Semi-Automated Planimetric Quantification of Dental Plaque Using an Intraoral Fluorescence Camera

Semi-automated planimetry allows for a rapid, accurate, and objective quantification of areas covered with dental plaque in clinical trials. Compared to traditional planimetry, where plaque covered areas are defined manually by the operator, semi-automated planimetry is more objective and it greatly reduces processing time. To begin, mount the custom made spacer on the fluorescence camera, then connect the intraoral camera to a computer, and open the camera software.

Click on Patient, then New patient to create and fill out the patient information in the system. Next, click on Patient and Save to save the pertinent data. Click on Video and the intraoral camera is now ready to use.

Apply a red disclosing dye, which is 5%erythrosine, with a cotton pellet on the tooth surfaces of interest to disclose the plaque. Instruct the patient to rinse with water for 10 seconds to remove the excess dye. Remove any gingival stain using a cotton pellet, and air dry each tooth for three seconds.

Place the intra-oral camera in a horizontal position in front of the tooth of interest with the spacer touching the gingiva or the adjacent teeth. Ensure that the entire tooth surface of interest is in focus and captured in the image without including antagonist or contralateral tooth surfaces. Acquire the fluorescence image by pressing the camera button.

Perform the staining and image acquisition for all teeth of interest. Then mark all the images in the camera software and click on Save Images and Videos in the menu, making sure that the images are saved in plaque mode and not in caries mode. The symbol P or C in the menu indicates the current mode.

To export the images, go to Viewer and choose the images to be exported. Click on File and Export, Save As, and then on all images of the patient to export the images. In the Export window choose the setting Mode Standard and click Export path.

Select the desired folder and under Image type selection, check off the left box and choose Image state as Original data from the pull down menu. Expand the export window to display more options and select File name contains to choose Cardnumber or Userinput or Patientname. Then select Format as TIF and click on OK to export the images.

Alternatively, set up an automated file export prior to imaging by sequentially clicking on Options, Show configuration, Modules, Viewer, Export or Email, Export options, and then select Autoexport mode. Click Export path and choose the desired folder and choose Image state as Original data. Select File name contains to choose Cardnumber or Userinput or Patientname.

Then select Format as TIF and click on OK to set up the default export settings. The digital image analysis can be performed at any time after the image acquisition, and up to 1000 fluorescence images can be processed in parallel. Rename all the images with sequential index numbers.

Import the fluorescence image series in a dedicated image analysis software in red, green, blue mode by clicking on File, Import images and Import as color. Perform a threshold base segmentation of the image series by clicking Segment, Automatic segmentation and then Custom threshold. Set the low threshold above the intensity of the oral soft tissues and leave the high threshold at 255.

Thus, the software recognizes only the teeth with clean and plaque covered areas as objects. Click Apply, OK, and Segment to initiate the segmentation. Open the visualizer by double clicking on the name of the image series and enter the object editor.

Perform a visual quality control of the segmented areas and delete artifacts by rejecting and deleting such objects. Merge the remaining objects in all the images by clicking in all images and merge selected objects. Now there is only one object per image.

Quantify the total tooth area in each image by sequentially clicking on Analysis, Measure objects, Clear all, and then Pixels. Finally, export the data. Import the fluorescence image series again into the software, this time with split red, green, and blue color channels by clicking on File, Import images, and Import as gray.

Close the blue channel images and transfer the object layer from the red, green, blue images to the red channel images by clicking Segment and Transfer object layer. Delete non-object pixels in the red channel images using the object editor in all images and delete non-object pixels. Soft tissues are now removed from the images.

Multiply the red channel image series by a factor of 2 by sequentially clicking on Edit, Image calculator, Multiplication, Parameters, and entering a factor of 2.00. Then click Apply and OK to enhance the contrast between plaque covered and clean tooth areas. To remove clean tooth areas from the images subtract the green channel image series from the enhanced red channel image series by clicking Edit, Image calculator, Second operand images, planimetry green, Subtraction, Apply, and then OK.To identify the plaque covered areas on the teeth, perform a threshold base segmentation, and merge the remaining objects as demonstrated earlier.

for quantification of the total tooth area Quantify the total plaque covered areas in each image by sequentially clicking on Analysis, Measure objects, Clear all, and then Pixels. Finally, export the data. Open the exported data tables in dedicated software and calculate the planimetric plaque index, PPI, according to equation one.

Plaque deposits are visualized by erythrosine, while clean tooth areas and the acquired pellicle are left unstained. Images acquired with a fluorescence camera considerably enhance the contrast between the clean tooth areas, plaque covered areas, and surrounding soft issues. Compared to the clean tooth areas, the plaque covered areas appear slightly brighter in the red channel.

In the green channel the autofluorescence of the tooth is masked considerably in the plaque covered areas. This masking effect is exploited to subtract the green channel images from the red channel. The strong contrast between the clean and plaque covered areas in the resulting images allows for an intensity threshold based semi-automated determination of the PPI.

The described method can be used for planimetric recordings of the super gingival plaque and calculus on both facial and oral tooth surfaces. Different tooth colored materials fluoresce in the green spectrum with varying intensities. Hence, the PPI can usually be determined with a standard image analysis algorithm on teeth with glass ionomer cement and composite restorations.

In contrast, amalgam and cast restorations usually emit faintly in both the red and the green channels, and it is thus not possible to determine the plaque coverage on such surfaces. The same holds true for metallic orthodontic brackets, but since the bracket surface is typically excluded from PPI recordings, semi-automated planimetry is suitable for orthodontic patients. In semi-automated identification of plaque covered areas, if too much ambient light enters differentiation between the teeth and soft tissues is difficult.

Insufficient mouth opening hampers the semi-automated processing. When planimetry is performed on pre-molars or molars, correct camera angulation is vital to avoiding imaging parts of the occlusal surface. It's very important to dry the teeth and dim the light in the room before taking an image.

Make sure not to capture antagonist teeth or parts of the occlusal surface.