Accuracy of four recent intraoral scanners with respect to two different ceramic surfaces.

OBJECTIVES: To investigate the complete arch accuracy of intraoral scanners (IOS) on two different ceramic surfaces. METHODS: Two maxillary master cast samples were prepared. The bases of both the master casts were made from zirconium oxide. The difference between the two casts was that the teeth of the [ZR] cast were produced from zirconium oxide and that of the [LD] cast were made of lithium disilicate glass-ceramic. Unlike the zirconia teeth of the [ZR] cast, the lithium disilicate teeth of the [LD] cast were glazed. The two master casts were digitized using a high-resolution scanner (Atos Compact Scan 5 M, GOM GmbH, Braunschweig, Germany) to obtain digital reference casts. Subsequently, each master cast was scanned 15 times using four IOSs. The IOSs were the Cerec Omnicam [OM], Primescan [PR], Trios 4 [TR4], and VivaScan [VS]. On surface comparison, the absolute mean deviation values were obtained for trueness and precision. For multiple comparisons, statistically significant differences were analyzed using one-way ANOVA and the Kruskal-Wallis H test. The p-value was adjusted to control for the increased risk of type I error (p < 0.0083). To compare the two means, the t-test and Mann-Whitney U test were used (p < 0.05). RESULTS: Trueness values for [ZR] ranged from 24.6 (±6.3) µm for [PR] and 77.1 (±8.3) µm for [OM]. Trueness values for [LD] were between 28.3 (±6.3) µm for [PR] and 72.8 (±15.6) µm for [OM]. Precision values for [ZR] ranged from 17.6 (±3.7) µm for [PR] to 37.3 (±9.9) µm for [OM]. Precision values for [LD] ranged from 17.5 (±3.6) µm for [PR] to 41.8 (±8.7) µm for [OM]. Statistically significant differences were found among all the IOSs (p < 0.0083). The trueness values of the four IOSs did not differ significantly (p < 0.05) with respect to either the [ZR] or [LD] cast. The precision values of [OM] and [VS] differed significantly with respect to the scanned surface. CONCLUSIONS: Complete arch scans achieved with the four IOSs showed significantly different trueness and precision results. [VS] and [OM] were more sensitive in terms of the scanned material. CLINICAL SIGNIFICANCE: The latest IOSs showed the required accuracy for complete arch digital impressions in-vitro investigations. These findings should be implemented under conditions relevant to complete arch deviations, such as the construction of occlusal splints, analysis of occlusal relationships, and long-span restorations. Clinicians should be aware that the clinically acceptable threshold varies depending on the purpose of the IOS.

Trueness evaluation of digital impression: The impact of the selection of reference and test object.

OBJECTIVES: This study evaluated the importance of defining the reference and the test object during 3D surface comparisons to assess the trueness of an intraoral scanner. MATERIALS AND METHODS: A maxillary complete-arch cast with interdental spaces was digitized with a high-resolution scanner to obtain the ground truth dataset [GT]. Fifteen intraoral scanning datasets [IOS] were obtained with an intraoral scanner. The trueness of the [IOS] datasets were evaluated by two different comparison procedures using a 3D analysis software: In the first comparison [REF-GT], the [GT] dataset was set as reference object and the [IOS] dataset was defined as test object. In the second comparison [REF-IOS], the [IOS] dataset were set as reference object and the [GT] dataset was defined as test object. The mean trueness of both comparisons was calculated with absolute mean deviation, (90-10)/2 percentile, and root-mean-squared (RMS) error method. Statistical significance was analyzed using the t-test (α=0.05). RESULTS: The mean trueness values of [REF-GT] were 31.4(±6.1) µm for (90-10)/2 percentile, 77.0(±5.3) µm for absolute mean deviation, and 203.1(±4.8) µm for RMS error method. [REF-IOS] revealed 23.9(±4.8) µm, 28.3(±6.3) µm, and 39.6(±9.5) µm, respectively. The results differed significantly. CONCLUSION: The datasets obtained from the intraoral scanner captured more adequately interproximal spaces in comparison to the [GT] dataset. Therefore, the [GT] dataset defined as reference object in the analysis software for 3D comparisons revealed misleading results. CLINICAL SIGNIFICANCE: The selection of the reference object and of the areas to be compared have to be defined carefully regarding complete arch scanning accuracy analysis.

Do "cut out-rescan" procedures have an impact on the accuracy of intraoral digital scans?

STATEMENT OF PROBLEM: The software programs of digital intraoral scanners typically offers the option to cut out areas from 3D casts, to do rescans, and to merge them with the initial scan. However, evidence of whether this procedure has an impact on the accuracy of the scan is lacking. PURPOSE: The purpose of this study was to determine whether "cut out-rescan" procedures change the accuracy of a 3D cast. MATERIAL AND METHODS: A maxillary master cast was digitized with an industrial structured light scanner to obtain a digital reference cast. This master cast was repeatedly scanned by 3 intraoral scanners: TRIOS 3 [TR], Cerec Primescan [PR], and Cerec Omnicam [OM]. The scan data were duplicated, and the posterior area from the right lateral incisor was cut out and rescanned to obtain complete-arch casts containing the rescanned data [TR_rs], [PR_rs], and [OM_rs]. The trueness and precision of the scans were evaluated by superimposing procedures of the relevant data sets. To evaluate statistical differences, either the Mann-Whitney U test or the t test was used (α=.05). RESULTS: The median precision values of the complete-arch scan data was 19 µm for [OM] and [TR], whereas the median for [PR] was 14 µm. In the "cut out-rescanned" data group, the values were 25 µm for [OM_rs], 16 µm for [TR_rs], and 14 µm for [PR_rs]. Statistically significant differences were found among the scanners [OM]/[PR], [OM_rs]/[TR_rs], and [TR_rs]/[PR_rs]. The mean ± standard deviation values of trueness for the complete-arch scan data were 54 ±4 µm for [OM], 42 ±5 µm for [TR], and 30 ±2 µm for [PR]. In the group of the "cut out-rescanned" data, the mean trueness results were 55 ± 6 µm for [OM_rs], 38 ±5 µm for [TR_rs], and 31 ±5 µm for [PR_rs]. Significant differences were found among the complete-arch scan data and the "cut out-rescanned" data of the different scanners, but not between the complete-arch scan data and the "cut out-rescanned" data within one scanning system. CONCLUSIONS: Significant differences were found among the scanners, but "cut out-rescan" procedures did not affect the accuracy within each scanning system.