Name: Measuring the Complete-arch Distortion of an Optical Dental Impression (Video) | JoVE Journal
Uploaded: 2019-05-30T13:00:00.000+00:00
Duration: 6 min 51 s
Description: Learn a coordinate system extraction protocol for measuring distortion in intraoral dental scans using a 3D-printed metal phantom. This method improves accuracy over best-fit alignment for evaluating scanner performance.

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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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</ol>

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 dev...

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

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 µm, 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 prin...

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

Research

JoVE Journal

Engineering

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.

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

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.

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

The Rub&amp;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.

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

The method presented here is designed to construct and validate an in vitro 3D model capable of measuring the force system generated by different archwires with V-bends placed between two brackets. Additional objectives are to compare this force system with different types of archwires and to previous models.

Force System with Vertical V-Bends: A 3D In Vitro Assessment of Elastic and Rigid Rectangular Archwires

The present protocol describes a method to capture intra- and extra-oral photographs for digital documentation in the clinical practice of dentistry. The protocol highlights all the critical components involved and the commonly utilized settings to capture dental photographs for clinical documentation.

A Standardized Approach to Extra-Oral and Intra-Oral Digital Photography

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.

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

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.

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

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.

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

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.

Construction and Testing of Coin Cells of Lithium Ion Batteries

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 μm diameter indium wires separated by ~100 μm, which exhibit a terahertz plasmonic response.

Fabricating Metamaterials Using the Fiber Drawing Method

Learn a coordinate system extraction protocol for measuring distortion in intraoral dental scans using a 3D-printed metal phantom. This method improves accuracy over best-fit alignment for evaluating scanner performance.

Measuring the Complete-arch Distortion of an Optical Dental Impression

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