Evaluation of morphology of maxillary and mandibular alveolar


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Evaluation of morphology of maxillary and mandibular alveolar bone in vertical and horizontal growers: A cone beam computed tomography study
Puneet Chaudhary, M S Sidhu, Seema Grover, Vikas Malik, Namrata Dogra*, Sandeep Kumar
Email: [email protected]

Abstract
The present study was conducted to evaluate and compare morphology of maxillary and mandibular alveolar bone in vertical and horizontal growth pattern individuals. Pretreatment cone-beam computed tomography (CBCT) images of 15 Hypodivergent, 10 Normodivergent and 15 Hyperdivergent subjects were analyzed. From the data obtained, the thickness of buccal, lingual and basal cortical bone was measured, and also an assessment of the bone and tooth inclination of 2nd premolar, 1st and 2nd molars of mandible were made. Axial and cross-sectional views were taken to assess for dehiscence and fenestration on the buccal and lingual surfaces. Independent t test and One Way Anova test were used for statistical results. A statistically significant difference was noted in the thickness of buccal and lingual cortical plates and tooth inclination among the hypodivergent group. Maximum prevalence of fenestration was around first premolar of maxilla and maximum dehiscence was found around central incisor of mandible. Cortical bone was found to be thicker in hypodivergent subjects and
the prevalence of dehiscence and fenestration was seen to differ among the different growth patterns.
Key words: Alveolar bone morphology, cone beam computed tomography, hyperdivergent, hypodivergent, norm divergent

Introduction
The tooth-alveolar bone complex is a complicated mechanical structure consisting of mineralized and periodontal soft tissue, and its main function is to transfer the occlusal force from the tooth to the surrounding bone. Orthodontic treatment planning,

assessment of progress of the treatment and the outcome of the treatment are largely dependent on the morphology of tooth-alveolar bone complex.1
In the 1870s, Julius Wolff came up with a theory claiming that the trabecular alignment was primarily due to functional forces. It was observed

Puneet Chaudhary Private practitioner, Gurgaon
M S Sidhu Professor and Head Department of Orthodontics and Dentofacial Orthopedics SGT Dental College, Gurgaon - 123505, Haryana, India
Seema Grover Professor Department of Orthodontics and Dentofacial Orthopedics SGT Dental College , Gurgaon - 123505, Haryana, India
Vikas Malik Reader, Department of Orthodontics and Dentofacial Orthopedics, SGT Dental College, Gurgaon - 123505, Haryana, India

Namrata Dogra Senior Lecturer Department of Orthodontics and Dentofacial Orthopedics SGT Dental College, Gurgaon - 123505, Haryana, India
Sandeep Kumar Senior Lecturer Department of Orthodontics and Dentofacial Orthopedics SGT Dental College, Gurgaon - 123505, Haryana, India
* Corresponding Author

How to cite this article: Puneet Chaudhary, M S Sidhu, Seema Grover, Vikas Malik, Namrata Dogra, Sandeep Kumar. (2017). Evaluation of morphology of maxillary and mandibular. MJDS, 2(2), 19-29.

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Chaudhary P, et al: Evaluation of maxillary and mandibular alveolar bone morphology using CBCT

that a variation in the internal morphology and external architecture of the bone was produced by any change in the intensity and direction of forces applied. This concept was referred to as the law of orthogonality. Bone, unlike other connective tissues responds to mild degrees of pressure and tension by changes in its form. Those changes are accomplished by means of resorption of existing bone and deposition of new bone. This is the basis of Wolff ’s Law of Transformation of Bone.2 Thus, it is seen that following changes or alterations in the loading forces that are developed through dentition and muscle contraction during function, there are changes observed in the tooth alveolar bone complex.3,4 Numerous investigations have been conducted to assess the relationship between the growth pattern and the tooth-alveolar bone complex.5-7
There are three basic types of facial vertical growth patterns: hypo-divergent (low angle), normodivergent (average) and hyper-divergent (high angle) growth patterns.8 Hyper-divergent growth pattern patients exhibit excessive vertical facial growth, anterior open bite, increased mandibular plane (MP), gonial and maxillo-mandibular plane angle.9 Conversely, hypo-divergent patterns show a reduced vertical growth, deep anterior overbite, reduced facial height and reduced MP angle. Between the two types lies the normodivergent facial growth pattern.10 The alveolar structures in different growth patterns are different in response to the varying forces and biological adaptations.3 The relationship between bite force and growth patterns has been investigated.11 The mean bite force in the molar region was reported to be two times as for normodivergent subjects as compared with hyper-divergent subjects, while hypodivergent subjects have still higher maximum forces than normodivergent subjects.12
The extent and boundary of tooth movement is defined by the thickness of the alveolar bone, and the deviation from this may have undesirable effects to the periodontal tissues. Orthodontic treatment is complicated, when there is insufficient thickness of alveolar bone.13 Dehiscence results when the marginal bone is lost, and when there is still some

bone in the cervical region, the defect is termed fenestration.14 Direction of tooth movement, frequency and magnitude of the force applied and the anatomic integrity of the periodontal tissues, determine the occurrence of dehiscence and fenestration.15 Determining bone morphology before orthodontic treatment through appropriate imaging might avoid these problems.16
The information provided by radiographic cephalometry is limited by its two-dimensional (2D) nature, resulting in projection errors, superimposition and magnification errors. Furthermore, the 2D images fail to represent the complex curving structures of the tooth-alveolar complex.17 CBCT provides comparable images to conventional computed tomography (CT) at a lower radiation dose and expense. A cross-sectional view of the tooth-alveolar bone complex generated from CBCT can reveal the dimensions of alveolar bone and the space limitations for intrusion or expansion. The multidimensional nature of imaging and reconstruction of CBCT allows for a comprehensive visualization of the tooth-alveolar bone complex, and ensures reliable and anatomically accurate measurements.
Hence, this study was done to measure the alveolar bone morphology of mandible and maxilla in hypodivergent and hyperdivergent patients, to evaluate the presence of maxillary and mandibular alveolar bone defects, that is, dehiscence and fenestration in hypodivergent and hyperdivergent patients.
Materials and methods The present study was conducted at the Department of Orthodontics and Dentofacial Orthopedics, SGT Dental College. The total sample for this study consisted of 40 preorthodontic patients. Inclusion criteria for the subjects were: age between 20 and 36 years, permanent dentition, lack of orthodontic treatment and/or functional orthopedic treatment.
The Cone Beam Computed Tomography (CBCT) scans of participants were taken from CBCT bank of Mahajan Imaging Centre, New Delhi, where they already had CBCT’s done of patients for any specific reason.

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The CBCT scans were acquired with i-CAT Cone Beam 3D Dental Imaging system (i-CAT Next generation, Imaging Sciences International, Hatfield, Pa). Each volumetric data set was acquired with a 26 seconds scan time with a 16 (diameter) and 22 (height) cm field of view and at a resolution of 0.25 mm voxels. The jpeg. images from the CBCT machine were obtained and transported to the Nemoceph NX software (Visiodent, SaintDenis, France) for calibration and analysis. Image calibration was done with scale present on the X-ray as 10mm measurement marked on the lateral cephalogram. The mandibular plane angle SN-MP was measured to categorize images into three types of growth patterns. They are:
Group I - 15 subjects having mandibular plane angle equal to or less than 26⁰ were denoted as hypodivergent. (Figure 1)
Group II - 10 subjects having mandibular plane angle between 28⁰ and 34⁰ were denoted as normodivergent. (Figure 1)
Group III - 15 subjects having mandibular plane angle equal to or greater than 37⁰ were denoted as hyperdivergent. (Figure 1)

The Digital imaging and Communications in Medicine (Dicom) images were imported to In Vivo Dental 5.2 (Anatomage, anatomy imaging software, San Jose, Ca). The rendering window allows viewing of the Coronal, Axial, Sagittal and Custom Sections or a 3D view simultaneously. (Figure 2)
The following measurements were made in crosssectional view of mandibular posterior teeth with X-axis parallel to Frankfurt horizontal plane, and Y-axis perpendicular on Frankfurt horizontal plane: height of alveolar bone, width of alveolar bone, buccal cortical bone thickness, lingual cortical bone thickness, tooth inclination. (Figure 3)
Teeth included in this study were second premolar (2P), first molar (M1) and second molar (M2) of both sides for each subject. The cross-sections were passing through the centre of the 2P, through the centre of the mesial root of the M1 and through the centre of the mesial root of the M2.
Each tooth root was evaluated in axial and crosssectional slices at the buccal and lingual surfaces. An alveolar defect was identified, when there was no cortical bone around the root in three sequential

Figure 1: Growth patterns (A - Hypodivergent, B - Normodivergent, C- Hyperdivergent)

Figure 2: Coronal, Axial, Sagittal and Custom Sections

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Chaudhary P, et al: Evaluation of maxillary and mandibular alveolar bone morphology using CBCT Figure 3: Measurements taken

Figure 3: Measurements taken
[(Height of alveolar bone (A-A’) - vertical length from the alveolar ridge crest to the inferior border of the alveolar bone. Width of alveolar bone (B-B’) - longest length from the buccal side to the lingual side and parallel to the standard plane.
Buccal cortical bone thickness (A-A’) - dimension of the cortical bone measured perpendicular to the bone surface from its outer surface to the border of the cortical and cancellous bones on buccal side at the mid-point. Lingual cortical bone thickness (B-B’) - dimension of the cortical bone measured perpendicular to the bone surface from its outer surface to the border of the cortical and cancellous bones on lingual side at the mid-point.
Tooth inclination (A-B-C)- the angle between the basal line and the tooth long axis. The long axis of the tooth was defined as the line passing through the mid-point at one-half of the crown width and the mid-point at one-third of the distance from the root apex.]

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views. If the alveolar bone height was more than 2 mm from the cementoenamel junction (Figure 4a), it was classified as dehiscence. When the defect did not involve the alveolar crest (Figure 4b), the case was classified as fenestration.

All measurements were made in coronal, axial and sagittal views of CBCT scans and were applied with statistical analysis for obtaining results.

Table 1: Comparision of mandibular alveolar bone morphology of Hypodivergent growers (Group I)) with Normodivergent growers (Group II)
Group Statistics

Parameters

Group

No of subjects

Mean

Std Deviation

p-value

Hypodivergent

15

2.56

0.73

0.49

BCBT 2nd PM

Normodivergent

10

2.39

0.28

BCBT 1st M

Hypodivergent Normodivergent

15

3.3533

0.256

10

2.94

0.45

0.008**

BCBT 2nd M

Hypodivergent Normodivergent

15

3.76

0.181

10

3.45

0.45

0.023*

Hypodivergent

15

2.60

0.54

0.12

LCBT 2nd PM

Normodivergent

10

2.31

0.20

LCBT 1st M

Hypodivergent Normodivergent

15

2.74

0.204

10

2.44

0.19

0.001**

LCBT 2nd M

Hypodivergent Normodivergent

15

2.4373

0.288

10

2.03

0.33

0.003**

Height 2nd PM Height 1st M Height 2nd M Width 2nd PM Width 1st M

Hypodivergent Normodivergent
Hypodivergent Normodivergent
Hypodivergent Normodivergent
Hypodivergent Normodivergent
Hypodivergent Normodivergent

15

28.31

3.41

10

29.12

2.45

15

27.25

3.86

10

27.72

3.46

15

26.13

3.48

10

25.23

2.67

15

17.79

1.55

10

17.46

2.72

15

18.93

2.09

10

18.54

1.98

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0.52 0.76 0.50 0.70 0.65
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Chaudhary P, et al: Evaluation of maxillary and mandibular alveolar bone morphology using CBCT

Parameters

Group

Group Statistics
No of subjects

Mean

Std Deviation

p-value

Hypodivergent

15

19.62

2.09

0.80

Width 2nd M

Normodivergent

10

19.38

2.44

Tooth inclination 2nd PM
Tooth inclination 1st M
Tooth inclination 2nd M

Hypodivergent Normodivergent
Hypodivergent Normodivergent
Hypodivergent Normodivergent

15

82.50

3.46

10

83.70

2.44

15

83.2333

2.539

10

79.30

3.22

15

84.3

2.819

10

78.00

4.00

0.35 0.002** 0.00***

BCBT- Buccal Cortical Bone Thickness, LCBT- Lingual Cortical Bone Thickness, , Height- Height of alveolar bone, Width- Width of alveolar bone, 2nd PM- Second Premolar, 1st M- First Molar, 2nd M- Second Premolar
* - p ≤0.05, ** - p ≤0.01, *** ≤0.001

Table 2: Comparision of mandibular alveolar bone morphology of Hyperdivergent growers (Group III) with Normodivergent growers (Group II)

Parameters BCBT 2nd PM BCBT 1st M BCBT 2nd M LCBT 2nd PM LCBT 1st M LCBT 2nd M Height 2nd PM

Group
Normodivergent Hyperdivergent
Normodivergent Hyperdivergent
Normodivergent Hyperdivergent
Normodivergent Hyperdivergent
Normodivergent Hyperdivergent
Normodivergent Hyperdivergent

Group Statistics No of subjects
10 15
10 15
10 15
10 15
10 15
10 15

Mean
2.39 2.12
2.94 2.55
3.45 3.02
2.31 2.19
2.44 2.04
2.03 1.72

Std Deviation
0.28 0.51
0.45 0.32
0.45 0.21
0.20 0.47
0.19 0.31
0.33 0.25

p-value 0.14 0.02*
0.00*** 0.45
0.00*** 0.01*

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Group Statistics

Parameters

Group

No of subjects

Mean

Std Deviation

p-value

Normodivergent

10

29.12

2.45

Hyperdivergent

15

30.07

4.42

0.54

Height 1st M

Normodivergent

10

27.72

3.46

Hyperdivergent

15

28.81

4.20

0.50

Height 2nd M

Normodivergent

10

25.23

2.67

Hyperdivergent

15

25.61

3.13

0.76

Width 2nd PM

Normodivergent

10

17.46

2.72

Hyperdivergent

15

16.32

1.41

0.18

Width 1st M

Normodivergent

10

18.54

1.98

Hyperdivergent

15

17.12

1.34

0.043*

Width 2nd M

Hypodivergent

15

19.62

2.09

0.80

Normodivergent

10

19.38

2.44

Hyperdivergent

15

18.70

1.69

0.42

Tooth inclination 2nd PM

Hypodivergent Normodivergent

15

82.50

3.46

0.35

10

83.70

2.44

Hyperdivergent

15

85.27

3.46

0.23

Tooth inclination 1st M

Hypodivergent

15

83.2333

2.539

0.002**

Normodivergent

10

79.30

3.22

Hyperdivergent

15

74.30

2.88

0.00***

Tooth inclination 2nd M

Hypodivergent

15

84.3

2.819

0.00***

Normodivergent

10

78.00

4.00

Hyperdivergent

15

73.03

2.87

0.00***

BCBT- Buccal Cortical Bone Thickness, LCBT- Lingual Cortical Bone Thickness, Height- Height of alveolar bone, Width- Width of alveolar bone, 2nd PM- Second Premolar, 1st M- First Molar, 2nd M- Second Premolar * - p ≤0.05, ** - p ≤0.01, *** ≤0.001

Table 3: Percentage of alveolar defects in subjects with different growth patterns according to tooth type of right and left side

Fenestration

Dehiscence

Tooth Type

Maxilla, %

Group Group

I

II

Group III

Mandible, %

Group Group Group

I

II

III

Maxilla, %

Group Group Group

I

II

III

Mandible, %

Group Group Group

I

II

III

Central

3.33

0

6.67 13.33 15 16.67 10

25

20

30

25 26.67

Lateral Canine

16.67 15 3.33 20

15 13.33 16.67 15

10 23.33 20 23.33

6.67 10

10 6.67

5 13.33 30

25 26.67 20

15

20

First Premolar 40

45 33.33 6.67

15

10

10

15 6.67 16.67 10 13.33

Second Premolar 6.67

5 16.67 10

50 16.67 3.33

5

0

3.33

5

6.67

First Molar 16.67 20 26.67 13.33 0

10 33.33 20

30

0

Second Molar 13.33 15 16.67 20

0

23.33 3.33

5

0

0

5

3.33

0

0

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Chaudhary P, et al: Evaluation of maxillary and mandibular alveolar bone morphology using CBCT

Results
Table 1 shows the comparison of mandibular alveolar bone morphology of Hypodivergent growers (Group I) with Normodivergent growers (Group II) using independent t test
Table 2 shows the comparison of mandibular alveolar bone morphology of Hyperdivergent growers (Group III) with Normodivergent growers (Group II) using independent t test.
Buccal cortical bone thickness: At the level of second premolar, there was no statistically significant difference in the thickness of buccal cortical bone in hypodivergent growers, hyperdivergent growers and normodivergent growers. However, as compared to other groups hypodivergent growers had maximum buccal cortical bone thickness (2.56mm).
At the level of first molar, there was significant increase (0.008)** in buccal cortical bone thickness in hypodivergent growers when compared with normodivergent growers. Also, there was significant increase (0.02)* in buccal cortical bone thickness in Hyperdivergent growers when compared with normodivergent growers. However, as compared to other groups hypodivergent growers had maximum buccal cortical bone thickness (3.35mm).
At the level of second molar, there was significant increase (0.023)** in buccal cortical bone thickness in hypodivergent growers, when compared with normodivergent growers. Also, there was significant increase (0.00)*** in buccal cortical bone thickness in hyperdivergent growers when compared with normodivergent growers. However, as compared to other groups hypodivergent growers had maximum buccal cortical bone thickness (3.76mm). Thus, buccal cortical bone thickness was maximum (3.76 mm) in hypodivergent group at level second molar.
Lingual cortical bone thickness: At the level of second premolar, there was no significant difference in lingual cortical bone thickness in hypodivergent growers and normodivergent growers. Also, there was no significant difference in lingual cortical bone thickness in hyperdivergent growers and normodivergent growers. However, as

compared to other groups hypodivergent growers had a maximum lingual cortical bone thickness (2.60mm).
At the level of first molar, there was significant increase (0.001)** in Lingual cortical bone thickness in Hypodivergent growers, when compared with normodivergent growers. Also, there was significant increase (0.00)*** in lingual cortical bone thickness in hyperdivergent growers, when compared with normodivergent growers. However, as compared to other groups hypodivergent growers had maximum lingual cortical bone thickness (2.74mm).
At the level of second molar, there was significant increase (0.003)** in Lingual cortical bone thickness in Hypodivergent growers when compared with normodivergent growers. Also, there was significant increase (0.01)* in Lingual cortical bone thickness in Hyperdivergent growers when compared with normodivergent growers. However, as compared to other groups hypodivergent growers had maximum Lingual cortical bone thickness (2.43mm). Thus, Lingual cortical bone thickness was maximum (2.7 mm) in hypodivergent group at level of first molar.
Height and width of alveolar bone: There was no significant difference in height of alveolar bone at second premolar level, first molar and second molar level, when both hypodivergent and hyperdivergent growers were compared with normodivergent growers.
There was no significant difference in width of alveolar bone at second premolar level, first molar level and second molar level when both hypodivergent and hyperdivergent growers were compared with normodivergent growers.
Height of alveolar bone was maximum (30.07 mm) in hyperdivergent group at level of second premolar. Width of alveolar bone was maximum (19.62 mm) in hypodivergent group at level of second molar.
Tooth inclination: In all the three groups, increasing lingual inclination of teeth were seen progressing from premolars to molars..

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Table 3 shows percentage shows presence of fenestrations and Dehiscence in maxilla and mandible of Group I (Hypodivergent), Group II (Normodivergent), Group III (Hyperdivergent) subjects, respectively.
Fenestration: Maximum prevalence of fenestration is seen in maxillary first premolar region with 40% in Group I (Hypo-divergent), 45% in Group II (Normodivergent) and 33.33% in Group III (Hyperdivergent).
Dehiscence: Maximum prevalence of dehiscence is seen in mandibular central incisor region with 30% in Group I (Hypodivergent), 25% in Group II (Normodivergent) and 26.67% in Group III (Hyperdivergent).
Discussion
This study was conducted on CBCT scans of 40 pre-orthodontic patients. The sample was divided in three groups, hypodivergent, normodivergent and hyperdivergent on the basis on SN-MP angle. The study was done to compare alveolar bone morphology among these groups.
Today, Temporary Anchorage Devices (TAD) are routinely used to provide absolute anchorage. The stability of TAD is affected by many factors, among which thickness of the cortical bone is of prime importance. The most used and easily accessible insertion sites are the buccal aspect of the alveolar process in both the maxilla and mandible as well as the palatal side of the maxillary alveolar process in the premolar and molar region. It has been reported that cortical bone should have a thickness of more than 1 mm in order to obtain good stability of orthodontic mini-implants.
Results of the present study show that the average thickness of buccal cortical bone of patients with horizontal growth patterns especially at first molar area and second molar area was greater than those with the average or vertical growth pattern. Similar type of significant findings was for lingual cortical bone thickness. The results of the present study were similar to those of Tsunori et al,18 Swasty et al.,19 and Han et al.,20 who reported that hyperdivergent group

had slightly narrower cortical bone than others. Subjects with the horizontal growth pattern have a stronger masseter. As the muscles contract during function, the structure of the tooth-alveolar bone complex changes following alterations in loading by forces. Thus, various growth patterns have different biting forces and biological adaptations resulting in different mandibular tooth-alveolar structures.3

A significant difference in the width of the

mandibular bone at first molar site between the

hyperdivergent (mean=17.12mm), normodivergent

(mean=18.54mm)

and

hypodivergent

(mean=18.93mm) was seen, similar to the findings

of Swasty et al. (2011)19, who reported that a long-

face group showed a statistically narrower cross-

section of the mandible compared with average-face

and short-face groups.

In all the three groups, increasing lingual inclination of teeth were seen as we progress from premolars to molars. There are three main factors, which affect the inclination of the teeth: lingual force (the muscles of the tongue), buccal force (buccinator and masseter), and occlusal force (loading during mastication). The 3D position of the teeth and jaw bone is dependent on the combination of these three forces. Initially, the mandibular molars erupt lingually, then move buccally due to tongue pressure and masseter function21; finally reaching their balanced position22 The lower molars are close to the attachment area of the masseter4 and therefore are more influenced by the force of the masseter.

Dehiscence and fenestration: Identification of these bone defects prior to orthodontic treatment is essential for a meticulous treatment planning. Moreover, the presence of these defects increases the chances of relapse.23 The maximum prevalence of fenestration in maxillary arch found in present study was around first premolar of maxilla as compared to other teeth in all group (40% in Group I, 45% in group II and 33.33% in group III which was similar to the findings of Enhos et al.24 (38.66% in Group I, 43.49% in Group II and 29.85% in Group III subjects). The possible reason for fenestrations at the first premolars could be the anatomical location of these teeth, which are

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Chaudhary P, et al: Evaluation of maxillary and mandibular alveolar bone morphology using CBCT

in an area that gets narrower upwards.25 These teeth provide clue during rapid maxillary expansion and are used as supporting teeth for orthopaedic devices. Because of the considerable force needed to split the median palatine suture, an evaluation of the periodontal structures, including alveolar bone and gingival biotype, is an important approach for the procedure.
In the present study, the maximum prevalence of dehiscence in mandibular arch was found around central incisor area of mandible as compared to other teeth in all groups. More incidence was found in Hypodivergent Group, as Group I showed 30% of dehiscence in mandible. Enhos et al.28 also, observed similar findings with prevalence of dehiscence with 30.55% in Group I. The incidence of dehiscence was positively correlated with thin alveolar bone. In the mandible, the bone becomes thinner from the posterior to the anterior region. Maximum fenestration was found in Hypodivergent group because they have strong masseteric action. This leads to heavy biting force resulting in higher incidence of dehiscence. Orthodontic mechanics may result in dehiscence or fenestration, based on the initial morphology of the alveolar bone as well as on the amount of tooth movement. Orthodontists must be aware of these predisposing factors, and movements in the labio-lingual direction should be limited.
Conclusion
1. In the posterior region, the average thickness of the buccal and lingual cortical bone of patients with the horizontal growth pattern were found greater than that of those with the average and vertical growth pattern.
2. Thickness of alveolar bone was maximum in Hypodivergent patients.
3. Maximum fenestration was seen in the maxillary first premolar region. Maximum dehiscence was seen in the mandibular central incisor region in Hypodivergent patients.

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Evaluation of morphology of maxillary and mandibular alveolar