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 Table of Contents  
Year : 2017  |  Volume : 29  |  Issue : 2  |  Page : 84-89

Fractal dimension analysis in digital periapical radiographs: A diagnostic indicator of osteoporosis in post-menopausal women

1 Department of Oral Medicine and Radiology, Madha Dental College and Hospital, Chennai, Tamil Nadu, India
2 Department of Oral Medicine and Radiology, Government Dental College and Research Institute, Bengaluru, Karnataka, India

Date of Submission04-Nov-2016
Date of Acceptance23-Oct-2017
Date of Web Publication9-Nov-2017

Correspondence Address:
Mathivanan Kavitha
Department of Oral Medicine and Radiology, Madha Dental College and Hospital, Kundrathur, Chennai, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jiaomr.JIAOMR_137_16

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Objectives: To assess the alveolar bone density by fractal dimension (FD) analysis in radiovisiograph of postmenopausal women of mandibular posterior region and to correlate FD values with t-scores of quantitative ultrasound of the calcaneus bone. Materials and Methods: This study, approved by the institutional review board, included 40 participants, aged 45–60 years divided into two groups. Twenty postmenopausal women with osteoporosis comprised group 1, and 20 postmenopausal women without osteoporosis comprised group 2 based on bone mineral density assessment of ultrasound of the calcaneus bone. Digital dental radiograph of mandibular first molar were obtained and used for assessing alveolar bone density by FD analysis and were correlated with t-scores of ultrasound of calcaneus bone. Results: The mean FD values were evaluated using SPSS 14 version software, and were found to be 1.738 and 1.867 for group 1 and group 2, respectively, which was statistically significant (P < 0.001). However, correlation between t-scores and FD values within the study group was not found to be statistically significant (P > 0.05). Conclusion: FD analysis using direct digital periapical radiographs is a novel method, which can be used for early diagnosis of osteoporosis in the alveolar bone.

Keywords: Dental, digital, fractals, osteoporosis, radiography

How to cite this article:
Kavitha M, Khan M, Vijayalakshmi KR. Fractal dimension analysis in digital periapical radiographs: A diagnostic indicator of osteoporosis in post-menopausal women. J Indian Acad Oral Med Radiol 2017;29:84-9

How to cite this URL:
Kavitha M, Khan M, Vijayalakshmi KR. Fractal dimension analysis in digital periapical radiographs: A diagnostic indicator of osteoporosis in post-menopausal women. J Indian Acad Oral Med Radiol [serial online] 2017 [cited 2022 Aug 19];29:84-9. Available from: https://www.jiaomr.in/text.asp?2017/29/2/84/217908

   Introduction Top

The World Health Organization (WHO) defines osteoporosis as a metabolic bone disease, characterized by low bone mass and micro-architectural deterioration of bone tissue leading to enhanced bone fragility and a consequent increase in fracture risk. Globally, it is estimated that over 200 million people suffer from this debilitating disease. However, in the Indian population, it is reported to be 25 million with 2 million fractures per year.[1] There are several causes proposed for osteoporosis, of which menopause is the leading cause, which decreases bone mass, followed by endocrine disorders, drugs such as corticosteroids, and genetic disorders.[2] Osteoporosis is a silent disease that shows no signs and symptoms at its onset, slowly progresses, and after reaching substantial levels of bone loss, clinically presents with vague pain, multiple fractures, especially in the spine, hip, and radius, and subsequently leading to deformity, disability, loss of function, and debilitation.[3] Hence, these serious complications can be overcome by early detection of the disease. Alveolar bone presents the early changes in osteoporosis in the form of trabecular disorientation, loss of lamina dura, mobility, and early loss of teeth and jaw bones, showing reduced cortical index of inferior border of mandible with reduced width of the ramus.[4],[5]

There are several methods for diagnosis of osteoporosis such as imaging and biochemical markers, including serum parathormone, vitamin D, calcium, and alkaline phosphatase.[6] However, the most reliable and standard method is dual energy X-ray absorptiometry (DEXA), computed tomography (CT) followed by conventional imaging.[7] Recently, ultrasound of calcaneus bone has been used for diagnosis of osteoporosis, which is reliable, noninvasive, portable, nonionizing with low cost, and is highly responsive to metabolic stimuli with high turnover rate.[8],[9],[10]

Conventional periapical radiographs has limitations in detecting early changes. However, fractal dimension (FD) analysis using direct digital periapical radiographs has shown significant results in the early diagnosis of osteoporosis.[11],[12] Hence, a study has been planned with objectives of assessing alveolar bone density by FD analysis in radiovisiograph of postmenopausal women of mandibular posteriors region and to correlate FD values with t-scores of quantitative ultrasound of the calcaneus bone.

   Materials and Methods Top

Ethical aspects

This study was approved by an institutional ethical board, and all procedures were conducted in full accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its subsequent revisions. The study was designed with 40 postmenopausal women aged 45–60 years in the Department of oral medicine and radiology and were selected based on set inclusion and exclusion criteria.

Inclusion criteria

The study included postmenopausal women in the age group of 45–60 years with a mean duration of menopause of 5 years and presence of mandibular first and second molar in good condition with good to fair oral hygiene index (OHI-S criteria).

Exclusion criteria

Patients with hysterectomy and those who used oral contraceptives during their reproductive years or hormone replacement therapy in the postmenopausal phase were excluded from the study. Individuals with a history of systemic diseases, hormone replacement therapy/long-term medication, smokeless and smoking tobacco habits were excluded from the study.[8]

Forty postmenopausal women who fulfilled the above mentioned inclusion and exclusion criteria were selected for the study. After obtaining the written informed consent, all the patients were subjected for bone mineral density using quantitative ultrasound of calcaneus (heel) bone,[8],[9],[10] and bone mineral density (BMD) was assessed at the Department of Orthopaedics.

Ultrasound parameters for assessment of calcaneal bone

The study used ultrasonometer device (Achilles InSight™ bone ultrasonometer, GE Healthcare, General Electric Company, Lunar, Madison, WI) based on quantitative ultrasound technique (QUS) to evaluate bone status by measuring stiffness index (SI) in the heel (calcaneus bone) for the assessment of BMD.[8],[9],[10] The working position and the components of the ultrasonometer are demonstrated below.

Measurement was performed with the patient seated and left foot placed on the foot positioner of the device. The heel was surrounded by warm water encapsulated in inflated membranes because water is the optimum medium for transmission of ultrasound. A transducer on one side of the heel (Tx) converted an electrical signal into sound wave, which passed through water membranes and the patient's heel. A transducer at a fixed distance on the opposite side of the heel (Rx) received the sound wave and converted it to an electrical signal that was analyzed by the ultrasonometer program. The ultrasonometer device measured the speed of sound (SOS, m/s) and the frequency-dependent broadband ultrasound attenuation (BUA, dB/MHz), and combined them to form a clinical measure called SI.

SI is a measure of bone strength and is sensitive to bone structures used to predict the risk of bone fracture caused by osteoporosis. To calculate SI, a resultant formula has been empirically derived such that the index has 50% contribution from SOS and 50% contribution from BUA

SI = [(0.67 × BUA) + (0.28 × SOS)] – 420

SI has been scaled in such a manner to make a young adult value equal to 100. The normalized and scaled BUA and SOS values contributed equally to the resulting SI over the adult age range. The SI was then used to create t-score by comparing with reference figures for a healthy young adult.[8],[9],[10]

Based on BMD assessment, patients were divided into two groups. Postmenopausal patients having t-scores ≤−2.5 SD were diagnosed with generalized osteoporosis, group 1, and postmenopausal patients having t-scores >−2.5 SD are diagnosed as nonosteoporotic, group 2 (controls).[7],[9] These patients were subjected to direct digital radiographs at the department of oral medicine and radiology.

Armamentarium for digital periapical image acquisition

Dental intraoral X-ray machine with standard exposure parameters of 65 kV peak, 7–8 mA, exposure time of 0.7 s, and 2.5 mm aluminium equivalent total filtration and 1 mm thick diaphragm made of lead with source to skin distance of 20 cm.[13] Equipment for digital radiography included charged coupled device KODAK RVG 5100 sensor with external dimensions of 27.5 × 37.7 mm and an active area dimension of 22 × 30 mm and matrix dimensions of 1200 × 1600 pixels. The true image resolution was set at 14 line pairs/mm. Posterior Rinn plastic ring paralleling device, Windows Vista operating system, KODAK 5100 software, Image J software-1.44 versions (NIH Public domain software, US National Institute of Health, Bethesda, MA), a Core 2 Duo processor with 3 GB RAM, 320 GB hard disk capacity, 14 inches Samsung monitor with maximum resolution of 1366 × 768 pixels for visualization of digital periapical images were used.

Acquisition of digital periapical image

Direct digital periapical radiographs of the permanent mandibular first and second molar were obtained for the study purpose by paralleling technique using posterior paralleling device with standard exposure parameters and 40 images acquired were then converted to uncompressed JPEG files as the DICOM (digital imaging and communication in medicine) files were not compatible with Image J software.

Selection of region of interest

A rectangular region of interest (ROI) [Figure 1] measuring 128 × 256 pixels was drawn between the mandibular first and second molar (JPEG image), placed within the interdental bone, and was limited by adjacent roots. Lamina dura, periodontal ligament space, and root structure were not included in the ROIs. Because it has been stated that beyond 2.5 mm there is no effect of bacterial plaque on alveolar process bone, the ROIs were created as far as possible from the crestal bone, and their inferior margin was always superior to the apex of the root.[13] The 40 ROIs obtained were saved in the computer memory.
Figure 1: A rectangular alveolar bone ROI outlined on digital periapical radiograph between mandibular first and second molar

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Assessment of fractal dimension

Image J 1.44 program was used to analyze the 40 ROI. The ROI was opened with the File option of Image J software, and then proceeded with the Image option and converted into 8-bit image as shown in [Figure 2].
Figure 2: Conversion of ROI into an 8-bit image using Image J software (1.44 versions)

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Then the Process option was selected and converted into 8-bit binary image as depicted in [Figure 3] and [Figure 4]. FD value was calculated using box counting method after selecting the Analyze option, as shown in [Figure 5], and at last clicking on to Enter key results in Plot containing FD value, as shown in [Figure 6].[13],[14],[15] The data obtained were analyzed statistically using the Statistical Package for the Social Sciences (SPSS 14.0, IBM SPSS Inc., Chicago, IL, USA) and MedCalc 9.0.1 for Windows.
Figure 3: Conversion into an 8-bit binary image using Image J software (1.44 versions)

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Figure 4: An 8-bit binary image

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Figure 5: Calculation of fractal dimension value from an 8-bit binary image using Image J software

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Figure 6: Plot showing fractal dimension value (D-value)

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   Results Top

The present study was planned to evaluate the diagnostic efficacy of FD analysis using digital periapical radiographs for the early diagnosis of osteoporosis. Forty postmenopausal women between the age group of 40-50 years were involved in the study. The data obtained were analyzed using the Statistical Package for the Social Sciences (SPSS 14.0) and MedCalc 9.0.1 for Windows and the results of study are presented below. Out of the 40 postmenopausal women included in the study, the overall mean age was found to be 48.62 years; in the study group mean age 48.7 years and in the control group it was 48.5 years [Table 1] and [Graph 1]. The FD values were compared between the two groups and were correlated with t-scores obtained by quantitative ultrasound of calcaneus bone.
Table 1: Age distribution between the groups

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The mean oral hygiene index-simplified (OHI-S) values, i.e., 2.0 and 1.905 in osteoporosis and control groups, respectively, were compared between the two groups and were not found to be statistically significant (P > 0.05) [Table 2]. The alveolar bone density, i.e., FD values between the two groups (mean FD value in study group –1.7386, mean FD value in the control group –1.8679) were found to be statistically significant using independent t-test (P< 0.001) [Table 3] and [Graph 2], and lower mean FD value were seen in the study group than the control group. [Table 4] and [Graph 3] present the correlation of alveolar bone density assessed using FD values with t-scores assessed by quantitative ultrasound of calcaneus bone. Within the study group, correlation between t-scores and FD values was not found to be statistically significant by linear correlation (P > 0.05).
Table 2: Comparison of oral hygiene index (OHI-S) values between the two groups

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Table 3: Comparison of alveolar bone density using mean fractal dimension values between two groups

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Table 4: Correlation of FD values and t-scores in the study group

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   Discussion Top

By innovative applications of digital dental images, it is now feasible to improve diagnosis by image enhancement and quantitative analysis of features in an image. Therefore, not only early diagnosis of some diseases but also more precise estimation of disease extent and prognosis has become available with these methods. In our study, one such inexpensive and readily available method, i.e., FD analysis via box counting, was applied to digital periapical radiographs of postmenopausal women to establish a noninvasive evaluation of their bone structures, facilititating early diagnosis of osteoporosis.[16]

Bone mass is the quantity of bone and bone density is the ratio of mass to volume. FD analysis gives a numerical measure of the degree of boundary irregularity or surface roughness. It describes how an object occupies space and is related to the complexity of its structure.[13] It quantifies the actual trabecular pattern by analyzing the trabecular bone and bone marrow interface and detects early changes in the alveolar bone mineral content. A higher FD indicates a more complex structure and in osteoporosis showed a change toward decreased complexity of bone, which directly relates to the reduction in the number of trabecular terminal points per sq.cm, as stated by White et al.[14],[17],[18] and thus correlated with reduced bone mineral density in patients with osteoporosis. It has been widely used in diagnosis of bone diseases such as hyperparathyroidism, haemolytic anemia, implant site assessment, and post-endodontic bone changes. It gained high importance as a diagnostic tool because of its reproducibility, reliability, widespread availability, noninvasiveness, and being cost effective.[14]

In our study, patients with hysterectomy were excluded as the main producers of estrogen, i.e., ovaries are not always removed with hysterectomy. Mean duration of menopause in both groups was minimum 5 years as it is estimated that the average woman loses up to 10% of her bone mass in the first five years of menopause.[19] In the present study, BMD was assessed using QUS, which evaluates bone status by measuring SI in the heel (calcaneus bone), similar to studies by Vishwanath et al.[8] and Angela Juby of University of Alberta, Edmonton.[20] In our study, ROIs from mandibular posterior bone were selected because this region was considered as an optimal area for image-textural studies of bone quality that is free from superpositions and obnoxious effects of accessory influential factors and have fewer errors of receptor placement.[16]

The results of our study showed FD values between 1.597 and 1.755 in the osteoporotic group and between 1.822 and 1.918 in the control group. The results of FD values was significant in our study, which directly relates to the reduction in the number of trabecular terminal points per sq cm, as stated by White et al.,[17] Tosani et al.,[15] and Lee et al., who in their study stated that radiographic variables that are associated with osteoporosis showed a change towards decreased complexity of the bone thereby decreasing FD values.[18] Similarly, studies by Southard et al.[12] substantiated that radiographic intensity surface or profile becomes smoother (less complex) in patients with osteoporosis, thereby decreasing the fractal dimension values. No positive correlation was found between FD values and t-scores, which could be explained by several factors such as nature of the sample, quality of bone present, and sensitivity of ultrasound compared to DEXA. The results are in accordance to the results of Southard et al.[21]

   Conclusion Top

FD analysis using direct digital periapical radiographs is a novel method, which can be used for early diagnosis of osteoporosis in the alveolar bone; thereby, dentists play a pivotal role in early identification of affected individuals. Future automated application of such image analysis could enable widespread, noninvasive, and cost-effective methods in screening for osteoporosis in dental environments.

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Conflicts of interest

There are no conflicts of interest.

   References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]

  [Table 1], [Table 2], [Table 3], [Table 4]

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