Evaluation of ridge lap accuracy and adaptation of the diagnostic tooth arrangement fabricated with CAD-CAM systems: An in vitro study.

STATEMENT OF PROBLEM: Digital light processing (DLP) and milling (MIL) are computer-aided design and computer-aided manufacturing (CAD-CAM) systems that have become popular for fabricating definitive complete dentures. However, few studies have compared the accuracy of the ridge laps of diagnostic tooth arrangements fabricated with these systems and their adaptation with the denture base sockets. PURPOSE: The purpose of this in vitro study was to comparatively analyze the accuracy of the ridge laps of the diagnostic tooth arrangements fabricated by using MIL and different layer thicknesses in DLP. MATERIAL AND METHODS: A virtual definitive complete denture was designed with a CAD software program on a scanned virtual digital cast, divided into diagnostic tooth arrangement and a denture base that accommodated the arrangement, and saved as a standard tessellation language (STL) file. From this file, 27 diagnostic tooth arrangements were fabricated by DLP (50 µm and 100 µm) and MIL. The ridge laps were scanned and overlapped on the file (reference data) to analyze the accuracy (trueness and precision). The ridge laps of all groups were overlapped on the reference denture base data to analyze their adaptation with the sockets. The measurements of the trueness, precision, and adaptation were analyzed statistically by using the nonparametric Kruskal-Wallis test and post hoc Mann-Whitney U test with Bonferroni correction. RESULTS: The diagnostic tooth arrangements showed significant differences among the groups (P<.001). The values were the lowest in the MIL group and highest in the DLP group for the following parameters: trueness root-mean-square (RMS) value, 173 ±7 µm versus 286 ±15 µm; precision RMS value, 22 ±3 µm versus 57 ±20 µm; and adaptation RMS value, 41 ±5 µm versus 112 ±13 µm. CONCLUSIONS: Of the 2 diagnostic tooth arrangements fabricated with the CAD-CAM systems, the one fabricated with MIL was clinically more appropriate.

In vitro precision evaluation of blue light scanning of abutment teeth made with impressions and dental stone casts according to different 3D superimposition methods.

PURPOSE: The purpose of this in vitro study was to determine the precision evaluation of blue light scanning of abutment teeth impressions and dental stone casts according to different 3D superimposition methods. METHODS: Impressions and dental stone casts of the maxillary canine, 1st premolar, and 1st molar were fixed; they were repeatedly scanned 11 times, (6 types, total n = 66). Stereolithography (STL) files were superimposed one by one, and used to obtain 10 root mean square (RMS) values with the 2 superimposition methods (best-fit-alignment, no control). Statistical analysis included the independent t test and one-way ANOVA with Tukey honest significant differences (α = 0.05). RESULTS: RMS ± Standard Deviation (SD) values for the best-fit-alignment method of the abutment teeth impressions of the maxillary canine, 1st premolar, and 1st molar was 8.07 ± 0.76, 5.03 ± 0.23, and 6.59 ± 0.24, respectively, and those of the no control method were 9.36 ± 0.82, 7.10 ± 1.14, and 8.17 ± 0.36 respectively. RMS ± SD values for the best-fit-alignment method for the dental stone casts were 4.07 ± 0.27, 3.39 ± 0.07, and 3.29 ± 0.07, respectively, and those for the no control method were 6.26 ± 2.50, 4.98 ± 1.16, and 4.55± 0.74, respectively. CONCLUSIONS: Using different 3D superimposition methods, blue light scanning of abutment teeth impressions and dental stone casts shows high precision. The no control method showed lower precision best-fit-alignment. However, the results may help advance the digital dental CAD/CAM research and the clinical field of Prosthodontics.

Trueness and precision of scanning abutment impressions and stone models according to dental CAD/CAM evaluation standards.

PURPOSE: The purpose of the present study was to compare scanning trueness and precision between an abutment impression and a stone model according to dental computer-aided design/computer-aided manufacturing (CAD/CAM) evaluation standards. MATERIALS AND METHODS: To evaluate trueness, the abutment impression and stone model were scanned to obtain the first 3-dimensional (3-D) stereolithography (STL) file. Next, the abutment impression or stone model was removed from the scanner and re-fixed on the table; scanning was then repeated so that 11 files were obtained for each scan type. To evaluate precision, the abutment impression or stone model was scanned to obtain the first 3-D STL file. Without moving it, scanning was performed 10 more times, so that 11 files were obtained for each scan type. By superimposing the first scanned STL file onto the other STL files one by one, 10 color-difference maps and reports were obtained; i.e., 10 experimental scans per type. The independent t-test was used to compare root mean square (RMS) data between the groups (α=.05). RESULTS: The RMS±SD values of scanning trueness of the abutment impression and stone model were 22.4±4.4 and 17.4±3.5 µm, respectively (P<.012). The RMS±SD values of scanning precision of the abutment impression and stone model were 16.4±2.9 and 14.6±1.6 µm, respectively (P=.108). CONCLUSION: There was a significant difference in scanning trueness between the abutment impression and stone model, as evaluated according to dental CAD/CAM standards. However, all scans showed high trueness and precision.

Evaluation of the reproducibility of various abutments using a blue light model scanner.

PURPOSE: To evaluate the reproducibility of scan-based abutments using a blue light model scanner. MATERIALS AND METHODS: A wax cast abutment die was fabricated, and a silicone impression was prepared using a silicone material. Nine study dies were constructed using the prepared duplicable silicone, and the first was used as a reference. These dies were classified into three groups and scanned using a blue light model scanner. The first three-dimensional (3D) data set was obtained by scanning eight dies separately in the first group. The second 3D data set was acquired when four dies were placed together in the scanner and scanned twice in the second group. Finally, the third 3D data set was obtained when eight dies were placed together in the scanner and scanned once. These data were then used to define the data value using third-dimension software. All the data were then analyzed using the non-parametric Kruskal-Wallis H test (α=.05) and the post-hoc Mann-Whitney U-test with Bonferroni's correction (α=.017). RESULTS: The means and standard deviations of the eight dies together were larger than those of the four dies together and of the individual die. Moreover, significant differences were observed among the three groups (P<.05). CONCLUSION: With larger numbers of abutments scanned together, the scan becomes more inaccurate and loses reproducibility. Therefore, scans of smaller numbers of abutments are recommended to ensure better results.

Accuracy of single-abutment digital cast obtained using intraoral and cast scanners.

STATEMENT OF PROBLEM: Scanners are frequently used in the fabrication of dental prostheses. However, the accuracy of these scanners is variable, and little information is available. PURPOSE: The purpose of this in vitro study was to compare the accuracy of cast scanners with that of intraoral scanners by using different image impression techniques. MATERIAL AND METHODS: A poly(methyl methacrylate) master model was fabricated to replicate a maxillary first molar single-abutment tooth model. The master model was scanned with an accurate engineering scanner to obtain a true value (n=1) and with 2 intraoral scanners (CEREC Bluecam and CEREC Omnicam; n=6 each). The cast scanner scanned the master model and duplicated the dental stone cast from the master model (n=6). The trueness and precision of the data were measured using a 3-dimensional analysis program. The Kruskal-Wallis test was used to compare the different sets of scanning data, followed by a post hoc Mann-Whitney U test with a significance level modified by Bonferroni correction (α/6=.0083). The type 1 error level (α) was set at .05. RESULTS: The trueness value (root mean square: mean ±standard deviation) was 17.5 ±1.8 µm for the Bluecam, 13.8 ±1.4 µm for the Omnicam, 17.4 ±1.7 µm for cast scanner 1, and 12.3 ±0.1 µm for cast scanner 2. The differences between the Bluecam and the cast scanner 1 and between the Omnicam and the cast scanner 2 were not statistically significant (P>.0083), but a statistically significant difference was found between all the other pairs (P<.0083). The precision of the scanners was 12.7 ±2.6 µm for the Bluecam, 12.5 ±3.7 µm for the Omnicam, 9.2 ±1.2 µm for cast scanner 1, and 6.9 ±2.6 µm for cast scanner 2. The differences between Bluecam and Omnicam and between Omnicam and cast scanner 1 were not statistically significant (P>.0083), but there was a statistically significant difference between all the other pairs (P<.0083). CONCLUSIONS: An Omnicam in video image impression had better trueness than a cast scanner but with a similar level of precision.

Reproducibility of different arrangement of resin copings by dental microstereolithography: Evaluating the marginal discrepancy of resin copings.

STATEMENT OF PROBLEM: Microstereolithography (µ-SLA), a form of additive manufacturing, can produce one or more platforms of resin copings. However, no evaluation has been made of the variation in marginal discrepancy using this method, even though this is an important factor for a successful restoration. PURPOSE: The purpose of this in vitro study was to evaluate the reproducibility and marginal discrepancy of resin copings fabricated using dental µ-SLA. MATERIAL AND METHODS: A master die of a mandibular right first molar tooth was made from Type IV stone and scanned to produce a stereolithography file. Resin copings were then fabricated using µ-SLA additive manufacturing by repeating 1, 3, or 6 arrays to give a total number of 18. The marginal discrepancies of these resin copings were measured using digital microscopy (at ×160 magnification), and the data obtained were analyzed using a nonparametric Kruskal-Wallis H test, post hoc Mann-Whitney U-test, and Bonferroni correction. RESULTS: The mean ±SD total marginal discrepancies of 1, 3, and 6 arrays were found to be 72.2 ±39.1 µm, 61.2 ±37.3 µm, and 92.5 ±54.1 µm. Statistically significant differences were found among the compared groups (P<.05). CONCLUSIONS: Based on the marginal discrepancy, µ-SLA of additive manufacturing is more precise when 3 arrays are used than when 1 or 6 arrays are used on a single build platform. Because the fit is affected by the number of copings fabricated, further research of multiple resin copings is required.

Repeatability and reproducibility of individual abutment impression, assessed with a blue light scanner.

PURPOSE: We assessed the repeatability and reproducibility of abutment teeth dental impressions, digitized with a blue light scanner, by comparing the discrepancies in repeatability and reproducibility values for different types of abutment teeth. MATERIALS AND METHODS: To evaluate repeatability, impressions of the canine, first premolar, and first molar, prepared for ceramic crowns, were repeatedly scanned to acquire 5 sets of 3-dimensional data via stereolithography (STL) files. Point clouds were compared and the error sizes were measured (n=10, per type). To evaluate reproducibility, the impressions were rotated by 10-20° on the table and scanned. These data were compared to the first STL data and the error sizes were measured (n=5, per type). One-way analysis of variance was used to assess the repeatability and reproducibility of the 3 types of teeth, and Tukey honest significant differences (HSD) multiple comparison test was used for post hoc comparisons (α=.05). RESULTS: The differences with regard to repeatability were 4.5, 2.7, and 3.1 µm for the canine, premolar, and molar, indicating the poorest repeatability for the canine (P<.001). For reproducibility, the differences were 6.6, 5.8, and 11.0 µm indicating the poorest reproducibility for the molar (P=.007). CONCLUSION: Our results indicated that impressions of individual abutment teeth, digitized with a blue light scanner, had good repeatability and reproducibility.

Three-dimensional evaluation of the reproducibility of presintered zirconia single copings fabricated with the subtractive method.

STATEMENT OF PROBLEM: Reproducibility is an important factor determining the success of a prosthesis. However, no studies have focused on identifying the location of errors on prostheses fabricated with the subtractive method, leading to a lack of standards for reproducibility evaluations. PURPOSE: The purpose of this in vitro study was to evaluate the reproducibility of the subtractive method by conducting 3-dimensional assessments of presintered single-tooth zirconia copings for different teeth. MATERIAL AND METHODS: Acrylic resin tooth molds for the canine (CAN), premolar (PRE), and molar (MOL) were used to prepare stone casts, and copings were designed and fabricated with the subtractive method. The intaglio surfaces of corresponding presintered zirconia copings were scanned with a blue light scanner. Initial scan data were used as a reference for comparisons with subsequent data for the measurement of errors. Nine color-difference maps were created for each of the 3 groups and used to calculate root-mean-square (RMS) error values. One-way analysis of variance and the Tukey honestly significant difference tests were used for statistical evaluations (α=.05). RESULTS: MOL copings exhibited the highest RMS error value (9.22 ±1.56 µm), which was significantly different from values for CAN (3.33 ±2.65 µm) and PRE (4.00 ±2.40 µm; P<.001) copings. Color-difference maps revealed maximum errors in the line angles. CONCLUSIONS: The highest reproducibility was observed for the CAN copings. The clinical reproducibility of the subtractive method can be improved by avoiding sharp angles during abutment preparation and careful reproduction of angles during prosthesis fabrication.

Accuracy of complete-arch model using an intraoral video scanner: An in vitro study.

STATEMENT OF PROBLEM: Information on the accuracy of intraoral video scanners for long-span areas is limited. PURPOSE: The purpose of this in vitro study was to evaluate and compare the trueness and precision of an intraoral video scanner, an intraoral still image scanner, and a blue-light scanner for the production of digital impressions. MATERIAL AND METHODS: Reference scan data were obtained by scanning a complete-arch model. An identical model was scanned 8 times using an intraoral video scanner (CEREC Omnicam; Sirona) and an intraoral still image scanner (CEREC Bluecam; Sirona), and stone casts made from conventional impressions of the same model were scanned 8 times with a blue-light scanner as a control (Identica Blue; Medit). Accuracy consists of trueness (the extent to which the scan data differ from the reference scan) and precision (the similarity of the data from multiple scans). To evaluate precision, 8 scans were superimposed using 3-dimensional analysis software; the reference scan data were then superimposed to determine the trueness. Differences were analyzed using 1-way ANOVA and post hoc Tukey HSD tests (α=.05). RESULTS: Trueness in the video scanner group was not significantly different from that in the control group. However, the video scanner group showed significantly lower values than those of the still image scanner group for all variables (P<.05), except in tolerance range. The root mean square, standard deviations, and mean negative precision values for the video scanner group were significantly higher than those for the other groups (P<.05). CONCLUSIONS: Digital impressions obtained by the intraoral video scanner showed better accuracy for long-span areas than those captured by the still image scanner. However, the video scanner was less accurate than the laboratory scanner.

Three-dimensional evaluation of the repeatability of scans of stone models and impressions using a blue LED scanner.

In this study, we evaluated the repeatability of scans of stone models and impressions of abutment teeth using a blue LED scanner and compared the findings between different abutment teeth types. For the stone models as well as impression of the canines, premolars, and molars, we generated 10 color-difference-maps and reports for each tooth type (n=10 per tooth type). One-way analysis of variance (ANOVA) and independent t-tests were performed to evaluate the repeatability of scans of the stone models and impressions obtained from a blue LED scanner. Our results indicate a high repeatability of scans of stone models and impressions of abutment teeth using the blue LED scanner and suggest a possible clinical advantage for scanning impressions of different abutment teeth types.

Three-dimensional evaluation of the repeatability of scanned conventional impressions of prepared teeth generated with white- and blue-light scanners.

STATEMENT OF PROBLEM: Digital scanning is increasingly used in prosthodontics. Three-dimensional (3D) evaluations that compare the repeatability of the blue-light scanner with that of the white-light scanner are required. PURPOSE: The purpose of this in vitro study was to evaluate the repeatability of conventional impressions of abutment teeth digitized with white- and blue-light scanners and compare the findings for different types of abutment teeth. MATERIAL AND METHODS: Impressions of the canine, premolar, and molar abutment teeth were made and repeatedly scanned with each scanner type to obtain 5 sets of 3D data for each tooth. Point clouds were compared, and error sizes per tooth and scanner type were measured (n=10). One-way ANOVA with Tukey honest significant differences multiple comparison and independent t tests were performed to evaluate repeatability (α=.05). RESULTS: Repeatability (mean ±SD) of the white- and blue-light scanners for canine, premolar, and molar teeth was statistically significant (means: P=.001, P<.001, P<.001; ±SD: P<.001, P<.001, P=.003). Means of discrepancies with the white-light scanner (P<.001) were 5.8 µm for the canine, 5.9 µm for the premolar, and 8.6 µm for the molar teeth and 4.4 µm, 2.9 µm, and 3.2 µm, respectively, with the blue-light scanner (P<.001). Corresponding SDs of discrepancies with the white-light scanner (P<.001) were 15.9 µm for the canine, 23.2 µm for the premolar, and 14.6 µm for the molar teeth and 9.8 µm, 10.6 µm, and 11.2 µm, respectively, with the blue-light scanner (P=.73). CONCLUSIONS: On evaluation of the digitized abutment tooth impressions, the blue-light scanner exhibited greater repeatability than the white-light scanner.

Accuracy of 3D white light scanning of abutment teeth impressions: evaluation of trueness and precision.

PURPOSE: This study aimed to evaluate the accuracy of digitizing dental impressions of abutment teeth using a white light scanner and to compare the findings among teeth types. MATERIALS AND METHODS: To assess precision, impressions of the canine, premolar, and molar prepared to receive all-ceramic crowns were repeatedly scanned to obtain five sets of 3-D data (STL files). Point clouds were compared and error sizes were measured (n=10 per type). Next, to evaluate trueness, impressions of teeth were rotated by 10°-20° and scanned. The obtained data were compared with the first set of data for precision assessment, and the error sizes were measured (n=5 per type). The Kruskal-Wallis test was performed to evaluate precision and trueness among three teeth types, and post-hoc comparisons were performed using the Mann-Whitney U test with Bonferroni correction (α=.05). RESULTS: Precision discrepancies for the canine, premolar, and molar were 3.7 µm, 3.2 µm, and 7.3 µm, respectively, indicating the poorest precision for the molar (P<.001). Trueness discrepancies for teeth types were 6.2 µm, 11.2 µm, and 21.8 µm, respectively, indicating the poorest trueness for the molar (P=.007). CONCLUSION: In respect to accuracy the molar showed the largest discrepancies compared with the canine and premolar. Digitizing of dental impressions of abutment teeth using a white light scanner was assessed to be a highly accurate method and provided discrepancy values in a clinically acceptable range. Further study is needed to improve digitizing performance of white light scanning in axial wall.

White light scanner-based repeatability of 3-dimensional digitizing of silicon rubber abutment teeth impressions.

PURPOSE: The aim of this study was to evaluate the repeatability of the digitizing of silicon rubber impressions of abutment teeth by using a white light scanner and compare differences in repeatability between different abutment teeth types. MATERIALS AND METHODS: Silicon rubber impressions of a canine, premolar, and molar tooth were each digitized 8 times using a white light scanner, and 3D surface models were created using the point clouds. The size of any discrepancy between each model and the corresponding reference tooth were measured, and the distribution of these values was analyzed by an inspection software (PowerInspect 2012, Delcamplc., Birmingham, UK). Absolute values of discrepancies were analyzed by the Kruskal-Wallis test and multiple comparisons (α=.05). RESULTS: The discrepancy between the impressions for the canine, premolar, and molar teeth were 6.3 µm (95% confidence interval [CI], 5.4-7.2), 6.4 µm (95% CI, 5.3-7.6), and 8.9 µm (95% CI, 8.2-9.5), respectively. The discrepancy of the molar tooth impression was significantly higher than that of other tooth types. The largest variation (as mean [SD]) in discrepancies was seen in the premolar tooth impression scans: 26.7 µm (95% CI, 19.7-33.8); followed by canine and molar teeth impressions, 16.3 µm (95% CI, 15.3-17.3), and 14.0 µm (95% CI, 12.3-15.7), respectively. CONCLUSION: The repeatability of the digitizing abutment teeth's silicon rubber impressions by using a white light scanner was improved compared to that with a laser scanner, showing only a low mean discrepancy between 6.3 µm and 8.9 µm, which was in an clinically acceptable range. Premolar impression with a long and narrow shape showed a significantly larger discrepancy than canine and molar impressions. Further work is needed to increase the digitizing performance of the white light scanner for deep and slender impressions.