CBCT Unit Research Articles

A 3D-CBCT Volumetric Analysis of Cervical Vertebrae Angulation and Airway Dimensions

Aim: To evaluate the relationship between airway dimensions and cervical vertebrae angulations in dental patients using three-dimensional cone beam computed tomography (3D-CBCT) technology. Materials and Methods: Pre-treatment CBCT scans and cephalometric radiographs were measured for 59 patients (mean age 22±2.3yrs.) using the Dolphin3D software system (version 11.7; Dolphin Imaging & Management Solutions, Chatworth, CA) to record airway dimensions and cervical vertebral angulations. All CBCT images were acquired using the same standard protocol for collection using the iCAT CBCT Unit (Imaging Sciences International, Hatfield, PA): 13cm field of view, 0.4mm voxel size, 8.9sec scan time. Intraclass Correlations (ICC) were performed on duplicate measurements of 10 CBCT scans after a two-week interval to assess reliability. P-value and Pearson correlation coefficients were used to statistically assess the relationship between vertebral angulations and airway dimensions. Results: ICC values from the reliability assessment were >0.90. Pearson correlation coefficients were categorized based on confidence level as follows: high (>0.75 or <-0.75), moderate (0.5 to 0.74 or -0.5 to -0.74), or weak (0.3 to 0.49 or -0.3 to -0.49). No high/moderate correlations were observed. Weak correlations (p<0.05) were observed between the nasopharyngeal volume and the soft tissue thickness at CV1(-0.47) and CV2(-0.34). A weak correlation was observed between the nasal cavity volume and S-N (+0.41) as well as ANS-PNS(+0.38). A weak correlation was observed between the total airway volume and the soft tissue thickness at CV2(-0.34). Conclusion: The soft tissue thickness of the posterior wall of the airway at the level of cervical vertebrae-2 appears to have a weak, negative correlation with several upper airway parameters and total airway volume. Soft tissue thickness of the posterior pharyngeal wall is crucial for dental clinicians to analyze prior to some procedures such as orthognathic surgery and orthodontic treatment that involve growth modification and jaw positioning, as it may have an association with decreased airway volume. Clinical Significance: The relationship between cervical vertebrae angulation, airway, and craniofacial morphology is a complex aspect of human anatomy. In dentistry, it is crucial that clinicians recognize the vital role cervical vertebrae angulation and airway interact in relation to craniofacial morphology. Knowledge of these interconnections will significantly inform treatment planning for multiple oral health conditions such as malocclusions, jaw discrepancies, and temporomandibular joint disorders.

CBCT unit for perfect clarity

CBCT unit for perfect clarity

Clinical Assessment of Bone Quality at Implant Site using CBCT and Hounsfield Unit.

The current research was done to assess the bone quality at implant site using CBCT. The present study was conducted on 50 partially edentulous patients of both genders. All subjects had their chests scanned using a Kodac machine set to 120 kVp, 12 mA, and a 17-second exposure time. Using Hounsfield units, bone quality was classified as D1, D2, D3, D4, and D5 (HU). Out of 50 patients, 27 were males and 23 were females. The average HU was 786.1 at the anterior maxilla, 1174.3 at the anterior mandible, 332.1 at the posterior maxilla, and 742.4 at the posterior mandible. The variation was considerable (P-0.01). The anterior mandible, anterior maxilla, posterior mandible, and posterior maxilla were found to have the highest densities. Based on Hounsfield units, CBCT is helpful in determining the bone density at the implant site.

Monitoring cone-beam CT radiation dose levels in a University Hospital.

To present patient dose levels for different CBCT scanners, acquired by a dose monitoring tool in a University Hospital, as a function of field of view (FOV), operation mode, and patient age. An integrated dose monitoring tool was used to collect radiation exposure data [type of CBCT unit, dose-area product (DAP), FOV size, and operation mode] and patient demographic information (age, referral department) performed on a 3D Accuitomo 170 and a Newtom VGI EVO unit. Effective dose conversion factors were calculated and implemented into the dose monitoring system. For each CBCT unit, the frequency of examinations, clinical indications, and effective dose levels were obtained for different age and FOV groups, and operation modes. A total of 5163 CBCT examinations were analyzed. Surgical planning and follow-up were the most frequent clinical indications. For the standard operation mode, effective doses ranged from 35.1 to 300 µSv and 9.26-117 µSv using 3D Accuitomo 170 and Newtom VGI EVO, respectively. In general, effective doses decreased with increasing age and FOV size reduction. Effective dose levels varied notably between systems and operation modes.Operation mode selection and FOV size were indication-oriented, with larger FOV sizes election serving surgical planning and follow-up. Seeing the influence of FOV size on effective dose levels, manufacturers could be advised to move toward patient-specific collimation and dynamic FOV selection. Systematically monitoring patient doses could be recommended for steering future CBCT optimization.

The metal post material influences the performance of artefact reduction algorithms in CBCT images.

This study aimed to assess the effect of the MAR tool on the expression of artefacts in different regions of a tooth restored with different types of metal posts. Alveolar sockets (anterior, and posterior region) of a mandible and an unirradicular tooth were used. Cone beam computed tomography scans of the tooth without a metal post, and with cobalt-chromium (Co-Cr), nickel-chromium (Ni-Cr), or silver-palladium (Ag-Pd) were individually obtained, with 2 MAR conditions: disabled, and enabled. In an axial reconstruction, lines of interest (LOIs) were set around the canal: 4 in oblique (mesiobuccal, distobuccal, mesiolingual, distolingual) directions, and 4 in orthogonal (mesial, distal, buccal, lingual) directions. Beam-hardening artefacts expression was determined by calculating the difference in the mean of gray values (DMGV) between the experimental and control groups for each LOI. There was no significant difference in the DMGV values between "without MAR" and "with MAR" for any LOI, in neither anterior nor posterior mandible (p>0.05), for the Ni-Cr and Co-Cr groups. For the Ag-Pd, significant differences in the DMGV values were observed between "without MAR" and "with MAR" for most LOIs (p<0.05), mainly in oblique directions in the anterior region, and mesio-distal direction in the posterior region. MAR acted mostly in hypodense artefacts (negative DMGV). The effectiveness of the MAR tool of the OP300 CBCT unit varied according to the post material tested. It was effective in reducing the expression of artefacts raised by the Ag-Pd post, mainly in the tooth regions affected by hypodense artefacts, regardless of the mandibular region.

Optimization of cone beam computed tomography for the assessment of alterations of the maxillary sinuses

Objective: To test the standard protocols of a CBCT unit in order to find lower-dose alternatives with diagnostically acceptable image quality for the maxillary sinuses visualization. Study design: An observational study was performed. Two dry skulls were used to simulate four conditions of the maxillary sinuses: normality, mucous retention pseudocyst, membrane thickening and bone graft. Cone beam computed tomography scans were obtained with an i-CAT classic unit using different acquisition protocols and a box of polystyrene to simulate soft tissue attenuation. All the protocols were established by the manufacturer, combining different energy parameters, fields of view and voxel sizes. Multiplanar reconstructions were presented to three Oral Radiologists through blind and randomized distribution. The specialists judged general image quality, sharpness, contrast, and the presence of noise and artifacts based on a 4-points scale. Results: Protocols with higher energy parameters had significant association with higher scores for general quality, sharpness and contrast (p&lt;0.05). Protocols with intermediate level of radiation dose had also significant association with good and excellent image quality; for the presence of noise and artifacts the images were rated acceptable. Conclusion: i-CAT default protocols with lower dose of radiation were able to deliver acceptable image quality for the visualization of the maxillary sinuses.

Assessment of interobserver reliability in localization of hard and soft tissue landmarks and three-dimensional measurements of the upper airway based on these landmarks using CBCT images

: To assess reliability in localization of hard and soft tissue landmarks of the upper airway and three-dimensional measurements of the upper airway based on these landmarks using CBCT images. : 22 full field of view (FOV) CBCT scan volumes were selected randomly and retrospectively made at the CBCT unit of Department of Oral Medicine and Radiology. Six anatomic landmarks that are relevant for upper airway analysiswere located and subsequently three-dimensional measurements (volume, minimum cross-sectional area (CSA), location of the CSA, anteroposterior and lateral dimensions of the CSA) in all planes (coronal, sagittal, axial) were performed based on these land marks by two observers, using Romexis software (4.2.0 R 10/13/15). : Correlation analysis by Cronbach’s Alpha.: Interobserver reliability of the landmark localization was excellent (Internal consistency 0.97-0.99) and for the three-dimensional upper airway measurements were good (Internal consistency 0.62-0.99).: The interobserver reliability of anatomical landmarks localization and three-dimensional measurements of the upper airway are good to excellent using Romexis software. Therefore, this methodology can be recommended for the upper airway analysis using CBCT images.

Mapping the expression of beam hardening artefacts produced by metal posts positioned in different regions of the dental arch.

To objectively assess the expression and direction of artefacts in the vicinity of metal posts positioned in different mandibular regions. A human mandible had two sockets prepared-anterior and posterior regions-to accommodate a single-rooted tooth. Two CBCT units, Picasso Trio and OP300, were used. CBCT images of the tooth without metal post, and with silver-palladium, nickel-chromium, or cobalt-chromium posts (experimental groups) were individually acquired. Then, 8 lines of interest (LOIs) were determined around the root canal, in an axial reconstruction: 4 in orthogonal (buccal, lingual, mesial, and distal) directions, and 4 in oblique (mesiobuccal, distobuccal, mesiolingual, and distolingual) directions. The mean of gray values was measured for each LOI. For the OP300, in general, all experimental groups showed greater expression of hyperdense streaks in orthogonal LOIs and greater expression of hypodense streaks in oblique LOIs. For the Picasso Trio, for both mandibular regions, the buccal LOI showed greater expression of hypodense streaks; conversely, greater expression of hyperdense streaks was observed in the distal and distobuccal LOIs in the anterior region and in the mesiolingual LOI in the posterior region. The silver-palladium group showed significantly greater expression of beam hardening artefacts in the posterior region of the mandible, regardless of the CBCT unit (p < 0.05). The mandibular posterior region showed significantly lower gray values than the anterior region (p < 0.05). The expression and direction of artefacts produced in the vicinity of metal posts vary according to the mandibular region, composition of the post, and CBCT unit. The mapping of artefacts produced by metal posts reveals the root regions with greater expression of hypodense and hyperdense artefacts, which may contribute to recognizing regions more likely to mimic or hide root fracture lines.

Quantitative analysis of metal artifact reduction using the auto-edge counting method in cone-beam computed tomography

The metal artifact reduction (MAR) algorithm is used in most CBCT unit to reduce artifact from various dental materials. The performance of MAR program of a CBCT unit according to the dental material type under different imaging mode was evaluated as introducing automatic quantification of the amount of artifact reduced. Four customized phantoms with different dental prostheses (amalgam, gold, porcelain-fused-metal, zirconia) underwent CBCT scanning with and without the MAR option. The imaging was performed under varied scanning conditions; 0.2 and 0.3 mm3 voxel sizes; 70 and 100 kVp. The amount of artifacts reduced by each prosthesis and scanning mode automatically counted using canny edge detection in MATLAB, and statistical analysis was performed. The overall artifact reduction ratio was ranged from 17.3% to 55.4%. The artifact caused by the gold crown was most effectively reduced compared to the other prostheses (p < 0.05, Welch’s ANOVA analysis). MAR showed higher performance in smaller voxel size mode for all prostheses (p < 0.05, independent t-test). Automatic quantification efficiently evaluated MAR performance in CBCT image. The impact of MAR was different according to the prostheses type and imaging mode, suggesting that thoughtful consideration is required when selecting the imaging mode of CBCT.

Accuracy of Linear Measurements Made on Cone Beam Computed Tomography Scans at Different Magnifications

Objective: This study aimed to evaluate the accuracy of linear measurements made on CBCT (New Tom VGi) scans with different image magnifications.&#x0D; Methods: Forty-two titanium pins were inserted into seven dry sheep mandibles. Lengths of the pins were measured using a digital caliper with 0.01 mm readability, and the mandibles were radiographed using a CBCT unit. After reconstruction of CBCT images, three experienced radiologists measured the length and diameter of titanium pins at100%, 200% and 400% magnifications. Accuracy of measurements was analyzed using descriptive statistics and one-way analysis of variance (ANOVA) P&lt;0.05 was considered statistically significant. Inter observer reliability was calculated using the intra class correlation coefficient (ICC) test.&#x0D; Results: The mean differences of linear measurements from the actual lengths of pins were 0.1960 mm, 0.2143 mm and 0.2047 mm at 100%, 200% and 400% magnifications, respectively (P&gt;0.05). The mean differences of linear measurements from the actual diameters of pins were 0.2206 mm, 0.2063 mm and 0.1984 mm at 100%, 200% and 400% magnifications, respectively (P&gt;0.05). Inter observer reliability of pin length measurements was estimated to be0.285, 0.707 and 0.479 at 100%, 200% and 400%magnifications, respectively. Inter observer reliability of pin diameter measurements was 0 .078, 0.469 and 0.587 at 100%, 200% and 400%magnifications, respectively.&#x0D; Conclusion: Based on the results, image magnification does not affect the accuracy of linear measurements made on CBCT scans. Inter observer reliability of pin length measurements was good at 200% magnification, while it was below the acceptable range at other magnifications. For measurement of pin diameters, this index was below the acceptable range at all magnifications.

Accuracy of Linear Measurements Made on Cone Beam Computed Tomography Scans at Different Magnifications

Objective: This study aimed to evaluate the accuracy of linear measurements made on CBCT (New Tom VGi) scans with different image magnifications.&#x0D; Methods: Forty-two titanium pins were inserted into seven dry sheep mandibles. Lengths of the pins were measured using a digital caliper with 0.01 mm readability, and the mandibles were radiographed using a CBCT unit. After reconstruction of CBCT images, three experienced radiologists measured the length and diameter of titanium pins at100%, 200% and 400% magnifications. Accuracy of measurements was analyzed using descriptive statistics and one-way analysis of variance (ANOVA) P&lt;0.05 was considered statistically significant. Inter observer reliability was calculated using the intra class correlation coefficient (ICC) test.&#x0D; Results: The mean differences of linear measurements from the actual lengths of pins were 0.1960 mm, 0.2143 mm and 0.2047 mm at 100%, 200% and 400% magnifications, respectively (P&gt;0.05). The mean differences of linear measurements from the actual diameters of pins were 0.2206 mm, 0.2063 mm and 0.1984 mm at 100%, 200% and 400% magnifications, respectively (P&gt;0.05). Inter observer reliability of pin length measurements was estimated to be0.285, 0.707 and 0.479 at 100%, 200% and 400%magnifications, respectively. Inter observer reliability of pin diameter measurements was 0 .078, 0.469 and 0.587 at 100%, 200% and 400%magnifications, respectively.&#x0D; Conclusion: Based on the results, image magnification does not affect the accuracy of linear measurements made on CBCT scans. Inter observer reliability of pin length measurements was good at 200% magnification, while it was below the acceptable range at other magnifications. For measurement of pin diameters, this index was below the acceptable range at all magnifications.

Evaluation of nasopalatine canal using cone beam computed tomography - A retrospective study

Background: Implantology is a very significant branch of dentistry that deals with the rehabilitation of edentulous patients. Thus, knowledge of anatomical variations of related neurovascular structures such as the nasopalatine canal is essential. Aim:The aim of study was to determine the form, length, and diameter of the nasopalatine canal using CBCT. Materials and Methods: In this retrospective study, images were archived from CBCT unit and visualized using Romexis software. The nasopalatine canals of 50 patients between the age range of 18-59years were analyzed. The shape of the nasopalatine canal, length of the nasopalatine canal and the diameter of incisive foramen were assessed in sagittal and coronal section. The width of labial and palatal alveolar bone around the canal and inclination of the nasopalatine canal to hard palate were evaluated. Statistics: (1) if there is any relation between the gender and the assessed parameters (2) if there is any relation between edentulous and partially edentulous patients with the assessed parameters. Results: The most common shape of the nasopalatine canal was cylindrical. The average length of the nasopalatine canal was 12.14±2.41 mm and the average diameter of incisive foramen 3.45±0.84 mm anteroposteriorly and 3.77±0.94mm mediolaterally. The average inclination of the nasopalatine canal to hard palate was 119.93±9.73° Conclusion: This study highlights the variations seen in the nasopalatine canal. The close vicinity of nasopalatine canal and implant can lead to sensory disturbances and damage of the tissues. Thus, a thorough knowledge before the surgical - implant procedure using cone beam computed tomography seems beneficial.

Accuracy of detecting vertical root fractures in non‐root filled teeth using cone beam computed tomography: effect of voxel size and fracture width

To investigate simultaneously the effect of voxel size and fracture width on the accuracy of detecting vertical root fractures (VRFs) in non-root filled teeth when using cone beam computed tomography. Fifty-one of 161 extracted human permanent teeth (16 anterior teeth, 132 premolars and 13 mandibular molars) were selected randomly for VRF induction with two fracture widths. All teeth were scanned with four CBCT units at different voxel sizes provided by the units. Three observers classified the presence or absence of VRF using a 5-point scale. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and area under the ROC curve (AUC) were calculated. AUCs amongst voxel sizes and between the fracture widths were compared using the Z test. Intra- and inter-observer agreement was assessed using weighted Cohen kappa. For the NewTom VGi and ProMax 3D Mid CBCT unit, no significant differences were found amongst voxel sizes for the AUCs, irrespective of the fracture width (P>0.05). There were significant differences between images scanned with voxel size 250 and 160μm (P=0.02), and images scanned with voxel size 250 and 80μm for AUCs in the narrow VRF group for the 3D Accuitomo 170 unit (P=0.03). For i-CAT FLX, significant differences were found between the voxel protocols of 300μm and of the other three voxel sizes for AUC, sensitivity and NPV (P<0.05). Significant differences between the wide and the narrow VRF groups for AUCs were found for 3D Accuitomo 170 (P=0.01) and ProMax 3D Mid (P<0.01). Cone beam computed tomography was accurate for detecting VRF in non-root filled teeth. Fracture width had an effect on the detection of VRF. The effect of the voxel size on the detection of VRF depended on the CBCT unit used.

Ultra-Low-Dose versus Normal-Dose Scan Protocol of Planmeca ProMax 3 D Mid CBCT machine in Detection of Second Mesi buccal Root Canal in Maxillary Molars: An ex vivo study

Objective: The aim of this study was to compare the ability of Normal and Ultra-Low-Dose protocols of Planmeca Promax 3 D Mid CBCT unit with different voxel sizes in detection of MB2 canal.Materials and Methods: This study was conducted on 36 extracted human maxillary first and second molars. Six acrylic models were prepared and six molars were embedded in each model using Inlay wax. Each acrylic model was then placed in a plastic container filled with water. CBCT imaging of the acrylic models containing the extracted molars was taken by Planmeca ProMax 3D Mid machine (Helsinky, Finland). Each model was scanned with three different voxel sizes (0.075, 0.1, 0.2 mm) and two different exposure protocols, namely the Normal-Dose (ND) and the Ultra-Low-Dose (ULD) protocol. Assessment of the number of MB canals was carried out by two Oral and Maxillofacial Radiologists. To verify the number of root canals of the mesiobuccal root, these roots were sectioned and visually inspected. The data obtained were tabulated and subjected to statistical analysis.Results: Transverse sections showed that 22 molars had two mesiobuccal root canals and 14 molars had only one mesiobuccal root canal. The results showed that the sensitivity and accuracy of CBCT images increase as the voxel size decrease. However, the results revealed no significant difference (p>0.05) between the (ND) and (ULD) protocol of the same voxel size used. Both intra and inter-observer reliability showed very good agreement (0.81–1).Conclusions: ULD CBCT protocol can be applied for the detection of MB2 of maxillary molars. The smaller the voxel size, the higher the image resolution and image quality. The 0.075 mm voxel size of both protocols is accurate enough to be used as a gold standard in laboratory studies instead of the standard root sectioning technique.

Stress Distribution on Root Dentin Analogous to Natural Teeth with Various Retentive Channels Design on the Face of the Root with Minimal or No Coronal Tooth Structure: A Finite Element Analysis

Aim:The aim of this study was to evaluate post-core design on Stress distribution in maxillary central incisor with various designs retentive channels placed on the face of the root with no remaining coronal tooth structure.Materials and Methods:3 dimensional finite element model of a maxillary central incisor was developed and seven other study modes were developed. Tooth was scanned using CBCT unit, with reverse engineering software. 3D wire mesh, with ten node tetrahedral element, developed was transferred to ANASYS software. Composite was used for post-core-crown as post endodontic restoration. Mechanical properties were assigned to each component for FEA. All the materials were assumed to be isotropic, linearly elastic, homogenous and tightly bonded. A load of 100N were applied from vertical, horizontal and lateral oblique from incisal and palatal surface respectively.Results:Analysis revealed that stresses were concentrated at the point of load application on crown(vertical(V) 14.35MPa, horizontal(H) 27.04 MPa and lateral oblique(L)13.75MPa) and depending on the post core design the stresses were homogenous evenly distributed over the root dentin, core and least over the post. There was variation in stress distribution under vertical horizontal and lateral oblique load.Conclusion:Teeth with no remaining coronal structure and by placing retentive channels on the face of the root will enable homogenous stress distribution, promote mechanical retention and stability to the post core crown post endodontic restoration.

The correlation between direction and amount of retrusive movement and condyle position and joint space

Objective: The direction and amount of retrusive movement may be correlated with the amount of joint space and the maximum intercuspal position of the condyle. The aim of this study was to identify any such correlation using an ultrasonic jaw motion analyzer and digital volumetric tomographic (DVT) scans.Methods: Thirty-five dental students were selected as subjects. DVT scans were obtained using a next-generation i-CAT CBCT unit, and the direction and amount of retrusive movement were measured with a 3-D analyzer.Results: Spearman Rho correlation tests showed no correlation between the amount of retrusive movement and the condyle position and joint space on either the right or left side.Discussion: There is sufficient reason to suggest that retrusive movement of the condyle does not occur in isolation but is influenced by glenoid fossa bone morphology.

Accuracy of linear measurements around dental implants by means of cone beam computed tomography with different exposure parameters.

The aim of this study was to determine the accuracy of linear measurements around dental implants when using CBCT unit devices presenting different exposure parameters. Dental implants (n = 18) were installed in the maxilla of human dry skulls, and images were obtained using two CBCT devices: G1-Care Stream 9300 (70 kVp, 6.3 mA, voxel size 0.18 mm, field of view 8 × 8 cm; Carestream Health, Rochester, NY) and G2-R100 Veraview® (75 kVp, 7.0 mA, voxel size 0.125 mm, field of view 8 × 8 cm; J Morita, Irvine, CA). Measurements of bone thickness were performed at three points located (A) in the most apical portion of the implant, (B) 5 mm above the apical point and (C) in the implant platform. Afterwards, values were compared with real measurements obtained by an optical microscopy [control group (CG)]. Data were statistically analyzed with the significance level of p ≤ 0.05. There was no statistical difference for the mean values of bone thickness on Point A (CG: 4.85 ± 2.25 mm, G1: 4.19 ± 1.68 mm, G2: 4.15 ± 1.75 mm), Point B (CG: 1.50 ± 0.84 mm, G1: 1.61 ± 1.27 mm; G2: 1.68 ± 0.82 mm) and Point C (CG: 1.78 ± 1.33 mm, G1: 1.80 ± 1.09 mm; G2: 1.64 ± 1.11 mm). G1 and G2 differed in bone thickness by approximately 0.76 mm for Point A, 0.36 mm for Point B and 0.08 mm for Point C. A lower intraclass variability was identified for CG (Point A = 0.20 ± 0.25; Point B = 0.15 ± 0.20; Point C = 0.06 ± 0.05 mm) in comparison with G1 (Point A = 0.56 ± 0.52; Point B = 0.48 ± 0.50; Point C = 0.47 ± 0.56 mm) and G2 (Point A = 0.57 ± 0.51; Point B = 0.46 ± 0.46; Point C = 0.36 ± 0.31 mm). CBCT devices showed acceptable accuracy for linear measurements around dental implants, despite the exposure parameters used.

Dose optimization for assessment of periodontal structures in cone beam CT examinations.

To investigate the relationship between dose and image quality for a dedicated dental CBCT scanner using different scanning protocols and to set up an optimal imaging protocol for assessment of periodontal structures. Radiation dose and image quality measurements were made using 3D Accuitomo 170 (J. Morita, Kyoto, Japan) dental CBCT scanner. The SedentexCT IQ phantom was used to investigate the relationship between contrast-to-noise ratio (CNR) and dose-area product. Subjective image quality assessment was achieved using a small adult skull phantom for the same range of exposure settings. Five independent observers assessed the images for three anatomical landmarks using a three-point visual grade analysis. When correlating the CNR of each scanning protocol to the exposure parameters used to obtain it, CNR decreased as these parameters decreased, especially current-exposure time product. When correlating to subjective image quality, the CNR level remained acceptable when 5 mA and 17.5 s or greater was selected and 80 kV could be used without compromising the CNR. For a dedicated CBCT unit, changing the rotation angle from 360° to 180° degrades image quality. By altering tube potential and current for the 360° rotation protocol, assessment of periodontal structures can be performed with a smaller dose without substantially affecting visualization.

Technical Note: Procedure for the calibration and validation of kilo-voltage cone-beam CT models.

The aim of this work is to propose a general and simple procedure for the calibration and validation of kilo-voltage cone-beam CT (kV CBCT) models against experimental data. The calibration and validation of the CT model is a two-step procedure: the source model then the detector model. The source is described by the direction dependent photon energy spectrum at each voltage while the detector is described by the pixel intensity value as a function of the direction and the energy of incident photons. The measurements for the source consist of a series of dose measurements in air performed at each voltage with varying filter thicknesses and materials in front of the x-ray tube. The measurements for the detector are acquisitions of projection images using the same filters and several tube voltages. The proposed procedure has been applied to calibrate and assess the accuracy of simple models of the source and the detector of three commercial kV CBCT units. If the CBCT system models had been calibrated differently, the current procedure would have been exclusively used to validate the models. Several high-purity attenuation filters of aluminum, copper, and silver combined with a dosimeter which is sensitive to the range of voltages of interest were used. A sensitivity analysis of the model has also been conducted for each parameter of the source and the detector models. Average deviations between experimental and theoretical dose values are below 1.5% after calibration for the three x-ray sources. The predicted energy deposited in the detector agrees with experimental data within 4% for all imaging systems. The authors developed and applied an experimental procedure to calibrate and validate any model of the source and the detector of a CBCT unit. The present protocol has been successfully applied to three x-ray imaging systems. The minimum requirements in terms of material and equipment would make its implementation suitable in most clinical environments.

Influence of exposure parameters on the detection of simulated root fractures in the presence of various intracanal materials.

To investigate how the exposure parameters used when producing CBCT scans affect diagnostic accuracy when detecting simulated vertical root fractures and how various filling materials affect image quality. A total of 160 extracted single-rooted human teeth were divided into four groups based on the materials within the root canals: unrestored, gutta-percha, metallic post and fibreglass post. Half of the sample of each group was selected for the induction of vertical root fractures. Each tooth was placed in an empty socket of a dry skull which was scanned on a CBCT unit (9000 3D scanner; Kodak Dental Systems, Carestream Health, Rochester, NY, USA) using the following exposure parameters: 74kV/12mA; 74kV/10mA; 74kV/8mA; 74kV/6.3mA; 70kV/12mA; 70kV/10mA; 70kV/8mA; 70kV/6.3mA. Two observers assessed all images using a 5-point confidence scale for fracture detection and a 4-point score for the presence of artefacts. Sensitivity, specificity, accuracy and area under ROC curve were compared by two-way anova and Tukey's test. Artefact formation was evaluated by descriptive statistics. There were no significant differences in the sensitivity (P=0.370), specificity (P=0.660), accuracy (P=0.084) and area under the ROC curve (P=0.674) values amongst the various exposure parameters within the same group. There were some significant differences when the groups were compared for each intracanal material. The sensitivity and accuracy of the group containing metallic posts were significantly lower than the unrestored and fibreglass post groups (P≤0.017). The variations in exposure parameters did not interfere with the diagnosis of vertical root fractures, independent of the root canal restorative status. Metallic posts were associated with greater artefact formation and compromised the diagnostic performance. It is possible to decrease the kVp/mA settings to reduce the probability of biological effects due to radiation, without losing diagnostic accuracy.