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’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°).

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.

Optimet Multi-Facet 3D Dental Scanner

(Marketed by Nobel Biocare)

Multi-Facet scanning technology

Optimet collinear measurement technology

Conoscopic holography

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.

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

diameters of 19.5mm) and comparing the sphere center position

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

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.

Deviation map – metrology cone

Green color indicate deviations within

±15µ from nominal dimensions

Optimet Multi Facet Dental Scanner

3 spheres metrology jig measurement set-up

3 spheres jig

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 19.062, 10µm from nominal value.

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 – metrology sphere Green color indicate deviations within ±10µm

Comparative Profile along the Titanium die

Measurement Vs. solid

Deviation map – Ti die

Green color indicate deviations within ±15µm

From nominal values

Deviation distribution chart – Ti die

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).

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.

3D view of deviation map of implant bridge

seats including angulations.

Green color indicate deviations within ±4µm

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

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.

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