|Year : 2016 | Volume
| Issue : 1 | Page : 1-5
Comparison of mesiodistal measurements of single implant sites on panoramic images generated at different horizontal levels: A cone beam CT study
Mustafa Alkhader1, Malik Hudieb2, Yousef Khader3
1 Department of Oral Surgery and Medicine, Public Health and Family Medicine, Jordan University of Science and Technology, Irbid, Jordan
2 Department of Preventive Dentistry, Public Health and Family Medicine, Jordan University of Science and Technology, Irbid, Jordan
3 Department of Community Medicine, Public Health and Family Medicine, Jordan University of Science and Technology, Irbid, Jordan
|Date of Web Publication||19-Feb-2016|
Department of Oral Surgery and Medicine, Faculty of Dentistry, Jordan University of Science and Technology, Irbid - 22110
Source of Support: None, Conflict of Interest: None
Background: This study aimed to compare mesiodistal measurements of single implant sites on cone beam CT (CBCT) panoramic images generated at different horizontal levels. Materials and Methods: CBCT images for 101 single implant sites of 66 patients referred for pre-surgical radiographic dental implant planning were selected for the study. In addition to automatic horizontal level determined by the CBCT software, panoramic images were generated at three different horizontal levels (central incisal edges, crest of the ridge at the implant site, and apices of central incisors) at jaw of interest and mesiodistal measurements were performed by two observers. The measurements were averaged and differences in the means were compared using repeated measures analysis and Bonferroni multiple comparison test. Results: The mean values of mesiodistal measurements at the automatic horizontal level and apices of central incisors level were significantly lower than the mean values at central incisal edges level and crest of the ridge level (8.09, 8.02, 8.54, 8.51 mm respectively). Conclusions: CBCT Panoramic images generated at different horizontal levels can yield different mesiodistal measurements of single implant sites, and further studies with a gold standard need to be conducted to determine the horizontal level of choice.
Keywords: CBCT, dental implant, mesiodistal, panoramic
|How to cite this article:|
Alkhader M, Hudieb M, Khader Y. Comparison of mesiodistal measurements of single implant sites on panoramic images generated at different horizontal levels: A cone beam CT study. J Oral Maxillofac Radiol 2016;4:1-5
|How to cite this URL:|
Alkhader M, Hudieb M, Khader Y. Comparison of mesiodistal measurements of single implant sites on panoramic images generated at different horizontal levels: A cone beam CT study. J Oral Maxillofac Radiol [serial online] 2016 [cited 2022 Dec 5];4:1-5. Available from: https://www.joomr.org/text.asp?2016/4/1/1/177052
| Introduction|| |
Since the introduction of dental implants into dentistry, the radiographic assessment of implant sites has been required as an essential step in treatment plan which can affect the surgical and prosthodontic steps afterward. Moreover, with the advent of three dimensional imaging modalities, the limitations of two dimensional imaging modalities in evaluating bone quantity (dimensions) and quality, diseases and vital anatomical structures at implant sites could be solved, and the incidence of complications could be decreased. 
Biomechanical studies in dental implants field supported by other types of studies ,,, have demonstrated the pronounced effect of implant dimensions on the success and survival rates of dental implants. Of the implant dimensions that include implant's length, diameter and abutment connection type, implant diameter has been shown to be the most important factor in the success of dental implants. ,, Implant diameter is governed mostly by the available mesiodistal and buccolingual dimensions of the available alveolar bone ridge. These dimensions can be determined accurately and noninvasively by cone beam computerized tomography (CBCT), ,,,, which is a low dose CT imaging modality. However, in CBCT, different reconstructed images can be used (coronal, sagittal, axial, oblique and panoramic) and differences in measurements can be anticipated due to several factors. ,,,,,,,,,,,
To generate panoramic images from CBCT, the operator has either to create a dental arch automatically by choosing auto create arch option, or manually by drawing a dental arch on any horizontal level of preference. These options might differ depending on CBCT software being used. It is unknown if panoramic images generated at horizontal levels other than the automatic horizontal level will affect the mesiodistal measurements of single implant sites. Therefore, this study was conducted to determine whether the mesiodistal measurements differ according to the predetermined horizontal level for generating panoramic images or not.
| Materials and Methods|| |
Images for sixty-six patients who underwent CBCT examination for treatment of single implant sites (101 single implant sites) at our dental radiology clinics between January 2011 and January 2013 were retrieved and evaluated. The patients consisted of 31 males and 35 females, with a mean age of 41 years. The exclusion criterion from this study was the presence of artifacts at implant sites, although we did not encounter such cases in this sample size.
As a CBCT apparatus, KODAK 9500 Cone Beam 3D System (Carestream, Rochester, NY, USA) with flat panel detector was used. The imaging area of CBCT is a cylinder with a height of 15-20.6 cm and a diameter of 9-18 cm, providing isotropic cubic voxels, with sides approximating 0.2 mm-0.3 mm. Maxillofacial areas were examined at a tube voltage of 60-90 kV, a tube current of 10-15 mA, and exposure time of 10-24 seconds.
Examinations were performed by 360 degree rotations in occlusal position, with the patient standing and closing his/her mouth.
Evaluation of images
For generating panoramic images, the curved slicing module was used. In this module an axial image is displayed and can be adjusted to any horizontal level of interest. For arch creation on axial image, there are two options; auto create arch or manual. In case the auto create arch option is used, the software will automatically set several control points (nodes of focal trough) on an axial image generated at a specific horizontal level, which we prefer to call automatic horizontal level. Otherwise, the arch can be created manually by setting several control points on an axial image generated at the desired horizontal level by the operator. Then, the reconstructed panoramic image is displayed with voxel setting at which the volume was acquired, whereby the focal trough can be adjusted to present the reconstructed panoramic image as a traditional panoramic image.
The first panoramic image generated, was at the automatic horizontal level which is displayed automatically when auto create arch function is chosen, then depending on this panoramic image and para-axial images generated, we allocated three different horizontal levels (central incisal edges, crest of the ridge at the implant site, and apices of central incisors) at jaw of interest to generate three different panoramic images. At all the horizontal levels, the arch was created manually, and the position of the control points was in the middle of the displayed arch. To allocate any horizontal level, the yellow indicators on either side of panoramic or para-axial images can be moved up and down to the desired level. Focal trough was set to be 15 mm thickness in all of the generated panoramic images.
Two calibrated observers: One oral radiologist and one oral implantologist with 8 years of experience with CBCT and dental implants were responsible for creating the different panoramic images and measuring the mesiodistal dimensions of implant sites on them [Figure 1], [Figure 2], [Figure 3] and [Figure 4]. Following the example of Mehra and Pai et al.,  the mesiodistal dimension was the horizontal distance connecting between the highest points located at alveolar crest of nearby teeth.
|Figure 1: CBCT based panoramic image generated at automatic horizontal level determined by the software showing the mesiodistal dimension of proposed implant site|
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|Figure 2: CBCT based panoramic image generated at central incisal edges level showing the mesiodistal dimension of proposed implant site at same area|
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|Figure 3: CBCT based panoramic image generated at crest of the ridge level showing the mesiodistal dimension of proposed implant site at same area|
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|Figure 4: CBCT based panoramic image generated at apices of central incisors level showing the mesiodistal dimension of proposed implant site at same area|
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All images were evaluated on LCD monitor with installed CS 3D imaging viewer (CS 3D imaging viewer, 3.2.9 Carestream, Rochester, NY, USA). When necessary, the window settings were adjusted to optimize the images for evaluation.
Intraclass correlation coefficients (ICCs) were calculated to assess inter-observer reliability of mesiodistal measurements at the four horizontal levels (automatic, central incisal edges, crest of the ridge at the implant site, and apices of central incisors) between the first and second observer.
General linear model repeated measure analysis was conducted to test the differences between the mean values of the mesiodistal measurements, then Bonferroni multiple comparison test was used to test the pairwise differences and a P value of less than .05 was considered to be significant.
All previous statistical analyses were done by using a statistical software (SPSS version 16; Chicago, IL, USA).
| Results|| |
The distribution of implant sites is shown in [Table 1].
The inter-observer reliability was excellent for mesiodistal measurements on panoramic images generated at the different horizontal levels (automatic level, central incisal edges, crest of the ridge at the implant site, and apices of central incisors); ICCs were: 0.96, 0.95, 0.89, and 0.91 respectively. Given the low interobserver variability, the measurements from the two observers were averaged to obtain mean values. The average mesiodistal measurements (mm) on panoramic images generated at different horizontal levels are shown in [Table 2].
|Table 2: The average mesiodistal measurements (mm) on panoramic images generated at different horizontal levels*|
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Reapeated measurements analysis showed that there were significant differences in the mesiodistal measurements on panoramic images generated at different horizontal levels (F test = 32.6, P < 0.001). Multiple comparisons using Boneferroni test showed that the average mesiodistal measurements at the automatic horizontal level [mean (SD) = 8.09 (2.53) mm] and apices of central incisors level [mean (SD) = 8.02 (2.48) mm] were almost the same (P = 0.664) and not significantly different. Moreover, the average mesiodistal measurements at the central incisal edge level [mean (SD) = 8.54 (2.60) mm] and the crest of the ridge level [mean (SD) = 8.51 (2.56) mm] were almost the same. However, the mean mesiodistal measurements at the automatic horizontal level and apices of central incisors level were significantly lower than those at other horizontal levels.
| Discussion|| |
A previous study  indicated that the mesiodistal measurements of single implant sites can be done on both panoramic and oblique images generated by CBCT. However, panoramic images were generated at the automatic horizontal level and other horizontal levels were not considered.
We found only one previous study in which CBCT based panoramic images were reconstructed at three different horizontal levels,  but only the effect on mesiodistal root angulations was studied and not the mesiodistal dimensions of implant sites.
Comparing CBCT based panoramic images to digital panoramic images, CBCT based panoramic images revealed comparable results in diagnostic image quality. , In addition to this, CBCT based panoramic images can produce very accurate measurements of root angulations. ,, Among previous studies, Peck et al.  used plaster model measurements as the gold standard for measuring root angulations, and they found that the CBCT based panoramic images revealed very accurate measurements, whereas panoramic images were not accurate.
To generate panoramic images from CBCT data, several parameters need to be considered, like the central plane of focal trough nodes, thickness of focal trough and the horizontal level for arch creation etc. The CBCT software manufacturers guidelines should be followed until international guidelines for creating panoramic images from CBCT data are met. In our case, focal trough nodes were in the centre of the displayed arch. The arch was created at jaw of interest, and the thickness of focal trough was set to be 15 mm according to Kodak software guidelines. However, at the date of writing this study, we could not find guidelines regarding the horizontal level at which we can generate panoramic images manually. On the other hand, there are guidelines for generating panoramic images from conventional CT  stating that the horizontal level must be obtained at the level of the teeth roots in the arch of interest.
In our current study, we generated three panoramic images at three different horizontal levels in addition to the one generated at automatic horizontal level, namely: The level of central incisal edges, the crest of the ridge at implant site and the level of apices of central incisors. Despite the small differences in the mean values of mesiodistal measurements, statistically significant differences were shown between measurements at the automatic horizontal level and apices of central incisors level with other levels. This finding could be due to the different shapes of the displayed arches. Although the central plane of focal trough was in the center of the displayed arch at all horizontal levels, positions of the nodes of the focal trough were different according to the shape of the displayed arch, and minimal changes in node position can result in apparent change in mesiodistal dimensions of single implant sites.  In addition to this, if the traced centered line is not going though the shortest point between cemento-enamel junction (CEJ) and CEJ of the teeth next to the crestal area of interest, average of voxels buccal and lingual to the traced centered line takes into account a different part of anatomy.
For measuring the mesiodistal dimensions of single implant sites clinically, the caliber should be at the level of the crest. Therefore, we think that panoramic images generated at the level of the crest at implant sites will be the one of choice. However, a study using a gold standard must be conducted to confirm that.
| Conclusions|| |
Finally, we can conclude that panoramic images generated by CBCT at different horizontal levels can yield different mesiodistal measurements of single implant sites, and further studies need to be conducted to determine the horizontal level of choice.
Financial support and sponsorship
Conflicts of interest
We declare that we have neither financial disclosure nor conflict of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]