Accuracy of data obtained from impression scans and cast scans using different impression materials.

AIM: Despite the expanding implementation of intraoral scanning (IOS) devices, indirect digitization of conventional impressions or casts still represents the primary access to CAD/CAM. The aim of this study was to evaluate the accuracy of data acquired from impression scans and cast scans with respect to impression material and type of cast used. MATERIALS AND METHODS: A standardized titanium model for a four-unit fixed dental prosthesis (FDP) served as a testing model. Industrial computed tomography (CT) was applied, generating a reference data set. Four different impression materials were utilized (n = 12 per material): 1) Impregum Penta (polyether/group PE); 2) Imprint 4 Penta Super Quick Heavy + Super Quick Light (polyvinyl siloxane (PVS)/group PVS-I); 3) Dimension Penta H Quick + L (PVS/group PVS-D); and 4) Imprint 4 Preliminary Penta Super Quick (PVS/group PVS-P). Data were obtained from three different model situations, ie, impressions (group IMP), unsectioned plaster casts (group UNSEC), and sectioned casts (group SEC). The surfaces were digitized three times each using a laboratory scanner. The resulting test data were superposed with the reference data using a best-fit algorithm to evaluate accuracy. Statistical analysis was conducted using the Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney tests (level of significance: P < 0.050). RESULTS: Imprint 4 Penta presented the highest overall accuracy, while Imprint 4 Preliminary Penta Super Quick displayed the poorest results. Regarding the model situation (impression scan vs cast scan), impression scans from Impregum Penta and Imprint 4 Penta showed superior results. CONCLUSION: Impression scans in combination with high-precision impression material results in the most accurate data.

Digital impressions in dentistry-accuracy of impression digitalisation by desktop scanners.

OBJECTIVES: To test if the partially digital workflow by digitalisation of the impression reveals a comparable accuracy as the indirect digitalisation of the gypsum cast for 4-unit fixed dental prostheses (FDPs). MATERIALS AND METHODS: A titanium model with a tapered full veneer preparation of a molar and premolar was used as analysis model. To receive a virtual three-dimensional reference dataset (REF), it was digitised by industrial computed tomography. Three impression materials were used with individual impression trays (N = 36, n/material = 12): (1) PE (Impregum Penta), (2) PVS-I (Imprint 4 Penta: Super Quick Heavy plus Super Quick Light), and (3) PVS-D (Dimension Penta: H Quick plus L). For partially digital workflow (group IMP), two desktop scanners were used: (1) D810 (3Shape D810) and (2) ZZ (Zirkonzahn S600ARTI). For indirect digitalisation (group CAST), gypsum master casts were manufactured and digitalised using the same desktop scanners. Virtual datasets were superimposed by best fit algorithm, and accuracy was analysed by calculating the Euclidean distances (ED) to the REF (Geomagic Qualify). Statistic was determined (Kruskal-Wallis H test, Mann-Whitney U post hoc analysis, two-sample Kolmogorov-Smirnov test, p < 0.05). RESULTS: ZZ showed for positive deviations superior accuracy for IMP than for CAST. PE and PVS-I showed superior accuracy than PVS-D. D810 showed partially significant better performance with PVS-I and PVS-D than ZZ. CONCLUSIONS: The partially digital workflow by digitalisation of the impression can be used for clinical indications of small-span fixed dental prostheses. However, for this indication, the impression material and the desktop scanner are more decisive for the accuracy of virtual model datasets. CLINICAL RELEVANCE: Despite the rapid advancement of the computer-aided technology for dental therapy purposes, the implementation of this technique is not as fast as the technical development. In order to combine the well-established procedure to use elastomeric materials for a conventional impression and to avoid the drawbacks of casting it by gypsum, the digitalisation of the impression itself by a desktop scanner may be a logical procedure as an access point to the digital workflow. However, there is only limited information about the accuracy of this partially digital workflow by the digitalisation of modern impression materials in comparison to the well-known process of indirect digitalisation of gypsum casts.

Accuracy of five intraoral scanners compared to indirect digitalization.

OBJECTIVES: Direct and indirect digitalization offer two options for computer-aided design (CAD)/ computer-aided manufacturing (CAM)-generated restorations. The aim of this study was to evaluate the accuracy of different intraoral scanners and compare them to the process of indirect digitalization. MATERIAL AND METHOD: A titanium testing model was directly digitized 12 times with each intraoral scanner: (1) CS 3500 (CS), (2) Zfx Intrascan (ZFX), (3) CEREC AC Bluecam (BLU), (4) CEREC AC Omnicam (OC) and (5) True Definition (TD). As control, 12 polyether impressions were taken and the referring plaster casts were digitized indirectly with the D-810 laboratory scanner (CON). The accuracy (trueness/precision) of the datasets was evaluated by an analysing software (Geomagic Qualify 12.1) using a "best fit alignment" of the datasets with a highly accurate reference dataset of the testing model, received from industrial computed tomography. RESULTS: Direct digitalization using the TD showed the significant highest overall "trueness", followed by CS. Both performed better than CON. BLU, ZFX and OC showed higher differences from the reference dataset than CON. Regarding the overall "precision", the CS 3500 intraoral scanner and the True Definition showed the best performance. CON, BLU and OC resulted in significantly higher precision than ZFX did. CONCLUSIONS: Within the limitations of this in vitro study, the accuracy of the ascertained datasets was dependent on the scanning system. The direct digitalization was not superior to indirect digitalization for all tested systems. CLINICAL RELEVANCE: Regarding the accuracy, all tested intraoral scanning technologies seem to be able to reproduce a single quadrant within clinical acceptable accuracy. However, differences were detected between the tested systems.