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Molar Root Canal Measuring
The root canal of a patient's molar is measured using VR techniques.

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Molar Root Canal Measuring

New : "the movie"

5.5 MB mpeg movie

The Procedure

Obtaining the CT volume data is done using the Localized CT method developed at the ACTA Dental Radiology group and is not covered by the scope of this webpage.

The method described here assumes a series of slides containing 16-bit grayscale voxel values, suitable for volume rendering. From this data, the iso-surface for a given threshold value is extracted, using the VTK Marching Cubes implementation. This isosurface, along with the original data slices are brought to an immersive virtual environment, like the CAVE. Using the experimental VIRPI 3D user interface the tooth is visualized in a virtual laboratory (figure 1).

figure 1: The isosurface of the patient's molar, surrounded by a VIRPI Manipulator (to rotate and scale the tooth). The green vertical line in the center is a flexible measuring stick, which has it's length displayed in the background (currently, 1.5 units).

The tooth is surrounded by the handles of a manipulator (the transparent green cylinders in figure 1). Using this, the user can rotate the tooth to get a better view at specific features (figure 2). The manipulator acts similar to the manipulators presented in SGI's Open Inventor system.

figure 2: The user rotates the tooth by dragging the cylinder.

As the user moves the pointer (in a CAVE this would be the Wand) inside the tooth, the corresponding volume data slices appear. From this, the user can navigate accurately inside the volume of the tooth, in order to place the points of the flexible measurement stick. The stick is a cubic Catmull-Rom spline, governed by four control points which the user can specify. Figure 3 shows how the user places the first control point in the peak of the root canal.

figure 3: The user places the first spline control point in the peak of the root canal. Note that the indicated length of the stick changes as the user moves the control point.

The original volume data stays on the same height as the pointer, indicating the true data from the CT scan. With this, the user can place all control points accurately in the tooth (figure 4).

figure 4: The user places the last control point in the top of the molar, between the two ivory lobes.

To see if the measuring stick is positioned correctly, the user can rotate the tooth to various orientations. If a control point is not correctly placed, the user can modify it (figure 5).

figure 5: From a different angle, we see that the user has misplaced the third control point. He can modify it's position in order to make the flexible stick more straight (giving a better estimate of the length).

Finally, when all control points are in place, the indicator shows how long the measuring stick (and thus the root canal) is. In the case of figure 6, it is 2.22 units.

figure 6: The measuring stick is in place and the length of the root canal is indicated (here 2.22 units).