Soontra Panmekiate

A pragmatic approach to determine the optimal kVp in cone beam CT: balancing contrast-to-noise ratio and radiation dose

OBJECTIVES To determine the optimal kVp setting for a particular cone beam CT (CBCT) device by maximizing technical image quality at a fixed radiation dose. METHODS The 3D Accuitomo 170 (J. Morita Mfg. Corp., Kyoto, Japan) CBCT was used. The radiation dose as a function of kVp was measured in a cylindrical polymethyl methacrylate (PMMA) phantom using a small-volume ion chamber. Contrast-to-noise ratio (CNR) was measured using a PMMA phantom containing four materials (air, aluminium, polytetrafluoroethylene and low-density polyethylene), which was scanned using 180 combinations of kVp/mA, ranging from 60/1 to 90/8. The CNR was measured for each material using PMMA as background material. The pure effect of kVp and mAs on the CNR values was analysed. Using a polynomial fit for CNR as a function of mA for each kVp value, the optimal kVp was determined at five dose levels. RESULTS Absorbed doses ranged between 0.034 mGy mAs(-1) (14 × 10 cm, 60 kVp) and 0.108 mGy mAs(-1) (14 × 10 cm, 90 kVp). The relation between kVp and dose was quasilinear (R(2) > 0.99). The effect of mA and kVp on CNR could be modelled using a second-degree polynomial. At a fixed dose, there was a tendency for higher CNR values at increasing kVp values, especially at low dose levels. A dose reduction through mA was more efficient than an equivalent reduction through kVp in terms of image quality deterioration. CONCLUSIONS For the investigated CBCT model, the most optimal contrast at a fixed dose was found at the highest available kVp setting. There is great potential for dose reduction through mA with a minimal loss in image quality.

Effect of electric potential and current on mandibular linear measurements in cone beam CT.

OBJECTIVES The purpose of this study was to compare mandibular linear distances measured from cone beam CT (CBCT) images produced by different radiographic parameter settings (peak kilovoltage and milliampere value). METHODS 20 cadaver hemimandibles with edentulous ridges posterior to the mental foramen were embedded in clear resin blocks and scanned by a CBCT machine (CB MercuRay(TM); Hitachi Medico Technology Corp., Chiba-ken, Japan). The radiographic parameters comprised four peak kilovoltage settings (60 kVp, 80 kVp, 100 kVp and 120 kVp) and two milliampere settings (10 mA and 15 mA). A 102.4 mm field of view was chosen. Each hemimandible was scanned 8 times with 8 different parameter combinations resulting in 160 CBCT data sets. On the cross-sectional images, six linear distances were measured. To assess the intraobserver variation, the 160 data sets were remeasured after 2 weeks. The measurement precision was calculated using Dahlbergs formula. With the same peak kilovoltage, the measurements yielded by different milliampere values were compared using the paired t-test. With the same milliampere value, the measurements yielded by different peak kilovoltage were compared using analysis of variance. A significant difference was considered when p < 0.05. RESULTS Measurement precision varied from 0.03 mm to 0.28 mm. No significant differences in the distances were found among the different radiographic parameter combinations. CONCLUSIONS Based upon the specific machine in the present study, low peak kilovoltage and milliampere value might be used for linear measurements in the posterior mandible.

Comparison of mandibular bone microarchitecture between micro-CT and CBCT images.

OBJECTIVES To compare microarchitecture parameters of bone samples scanned using micro-CT (µCT) to those obtained by using CBCT. METHODS A bone biopsy trephine bur (3 × 10 mm) was used to remove 20 cylindrical bone samples from 20 dry hemimandibles. Samples were scanned using µCT (µCT 35; SCANCO Medical, Brüttisellen, Switzerland) with a voxel size of 20 µm and CBCT (3D Accuitomo 170; J. Morita, Kyoto, Japan) with a voxel size of 80 µm. All corresponding sample scans were aligned and cropped. Image analysis was carried out using BoneJ, including the following parameters: skeleton analysis, bone surface per total volume (BS/TV), bone volume per total volume (BV/TV), connectivity density, anisotropy, trabecular thickness and spacing, structure model index, plateness and fractal dimension. Pearson and Spearman correlation coefficients (R) were calculated. CBCT values were then calibrated using the slope of the linear fit with the µCT values. The mean error after calibration was calculated and normalized to the standard deviation of the µCT values. RESULTS R-values ranged between 0.05 (plateness) and 0.83 (BS/TV). Correlation was significant for both Spearman and Pearsons R for 8 out of 16 parameters. After calibration, the smallest normalized error was found for BV/TV (0.48). For other parameters, the error range was 0.58-2.10. CONCLUSIONS Despite the overall correlation, this study demonstrates the uncertainty associated with using bone microarchitecture parameters on CBCT images. Although clinically relevant parameter ranges are not available, the errors found in this study may be too high for some parameters to be considered for clinical application.

Reduction of scatter-induced image noise in cone beam computed tomography: effect of field of view size and position

OBJECTIVE To measure the effect of field of view (FOV) size and position on scatter-induced image noise in cone beam computed tomography (CBCT). STUDY DESIGN A polymethyl methacrylate (PMMA) phantom containing air and aluminum underwent CBCT scanning, using seven FOVs ranging between 4 × 4 cm and 14 × 10 cm, positioned both centrally and according to a dental scan. Signal difference to noise ratio (SDNR) was measured on two-dimensional (2-D) projection images. RESULTS At a central position, SDNR decreased with increasing FOV size, ranging between 9.8 (14 × 10 cm) and 10.9 (4 × 4 cm). For dental FOV positions, SDNR values were between 6.3 (14 × 10 cm) and 9.5 (4 × 4 cm). To reach a constant SDNR, a dose reduction up to 76% was possible for small FOVs compared with the 14 × 10 cm FOV. CONCLUSIONS The use of small FOVs and peripheral FOV positioning decreases scatter at the detector, resulting in a considerable potential for reduction of radiation dose to the patient.

A Cone-beam Computed Tomographic Study of Root and Canal Morphology of Maxillary First and Second Permanent Molars in a Thai Population

Introduction: Understanding tooth anatomy is crucial for effective endodontic treatment. This study investigated the roots and root canal morphology of maxillary first and second permanent molars in a Thai population using cone‐beam computed tomographic (CBCT) imaging. Methods: This study evaluated 476 maxillary first molars and 457 maxillary second molars receiving CBCT examination and determined the number of roots and canal morphology according to Vertuccis classification, and the prevalence of a second mesiobuccal (MB2) canal in the mesiobuccal (MB) root was correlated with sex, age, and tooth side. Results: Three roots were most commonly found in maxillary first and second molars. MB2 canals in the MB root were found in 63.6% and 29.4% of first and second molars, respectively. The most common canal morphology in the first molar MB roots was type I (36.4%) followed by type II (28.8%), and type IV (25.3%). The most common canal morphology in the second molar MB roots was type I (70.6%) followed by type II (14.6%) and type IV (7.5%). Bilateral MB2 canals in the MB roots were present in 80.93% and 82.59% of the first and second molars, respectively. There was a significant correlation between males and the prevalence of MB2 canals in first molars (P < .05). Conclusions: CBCT imaging is useful to determine root canal morphology. The prevalence of MB2 canals is approximately 60% and 30% in first and second molars, respectively. Furthermore, bilateral MB2 canals were commonly found. Our results can help endodontists to improve endodontic treatment outcomes.

Corrected sagittal tomography of the temporomandibular joint. Influence of errors in film and patient positioning on linear and angular measurements.

The aim of this study was to assess the variation in film and patient positioning in horizontally corrected sagittal tomography of the temporomandibular joint (TMJ). The influence of this variation on linear and angular measurements of some anatomic structures of the TMJ was also studied. There was no significant variation in film positioning in the tomograph, using a multi-film cassette. The variation in positioning the patient in the tomograph was significant when four dental assistants were asked to place the Frankfort plane parallel to the horizontal plane. The measurements with the film in a straight position were compared with the measurements with the film angulated, to simulate the mean variation in film and patient positioning. Linear and angular measurements of anatomic structures were performed in arthrotomograms of 58 joints, representing joints with superior disk position and joints with anterior disk position with and without reduction. There was a difference between the two measurements for four different distances and one angle independent of diagnosis. No differences could be found between patients belonging to the different diagnostic groups. The results indicate that variation in patient positioning influences linear and angular measurements of anatomic structures in TMJ arthrotomograms.

The Stability of Augmented Bone Between Two Different Membranes Used for Guided Bone Regeneration Simultaneous with Dental Implant Placement in the Esthetic Zone

PURPOSE This randomized controlled clinical trial compared the stability of augmented bone between a synthetic resorbable membrane and a collagen resorbable membrane with guided bone regeneration (GBR) simultaneous with dental implant placement in the esthetic zone in terms of facial bone thickness. MATERIALS AND METHODS A total of 60 dental implants from patients requiring implant placement with simultaneous GBR in the esthetic zone were equally allocated to the test group or control group by block randomization. Biphasic calcium phosphate ceramic bone was used in combination with either a polylactic acid (PLA) membrane (test group, 30 implants) or a resorbable collagen membrane (control group, 30 implants). Cone beam computed tomographic (CBCT) images were used to assess the facial bone thickness postimplantation and then 6 months later at four levels: implant platform and 2 mm, 4 mm, and 6 mm apical to the implant shoulder. RESULTS All implants were osseointegrated, and no implant loss was found during this study. Facial bone was detected in all cases; however, the thickness of the facial bone was reduced at the 6-month follow-up in both groups. The percentage of facial bone thickness reduction was 34.30%, 27.94%, 24.25%, and 19.81% in the test group and 34.80%, 24.06%, 19.52%, and 20.45% in the control group at the level of the implant platform and at 2 mm, 4 mm, and 6 mm apical to the implant shoulder, respectively. Nevertheless, there was no statistically significant difference between the groups (P > .05). CONCLUSION A synthetic resorbable membrane revealed an amount of stable augmented bone similar to that of a collagen resorbable membrane.

Optimization of exposure parameters in dental cone beam computed tomography using a 3-step approach

OBJECTIVE The aim of this study was to find the optimal balance among tube voltage (kV), tube current (mA), and exposure time (s) in cone beam computed tomography (CBCT). STUDY DESIGN Three human hemimandibles were scanned by using the 3D Accuitomo 170 scanner (J. Morita, Kyoto, Japan). First, 3 combinations of kilovolt (kV) and milliampere (mA) were used at a constant radiation dose. Seven observers evaluated the images; the kV of the highest-scoring scan was considered optimal. Second, the lowest acceptable mA for visualizing different anatomic structures was determined. Finally, the samples were scanned by using 3 combinations of tube current and exposure time; the observers determined the combination with the highest image quality. RESULTS At a constant radiation dose, the highest available voltage (i.e., 90 kV) resulted in the highest image quality in terms of general impression, sharpness, noise, and artefacts. Depending on the anatomic structure, mA reductions of 20% to 40% compared with the default setting were possible. Fast-scan protocols showed equal or slightly better image quality compared with the standard-scan mode. CONCLUSIONS For the CBCT model used in this study, optimization implies the use of the highest kV along with the shortest exposure time and a task-specific mA. The proposed stepwise optimization approach could be applied to any CBCT unit, preferably during commissioning.

Relationship between mandibular symphysis dimensions and mandibular anterior alveolar bone thickness as assessed with cone-beam computed tomography

ABSTRACT Objective: To determine the relationship between symphysis dimensions and alveolar bone thickness (ABT) of the mandibular anterior teeth. Methods: Cone-beam computed tomography images of 51 patients were collected and measured. The buccal and lingual ABT of the mandibular anterior teeth was measured at 3 and 6 mm apical to the cemento-enamel junction (CEJ) and at the root apices. The symphysis height and width were measured. The symphysis ratio was the ratio of symphysis height to symphysis width. Kendall’s tau correlation coefficient was used to determine the relationships between the variables at a 0.05 significance level. Results: The mandibular anterior teeth lingual and apical ABT positively correlated with symphysis width (p<0.05). Moreover, these thicknesses negatively correlated with the symphysis ratio (p<0.05). Symphysis widths and ratios showed higher correlation coefficients with total and buccal apical ABT, compared with lingual ABT. Buccal ABT at 3 and 6 mm apical to the CEJ was not significantly correlated with most symphysis dimensions. The mean thickness of the buccal alveolar bone at the upper root half was only 0.2-0.6 mm, which was very thin, when compared with other regions. Conclusion: For mandibular anterior teeth, the apical alveolar bone and lingual alveolar bone tended to be thicker in patients with a wide and short symphysis, compared to those with a narrow and long symphysis. Buccal alveolar bone was, in general, very thin and did not show a significant relationship with most symphysis dimensions.

Mandibular Bone Structure Analysis Using Cone Beam Computed Tomography vs Primary Implant Stability: An Ex Vivo Study

PURPOSE To evaluate the relationship between mandibular bone structure parameters measured on preimplant cone beam computed tomography (CBCT) images and primary implant stability. MATERIALS AND METHODS Twenty-one hemimandibles were scanned on the 3D Accuitomo 170 CBCT. Next, an implant was placed in each hemimandible, after which insertion torque and implant stability quotient (ISQ) measurements were acquired. The following measurements were performed on the preimplant CBCT scans: bone surface, bone volume, fractal dimension, connectivity, trabecular thickness and spacing, and skeleton analysis. Measurements were performed using various regions of interest in the vicinity of the implant site. In addition, cortical thickness was measured. The correlation between bone structure parameters, insertion torque, and ISQ was calculated. RESULTS The overall correlation was low to medium (|R| = 0.002-0.723). For the bone around the entire implant site, the highest correlation with ISQ was found for skeleton analysis and trabecular thickness. The highest overall correlation between bone structure and ISQ was found in the coronal region. For insertion torque, no significant correlation was found for the bone around the entire implant; the highest overall correlation was found in the apical region. The highest number of significant correlations between bone structure and primary implant stability were found for trabecular thickness and fractal dimension. CONCLUSION While each of the investigated bone structure parameters can have a predictive value in terms of primary implant stability, they should be measured at specific regions surrounding a planned implant site, and can provide complementary information regarding the local bone quality.