Optimet 3D Dental Multi-Facet Scanner Attainable Accuracy for Dental Application Cases

Transcription

1 Optimet 3D Dental Multi-Facet Scanner Attainable Accuracy for Dental Application Cases Optimet Dental 3D Scanner This paper presents an overview of the Optimet multi-facet Dental Scanner used for 3D scanning of dental objects for CAD/CAM procedures and the Scanner accuracy. Optimet Multi-Facet 3D Dental Scanner (Marketed by Nobel Biocare) Optimet s CAD/CAM Dental Scanner provides accurate 3-D scans for an extensive range of dental objects and CAD/CAM products including single to multi unit implant bridge cases, over-dentures, individualized abutments, cast models (gypsum), wax-up s and impressions. The Scanner, developed and manufactured by Optimet, is marketed globally by Nobel Biocare under NobelProcera. The Dental Scanner integrates Optimet s patented conoscopic holography (collinear) measurement technology combined with multi-facet optical technology enabling accurate 3D scanning of undercuts, concavities and complex geometries, including undercut coverage and double sided scans (360 ). Optimet collinear measurement technology Conoscopic holography In the Dental CAD/CAM application, accurate 3D measurements provided by Optimet Dental Scanner are used for planning, design and manufacturing of individualized dental restoration, including crowns, bridges, single unit abutments and implant bridges and frameworks. The design is performed by dedicated dental CAD software based on 3D scan data of the cast models and impressions representing the dental situation. Multi-Facet scanning technology

2 Metrology definitions Measurement Precision, Accuracy, Reproducibility and measurement Certainty (or Uncertainty) are defined in different standards and publications (such as the German DIN). Dental objects under measurement are characterized as free form geometries and surfaces. Relevant methods analyze the accuracy as deviations of the 3D surface and dimension measurement from independent and accurate dimensions (nominal values) of the object in defined coordinate system. The analysis provides the level of certainty or uncertainty stipulated by statistical parameters based on the deviations distribution (such as 2σ or 3σ) and related statistical tests. Reproducibility analysis tests the ability of the Scanner to provide similar measurement results for the same measure and under different and repeated measurement conditions. Accuracy results on metrology objects Optimet Dental Scanner accuracy was tested in several methods and analyzed with Geomagic Qualify 11 software, based on surface output format (STL) of the scanner while additional tests were performed based on the cloud of points output where specified. The first object scanned and tested was a metal (brass) metrology cone with undercuts and an edge radius of 0.150mm. The actual dimensions of the metrology jig were certified by a CMM machine (with an accuracy of 1µm). The scans were performed by several Scanners in standard environmental conditions and the results were compared to the solid model file of the metrology jig. Deviation map metrology cone Green color indicate deviations within ±15µ from nominal dimensions The average deviations between scanned surface and the solid dimensions are within -5µm to +7µm with Std. of 7µm. More than 95% of the surface (~2σ) is within ± 15µm from the nominal surfaces. The results are typical for all object's area s including the sharp margin/edge area. See the deviation map and deviation distribution in the images herein. Volumetric accuracy multi spheres test A volumetric accuracy test was performed by scanning a 3 spheres metrology jig with distances between the spheres of 30mm, 40mm and 50mm (sphere Optimet Multi Facet Dental Scanner diameters of 19.5mm) and comparing the sphere center position 3 spheres metrology jig measurement set-up and distance with the nominal values. The metrology jig is certified by a CMM machine (with 1µm accuracy). Results of 40 measurement tests on 10 3 spheres jig different Scanners show average deviations of 7.9µ from the nominal dimensions (with Std. of 5.26µm). The average deviations of distances between the spheres were 6.67µm (30mm distance), 7.93µm (40mm distance) and 9.10µm (50mm distance). The maximum deviation from the nominal distance values in all tests (120 test scans by 10 different scanners) was 19µm.

3 A multi facet scan test performed by the Dental Scanner on the metrology sphere with a nominal radius of 19.5mm (tolerance of ±2µm) with average deviations from a sphere surface of ±5µm with Std. of diameter of 6µm. The actual measured radius is , 10µm from nominal value. Deviation map metrology sphere Green color indicate deviations within ±10µm Accuracy in dental objects scans (free form) Ten different Gypsum dies (anterior and posterior teeth) as well as a titanium die were scanned by Optimet's Dental Scanner. The accuracy was analysed by comparing and calculating the deviations between the scan results (surface) to accurate scans performed by a high accuracy industrial scanner (having accuracies within ±4µm). The average deviations of the scan results of the dies surface (on all the 10 test dies) were ±7µm with Std. of 8µm (deviations are measured from the nominal values as scanned by the high accuracy industrial scanner). 97.1% of the surface area of all dies was within ±15µm from nominal dimension values. The deviation varied (according to the specific test die) between 95.5% 98.5% of the scan surface was within ± 15µm the different dies showed that on average Reproducibility analysis performed by comparing scans of the dies by different Optimet scanners showed accuracies with average deviations of -6.7µm / +5.8µm with a Std of 8.2µm (1σ = 15µm), similar to the accuracy analysis above. Deviation Maps - 3 dental test samples measured and compared to high accuracy industrial scans. (green color represents surfaces deviations up to ±19µm deviations in scale). An additional accuracy test was performed on a Titanium die (in a tooth shape) in height of 10mm with edges in radiuses (simulating a sharp crown margin line) between 0.03mm - 0.1mm. The scan was performed with no spray. Average deviations from the accurate nominal values were within -9µm / +7µm. 93% of the surface area was within ±15µm of the nominal surface (as measured by the high accuracy industrial scanner after deducting the reference measurement uncertainty), including in the sharp margin area. See below for a color deviation map and deviation distr ibution chart. Deviation map Ti die Green color indicate deviations within ±15µm From nominal values Comparative Profile along the Titanium die Measurement Vs. solid Deviation distribution chart Ti die

4 Accuracy results on Implant bridges The design and manufacturing of Implant bridges require specifically very high accuracies. Special algorithms embedded in the Dental Scanner software enable measurement of the implants accurate position and inclination angle. This high accuracy 3D scan data enable design of the implant bridge framework or bar as well as an over-denture in CAD/CAM procedures. A comprehensive accuracy test performed included scans of multiple implant bridge cases on cast models with 3-6 implants (with distances of up to 45mm between implants). The implant seats exact position (implant interface seat center) and angle was extracted by the Dental Scanner software and then compared to high precision measurements performed on a CMM measurement system (accuracy within 1µm). The accuracy analysis on the exact implant seats ZXY position and inclination angle (of the implant), show deviations within ±5µm. Note that the most critical parameters are the Z (height) and inclination angles (of the implants). 3D view of deviation map of implant bridge seats including angulations. Green color indicate deviations within ±4µm Deviation colour maps (below) show two examples of the deviation analysis of the implant seat in comparison to the nominal values (as measured by the CMM machine). In addition, the chart below shows the accuracy in different test cases within ±4.5µm as well as the reproducibility of the test results. Deviation map - implant bridge seats Green color indicate deviations within ±4µm Orange color represent ±6-8µm Deviation chart - implant bridge seats scanning accuracies multiple test cases result Average deviations from nominal position within ±4.5µm

5 General Metrology Applications The Multi Facet Scanner is capable of 3D scanning different objects with complicated geometries for general metrology and reverse engineering applications. Optimet s Conoscopic sensors have standard interchangeable objective lenses from 16mm up to 250mm lens reaching accuracies up to sub-micron range. The Scanner can be provided for metrology applications with lens objective from 25mm-100mm allowing flexible resolutions and working ranges for different purposes. 3-D Multi facet measurement: a cutting tool and a plastic part measured by the multi facet scanner. Measurements performed in one set-up and include holes and other geometries. Summary Dental and CAD/CAM procedures and tolerances should aim for reaching adequate clinical results in planning, design and manufacturing of dental restorations. The accuracy results and analysis in this paper represent the accuracies in digital data acquisition as part of the CAD/CAM process. Optimet CAD/CAM Dental Scanner metrological accuracy and reproducibility were tested and analyzed on different objects and cases. The accuracy results on dental die cases as well as verified metrology jigs are within 15µm. Optimet s Dental Scanner operational principle keeps the object being measured in a Cartesian coordinate system (XY) with no angulations or rotation of the object during the measurement. The volumetric accuracy as shown in the tests is therefore kept at the same level of accuracy 15µm with no accuracy degradation in the scanning volume. The accuracy results on multiple implant bridges cases (implants seats including height and angulations) were within a range of 5µm with similar results in reproducibility tests. References: 1. G.Y. Sirat; Conoscopic holography. Basis principles and physical basis J. Opt. Soc. Am. ( 1992) 2. Redlich M, Weinstock T, Abed Y, Schneor R, Holdstein Y, Fischer A " A new system for scanning, measuring and analyzing dental casts based on a 3D holographic sensor" Orthod Craniofac Res 2008;11: I Alvarez, J M Enguita, M Frade, J Marina and G Ojea "On-Line Metrology with Conoscopic Holography: BeyondTriangulation" Sensors 2009, 9, DIN , Grundlagen der Messtechnik Teil 1:Grundbegriffe Fundamentals of metrology Part 1: Basic terminology (German and English) 5. DIN 32877, Optoelectronic measurement of form, profile and distance, August Eurolab, European Federation of National Associations of Measurement, Testing and Analytical Laboratories, Technical Report No. 1/2006 August International Organization of Standards "Guide to the Expression of Uncertainty in Measurement"