Abstract
Objective:
To create and validate two new Image Receptor-Holding devices (IRHDs) to reduce proximal surfaces overlapping in bitewing radiography in comparison to a regular well-established and commercially available IRHD.
Methods:
Two IRHDs for bitewing radiographs with a wedge on the biting surface were designed and 3D-printed. These IRHDs, with a large wedge (Pr-Lw) and small wedge (Pr-Sw), were compared with a regular commercially available IRHD (Rinn XCP®) during image acquisition of bitewing radiographs of four posterior regions (one upper region and three lower regions) in two dry skulls and mandibles. A total of 156 interproximal regions on bitewing radiographs were radiographed by 13 oral radiology graduate students and independently assessed by two oral radiologists (10 years of experience). IRHDs were compared by Cochran’s Q test regarding the number of overlapped proximal surfaces in the acquired radiographs with a significance level of 5%.
Results:
The observers were in perfect agreement (κ = 1.0) to classify the proximal surfaces overlapping. The Pr-Lw IRHD presented the lowest number of surfaces overlapping (19.2%) followed by the Pr-Sw IRHD (48.1%) and the XCP®IRHD with the highest surfaces overlapping (71.2%). The Pr-Lw IRHD surfaces overlapping was statistically different from the XCP IRHD (p < 0.001), and the Pr-Sw IRHD (p = 0.014).
Conclusions:
The Pr-Lw IRHD demonstrated the most efficient performance in overlapping surfaces reduction, compared with the Pr-Sw IRHD and the XCP® IRHD in adult dry skulls and mandibles.
Keywords: Bitewing radiograph, Interproximal technique, Image receptor holder, Caries diagnosis, Intraoral radiography
Introduction
Since its introduction into dental practice, in 1925, the interproximal technique was proven to help the diagnose of caries lesions.1 This technique requires the use of an image receptor-holding device (IRHD) with a bitewing in which the patient occludes. Thus, the resulting images are also known as bitewing radiographs.2 The most commonly used IRHDs have an outer ring that guides the X-ray beam perpendicularly to the image receptor and prevents its partial exposure.3 Other devices simply use the stem as a guide for the X-rays beam, orienting it parallelly to teeth’s proximal surfaces.4
Correct performance of bitewing technique reduces the probability of image overlapping of the proximal surfaces of adjacent teeth, a crucial fact to avoid radiographic misinterpretations.2,3 However, the central X-ray beam may not always be parallel to the proximal surfaces between adjacent teeth. Anatomic variations in the interproximal surfaces’ angles and incorrect positioning of either the IRHD or X-rays orientation, make this technique highly operator-dependent. Consequently, proximal surfaces may overlap, impairing the diagnosis of not clinically visible caries lesions present in these areas.3
The presence of overlapped surfaces leads to the repetition of radiographs to obtain diagnostically acceptable images, which results in subsequent increase in the patient’s absorbed radiation dose. Besides, the reproducibility and the number of overlapped surfaces have the potential to alter the results of epidemiological and longitudinal studies. Therefore, it seems essential to improve and standardize the bitewing technique by modifying the existent IRHDs so that particular angulations of the proximal regions are used as guides for the orientation of the X-ray beam through the contact areas.
Thus, this study aims to create and validate two new IRHDs to reduce proximal surfaces overlapping in bitewing radiography in comparison to a regular well-established and commercially available IRHD.
Methods and materials
The local Research Ethics Committee approved this project under the number of protocol 18954619.1.0000.5418.
IRHD prototype development
The new IRHDs (Figure 1) were designed with 3D Builder Virtual Modeling Software (Microsoft, Seattle, USA) based on the pre-existent commercial IRHD Rinn® XCP® (Dentsply, New York, USA) because of its simplified design, an essential characteristic regarding the 3D printing. The main feature of the new devices is the presence of a wedge in the biting region. The wedge acts as a guide for the IRHD positioning when the patient occludes and fixes it into the interproximal region of interest and, consequently, for the X-rays central beam orientation (Figure 2). Two versions of the IRHD were printed using Simplify3D 3D Printing Software and Sethi S3 Printer (Sethi 3D, Campinas, Sao Paulo, Brazil) with a thermoplastic acrylonitrile butadiene styrene type filament of 1.75 mm diameter. The first IRHD, named Pr-Sw, has a small wedge (2 mm base, 2 mm height, 17 mm long) and a 17-mm-wide biting surface, and the second one, named Pr-Lw, has a larger wedge (3 mm base, 3 mm height, 17 mm long) and a 22-mm-wide biting surface. The wedge was placed perpendicular to the receptor and parallel to the stem to accomplish the parallelism during image acquisition. Unlike the XCP IRHD, both IRHDs prototype versions did not have an outer projection ring because it was not viable to print efficiently at that point.
Figure 1.
Proposed design of the new Image Receptor Holding Devices. (a) Tridimensional perspective showing the wedge; (b) Lateral view; (c) Frontal view showing the detail of the wedge on the bitewing region.
Figure 2.
Bitewing radiograph and diagram showing the characteristic triangular shape above the posterior teeth' interproximal space, which inspired the wedge design of the new Image Receptor Holding Device prototype.
Images acquisition
A preclinical ex-vivo study design was carried out to validate the IRHDs developed in the present study. For this, adult size dry bone skulls and mandibles were selected, which presented both the mandibular and maxillary molars or premolars with stable occlusion and proximal surfaces in contact, so the different IRHDs had the potential to obtain acceptable diagnostic bitewing radiographs. Skulls and mandibles without occlusion stability were not used. Two skulls were selected and were fixed in a stable position such that the occlusion plane was parallel to the floor. Additionally, the occlusion force to maintain the IRHDs stability was simulated using elastic bands placed horizontally and vertically around the skull.
13 oral radiology graduate students were invited and agreed to participate in the study. Six of the participants were males, and seven were females. The age range was between 23 and 36 years old. The participants were asked to randomly acquire interproximal radiographs of four posterior regions (three at the molar region and one at the premolar region) of the two dry bone skulls and mandibles. These posterior regions were conveniently selected based on the occlusion stability for the three IRHDs. The participants were asked to focus on the proximal region, where the three IRHDs had to be placed. Thus, even when the interproximal radiographs show upper and lower teeth, this study analyzed just those where the wedges were used, to avoid bias related to teeth mobility caused by some teeth' absence.
During image acquisition, the participants were randomly assigned to use the IRHD (XCP, Pr-Sw, and Pr-Lw) and also to radiograph a random skull region to avoid biases due to repetition of IRHD use or the same region radiographed sequentially. This random assignment was done until the participant had radiographed all regions with all IRHDs. They applyed the bitewing technique’s principles. They were asked to use the XCP IRHD as in a clinical condition, while in the modified IRHDs using the wedge as a guide, placing it into the adjacent marginal ridges, coronally to the contact zone of the region of interest, previously selected by the research group. The participants used the projection ring just for the XCP IRHD, but no projection ring was available for the prototypes due to limitation in 3D printing. For reaching the parallelism between the new IRHDs and the X-ray localization cylinder, the participants were asked to position the cylinder lateral surface parallel to the IRHD stem and the stem should be in the middle of the cylinder height, so the central X-ray beam was perpendicular to the teeth and the image receptor (Figure 3). They were allowed to modify the IRHD’s position and the position or angulation of the X-ray tube according to their clinical judgment to avoid overlapping of the proximal surfaces. However, they were not allowed to modify the skull position, which had its movement restricted by masking tape (3M Scotch High-Temperature Masking Tape, 3M, Minneapolis, USA).
Figure 3.
Application of the Parallelism principle between the new Image Receptor Holding Devices and the X-ray localization cylinder. (a) superior view showing the parallelism between the cylinder and the stem; (b) lateral view showing the stem in the middle height of the cylinder; (c) frontal view showing the central relationship between the bitewing and the cylinder.
All images were acquired in an oral radiology clinic following radioprotection principles and protocols, using a GX-770 intraoral X-ray machine (Gendex, Wisconsin, USA) and size 2 VistaScan photostimulable phosphor image receptors (Dürr Dental, Bietigheim, Germany). The acquisition parameters were fixed at 70 kV, 7 mA, and 0.16 s to obtain radiographs with diagnostic image quality without image enhancement adjustment for correct visualization of the interproximal region.
After image acquisition, the participants were asked to answer a questionnaire regarding the IRHDs for interproximal radiographs. This questionnaire consisted of 10 questions, which were divided into an introductory section and a specific section about the use of the IRHD. The questions in the introductory section were about the interproximal technique: IRHD frequently used; difficulty of applying the technique; importance of both projection ring and stem to achieve parallelism; and repetition frequency during clinical practice. The second section of the questionnaire was about the use of the three IRHDs during this study: perception of achieving the parallelism principle; perception of occlusion stability; and the perception about the lack of the projection ring.
Images assessment
All acquired images were exported in 8-bit TIFF format and randomized to analyze the frequency of overlapping proximal surfaces by two oral radiologists with 10 years of experience in oral diagnosis. They independently determined the presence or absence of overlapped proximal surfaces in the bitewing radiographs' regions of interest, without knowing the aim of the study neither the differences between the IRHDs. They used a computer with a 24.1 inch LCD monitor with a resolution of 1920 × 1080 pixels. The interproximal regions where the observers recognized the proximal surfaces' outer margin were considered not overlapped. On the other hand, those interproximal regions where the observers recognized even a minimal addition of the proximal surfaces were considered overlapped. In addition, teeth without interproximal contact, with restorations, or cavitated caries at the proximal surfaces were not considered for assessment.
Statistical analysis
Data were analyzed using SPSS software (IBM Corp., Armonk), with a significance level of 5%. κ test was used to verify the agreement between observers to classify the overlapping of the proximal surfaces. The upper or lower regions, where wedges were not tested, were excluded for the statistical analysis (Figure 4). All operators performed radiographs of the same regions and skulls. Therefore, Cochran’s Q test compared the three types of IRHDs regarding the number of overlapped proximal surfaces in the acquired radiographs. The questionnaire responses were descriptively analyzed.
Figure 4.
Resulting images from the Image Receptor Holding Devices; (a) Commercial XCP; (b) Prototype Small wedge (Pr-Sw); (c) Prototype Large wedge (Pr-Lw), of a lower molar region. (d), Commercial XCP; (e) Pr-Sw; (f) Pr-Lw, of an upper molar region. The arrows show examples of the proximal surfaces used for statistical analysis.
Results
The observers were in perfect agreement (κ = 1.0) in the classification of the proximal surfaces regarding the presence of image overlapping. This means that the data used for the analysis of the efficacy of the IRHDs in avoiding the proximal surfaces overlap were reliable. Table 1 shows comparative data regarding the overlapping of proximal surfaces in the three positioning IRHDs tested. The highest number of overlapped proximal surfaces was for the XCP device, with 71.2% of the surfaces, followed by the Pr-Sw IRHD (48.1%). The number of overlapped proximal surfaces was not different between those devices (p = 0.070). On the other hand, the Pr-Lw IRHD presented the lowest number of surfaces overlapping, only in 19.2% of the cases, and was statistically different from the XCP IRHD (p < 0.001), and the Pr-Sw IRHD (p = 0.014).
Table 1.
Absolute and relative frequency of proximal surfaces overlapping using for the three different positioning devices tested.
| Image Receptor-Holding Device | Proximal surfaces – n (%) | p-value* | ||
|---|---|---|---|---|
| Not overlapped | Overlapped | |||
| XCP® | 15 (28.8) | 37 (71.2) | 0.070 | <0.001 |
| Pr-Small wedge | 27 (51.9) | 25 (48.1) | ||
| Pr-Large wedge | 42 (80.8) | 10 (19.2) | 0.014 | |
*p-values according to Cochran’s Q test.
Figure 5 shows the participants' perception of the interproximal technique. In clinical practice, 57.1% of the participants declared using the RINN XCP IRHD, while 28.6% use the Hawe Kerr IRHD, 14.3% adhesive bitewing tabs. About the overall technique’s difficulty, 14.3% of the participants considered it very low, 42.9% of the participants considered it as low, 42.9% as medium.Furthermore, 85.7% answered that they rarely repeat interproximal radiographs o improve the technique. To achieve parallelism between the IRHD and the localization cylinder, 42.9% of the participants answered that the stem is more critical than the projection ring, 42.9% answered that both the localization cylinder and the projection ring are essential, and 14.3% answered that the projection ring is the most important.
Figure 5.
Participants' perception concerning interproximal technique generalizations.
Figure 6 shows the participants' perception of the parallelism between the three IRHDs used in this study. The parallelism between the RINN XCP IRHD and the localization cylinder was always (85.7%) or often (14.3%) achieved. The parallelism between the Pr-Sw IRHD and the localization cylinder was always (57.1%) or often (28.6%) achieved while 14.3% did not realize. The parallelism between the Pr-Sw IRHD and the localization cylinder was always (28.6%) or often (57.1%) achieved while 14.3% did not realize. Regarding the stabilization during occlusion (Figure 7), 85.7% of the participants answered it was often achieved with the three IRHDs. Finally, concerning the lack of the projection ring in the new IRHDs, 71.4% of the participants answered that this neither helped nor obstructed the image acquisition. In comparison, 28.6% answered it helped.
Figure 6.
Participants' perception concerning achieving parallelism between the Image Receptor Holding Devices.
Figure 7.
Participants' perception concerning achieving occlusion stability between the Image Receptor Holding Devices.
Discussion
In this preclinical in-vitro study, we validated the performance of both new IRHDs as they succeed in acquiring bitewing radiographs with less overlapped proximal surfaces than a commercially available IRHD. Those images obtained with the newly designed IRHD Pr-Lw presented less overlapped proximal surfaces (19.2%) compared with the Pr-Sw IRHD (48.1%) and the XCP IRHD (71.2%). These results contrast with the participants positive perception about the parallelism between the RINN XCP IRHD and the localization cylinder (85.7%), showing that the technique is highly operator dependent. While the participants perception about the parallelism between the new IRHDs and the localization cylinder was lower than the RINN XCP IRHD, the presence of a wedge in the bitewing of IRHD improved its correct angulation and, consequently, the resulting image. The motivation for adding a wedge to the IRHD was based on clinical observation of the triangular shape between the adjacent marginal ridges placed just above the proximal surfaces. Thus, the wedge could orient the image acquisition functioning as a mechanical guide.
The IRHD with the largest wedge (Pr-Lw) delivered a better performance than the IRHD with the smallest one (Pr-Sw). The Pr-Sw may have had a worse performance than the Pr-Lw because the skulls and mandibles were adult sizes. Thus, the largest wedge could fit better than the smaller wedge, even though the participants perception about the performance of the three IRHDs was similar about the occlusion stability (85.7%). Future research will be carried out to verify the IRHD Pr-Sw’s performance in pediatric dentistry by using children’s skulls and mandibles, as the present study showed promising results.
Another characteristic of both prototypes is that they do not have an outer ring for orientation in the cylinder positioning, but the stem is used to guide the operator. Although it could be expected a preference for IRHD with an outer ring, the majority of the participants answered that the absence of the ring did not interfere negatively in the image acquisition. This may be related to the fact that the most spread IRHD in our region also do not have an outer ring. In further refinement of the prototypes described here, an outer ring should be designed and tested to check its influence on the iterproximal technique.
Previous studies have attempted to improve interproximal and periapical IRHDs. Wamasing et al3, developed a periapical IRHD to orientate the horizontal X-rays beam angulation based on anatomical data from multidetector CT images. They showed that their modified instrument reduced the amount of overlap in proximal surfaces. However, they recognized the potential image distortion due to the X-ray beam diagonal penetration into the receptor from a direction of 10 degrees, breaking the parallelism principles, unlike our IRHDs. Furthermore, the resulting images in their study presented a significant attenuation of the X-rays beam at the crown area because of using a putty type material to individualize the image acquisition, which could interfere in several diagnosis tasks. In our study, the IRHD individual adaptation was achieved by the wedge, which did not produce any additional interference on the final image.
Another clinical study by Safi et al5, aimed to evaluate and compare a modified IRHD’s efficacy from the conventional interproximal XCP IRHD. For this, they added an orthodontic retractor to facilitate the direct visualization of the interproximal region, and consequently, enable better positioning of the IRHD. They found that their modified design was able to decrease technical errors in bitewing radiographs. However, it was not comfortable for the patients, although the clinicians (expert oral and maxillofacial radiologists) could easily use it. The operator in their study was an oral and maxillofacial radiologist, which could be an influencing factor, but in general, this technique is used by different levels of experienced operators. Our study did not evaluate the operators' experience. For this first preclinical study, operators were all oral radiology graduate students and could be considered moderately to highly experienced. Therefore, in next studies it will be assessed operators with different experience level (i.e. undergraduate students) using our newly designed IRHDs.
A recent study by Mauriello et al6, examined the utility of a stationary intraoral tomosynthesis prototype to reduce proximal contact overlap in bitewing radiography compared to a standard IRHD. They showed that this experimental technique reduced proximal contact overlap compared to standard bitewing radiography for an experienced radiographer. Another study by Johnson et al,7 assessed effective doses from conventional and stationary intraoral tomosynthesis radiography for posterior bitewing examinations. They concluded that the effective dose for stationary intraoral tomosynthesis is smaller than that for conventional circular collimated intraoral radiography but larger than for rectangular collimated intraoral radiography. Even with these positive results, the cost to produce such devices is higher than producing plastic IRHDs and, in terms of dose reduction, our new IRHDs could be more effective than the new stationary intraoral tomosynthesis radiography for posterior bitewing examinations. However, more studies comparing these two new imaging options must establish the efficacy to accomplish this objective.
The main limitation of the present preclinical in-vitro study was the lack of soft tissue simulation. It is a crucial factor for the correct application of the intraoral techniques because the soft tissues could limit the adequate positioning of the IRHD in different ways: decreasing the direct visualization of the interproximal area; restricting the mouth opening; diminishing the patient acceptance of the IRHD due to gag reflex or pain. However, one must bear in mind that in vitro studies are essential to validate new IRHDs as it allows radiographs of the same area to compare the different IRHDs without unnecessary X-rays exposition to a patient. Next steps in our research include the use of mannequins with soft tissue simulation and clinical validation of the Pr-Lw for adult patients and Pr-Sw for pediatric patients.
The findings of our study demonstrated an improvement in image quality of interproximal radiographs with the new IRHDs, because of the overlapping reduction. It could mean a better diagnosis of carious lesions, mainly those visible only in enamel, which diagnosis is more affected by the overlapping of proximal surfaces. It would eventually imply a reduction in the radiation dose received by patients due to less repetition of the technique caused by positioning errors. Moreover, the wedges may allow better control of the positioning, which may result in greater standardization of the technique, with possible applications in the follow up of carious lesions as part of minimally invasive treatments. Finally, wedge modification could be worth testing with the periapical technique as well.
Conclusion
Both IRHDs (Pr-Lw and Pr-Sw) were capable of acquiring bitewing radiographs as the existent commercial interproximal IRHD. Of these, the Pr-Lw was more effective in reducing proximal surfaces overlapping in bitewing radiography examination on adult skulls than the commercially available IRHD.
Footnotes
Acknowledgments: The first author acknowledges the University of Costa Rica for funding his graduate studies.
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