs were obtained from the patients who reported seeking

treatment to the Department of Orthodontics and Dentofacial Orthopedics at

Ragas Dental College and Hospital, Uthandi, Chennai, India, between January

and June 2016.

Descriptive statistics was carried out to statistically to determine the

cortical and cancellous bone thickness in the study group,

The results are discussed under the following headings:

1. Comparison of cortical and cancellous bone thickness in class I

subjects between low and high angle cases at various mandibular

sites.

2. Comparison of cortical and cancellous bone thickness in class III

subjects between low and high angle cases at various mandibular

(56)

Results

35

3. Comparison of cortical and cancellous bone thickness between

class I and class III low and high angle subjects at various

mandibular sites.

4. Comparison of cortical and cancellous bone thickness in class I

and class III subjects between the right and left side of the

mandibular arch at various sites.

5. Comparison of cortical and cancellous bone thickness at 5

different mandibular sites in Class I and Class III low and high

angle subjects.

COMPARISON OF CORTICAL AND CANCELLOUS BONE

THICKNESS IN CLASS I SUBJECTS BETWEEN LOW AND HIGH

ANGLE CASES AT VARIOUS MANDIBULAR SITES

The non-parametric Mann Whitney test was done to determine bone

thickness in the class I low and high angle cases.

Table 1 shows mean mandibular cortical and cancellous bone

thickness and their standard deviation measurements at 3 mm, 5 mm and 7

mm level from the alveolar crest at the mesial of mandibular first molar in low

and high angle class I subjects bilaterally.

The mean mandibular cortical and cancellous bone thickness

measurements at 3 mm, 5 mm and 7 mm level at the mesial of mandibular first

molar in the low and high angle class I subjects bilaterally are statistically not

(57)

Results

36

mm level from the alveolar crest at the middle of mandibular first molar in low

and high angle class I subjects bilaterally.

measurements at 3 mm, 5 mm and 7 mm level at the middle of mandibular

first molar in the low and high angle class I subjects bilaterally are statistically

not significant (p> 0.05).

mm level from the alveolar crest at the interdental region of mandibular first

and second molar in low and high angle class I subjects bilaterally.

measurements at 3 mm, 5 mm and 7 mm level at the interdental region of

mandibular first and second molar in the low and high angle class I subjects

bilaterally are statistically not significant (p> 0.05).

mm level from the alveolar crest at the middle of mandibular second molar in

(58)

Results

37

second molar in the low and high angle class I subjects bilaterally are

statistically significant only in right cancellous region at the 3 mm level with

a p value of 0.028 (p <0.05).

mm level from the alveolar crest at the distal of mandibular second molar in

low and high angle class I subjects bilaterally.

measurements at 3 mm, 5 mm and 7 mm level at the distal of mandibular

second molar in the low and high angle class I subjects bilaterally are

statistically significant only at the right cortical region at the 3 mm and 5

mm level with a p values of 0.009 and 0.047 (p <0.05) respectively.

COMPARISON OF CORTICAL AND CANCELLOUS BONE

THICKNESS IN CLASS III SUBJECTS BETWEEN LOW AND HIGH

ANGLE CASES AT VARIOUS MANDIBULAR SITES

thickness in the class III low and high angle cases.

(59)

Results

38

mm level from the alveolar crest at the mesial of mandibular first molar in low

and high angle class III subjects bilaterally.

measurements at 3 mm, 5 mm and 7 mm level at the mesial of mandibular first

molar in the low and high angle class III subjects bilaterally are statistically

mm level from the alveolar crest at the middle of mandibular first molar in low

and high angle class III subjects bilaterally.

first molar in the low and high angle class III subjects bilaterally are

statistically significant only in the right cancellous region at the 7 mm level

with a p value of 0.044 (p <0.05).

and second molar in low and high angle class III subjects bilaterally.

(60)

Results

39

mandibular first and second molar in low and high angle class III subjects

bilaterally are statistically significant in the bilateral cortical regions at 3

mm, 5 mm and 7 mm level with a p value of 0.009 (0.028 on the right7 mm

level) (p <0.05) and in the cancellous regions at the right side 5 mm level

and bilateral 7 mm level with a p value of 0.009 (p <0.05).

low and high angle class III subjects bilaterally.

measurements at the 3 mm, 5 mm and 7 mm level at the middle of mandibular

second molar in the low and high angle class III subjects bilaterally are

statistically significant only in the left cancellous region at the 7 mm level

with a p value of 0.016 (p <0.05).

mm level from the alveolar crest at the distal of mandibular second molar in

low and high angle class III subjects bilaterally.

measurements at 3mm, 5 mm and 7 mm level at the distal of mandibular

(61)

Results

40

statistically significant only in the right cortical region at the 7 mm level

with a p value of 0.036 (p <0.05).

COMPARISON OF CORTICAL AND CANCELLOUS BONE

THICKNESS BETWEEN CLASS I AND CLASS III LOW AND HIGH

ANGLE SUBJECTS AT VARIOUS MANDIBULAR SITES

thickness in the class I and III low and high angle cases.

mm level from the alveolar crest at the mesial of mandibular first molar in the

low angle class I and class III subjects bilaterally.

measurement at 3 mm, 5 mm and 7 mm level at the mesial of mandibular first

molar in low angle class I and III subjects bilaterally are statistically

significant only in the left cortical region at the 3 mm and 7 mm level with a

p value of 0.047 and 0.009 (p <0.05) respectively and right cortical region at

the 5 mm level with a p value of 0.009 (p <0.05).

mm level from the alveolar crest at the mesial of mandibular first molar in the

(62)

Results

41

measurement at the 3mm, 5 mm and 7 mm level at the mesial of mandibular

first molar in high angle class I and III subjects bilaterally are statistically

significant only in the right cortical region at the 7 mm level with a p value

of 0.009 (p <0.05).

mm level from the alveolar crest at the middle of mandibular first molar in the

low angle class I and class III subjects bilaterally.

first molar in low angle class I and class III subjects bilaterally are statistically

mm level from the alveolar crest at the middle of mandibular first molar in the

high angle class I and class III subjects bilaterally.

first molar in high angle class I and class III subjects bilaterally are

(63)

Results

42

and second molar in the low angle class I and class III subjects bilaterally.

mandibular first and second molar in low angle class I and class III subjects

bilaterally are statistically significant only in the right cancellous region at

the 5 mm level and bilaterally at 7 mm level with a p value of 0.009

(p> 0.05).

and second molar in the high angle class I and class III subjects bilaterally.

mandibular first and second molar in high angle class I and class III subjects

bilaterally are statistically significant only in the cortical regions at all levels

with a p value of 0.009 (p> 0.05) and in the right cancellous region at 3 mm

level with a p value of 0.28 (p <0.05).

(64)

Results

43

the low angle class I and class III subjects bilaterally.

second molar in low angle class I and class III subjects bilaterally are

statistically not significant (p> 0.05).

thickness and their standard deviation measurements at 3 mm, 5 mm

Bone Mapping of the Mandibular Buccal Shelf: A CBCT study