Utility of intraoral scanner imaging for dental plaque detection

Oral hygiene, maintained through plaque control, is crucial for preventing periodontal disease and dental caries.1, 2, 3 Consequently, it is essential to effectively control plaque, both by instructing patients regarding oral hygiene and by providing precise assessment of plaque adhesion areas.3, 4 Traditionally, the O’Leary plaque control record (PCR) has been used to evaluate oral hygiene in clinical settings.5 While straightforward and useful, this method cannot visually capture the oral status during evaluation, with associated drawbacks including issues with reproducibility and challenges in collaborative assessment.

In contrast, the oral hygiene status can be documented and archived through the capture of intraoral photographs using a camera. However, while images obtained with an optical camera can offer an indirect evaluation of oral hygiene, this method is time-intensive and burdensome for patients. Conversely, in recent years, digital dentistry has made remarkable progress. Intraoral scanners (IOSs) are capable of capturing digital color images of the dentition and are utilized in the creation of crown prostheses via computer-aided design/computer-aided manufacturing.6, 7, 8 The digital color images obtained with an IOS can be manipulated on a monitor, with features including rotation and magnification; this enables observation of the dentition from angles that are otherwise not accessible.9, 10 Efforts have been made to apply IOS technology in the evaluation of oral hygiene.11, 12, 13 In particular, an IOS can be used to rapidly record the oral status, potentially addressing the challenges associated with the technical demands of intraoral photography.

In a prior study, these authors reported that an IOS system was capable of detecting sites of plaque adhesion.10 Furthermore, Giese-Kraft et al.14 used an intraoral camera and an IOS to document the oral status following plaque staining, revealing that the areas with stained plaque could be visualized similarly with both technologies.

Three-dimensional (3D) intraoral imaging serves as an appropriate instrument for whole-mouth planimetry, enabling the identification and monitoring of dental plaque. However, the disclosure of plaque on intraoral scans is subject to error, among other problems. With an IOS, the oral condition is captured as a digital image, which facilitates the manipulation of the image through rotation, enlargement, and digital processing for the accurate detection of dental plaque. By displaying the areas with adherent plaque as a digital image on a monitor, one can evaluate the oral hygiene status while also encouraging patient motivation.

As such, IOS may emerge as a novel method for assessing oral hygiene by detecting areas of plaque. The presence of dental plaque is typically revealed through the application of a staining agent. Traditionally, most plaque-disclosing solutions have included a red dye. However, few studies have been conducted on the accuracy with which plaque deposits are captured on IOS images, including the influence of color tone.

In this study, the impact of dye color on IOS imaging was explored. Additionally, the accuracy of detection in clinical practice was compared between IOS images and photographs captured with an optical camera.

Areas stained red, blue, and green were identified on the photographs acquired with the camera, as well as the IOS images (Fig. 2).

Fig. 2
Images captured using a digital single-lens reflex (DSLR) camera and an intraoral scanner (IOS), depicting red, blue, and green markings. A. DSLR camera image of a red marking. B. DSLR camera image of a blue marking. C. DSLR camera image of a green marking. D. IOS image of a red marking. E. IOS image of a blue marking. F. IOS image of a green marking.

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The stained surface ratios of the IOS images tended to exceed those of the DSLR camera images for the red and blue stains. Nevertheless, no significant differences were observed for any color group (P>0.05 for red, blue, and green). When comparing the rates of deviation, no significant differences were found across these colors (P>0.05) (Table 1).

Table 1
Surface staining and deviation rates for red, blue, and green markings, captured by a digital single-lens reflex (DSLR) camera and an intraoral scanner (unit: %)

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Dental plaque staining was also examined on the IOS and camera images (Figs. 3A and B). On the IOS images, the color of the stained areas appeared slightly lighter than on the images acquired with the camera. Additionally, the edges of the stained areas in the DSLR camera images appeared sharp. In contrast, the IOS images displayed comparatively blurred outlines (Figs. 3C and D).

Fig. 3
Images captured following dental plaque disclosure, using a digital single-lens reflex (DSLR) camera and an intraoral scanner (IOS). A. DSLR camera image. B. IOS image. C. Magnified view of the DSLR camera image. D. Magnified view of the IOS image.

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The stained surface ratio was significantly higher for the IOS than for the camera images (P<0.05) (Fig. 4).

Fig. 4
The stained surface ratio was significantly higher on intraoral scanner (IOS) images than on photographs captured with a digital single-lens reflex camera (P<0.05).

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This study involved examining the color tones of plaquedisclosing agents, as visualized by IOS. To the knowledge of these authors, this is the first study to examine the color representation and dental plaque staining visualization of IOS imaging. Identifying sites of plaque adhesion and providing oral hygiene guidance, whether in the oral cavity or on a jaw model, is crucial for maintaining optimal oral health. The evaluation of oral hygiene necessitates: 1) superior objective assessment, 2) quantification, 3) simple and accurate measurement and documentation, 4) high reproducibility, and 5) assessments that are easily understood by both practitioners and patients. While documenting oral hygiene status with an optical camera can offer an indirect assessment of oral hygiene, the process is time-consuming, requires assistance, and is burdensome for the patient. Consequently, this procedure places repeated demands on both the practitioner and the patient if executed at every clinical visit.

IOS devices can capture 3D images of intraoral conditions. This technique can be performed by a single surgeon, representing a rapid process that minimizes patient burden. Recent studies have explored the use of IOS for oral hygiene assessment.10, 14, 15 For instance, Jung et al.15 conducted a planimetric analysis of disclosed plaque areas using both an IOS device and a camera. Due to the convex nature of tooth surfaces, a single image from an intraoral camera may not fully represent the central portion of the tooth. In contrast, IOS imaging can capture the entire tooth surface in 1 image; in the present study, this likely contributed to the slightly higher observed plaque coverage in IOS scans compared to camera images. In a previous investigation, the present authors examined the utility of IOS in PCR measurements. After applying a plaque-staining agent and visualizing the dentition with IOS, the images clearly showed the stained dental plaque.10 These scans were particularly useful for visualizing plaque in hard-to-see areas, such as the lingual and distal aspects of the tooth surface. This research suggests that images recorded using IOS equipment can reflect plaque disclosure. Dental plaque staining solutions are typically red in color.16 However, the use of this color for plaque detection with IOS has not been validated. In this preliminary study, red, blue, and green colors were used for staining. Again, red is commonly used in clinical settings, while blue and green were chosen for comparison. In the chromaticity diagram, which depicts the color spectrum from the lightest whites to the most vivid colors, the color triangle is defined by the presence of the 3 primary colors at its vertices.17 This triangle represents the broad range of colors that can be produced by mixing the primary colors. Red, which is composed of green and blue within this color triangle, is also employed in additive color mixing to create a variety of colors, including the RGB (red, green, and blue) colors used in the image sensors of digital cameras. In the present study, no significant difference was found in the deviation rate across these colors. These findings suggest that the use of a red dental plaque staining solution is acceptable for identifying stained plaque areas using IOS.

Preliminary studies revealed no significant differences in measurements between the DSLR and IOS images, although the IOS measurements were non-significantly higher for the red and blue stains. In the clinical results, the stained regions depicted on IOS images exhibited larger relative areas than those captured by the camera. The IOS system benefits from digital processing capabilities, including magnification and rotation, which likely contribute to its tendency to yield higher values for the ratio of stained surfaces compared to conventional measurement methods.

Meseli et al.18 examined the relationship between scores determined using the FluoreCam method and the dental plaque index obtained following the application of a plaque staining agent. The findings indicated that plaque scores obtained through the FluoreCam approach exceeded those recorded after plaque staining in a clinical setting. In the present study, visual and IOS image recordings of the PCR measurements were compared, with higher readings observed for the IOS images. This discrepancy may stem from the ability to view IOS images on a monitor, which enables enhanced magnification and rotation to ultimately facilitate a more detailed plaque inspection. Consequently, higher PCR scores are obtained. The clinical data regarding the plaque deposition area ratio indicated that the IOS images produced higher values. Under the present measurement conditions, both camera and IOS images were captured at the same level of magnification. Consequently, the potential effects of rotation and magnification, which are advantages of IOS, were not considered.

The IOS device used in this study was equipped with a complementary metal oxide semiconductor reading sensor, which enabled full-color scanning. Consequently, differences in color tone appeared to exert minimal impact on the findings.

One contributing factor is that camera images are captured at a resolution of 1980×1080 pixels, whereas IOS devices operate at a lower reading resolution of 1280×870 pixels due to equipment performance limitations. Consequently, when IOS images are enlarged, the contours appear blurred relative to camera images, and the measured area seems larger. The deviation value is appropriate for evaluations such as confirming plaque attachment areas and conducting PCR measurements. The benefits of image processing, including rotation and magnification, underscore the potential utility of IOS in assessing oral hygiene status. Nonetheless, for the development and implementation of new indices, such as the area ratio of stained plaque and the volume ratio of plaque accumulation, IOS images would require a resolution on par with that of a DSLR camera.

The use of IOS images in the assessment of oral hygiene is potentially useful. However, these images tended to appear blurred and enlarged relative to the true condition of the teeth, due to their reduced sharpness relative to camera images.2, 3, 4, 5