An arch-shaped master model measuring 14 mm in height and 16 mm in width was designed using CAD software (RapidForm XOR2; 3D Systems). Six abutments representing prepared teeth (right and left mandibular second molar, right and left mandibular second premolar, right and left mandibular canine) with a height of 10.15 mm and 6° total angle of convergence with 1mm shoulder finish line were placed on the arch. The abutments were designed according to ANSI /ADA specifications, which are also similar to abutments on the test model used in ISO 12836:2015 specification (Digitizing devices for CAD/CAM systems for indirect dental restorations-Test methods for assessing accuracy) [16 (link)].
The digital master model was then saved in Standard Tessellation Language (.stl) format and printed using a Polyjet 3D printer (Objet30 Prime, Stratasys Ltd.). The Polyjet 3D printers utilize materials that are extruded from nozzles or a photopolymer that is jetted over the workspace. Then the object is solidified through polymerization with the use of a UV light source [17 (link)]. The Objet30 Prime printer uses the intuitive “Objet Studio” 3D printing software. A rigid and transparent photopolymer material named VeroClear was used to print the master model, while the SUP705 material was used for support structures. The SUP705 material is removable with a waterjet, so no post-curing process was necessary. The production time of the master model took 4 hours and 10 minutes.
An industrial structured blue LED light 3D scanner (ATOS Core 200 5M, GOM GmbH, Braunschweig, Germany) was selected for use. The scanner was calibrated and tested according to VDI/VDIE 2634 (VDI e.V.; Düsseldorf, Germany), displaying maximum deviations: 2 μm probing error form (sigma), 4 μm probing error (size), 7 μm sphere spacing error and 8 μm length measurement error. The printed master model was then scanned ten times with the ATOS scanner and the scan data was merged into a single file using computer software. The data was then exported in STL format.
Polyvinyl siloxane (PVS) impression material and a one-step impression technique were used for the impression procedure. The impression materials were mixed according to the manufacturer’s instructions. The PVS putty impression material (Vinlybest; BMS DENTAL, Capannoli, Italy) was hand-mixed until a homogeneous mixture was obtained within 30 seconds, and it was then inserted into the customized tray. The light-body material (Vinlylight; BMS DENTAL, Capannoli, Italy) was simultaneously spread on the master model. The impressions were allowed to polymerize, and the trays were removed after the materials had set. A total of 30 impressions were made under the same room conditions and stored at room temperature (22° C) for 2 hours before the pouring procedure. All impressions were examined visually, and impressions with voids were excluded from the study.
The dental gypsum products used in this study included two CAD/CAM optimized stones (CEREC Stone BC, Sirona Dental Systems GmbH Bensheim, Germany) (BC) and (Elite Master, Zhermack S.p.A, Italy) (EM) and one conventional type IV stone (Elite Rock Fast, Zhermack S.p.A, Italy) (ERF) (Fig 1 ). The composition and characteristics of the materials are summarized in Table 1 . All dental stones were mixed according to the respective manufacturer’s recommendations. Deionized water was used. Each stone cast was poured under vibration (Degussa Vibrator R2; Degussa AG, Germany) and allowed to set for 2 hours at room temperature. A total of 30 stone casts were made (n = 10). Then, all stone models were scanned with the Activity 885 blue light scanner (Smart Optics; Bauman Sensortechnik GmbH, Germany, the accuracy of 6 μm according to DIN ISO 12836) [18 (link)], and digital models were obtained.
In the 3D analysis (Geomagic Control, 3D Systems) procedure, a sample size of 15,000 points with a tolerance of 0.001 mm and the best-fit alignment method was used. The 3D analysis software gave the root mean square (RMS) and average maximum and minimum values. Trueness was determined by superimposing the digital master model data on the digital models. Precision was assessed for each digital model by overlaying combinations of the 10 datasets in each group.
The color-coded maps of deviations were created using scans of the stone models. The maps were presented using 3D analysis software. Yellow to red fields represent enlargements, while turquoise to dark blue fields represent contractions on the digital models (Fig 2 ). The point cloud density of each model was calculated using MeshLab software (ISTI—CNR, Pisa, Italy) (Fig 3 ). The number of all points that construct the complete digital model was divided by the model’s surface area in mm2.
Statistical analysis was performed with a significance level of 95% and %99 using software NCSS (Number Cruncher Statistical System) 2007 (Kaysville, Utah, USA). The distribution of study data was evaluated with the Shapiro-Wilk Test. Since the assumption of normality was not met, Kruskal Wallis and Mann-Whitney non-parametric tests were used to compare the different dental stones and the statistical analysis of the measurements.
The digital master model was then saved in Standard Tessellation Language (.stl) format and printed using a Polyjet 3D printer (Objet30 Prime, Stratasys Ltd.). The Polyjet 3D printers utilize materials that are extruded from nozzles or a photopolymer that is jetted over the workspace. Then the object is solidified through polymerization with the use of a UV light source [17 (link)]. The Objet30 Prime printer uses the intuitive “Objet Studio” 3D printing software. A rigid and transparent photopolymer material named VeroClear was used to print the master model, while the SUP705 material was used for support structures. The SUP705 material is removable with a waterjet, so no post-curing process was necessary. The production time of the master model took 4 hours and 10 minutes.
An industrial structured blue LED light 3D scanner (ATOS Core 200 5M, GOM GmbH, Braunschweig, Germany) was selected for use. The scanner was calibrated and tested according to VDI/VDIE 2634 (VDI e.V.; Düsseldorf, Germany), displaying maximum deviations: 2 μm probing error form (sigma), 4 μm probing error (size), 7 μm sphere spacing error and 8 μm length measurement error. The printed master model was then scanned ten times with the ATOS scanner and the scan data was merged into a single file using computer software. The data was then exported in STL format.
Polyvinyl siloxane (PVS) impression material and a one-step impression technique were used for the impression procedure. The impression materials were mixed according to the manufacturer’s instructions. The PVS putty impression material (Vinlybest; BMS DENTAL, Capannoli, Italy) was hand-mixed until a homogeneous mixture was obtained within 30 seconds, and it was then inserted into the customized tray. The light-body material (Vinlylight; BMS DENTAL, Capannoli, Italy) was simultaneously spread on the master model. The impressions were allowed to polymerize, and the trays were removed after the materials had set. A total of 30 impressions were made under the same room conditions and stored at room temperature (22° C) for 2 hours before the pouring procedure. All impressions were examined visually, and impressions with voids were excluded from the study.
The dental gypsum products used in this study included two CAD/CAM optimized stones (CEREC Stone BC, Sirona Dental Systems GmbH Bensheim, Germany) (BC) and (Elite Master, Zhermack S.p.A, Italy) (EM) and one conventional type IV stone (Elite Rock Fast, Zhermack S.p.A, Italy) (ERF) (
In the 3D analysis (Geomagic Control, 3D Systems) procedure, a sample size of 15,000 points with a tolerance of 0.001 mm and the best-fit alignment method was used. The 3D analysis software gave the root mean square (RMS) and average maximum and minimum values. Trueness was determined by superimposing the digital master model data on the digital models. Precision was assessed for each digital model by overlaying combinations of the 10 datasets in each group.
The color-coded maps of deviations were created using scans of the stone models. The maps were presented using 3D analysis software. Yellow to red fields represent enlargements, while turquoise to dark blue fields represent contractions on the digital models (
Statistical analysis was performed with a significance level of 95% and %99 using software NCSS (Number Cruncher Statistical System) 2007 (Kaysville, Utah, USA). The distribution of study data was evaluated with the Shapiro-Wilk Test. Since the assumption of normality was not met, Kruskal Wallis and Mann-Whitney non-parametric tests were used to compare the different dental stones and the statistical analysis of the measurements.
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