The measurements were made between the centers of the high-precision cylinders.

<p>Three 3D CAD models of the cylinders in the model were imported and registered with each of the scanned equivalents. The distance between the centre-lines was measured in the software using a linear measurement tool. The angular deflection of the cylinders was measured with an angular measurement tool, using the cylinder at the location of the lower right molar as the baseline.</p

The distance errors between the cylinders 1 and 3 in millimeters for the three intra-oral scanners.

<p>The smallest distance error between cylinders 1 and 3 was −32,0 µm (iTero), while the largest error was −171,1 µm (CEREC). The Lava COS scanner showed the smallest mean distance error and also showed the smallest variations.</p

The angulation errors between the cylinders 1 and 2 in degrees for the three intra-oral scanners.

<p>The angulation errors were small and ranged from −0,0061° (CEREC) to 1,8585° (CEREC). The Lava COS showed the smallest mean angulation error and also the smallest variations. The Lava COS also showed only positive errors.</p

The distance errors between the cylinders 1 and 2 in millimeters for the three intra-oral scanners.

<p>The smallest distance error between cylinders 1 and 2 was −22,0 µm (Lava COS), while the largest error was −287,5 µm (CEREC). The Lava COS scanner showed the smallest mean distance error and also showed the smallest variations.</p

The technical principle of the iTero scanner.

<p>The iTero scanner uses confocal laser scanning in which a laser beam (red) is projected on an object. Via a beam splitter, the reflected beam (purple) is led through a focal filter so that only the image that lies in the focal point of the lens can project on the sensor. As the focal distance is known, the distance of the scanned part of the object to the lens is known (the focal distance). To scan the whole object, the lens is moved up and down, each time projecting a part of the object onto the sensor.</p

The hi-res scanning protocol for the Lava COS scans.

<p>The scanning protocol for the scans for the Lava COS is the normal scanning protocol, except that the scan-path is a slow zigzag scan and that at the end of the scan a second calibration is performed.</p

The technical principle of the CEREC scanner.

<p>The Cerec projects a light stripe pattern on the object. As each light ray is reflected back on the sensor, the distance between the projected ray and reflected ray is measured. Because the fixed angle between the projector and sensor is known, the distance to the object can be calculated through Pythagoras theorem, as one side and one angle (the fixed angle) of the triangle are now known. Hence the name “triangulation”.</p

Absolute errors in the angle between the cylinders in degrees.

<p>Absolute errors in the angle between the cylinders in degrees.</p

The technical principle of the Lava COS scanner.

<p>The Lava COS uses “active wavefront sampling” to calculate the 3D model of the teeth. For this the image reflected from the teeth is led through a lens system and eventually projected onto a sensor. If the image is in focus, the distance of the object coincides with the focal length of the lens. If the image is out of focus, the distance from the lens to the object can be calculated from the size of the blurred image through a simple mathematical formula.</p

The angulation errors between the cylinders 1 and 3 in degrees for the three intra-oral scanners.

<p>The angulation errors were small and ranged from −0,1447° (CEREC) to 1,0456° (CEREC). The iTero showed the smallest mean angulation error. The Lava COS showed the smallest variations. The Lava COS showed only positive errors, while the iTero showed only negative errors. Only the Lava COS showed consistent positive errors in all cases, this could be regarded as an offset which may be compensated.</p