This study was supported by a grant of the Korea Health Technology R&#38;D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health &#38; Welfare (grant number: HI18C0435).

1. Master specimen preparation
<ol>
	<li>Model preparation
	<ol>
		<li>Remove the artificial teeth (left and right canines, second premolar, and the second molar) on the mandibular complete-arch model with only 1/5 of the cervical portion left.</li>
	</ol>
	</li>
	<li>CAD design
	<ol>
		<li>Acquire the data of the master specimen with a reference scanner.</li>
		<li>Design the cylinders (with a top diameter of 2 mm and a cylinder height of 7 mm) on top of the trimmed six teeth with the reverse engineering software.</li>
		<li>Add three reference spheres (3.5 mm in diameter) posterior to the left second molar for the purpose of defining the reference 3D coordinate system from the reverse engineering software.</li>
		<li>Locate one sphere on the distal side of the distal and buccal side of the cylinder on the left second molar so that the coordinates of all the cylinders have positive values.</li>
		<li>Design the left second molar cylinder so that it is inclined 30&#176; medially and the right second molar cylinder so that it is tilted 30&#176; distally. Set the other cylinders at right angles from the model.</li>
	</ol>
	</li>
	<li>Metal 3D printing
	<ol>
		<li>Manufacture a phantom model with CoCr alloy by a metal 3D printer to serve as a patient&#8217;s dentition (Figure 1).</li>
	</ol>
	</li>
</ol>
2. Reference data acquisition and software analysis
<ol>
	<li>Scan the phantom with the testing intraoral scanner.
	<ol>
		<li>Obtain the reference image by scanning the metal phantom model with the industrial-level model scanner.</li>
	</ol>
	</li>
	<li>Establish a coordinate system by extracting points from reference spheres.
	<ol>
		<li>Load the reference image to the reverse engineering analysis software to calculate the reference coordinates of each cylinder position.</li>
		<li>Extract the sphere by selecting the Ref. geometry | Create | Sphere | Pick boundary points command and picking the four points on the surface of the reference sphere that are furthest apart from each other (Supplemental Figure 1 and Supplemental Figure 2).</li>
		<li>Calculate the center of three reference spheres.</li>
		<li>Use the Ref. geometry | Create | Plane | Pick points command to connect the centers of three spheres and create a plane (Supplemental Figure 3).</li>
		<li>Set the formed plane as XY plane.</li>
		<li>Select the Ref. geometry | Create | Plane | Offset plane command to create a tangent plane above the xy plane (Supplemental Figure 4).</li>
		<li>Create points where the tangent plane and two lingual spheres meet by choosing the Ref. geometry | Create | Point | Project on ref. plane command (Supplemental Figure 5).</li>
		<li>Generate a plane between the points created and the center of the two lingual spheres by using the Ref. geometry | Create | Plane | Pick points command (Supplemental Figure 6).</li>
		<li>Measure the distance from this plane to the center of the buccal sphere with the Inspection | Dimension | Linear command (Supplemental Figure 7).</li>
		<li>Create a parallel plane that passes through the midpoint of the buccal sphere with the Geometry | Create | Plane | Offset Plane command (Supplemental Figure 8).</li>
		<li>Set the formed plane as YZ plane (Supplemental Figure 9).</li>
	</ol>
	</li>
	<li>Set the x, y, and z axes.
	<ol>
		<li>Set the center of the buccal sphere as the &#8216;origin&#8217; of the coordinate system.</li>
		<li>Set a line parallel to the line connecting the center points of the remaining two spheres while traveling in the forward and backward direction of the model through the origin as the Y-axis.</li>
		<li>Set the line on the xy plane that passes the origin and is perpendicular to the y axis as the X-axis.</li>
		<li>Use the Ref. geometry | Create | Coordinate | Pick origin &#38; X, Y direction command to create a new coordinate system with the buccal sphere center as the origin (Supplemental Figure 10).</li>
		<li>Set the line perpendicular to the xy plane and passing through the origin as the Z-axis (Supplemental Figure 11).</li>
	</ol>
	</li>
	<li>Transfer this detail from the scan coordinate system to the newly established coordinate system.
	<ol>
		<li>Use the Ref. geometry | Bind to shell command to fix the geometries created during this process on top of the scan data (Supplemental Figure 12).</li>
		<li>Execute the Ref. geometry | Transform | Coordinate | Align coordinate command to transit from the basic coordinate system to the newly created coordinate system (Supplemental Figure 13).</li>
		<li>In this way, assign a coordinate system to the metal master specimen with reference to the three reference spheres (Supplemental Figure 14).</li>
	</ol>
	</li>
	<li>Extract the measurement points from the cylinders at the main area.
	<ol>
		<li>Extract the x, y, and z coordinates for the upper circle centers of six cylinders to be analyzed for the distortion of the specified regions by the reverse engineering process.</li>
		<li>For this, use the Ref. geometry | Create | Cylinder | Pick boundary points command and specify at least 10 points on the top border of the cylinder and designate the same amount of points on the ellipse that meets the tooth at the bottom of the cylinder (Supplemental Figure 15, Supplemental Figure 16, and Supplemental Figure 17).</li>
		<li>Obtain the extracted coordinates of the cylinder top center. Evaluate the 3D deformation at each position by comparing it with the coordinate values of the same cylinder of the digital impression acquired by the intraoral scanner to be evaluated.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

Among the studies evaluating the accuracy of the intraoral scanner by evaluating the resultant digital impression body, the most common method is to superimpose the digital impression data on the reference image and calculate the shell-to-shell deviation12,13,14,15,20,23. However, this method is limited to calculating the deviation value from the paired data or evaluating the distribution qualitatively through the color map. In a study which measured the deviation of the local site by selecting points to be analyzed on the color map, the deviation in the x, y, and z direction was not considered29. In addition, these methods have limitations in that they should be analyzed after overlapping with reference data. Alignment can vary from one data point to another, and the results vary depending on the sorting criteria. In clinical trials involving patients, it is difficult to apply these methods because it is not possible to scan the complete dental arch through the mouth with an industrial scanner located outside the oral cavity. 
In this study, a master specimen made of metal, which is less affected by temperature and humidity, was proposed. The coordinate system for the specific 3D-printed metal specimen was set and the six cylinders' position coordinates were calculated in advance. In this way, regardless of the intraoral scanner, an individual coordinate system was formed from each digital impression through the reference spheres of the scan data so that the analysis could be performed with the scanned data only, without the reference image superimposition. The reference image obtained with the high-precision industrial reference scanner was used only to acquire the coordinate values of the six cylinders when the metal master specimen was first produced. The comparative evaluation between the reference and intraoral scan data was done just by simple arithmetic calculation through coordinate values. In addition, since the deviations in the x, y, and z directions of the cylinder coordinates were expressed as positive and negative values, 3D positional changes were shown for each region. Therefore, the method used in this study is suitable for evaluating the data distortion of the handheld device, the oral scanner. Since the deviation of the cylinder coordinates in the x, y, and z direction was displayed with positive and negative values, a 3D position change of each location becomes obvious. Therefore, the method used in this study is suitable for evaluating the distortion of digital impression data acquired with the handheld intraoral scanner.
Most of the coordinate values of each cylinder calculated from the original CAD data and the reference image of the metal master specimen showed values of less than 50 &#181;m. This is related to the performance peculiar to metal 3D printers. Since the master specimen after 3D printing is used as a new reference rather than using standard CAD data, the limitations of these 3D printers do not need to be considered. The change in the master specimen was large at the z coordinate of the right second molar. It was because the cylinder was tilted distally and the length of the cylinder exposed above the tooth was short, which was disadvantageous for the reverse engineering process. Also, the cylinder's upper circle of this tooth was inclined to the xy plane of the 3D printer when metal printing was performed in this study. It seems that the characteristics of the 3D printer, in which xy accuracy and z accuracy are expressed separately, were also reflected. In future research, designing and using all cylinders without tilting can be a good alternative.
If there is a cost problem in fabricating a master specimen with a metal 3D printer, it can be made of gypsum or resin. As the new coordinate system was set and the coordinates of the six cylinders were calculated after specimen fabrication, the dimensional change that could be caused by the expansion and contraction of the material during the manufacturing process does not affect the final result. However, when using such a specimen for a long period of time, there may be a slight volume change due to moisture and temperature, and there is a possibility that it will be deformed due to breakage or abrasion. Therefore, a calibration procedure is required to periodically calculate the cylinder coordinate value with a reference scanner. In addition, instead of using an industrial reference scanner, the coordinate measuring machine (CMM) may be used to measure the reference coordinates of the master specimen. In this case, it is recommended to carry out a superimposing investigation with reference data for the purpose of evaluating the complicated tooth surface in addition to the deviation inspection through the coordinates of cylinders.
The limitations of this method are that the time required for reverse engineering analysis becomes longer when the number of digital impressions to be evaluated increases. However, recently introduced 3D image analysis software enables inspection automation through a macro function. Since the global shape of the master specimen is the same, it is possible to shorten the analysis time by automating the coordinate system setting and the cylinder coordinate calculation of the acquired digital impression.
By measuring the degree of distortion in each part of the complete-arch digital impression as a numerical value, it can be used to find and improve the inherent problems of the intraoral scanner to be evaluated for its performance. Since the intraoral scanner is a complicated optical device consisting of a projection lamp, a lens, a lens barrel, a camera, etc., hardware consideration factors are large. Also, a software algorithm that enables stitching together the acquired 3D data in real-time at more than 30 frames per second is also important19. It is possible to evaluate and improve the performance of the intraoral scanner by understanding the relationship between the recurrence pattern of the metal master specimen and the consideration factors of intraoral scanners. The scanning strategy determined by the direction and sequence of acquiring images is also an important element for acquiring digital impressions30. This method can be used to establish a strategy that minimizes deformation.

In the traditional dental treatment process, a fixed restoration or a removable denture is made on a model made of gypsum and impregnated with a silicone or irreversible hydrocolloid material. Because an indirectly made prosthesis is delivered in the oral cavity, a lot of research has been done to overcome the errors caused by a series of such manufacturing processes1,2. Recently, a digital method is used to fabricate a prosthesis through the CAD process by manipulating models in the virtual space after acquiring 3D images instead of making impressions3. In the early days, such an optical impression method was used in a limited range such as a dental caries treatment of one or a small number of teeth. However, as the base technology of the 3D scanner was developed, a digital impression for the complete arch is now used for the fabrication of large-scale fixed restorations, removable restorations such as a partial or full denture, orthodontic appliances, and implant surgical guides4,5,6,7. The accuracy of the digital impression is satisfactory in a short region such as the unilateral arch. However, since the intraoral scanner is a handheld device that completes the entire dentition by stitching together the image obtained through a narrow optical window, the distortion of the model can be seen after completing the U-shaped dental arch. Thus, an appliance of a large range made on this model might not fit well in the patient&#39;s mouth and require a lot of adjustment.
Various studies have been reported on the accuracy of the virtual impression body obtained with an intraoral scanner, and there are various research models and measurement methods. Depending on the research subject, it can be divided into clinical research8,9,10,11,12 for actual patients and in vitro studies13,14,15,16 conducted in models separately produced for research. Clinical studies have the advantage of being able to evaluate the conditions of an actual clinical setting, but it is difficult to control the variables and increase the number of clinical cases indefinitely. The number of clinical studies is not large because there is a limit to being able to evaluate the desired variables. On the other hand, many in vitro studies that evaluate the basic performance of the intraoral scanner by controlling variables have been reported17. The research model also includes a partial or complete arch of natural teeth18,19,20,21,22 and a fully edentulous jaw with all teeth lost23, or the case where the dental implant is installed and spaced apart at a certain interval24,25,26,27, or a form in which the majority of the teeth remain and only a part of a tooth is missing16,28. However, studies on the distortion of the virtual impression body made by a handheld intraoral scanner have been limited to the qualitative evaluation of deviations through a color map created by superimposing it with reference data and expressed as one numerical value per data. It is difficult to accurately measure the 3D distortion of the complete arch because most studies only examine the localized portion of the dental arch with a nondirectional distance deviation.
In this study, the distortion of the dental arch during optical impression with an intraoral scanner is investigated by using a standard model with a coordinate system. The aim of this study is to provide information on a method for evaluating the accuracy performance of the intraoral scanners which exhibit various characteristics by the difference in optical hardware and processing software.

<table><tbody><tr><td>EOS CobaltChrome SP2</td><td>Electro Oprical Systems</td><td>H051601</td><td>Powder type metal alloy for 3D printing</td></tr><tr><td>Geomagic Verify</td><td>3D Systems</td><td>2015.2.0</td><td>3D inspection software</td></tr><tr><td>Prosthetic Restoration Jaw Model</td><td>Nissin Dental Products Inc.</td><td></td><td>Mandibular complete-arch model</td></tr><tr><td>Rapidform</td><td>Inus technology</td><td>RF90600-10004-010000</td><td>Reverse engineering software</td></tr><tr><td>stereoSCAN R8</td><td>AICON 3D Systems GmbH</td><td></td><td>Industrial-level model scanner</td></tr></tbody></table>

measuring the complete-arch distortion of an optical dental impression

Digital workflows have actively been used to produce dental restorations or oral appliances since dentists started to make digital impressions by acquiring 3D images with an intraoral scanner. Because of the nature of scanning the oral cavity in the patient&#39;s mouth, the intraoral scanner is a handheld device with a small optical window, stitching together small data to complete the entire image. During the complete-arch impression procedure, a deformation of the impression body can occur and affect the fit of the restoration or appliance. In order to measure these distortions, a master specimen was designed and produced with a metal 3D printer. Designed reference geometries allow setting independent coordinate systems for each impression and measure x, y, and z displacements of the cylinder top circle center where the distortion of the impression can be evaluated. In order to evaluate the reliability of this method, the coordinate values of the cylinder are calculated and compared between the original computer-aided design (CAD) data and the reference data acquired with the industrial scanner. The coordinate differences between the two groups were mostly less than 50 &#181;m, but the deviations were high due to the tolerance of 3D printing in the z coordinates of the obliquely designed cylinder on the molar. However, since the printed model sets a new standard, it does not affect the results of the test evaluation. The reproducibility of the reference scanner is 11.0 &#177; 1.8 &#181;m. This test method can be used to identify and improve upon the intrinsic problems of an intraoral scanner or to establish a scanning strategy by measuring the degree of distortion at each part of the complete-arch digital impression.

The coordinates of each cylinder calculated from the originally designed CAD data and the reference scan image of the 3D-printed metal master specimen scanned by the industrial-level model scanner are shown in Table 1. The difference between the two showed a value of lower than 50 &#181;m, but the z coordinate value of the right second molar cylinder from the 3D-printed master specimen was low. Although the metal phantom was produced from a high-end industrial 3D printer, a small difference in the height of one cylinder was found. While the design was done with CAD software, the metal phantom was used as a reference which was scanned with the various testing intraoral scanners, and the difference was negligible. If another evaluator fabricates a new phantom from the same shared data and executes the same process, the phantom should be scanned again with an industrial-level reference scanner to obtain reference coordinates and then proceed with the subsequent process. Table 2 shows the coordinates of the master specimen which was scanned five times with an industrial scanner. Evaluating from the standard deviation, the average deviation was 45 &#181;m, showing a large deviation in the y coordinate value of the right second molar cylinder. It could be concluded that the precision of the reference scanner was good enough for extracting the reference coordinates of point zero and six cylinders.
The evaluation of the reproducibility of the reference scanner was conducted through overlap comparison among five datasets of the metal master specimen scanned with the reference scanner. A total of 10 pairs were aligned and evaluated. The deviation of each pair resulted in reproducibility of 0.011 &#177; 0.002 mm (Table 3). The reproducibility of the reference scanner was calculated differently, and it was concluded that the results from both methods were reliable and the latter could be omitted.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/59261/59261fig01.jpg" /> 
Figure 1: Design and manufacturing process of a phantom model for the distortion evaluation. (A) Originally designed CAD data. (B) 3D-printed master specimen made of CoCr alloy. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 1" src="/files/ftp_upload/59261/59261fig1.jpg" /> 
Supplemental Figure 1: Extract sphere picking points. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/59261/59261fig2.jpg" /> 
Supplemental Figure 2: Picking points on the surface of the reference sphere. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/59261/59261fig3.jpg" /> 
Supplemental Figure 3: Creation of the XY plane by picking the center of three spheres. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/59261/59261fig4.jpg" /> 
Supplemental Figure 4: Creation of the offset plane, half a diameter of the sphere above the XY plane. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/59261/59261fig5.jpg" /> 
Supplemental Figure 5: Creation of the points where the offset plane and two lingual spheres meet. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" src="/files/ftp_upload/59261/59261fig6.jpg" /> 
Supplemental Figure 6: Creation of the plane that passes both centers of the lingual spheres by picking four points. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" src="/files/ftp_upload/59261/59261fig7.jpg" /> 
Supplemental Figure 7: Measurement of the distance from this plane to the center of the buccal sphere. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" src="/files/ftp_upload/59261/59261fig8.jpg" /> 
Supplemental Figure 8: Creation of the parallel plane that passes through the center of the buccal sphere. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" src="/files/ftp_upload/59261/59261fig9.jpg" /> 
Supplemental Figure 9: Setting of the formed plane as YZ plane. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig9large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" src="/files/ftp_upload/59261/59261fig10.jpg" /> 
Supplemental Figure 10: Creation of a new coordinate system with the center of the buccal sphere as origin. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 11" src="/files/ftp_upload/59261/59261fig11.jpg" /> 
Supplemental Figure 11: Setting of the line perpendicular to the XY plane and passing through the buccal sphere center as the Z-axis. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig11large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 12" src="/files/ftp_upload/59261/59261fig12.jpg" /> 
Supplemental Figure 12: Fixing of the created geometries to the scan data. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig12large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 13" src="/files/ftp_upload/59261/59261fig13.jpg" /> 
Supplemental Figure 13: Transfer of the basic coordinate system to the newly created coordinate system. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig13large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 14" src="/files/ftp_upload/59261/59261fig14.jpg" /> 
Supplemental Figure 14: Checking whether the origin and coordinate system are correctly moved to the one extracted from the scan data. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig14large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 15" src="/files/ftp_upload/59261/59261fig15.jpg" /> 
Supplemental Figure 15: Using the Pick boundary points command to extract the cylinder. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig15large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 16" src="/files/ftp_upload/59261/59261fig16.jpg" /> 
Supplemental Figure 16: Picking sufficient points on the top circle and bottom ellipse around the cylinder. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig16large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 17" src="/files/ftp_upload/59261/59261fig17.jpg" /> 
Supplemental Figure 17: Checking whether the extracted cylinder was reverse engineered correctly. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59261/59261fig17large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td rowspan="2"></td>
			<td rowspan="2"></td>
			<td>CAD</td>
			<td>3D printed</td>
			<td rowspan="2">Difference</td>
		</tr>
		<tr>
			<td>data</td>
			<td>metal master specimen</td>
		</tr>
		<tr>
			<td rowspan="3">37i</td>
			<td>x</td>
			<td>7.897</td>
			<td>7.875</td>
			<td>0.022</td>
		</tr>
		<tr>
			<td>y</td>
			<td>6.418</td>
			<td>6.373</td>
			<td>0.045</td>
		</tr>
		<tr>
			<td>z</td>
			<td>7.312</td>
			<td>7.265</td>
			<td>0.047</td>
		</tr>
		<tr>
			<td rowspan="3">35i</td>
			<td>x</td>
			<td>8.481</td>
			<td>8.427</td>
			<td>0.054</td>
		</tr>
		<tr>
			<td>y</td>
			<td>26.045</td>
			<td>25.99</td>
			<td>0.055</td>
		</tr>
		<tr>
			<td>z</td>
			<td>7.846</td>
			<td>7.846</td>
			<td>0</td>
		</tr>
		<tr>
			<td rowspan="3">33i</td>
			<td>x</td>
			<td>11.889</td>
			<td>11.85</td>
			<td>0.04</td>
		</tr>
		<tr>
			<td>y</td>
			<td>40.16</td>
			<td>40.106</td>
			<td>0.054</td>
		</tr>
		<tr>
			<td>z</td>
			<td>8.346</td>
			<td>8.409</td>
			<td>-0.063</td>
		</tr>
		<tr>
			<td rowspan="3">43i</td>
			<td>x</td>
			<td>37.246</td>
			<td>37.196</td>
			<td>0.051</td>
		</tr>
		<tr>
			<td>y</td>
			<td>45.738</td>
			<td>45.686</td>
			<td>0.052</td>
		</tr>
		<tr>
			<td>z</td>
			<td>9.445</td>
			<td>9.5</td>
			<td>-0.055</td>
		</tr>
		<tr>
			<td rowspan="3">45i</td>
			<td>x</td>
			<td>47.21</td>
			<td>47.178</td>
			<td>0.032</td>
		</tr>
		<tr>
			<td>y</td>
			<td>35.115</td>
			<td>35.081</td>
			<td>0.034</td>
		</tr>
		<tr>
			<td>z</td>
			<td>8.707</td>
			<td>8.708</td>
			<td>-0.001</td>
		</tr>
		<tr>
			<td rowspan="3">47i</td>
			<td>x</td>
			<td>56.397</td>
			<td>56.386</td>
			<td>0.011</td>
		</tr>
		<tr>
			<td>y</td>
			<td>13.038</td>
			<td>13.041</td>
			<td>-0.002</td>
		</tr>
		<tr>
			<td>z</td>
			<td>7.558</td>
			<td>7.451</td>
			<td>0.107</td>
		</tr>
	</tbody>
</table>
Table 1: Differences in cylinders&#8217; coordinates between CAD data and the 3D-printed metal master specimen. Unit: mm.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td></td>
			<td></td>
			<td>Ref. 1</td>
			<td>Ref. 2</td>
			<td>Ref. 3</td>
			<td>Ref. 4</td>
			<td>Ref. 5</td>
			<td>Mean &#177; SD</td>
		</tr>
		<tr>
			<td rowspan="3">37i</td>
			<td>x</td>
			<td>7.856</td>
			<td>7.874</td>
			<td>7.871</td>
			<td>7.89</td>
			<td>7.885</td>
			<td>7.875 &#177; 0.013</td>
		</tr>
		<tr>
			<td>y</td>
			<td>6.406</td>
			<td>6.375</td>
			<td>6.358</td>
			<td>6.356</td>
			<td>6.368</td>
			<td>6.373 &#177; 0.020</td>
		</tr>
		<tr>
			<td>z</td>
			<td>7.259</td>
			<td>7.274</td>
			<td>7.269</td>
			<td>7.265</td>
			<td>7.258</td>
			<td>7.265 &#177; 0.007</td>
		</tr>
		<tr>
			<td rowspan="3">35i</td>
			<td>x</td>
			<td>8.435</td>
			<td>8.379</td>
			<td>8.393</td>
			<td>8.471</td>
			<td>8.46</td>
			<td>8.427 &#177; 0.040</td>
		</tr>
		<tr>
			<td>y</td>
			<td>26.032</td>
			<td>25.98</td>
			<td>25.996</td>
			<td>25.962</td>
			<td>25.979</td>
			<td>25.990 &#177; 0.026</td>
		</tr>
		<tr>
			<td>z</td>
			<td>7.838</td>
			<td>7.883</td>
			<td>7.837</td>
			<td>7.858</td>
			<td>7.816</td>
			<td>7.846 &#177; 0.025</td>
		</tr>
		<tr>
			<td rowspan="3">33i</td>
			<td>x</td>
			<td>11.839</td>
			<td>11.779</td>
			<td>11.794</td>
			<td>11.925</td>
			<td>11.91</td>
			<td>11.850 &#177; 0.066</td>
		</tr>
		<tr>
			<td>y</td>
			<td>40.129</td>
			<td>40.085</td>
			<td>40.112</td>
			<td>40.097</td>
			<td>40.106</td>
			<td>40.106 &#177; 0.017</td>
		</tr>
		<tr>
			<td>z</td>
			<td>8.372</td>
			<td>8.485</td>
			<td>8.391</td>
			<td>8.414</td>
			<td>8.381</td>
			<td>8.409 &#177; 0.046</td>
		</tr>
		<tr>
			<td rowspan="3">43i</td>
			<td>x</td>
			<td>37.177</td>
			<td>37.115</td>
			<td>37.155</td>
			<td>37.269</td>
			<td>37.262</td>
			<td>37.196 &#177; 0.068</td>
		</tr>
		<tr>
			<td>y</td>
			<td>45.711</td>
			<td>45.723</td>
			<td>45.725</td>
			<td>45.622</td>
			<td>45.65</td>
			<td>45.686 &#177; 0.047</td>
		</tr>
		<tr>
			<td>z</td>
			<td>9.437</td>
			<td>9.568</td>
			<td>9.541</td>
			<td>9.498</td>
			<td>9.457</td>
			<td>9.500 &#177; 0.055</td>
		</tr>
		<tr>
			<td rowspan="3">45i</td>
			<td>x</td>
			<td>47.15</td>
			<td>47.123</td>
			<td>47.142</td>
			<td>47.246</td>
			<td>47.23</td>
			<td>47.178 &#177; 0.056</td>
		</tr>
		<tr>
			<td>y</td>
			<td>35.109</td>
			<td>35.148</td>
			<td>35.135</td>
			<td>34.988</td>
			<td>35.025</td>
			<td>35.081 &#177; 0.071</td>
		</tr>
		<tr>
			<td>z</td>
			<td>8.609</td>
			<td>8.785</td>
			<td>8.728</td>
			<td>8.738</td>
			<td>8.681</td>
			<td>8.708 &#177; 0.067</td>
		</tr>
		<tr>
			<td rowspan="3">47i</td>
			<td>x</td>
			<td>56.369</td>
			<td>56.373</td>
			<td>56.371</td>
			<td>56.409</td>
			<td>56.407</td>
			<td>56.386 &#177; 0.020</td>
		</tr>
		<tr>
			<td>y</td>
			<td>13.085</td>
			<td>13.122</td>
			<td>13.114</td>
			<td>12.923</td>
			<td>12.959</td>
			<td>13.041 &#177; 0.093</td>
		</tr>
		<tr>
			<td>z</td>
			<td>7.349</td>
			<td>7.445</td>
			<td>7.457</td>
			<td>7.527</td>
			<td>7.478</td>
			<td>7.451 &#177; 0.065</td>
		</tr>
	</tbody>
</table>
Table 2: Cylinders&#8217; coordinates of reference datasets acquired from the 3D-printed metal master specimen. Unit: m.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Precision</td>
			<td>1</td>
			<td>2</td>
			<td>3</td>
			<td>4</td>
			<td>5</td>
			<td>6</td>
			<td>7</td>
			<td>8</td>
			<td>9</td>
			<td>10</td>
			<td>Mean &#177; SD</td>
		</tr>
		<tr>
			<td>Reference scanner</td>
			<td>8.3</td>
			<td>12.4</td>
			<td>9.5</td>
			<td>13.2</td>
			<td>11.7</td>
			<td>8</td>
			<td>12.1</td>
			<td>10.7</td>
			<td>12.1</td>
			<td>11.8</td>
			<td>11.0 &#177; 1.8</td>
		</tr>
	</tbody>
</table>
Table 3: Precision of the dataset acquired from the reference scanner. Unit: &#181;m.

Watch this Scientific Journal Video about Measuring the Complete-arch Distortion of an Optical Dental Impression at JoVE.com

Measuring the Complete-arch Distortion of an Optical Dental Impression

Here, we present a protocol to measure the degree of distortion at each part of the compete-arch digital impression acquired from an intraoral scanner with 3D-printed metal phantom with standard geometries.

Digital workflows have actively been used to produce dental restorations or oral appliances since dentists started to make digital impressions by ...

measuring-the-complete-arch-distortion-of-an-optical-dental-impression

Nanyang Technological University

Research

JoVE Journal

Engineering

7.5K Views.  Yonsei University. Intraorale scanners introduceren boogvervorming in gegevens die ze verzamelen voor tandheelkundige processen. Ons coördinatensysteemextractieprotocol biedt een instrument voor het evalueren van intraorale scanners op de markt. Het is van het grootste belang om te transformeren van de willekeurige coördinaten van de intraorale scan naar het nieuw gecreëerde coördinatensysteem met behulp van de referentiesfeer van reverse engineering.Een techniek van de analyse van vervorming in het ...

Video: Measuring the Complete-arch Distortion of an Optical Dental Impression

Construction and Testing of Coin Cells of Lithium Ion Batteries

Rechargeable lithium ion batteries have wide applications in electronics, where customers always demand more capacity and longer lifetime. Lithium ion batteries have also been considered to be used in electric and hybrid vehicles1 or even electrical grid stabilization systems2. All these applications simulate a dramatic increase in the research and development of battery materials3-7, including new materials3,8, doping9, nanostructuring10-13, coatings or surface modifications14-17 and novel binders18. Consequently, an increasing number of physicists, chemists and materials scientists have recently ventured into this area. Coin cells are widely used in research laboratories to test new battery materials; even for the research and development that target large-scale and high-power applications, small coin cells are often used to test the capacities and rate capabilities of new materials in the initial stage. 
 In 2010, we started a National Science Foundation (NSF) sponsored research project to investigate the surface adsorption and disordering in battery materials (grant no. DMR-1006515). In the initial stage of this project, we have struggled to learn the techniques of assembling and testing coin cells, which cannot be achieved without numerous help of other researchers in other universities (through frequent calls, email exchanges and two site visits). Thus, we feel that it is beneficial to document, by both text and video, a protocol of assembling and testing a coin cell, which will help other new researchers in this field. This effort represents the "Broader Impact" activities of our NSF project, and it will also help to educate and inspire students.
In this video article, we document a protocol to assemble a CR2032 coin cell with a LiCoO2 working electrode, a Li counter electrode, and (the mostly commonly used) polyvinylidene fluoride (PVDF) binder. To ensure new learners to readily repeat the protocol, we keep the protocol as specific and explicit as we can. However, it is important to note that in specific research and development work, many parameters adopted here can be varied. First, one can make coin cells of different sizes and test the working electrode against a counter electrode other than Li. Second, the amounts of C black and binder added into the working electrodes are often varied to suit the particular purpose of research; for example, large amounts of C black or even inert powder were added to the working electrode to test the "intrinsic" performance of cathode materials14. Third, better binders (other than PVDF) have also developed and used18. Finally, other types of electrolytes (instead of LiPF6) can also be used; in fact, certain high-voltage electrode materials will require the uses of special electrolytes7.

A protocol to construct and test coin cells of lithium ion batteries is described. The specific procedures of making a working electrode, preparing a counter electrode, assembling a cell inside a glovebox and testing the cell are presented.

Rechargeable lithium ion batteries have wide applications in electronics, where customers always demand more capacity and longer lifetime.  Lithium ion ...

Fabricating Metamaterials Using the Fiber Drawing Method

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe their electromagnetic properties to the structure of their constituents, instead of the atoms that compose them. For example, sub-wavelength metal wires can be arranged to possess an effective electric permittivity that is either positive or negative at a given frequency, in contrast to the metals themselves 2. This unprecedented control over the behaviour of light can potentially lead to a number of novel devices, such as invisibility cloaks 3, negative refractive index materials 4, and lenses that resolve objects below the diffraction limit 5. However, metamaterials operating at optical, mid-infrared and terahertz frequencies are conventionally made using nano- and micro-fabrication techniques that are expensive and produce samples that are at most a few centimetres in size 6-7. Here we present a fabrication method to produce hundreds of meters of metal wire metamaterials in fiber form, which exhibit a terahertz plasmonic response 8. We combine the stack-and-draw technique used to produce microstructured polymer optical fiber 9 with the Taylor-wire process 10, using indium wires inside polymethylmethacrylate (PMMA) tubes. PMMA is chosen because it is an easy to handle, drawable dielectric with suitable optical properties in the terahertz region; indium because it has a melting temperature of 156.6 &deg;C which is appropriate for codrawing with PMMA. We include an indium wire of 1 mm diameter and 99.99% purity in a PMMA tube with 1 mm inner diameter (ID) and 12 mm outside diameter (OD) which is sealed at one end. The tube is evacuated and drawn down to an outer diameter of 1.2 mm. The resulting fiber is then cut into smaller pieces, and stacked into a larger PMMA tube. This stack is sealed at one end and fed into a furnace while being rapidly drawn, reducing the diameter of the structure by a factor of 10, and increasing the length by a factor of 100. Such fibers possess features on the micro- and nano- scale, are inherently flexible, mass-producible, and can be woven to exhibit electromagnetic properties that are not found in nature. They represent a promising platform for a number of novel devices from terahertz to optical frequencies, such as invisible fibers, woven negative refractive index cloths, and super-resolving lenses.

Metamaterials at terahertz frequencies offer unique opportunities, but are challenging to fabricate in bulk. We adapt the fabrication procedure for microstructured polymer optical fibers to inexpensively fabricate metamaterials potentially on an industrial scale. We produce polymethylmethacrylate fibers containing ~10 &mu;m diameter indium wires separated by ~100 &mu;m, which exhibit a terahertz plasmonic response.

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe ...

Shrinkage of Dental Composite in Simulated Cavity Measured with Digital Image Correlation

Polymerization shrinkage of dental resin composites can lead to restoration debonding or cracked tooth tissues in composite-restored teeth. In order to understand where and how shrinkage strain and stress develop in such restored teeth, Digital Image Correlation (DIC) was used to provide a comprehensive view of the displacement and strain distributions within model restorations that had undergone polymerization shrinkage.
Specimens with model cavities were made of cylindrical glass rods with both diameter and length being 10 mm. The dimensions of the mesial-occlusal-distal (MOD) cavity prepared in each specimen measured 3 mm and 2 mm in width and depth, respectively. After filling the cavity with resin composite, the surface under observation was sprayed with first a thin layer of white paint and then fine black charcoal powder to create high-contrast speckles. Pictures of that surface were then taken before curing and 5 min after. Finally, the two pictures were correlated using DIC software to calculate the displacement and strain distributions.
The resin composite shrunk vertically towards the bottom of the cavity, with the top center portion of the restoration having the largest downward displacement. At the same time, it shrunk horizontally towards its vertical midline. Shrinkage of the composite stretched the material in the vicinity of the &#8220;tooth-restoration&#8221; interface, resulting in cuspal deflections and high tensile strains around the restoration. Material close to the cavity walls or floor had direct strains mostly in the directions perpendicular to the interfaces. Summation of the two direct strain components showed a relatively uniform distribution around the restoration and its magnitude equaled approximately to the volumetric shrinkage strain of the material.

In order to understand the spatial development of polymerization shrinkage stress in dental resin-composite restorations, Digital Image Correlation was used to provide full-field displacement/strain measurement of restored model glass cavities by correlating images of the restoration taken before and after polymerization.

Polymerization shrinkage of dental resin composites can lead to restoration debonding or cracked tooth tissues in composite-restored teeth. In order to ...

Medicine

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

Reference scanners are used in dental medicine to verify a lot of procedures. The main interest is to verify impression methods as they serve as a base for dental restorations. The current limitation of many reference scanners is the lack of accuracy scanning large objects like full dental arches, or the limited possibility to assess detailed tooth surfaces. A new reference scanner, based on focus variation scanning technique, was evaluated with regards to highest local and general accuracy. A specific scanning protocol was tested to scan original tooth surface from dental impressions. Also, different model materials were verified. The results showed a high scanning accuracy of the reference scanner with a mean deviation of 5.3 &#177; 1.1 &#181;m for trueness and 1.6 &#177; 0.6 &#181;m for precision in case of full arch scans. Current dental impression methods showed much higher deviations (trueness: 20.4 &#177; 2.2 &#181;m, precision: 12.5 &#177; 2.5 &#181;m) than the internal scanning accuracy of the reference scanner. Smaller objects like single tooth surface can be scanned with an even higher accuracy, enabling the system to assess erosive and abrasive tooth surface loss. The reference scanner can be used to measure differences for a lot of dental research fields. The different magnification levels combined with a high local and general accuracy can be used to assess changes of single teeth or restorations up to full arch changes.

Accuracy is a major demand in dental medicine. To verify accuracy, reference scanners are needed. This article presents a new reference scanner with an adjusted scanning method to acquire a broad variety of dental morphologies with high trueness and precision.

Reference scanners are used in dental medicine to verify a lot of procedures. The main interest is to verify impression methods as they serve as a base ...

Ratiometric Imaging of Extracellular pH in Dental Biofilms

The pH in bacterial biofilms on teeth is of central importance for dental caries, a disease with a high worldwide prevalence. Nutrients and metabolites are not distributed evenly in dental biofilms. A complex interplay of sorption to and reaction with organic matter in the biofilm reduces the diffusion paths of solutes and creates steep gradients of reactive molecules, including organic acids, across the biofilm. Quantitative fluorescent microscopic methods, such as fluorescence life time imaging or pH ratiometry, can be employed to visualize pH in different microenvironments of dental biofilms. pH ratiometry exploits a pH-dependent shift in the fluorescent emission of pH-sensitive dyes. Calculation of the emission ratio at two different wavelengths allows determining local pH in microscopic images, irrespective of the concentration of the dye. Contrary to microelectrodes the technique allows monitoring both vertical and horizontal pH gradients in real-time without mechanically disturbing the biofilm. However, care must be taken to differentiate accurately between extra- and intracellular compartments of the biofilm. Here, the ratiometric dye, seminaphthorhodafluor-4F 5-(and-6) carboxylic acid (C-SNARF-4) is employed to monitor extracellular pH in in vivo grown dental biofilms of unknown species composition. Upon exposure to glucose the dye is up-concentrated inside all bacterial cells in the biofilms; it is thus used both as a universal bacterial stain and as a marker of extracellular pH. After confocal microscopic image acquisition, the bacterial biomass is removed from all pictures using digital image analysis software, which permits to exclusively calculate extracellular pH. pH ratiometry with the ratiometric dye is well-suited to study extracellular pH in thin biofilms of up to 75 &#181;m thickness, but is limited to the pH range between 4.5 and 7.0.

A pH-sensitive ratiometric dye is used in combination with confocal laser scanning microscopy and digital image analysis to monitor extracellular pH in dental biofilms in real-time.

The pH in bacterial biofilms on teeth is of central importance for dental caries, a disease with a high worldwide prevalence. Nutrients and metabolites ...

Immunology and Infection

Roughness Impact of Piezoelectric Dental Scaler on Two Distinct Flowable Composite Filling Materials

Dental ultrasonic scalers are commonly employed in periodontal treatment; however, their ability to roughen tooth surfaces is a worry since roughness may increase plaque production, a key cause of periodontal disease. This research studied the influence of a piezoelectric ultrasonic scaler on the roughness of two distinct flowable composite filling materials. To do this, 10 disc-shaped samples were generated from each of the two flowable composite materials. After standardized polishing, samples were submerged in water for 24 h before the first surface examination using electron microscopy and profilometry. The ultrasonic scaler was applied to a specified location of each sample for 60 s under water cooling and regulated force. Post-scaler surface parameters were again examined. Following the application of the scaler, both composite materials exhibited a notable increase in surface roughness, as determined by profilometry (p &lt; 0.01). Additionally, the observed surface roughness was also qualitatively visualized with scanning electron microscopy. While initial roughness levels were comparable across the two composites (p = 0.143) after scaler application, no substantial discrepancy in surface texture was noticed between them (p = 0.684). The use of a high-power piezoelectric ultrasonic scaler on routinely used flowable composite restorations might generate considerable surface roughness, possibly leading to increased plaque accumulation. Nevertheless, it might be postulated that nanohybrid flowable composite materials having conventional monomer ingredients may demonstrate comparable surface alterations within the limitations of this experiment.

This methodology allows applying a dental appliance on any specimen at any angle with standardized force and stability. This approach might be extensively used in health sciences to standardize the impacts of dental equipment with hand-holding elements such as micromotors, turbines, and ultrasonic scalers on varied surfaces.

Dental ultrasonic scalers are commonly employed in periodontal treatment; however, their ability to roughen tooth surfaces is a worry since roughness may ...

Behavior

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

Chewing, drinking, and occasional tooth grinding will result in physiological tooth wear during a lifetime. Extreme challenges, such as bruxism or habitual chewing on foreign objects, may lead to excessive wear. Recently, the role of erosion in accelerating mechanical tooth wear has been recognized, but the interplay between chemical and mechanical wear processes has not been extensively studied. Our laboratory recently introduced a novel oral wear simulation device, the Rub&#38;Roll, that enables the user to perform wear and loading studies separately or simultaneously in an erosive and/or abrasive environment. This manuscript describes an application of the device: the combined mechanical and erosive loading of extracted human (pre)molars in a simulated chewing movement, with a controlled application of force, velocity, fluid, and time, and the application of non-contact profilometry in visualizing and measuring the resulting wear pattern. The occlusal morphology that was created in the experiment with the highest loading level is very similar to the clinical presentation of erosive wear.

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

The Rub&#38;Roll can mimic the chewing cycle, allowing variation of chewing force, sliding distance, chewing velocity, number of cycles, and frequency, and with a combination of erosive and abrasive challenges can result in a complex simulation of oral ageing.

Chewing, drinking, and occasional tooth grinding will result in physiological tooth wear during a lifetime. Extreme challenges, such as bruxism or ...

Bioengineering

Precision of In Vivo Quantitative Tooth Wear Measurement Using Intra-Oral Scans

Quantitative wear measurement is of increasing interest for measuring tooth wear progression. However, most research on quantitative wear measurement has focused on simulated wear or scanned gypsum casts. A 3D Wear Analysis (3DWA) protocol has been developed that analyzes tooth wear in vivo through intra-oral scanners available to dental clinicians. This study investigated the precision of the 3DWA protocol for measuring wear through maximum height loss (mm) and volume change (mm3). Observational prospective wear data from 55 patients were analyzed after 0-1-, 0-3-, and 0-5-year intervals to determine rates of wear, and convenience samples were chosen to test the protocol&#39;s precision on dentitions scanned twice in one sitting and its intra- and inter-rater precision on scans with 0-3- and 0-5-year intervals. Scans were made using intra-oral scanners (IOS) and superimposed using 3D measurement software. T-tests were performed to determine the structural and random error, and trimmed ranges were calculated to interpret the error. For protocol precision, the mean difference was 0.015 mm (-0.002; 0.032, p = 0.076) for height and -0.111 mm3 (-0.250; 0.023, p = 0.101) for volume. The duplicate measurement error was 0.062 mm for height and 0.268 mm3 for volume. The height measurements were precise enough to measure wear after intervals of 0-3 or 0-5 years; however, volume measurements were susceptible to procedural error and operator sensitivity. The 3DWA protocol is precise enough to adequately measure tooth height loss after intervals of a minimum of 3 years or in patients with severe wear progression, but it is not suited to measuring volumetric changes.

Precision of In Vivo Quantitative Tooth Wear Measurement Using Intra-Oral Scans

Quantitative wear measurement is a method of increasing importance in measuring tooth wear progression. We here describe a protocol, its precision, and its intra/inter-rater precision for the acquisition and superimposition of repeated in vivo scanned dentitions in patients with moderate to severe wear, reporting on both height and volume measurements.

Quantitative wear measurement is of increasing interest for measuring tooth wear progression. However, most research on quantitative wear measurement has ...

Evaluation of Maxillary Posterior Tooth Movement Using Digital Superimposition

Measuring Maxillary Posterior Tooth Movement: A Model Assessment using Palatal and Dental Superimposition

Since the introduction of Invisalign by Align Technology, Inc. in 1999, questions and debates have persisted regarding the precision of Invisalign (clear aligner) therapy, particularly when compared to the use of traditional fixed appliances. This becomes particularly significant in cases involving anteroposterior, vertical, and transverse corrections, where precise comparisons are of paramount importance. To address these inquiries, this study introduces a meticulously devised protocol, placing a primary emphasis on digitally superimposing the movement of maxillary posterior teeth to facilitate accurate analysis. The sample included 25 patients who had completed their first series of Invisalign (clear) aligners. Four maxillary digital models (pre-treatment, post-treatment, ClinCheck-initial, and final models) were digitally superimposed using the palate rugae and dentitions as stable references. A software combination was used for model superimposition and tooth segmentation. Transformation matrices then expressed the differences between the achieved and predicted tooth positions. Thresholds for clinically relevant differences were at &plusmn;0.25 mm for linear displacement and &plusmn;2&#176; for rotation. Differences were assessed using Hotelling's T-squared tests with Bonferroni correction. The mean differences in rotation (2.036&#176; &plusmn; 4.217&#176;) and torque (-2.913&#176; &plusmn; 3.263&#176;) were significant statistically and clinically, with p-values of 0.023 and 0.0003 respectively. De-rotation of premolars and torque control for all posterior teeth were less predictable. All mean differences for the linear measurements were statistically and clinically insignificant, except that the first molars seemed slightly (0.256 mm) more intruded than their predicted position. The clear aligner system appears to meet its prediction for most translational tooth movements and mesial-distal tipping in maxillary posterior teeth for non-extraction cases with mild to moderate malocclusions.

Author Spotlight: 3D Movement Assessment of Maxillary Posterior Teeth in Clear Aligner Treatment

This manuscript presents a comprehensive protocol to evaluate the three-dimensional (3D) movement of maxillary posterior teeth with clear aligners using digital model superimposition, an invaluable tool in orthodontics and dentofacial orthopedics.

Since the introduction of Invisalign by Align Technology, Inc. in 1999, questions and debates have persisted regarding the precision of Invisalign (clear ...

Quasistatic Load-to-Fracture Test of CAD/CAM Occlusal Veneers on Dentin Analogs

Quasistatic Mechanical Testing for Computer-Aided Design and Manufacturing Occlusal Veneers Cemented to Milled Dentin Analog Material

Under current minimally invasive treatment regimes, minor tooth preparation and thinner biomimetic ceramic restoration are used to preserve the restored tooth&#39;s vitality, aesthetics, and function. New computer-aided design and computer-aided manufacturing (CAD/CAM) ceramic-like material are&#160;now available. To guarantee longevity, a dental clinician must know these&#160;newly launched product&#39;s mechanical strength compared to the relatively brittle glass-matrix ceramic. Furthermore, a tooth substitute has been promoted for laboratory investigation, especially after the pandemic, and more evidentiary support is required for its application.
This study developed a laboratory protocol for a monotonic load-to-fracture test to determine the fracture strength of 1 mm-thick CAD/CAM occlusal veneers. Master dies were milled from high-pressure fiberglass laminate, which has&#160;similar elastic modulus and bond strength as hydrated dentin. They were mounted into polyvinyl chloride (PVC) end caps with cold-curing epoxy resin. Occlusal veneers, also called tabletop restorations, were milled from lithium disilicate (LD) and resin nanoceramic blocks (RNC) and cemented to prepared master dies using dual-cured adhesive resin cement. They were&#160;allowed to cure fully by storing in distilled water for 48 h at 37 &#176;C.
All samples were then placed in a universal testing machine and loaded via a non-fixed 5.5 mm stainless-steel ball that allows lateral movement as would occur against the antagonist&#160;teeth. Compression was applied at a 1 mm/min rate, and the load-displacement graph was generated. The average maximum load-bearing capacity of restorations in the RNC group (3,212.80 &#177; 558.67 N) was significantly higher than in the LD group (2727.10 &#177; 472.41 N) (p &#60; 0.05). No debonding was found during the test.&#160;Both CAD/CAM materials may have a similar flaw distribution. Hertzian cone crack was found at the loading site, whereas radial cracks propagating from the cementation surface were found close to the margin in both groups.

A quasistatic load-to-fracture test with a non-fixed stainless steel ball was developed to determine the fracture strength of minimally invasive posterior computer-aided design and manufacturing restorations cemented to dentin analog materials. This test models the typical loading regime responsible for the fracture of dental restorations.

Under current minimally invasive treatment regimes, minor tooth preparation and thinner biomimetic ceramic restoration are used to preserve the restored ...

Measuring the Complete-arch Distortion of an Optical Dental Impression

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