| Abstract|| |
Context: Determining the amount of cortical and cancellous bone present in the mandible is an important criterion for the selection of proper implant size and reduction of post implant placement complications. It becomes difficult to manage the presence of lingual undercuts when there is perforation of either the buccal or lingual cortical plates. Computed tomography (CT) images of the mandible can reduce the risk of complications by evaluating the thickness of cortical and cancellous bone in the mandible. Aims: Evaluate thickness of the buccal and lingual cortical plates and cancellous bone. Gender variation in the cancellous bone and cortical bone thickness. Determine the shape of the mandible. Settings and Design: A retrospective study was conducted using the CT scan images of pathologies pertaining to the Head and Neck region. Methods and Material: CT scan images of 30 patients, comprising of 22 males and 8 females. The mental foramen was considered as the anatomical landmark and the vertical marking was considered at a height of 20 mm from basal bone. The thickness of both cortical and cancellous bone was noted 6 mm anterior to it and 18 mm posterior. The shape of the buccal and lingual cortical bone was also considered. Statistical Analysis: Statistical analysis was done using Student's t-test or Chi-square test. Results: The mean thickness of cortical bone was more in anterior mandible than posterior mandible and cortical bone density was thickest at height of 20 mm, whereas for cancellous bone, it was highest at 5 mm from the basal bone, thickness. Buccal concavity, type A (68.2%), was the most common in the anterior region for males, followed by round shape, type C (56–58%) in the posterior region. For females, type C (25–31%) in the posterior region and lingual concavity, type B (18–30%) were the most common types in the anterior region. Conclusions: Lingual concavity may pose serious problems in cases of perforations during implant placement. Lingual cortical plates were thicker than the buccal cortical plates and it is concave anterior mandible. Thus, CT imaging can help in characterizing the quantity and morphology of the mandible.
Keywords: Cancellous bone thickness, computed tomography, cortical bone thickness, dental implants
|How to cite this article:|
Priyadarshini SR, Sahoo PK, Niyogi S, Patnaik S, Bhuyan SK. Qualitative and morphological evaluation of the mandibular bone using computed tomography. Indian J Dent Res 2020;31:899-903
|How to cite this URL:|
Priyadarshini SR, Sahoo PK, Niyogi S, Patnaik S, Bhuyan SK. Qualitative and morphological evaluation of the mandibular bone using computed tomography. Indian J Dent Res [serial online] 2020 [cited 2021 Apr 15];31:899-903. Available from: https://www.ijdr.in/text.asp?2020/31/6/899/311648
| Introduction|| |
Knowledge of thickness of the cortical bone in various areas can ensure clinicians in selecting the placement site and placement protocol. The osteointegration is dependent on the screw and host response. That includes the design of the implant, that is, diameter and length. The aim is to increase initial fixation by inducing compressive forces in a controlled manner in the cortical bone layer. The cortical bone thickness affects the initial stability of implants.
In dental implant placement, numerous complications can be faced by the surgeons as a result of inadequate planning in surgery, perforation of the cortical bone, infection of the implant site because of improper manipulation, incorrect implant handling and placement, or during surgery.
The morphology and quantity of bone in the mandible is an important criterion for assessing the strength and support of an implant. The thickness of cortical bone determines the stability of the implant. Determining the quantity of both the cortical and cancellous bone in the mandible will be a key in successful implant placement and its long-term stability.
In recent times, numerous imaging modalities are being used in early and prompt imaging of the implants to facilitate immediate implant loading. Mostly, panoramic radiographs were used to estimate the bone density before implant placement, but because of errors in panoramic imaging, CT and cone beam computed tomography (CBCT) have emerged as an alternative diagnostic modality., CT provides accurate measurement of the bone thickness in the mandible, because multiplanar reformation can be obtained for assessing the thickness of both cortical and cancellous bone. CT was considered in the study because of easy accessibility and literature has revealed CT produces superior images to that of on-board imaging CBCT systems.
The quantity of bone is an important factor for long-term maintenance of the stability of the bone–implant interface, Implant Stability, osteointegration, and even in adequate cortical engagement. It is crucial in determination of morphology and quality of bone, thereby predicting treatment outcome during implant therapy. Also enables prevention of perforation during implant placement which might lead to a severe oral complication.
| Subjects and Methods|| |
CT images of the mandible of 30 patients, comprising of 22 males and 8 females, were obtained. A total of 30 sections of the mandible were studied. Pathologies of head and neck region indicated for CT were taken and the sides which had no pathologies and bone could be measured were included in the study.
CT examinations were performed with Optima GE scanner (India) operated at 120 kV and 85–110 mA with a 1-mm slice thickness and a table speed of 2 mm/s. After the examination, contiguous 1-mm thick axial CT images parallel to the inferior border of the mandibles were reconstructed. These images were examined using DIACOM CT reformatting imaging software; with 2 mm intervals.
In order to measure the borders of the cortical plates, the demarcation between the cortical and cancellous bone was marked by visual method. Hypodense areas in CT are the cancellous bone, and hyperdense area is the cortical bone. A line is drawn perpendicular to the basal bone. The body of the mandible was divided into five sections, taking the region of mental foramen as reference section. In sagittal section, image in which the mental foramen was recognized was defined as section 2, and the image 6 mm anterior to section 2 was defined as section 1. Similarly, sections 6 mm posterior to section 2 were further labelled up to section 4 [Figure 1].
In each section, the thickness of cortical bone was measured for both buccal and lingual side as the distance between the inner and outer border. The distance from the inner border of the buccal side to the inner border of the lingual side was measured as the thickness of cancellous bone. The cortical and cancellous bone thicknesses A, B, C, and D were measured at 5, 10, 15, and 20 mm, respectively, perpendicularly from the basal bone, above the inferior border of the mandible toward the alveolar crest. Three types of shape of the mandibles were noted: Type A – Buccal Concavity, Type B – Lingual Concavity, Type C- Round [Figure 2].
All data are presented as means and standard deviations (SD). The statistical differences were tested using Student's t-test or Chi-square test. A P value less than 0.05 indicated significance.
| Results|| |
Thickness of cortical bone
The thickness of the cortical bone was more in section 1 and section 2 of the mandible, which was 8.06 mm and 9.2 mm in males, respectively, and 9.3 mm and 8.2 mm in females, respectively. The cortical bone thickness was greatest at level D and was thickest in females as compared to males [Table 1].
Buccal cortical plates (BCP) thickness increased from anterior to posteriors and in either gender it was thickest at level D. Similarly, Lingual Cortical Plates progressively increased from anterior to posteriors and this too been thickest at level D. But the lingual cortical plates were thicker than the BCP in either gender [Table 2].
Thickness of cancellous bone
The thickness of cancellous bone was more in section 3 and section 4 of the mandible, which was 12.5 mm and 11.4 mm in males, respectively, and 10.9 mm and 11.63 mm in females, respectively. The cancellous bone thickness was greatest in level A, or the crest of mandible.
The thickness of the buccal cortical plate increased from anterior to posteriors and in either gender it was thickest at level D. Similarly, thickness of lingual cortical plate progressively increased from anteriors to posteriors and this too been thickest at level D but the lingual cortical plates were thicker than the buccal in either gender [Table 3].
Shape of the mandible
Buccal concavity, type A (68.2%), was the most common in the anterior region for males, followed by type C (56–58%) in the posterior region. For females, type C (25–31%) in the posterior mandible and type B (18–30%) were the most common types in the anterior mandible [Table 4].
| Discussion|| |
The thickness of the cortical plates was highest in the anterior region at level D, that is the inferior border of the mandible, whereas in a study conducted by Cassetta M et al., the cortical bone was comparatively more thinner anteriorly and the bone density thickens in the posterior regions. The cortical bone was thicker in females as compared to males in our study, while Cassetta M et al. reported increased thickness of cortical bones in males than the females.
The lingual cortical plates were noted to be thicker as compared to the buccal plates which are in correlation with the studies performed by Sadeghian S et al. where similar findings were present. Accordingly, the lingual cortical plates were more thicker in the anterior part of the mandible as compared to the posterior., As the stability of implant is mostly dependent on the thickness of the cortical bone, the minimum thickness should be atleast 1 mm for proper implant stability. According to the study by Sadek MM et al. the thickness of the buccal cortical plates was less near the alveolus than in the inferior border of the mandible. As the buccal cortical plates was thinner, so it has higher chances of perforations. Therefore, implant placement should be done with slight lingual angulation.
Flanagan D confirmed from their study that the lingual cortex of the maxilla and mandible is thicker than the facial cortex at a ratio of 1:1.3. This ratio was consistent for maxilla and mandible.
The thickness of the cancellous bone was greater in the posterior mandible in our study and it was thickest at level A, which is the crest of the mandible or the tooth-bearing region, which is in accordance with study done by Momin MA et al., where significant difference was noted in cancellous bone thickness between both the genders in the posterior body of the mandible.
Implant stability is determined by the ratio of cortical to cancellous bone and since cortical bone is more resistant to deformation, because of its high modulus of elasticity, it can bear more implant loading stress than the cancellous bone. Kim HJ et al. reported that cancellous bone thickness of middle level of the root should be considered at first to select the diameter of implant fixture on the anterior mandibular region. In addition, the cancellous bone thickness and bone quality are important for implant placement.
Four different types of shape of the mandible were considered in the sagittal CT sections, type A with buccal concavity, type B with lingual concavity, and type C being round in shape. In our study, male population had type A in the anterior mandible followed by type C in the posterior region and females have type B in anterior mandible followed by type C in the posterior region.
The shape and location of the mandibular canal is important prior to dental implant procedures. The use panoramic radiographs 2D method often causes distortion and causes error in measurement of the mandibular canal so cross-sectional images act as important reference while determining the location of the mandibular canal.,
Momin MA et al. reported lingual concavity, type B (62–72%), being the most common in the anterior region for males, followed by type C or round configuration (56–58%) in the posterior region and in females, type C (25–31%) in the posterior region and type B (18–30%) were the most common types in the anterior region. Similarly, Watanabe H et al. reported at the posterior region, type C (round) was the most commonly found (59–61%), followed by type A (lingual concavity) (36–39%). There was prevalence in lingual concavity in the shape of the mandible but no differentiation in the genders was noted based on the shape of the mandible.
We should also evaluate bone mineral density of cortical bone. As well as bone quantity (bone thickness), bone quality (mineralization) can affect initial stability values for implants.
| Conclusion|| |
For implant placement, one should have exact information regarding the thickness of the cortical and cancellous bone. The lingual cortical bone being thicker than the buccal bone, there is less chance of perforation in the lingual cortical plates during implant placement. The cortical bone was found to be more in the inferior border of the anterior body of the mandible, whereas the cancellous bone near the crest of the mandible in the posterior region. Thus computed tomographic images can provide better differentiation and insight in the type and quantity of bone present in both the maxilla and mandible and can be helpful in proper implant guidance.
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Dr. Smita R Priyadarshini
Dent PLUS Plot No. 476 Near Radha Rani Towers Nayapalli, Bhubaneswar, Orissa - 751 012
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]