Mimicking and Measuring Occlusal Erosive Tooth Wear with the "Rub&Roll" and Non-contact Profilometry

The overall goals of this experiment are to apply mechanical loading in an erosive environment to mimic the clinical dental wear process and to use non-contact profilometry for visualization and measurement of the resulting wear pattern. This method can help answering key questions about etiology in erosive tooth wear, such as which factors influence erosive tooth wear and how do they interact? The main advantage of this technique is that it facilitates a simulation of the clinical interplay between chemical and mechanical wear processes.

Though this method can provide insight in etiology and pathogenesis of tooth wear, it can also be applied to other system, such as cyclic loading to mimic fatigue and to test the amount of wear of dental restorations. Begin by using a low-speed hand piece to brush 24 sound extracted human molars with pumice until no debris or gingival remnants remain. When all of the teeth have a smooth surface, rinse each specimen for 15 seconds under running tap water.

Next, melt one 113 gram stick of impression compound on a 50 degree Celsius hot plate for approximately 10 minutes. And dip the occlusal end of the first molar into the molten substance until the entire occlusal surface is covered. Place the molar upside down on a glass microscope slide and press down until all of the cup tips touch the glass.

When all of the molars have been set, use a syringe to dispense 10 milliliters of polymethylmethacrylate, or PMAA mixture, until one 12 x 15 x 27.5 millimeter silicon mold per tooth, and suspend each molar upside down in the PMAA, pressing the slides down until they touch the molds. When all of the samples have been immersed, allow the PMAA to set at room temperature and 1, 000 hectopascals. After 20 minutes, remove the teeth from the molds and use a milling machine equipped with a 16 millimeter milling cutter to adjust the height of each sample to exactly 27.3 millimeters.

To scan the specimens, turn on the profilometer equipment and secure the appropriate sensor with a thumb screw. Carefully insert the optical fiber in the sensor controller and select the correct sensor on the sensor controller. Press F4 twice to display the confocal sensor menu, then press F3 and scroll to 2 to 10, 000 micrometers.

Select 10 millimeters and press F4.Press F1 and select F4 to save the settings to memory, then select LED intensity and adjust the position to plus or minus 9-o'clock. Press F4 then F2 then F4 again to obtain a dark reference of the sensor. Next, open the software and connect to the device.

The measuring table will automatically move to the home position search. Under the tools menu, click sensor selection. Then set sensor S29 to 10 to 10, 000 micrometers.

Set the sample rate 300 Hertz. And the speed sensor to 0 to 100%Under scan, select key move stage and select the yellow area in the middle of the screen to move the measuring table to the center of the viewing area. Place the sensor above the area of interest on the specimen and adjust the distance of the sensor until the complete sample area to be scanned is located within the focus range of the sensor.

When the height is within the range of the sensor, the sensor controller will display a green area in the live data height. Set the average to 2 to ensure that each recorded data point is the average of two measurements. Click OK to return to the main scanning setup and position the sensor beam on the upper left corner of the specimen.

Set the total scan area to 15 x 12 millimeters with the step size of 40 micrometers in the X and Y directions and click scan to begin the scanning, saving the file when the scan is over. To analyze the scanned files, under the warpage menu, apply a warpage filter of 1 to eliminate the noise of the scanning table and sensor, and select the highest point menu to find the highest point on the molar. Under tools, select option scale for the scan configuration and set the offset in millimeters as calculated by the Z value of the highest point minus 3, 500.

Set the range from 0 to 3.6 millimeters and click OK.Then open the load area menu bar to reset the scale and save the file. When all of the molars have been scanned, remove the cylinder from the Rub&Roll machine container and place the molars into the cylinder recesses. To adjust the loading force, place a 1 millimeter shim in the recess underneath eight specimens and a 1.5 millimeter shim under a second set of eight specimens, leaving the last set of eight specimens load free.

Next, mount the two halves of the cylinder, then secure the cylinder with an M6 bolt. Place the cylinder back into the container and fill the container with 500 millimeters of demineralization solution. Insert the loading rod and set the rotation speed to 20 RPM to simulate a relevant clinical chewing frequency.

Without interrupting the rotation, replace the demineralization solution and loading tube and use a calibrated glass electrode to check the pH twice a week. After three months, disconnect the cylinder from the container and disassemble the cylinder to remove the samples. Then scan the specimens as just demonstrated and store them in the ionized water.

For profilometric subtraction of the scanned data, open the original and modified scan files and select manual leveling for the original scanned file and offset for the modified scan file. Under the window menu, select Create View and Cross Section. Select the modified scan file surface and use the control and arrow keys to move the modified file surface over the surface of the original file until the subtracted volume and height appear in the difference view and are as low as possible.

Light microscopy reveals the presence of saucer-shaped lesions on the occlusal cusped tips of molars exposed to three moths of acidic aqueous solution under mechanical loading conditions in the rub and roll, as just demonstrated. This cupping closely resembles the clinical phenomenon associated with erosive tooth wear and is further apparent by color mapping after scanning with a non-contact profilometer, as just demonstrated. Indeed, profilometric scanning before and after exposure allows comparison of the differences in molar cusp tip erosion over time as well as the quantification of the mean occlusal surface height loss for each sample under various mechanical load pressure conditions.

Following this procedure, other processes may be investigated, such as aging of dental restorations, or the development of carious lesions in mechanically loaded teeth. After watching this video, you should have a good understanding how to use the Rub&Roll for mechanical and chemical loading in simulated chewing movements under controlled force, velocity, fluids and time conditions.