Effect of different span lengths with different total occlusal convergences on the accuracy of intraoral scanners

Critical methodological factors influencing the accuracy of intraoral scanners in digital dentistry research

This in vitro study aimed to identify the key methodological factors influencing the accuracy of intraoral scanners (IOS). The primary factors analyzed included the length of the scanned area, the total number of alignment points, the software used for analysis, and the operator's expertise. Three IOS systems were assessed-CEREC Primescan, Trios 3, and Omnicam-along with a laboratory desktop scanner (inEos X5). Scans were performed on a mandibular typodont, with the Root Mean Square (RMS) error used to measure the discrepancies between reference and experimental scans. The results indicated that the length of the scanned area significantly affected the RMS values, with full-arch scans producing greater errors compared to those of quadrant scans. Additionally, the total number of alignment points in the standard tessellation language files positively influenced accuracy, although improvements plateaued beyond 20 points. The choice of processing software also impacted accuracy, with Geomagic Control X yielding significantly lower RMS values than those of MeshLab and CloudCompare. Finally, user expertise played a significant role in scanning accuracy, with the experience user achieving more precise results, especially when using the Trios 3 scanner. Thus, the length of the scan, number of alignment points, software tools, and operator expertise significantly influence the accuracy of IOS, highlighting the importance of considering these methodological factors in both clinical and research settings for digital impressions.

Effect of different preparation designs of minimally invasive occlusal onlays on the accuracy of different intraoral scanners: An in vitro study

PURPOSE

The aim of this in vitro study was to assess and compare three different preparation designs of minimally invasive occlusal onlays on the trueness and precision of three different intraoral scanners under two different scanning conditions.

MATERIALS AND METHODS

Three maxillary premolars were prepared in three different designs and divided accordingly into three groups, Group 1: Anatomical (n = 60), Group 2: Flat (n = 60), and Group 3: Ferrule (n = 60). The samples were then further divided into subgroups according to scanners as subgroup A: Medit i500 (n = 20), subgroup B: 3Shape TRIOS 4 (n = 20), and subgroup C: Cerec Primescan (n = 20). Last, the samples were further divided according to scanning conditions: Division i: As prepared (n = 10) and Division ii: Sprayed - scan spray (n = 10). An industrial 3D scanner was used to obtain the reference STL files. Accuracy was assessed in terms of trueness and precision and recorded in terms of root mean square in micrometers. Numerical data were explored for normality using Shapiro-Wilk test and were analyzed using 3-way ANOVA followed by Tukey's post hoc test.

RESULTS

Regarding trueness, 3-way ANOVA showed that all tested variables had a significant effect on trueness. Significant interactions were found between the different variables (p < 0.001). For preparation design the highest value was found in ferrule preparation (27.88 ± 7.11), followed by flat preparation (22.99 ± 7.56), while the lowest value was found in anatomical preparation (18.83 ± 5.71) (p < 0.001). For scanner type, the highest value was found in Primescan (25.36 ± 10.66), followed by TRIOS 4 (22.75 ± 5.98), while the lowest value was found in Medit i500 (21.59 ± 5.03) (p < 0.001). As for the scanning condition, sprayed samples (26.54 ± 8.24) had a significantly higher value than non-sprayed samples (19.93 ± 5.53) (p < 0.001). Regarding precision, both preparation design and scanner type had a significant effect on precision. Scanning conditions had no significant effect. There was a significant interaction between the three tested variables (p = 0.012).

CONCLUSIONS

Anatomical preparation of minimally invasive occlusal onlays produced the most accurate scans. Within the tested preparation designs, Medit i500 and 3Shape TRIOS 4 have better trueness than Cerec Primescan. Cerec Primescan is more precise than 3Shape TRIOS 4 and Medit i500 Scan spray application causes a higher deviation in the trueness of the tested intraoral scanners while it does not affect their precision.

Parameters to Improve the Accuracy of Intraoral Scanners for Fabricating Tooth-Supported Restorations

OBJECTIVES

To review the factors that impact the accuracy of intraoral scanners (IOSs) when fabricating tooth-supported restorations.

OVERVIEW

Factors can have a different impact on IOS accuracy depending on the scanning purpose. If the goal is to fabricate tooth-supported restorations, it is essential to review the following operator-related factors: IOS technology and system, scan extension and starting quadrant, scanning pattern, scanning distance, and rescanning methods. Additionally, it is critical to interpret the following patient-related factors differently: edentulous spaces, presence of existing restorations on adjacent teeth, and characteristics of the tooth preparation (build-up material, geometry, total occlusal convergence [TOC], finish line location, and surface finishing), and interdental spaces (between tooth preparations or between preparation and the adjacent tooth).

CONCLUSIONS

For crown or short-span fixed dental prostheses, a reduced scan extension is recommended. For complete-arch scans, it is advisable to start the scan in the same quadrant as the preparation. If the IOS permits locking the scan, rescanning may be indicated. Restorations on tooth preparations and adjacent teeth reduce accuracy. The simpler the geometry and the larger the TOC, the higher the IOS accuracy. Intracrevicular finish lines result in lower accuracy than equigingival or supragingival positions. Air-particle procedures showed better accuracy than coarse and fine grit and immediate dentin sealing. The greater the space between a preparation and the adjacent tooth, the better the accuracy.

CLINICAL IMPLICATIONS

Dental professionals must understand and handle the factors that impact the scanning accuracy of intraoral scanners differently depending on the purpose of the scan.

Application of the virtual-fit method for fixed complete denture cases designed on intraoral scans: Effect of cement spacing

OBJECTIVES

To validate the virtual-fit alignment, analyze the impact of cement spacing on internal/marginal gaps, and correlate results with conventional trueness measures.

METHODS

Four dental abutment models were scanned using an industrial reference scanner (one time each), Emerald S (three times each), and Medit i700 (three times each) intraoral scanners (IOS). On each IOS scan (n = 24), three complete-arch fixed frameworks were designed with 70 or 140 µm cement space with no marginal space (groups 70 and 140) and 70 µm with an additional 20 µm space, including the margin (group 70+20). Two types of alignment were performed by GOM Inspect software. The reference and IOS scans were aligned through a conventional iterative closest point algorithm (ICP) where the penetration of the two scans was permitted into each other (conventional trueness method). Second, the computer-aided designs were superimposed with the reference scan also using an ICP, but preventing the design from virtual penetration into the model (virtual-fit method). The virtual-fit algorithm was validated by non-penetration alignment of the designs with the IOS scans. Internal and marginal gap was measured between the design and the abutments. The difference between spacing groups was compared by Friedman's test. A statistical correlation (Spearman's Rho Test) was computed between the measured gaps and the conventional trueness method. A significant difference was accepted at p<0.05 after the Bonferroni correction.

RESULTS

The gaps deviated from the set cement space by 3-13 µm on IOS scans (validation of virtual-fit algorithm). The internal gap of the design on the reference scan was not affected by cement spacing (Emerald S, p = 0.779; Medit i700, p = 0.205). The marginal gap in groups 70 and 70+20 was significantly lower than in group 140 in Emerald S (p<0.05). In Medit i700, it was lower in the 70+20 group than in the group 70 (p<0.01) and in the group 140 (p<0.05). Some Medit i700 scans exhibited high marginal gaps within group 70 but not in groups 70 and 140. The measured gaps correlated significantly (r = 0.51-0.81, p<0.05-0.001) with the conventional trueness but were 2.6-4.6 times higher (p<0.001).

CONCLUSION

Virtual-fit alignment can simulate restoration seating. A 20 µm marginal and 90 µm internal spacing could compensate for scan errors up to several hundred micrometers. However, 140 µm internal spacing is counterproductive. The conventional trueness method could only partially predict framework misfit.

CLINICAL SIGNIFICANCE

The virtual-fit method can provide clinically interpretable data for intraoral scanners. Emerald S and Medit i700 intraoral scanners are suitable for fabricating complete-arch fixed tooth-supported prostheses. In addition, a slight elevation of spacing at the margin could compensate for moderate inaccuracies in a scan.

Accuracy comparison of scan segmental sequential ranges with two intraoral scanners for maxilla and mandible

Background/purpose

The accuracy of a full-arch scan by using an intraoral scanner should be validated under clinical conditions. This study aimed to compare the accuracy of full-arch digital impressions in the maxilla and mandible using two intra oral scanners with three different scan segmental sequential ranges.

Materials and methods

A dental model with 28 teeth in their normal positions served as the reference. Sixty full-arch scans were performed using Trios 3 and Trios 4, employing scanning strategy O (manufacturer's original method), OH (segmental sequential ranges one half), and TQ (segmental sequential ranges third quarter). Trueness was evaluated by comparing digital impressions with a reference dataset using specialized software. One-way ANOVA and Tukey tests assessed differences between the groups.

Results

For Trios 3 on the maxilla, no significant difference was found among the groups of trueness; in the mandible, strategy O exhibited a significant difference (P = 0.008) with the highest deviation. For Trios 4 on the maxilla, strategy TQ demonstrated the lowest deviation with a significant difference (P = 0.006); in the mandible, no significant difference was found among the groups of trueness.

Conclusion

Strategy TQ exhibited the best trueness for Trios 3 and Trios 4, suggesting it may be preferred for higher accuracy. Clinicians should consider these findings when selecting scanning strategies and intraoral scanners for specific cases.

Compatibility of digital and analog methods in assessment of gingival zeniths

OBJECTIVE

The compatibility of digital and analog methods assessing the positions of gingival zenith (GZ) points has not been evaluated before. Therefore, the aim of this study was to investigate the accuracy of a digital scanner and a three-dimensional (3D) measuring tool in specifying positions of GZs by comparing it to the conventional method, an analog plaster cast and a caliper.

MATERIALS AND METHODS

Both analog and digital impressions were obtained from 32 individuals. Following measurements were conducted in the anterior maxillary region from canine to canine on both the plaster casts and 3D images: (1) The distance from GZ to the corresponding vertical midline in each tooth (GZVM), (2) The distance from GZ of lateral incisor to the corresponding tangent that connects GZs of central incisor and canine (GZLI).

RESULTS

The intraclass correlation coefficients (ICC) of GZVM in each tooth varied between 0.366 and 0.755, demonstrating moderate to good compatibility between the two methods. The ICC of analog and digital GZLI for the right and left lateral incisors was 0.788 and 0.395, respectively.

CONCLUSION

The digital and analog methods used in this study are compatible in determining the positions of GZs. Therefore, within the limitations of the present study, the choice of method can be based on the available equipment, time, comfort, and personal preference of the researcher.

CLINICAL SIGNIFICANCE

Both digital and analog methods have the capability of determining the positions of GZs in compatible way.