Ceramic molar crown reproducibility by digital workflow manufacturing: An in vitro study.

PURPOSE: This in vitro study aimed to analyze and compare the reproducibility of zirconia and lithium disilicate crowns manufactured by digital workflow. MATERIALS AND METHODS: A typodont model with a prepped upper first molar was set in a phantom head, and a digital impression was obtained with a video intraoral scanner (CEREC Omnicam; Sirona GmbH), from which a single crown was designed and manufactured with CAD/CAM into a zirconia crown and lithium disilicate crown (n=12). Reproducibility of each crown was quantitatively retrieved by superimposing the digitized data of the crown in 3D inspection software, and differences were graphically mapped in color. Areas with large differences were analyzed with digital microscopy. Mean quadratic deviations (RMS) quantitatively obtained from each ceramic group were statistically analyzed with Student's t-test (α=.05). RESULTS: The RMS value of lithium disilicate crown was 29.2 (4.1) µm and 17.6 (5.5) µm on the outer and inner surfaces, respectively, whereas these values were 18.6 (2.0) µm and 20.6 (5.1) µm for the zirconia crown. Reproducibility of zirconia and lithium disilicate crowns had a statistically significant difference only on the outer surface (P<.001). The outer surface of lithium disilicate crown showed over-contouring on the buccal surface and under-contouring on the inner occlusal surface. The outer surface of zirconia crown showed both over- and under-contouring on the buccal surface, and the inner surface showed under-contouring in the marginal areas. CONCLUSION: Restoration manufacturing by digital workflow will enhance the reproducibility of zirconia single crowns more than that of lithium disilicate single crowns.

Evaluation of marginal and internal gaps of Ni-Cr and Co-Cr alloy copings manufactured by microstereolithography.

PURPOSE: The purpose of this study was to evaluate the marginal and internal gaps of Ni-Cr and Co-Cr copings, fabricated using the dental µ-SLA system. MATERIALS AND METHODS: Ten study dies were made using a two-step silicone impression with a dental stone (type IV) from the master die of a tooth. Ni-Cr (NC group) and Co-Cr (CC group) alloy copings were designed using a dental scanner, CAD software, resin coping, and casting process. In addition, 10 Ni-Cr alloy copings were manufactured using the lost-wax technique (LW group). The marginal and internal gaps in the 3 groups were measured using a digital microscope (160 ×) with the silicone replica technique, and the obtained data were analyzed using the non-parametric Kruskal-Wallis H test. Post-hoc comparisons were performed using Bonferroni-corrected Mann-Whitney U tests (α=.05). RESULTS: The mean (±standard deviation) values of the marginal, chamfer, axial wall, and occlusal gaps in the 3 groups were as follows: 81.5±73.8, 98.1±76.1, 87.1±44.8, and 146.8±78.7 µm in the LW group; 76.8±48.0, 141.7±57.1, 80.7±47.5, and 194.69±63.8 µm in the NC group; and 124.2±52.0, 199.5±71.0, 67.1±37.6, and 244.5±58.9 µm in the CC group. CONCLUSION: The marginal gap in the LW and NC groups were clinically acceptable. Further improvement is needed for CC group to be used clinical practice.

Evaluation of accuracy and repeatability using CBCT and a dental scanner by means of 3D software.

OBJECTIVE: The objective of the present study was to compare and evaluate the accuracy of three-dimensional (3D) image data acquired from cone beam computed tomography (CBCT) and a dental scanner using 3D software. MATERIALS AND METHODS: After selecting the full-arch forms of the maxilla and mandible as the master cast, the master cast was scanned via a high-precision optical scanner for use as master model data. The model was scanned 12 times each using CBCT and a dental scanner. Scanned data were superimposed onto the master cast data for evaluation of accuracy and repeatability. RESULTS: Although significant differences in both accuracy and repeatability were seen between CBCT and dental scanner (P < 0.05), repeatability of the maxillary arch showed little difference, with CBCT and scanner having values of 17 ± 2 µm and 22 ± 5 µm, respectively. Meanwhile, repeatability of the mandibular arch with CBCT and scanner was 15 ± 0 µm and 19 ± 3 µm, respectively. Since good repeatability was shown, this demonstrated that data can be stably acquired. CONCLUSIONS: The present study demonstrated the feasibility of using a dental scanner to create a digital model as a substitute for a plaster model for use in orthodontic diagnosis and device fabrication.

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.

Trueness of milled prostheses according to number of ball-end mill burs.

STATEMENT OF PROBLEM: Making a computer-aided design/computer-aided manufacturing (CAD/CAM) prosthesis with a milling machine often requires 2 (2- and 1-mm diameter) or 3 (2-, 1-, and 0.6-mm diameter) burs; however, using 3 burs can reduce time effectiveness and increase cost. Studies evaluating the trueness of prostheses made with 2 and 3 burs are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the 3-dimensional trueness of crown prostheses made using 2 and 3 ball-end mill burs in the milling process. MATERIAL AND METHODS: The abutment die of the maxillary right first molar for ceramic crowns was designed with computer-aided design software. After the crown prosthesis design was completed, polyurethane blocks were milled using 2 and 3 burs with a 5-axis milling machine. The outer and inner surfaces of the milled crown prostheses were scanned with a dental scanner. The inner part was separated into a marginal part and an internal part using 3-dimensional evaluation software. The 3-dimensional trueness of the prostheses milled with 2 or 3 burs was compared. RESULTS: No significant differences in trueness were found for the inner or internal parts of the prosthesis (P>.05). However, the outer and marginal parts of the prosthesis did show significant differences in trueness (P<.05). CONCLUSIONS: Milling the marginal part of the inner prosthesis was better with 2 burs, whereas milling the outer part was better with 3 burs.

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.