Indian Journal of Dental Research

: 2015  |  Volume : 26  |  Issue : 1  |  Page : 5--10

Detection of proximal caries using digital radiographic systems with different resolutions

Sima Nikneshan1, Fatemeh Mashhadi Abbas2, Sedigheh Sabbagh3,  
1 Department of Oral and Maxillofacial Radiology, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran
2 Department of Oral and Maxillofacial Pathology, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran
3 Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran

Correspondence Address:
Sedigheh Sabbagh
Dental School, Shahid Beheshti University of Medical Sciences, Tehran


Background: Dental radiography is an important tool for detection of caries and digital radiography is the latest advancement in this regard. Spatial resolution is a characteristic of digital receptors used for describing the quality of images. Aim: This study was aimed to compare the diagnostic accuracy of two digital radiographic systems with three different resolutions for detection of noncavitated proximal caries. Settings and Design: Diagnostic accuracy. Materials and Methods: Seventy premolar teeth were mounted in 14 gypsum blocks. Digora; Optime and RVG Access were used for obtaining digital radiographs. Six observers evaluated the proximal surfaces in radiographs for each resolution in order to determine the depth of caries based on a 4-point scale. The teeth were then histologically sectioned, and the results of histologic analysis were considered as the gold standard. Data were entered using SPSS version 18 software and the Kruskal-Wallis test was used for data analysis. P <0.05 was considered as statistically significant. Results: No significant difference was found between different resolutions for detection of proximal caries (P > 0.05). RVG access system had the highest specificity (87.7%) and Digora; Optime at high resolution had the lowest specificity (84.2%). Furthermore, Digora; Optime had higher sensitivity for detection of caries exceeding outer half of enamel. Judgment of oral radiologists for detection of the depth of caries had higher reliability than that of restorative dentistry specialists. Conclusion: The three resolutions of Digora; Optime and RVG access had similar accuracy in detection of noncavitated proximal caries.

How to cite this article:
Nikneshan S, Abbas FM, Sabbagh S. Detection of proximal caries using digital radiographic systems with different resolutions.Indian J Dent Res 2015;26:5-10

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Nikneshan S, Abbas FM, Sabbagh S. Detection of proximal caries using digital radiographic systems with different resolutions. Indian J Dent Res [serial online] 2015 [cited 2021 Dec 2 ];26:5-10
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Dental caries is a major threat to the dental pulp. [1] By diagnosing the earliest signs of enamel demineralization by interfering in the first phase, we can accelerate the process of remineralization and obviate the need for restorative treatments. [2] On the other hand, failure to diagnose incipient caries can compromise the results of remineralization treatments. [3] Proximal caries (immediately beneath the contact area) are ranked second in terms of prevalence among dental caries. [4] These caries is commonly diagnosed by visual observation associated with radiography. [5]

In 1980, the first intraoral sensor was produced for dental use. Recent advances in imaging systems, introduction of new receptors and advanced software programs have significantly enhanced the clinical advantages of these systems. Digital imaging is a superior alternative to conventional radiography and has taken its place in many cases. Some of the advantages of digital systems over conventional ones are dose reduction, the ease of image storage and the possibility of image enhancement. Digital radiography is now increasingly used in the clinical setting. [6],[7],[8] At present, digital sensors are categorized into two major groups of solid-state detectors including charge-coupled device (CCD) systems and complementary metal oxide semiconductor systems (CMOS), and photostimulable storage phosphor (PSP) systems. [9]

Spatial resolution is a characteristic of digital receptors that differentiates between the details in an image. This characteristic is usually expressed as line pairs per millimeter (lp/mm). It is stated that images with high spatial resolution can better detect fine radiographic details. However, it should be emphasized that in the clinical setting, effective resolution of the device is influenced by other characteristics of the receptor such as noise and contrast. [10],[11]

Some studies have evaluated and compared the spatial resolution of intraoral digital systems and computerized tomography; while some others have evaluated its effect on digitized (indirect) radiographic images. [12],[13],[14] Other studies have assessed the effect of spatial resolution on diagnostic processes namely detection of caries, [10],[15],[16],[17],[18] locating the endodontic file tip and detection of root fractures. [19],[20]

This study sought to assess the diagnostic accuracy of two intraoral digital radiographic systems for detection of noncavitated proximal caries using three different resolutions. Expertise and experience of radiologists and restorative dentistry specialists were also evaluated and compared in this respect.


In this study, first, 70 premolar teeth were selected by direct visual observation and use of radiography; 10 teeth were caries-free (to prevent observer bias) and 60 teeth had at least one surface with a noncavitated carious lesion (in the range of enamel caries to dentin caries).

Tooth blocks were then prepared as follows: First, in order to simulate periodontal ligament in the radiography and facilitate the future laboratory phases, root surfaces (from below the cementoenamel junction) were uniformly covered with a thin layer of wax. Then, the teeth were randomly divided into 14 groups of five and the teeth in each group were separately fixed with sticky wax on a piece of a wooden tongue depressor in such way to reconstruct natural contact [Figure 1]. Two groups of teeth were mounted in a cubic container measuring 2.5 cm × 4 cm × 5.7 cm using sawdust and gypsum in a 1:1 ratio. After preparation of blocks, in order to reconstruct the bite, two blocks that provided the best occlusion were selected and fixed in the desirable position with sticky wax [Figure 2].{Figure 1}{Figure 2}

In the next step, radiographic images were obtained using two digital receptors: (1) Seven images with RVG access sensor (Trophy Radiology, Vincennes, France) and (2) 14 images with Digora® Optime (Soredex, Helsinki, Finland) [Figure 3] and [Figure 4]. Plexiglass (with 2.35 cm thickness) was used for soft tissue reconstruction. The images of RVG Access were obtained by Planmeca Prostyle Intra (Planmeca, Helsinki, Finland) at 63 kVp and 0.25 s time. Images of Digora® Optime were obtained by Soredex unit (Sordex, Helsinki, Finland) at 70 kVp and 0.20 s time. In the latter system, plates were scanned by Digora® Optime reader at two different resolutions (high and super). Eventually, using the respective software the images were saved and the densitometric characteristics of the images were adjusted to a reference image by a maxillofacial radiologist.{Figure 3}{Figure 4}

Six surfaces were excluded from the study due to the presence of enamel cracks. Also, the last tooth surface in each image was excluded from the study in order to prevent the caries bias due to the black background. [10] Then, three oral and maxillofacial radiologists and three restorative specialists evaluated the images in two sessions. These sessions were held with an interval of at least 10 days with no time limit for evaluation of images. The images were evaluated by the observers using Microsoft Office Picture Manager 2007 software in a dimly lit room on an LG monitor with 1024 × 768 resolution. Furthermore, the observers were asked not to change the image quality such as contrast or brightness. The observers were blinded to the study design. The diagnosis of observers was recorded based on a 4-point scale. This scale was defined as follows:

Proximal surface free from cariesRadiolucency extending to the outer half of enamelRadiolucency exceeding outer half of enamel and extending to dentinoenamel junction (DEJ) but not exceeding the DEJRadiolucency exceeding the DEJ and entering dentin.At the end, in order to assess reproducibility, six images were evaluated again.

In order to determine the actual depth of caries, ground section machine with 0.5 mm blade thickness was used for sectioning of teeth. Based on the tooth size, two to three longitudinal sections were made in the mesiodistal direction in each tooth. In order to determine the actual depth of caries (gold standard), an oral and maxillofacial pathologist evaluated the sections under a stereomicroscope (Olympus SZX9, Tokyo, Japan) at ×10 magnification and recorded her diagnosis based on the same 4-point scale.

Finally, data obtained from radiographic and histological examinations were transferred to SPSS version 18 software (SPSS Inc, Chicago, USA) and the Kruskal-Wallis test was used for the comparison of understudy resolutions. P < 0.05 was considered as statistically significant. In addition, intraclass correlation coefficient (ICC) was also used to calculate Inter- and intra-observer reproducibility.


Of 105 teeth surfaces evaluated in this study, 38 (36.2%) were caries-free, 13 (12.4%) had caries extending to outer half of enamel, 10 (9.5%) had caries extending to DEJ and the remaining 44 surfaces (41.9%) had dentin caries. The mean performance of the six observers for each resolution is shown in [Table 1]. Diagram 1 shows the diagnostic indices for the three understudy resolutions.{Table 1}

According to the Kruskal-Wallis test, none of the diagnostic indices of observers had significant differences with each other in the understudy resolutions (P > 0.05). The ICC of the interobserver reproducibility was 0.90 for the resolution of RVG access system and 0.88 for the resolutions of Digora® Optime system. The intraobserver reproducibility was as follows:The ICC was 0.66 for RVG access system resolution, 0.99 for Digora® Optime system super resolution and 0.15 for high resolution of Digora® Optime system. The ICC for the two groups of observers and different understudy resolutions is listed in [Table 2].{Table 2}


Detection of caries is among the most common diagnostic challenges in dentistry. [18] Diagnosis of incipient noncavitated caries is especially important because if diagnosed at this stage, their progression can be prevented, and the need for future restorative treatments will be eliminated. [21] Thus, in this study we focused on the accuracy of diagnosis of these lesions. Radiography is still the most commonly used diagnostic tool for detection of tooth decay. [21] At present, digital intraoral radiographic systems are widely used in the clinical setting. Studies have shown that these systems have diagnostic accuracy equal to that of conventional radiography for detection of caries. [12] Thus, we compared two intraoral digital radiography systems: Digora® Optime, which falls into the category of PSPs and RVG Access that works based on CMOS technology. Both these systems are available and widely used in Iran.

Spatial resolution is one of the four cardinal characteristics for each image receiver. [22] This characteristic is defined as the ability to show two close, but distinct entities. [23] Digora® Optime provides "high" and "super" resolutions that are equal to 7.8 lp/mm and 12.5 lp/mm, respectively; whereas, RVG access provides the clinician with only one spatial resolution option which is more than 14 lp/mm. [10],[15],[24] The number of studies on the effect of spatial resolution of intraoral digital radiography systems on the diagnostic accuracy of noncavitated caries is sparse. [10],[15],[17],[18] Therefore, this study sought to assess the effect of this characteristic on the diagnostic accuracy of these two radiographic systems.

In order to eliminate the effect of confounding variables on the results, such as monitor settings, conditions of the place of observation and time of observation sessions, in the present study, we used the same monitor and software program to show the radiographs. Furthermore, observation sessions were held in the same room with the same background lighting and at a specific time of day.

In our study, none of the understudy resolutions had any superiority over the others. The specificity of the RVG Access resolution (resolution 1) was higher than the other two resolutions. "Super" resolution of Digora® Optime (resolution 2) ranked second and "high" resolution of Digora® Optime (resolution 3) had the lowest amount and highest dispersion of specificity [Diagram 1].

Moreover, the sensitivity of correct detection of dentin caries was higher than that of other types of caries (at all resolutions). In other words, the understudy devices did better in cases where the carious lesion was greater. It should be mentioned that for the resolutions of Digora® Optime, the sensitivity for correct detection of caries located in the outer half of enamel was the lowest. In general, the "super" resolution of Digora® Optime had higher sensitivity for correct detection of enamel caries. Overall, the specificity value was higher than the sensitivity for different extents of caries [Diagram 1].

Despite the characteristics of each radiography system, it should be noted that the highest information regarding each system could be achieved by education and experience of the observer. [25] Considering the ICC, we found that oral radiologists performed better than restorative dentistry specialists in the detection of caries. This finding is probably due to the higher familiarity and experience of radiologists with interpretation of radiographs and their field of work. The difference between these two groups was the lowest for resolution 1 and the highest for resolution 3; which means that the judgments of these two groups are more similar when the resolution of the device is higher. [INLINE:1]

In our study, the intraobserver reproducibility just for high resolution of Digora® Optime system was very low, that is 0.15. This value suggests that decision-making using images scanned at this resolution was random. Hence, for detection of noncavitated proximal caries, using this resolution setting is not recommended.

In 2007, Berkhout et al., evaluated the effect of high and standard resolutions of digital radiography systems and concluded that spatial resolution had no effect on enhancing the diagnosis of caries. Furthermore, the results showed different functions of sensors in the aforementioned study. [15] Our results also confirmed their finding regarding the insignificant effect of spatial resolution on caries detection. Superiority of Gendex Visualix HDI CCD sensor in their study over PSP sensors may be attributed to the higher spatial resolution of CCD sensors. However, their study was not performed blinded, and only one tooth surface was selected and evaluated. Each of these factors can cause a bias in the results.

Li et al., in their study on the effect of resolution of PSP devices showed that scanned images with 10 lp/mm resolution of the Durr VistaScan device did not provide adequate quality for detection of caries and also had significant differences with other resolutions studied. However, similar to our study, they concluded that increasing the spatial resolution did not have a significant effect on detection of proximal caries. [10]

Wenzel et al., also assessed the effect of spatial resolution on the diagnostic accuracy of caries. In their study, the observers were allowed to use enhancement filters and occlusal caries were also evaluated in addition to proximal caries. They found no significant difference between different resolutions of receptors except for the VistaScan® system. They concluded that diagnostic accuracy of caries is slightly affected by increasing the spatial resolution. Also, significant differences were found between the understudy receptors and it was concluded that Digora® Optime system had higher sensitivity and lower specificity than the other systems. [18] Although in our study due to the variability of caries assessment criteria, accurate calculation of sensitivity was not feasible, Digora® Optime system was found to have higher sensitivity in correct detection of caries exceeding half of the enamel.

Mehdizadeh et al., concluded that changing the resolution had very little effect on the diagnostic accuracy for detection of proximal caries and the standard resolution of the understudy systems had insignificant superiority over their high resolution for caries diagnosis. Moreover, they reported that the results of interpretation of radiographs obtained by Schick system at standard resolution had the highest similarity to pathologic examination results compared to other systems. [17] Superiority of Schick over Soredex system in their study may be attributed to the higher spatial resolution of CMOS systems over PSP. However, they had a small sample size and extent and distribution of caries were not specified; these factors may have affected the obtained result.

It should be noted that the differences between studies may be explained by the different devices used, the criteria for severity of caries, software programs and the monitor, statistical tests and other influential variables. Overall, based on our results and those of similar studies, we may conclude that spatial resolution has no or minimal effect on the diagnostic accuracy for detection of caries. This finding may be due to the fact that the physical properties of the receptor such as the signal-to-noise ratio, detective quantum efficiency and dose-response function play a more important role than the pixel size alone in determining the sensor quality. On the other hand, it should be kept in mind that human eye has limited power and cannot perceive all the details recorded in an image. However, this small effect on detection of caries does not mean that it is not effective because changing the spatial resolution can affect other dental diagnostic processes. [15] Last but not least, images with higher resolution occupy more storage space than images with low spatial resolution; this issue per se can complicate the process of display or transfer of these images and interfere with this unique property of digital systems. [18],[22]


The results showed no significant differences between different resolutions evaluated in this study. Digora® Optime in "super" resolution had higher sensitivity for correct detection of enamel caries while RVG Access had higher specificity. Moreover, Digora® Optime had higher sensitivity than RVG Access for caries exceeding half of the enamel. Oral radiologists had better performance than restorative dentistry specialists in this respect.


This study was part of the doctoral thesis of Sedigheh Sabbagh, supported financially by Dental School, Shahid Beheshti University of Medical Sciences. The thesis supervisor was Dr. Sima Nickneshan. Moreover, the authors would like to thank Dr. Maryam Abdoh Tabrizi, Dr. Elham Moravej Salehi, Dr. Zeinab Azizi, Dr. Zahra Vasegh and Dr. Azam Valian for their contribution as observers in this study.


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