Mechanical Properties of Dental Alloys According to Manufacturing Process.

The purpose of this study is to investigate the effect of the fabrication method of dental prosthesis on the mechanical properties. Casting was produced using the lost wax casting method, and milling was designed using a CAD/CAM program. The 3D printing method used the SLS technique to create a three-dimensional structure by sintering metal powder with a laser. When making the specimen, the specimen was oriented at 0, 30, 60, and 90 degrees. All test specimens complied with the requirements of the international standard ISO 22674 for dental alloys. Tensile strength was measured for yield strength, modulus of elasticity and elongation by applying a load until fracture of the specimen at a crosshead speed of 1.5 ± 0.5 mm/min (n = 6, modulus of elasticity n = 3). After the tensile test, the cross section of the fractured specimen was observed with a scanning electron microscope, and the statistics of the data were analyzed with a statistical program SPSS (IBM Corp. Released 2020. IBM SPSS Statistics for Windows, Version 27.0. Armonk, NY, USA: IBM Corp.) and using Anova and multiple comparison post-tests (scheffe method). The yield strength was the highest at 1042 MPa at an angle of 0 degrees in the specimen produced by 3D printing method, and the elongation was the highest at 14% at an angle of 90 degrees in the specimen produced by 3D printing method. The modulus of elasticity was the highest at 235 GPa in the milled specimen. In particular, the 3D printing group showed a difference in yield strength and elongation according to the build direction. The introduction of various advanced technologies and digital equipment is expected to bring high prospects for the growth of the dental market.

Effect of rinsing time on the accuracy of interim crowns fabricated by digital light processing: An in vitro study.

PURPOSE: This study was to evaluate the effect of rinsing time on the accuracy of interim crowns fabricated by digital light processing. MATERIALS AND METHODS: The maxillary right first molar master die was duplicated using a silicone material, while a study die was produced using epoxy resin. Scans of the epoxy resin die were used in combination with CAD software to design a maxillary right first molar interim crown. Based on this design, 24 interim crowns were fabricated with digital light processing. This study examined the trueness and precision of products that were processed with one of the three different postprocessing rinsing times (1 min, 5 min, and 10 min). Trueness was measured by superimposing reference data with scanned data from external, intaglio, and marginal surfaces. Precision was measured by superimposing the scan data within the group. The trueness and precision data were analyzed using Kruskal-Wallis, nonparametric, and post-hoc tests, and were compared using a Mann-Whitney U test with Bonferroni correction (α=.05). RESULTS: The trueness of the external and intaglio surfaces of crowns varied significantly among the different rinsing times (P =.004, P =.003), but there was no statistically significant difference in terms of trueness measurements of the marginal surfaces (P =.605). In terms of precision, statistically significant differences were found among the external, intaglio, and marginal surfaces (P =.001). CONCLUSION: Interim crowns rinsed for 10 minutes showed high accuracy.

Evaluation of the adaptation of complete denture metal bases fabricated with dental CAD-CAM systems: An in vitro study.

STATEMENT OF PROBLEM: Conventional fabrication of complete denture metal bases is being replaced by the computer-aided design and computer-aided manufacturing (CAD-CAM) systems. However, a comparative analysis of subtractive and additive CAD-CAM manufacturing techniques is lacking. PURPOSE: The purpose of this in vitro study was to compare the adaptation of complete denture metal bases fabricated by milling (subtractive manufacturing) and stereolithography apparatus (SLA) and digital light processing (DLP) (additive manufacturing). MATERIAL AND METHODS: Thirty metal bases were manufactured by using the milling (MIL group), SLA (SLA group), and DLP (DLP group) techniques. The silicone replica technique was used to evaluate the adaptation of the complete denture metal bases, and 30 silicone blocks were fabricated. The silicone block was cut equally in the canine, first molar, and second molar areas. The gap between the model and the metal base was measured by using a digital microscope at the 3 locations, and the measured data were statistically analyzed by using a statistical software program (α=.05). RESULTS: The gaps measured at the 3 areas showed significant differences in all 3 groups (P<.05). At the anterior, middle, and posterior areas, the SLA group showed the narrowest gap (302 ±31 µm, 241 ±39 µm, 201 ±43 µm, respectively). The SLA group also had the narrowest total gap of the metal bases (218 ±33 µm). CONCLUSIONS: The adaptation of the fabricated metal bases varied significantly across the techniques used but fell within a clinically allowable range. The SLA group was the most precise in the fabrication of complete denture metal bases. Further studies are required to analyze the effects of the layer thickness setting, wax elimination, and casting temperature on the adaptation of metal bases manufactured by using SLA.

Evaluation of the accuracy (trueness and precision) of a maxillary trial denture according to the layer thickness: An in vitro study.

STATEMENT OF PROBLEM: Layer thickness in additive manufacturing has stair-step effects that greatly affect the accuracy of the definitive prosthesis. Although the layer thickness can be set, insufficient data comparing and analyzing the accuracy of the fabricated prosthesis after adjusting the layer thickness are available. PURPOSE: The purpose of this in vitro study was to evaluate and compare the accuracy of trial dentures fabricated with different layer thicknesses by using stereolithography (SLA) apparatus. MATERIAL AND METHODS: A maxillary complete edentulous cast was duplicated with silicone material to make a master gypsum cast which was scanned by using a laboratory scanner and saved as a standard tessellation language (STL) file. This was exported into a computer-aided design software program to produce and store the trial denture. Twenty dentures were fabricated according to the set layer thicknesses (50 µm and 100 µm) by using the SLA. The trueness was measured by scanning the intaglio and cameo surfaces to find the best overlap with the reference model to obtain the root mean square value. The precision was evaluated based on the RMS value gained by superimposing the identical scan data from each group and using the combination formula. The Mann-Whitney U-test was used to confirm significant differences among the groups (α=.05). RESULTS: The trueness of the 50-µm-SLA trial denture and the 100-µm-SLA trial denture was significantly different for the intaglio and cameo surfaces (P<.05). However, the intaglio surface did not show a statistically significant difference (P=.987) for precision, but the cameo surface did (P<.05). CONCLUSIONS: It is clinically more appropriate to set the layer thickness to 100 µm rather than 50 µm for the fabrication of accurate trial dentures by using SLA.

Evaluation of the Milling Accuracy of Zirconia-Reinforced Lithium Silicate Crowns Fabricated Using the Dental Medical Device System: A Three-Dimensional Analysis.

This study aimed to analyze the milling accuracy of lithium disilicate and zirconia-reinforced silicate crown fabricated using chairside computer-aided design/manufacturing (CAD/CAM) system. Mandibular left first premolar was selected for abutment. A master model was obtained for digital impression using an intraoral scanner, and crowns were designed using a CAD software design program. Amber Mill (AM), IPS e max CAD (IPS), and CELTRA DUO (CEL) were used in the CAD/CAM system, and a total 45 crowns (15 crowns each for AM, IPS, and CEL) was fabricated. Milling accuracy was analyzed with respect to trueness, measured by superimposing CAD design data and scan data through a three-dimensional program to compare the outer and inner surfaces and internal and external parts, thereby acquiring both quantitative and qualitative data. Data were analyzed using the non-parametric test and Kruskal-Wallis H test. In addition, the Mann-Whitney U test was used by applying the level of significance (0.05/3 = 0.016) adjusted by post-analysis Bonferroni correction. All the measured parts of the lithium disilicate and zirconia-reinforced silicate crowns showed statistically significant differences (p < 0.05). The lithium disilicate (AM and IPS) materials showed superior milling accuracy than the zirconia-reinforced lithium silicate (CEL) materials.

Influence of Orthodontic Anchor Screw Anchorage Method on the Stability of Artificial Bone: An In Vitro Study.

This study aims to compare the torque values for various lengths of the titanium-based orthodontic anchor screw (OAS), different anchorage methods and varying artificial bone densities after predrilling. Furthermore, the effects of these parameters on bone stability are evaluated. A total of 144 OASs were prepared with a diameter of 1.6 mm and heights of 6, 8 and 10 mm. Artificial bones were selected according to their density, corresponding to Grades 50, 40 and 30. Torque values for the automatic device and manual anchorage methods exhibited a statistically significant difference for the same-sized OAS, according to the bone density of the artificial bones (p < 0.05). However, when insertion torque was at the maximum rotations, there was no significant difference in the torque values for the Grade 30 artificial bone (p > 0.05). When the torque values of both anchorage methods were statistically compared with the mean difference for each group, the results of the manual anchorage method were significantly higher than those of the automatic device anchorage method (p < 0.05). A statistically significant difference was observed in the bone stability resulting from different OAS anchorage methods and artificial bone lengths. These findings suggest that the automatic anchorage method should be used when fixing the OAS.

Three-dimensional trueness analysis of ceramic crowns fabricated using a chairside computer-aided design/manufacturing system: An in vitro study.

PURPOSE: This study analyzed the trueness of polymer-infiltrated ceramic and glass ceramic crowns manufactured using the chairside computer-aided design/manufacturing (CAD/CAM) system. METHODS: The master model designs crowns using a CAD program after acquiring a digital impression with an intraoral scanner. Vita Enamic (VE), Vita Suprinity (VS), and IPS e.max CAD (IPS) were used to manufacture 10 crowns each (total: 30 crowns), using the chairside CAD/CAM system (inLab MC XL). Trueness was evaluated by superimposing the CAD data on the scan data using a three-dimensional program. The Kruskal-Wallis H test, a nonparametric test, and the Mann-Whitney U test were performed by applying the significance level (0.05/3=0.016), which was adjusted by post-analysis Bonferroni testing. RESULTS: There was a significant difference in the trueness between the samples (p<0.05). However, there was no statistically significant difference in the outer surface trueness between the samples (p>0.05). CONCLUSIONS: These findings show that the milling accuracy of VE is better than that of VS and IPS.

Effect of core materials for core fabrication for dental implants on in-vitro cytocompatibility of MC3T3-E1 cells.

BACKGROUND: Despite the wide use of dental materials for CAD/CAM system in prosthetic treatment, the effect of the materials, which are used as dental implants core fabricated, on cells involved in dental implant osseointegration is uncertain. This study aimed to investigate and compare the effect of single core materials used for dental implants fabricated by the dental prostheses fabrication process and the CAD/CAM milling method on MC3T3-E1 cells. METHODS: The materials used for prostheses restoration in this experiment were Porcelain Fused Gold (P.F.G), Lithium disilicate glass ceramic (LiSi2), Zirconia (ZrO2), Nickel-Chromium (Ni-Cr) and Cobalt-Chromium (Co-Cr). MC3T3-E1 cells were cultured and used, the cell adhesion and morphology were observed and analyzed using confocal laser scanning microscopy (CLSM). Methoxyphenyl tetrazolium salt (MTS) and alkaline phosphatase (ALP) assay were used to observe the cell proliferation and differentiation. RESULTS: CLSM revealed irregular cell adhesion and morphology and the filopodia did not spread in the Ni-Cr specimen group. Significantly high cell proliferation was observed in the ZrO2 specimen group. The LiSi2 specimen group presented significantly high cell differentiation. Intergroup comparison of cell proliferation and differentiation between the Ni-Cr specimen group and all other specimen groups showed significant differences (p < .05). CONCLUSION: Cell proliferation and differentiation were observed from the cores, which were fabricated with all specimen groups on cytocompatibility except the Ni-Cr specimen group.

Evaluation of marginal discrepancy of pressable ceramic veneer fabricated using CAD/CAM system: Additive and subtractive manufacturing.

PURPOSE: The purpose of this study was to evaluate the marginal discrepancy of heat-pressed ceramic veneers manufactured using a CAD/CAM system. MATERIALS AND METHODS: The ceramic veneers for the abutment of a maxillary left central incisor were designed using a CAD/CAM software program. Ten veneers using a micro-stereolithography apparatus (AM group), ten veneers using a five-axis milling machine (SM group), and ten veneers using a traditional free-hand wax technique (TW group) were prepared according to the respective manufacturing method. The ceramic veneers were also fabricated using a heat-press technique, and a silicone replica was used to measure their marginal discrepancy. The marginal discrepancies were measured using a digital microscope (×160 magnification). The data were analyzed using a nonparametric Kruskal-Wallis H test. Finally, post-hoc comparisons were conducted using Bonferroni-corrected Mann-Whitney U tests (α=.05). RESULTS: The mean±SD of the total marginal discrepancy was 99.68±28.01 µm for the AM group, 76.60±28.76 µm for the SM group, and 83.08±39.74 µm for the TW group. There were significant differences in the total marginal discrepancies of the ceramic veneers (P<.05). CONCLUSION: The SM group showed a better fit than the AM and TW groups. However, all values were within the clinical tolerance. Therefore, CAD/CAM manufacturing methods can replace the traditional free-hand wax technique.

Accuracy of provisional crowns made using stereolithography apparatus and subtractive technique.

PURPOSE: To compare and analyze trueness and precision of provisional crowns made using stereolithography apparatus and subtractive technology. MATERIALS AND METHODS: Digital impressions were made using a master model and an intraoral scanner and the crowns were designed with CAD software; in total, 22 crowns were produced. After superimposing CAD design data and scan data using a 3D program, quantitative and qualitative data were obtained for analysis of trueness and precision. Statistical analysis was performed using normality test combined with Levene test for equal variance analysis and independent sample t-test. Type 1 error was set at 0.05. RESULTS: Trueness for the outer and inner surfaces of the SLA crown (SLAC) were 49.6±9.3 µm and 22.5±5.1 µm, respectively, and those of the subtractive crown (SUBC) were 31.8±7.5 µm and 14.6±1.2 µm, respectively. Precision values for the outer and inner surfaces of the SLAC were 18.7±6.2 µm and 26.9±8.5 µm, and those of the SUBC were 25.4±3.1 µm and 13.8±0.6 µm, respectively. Trueness values for the outer and inner surfaces of the SLAC and SUBC showed statistically significant differences (P<.001). Precision for the inner surface showed significance (P<.03), whereas that for the outer surface showed no significance (P<.58). CONCLUSION: The study demonstrates that provisional crowns produced by subtractive technology are superior to crowns fabricated by stereolithography in terms of accuracy.