Direct digital radiography for the detection of defects in a standard aluminium test object through composite resin restorative materials

Effects of the automatic exposure compensation on the proximal caries diagnosis

OBJECTIVE

To elucidate the effect of automatic exposure compensation (AEC) on the diagnostic accuracy of proximal caries by comparing several digital intraoral imaging systems with a film.

MATERIALS AND METHODS

Twenty-seven extracted teeth served as proximal caries samples. Three digital radiographic systems; the Compuray, the Dixel, and the Sens-A-Ray without scintillator layer, and Kodak Ekta-speed Plus films were used as recording media. Radiographs of the teeth samples were obtained with each recording medium under seven to eight different exposures including the optimum level. Six oral radiologists evaluated the possibility of proximal caries with the five-grade-confidence-scale. On digital radiographs, image manipulations were allowed after the initial assessment. Receiver operating characteristic (ROC) curves were obtained at each exposure in each recording medium. The area under the ROC curve (Az) was used as the representative value of diagnostic accuracy. Diagnostic accuracy (DA) curves were obtained by plotting averaged Az values from all observers as a function of incident exposure in each system.

RESULTS

The effect of exposure variation on the DA was slight in the film while it was significantly larger in the digital systems without AEC. Among digital systems, the effect of exposure variation was smaller in the system with AEC than those without AEC. There was no significant effect on the diagnostic accuracy even if digital image manipulation was employed.

CONCLUSION

AEC minimizes the decrease of DA due to inadequate exposures. Since it compensates for the narrow exposure range in the digital intraoral sensor systems, the system with AEC may be preferable for the clinical diagnostic tasks.

Comparison of the diagnostic potential of direct digital and conventional intraoral radiography in the evaluation of peri-implant conditions

The aims of this study were to examine whether viewers agreed on details seen in direct (real time) digital and conventional film radiographs of implants, and whether there were differences in agreement between the systems. Intra-oral radiographs of implants were exposed both as direct digital and conventional film radiographs. Fifty pairs of radiographs with similar projection and exposure were selected, showing 59 implants. Ten viewers assessed the radiographs separately and noted eight different details. The viewers showed very high agreement in their assessments of radiographs of each technique separately, and there were no statistically significant differences. However, there was a tendency to stronger agreement in the direct digital radiographs in four assessed points out of eight. The patients' experience of having radiographs exposed with the two methods was also studied by questionnaire. The patients' opinions on the two techniques did not differ statistically. This study shows that digital radiography has at least equal diagnostic yield compared to film radiography.

Conventional and predicted perceptibility curves for contrast-enhanced direct digital intraoral radiographs

OBJECTIVES

To construct Perceptibility Curves (PCs) for contrast-enhanced digital intraoral radiographs.

METHODS

Radiographs of a test object having holes of increasing depths were exposed using three digital systems, the CDR (Schick Technologies, Long Island, NY, USA), the Dixel (J Morita MFG, Kyoto, Japan) and the Sens-A-Ray (Regam Medical Systems, Sundsvall, Sweden). The radiographs were contrast-enhanced and PCs constructed in the conventional way using 10 observers. Predicted PCs were calculated and compared with observer data.

RESULTS

The PCs showed that contrast enhancement is effective for the perception of small contrast details, especially in the low exposure range. Predicted PCs demonstrated excellent agreement with observer data.

CONCLUSIONS

Contrast enhancement should be advantageous in digital radiography. The effects of contrast enhancement on PCs may be predicted without previous knowledge of observer performance.

Assessment of image quality in dental radiography, part 1: phantom validity

OBJECTIVE

The purpose of this study was to describe and validate an image-quality phantom to be used in dental radiography for comparison of film and digitally acquired images.

STUDY DESIGN

An aluminum block of 12 steps, with 7 holes in each step, was covered by acrylic blocks. This phantom was radiographed with Kodak Ultra-speed and Ektaspeed Plus films at 70, 65, and 60 kVp with the whole exposure range available. All together, 50 dental films were randomly sequenced and presented to 7 observers. The average number of perceptible holes from all steps was plotted against exposure for each tube voltage and film type, generating a modified perceptibility curve. The tentative optimum exposure level was determined from perceptibility curves in each experimental condition and compared with that determined by means of the standard aluminum stepwedge and the preset time of the x-ray machine. The density range of this phantom at the optimum exposure was compared with that of clinical dental radiographs. Validity of the phantom was evaluated according to the optimum exposure level from the modified perceptibility curves and the overall density range. Finally, the average maximum numbers of perceptible holes at the tentative optimum exposure level were compared for each tube voltage and film type. The statistical test used was a 2-way factorial analysis of variance.

RESULTS

The exposure at the perceptibility curve peak approximated that obtained by means of the standard aluminum step-wedge and the time preset by the manufacturer. The overall density range at the perceptibility curve peak covered the clinical density range for each tube voltage and film type. There were no statistically significant differences between film types or among tube voltages.

CONCLUSIONS

The x-ray attenuation range for this phantom seemed to approximate clinical conditions. In addition, differences in image quality could be quantitatively evaluated by means of the number of the holes seen in the phantom.

Observer differentiation of proximal enamel mechanical defects versus natural proximal dental caries with computed dental radiography

OBJECTIVES

Various models have been used to study the accuracy of imaging systems for detection of dental caries. This study compares the ability of dentists to detect mechanically created defects versus natural dental caries cavitations on the proximal surfaces of extracted teeth with Computed Dental Radiography (Schick Industries, Long Island City, N.Y.). Detection rates are investigated according to lesion depth to permit comparisons to be made between studies in the literature with other mechanical defects or natural caries models. Discrimination of natural caries versus artificial defects with Computed Dental Radiography is also compared with a previous report that used standard dental film.

STUDY DESIGN

Fifty-two extracted molar and premolar teeth were mounted into representative sets of maxillary and mandibular posterior arches for bite-wing radiography. There were 16 proximal surfaces with natural caries and 28 proximal surfaces with mechanical defects. An optical bench was used to ensure constant beam geometry. A 1.8 cm acrylic soft tissue equivalent attenuator was placed in front of the receptor. Thirty dentists acted independently as observers to differentiate between sound proximal tooth surfaces, natural dental caries, and mechanical defects. Evaluation of intra- and interobserver variability was made with use of the kappa statistic. The Zelen test of odds ratios was used to test for homogeneity, and the Mantel-Haenszel analysis plus stratified logistic regression were used for inference about the common odds ratio. Significance was set at p < 0.05.

RESULTS AND CONCLUSIONS

Ignoring stipulation of cavity type, detection was 74% for mechanical defects and 67% for natural caries. The odds of detecting a mechanical defect were 1.40 times the odds of finding natural dental caries cavitation of the same depth. Lesion depth did influence the probability of correctly identifying the presence of a lesion; the odds of identifying cavitation increased 1.41 times with every 0.1 mm increase in lesion depth. Correct designation of lesion type was 1.42 times more likely with mechanical defects than with natural caries (p = 0.003). Intraobserver (kappa = 0.65) and interobserver (kappa = 0.43) agreements were fair to good. Discrimination between natural and artificial lesions was less with the Computed Dental Radiography than that found in our previous study with standard direct emulsion x-ray film.