Scanning accuracy and precision in 4 intraoral scanners: an in vitro comparison based on 3-dimensional analysis.

STATEMENT OF PROBLEM: Intraoral scanners may use proprietary acquisition and manufacturing processes. However, limited information is available regarding their accuracy, their precision, and the influence that refraction or coating may have on their output. PURPOSE: The purpose of the study was to evaluate the scanning accuracy and precision of 4 intraoral scanners and to assess the influence of different test materials and coating thicknesses. MATERIAL AND METHODS: Models were fabricated in 3 materials (polymethyl methacrylate [Telio CAD], titanium, and zirconia) and reference scanned with an industrial optical scanner. The models were scanned with intraoral scanners (3M Lava COS, Cerec AC/Bluecam, E4D, and iTero). A thick layer of coating was applied and scanned (3M Lava COS). Further evaluation on a gypsum cast was undertaken for the E4D system. Data were evaluated by using 3-dimensional analysis with "3D compare" software commands (3D compare analysis) regarding standard, mean, and maximum deviations, with subsequent statistical analysis. RESULTS: The 3M Lava COS, Cerec AC/Bluecam, and iTero generally displayed similar results regarding deviations. Maximum deviations, however, increased by several factors for the noncoating scanners (iTero and E4D). Statistical significance was found regarding material properties for noncoating scanners (P<.05). iTero displayed consistent material-specific, localized errors on the translucent material (Telio CAD). E4D showed the largest deviations. Scans of the gypsum cast displayed specific localized areas with greater deviations. Excessive coating was nonsignificant. CONCLUSIONS: Significant differences were found between the coating and noncoating scanners, and specific scanning errors for the system with parallel confocal microscopy were found for certain model materials. Specific areas of sizable deviations for the system with laser triangulation technology can be explained by the scanner design and noncoating technology. Excessive coating had no negative effect.

Digitization of simulated clinical dental impressions: virtual three-dimensional analysis of exactness.

OBJECTIVES: To compare the exactness of simulated clinical impressions and stone replicas of crown preparations, using digitization and virtual three-dimensional analysis. METHODS: Three master dies (mandibular incisor, canine and molar) were prepared for full crowns, mounted in full dental arches in a plane line articulator. Eight impressions were taken using an experimental monophase vinyl polysiloxane-based material. Stone replicas were poured in type IV stone (Vel-Mix Stone; Kerr). The master dies and the stone replicas were digitized in a touch-probe scanner (Procera) Forte; Nobel Biocare AB) and the impressions in a laser scanner (D250, 3Shape A/S), to create virtual models. The resulting point-clouds from the digitization of the master dies were used as CAD-Reference-Models (CRM). Discrepancies between the points in the pointclouds and the corresponding CRM were measured by a matching-software (CopyCAD 6.504 SP2; Delcam Plc). The distribution of the discrepancies was analyzed and depicted on color-difference maps. RESULTS: The discrepancies of the digitized impressions and the stone replicas compared to the CRM were of similar size with a mean+/-SD within 40microm, with the exception of two of the digitized molar impressions. The precision of the digitized impressions and stone replicas did not differ significantly (F=4.2; p=0.053). However, the shape affected the digitization (F=5.4; p=0.013) and the interaction effect of shape and digitization source (impression or stone replica) was pronounced (F=28; p<0.0001). The reliability was high for both digitization methods, evaluated by repeated digitizations. SIGNIFICANCE: The exactness of the digitized impressions varied with shape. Both impressions and stone replicas can be digitized repeatedly with a high reliability.

Computer aided analysis of digitized dental stone replicas by dental CAD/CAM technology.

OBJECTIVES: To determine the reproducibility of digitized dental stone replicas compared to the master model and the reliability of the computer aided analysis. METHODS: Four master dies, prepared for complete crowns were fabricated in presintered yttria-stabilized tetragonal zirconia (Y-TZP). Eight vinyl polysiloxane impressions (PROVIL novo; Heraeus Kulzer) were taken of each die and stone replicas were poured in type IV stone (Vel-Mix Stone; Kerr). The master dies and the stone replicas were digitized in a touch-probe scanner (Procera Forte; Nobel Biocare AB), to create triangulated surface-models. The point-cloud from the first of the repeated digitizations of each master die was used as CAD-reference-models (CRM). Discrepancies between the points in the triangulated surface-models and the corresponding CRM were measured by a matching-software (CopyCAD 6.504 SP2; Delcam Plc). The distribution of the discrepancies was analyzed and presented in color-difference-maps. RESULTS: The precision of the measuring method, presented as the repeatability coefficient, ranged between 7 and 16 microm (entire surface), whereas the analysis of the stone replicas revealed a precision (repeatability coefficient) ranging from 19 to 26 microm. The accuracy of the replica to master (the mean discrepancy) ranged from 0.5 to 2.0 microm (95% confidence interval 1.5-2.9 microm). SIGNIFICANCE: The greatest precision of the measurement was seen in the jacket surface of the die. The size of the stone replicas varied and the repeatability coefficient was on average 15 microm (2-25 microm) greater for the replica-to-master alignment than the repeated digitizations of the master.