ORIGINAL RESEARCH | https://doi.org/10.5005/jp-journals-10015-1831 |
A Cone-beam Computed Tomography Evaluation of Mandibular Anterior Alveolar Bone Dimensions in Class I and Class II Skeletal Patterns
1–6Department of Orthodontics and Dentofacial Orthopaedics, Kalinga Institute of Dental Sciences, Kalinga Institute of Industrial Technology (Deemed to be University), Bhubaneswar, Odisha, India
Corresponding Author: Saranya Sreedhar, Department of Orthodontics and Dentofacial Orthopaedics, Kalinga Institute of Dental Sciences, Kalinga Institute of Industrial Technology (Deemed to be University), Bhubaneswar, Odisha, India, Phone: +91 7012125875, e-mail: saranyaageesh@gmail.com
How to cite this article Sreedhar S, Sahoo N, Rami Reddy MS, et al. A Cone-beam Computed Tomography Evaluation of Mandibular Anterior Alveolar Bone Dimensions in Class I and Class II Skeletal Patterns. World J Dent 2021;12(3):230–233.
Source of support: Nil
Conflict of interest: None
ABSTRACT
Aim and objective: The study aims to compare the alveolar bone thickness in the lower incisors area in skeletal class I average growing adults with two different growth patterns of class II adults using cone-beam computed tomography (CBCT) imaging technique.
Materials and methods: The CBCT images of 20 class II and 10 class I average growth pattern patients were examined. Class II patients were subdivided into high- and low-angle groups of 10 patients each. The alveolar bone thickness of mandibular incisors in the buccal and lingual region was measured at the level of the alveolar crest and 3, 6, and 9 mm from the alveolar crest.
Results: Buccal and lingual alveolar bone thickness in class II high- and low-angle patients was not significantly different at all levels except at 3 and 9 mm apical levels where lingual bone shows more thickness than buccal. Class II high-angle group showed thinner alveolar bone than low-angle and class I average groups, in most areas.
Conclusion: Skeletal class II subjects with hyperdivergent growth patterns showed thinner mandibular alveolar bone in most areas compared with average/low-angle subjects. In class I average growing patients, the lingual alveolar bone is thicker in all sites. In class II high-angle patients, most sites exhibit thicker lingual bone thickness. In class II low-angle cases, all sites have a greater buccal bone thickness.
Clinical significance: The anatomic limit set by the alveolar cortical bone should be considered during treatment planning during the sagittal correction, retraction of teeth, and miniscrew insertion. It is important to consider these boundaries as a limit to reposition teeth. Considering the anatomy of the alveolus is one of the keys to minimize unfavorable sequelae.
Keywords: Alveolar bone, Cone-beam computed tomography, Skeletal patterns..
INTRODUCTION
A healthy periodontium, alveolar bone, and gingiva determine the life span of a tooth in the oral cavity. A basic criterion for efficient tooth movement during orthodontic treatment and stable tooth position after orthodontic treatment is the viable bone width around the tooth. Applying unplanned orthodontic forces can result in unhealthy bone remodeling around the alveolus, thus leading to gingival recession, external root resorption, fenestration, and dehiscence.1
Current literature proves the correlation exists between vertical growth patterns and the thickness of the surrounding bone.2,3 In a study by Handelman, patients with low mandibular plane angles possess wider lingual bone widths in the maxillary and mandibular incisor region and high mandibular angle cases have a thinner labial bone in the region of the mandibular incisor.4 Patients with the increased vertical dimension of the face have a reduced amount of supporting bone compared with short face or horizontal growth pattern patients and so it restricts the range of movements available for teeth. To maintain an ideal overbite in long face patients, there is a continuous eruption of incisors and thus the alveolus undergoes thinning and weakening of the buccolingual walls.4
During orthodontic treatment, the position and movement of the mandibular incisors play a crucial role in the diagnosis and treatment planning of skeletal class II and class III malocclusions. In a recent study by Coşkun and Kaya,5 no significant difference was found between skeletal class I, class II, and class III groups when the buccal and lingual cortical bone thickness was concerned, but a significant difference was noticed between the three groups for the thickness of cancellous bone (Figs 1 to 4).
Therefore, the maximum anterior limit of the mandibular incisors should be set before the treatment, especially in patients with severe skeletal discrepancies where incisor movement is limited by the health of the periodontal tissues, condition of the surrounding bone, and the anatomy of the symphysis.6,7
MATERIALS AND METHODS
The cone-beam computed tomography (CBCT) scans of 30 patients [class I-10 patients, class II-20 (10-high angle, 10-low angle)], collected from the Department of Oral Medicine and Radiology, Kalinga Institute of Dental Sciences, Bhubaneswar, Odisha were evaluated. To standardize the parameters, the patient selection was done under the following criteria:
- Orthodontically untreated, nongrowing adults with class I and II malocclusion in the age group of 20 to 40 years.
- Patients with healthy periodontium and without any radiographic bone pathology.
- Patients without any craniofacial anomalies or systemic diseases.
- Patients without any missing or unerupted mandibular permanent incisors.
- Patients without any history of trauma to the lower anterior teeth.
- Patients without any crowding or spacing in the mandibular anterior alveolar segment.
- Patients without any prosthetic crowns on the mandibular incisors.
The CBCT apparatus used in the study was HYPERION X9 (QR SRL Co, Verona, Italy) at 90 kV, 10 mA, and voxel size 0.3 × 0.3 × 0.3 with a field of view (FOV) 11 × 8 cm. The images obtained were analyzed with NNT software (version 4.6, Italy). A multiplanar reconstruction (MPR) was taken and the facial height index (FHI) was used to find out the facial growth pattern.8 Facial height index is the ratio of the posterior facial height (PFH) to the anterior facial height (AFH).9 Based on FHI, facial growth pattern was classified as hyperdivergent (FHI values %3C;0.649), normal (FHI values between 0.65 and 0.75), and hypodivergent (FHI values %3E;0.751). Wit’s analysis was used to find out the skeletal anteroposterior relationship.10
The CBCT images of the mandible were not distorted or magnified and were displayed simultaneously with their coronal, axial, and sagittal slices so that the mandibular anterior tooth regions could be accurately measured in three dimensions. The axial plane was selected to derive the cross-section of the mandibular central incisors. The sagittal and coronal planes were adjusted so that they would pass through the center of the long axis of the root of the central incisor with the sagittal plane perpendicular to the patient’s arch in the axial view. In the sagittal section, buccal and lingual alveolar crestal thickness was measured. Along the long axis of the root, from the most coronal level of the alveolar bone crest, alveolar bone width measurements were made along the sagittal reference planes at the alveolar crest level and 3, 6, and 9 mm apical to the CEJ. Buccal and lingual bone thickness was measured from the most buccal and lingual aspects of the root outline to the most buccal and lingual aspects of the alveolar bone outline in the sagittal plane.
Growth pattern | BT0 | BT3 | BT6 | BT9 | LT0 | LT3 | LT6 | LT9 | |
---|---|---|---|---|---|---|---|---|---|
Average | Mean | 0.52 | 1.17 | 2.02 | 3.61 | 0.63 | 1.41 | 2.22 | 3.33 |
SD | 0.05 | 0.11 | 0.13 | 0.20 | 0.08 | 0.16 | 0.16 | 0.17 | |
High | Mean | 0.60 | 0.49 | 1.33 | 1.85 | 0.69 | 1.07 | 1.62 | 2.52 |
SD | 0.07 | 0.03 | 0.43 | 0.18 | 0.09 | 0.08 | 0.06 | 0.07 | |
Low | Mean | 0.64 | 0.93 | 1.67 | 3.08 | 0.61 | 0.80 | 1.73 | 2.46 |
SD | 0.11 | 0.14 | 0.18 | 0.11 | 0.12 | 0.30 | 0.08 | 0.14 | |
Total | Mean | 0.59 | 0.86 | 1.67 | 2.85 | 0.64 | 1.09 | 1.85 | 2.77 |
SD | 0.09 | 0.31 | 0.39 | 0.77 | 0.10 | 0.32 | 0.28 | 0.42 | |
p value | 0.01 | 0.00 | 0.00 | 0.00 | 0.27 | 0.00 | 0.00 | 0.00 |
Statistical Analysis
The data were analyzed by Statistical Package for Social Sciences version 20.0 (SPSSCorp, Chicago, IL, USA). The statistical significance was determined at 0.001 level. The mean and SD of every level were also calculated.
RESULTS
As noted in Table 1, in class I average growing patients, the minimum and maximum mean buccal alveolar bone thickness was recorded at the alveolar crest (0.52 ± 0.05 mm) and 9 mm from the alveolar crest (3.61 ± 0.20 mm), respectively. A similar trend was noted with the lingual alveolar bone thickness too. But in the class II patients, the high-angle patients showed minimum buccal and lingual alveolar thickness at 3 mm (0.49 ± 0.03 mm) and the alveolar crest level (0.69 ± 0.09 mm), respectively, whereas both maximum buccal (1.85 ± 0.18 mm) and lingual (2.52 ± 0.07 mm) bone thickness was seen at 9 mm from the alveolar crest. In class II low-angle cases, both the minimum buccal (0.64 ± 0.11 mm) and minimum lingual (0.61 ± 0.12 mm) alveolar bone thickness was noted at the alveolar crest level. At a level 9 mm from the alveolar crest, a maximum buccolingual thickness of 3.08 ± 0.11 and 2.46 ± 0.14 mm, respectively, was observed in class II low-angle patients.
DISCUSSION
This study was conducted on CBCT scans of 30 nonorthodontically treated patients. The sample was divided into three groups class I average, class II cases based on Wit’s appraisal. The class II group was further divided into low- and high-angle cases basing on the FHI. The study was done to compare mandibular anterior alveolar bone morphology among these groups.
The amount of bone present in the mandibular incisor region is important when sagittal movements are considered in orthodontics like cases of premolar extractions,11 distalization using temporary anchorage devices, and cases requiring large compensations.2 The structure of the mandibular symphysis plays a pivotal role in restricting the movement of the incisors as the buccolingual alveolar bone thickness of the lower anterior teeth is thinner than other areas intraorally and definitely more susceptible to periodontal disease.12 It has been reported in the literature that any kind of tooth movement on average causes 10% shortening of roots.13–15
Cone-beam computed tomography used in the study has emerged as an efficient diagnostic imaging tool for studying the anatomical and pathological aspects of the oral and maxillofacial region. Technical efficacy in CBCT imaging is related to the quality of the image. The dimensional accuracy of CBCT images with a typical voxel size of 0.3 to 0.4 mm has been already well established.16 Tomographic imaging is still considered as the gold standard method for the evaluation of the bone anatomy, but according to the current recommendation of the American Academy of Oral and Maxillofacial Radiology (AAOMR) CBCT can be advised for cases where its use will be essential for the establishment of diagnosis or treatment planning but only after analyzing the radiation burden and stochastic effects.17
In this study, class I average growing patients have thicker buccal and lingual alveolar thickness at all levels except at the alveolar crest where the class II patients exhibit greater marginal bone thickness. When we further compare among the high and low growth patterns in skeletal class II patients, at the alveolar crest level, the lingual alveolar thickness is more in high-angle cases and less in low-angle cases. At a level 3 mm from the alveolar crest, the low-angle cases exhibit thicker buccal and thinner lingual bone width. A similar trend was noted at 9 mm from the alveolar bone crest, where buccal bone thickness in low-angle cases and lingual bone thickness is more in high-angle cases. At 6 mm from the alveolar crest, low-angle cases show greater buccal and lingual alveolar bone thickness.
If we compare within the groups, in class I average growing patients the lingual alveolar bone is thicker in all sites except at 9 mm from the alveolar crest level. But a study by Baysal et al.18 concluded that labial alveolar bone thickness of lower incisors was significantly higher in the class I group compared with that of the class II group.
In the current study, all sites in class II high-angle patients exhibit thicker lingual bone thickness than the buccal counterpart. Whereas in class II low-angle cases, all sites have a greater buccal bone thickness except at 6 mm from the alveolar crest level. As concluded by Veli et al.,19 the buccal cortical bone thickness varies depending on the sites between and within the jaws and according to the growth pattern. The thickness of mandibular and maxillary buccal cortical bone increased toward the apical area in all regions which were studied regardless of the growth pattern. As the buccal cortical bone is thinner in high-angle patients, difficulties may be encountered in achieving primary stability during miniscrew treatment.20
Yet another study by Baysal and Uysal21 in the year 2014 concluded that myofunctional appliances used for sagittal correction in class II division 1 patients resulted in proclined lower anteriors as an adverse effect along with an increase in the mandibular length as the desired effect. So, while treating such patients we should keep the mandibular anterior bone dimensions in mind to manage iatrogenic effects if any.
Pandis et al.,22 Pandis et al.,23 and Fleming et al.24 reported that the self-ligating bracket system produced greater expansion in the intercanine, interpremolar, and intermolar regions when compared with the conventional system. The conventional extraction series bracket system also results in root prominences due to inadvertent expression of tip and torque values. Therefore, during treatment planning with a self-ligating or conventional bracket system, the buccal and lingual alveolar bone dimensions in the maxilla and mandible should be examined preferably through 3D radiography to offer the patients with favorable outcomes.
CONCLUSION
This study was conducted with CBCT images obtained from 30 nonorthodontically treated patients. The sample was further divided into two groups class I average growing patients and class II patients based on the value from Wit’s appraisal. The class II group was further divided into low- and high-angle cases based on the FHI value. The study was done to compare mandibular anterior alveolar bone thickness among these groups. The following conclusions were derived from the study:
- In class I average growing patients, the lingual alveolar bone is thicker than the buccal alveolar bone.
- Class II high-angle patients exhibit thicker lingual bone thickness and class II low-angle cases have a greater buccal bone thickness in the mandibular anterior region.
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