In the 2011 project "Safety and efficacy of a new and emerging dental X-ray modality (SEDENTEXCT)", it was suggested that dose index (DI) and dose-area product (DAP) could be easily measured and used as diagnostic reference levels (DRLs), which would help in the management of radiation doses to patients in optimum exposure settings. Such indices could be directly related to effective dose. The purposes of this study, therefore, were to measure and calculate the DI and DAP in cone beam CT (CBCT) machines and to evaluate the correlation between the two.Dose measurements were performed on three-dimensional cone beam CT (3D-CBCT) machines [3D Accuitomo (J. Morita Mfg. Corp., Kyoto, Japan), Veraviewepocs (J. Morita Mfg. Corp.) and CS9300 (Carestream, New York, NY)] by exposing a cylindrical poly-methyl methacrylate (PMMA) phantom using a CT ionization chamber. These dose measurements were used for the calculation of Dose Indices 1 and 2, according to the methodology suggested by SEDENTEXCT. The DAP was measured using a DAP meter that was attached to the detector to cover the entire irradiated area.The DI1 ranged from 53.6 mR to 216.6 mR, the DI2 ranged from 77.1 mR to 325.0 mR and the DAP ranged from 101.1 mGy cm(2) to 457.9 mGy cm(2), depending on the machines and exposure settings. Index 2 had a better correlation with the DAP than Index 1.The DIs and DAP proposed by SEDENTEXCT may be useful for establishing DRLs for dental CBCT machines; however, further studies are necessary to determine which of these indices provide accurate dose estimates proportionally relating to the effective dose.
Abstract Aim To determine the relationship between radiographic signs on panoramic radiographs and anatomic features of thinning of the cortical plates and closeness of the root of the third molar to the mandibular canal on cone beam computed tomography images ( CBCT ). Methods Panoramic images were analysed for the relationship of the root of the third molar to the mandibular canal. The CBCT images were analysed for the relation between mandibular canal and the third molar root. The results were tabulated, and C hi square test ( P < 0.05) was used for the assessment of the relationship between the panoramic sign and the CBCT findings. Results The panoramic signs, especially, darkening of the root and interruption of the white line of the canal correlated with the location of the mandibular canal to the impacted tooth, thinning of the lingual cortical plate and the closeness of the canal and the molar. Conclusion Darkening of the root and interruption of the white line of the canal on panoramic radiograph can predict lingual cortical plate thinning and close relation between third molar root and the mandibular canal.
To measure the scatter fraction in cephalometric radiography with and without a grid and to estimate the patient's dose reduction by using a specially fabricated collimator without a grid.A 16 cm thick water-equivalent phantom was used to measure the scatter fraction. The projection geometry was the same as our conventional one, i.e. the distance from the X-ray source to the centre of the phantom was 200 cm. A photostimulable phosphor plate was used as an X-ray sensor and was 20 cm from the centre of the phantom. The measurements were performed in four combinations: with an antiscatter grid in place, with a specially fabricated collimator in place, with neither in place, and with both in place. The images of a human dried skull were obtained by using the above parameters and were subjectively assessed for a visibility of several reference points.The scatter fraction in the regularly collimated geometry with the antiscatter grid in place was 0.35 for a relative exposure of 1. With the antiscatter grid removed, the scatter fraction increased to 0.68, but the relative exposure was reduced to 0.3. With a special collimator, the scatter fraction was reduced to some extent in all instances, but the exposure was reduced to 0.45. The visibility of the reference points was acceptable in all conditions.In cephalometric radiography, removal of the antiscatter grid yields a significant reduction in exposure with no significant loss of information.
Digital subtraction radiography (DSR) is a suitable technique for detecting incipient bone changes. However, in DSR, one or more follow-up radiographs must be taken. The aim of this study was to assess the possibility of reducing the exposure time for the radiographs that follow the initial one. Maxillary premolar and molar radiographic images of a dry skull were taken with a digital radiography system. The initial radiographs, without bone chips, were taken at 0.32 and 0.16 s. Then, five bone chips (weight range 7–15 mg) were placed on the maxillary molar buccal side of the dry skull. Secondary radiographs were taken at 0.32-, 0.16-, 0.08-, 0.04-, and 0.02-s exposure times. For each bone chip, radiographs were taken three times. The secondary and initial images were subtracted to yield subtraction images. Four observers were asked to evaluate bone change visibility in the subtraction images. The Friedman test was used for statistical analysis. Significant differences were seen at each of the settings for the 0.32-s group (p = 1.24e−030) and 0.16-s group (p = 7.52e−009). By comparing the different groups, observer evaluations indicated that visibility changed when the secondary radiograph was taken at 1/8 of the exposure time of the initial radiograph. In both groups, the visibility of the 0.02-s subtraction image was significantly lower than that of the other subtraction images. In DSR, the exposure time of the secondary radiograph can be reduced to 1/4 of the exposure time of the initial radiograph.
Objective: To know the prevalence three-rooted mandibular first molars in a Saudi Arabian population by using CBCT. Material and Methods: A total of 428 CBCT scans in the database of the College of Dentistry, Jouf University, Kingdom of Saudi Arabia were analyzed. All well-developed permanent mandibular first molars were analyzed for the presence of extra root in three dimensions and the reconstructed volumetric images by two qualified and experienced observers. The total incidence, distribution and comparison regarding gender, bilateral and unilateral appearance, and the side of occurrences of these permanent three-rooted mandibular first molars were analyzed by the Chi-square test. The level of significance was set at 5%. Results: The CBCT scans of 14 subjects had three rooted mandibular first molars with a prevalence of 3.27%. The prevalence in males and females was 2.96% respectively, with no significant differences between genders (p=0.865). The frequency of bilateral three-rooted mandibular first molars was 1.16%, with unilateral frequencies of 1.40% and 0.70% on the right and left sides, respectively. No significant relationship between sides (p=0.981) and the bilateral prevalence of three-rooted mandibular first molars (p=0.668) was observed. Conclusion: Dental practitioners must be aware of the fact that though it is rare, an extra or third root can be present in mandibular first molars and CBCT can aid in accurate diagnosis of the presence of third root.
Objective: To determine the prevalence of hypercementosis in a Saudi Arabian population. Material and methods: A total of 642 CBCT scans from patients comprising 4471 teeth were incorporated in the study sample. All teeth were analyzed for the presence of hypercementosis in sagittal, axial and coronal plains by two qualified and experienced observers. The characteristics of the involved tooth in terms of gender, jaw and location were recorded from the CBCT scans. The obtained data were statistically analyzed using SPSS 21.0. The reliability of measurements was evaluated by kappa statistics. Results: Out of total 642 subjects hypercementosis was observed in 31 patients (4.82%) and 43 teeth (0.96%). Eight (2.68%) maxillary 1st molars, 6 (1.88%) mandibular 1st molars, 5 (1.46%) maxillary second molars, 7 (1.95%) mandibular 2nd molars, 9 (4.76%) maxillary 3rd molars and 8 (3.58%) mandibular 3rd molars were observed to have hypercementosis. Among males, 4.76% were affected with hypercementosis as compared to 4.86% of females (p=0.97). Likewise, no significant difference in the occurrence of hypercementosis was observed between maxillary and mandibular arches or between sides (p>0.05). Conclusion: The prevalence of hypercementosis in a Saudi population was found to be 4.82% with respect to patients and 0.96% with respect to teeth. No significant propensity for gender, jaw and arch side was noted.
