Journal of Research in Dental

Abstract

Background and Aim: Considering the importance of detection of secondary caries, the adverse consequences of false positive and false negative diagnoses and the gap of information on the diagnostic efficacy of digital sensors for detection of secondary caries, this in vitro study sought to compare the diagnostic efficacy of two different resolutions of radiographs obtained by photostimulable phosphor (PSP) plate intraoral sensors for detection of secondary caries in class II composite restorations using a standard technique.
Materials and Methods: This diagnostic study was conducted on 40 extracted second human premolars. A classic class II cavity was prepared on one proximal surface of each tooth and restored with composite resin. Intraoral digital radiographs were obtained of the teeth and saved in High and Super resolutions in a computer. Secondary caries were artificially created using a round bur and high-speed handpiece and the teeth were radiographed again. Radiographs were saved in the above-mentioned two resolutions. All radiographs were observed by four observers. Caries detection was classified using a 5-point Likert scale and statistically analyzed using kappa coefficient.
Results: No significant difference was found in sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the two resolutions with regard to caries detection (P>0.05).
Conclusion:  The High and Super resolutions of radiographs taken with digital intraoral PSP plates showed no significant difference in detection of artificially created secondary caries.
Key words: Radiography, Dental, Digital, Diagnosis, Dental Caries, Composite resin
 

Introduction

Secondary caries is a common challenge for clinicians and often occurs adjacent to an existing restoration due to microleakage, inadequate extension of the restoration margins or insufficient caries removal.⁽¹⁾ Replacement of restorations due to the occurrence of secondary caries is among the most commonly performed clinical procedures in a dental setting.⁽²⁾Secondary caries was defined as reversible recurrence of caries at the margins of a restoration by GV Black.⁽³⁾ Presently, secondary caries is often detected via clinical examination in a clean and dry environment under adequate lighting, visual inspection, tactile sense of the clinician using the sharp tip of a dental explorer, use of caries detectors and dental floss, radiography and the knowledge of possibilities (to find out the health or disease status of a presumed situation.⁽⁴⁾ According to the literature, 25-42% of carious lesions are missed during a clinical examination without the use of radiography.⁽⁵⁾ For this reason, replacement of restorations suspected for secondary caries is often postponed until approved radiographically. However, controversy exists regarding the accuracy of diagnosis made based on radiography and misinterpretations may occur due to the presence of radiolucent bases and liners mimicking secondary caries.⁽¹⁾ Moreover, the cervical burnout in some regions and the Mach bands (contrast of dark and light areas) can also result in diagnostic errors and misdiagnosis of caries.^(1,2,4) In some cases, radiopaque restorations mask the radiolucent dentin caries.⁽⁶⁾ Optical resolution: is the ability of sensor to reconstruct the details in the original model and depends on the quality of optics and sensors along with spatial density (number of pixels in a digital image).⁽⁷⁾  Cheng et al, in 2012 reported that increasing the resolution of images directly affected the detection of proximal dentin caries; ⁽⁸⁾ whereas, Haiter-Neto stated that enhancing the resolution had no effect on detection of proximal or occlusal caries.⁽⁹⁾ Thus, the diagnostic efficacy of digital radiography for detection of secondary caries is a matter of controversy.⁽¹⁰⁾ Considering the existing controversy and gap of information on the diagnostic efficacy of PSP plates for detection of secondary caries, this in vitro study sought to assess the diagnostic efficacy of two different resolutions of radiographs obtained byPSP sensorsfor detection of secondary caries artificially created in class II composite restorations compared to the gold standard.(10)   


Materials and Methods

This was a diagnostic In vitro study.
Tooth preparation:
Sample size was calculated to be 40 teeth according to a previous diagnostic study.Thus, 40 permanent premolar teeth with no clinically visible cracks, caries or restorations were collected (age and sex of patients and the reason for tooth extraction were not important). The teeth were immersed in 0.1% thymol solution for disinfection. Radiographs were obtained from the teeth before and after creating artificial secondary caries. Class II cavities with 1.25×2.5×3mm occlusal, gingival and axial dimensions, respectively were prepared using 008 bur (D & Z, Switzerland) and high-speed handpiece (Kavo, Brazil) and restored with composite resin (P60, 3M ESPE, St. Paul, MN, USA). First, the prepared cavity was dried and isolated. Then, it was etched with 37% phosphoric acid for 15 seconds, rinsed for 30 seconds and dried. Two layers of bonding agent (Single Bond, 3M, ESPE, St. Paul, MN, USA) were applied using a microbrush and light cured for 10 seconds using LED light-curing unit (Starlight Pro; Mectron SpA, Carasco, Italy). Composite was then applied incrementally and each layer was cured for 40 seconds. The restoration was then finished using flame-shaped composite finishing burs (D&Z, Switzerland) and polished with paper discs.
Radiographing the teeth:
Digital radiographs were obtained using PSP plate sensors (Orion Crop #2, Soredex, Digora®Optime, Helsinki, Finland) with exposure settings of 70 kVp, 0.3 seconds and 8mA. The sensor had 1cm distance from the tooth and the distance from the X ray tube to the sensor was 20cm. This distance was adjusted using Kerr sensor holder (Kerr,USA). All teeth were positioned in jaws of a dry human skull. The X ray tube was adjusted at zero-degree faciolingual angle. Radiographs were obtained and saved in a computer with two different resolutions of High and Super (High resolution: 675×1350 pixels, image size=40Mm 1078MB capacity, Super resolution: 844×422 pixels, image size=64Mm 695KB capacity) using SCANORA Lite Viewer software (Soredex, Finland). (11)
Simulating secondary caries:
After obtaining the primary radiographs, secondary caries were artificially created using #1 round bur (D&Z) and high-speed handpiece with one millimeter depth in the gingival wall at the cementoenamel junction in such a way that the prepared cavity did not extend to the margins of the restoration and was filled with red wax.⁽¹²⁾ (Figur1)
 
Fig. 1. The illustration shows artificial caries prepared at the gingival floor and sealed with red wax.
 
Obtaining radiographs of the simulated secondary caries:
Radiographs were obtained again using PSP plate sensor with the same exposure settings as mentioned above.
Observation and assessment of radiographs:
Four observers including two oral and maxillofacial radiologists, one restorative dentist and one dental student observed the radiographs by using Power Point (Microsoft office 2010, NK, USA) on a 15-inch monitor (TOSHIBA, Japan) in a semi-dark room. The observers had 20-30cm distance from the monitor. No time limit was set for observation of radiographs. Observers viewed all radiographs randomly and recorded their opinions in a data sheet using a 5-point Likert scale as follows:

0. Definite absence of secondary caries

1. Probable absence of secondary caries

2. Indefinite

3. Probable presence of secondary caries.

4. Definite presence of secondary caries

Kappa statisticswerecomputed to assess the intra- and inter-rater agreement and the results were analyzed using the correlation tests. Diagnostic parameters including the sensitivity, specificity, PPV and NPV were separately calculated for each method and analyzed.


Results

This study was conducted on 40 teeth and 160 radiographs. No significant difference was found between the High and Super resolutions with regard to intra- and inter-examiner reliability of the four observers (P>0.05). Tables 1-4 present the sensitivity, specificity, PPV and NPV for the two resolutions.
 
Table 1- . Sensitivity, Specificity, PPV, NPV and Accuracy of High and Super resolution images
No difference in sensitivity was found between the two resolutions (P=1). The Super resolution showed the highest specificity, PPV, NPV and accuracy, but Chi-square test showed that the differences were not significant. The statistical power of the test was 0.06-0.16. Overall, no significant differences were found between the two resolutions in detection of secondary caries.

Discussion

In this study, a five-point Likert scale (0-4) was used for detection of secondary caries. Also, diagnostic parameters were calculated as absolute and complete values. The High resolution showed slightly (but not significantly) higher values than Super resolution and since for detection of secondary cries sensitivity is more important than specificity, this finding must be taken into account since it might be of clinical significance.
The literature is scarce on the efficacy of two different resolutions for detection of secondary caries; thus, we discuss other relevant factors reported in the literature. Cheng et al. compared the cone beam computed tomography (CBCT) scans (Promax 3D, DCT Pro scanner) in three different resolutions of high, normal and low with digital images captured with PSP sensor. They showed that different resolutions of CBCT scans had no effect on caries detection (P=0.989) but a significant difference was noted in detection of dentin caries between PSP plates and CBCT (P<0.001).⁽⁸⁾ Their results regarding different resolutions was somehow in accordance with our findings. Hellen-Halme evaluated the effect of two different voltages on detection of proximal caries. No significant difference was noted between 60 and 70 kV in detection of proximal caries.⁽¹³⁾ It shows that exposure settings of radiographic units such as voltage or resolution have no significant effect on caries detection.Haiter-Neto et al. compared original and enhanced (Fine, Caries1, and Caries2 filters) PSP digital radiographs and showed that the Fine filter was not significantly different from the original radiographs in terms of sensitivity, specificity and accuracy, which is in line with our findings. However, the Fine filter showed the highest sensitivity in a narrow range. Also, the Fine filter had significantly higher sensitivity and specificity than Caries 1 and Caries 2 modalities; ⁽¹⁴⁾ which is different from our findings.  Nair et al, compared conventional films with PSP and CCD digital sensors for detection of secondary caries and showed that unenhanced PSP radiographs yielded the worst and CCD and enhanced PSP images yielded the best results.⁽¹⁵⁾
Another study compared intraoral film-based radiography, digital radiography and unprocessed, iteratively restored tuned aperture computed tomography (TACT) images for detection of secondary caries and showed that iteratively restored TACT yielded the best results in terms of sensitivity (82.50) and specificity (96.25).⁽¹⁶⁾Haiter-Neto et al. compared the diagnostic accuracy of CBCT (NewTom, Accuitomo) with that of intraoral film-based and digital radiography and found no significant difference in different resolutions of NewTom CBCT in terms of sensitivity and specificity, similar to our study.⁽⁸⁾
Ilguy et al. assessed the detection of secondary caries ondigital PSP and conventional radiographs with two types of LCD monitors and showed that the radiographs displayed on the conventional monitor had the poorest and PSP images displayed on a medical monitor had the highest diagnostic value.⁽¹⁷⁾ Prapayasatok et al. assessed different resolutions of digital camera for detection of proximal caries and found no significant difference in this regard between different resolutions.⁽¹⁸⁾
Based on all the above, it may be concluded that variables such as voltage and different resolutions of radiographic units do not significantly affect the detection of caries by different observers; but the same studies show that significant differences may be found between different radiography systems such as CBCT, CCD and PSP for detection of caries. The applicable resolutions in this study included:
Spatial resolution: is defined as the ability to detect fine details in an image. Spatial resolution is expressed in line pairs per millimeter.
Based on the above-mentioned information, these two resolutions are probably similar physically and the human eye would not be able to perceive the difference between them; this explains the clinically insignificant differences between these two resolutions. However, High resolution showed slightly but not significantly higher values compared to Super resolution and since sensitivity is more important than specificity for detection of secondary caries, this finding should be taken into account. Another important issue is the size of radiographs savedwith these two resolutions. Super resolution of images occupies less space and thus can be more easily saved and transferred. Future studies are required to assess the efficacy of other options of radiographic units for detection of oral and dental conditions.
 

Conclusion

No significant difference was found between the High and Super resolutions of images captured with PSP plate sensors for detection of secondary caries.