Accuracy in Dental Medicine, A New Way to Measure Trueness and Precision

The overall goal of the following experiment is to demonstrate the measurement accuracy possible with a reference scanner. This is achieved by preparing a specimen and using the reference scanner to scan it as a second step. The scanned image is edited and aligned with a previous scan of the specimen.

Next, a difference analysis is performed in order to show variations between scans. Results are obtained that show the reference scanner has a high accuracy and offers benefits for evaluating impression accuracy. The main advantage of this technique over existing methods like coordinate measure machines, is that you can scan individual detailed mythology structures.

Though this method can provide new insight into tenile impression techniques, it can also be applied to other systems such as measuring surface roughness, erosion, and operation. Begin by preparing a specimen for study. This metal reference model will be used for this video, place this specimen on a surface and apply putty around it.

After the putty has been applied, it should appear like this. Flatten the putty to create a flat base around the specimen. The specimen is now ready for use in the protocol.

Next place the specimen on the scanning table of the reference scanner. Orient the occlusal surface to the horizontal plane. Then start the software, including the laboratory measurement module via software.

Use the motor control of the instrument to ensure the specimen is at the center of the scanning surface. Now choose the correct magnification lens in this case. The five x objective.

Move the scan optic by using the 3D mouse until the surface of the specimen is displayed. Live on the view window. Go to the sensor control panel.

Set exposure and contrast to achieve optimal scanning parameters. Check the show image quality in live preview button for feedback. Adjust the settings if necessary.

Next, go to the measurement control panel. Set the measurement type to 3D dataset. Set the image field type to general image field.

Then click on new image field. To define the scan volume first, use the 3D mouse to move the specimen to the highest level. Click add position.

Then move the specimen to the lowest scan level and click add position. The Z range value shows the actual height of the scan volume. Repeat similar steps in the x and Y directions.

The dimensions of the scan volume are shown under the information tab. Click on advanced settings as configured. The number of surface points to be scanned exceeds the software capabilities.

Move the lateral down sampling slider to the right until points is reduced below 100 million. Now click on start measurement to start the preview mode and begin a pre-scan of the volume once the pre-scan is complete. After about 20 minutes, select the region of interest.

This helps reduce file size and scanning time. Click on start to begin the scan. After 24 to 36 hours, the scan will be completed.

Once it is ready, the scan will appear in the image viewer. Hold down the left mouse button and move the mouse to control the view in the image viewer. Proceed by clicking on view pseudo color only.

Click on settings and pseudo coloring. Next, choose repeatability. Set the max value to 0.2.

Click on apply range. This view gives an estimate of the repeatability of the measurements at each point. The base should show a homogenous repeatability as should areas with the same incline and material.

When done, click on database and save the scan. Continue work with the scan in the 3D editor to perform a difference analysis. First, use the 3D editor to cut away the base and save the image.

Start the difference measurement software. Then load the sample image in that of a second model. For comparison, click on automatic rough alignment to perform a rough match of models.

Next, click on manual adjustment. Align the models until they're in the same orientation. Click automatic alignment and apply to start the best fit algorithm for optimal model matching.

After the alignment is completed, click on differences. To view the difference map of the two matched models, select a color range to display deviations. Save this visual deviation pattern as a screenshot for analysis.

When verifying scanner accuracy, different images like this one can be used to visualize the limitations of the scanning process. Areas with steep inclines, like the palatal aspect of the incisors shown here, showed higher local deviations. Because of the lower scanning quality of the surface, the deviations caused by different impression methods were significantly higher than the internal accuracy of the reference scanning system.

The difference images of different impression methods compared with the master model are shown here. Purple and blue indicate a more negative deviation, green and red, a more positive deviation on the left. The conventional impression method shows positive and negative defamations towards the distal end of the dental arch.

On the right, the digital impression has higher deviations, especially towards the distal teeth. Abrasion of dental materials can also be studied. Here's a test specimen before and a chewing simulation surface loss is visible in the difference image with orange corresponding to small differences and purple to large mean vertical loss of height and the volume changes can be measured with the difference analysis software.

This makes in vivo and in vitro tests of different restorative materials possible Following this procedure. Other methods like micro CT and optical occurrence tomography can be performed in order to answer additional questions like structural changes in dental tissue and material After its development. This technique paved the way for researchers in the field of dentistry to explore many single procedural steps in restoration fabrication processes.