|Year : 2021 | Volume
| Issue : 4 | Page : 401-408
Assessment of artifacts induced by various dental restorative materials on cone- beam computed tomography- An in vitro study
Laboni Ghorai1, ML Asha2, Jigna V Raja3
1 Department of Oral Medicine and Radiology, Kusum Devi Sunderlal Dugar Jain Dental College and Hospital, Kolkata, West Bengal, India
2 Department of Oral Medicine and Radiology, Dr. Syamala Reddy Dental College, Hospital and Research Centre, Bengaluru, Karnataka, India
3 Department of Radiology, Consultant CBCT Radiologist, Magnus Diagnostic Centre, Bengaluru, Karnataka, India
|Date of Submission||20-May-2021|
|Date of Decision||27-Sep-2021|
|Date of Acceptance||24-Nov-2021|
|Date of Web Publication||27-Dec-2021|
Dr. Laboni Ghorai
Department of Oral Medicine and Radiology, Kusum Devi Sunderlal Dugar Jain Dental College and Hospital, 6 Ram Gopal Ghosh Road, Cossipore, Kolkata - 700 002, West Bengal
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Objectives: The aim of this study was to assess and compare quantitatively and qualitatively the artifacts induced by various commonly used dental restorative materials in different sections of CBCT image and to characterize the pattern of artifact. Material and Methods: Thirty dental plaster blocks, each with one of each of mandibular second premolar, first molar and second molar teeth with crowns aligned as in the natural dentition were scanned by CBCT device and analyzed using CS 3D imaging software, before and after the first molar was prepared and restored with dental amalgam, composite resin or glass ionomer cement (GIC), 10 plaster blocks being randomly selected for each restorative material. The reformatted axial, coronal and sagittal scans were then quantitatively assessed for artifact by two calibrated dento- maxillofacial radiologists by comparing the control and restored scans of each plaster block in a blinded manner and documented the slice numbers from which the image became diagnostic. Then, the slice numbers were converted into millimeters away from the restoration. Results: Paired t test, ANOVA and post hoc Tukey tests were used for statistical analyses. The level of significance was set at α = 5%. Depending on the extent, the majority of artifacts produced were as follows: Dental amalgam >Composite resin >GIC. The artifact was most extensive in the coronal section. Streaks and scatter artifacts, linear artifacts extending outward from tooth surface and hypodense halo were predominant. Conclusion: Different dental restorative materials cause various amounts of artifacts in different planes of projection of CBCT image due to differences in density and atomic number.
Keywords: Artifact, composite resin, cone-beam computed tomography, dental amalgam, glass ionomer cement
|How to cite this article:|
Ghorai L, Asha M L, Raja JV. Assessment of artifacts induced by various dental restorative materials on cone- beam computed tomography- An in vitro study. J Indian Acad Oral Med Radiol 2021;33:401-8
|How to cite this URL:|
Ghorai L, Asha M L, Raja JV. Assessment of artifacts induced by various dental restorative materials on cone- beam computed tomography- An in vitro study. J Indian Acad Oral Med Radiol [serial online] 2021 [cited 2022 Aug 16];33:401-8. Available from: https://www.jiaomr.in/text.asp?2021/33/4/401/333860
| Introduction|| |
In the field of dentistry, bi-dimensional radiographic methods are being widely used. However, the superimposition of adjacent structures and consequent loss of anatomic details may occur. To overcome these disadvantages, computed tomography (CT), has been employed in dentistry for the diagnosis of soft and hard tissue lesions since 1978 enabling more precise quantitative and qualitative evaluation of adjacent structures. However, the limitations of CT scan in dental procedures include its high costs, large equipment size, image artifacts, and high radiation doses., Since 1990, the development of cone-beam computed tomography (CBCT) has become a very important alternative diagnostic tool for overcoming these drawbacks., Present state-of-the-art CBCT units produce three-dimensional images of oral bony anatomy with excellent high resolution.
However, several artifacts may occur with CBCT, related to the technique itself and the object being examined. Artifacts are caused due to differences in density of the material and atomic number of the elements used in the components of the dental restorations or implants, thereby significantly degrading the visual quality of the images., Many studies have evaluated the artifacts induced by metals in CBCT imaging systems.,, However, there have been few studies aimed at evaluating the artifacts induced by restorative materials in CBCT imaging.
Hence, the present study was designed to measure and compare the artifacts induced by various commonly used dental restorative materials in axial, coronal and sagittal sections of CBCT, to identify the section of CBCT in which the artifact is most prominent and extensive and to identify and characterize the pattern of artifact induced by various dental restorative materials.
| Materials and Methods|| |
An in vitro study was carried out using freshly extracted sound adult human mandibular premolars and molars. The patients visiting the OPD of Dental College, Hospital and Research Centre, Bangalore were examined and the mandibular second premolars and molars with sound tooth structure but required to be extracted due to weak periodontal status or, due to orthodontic or prosthetic reasons were indicated for extraction. Following extraction, the teeth were collected for this study. Since the study was carried out in-vitro, hence ethical committee had declared non-requirement of ethical clearance for this study. The study was conducted according to the principles of the Helsinki Declaration of 1975, as revised in 2000.
- Mandibular second premolar, first molar and second molar teeth
- Freshly extracted sound adult human teeth.
- Maxillary premolars and molars
- Teeth other than premolars and molars
- Carious, severely attrited and cervically abraded teeth
- Fractured teeth
- Treated teeth
- Teeth with developmental anomaly.
Sample size estimation
Sample size calculation is concerned with quantification of data required to make a correct decision on particular research. In this type of regression analysis which is a set of statistical processes for estimating the relationships between a dependent variable (artifact) and one or more independent variables (restorative materials), researchers opine that there should be at least 10 observations per variable. Hence, if we used three independent variables, then a clear rule would be to have a minimum sample size of 30.
The collected teeth were immersed in 5% sodium hypochlorite for 30 minutes to remove the external organic tissues and calculi.
30 dental plaster blocks, each one being trimmed to have identical length, breadth and height were made with one of each of mandibular second premolar, first molar and second molar teeth embedded in each plaster block such that their crowns were aligned as in the natural dentition [Figure 1].
|Figure 1: Teeth embedded in plaster block with crowns aligned as in the natural dentition|
Click here to view
In each plaster block, class I cavity preparation was decided to be done in the mandibular first molar tooth according to the standard methods. The unprepared non-restored tooth was considered as control in each block, followed by standard occlusal restoration [Figure 2] being done in each mandibular first molar. Before cavity preparation, the distance (V1) between the central pit of the tooth and the base of plaster block was first measured using Vernier's callipers and following preparation, the distance (V2) between the prepared cavity floor and the base of plaster block was similarly recorded. The cavity preparation was done until V1-V2 is 3 mm, that is, the occluso-cervical depth of preparation was maintained at 3 mm for each tooth preparation. The teeth were then restored with dental amalgam, composite resin cement and glass ionomer cement, 10 plaster blocks being randomly selected for each restorative material.
Each plaster block was subjected to CBCT examination. The block was placed in a designated rectangular area conforming to the base of the plaster blocks over the chin support platform of the CBCT machine, maintaining the same antero-posterior and medio-lateral position for all the scans [Figure 3]. Two sequential scans were obtained with the CBCT scanner (Gendex DP 700 SC, PaloDEx Group Oy Nahkelantie 160, FI-04300 TUUSULA, Finland) before and after the restoration under the following conditions: 90 kV, 8 mA, 133 μm voxel size and 6 × 4 cm field of view (FOV). The exposure time was 6 seconds per scan.
|Figure 3: Positioning of plaster block over the chin support platform of the CBCT machine|
Click here to view
The images were saved in Digital Imaging and Communication in Medicine (DICOM) format and imported into imaging software (CS 3D imaging software version 7, Care stream DENTAL, USA).
The control and restored scans for each block of each of the dental restorative materials were compared in all the axial, coronal and sagittal sections. 40 slices of axial scan, 150 slices of coronal scan and 55 slices of sagittal scan with a slice spacing of 0.2 mm for each of control and restored scans were created for comparison.
Two experienced dentomaxillofacial radiologists were trained in a single session with the purpose of presenting the image software, explaining the method of evaluation and verifying the assimilation of the training. Then, they were asked to carry out the quantitative assessment of artifact separately in a blinded condition, being unaware of the slicing procedure and the type of restorative material. The images were evaluated on a 22-inch monitor of a desktop computer with resolution of 1366 X 768 pixels and 64 bit color depth. The evaluation was carried out in a windowless room under mild lighting conditions.
Each radiologist documented the slice numbers above and under the restoration in axial scans, mesial and distal to the restoration in coronal scans and buccal and lingual to the restoration in sagittal scans from which the image became diagnostic. Then, on the basis of their documentation, the slice numbers were converted into linear measurements in millimeters away from the restoration. This was done for each type of dental restorative materials and was documented.
From the documentation, the section of CBCT (Axial/Coronal/Sagittal) in which artifact was most prominent and extensive was also identified for each of the dental restorative material.
The patterns of the artifacts induced by the different dental restorative material in axial, coronal and sagittal sections were also observed and documented.
A thorough statistical analysis was carried out using statistical package for social sciences version 16.0. The measurements obtained were subjected to Paired t test, One-way analysis of variance (ANOVA) and post hoc Tukey tests. The level of significance was set at α = 5%.
| Results|| |
The paired t test was applied to rule out inter-observer variation. The result of inter-observer analysis shows no significant differences in the readings between the two observers [Table 1] and [Table 2].
One-way analysis of variance (ANOVA) was applied to grossly evaluate whether there was any significant difference between groups or not. Descriptive statistical analysis was performed for each of the dental restorative materials in each of axial, coronal and sagittal planes of projection. The result presented in [Table 3] shows statistically significant difference between the groups. From the means of extent of artifact in millimeters induced by three dental restorative materials, it is evident that the majority of artifacts produced were as follows: Dental amalgam >Composite resin >Glass ionomer cement, in all the planes of projection. It has been observed that artifact extension is more above the restoration in axial section, distal to the restoration in coronal section and buccal to the restoration in sagittal section for all the three dental restorative materials used in this study. It has also been observed that the artifact is most extensive in coronal section for all the three dental restorative materials and least in axial section for dental amalgam and composite resin but glass ionomer cement has the least artifact in sagittal section.
|Table 3: Descriptive statistics for Dental Amalgam, Composite Resin and Glass Ionomer Cement in Axial, Coronal and Sagittal Sections|
Click here to view
The Post Hoc Tukey test was applied to know which group differs significantly with each which other group. The result presented in [Table 4], [Table 5], [Table 6] reveal that the extent of artifact induced by dental amalgam was significantly higher than that of composite resin (P < 0.05) and glass ionomer cement (P < 0.05), that of composite resin was significantly lower than that of dental amalgam (P < 0.05) and was higher than that of glass ionomer cement but was not statistically significant (P > 0.05) and that of glass ionomer cement was significantly lower than that of dental amalgam (P < 0.05) and was also lower than that of composite resin but was not statistically significant (P > 0.05) above and under the restoration in axial section and lingual to the restoration in sagittal section while the extent of artifact induced by dental amalgam was significantly higher than that of composite resin (P < 0.05) and glass ionomer cement (P < 0.05), that of composite resin was significantly lower than that of dental amalgam (P < 0.05) and was significantly higher than that of glass ionomer cement (P < 0.05) and that of glass ionomer cement was significantly lower than that of dental amalgam (P < 0.05) and composite resin (P < 0.05) mesial and distal to the restoration in coronal section and buccal to the restoration in sagittal section.
| Discussion|| |
The three dimensional visualization of a tooth and oral structures using CBCT imaging represents an impressive advancement in dentistry as the highest-quality images are necessary for proper diagnosis and treatment planning. However, it becomes a more important issue when the patient has extensive prostheses, amalgam restorations or implants in the oral cavity. The artifacts produced by these metallic objects are the result of beam hardening phenomenon which occurs in all the CBCT x-ray machines. With this background, the present study concentrated on the quantitative and qualitative assessment of artifacts induced by commonly used dental restorative materials in different planes of projection of CBCT image.
Schulze et al., Kıvanç Kamburoğlu et al., Esmaeili F et al., Pauwels R et al. and Omar G et al. in their studies evaluated and compared different CBCT machines in relation to the extent of metallic artifacts whereas Draenert et al. and Chindasombatjaroen J et al. have compared image quality of CBCT with MDCT as exposure conditions can have a great role in producing artifacts by influencing the energy of photons. In the current study, CBCT scanner (Gendex DP 700 SC, PaloDEx Group Oy Nahkelantie 160, FI-04300 TUUSULA, Finland) with exposure parameters of 90 kV, 8 mA, 133 μm voxel size and 6 × 4 cm field of view (FOV) was used as aim of the current study was not to compare the accuracy of scan of different CBCT machines and different energy levels but to assess the artifacts produced by different dental restorative materials quantitatively and qualitatively using the same scanning parameters.
The difference in the amount of X-ray absorption in different materials depending on their atomic number and densities led to different amounts of induced artifacts. In the current study, high density material like dental amalgam containing silver, tin, copper and zinc resulted in more artifacts (a: 0.96 ± 0.3978 mm, u: 0.4 ± 0.1633 mm, m: 7.02 ± 1.064 mm, d: 9.9 ± 1.547 mm, b: 1.22 ± 0.3824 mm, l: 0.6 ± 0.1886 mm) than composite resin containing barium, aluminum mainly (a: 0.22 ± 0.1135 mm, u: 0.14 ± 0.0966 mm, m: 3.4 ± 1.054 mm, d: 5.76 ± 0.539 mm, b: 0.64 ± 0.1838 mm, l: 0.14 ± 0.1350 mm) and glass ionomer cement containing chiefly calcium and aluminum (a: 0.12 ± 0.1033 mm, u: 0.04 ± 0.0843 mm, m: 0.6 ± 0.365 mm, d: 1.32 ± 0.559 mm, b: 0.12 ± 0.1398 mm, l: 0.02 ± 0.0632 mm) and showed that the amount of artifacts produced were as follows: Dental amalgam > Composite resin > Glass ionomer cement. This is in agreement with the studies conducted by Sanders MA et al., Zimmermann KP et al. and Zhang et al. where they observed metallic materials produce significantly more artifacts than the non-metallic ones due to higher atomic number. Kuusisto N et al. found that artifacts were clearly present in CBCT images caused by titanium and zirconia and when the composite material consisted at least 20% BaAlSiO2. Study result of Manuel Sancho-Puchades et al. showed that zirconium dioxide implants generate significantly more artifacts as compared to titanium and titanium–zirconium implants. Moshfeghi M et al. evaluated the artifacts produced by different cements using CBCT and showed that the amount of artifacts were produced as follows: TempBond > ZOE > MTA > GI (ChemFil Densply) > GI (GC, Fuji IX). The current study result was in accordance with the above studies.
CBCT measurement tools provide satisfactory information about linear distances within an anatomic volume. However, dental metallic restorative materials may generate artifacts on reconstructed images, which may affect CBCT measurements. In the present study, in comparison to composite resin and glass ionomer cement, dental amalgam restoration showed greater variation in dimension (a: 0.74 mm more than composite resin and 0.84 mm more than glass ionomer cement, u: 0.26 mm more than composite resin and 0.36 mm more than glass ionomer cement, m: 3.62 mm more than composite resin and 6.42 mm more than glass ionomer cement, d: 4.14 mm more than composite resin and 8.58 mm more than glass ionomer cement, b: 0.58 mm more than composite resin and 1.1 mm more than glass ionomer cement, l: 0.46 mm more than composite resin and 0.58 mm more than glass ionomer cement). This result is in accordance with the study conducted by Estrela et al. and Decurcio et al. However, Vazquez L et al. in a study compared the accuracy of implant length measurement on CBCT images and found that actual implant length is not influenced by image viewer or by the presence of implant induced artifact.
Draenert et al. evaluated the amounts of artifacts in three planes of reconstructions. The observations were all done in axial, coronal and three-dimensional reformatted images. The ability to demonstrate the intensity of the artefact was the same. Additionally, they concluded that increasing the distance from the center of the FOV resulted in a decrease in radial-shaped artifact production. Goran I. Benic et al. conducted a study to evaluate the geometric pattern and the intensity of artifacts around titanium implants in CBCT using an in vitro model and found that artifacts reflected by altered grey scale value were located at the buccal and lingual aspects of implant site and along the long axis of mandibular body of the test models. A significant decrease in artifact intensity was found with increasing distance from the buccal implant surface. Nabha W et al. found the artifacts mostly on the buccal and lingual surfaces of their restored tooth models. Kuusisto N et al. found that the intensity of artifact increased when the radio-opacity of the composite materials increased. Manuel Sancho-Puchades et al. in their study observed that intensity around zirconium dioxide implant exhibited in average three-fold in comparison with titanium implants. In the present study, dental amalgam caused the most intense and extensive artifacts compared to that caused by composite resin and glass ionomer cement. It was also noted that the artefact decreased in intensity with increasing distance from the restoration in all the planes of projection. A greater artifact extension was found above the restoration in axial section, distal to the restoration in coronal section and buccal to the restoration in sagittal section for all the three restorative materials.
Regarding the pattern of artifact, Yuan Fu-Song et al. in their study observed strip-like and radial artifacts around the zirconia all-ceramic crown and metal-based PFM crowns, while no artifact was caused around the natural teeth in vitro, glass-ceramic crown and ceramage crown. In another study, Vasconcelos et al. evaluated the characteristic artifact pattern associated with tooth root filled with gutta percha and found that cupping artifact was most prevalent (70%) followed by a hypodense halo (35%) and streak artifacts (16%). In the present study, streak-like fan-shaped artifact was observed occlusally and scatter artifact was predominant apical to the restoration on axial scans while linear artifacts extending outward from tooth surface and a hypodense halo within the tooth were seen in coronal scans and artifact in the form of hypodense halo was predominantly noted on restored and adjacent tooth surfaces in sagittal scans.
Zhang et al. in their study observed that different root canal filling materials like gutta percha and silverpoint produce artifacts as mesio-distal lines axially mimicking vertical root fracture on coronal and sagittal sections. Kulczyk T et al. in a study concluded that amalgam restoration may interfere with the diagnosis of dental caries. So, in those cases CBCT interpretation must be done cautiously. The present study quantitatively defined the distance from the restoration in axial, coronal and sagittal planes, within which artifact would interfere in diagnosis.
Limitations and Future Prospects
However, pitfalls in this study are as follows:
- The study was limited to the assessment in vitro
- It is a static model used in the measurement instead of a patient
- A wide range of dental restorative materials have not been used for comparison
- Increasing sizes of the restorations have not been taken into consideration.
It is suggested that further study is needed using patients and more improved software. Here, the small number of sample acts as the basic data for further investigation using other dental restorative materials and with varying sizes of the restoration, implant and various prosthetic materials. Also further investigation is needed on accuracy among different CBCT machines using different exposure parameters and slice spacing.
As a future prospective, attempts should be encouraged not only to produce improved dental restorative material which will produce least artifact but also to develop improved software for the correction of artifacts induced by commonly used dental restorative materials for proper diagnosis and better treatment planning.
However, the present study is unique as the methodology employed here has not been tried before and has a great clinical implication that may open up a new horizon in dentistry.
| Conclusion|| |
Cone-Beam Computed Tomography is a valuable tool in dento-maxillofacial imaging. However, metallic restorations can induce considerable artifacts in CBCT scans. Therefore, artifact assessment and artifact reduction should be taken into consideration to avoid clinical misdiagnosis when using CBCT scan for dental patients.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]