Journal of Dental Medicine

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Concern for adverse effects must accompany any use of ionizing radiation. Such concern for the expanded use of CT scanning, conventional tomography and panoramic in dental implant radiology can be expressed by the establishment of absorbed radiation dose for critical tissues (resulting from these radiographic procedures). Potential patient benefit should be weighted against the risk and other disadvantages and/or advantages of a particular radiographic imaging technique. Measurement of dose values can act as a guidline for such risk determinations. The purpose of this study was to measure and compare the absorbed doses of various anatomic sites during these radiographic techniques. The absorbed radiation doses in bone marrow, thyroid gland, salivary gland, eye, brain and skin entrance were determined by placement of lithium fluoride thermoluminescent dosimetres (TLD, S) at selected anatomic sites within and on a humanlike x-ray phantom. The phantom was exposed to radiation from panoramic, linear tomographic and computer- assisted tomographic (CT) stimulated dental implant radiographic examinations. The mean dose was determined for each anatomic site. CT examination showed disruption dose, while panoramic radiography was generally the lowest. The mean absorption value by paratid gland was higher than of other salivary glands.

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Background and Aim: Accurate measurement of bone height and width is essential prior to dental implant placement. The method of surgery as well as, the type and size of implants are determined according to dimensions of the residual bone. The purpose of this study was to evaluate the accuracy of linear tomography in localization of the floor of nasal fossa and maxillary sinus, and to determine the width of maxillary bone at the designated site for implant placement.

Materials and Methods: In this test evaluation study, the vertical distances between the alveolar crest and the floor of nasal fossa and the floor of maxillary sinus was measured by the tomographic slices in 12 sites of three dry human skulls. In addition, the width of maxillary bone was measured at the same slices. The skulls were then sectioned through the marked places. Then the radiographic values were compared with the real values of bone sections.

Results: After correction of tomographic values by the magnification factor of the unit, the mean absolute measurement error for vertical values at nasal fossa and maxillary sinus area in tomographic slices were 0.28 mm (SD= 0.24) and 1.1 mm (SD= 0.68) respectively. The mean absolute measurement error for maxillary width at the nasal fossa and maxillary sinus area were 0.65 mm (SD= 0.50) and 0.55 mm (SD= 0.45) respectively. 100 % of vertical values at nasal fossa area and 50 % of vertical values at maxillary sinus area were within ± 1 mm error limit. In addition, 50 % of width measurements at nasal fossa area and 83.3 % at maxillary sinus area were within ± 1 mm error limit.

Conclusion: The linear tomography is more accurate in height estimation at nasal fossa area and in width estimation at maxillary sinus area. The accuracy of linear tomography in height and width estimation is within acceptable limits at both nasal fossa and maxillary sinus area.

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Background and Aim: Accurate bone measurements are essential to determine the optimal size and length of dental implants. The magnification factor of radiographic images may vary with the imaging technique used. The purpose of this study was to compare the accuracy of linear tomography and panoramic radiography in vertical measurements, as well as the accuracy of linear tomography in mandibular width estimation.

Materials and Methods: In this test evaluation study, the vertical distances between the crest and the superior border of the inferior alveolar canal, marked with a metal ball, was measured by linear tomography and panoramic radiography in 23 sites of four dry mandible bones. Also the mandibular width was measured at the same sites. Then, the bones were sectioned through the marked spots and the radiographic measurements were compared with actual values.

Results: The vertical magnification factor in tomograms and panoramic radiographs was 1.79 (SD=0.17) and 1.69 (SD=0.23), respectively. The horizontal magnification of tomograms was 1.47 (SD=0.17). A significant correlation was found between the linear tomographic and actual values, regarding vertical dimensions (p<0.001, r=0.968) and width (p<0.001, r=0.813). The correlation was significant but lower in panoramic radiographs (p<0.001, r=0.795). Applying the magnification values suggested by the manufacturer, the mean difference of vertical measurements between the tomographic sections was 2.5 mm (SD=3.4) but 3.8 mm (SD=1.65) in panoramic radiographs. The mean of absolute difference in mandibular width between the tomographic sections and reality was 0.3mm (SD=1.13). In the linear tomograms, 4.3% of vertical and 56.5% of the width measurements were in the ±1mm error limit. Only 4.3% of the vertical measurements were within this range in the panthomographs. The linear regression equation between the actual values and those obtained by radiography in vertical dimensions showed that 87.5% of tomograms and 51.8% of panoramics were located in the ±1 mm error limit.

Conclusion: Based on the results of this study, the linear tomography is more accurate than panoramic radiography in mandibular height estimation. The accuracy of linear tomography in width estimation is within acceptable limits.