The purpose of this study was to investigate the accuracy of distance measurements of implant length based on periapical radiographs compared with that of other modalities. We carried out an experimental trial to compare precision in distance measurement. Dental implant fixtures were buried in the canine and first molar regions. These were then subjected to periapical (PE) radiography, panoramic (PA) radiography, conventional (CV) and medical computed (CT) tomography. The length of the implant fixture on each film was measured by nine observers and degree of precision was statistically analyzed. The precision of both PE radiographs and CT tomograms was closest at the highest level. Standardized PE radiography, in particular, was superior to CT tomography in the first molar region. This suggests that standardized PE radiographs should be utilized as a reliable modality for longitudinal and linear distance measurement, depending on implant length at local implantation site.
For the Dexis intraoral radiographic imaging system, estimated SNR improved both with higher filtration and with lower kVp. The Dexis detector was capable of generating acceptable images of the step wedge at a wide range of kVp settings.
The perceptibility curve test is a method for evaluating the psychophysical properties of radiographic systems. The concept of the perceptibility curve is based on the minimum perceptible exposure differences that are recorded by a particular imaging system. The perceptibility curve test was applied to a Charge-Coupled Device (CCD)-based digital intraoral radiography system in this study. A test object was made of a square aluminum block, 28 mm in both height and length and 10 mm in thickness. The test object had ten contrast details in the form of round holes with diameters of 1.5 mm. The depths of the holes ranged from 0.05 mm to 0.5 mm in steps of 0.05 +/- 0.01 mm. An X-ray unit was used that operated in the range of 60 to 90 kVp. Test radiographs were shown to observers in random order. Six observers were asked to rate them regarding the number of spots representing holes that they could perceive. The smallest perceptible difference in gray level on the computer monitor, a 15-inch cathode-ray tube (CRT), was then found. The minimum difference in gray level between a perceptible detail and the background was determined. Dose response functions were employed to determine exposures corresponding to these gray levels. For each case, delta logE as a function of the number of object details was calculated. Finally the reciprocal of all values of (delta logE)min were calculated. The number of details which the observers perceived decreased linearly with decreasing delta logE values. The maximum number of details that observers perceived was eight or nine. The perceptibility curves showed that their peaks shifted slightly with a change of the kVp but that their shapes were similar at different kVp settings.
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