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Egyptian Journal of Oral & Maxillofacial Surgery:
doi: 10.1097/01.OMX.0000395513.60344.ff
Research Papers

Assessment of periodontal defects using cone beam computed tomography: an in-vitro study

el Zoheiry, Hany Salah; Abou-Khalaf, Ashraf; Farid, Mary Medhat

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Author Information

Department of Oral Medicine, Periodontology, Radiology and Diagnosis, Faculty of Dentistry, Ain Shams University, Egypt

Correspondence to Hany Salah el Zoheiry, 257 Hegaz St., Heliopolis, Cairo, Egypt, Tel: +012 75 73 296; e-mail: honnelsihonn@hotmail.com

Received November 4, 2010

Accepted January 6, 2011

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Abstract

Radiological diagnostics are essential aids in making a specific diagnosis and treatment plan of cases of periodontal diseases. The aim of this study is to explore the diagnostic value of cone beam computed tomography (CBCT) in the assessment of periodontal bone loss. Four human dry skulls were used for the measurement of 184 selected periodontal defects. Bone height was measured at six points on each selected tooth using an electronic digital caliper. Skulls were then imaged using CBCT and the same measurements were taken on CBCT images using the digital measurement tool of the software. The measurements were taken on buccal and lingual panoramic reconstruction views with 5.1 mm thickness and also on cross-sectional views with 0.32 mm thickness. Statistical analysis was carried out to find whether there is a significant difference between the CBCT findings and the measurements of dry skulls. The present results showed an accuracy of periodontal bone-level measurements using panoramic reconstruction and cross-sectional views. There was no statistically significant difference between the cross-sectional images and the panoramic reconstruction images. CBCT images allowed accurate measurements of periodontal defects on panoramic reconstruction images of 5.1 mm slice thickness and cross-sectional slices of 0.32 mm. Cross-sectional images showed a more accurate assessment than panoramic reconstruction images because of an absence of overlapping structures. Further studies are required for the evaluation of the diagnostic validity during clinical follow-up, for justification of the applicability of CBCT in periodontal diagnosis.

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Introduction

Detection of periodontal disease is important in the prevention of tooth loss [1,2]. Assessment of periodontal bone loss is essential for planning periodontal surgeries. Several methods are used for the measurement of periodontal bone loss. Clinical probing is dependent on the probing force [3,4]. Electronic probes have not shown more advantages over manual probing [5–7]. Periapical radiographs or bitewings may overestimate or underestimate the amount of bone loss because of projection error and the overlap of anatomical structures, which hinders a true distinction between the buccal and lingual cortical plates [8–13]. Conventional computed tomography (CT) provides axial slices throughout the object of interest but has major drawbacks including high radiation dose, high cost, and low resolution [14–16].

Cone beam computed tomography (CBCT) offers many advantages compared with conventional CT. CBCT produces images with submillimeter voxel resolution. This level of spatial resolution is applicable for maxillofacial applications [14,16,17]. CBCT equipment is approximately one-fourth to one-fifth the cost of conventional CT. The time for the CBCT scanning is substantially reduced when compared with conventional CT [14,16,17]. CBCT considerably reduces radiation exposure to patients [14–17].

Using CBCT for periodontal assessment may offer new perspectives on periodontal diagnosis and treatment planning [18–20]. Therefore, we thought it is worthwhile to explore the use of CBCT in the assessment of periodontal defects.

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Materials and methods

Skull measurements

One hundred and forty-eight measurements of naturally occurring horizontal bone defects on four human dry skulls were taken. To assess bone levels, the cemento–enamel junction (CEJ) was used as a reference point. Owing to dehydration of the dry skull, gutta purcha was used as a standardized fiducial to substitute for the faded CEJ. Radiopaque gutta purcha fragments with a small central indentation were glued onto the buccal and lingual surface along the CEJ. Periodontal defects were measured at six points: mesiobuccal, midbuccal, distobuccal, mesiolingual, midlingual, and distolingual (Fig. 1).

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An electronic digital caliper (Shenhan Measuring Tools Co., Ltd, Shanghai, China) was used for measuring bone height of the dry skulls. The digital caliper was aligned with the long axis of the tooth while taking measurements. When accessibility did not allow the digital caliper to be oriented along the long axis of the tooth, this measurement was dropped. Mesial and distal bone levels were measured at the mesial and distal ends of the gutta purcha, whereas central bone levels were measured at the central indentation.

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Image acquisition

CBCT was performed for the skulls using Planmeca ProMax (Planmeca Oy, Finland). The occlusal plane of the jawbones was positioned horizontally to the scan plane and the midsagittal plane was centered. Pink modeling wax was used to stabilize the skull. The beam height at the surface of the image receptor was set to visualize the entire jaw, giving 463–464 slices of 0.32 mm thickness. Exposure factors used for image acquisition were 68 kVp and 19.2 mAs (6 mA×3.2 s) with a 320-μm voxel size.

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Cone beam computed tomography image measurements

Periodontal defects were measured while seated at a distance of 60 cm from a 21-inch liquid crystal display high-resolution screen (1600×1200 pixels) of a personal computer. Images were viewed with a Planmeca Romexis Viewer 2.2.7.R. (Planmeca Oy). Measurements were taken using the digital measurement tool of the software. When the bone height measurement was less than 1.2 mm, the digital measurement tool could not give a reading. Therefore, bone heights less than 1.2 mm were dropped.

Three maxillofacial radiologists sitting together in four sessions determined each quantitative measurement. When they differed in their opinion, the final decision was taken by consensus.

One hundred and forty-eight bony defects were measured on CBCT images twice. First measurements were taken on buccal and lingual panoramic reconstructed views and the second measurements were taken on cross-sectional images.

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Panoramic reconstructed images

Panoramic view was reconstructed with 5.1 mm slice thickness. Two panoramic reconstruction images were used for measuring bone height for every jaw. The first one was aligned along the buccal cortical plate of bone and the second one was aligned along the lingual cortical plate of the bone (Fig. 2). The buccal panoramic image was used for measuring the three buccal points and the lingual panoramic image was used for measuring the three lingual points. Bone height was measured from the gutta purcha to the alveolar crest level (Fig. 3). Gutta purcha facilitated identification of the faded CEJs and allowed standardization of measurement localization. In a clinical setting, identification of CEJs would not be as hard as that with dry skulls (Fig. 4).

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Fig. 3
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Cross-sectional images

The CBCT measurements that were done on panoramic slices were also taken on cross-sectional slices (0.32 mm slice thickness). When measuring bone height on cross-sectional slices, the axial plane was first aligned along the gutta purcha glued to the tooth (Fig. 5), and the coronal plane was then aligned with the long axis of the tooth and through the point at which the measurement should be carried out (Fig. 6). Bone height was then measured on the coronal slice from the gutta purcha to the alveolar crest (Fig. 7). Six bone height measurements were taken for each selected tooth including mesiobuccal, midbuccal, distobuccal, mesiolingual, midlingual, and distolingual.

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Fig. 6
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Statistical analysis

Bone height measurements obtained from panoramic reconstruction images and cross-sectional images were subsequently compared with the gold standard (quantitative assessment). Statistical analysis was carried out to find out whether there is a significant difference between the CBCT findings and the gold standard.

Data were analyzed by the Statistical Package for Social Science (SPSS, IBM Corporation, Somers, NY) version 16. Data were expressed as mean±standard deviation. Comparing the mean±standard deviation of two groups was carried out using unpaired Student's t-test. A P value of less than 0.05 was considered significant.

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Results

Bone height was measured on human dry skulls. CBCT was performed on the skulls. Bone height was measured on CBCT images twice. First measurements were taken on buccal and lingual panoramic reconstructed views and the second measurements were taken on cross-sectional images.

No significant difference was found between bone height measurements on the skull and on the panoramic reconstruction images using 5.1 mm slice thickness (P=0.256) (Fig. 8). No significant difference was found between bone height measurements on the skull and on the cross-sectional images using 0.32 mm slice thickness (P=0.178) (Fig. 9).

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Fig. 9
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For panoramic reconstruction images, underestimation and overestimation were 89 and 11%, respectively (Figs. 10 and 12). For cross-sectional images, underestimation and overestimation were 97 and 3%, respectively (Figs. 11 and 12).

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No significant difference was found between the error in panoramic reconstruction images and in cross-sectional images (P=0.511) (Fig. 13). However, panoramic reconstruction images showed a wider deviation range than cross-sectional images. Deviations from the gold standard were between 0.01 and 2.1 mm for the panoramic reconstruction images, whereas it was between 0 and 0.99 mm for the cross-sectional slices.

Fig. 13
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Discussion

Detection of periodontal disease is important in the prevention of tooth loss [1,2]. In periodontal disease, a precise clinical estimation of the loss of supporting bone is not possible. Radiological diagnostics are an essential aid for making a specific diagnosis and for planning treatment [21].

CBCT offers many advantages compared with conventional CT. CBCT provides images with higher resolution at a lower cost, shorter examination time, and less radiation dose [14,16,17,22].

Many investigations of the recent CBCT technology have validated its usefulness for several diagnostic purposes, such as implant planning or orthodontics [16,23,24]. However, limited studies have been reported on the advantages of CBCT for periodontal diagnosis [18–20,25,26].

Using CBCT for periodontal assessment may offer new perspectives on periodontal diagnosis and treatment planning [18–20]. Therefore, we thought it is worthwhile to explore the use of CBCT in the assessment of periodontal defects.

Four human dry skulls were used for the measurement of bone height in 148 selected periodontal defects. The CEJ was used as a reference point to assess bone levels. Owing to dehydration of the dry skull, gutta purcha was used as a standardized fiducial to substitute for the faded CEJ.

Gutta purcha facilitated identification of the faded CEJs and allowed standardization of measurement localization. In a clinical setting, identification of CEJs would not be as hard as that with dry skulls (Fig. 7).

When accessibility did not allow the digital caliper to be oriented along the long axis of the tooth, this measurement was dropped. Missed readings were more common on the lingual side than on the buccal side.

The dry skulls were imaged with CBCT. An essential advantage of the CBCT technique is that different views can be retroactively synthesized from the volume data and combined at will. Two-dimensional slices have proven to be the most effective for detailed diagnosis [22].

Images were viewed with a Planmeca Romexis Viewer 2.2.7.R. Measurements were taken using the digital measurement tool of the software. When the bone height measurement was less than 1.2 mm, the digital measurement tool did not show any reading. Therefore, bone heights less than 1.2 mm were dropped. Recently developed versions of the software do not present the same problem.

Panoramic reconstruction views were used for measuring bone height. They provide the user with an overall view and allow a quick assessment of the periodontal bone. The slice thickness was 5.1 mm, which is large enough to visualize the buccal or lingual fiducials with the alveolar crest on one reconstruction. Therefore, one panoramic view was reconstructed for the buccal measurements and another was constructed for the lingual measurements.

However, panoramic reconstruction images of 5.1 mm would not allow complete exploitation of the acquired three-dimensional CBCT data. Therefore, the selected sites were measured again on coronal and sagittal images of 0.32 mm thickness through the specific fiducials. The highest resolution the CBCT machine used in this study could offer was 0.32 mm slice thickness. CBCT voxel resolutions can range from 0.076 to 0.4 mm [27].

There was no significant difference between panoramic reconstructed images and the gold standard regarding bone-height measurement (P=0.256). This highlights the accuracy of periodontal bone-level measurements using buccal and lingual panoramic reconstruction images with 5.1 mm slice thickness. The mean error was 0.27 mm. Vandenberghe et al. [19] used 5.2 mm-thickness panoramic reconstruction images and reported similar results with a mean error of 0.47 mm.

Moreover, there was no significant difference between bone height measurements taken on cross-sectional images and the gold standard (P=0.178). This proves the accuracy of periodontal bone-level measurements using cross-sectional images with 0.32 mm slice thickness. The mean error was 0.3 mm. Vandenberghe et al. [19] used 0.4 mm-thickness cross-sectional images and reported similar results with a mean error of 0.29 mm. Misch et al. [18] and Fuhrmann et al. [28] used 1 mm-thickness cross-sectional images and found similar results (mean error of 0.41 and 0.2, respectively).

There was no statistically significant difference between the panoramic reconstructed images and cross-sectional images (P=0.511). Deviations from the gold standard were between 0.01 and 2.1 mm for the panoramic reconstruction slices and between 0 and 0.99 mm for the cross-sectional slices.

In our opinion, aligning the cross-sectional slices to pass through the points of interest was a lot easier than reconstructing a panoramic image that includes the fiducials of all teeth and the alveolar crest. In addition, the statistics showed the cross-sectional images to be more accurate with a narrower deviation range. Therefore, we recommend the cross-sectional images for any periodontal measurements.

Small or large errors in locating the CEJ and the alveolar crest can, respectively, lead to overestimation and underestimation of disease prevalence [13]. If we considered a 0.5 mm discrepancy acceptable at a clinical level, panoramic reconstructed images were accurate in 76% of the measurements and cross-sectional images were accurate in 82% of the measurements. If we even considered a 1 mm discrepancy acceptable at a clinical level, this leads to 98% accuracy for panoramic reconstructed images and 100% accuracy for cross-sectional images.

In this study, we were able to confirm our hypothesis that CBCT would allow an accurate assessment of bone levels. Statistics show a smaller deviation range from the gold standard for the measurements on 0.32 mm cross-sectional slices (between 0.01 and 2.1 mm) compared with those on the 5.1 mm panoramic reconstruction image (between 0 and 0.99 mm). This finding indicated that the current CBCT system might become more influential in the diagnosis of periodontal diseases.

As the radiation dose of CBCT has been reported to be less than conventional CT, there is a growing concern about the overconsumption of CBCT and its radiation safety [14–16,29].

In our opinion, the use of CBCT should still be carefully justified, and optimized exposure protocols should always be considered. Moreover, specialists in this field must perform the image acquisition and further interpretation. Ludlow et al. [15] reported dose reduction when using smaller field of view examinations. More studies in the future with a large sample size will determine ideal exposure settings that optimize the image quality for a certain diagnostic task with the lowest radiation exposure possible.

Considering the several advantages, limitations, and risks of CBCT, we would like to suggest that the currently tested model of CBCT should only be used for a relatively more complex periodontal treatment planning, such as prognostic planning and surgery for complex periodontal defects, and the potential use of dental implants.

For proper justification of the applicability of CBCT in periodontal diagnosis, further studies are required for the assessment of various exposure and reformatting protocols and the evaluation of the diagnostic validity during clinical follow-up, especially when surgery is involved. These findings may help in establishing selection criteria for the assessment of periodontal bone loss.

In conclusion, CBCT images allowed accurate measurements of periodontal defects on panoramic reconstruction images of 5.1 mm slice thickness and cross-sectional slices of 0.32 mm thickness. Cross-sectional images showed a more accurate assessment than panoramic reconstruction images, because of the absence of overlapping structures.

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Keywords:

cone beam computed tomography; periodontal defects; periodontal diagnosis

© 2011 Egyptian Associations of Oral and Maxillofacial Surgery

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