Evaluation of morphology of maxillary and mandibular alveolar bone in vertical and horizontal growers: A cone beam computed tomography study

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1 Original article 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 namratasgt@gmail.com 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, Puneet Chaudhary Private practitioner, Gurgaon M S Sidhu Professor and Head Department of Orthodontics and Dentofacial Orthopedics SGT Dental College, Gurgaon , Haryana, India Seema Grover Professor Department of Orthodontics and Dentofacial Orthopedics SGT Dental College, Gurgaon , Haryana, India Vikas Malik Reader, Department of Orthodontics and Dentofacial Orthopedics, SGT Dental College, Gurgaon , Haryana, India 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 Namrata Dogra Senior Lecturer Department of Orthodontics and Dentofacial Orthopedics SGT Dental College, Gurgaon , Haryana, India Sandeep Kumar Senior Lecturer Department of Orthodontics and Dentofacial Orthopedics SGT Dental College, Gurgaon , 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), Manipal Journal of Dental Sciences October 2017 Volume 2 Issue 2 19

2 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. 20 Manipal Journal of Dental Sciences October 2017 Volume 2 Issue 2

3 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, Saint- Denis, 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: I - 15 subjects having mandibular plane angle equal to or less than 26⁰ were denoted as hypodivergent. (Figure 1) II - 10 subjects having mandibular plane angle between 28⁰ and 34⁰ were denoted as normodivergent. (Figure 1) 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 Manipal Journal of Dental Sciences October 2017 Volume 2 Issue 2 21

4 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.] 22 Manipal Journal of Dental Sciences October 2017 Volume 2 Issue 2

5 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 ( I)) with Normodivergent growers ( II) Statistics No of Parameters Mean Std Deviation p-value subjects BCBT 2nd PM BCBT 1st M BCBT 2nd M LCBT 2nd PM Hypodivergent Normodivergent Hypodivergent ** Normodivergent Hypodivergent * Normodivergent Hypodivergent Normodivergent LCBT 1st M Hypodivergent ** Normodivergent LCBT 2nd M Hypodivergent ** Normodivergent Height 2nd PM Hypodivergent Normodivergent Height 1st M Hypodivergent Normodivergent Height 2nd M Hypodivergent Normodivergent Width 2nd PM Hypodivergent Normodivergent Hypodivergent Width 1st M Normodivergent Manipal Journal of Dental Sciences October 2017 Volume 2 Issue 2 23

6 Statistics Parameters No of subjects Mean Std Deviation p-value Width 2nd M Hypodivergent Normodivergent Tooth inclination 2nd PM Hypodivergent Normodivergent Tooth inclination 1st M Hypodivergent ** Normodivergent Tooth inclination 2nd M Hypodivergent *** Normodivergent 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, *** Table 2: Comparision of mandibular alveolar bone morphology of Hyperdivergent growers ( III) with Normodivergent growers ( II) Statistics Parameters No of subjects Mean Std Deviation p-value BCBT 2nd PM Normodivergent Hyperdivergent BCBT 1st M Normodivergent Hyperdivergent * BCBT 2nd M Normodivergent Hyperdivergent *** LCBT 2nd PM Normodivergent Hyperdivergent LCBT 1st M Normodivergent Hyperdivergent *** LCBT 2nd M Normodivergent Hyperdivergent * Height 2nd PM 24 Manipal Journal of Dental Sciences October 2017 Volume 2 Issue 2

7 Statistics Parameters No of subjects Mean Std Deviation p-value Height 1st M Height 2nd M Width 2nd PM Width 1st M Normodivergent Hyperdivergent Normodivergent Hyperdivergent Normodivergent Hyperdivergent Normodivergent Hyperdivergent Normodivergent Hyperdivergent * Width 2nd M Hypodivergent Tooth inclination 2nd PM Normodivergent Hyperdivergent Hypodivergent Normodivergent Hyperdivergent Tooth inclination 1st M Hypodivergent ** Normodivergent Hyperdivergent *** Tooth inclination 2nd M Hypodivergent *** Normodivergent Hyperdivergent *** 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, *** Table 3: Percentage of alveolar defects in subjects with different growth patterns according to tooth type of right and left side Fenestration Dehiscence Maxilla, % Mandible, % Maxilla, % Mandible, % Tooth Type I II III I II III I II III I II III Central Lateral Canine First Premolar Second Premolar First Molar Second Molar Manipal Journal of Dental Sciences October 2017 Volume 2 Issue 2 25

8 Results Table 1 shows the comparison of mandibular alveolar bone morphology of Hypodivergent growers ( I) with Normodivergent growers ( II) using independent t test Table 2 shows the comparison of mandibular alveolar bone morphology of Hyperdivergent growers ( III) with Normodivergent growers ( 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.. 26 Manipal Journal of Dental Sciences October 2017 Volume 2 Issue 2

9 Table 3 shows percentage shows presence of fenestrations and Dehiscence in maxilla and mandible of I (Hypodivergent), II (Normodivergent), III (Hyperdivergent) subjects, respectively. Fenestration: Maximum prevalence of fenestration is seen in maxillary first premolar region with 40% in I (Hypo-divergent), 45% in II (Normodivergent) and 33.33% in III (Hyperdivergent). Dehiscence: Maximum prevalence of dehiscence is seen in mandibular central incisor region with 30% in I (Hypodivergent), 25% in II (Normodivergent) and 26.67% in 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 longface group showed a statistically narrower crosssection 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 function 21 ; finally reaching their balanced position 22 The lower molars are close to the attachment area of the masseter 4 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 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 I, 43.49% in II and 29.85% in III subjects). The possible reason for fenestrations at the first premolars could be the anatomical location of these teeth, which are Manipal Journal of Dental Sciences October 2017 Volume 2 Issue 2 27

10 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, as I showed 30% of dehiscence in mandible. Enhos et al. 28 also, observed similar findings with prevalence of dehiscence with 30.55% in 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. References 1. Aasen TO, Espeland, L. An approach to maintain orthodontic alignment of lower incisors without the use of retainers. Eur J Orthod. 2005; 27: Graber TM.Orthodontics-Principles and Practice. 3rd ed. Philadelphia: Saunders; 1992: Dechow PC, Hylander WL. Elastic properties andmasticatory bone stress in the macaque mandible. Am J Phys Anthropol. 2000; 112: Ingervall B, Thilander B. Relation between facialmorphology and activity of masticatory muscles. J Oral Rehabil. 1974; 1: Kasai K, Kawamura A, Kanazawa E. A comparativestudy of dental arches and mandibular bases in Jomonandmodern Japanese using CT scanning. Orthodontic Waves. 1999; 58: Kawamura A. Relationship between buccolingual inclination of mandibular molars and dentofacial morphology. Nihon Univ J Oral Sci. 1999; 25: Masumoto T, Hayashi I, Kawamura A, Tanaka K, Kasai K. Relationships among facial type, buccolingual molar inclination, and cortical bone thickness of the mandible. Eur J Orthod. 2001; 23: Fields HW, Profitt WR, Nixon WL, Phililips C, Stanek E. Facial pattern differences in long faced children and adults. Am J Orthod. 1984; 85: Cangialosi TJ. Additional criteria for sample division suggested. Am J Orthod Dentofacial Orthop. 1989; 96:24A. 10. Opdebeeck H, Bell WH. A short face syndrome, Am J Orthod. 1978; 73: Ingervall B, Helkimo E. Masticatory muscle force and facial morphology in man. Arch Oral Biol. 1978; 23: Proffit WR, Fields HW, Nixon WL. Occlusal forces in normal and long-face adults. J Dent Res. 1983; 62: Handelman CS. The anterior alveolus: its importance in limiting orthodontic treatment and its influence on the occurrence of iatrogenic sequelae. Angle Orthod. 1996; 66: Manipal Journal of Dental Sciences October 2017 Volume 2 Issue 2

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