Perception versus reality—findings from a phosphor plate quality assurance study

Effect of 3 different disinfection methods on the image quality of photostimulable phosphor plates

OBJECTIVE

The aim of this study was to assess the effects of 3 disinfection protocols on the quality of images acquired with a photostimulable phosphor (PSP) plate system.

STUDY DESIGN

Thirty DIGORA Optime PSP plates were divided into 3 groups of 10. Group 1 was disinfected with 95% ethanol. Group 2 was disinfected using germicidal disposable wipes. Group 3 was disinfected with 95% ethanol, followed by hydrogen peroxide gas sterilization. Images of a quality assurance phantom were acquired on each plate before disinfection (baseline images). Disinfection and imaging cycles were repeated 45 times for each plate. Changes in image quality were assessed between baseline and final images. Image quality was evaluated for dynamic range, spatial resolution, and contrast perceptibility. The Fisher exact test was used to detect statistically significant differences among the 3 disinfection methods relative to decreases in image quality parameters between the baseline and final radiographs. Additionally, for each group, the Z-test was used to detect statistically significant decreases in image quality parameters between baseline and final images. The significance level was established at P < .05.

RESULTS

No statistically significant differences were detected among the disinfection groups or relative to baseline values for any group at a 5% significance level.

CONCLUSIONS

Hydrogen peroxide gas may be considered to prevent cross-contamination while preserving image quality. Regular quality assurance testing is recommended to maintain image quality over time.

Effect of image acquisition parameters on the radiopacity of bulk-fill and nanocomposite resins

OBJECTIVE

This study evaluated the radiopacity of 2 bulk-fill resins (SonicFill and Filtek Bulk Fill) and a nanocomposite (Filtek Z350 XT) resin compared with enamel, dentin, and aluminum as measured with different exposure parameters.

STUDY DESIGN

Resin disks were radiographed together with a 1-mm human tooth section and an aluminum stepwedge, at exposure times of 0.2 and 0.32 s, and source-image (S-I) distances of 30 and 40 cm, using complementary metal oxide semiconductor (CMOS) and photostimulable phosphor systems. Grayscale values were measured using ImageJ software. Paired Student t tests were used to compare the effect of the receptor on grayscale values for each material. Analysis of variance was used to evaluate the effects of receptor, exposure parameters, and the resins on radiopacity.

RESULTS

All resins exhibited greater radiopacity scores than enamel and were significantly different from each other. Filtek Z350 produced the lowest radiopacity values, whereas SonicFill produced the highest. The radiopacity values were higher on images acquired with CMOS receptors. Receptor type, exposure time, S-I distance, and material, as well as many interactions of these parameters, affected the radiopacity of the resins.

CONCLUSION

The tested resins complied with ISO 4049. Exposure parameters and digital receptors affected their radiopacity.

Postprocessing of all-zirconia restorations in digital dental radiographs: a quality assurance predicament

OBJECTIVES

The aim of this study was to describe a quality assurance issue, that is, the production of nondiagnostic high-contrast radiographs when imaging teeth restored with all-zirconia crowns on bitewing radiographs.

STUDY DESIGN

All-zirconia crowns were imaged with DIGORA Optime photostimulable phosphor (PSP) plates (Soredex/Orion Corp., Helsinki, Finland). To assess the differences in software processing, the PSP plates were scanned into third-party software as well as directly into the twain and native software provided by the manufacturer. Gamma correction, histogram stretch, and scanner resolution settings were adjusted. Vertical bitewings were acquired to increase anatomic coverage.

RESULTS

Scanning into third-party software or directly into the twain and native software did not improve contrast. Shifting the lower limit of the histogram stretch to 3 with a gamma correction of 2 resolved the problem. Neither scanner resolution setting nor vertical bitewings improved contrast.

CONCLUSIONS

The nondiagnostic high-contrast radiographs result from imaging software not effectively displaying the available gray scale. The software processing error appears to be initiated by the high-attenuation characteristics of zirconia. Consequently, radiographs with a high ratio of zirconia crown to normal anatomy are particularly susceptible.

Fish scale artefact on an intraoral imaging receptor

OBJECTIVES

To describe an artefact, termed the fish scale artefact, present on an intraoral imaging receptor.

METHODS

Thirty brand new DIGORA Optime photostimulable phosphor (PSP) plates (Soredex/Orion Corp., Helsinki, Finland) were imaged using the dental digital quality assurance radiographic phantom (Dental Imaging Consultants LLC, San Antonio, TX). All PSP plates were scanned at the same spatial resolution (dpi) using the high resolution mode. Two evaluators assessed all 30 plates. Each evaluator assessed the 30 PSP plates separately for purposes of establishing interrater reliability, and then together in order to obtain the gold standard result.

RESULTS

The fish scale artefact was detected on 46.7% of the PSP plates. The kappa coefficient for interrater reliability was 0.86 [95% CI (0.69-1.00)], indicating excellent interrater reliability. For Evaluator 1, sensitivity was 0.85 [95% CI (0.55-0.98)]; specificity was 0.94 [CI (0.71-1.00)] and overall accuracy was 0.90 [95% CI (0.73-0.98)]. For Evaluator 2, sensitivity was 1.00 [95% CI (0.75-1.00)]; specificity was 0.94 [CI (0.71-1.00)] and overall accuracy was 0.97 [95% CI (0.83-1.00)]. These results indicate excellent agreement with the gold standard for both evaluators.

CONCLUSIONS

Utilizing a comprehensive quality assurance protocol, we identified a fish scale artefact inherent to the image receptor. Additional research is needed to determine if the artefact remains static over time or if it increases over time. Likewise, research to determine the potential sources contributing to an increase in the artefact is needed.

In-vitro Thermal Maps to Characterize Human Dental Enamel and Dentin

The crown of a human tooth has an outer layer of highly-mineralized tissue called enamel, beneath which is dentin, a less-mineralized tissue which forms the bulk of the tooth-crown and root. The composition and structure of enamel and dentin are different, resulting in different thermal properties. This gives an opportunity to characterize enamel and dentin from their thermal properties and to visually present the findings as a thermal map. The thermal properties of demineralized enamel and dentin may also be sufficiently different from sound tissue to be seen on a thermal map, underpinning future thermal assessment of caries. The primary aim of this novel study was to produce a thermal map of a sound, human tooth-slice to visually characterize enamel and dentin. The secondary aim was to map a human tooth-slice with demineralized enamel and dentin to consider future diagnostic potential of thermal maps for caries-detection. Two human slices of teeth, one sound and one demineralized from a natural carious lesion, were cooled on ice, then transferred to a hotplate at 30°C where the rewarming-sequence was captured by an infra-red thermal camera. Calculation of thermal diffusivity and thermal conductivity was undertaken, and two methods of data-processing used customized software to produce thermal maps from the thermal characteristic-time-to-relaxation and heat-exchange. The two types of thermal maps characterized enamel and dentin. In addition, sound and demineralized enamel and dentin were distinguishable within both maps. This supports thermal assessment of caries and requires further investigation on a whole tooth.