Titanium Master Research Articles

A combined effect of the structure of aluminium – silicon and aluminium – titanium master alloys on the structure and properties of Al – Si – Mg alloy

A combined effect of the structure of aluminium – silicon and aluminium – titanium master alloys on the structure and properties of Al – Si – Mg alloy

42 - Fatigue Resistance of CAD/CAM and 3D-Printing Provisional Restorations

3D-printed provisional restorations can be fabricated using additive manufacturing (AM) technologies. However, little information about their performance is available. The aim of this study was to compare the fatigue resistance of 3-teeth provisional resin restorations obtained by 3D printing with those made from polymethylmethacrylate (PMMA) blocks using a CAD/CAM system. A titanium master model for 3-teeth fixed dental prostheses (FDPs) (abutment teeth 45 and 47) was prepared. The master model was scanned and 14 provisional FDPs were produced using respectively: group 1 (N=7): CAD/CAM + BreCAM HIPC-Bredent (BH); group 2 (N=7): 3D printing + NextDent (ND). The FDPs were cemented on the titanium master model with a provisional cement (Temp Bond, Kerr) and submitted to a 5-step incremental cyclic isometric loading: step 1: 5.000 cycles at 10 Hz with 200 N compressive load; steps 2 to 5: 30.000 cycles at 3 Hz with a compressive load respectively of 400 N, 600 N, 800 N and 950 N. Group 1 and 2 were compared using the life table survival analysis and t-test. In group 1 (BH), only 5 specimens endured the entire fatigue process, while 2 specimens failed at 950 N. In group 2 (ND), 1 specimen failed at 400 N, 5 specimens (ND) failed at 600 N) and 1 specimen failed at 800 N. PMMA CAD/CAM provisional FDPs showed higher fatigue resistance when compared to the ones made via 3D printing.

Dimensional Changes of Yttria-stabilized Zirconia under Different Preparation Designs and Sintering Protocols.

To evaluate the linear and volumetric dimensional changes that occur throughout the fabrication process of monolithic 4.5-6% yttria-stabilized zirconia copings under the influence of different preparation designs and two sintering protocols. A titanium master die was fabricated using Atlantis core file implant-abutment. Six copings were designed virtually according to different finish line offsets and coping thicknesses, with four equidistant occlusal posts for linear measurements. Zirconia copings were milled using IPS e.max ZirCAD LT zirconia blanks. The experimental groups according to the coping designs were the following: G1: 0.5 mm finish line offset, 0.5 mm thickness; G2: 0.5 mm finish line offset, 1.0 mm thickness; G3: 0.5 mm finish line offset, 1.5 mm thickness; G4: 1.2 mm finish line offset, 0.5 mm thickness; G5: 1.2 mm finish line offset, 1.0 mm thickness; G6: 1.2 mm finish line offset, 1.5 mm thickness. Six samples per group were sintered by standard sintering (SS) and the other six by fast sintering (FS). Linear and volumetric measurements were taken at the three fabrication stages (virtual design, milling stage, and sintering) by using an intraoral scanner and imported as the .stl file to Meshmixer software for analysis. Statistical analysis was performed by a linear mixed effect model via statistical software R (R Core team, 2018). There was a significant interaction between the coping design group, stage of fabrication and sintering protocol on the linear (F = 4.451, p < 0.001) and volumetric (F = 2.716; p < 0.001) dimensional changes. Standard sintering G1 showed the smallest linear and dimensional changes among the groups compared to the reference design. Sintered copings had shrunk on average 1.32% within SS and 1.54% within FS linearly and 3.82% within SS and 3.90% within FS volumetrically compared to the initial design parameters. The linear and volumetric dimensional changes did not differ significantly between standard and fast sintering protocols, and the preparation designs had more influence on the dimensional changes compared to sintering protocols.

Impact of Different Scan Bodies and Scan Strategies on the Accuracy of Digital Implant Impressions Assessed with an Intraoral Scanner: An In Vitro Study.

Sufficient data are not currently available on how the various geometries of scan bodies and different scan strategies affect the quality of digital impressions of implants. The purpose of this study was to present new data on these two topics and give clinicians a basis for decision making. A titanium master model containing three Nobelreplace Select™ implants (Nobelbiocare Services AG, Zurich, Switzerland) was digitized using an ATOS industrial noncontact scanner. Digitization was repeated three times with different types of scan bodies integrated into the implants: ELOS A/S, nt-trading GmbH, and TEAMZIEREIS GmbH. These three scans served as virtual master models. The titanium master model was then scanned with the TRIOS3© digital intraoral scanner (ELOS A/S, Copenhagen, Denmark), which was used for two different scanning strategies. Strategy A was a one-step procedure that included both the titanium master model and the integrated scan bodies. Strategy B comprised two steps. First, a digital overlay was performed with a scan of the titanium master model without integrated scan bodies. A second scan was performed with the titanium master model and integrated scan bodies. By repeating both strategies 10 times for each type of scan body, 60 scans were generated and the corresponding standard tessellation language data sets overlaid with the corresponding virtual master model. Deviations in the resulting superimpositions were calculated and evaluated separately in the individual axes (x, y, z) and in three-dimensional space (Euclidean distance). Statistical evaluation was performed using the R-project software. Level of significance was determined at p ≤ 0.05. With regard to the geometry of the scan bodies, strategy A significantly influenced the accuracy of the digital implant impression in regards to Euclidean distance (p = 0.003). No significant difference was found for strategy B in this context. Comparing the two scan strategies revealed that strategy A achieved significantly higher accuracy overall (p = 0.031). The quality of digital intraoral impressions seems to be influenced by both the geometry of the scan body and the scan strategy. For clinical practice, the one-step scan strategy seems beneficial. Furthermore, the scan bodies of ELOS A/S showed a potential clinical advantage.

Dimensional stability of double-processed complete denture bases fabricated with compression molding, injection molding, and CAD-CAM subtraction milling

Statement of problemStudies evaluating the dimensional stability of denture bases fabricated by the double processing method are lacking. PurposeThe purpose of this in vitro study was to evaluate the dimensional stability of denture bases fabricated by 3 different techniques: compression molding, injection molding, and computer-aided design and computer-aided manufacturing (CAD-CAM) subtraction milling. Material and methodsForty-five mandibular denture bases were fabricated from a master cast by a standardized process. A double processing protocol was used with 3 methods: compression molding (PRESS), injection molding (INJECT), or CAD-CAM (CAD). The bases were compared with the titanium master cast after the first processing. By a digital subtraction process, the dimensional stability of the bases was measured at 22 different locations on the intaglio surface. Denture teeth were then positioned according to a standardized protocol, and the denture was processed a second time and finished. The dimensional discrepancy was reassessed after the second processing and compared with the titanium master cast. ResultsIn all groups, most of the dimensional changes occurred during the first processing (P<.05), with no statistically significant deformation occurring during the second processing (P>.05). The CAD group presented significantly smaller dimensional changes than PRESS (P<.05) and INJECT (P<.05) groups. No significant difference was found in the dimensional stability in the PRESS and INJECT groups (P>.05). ConclusionsDenture bases fabricated by a CAD-CAM methodology exhibit fewer dimensional changes than either compression or injection molding. Distortion occurred during the fabrication of the denture base, and a second processing did not significantly affect the dimensional stability of the denture base.

Influence of finish line design on the marginal fit of nonprecious metal alloy coping fabricated by 3D printing, milling and casting using CAD CAM

Background The marginal fit is one of the key factors for the clinical success of dental restorations. Ideal marginal adaptation can reduce gingival irritation and cement dissolution. After clinically examining over 1000 metal ceramic crowns, McLean and von Fraunhofer reported that marginal discrepancies up to 120 μm were acceptable. Other clinicians considered a marginal fit of 100 μm to be clinically acceptable for the longevity of the restorations. Aim/Hypothesis The purpose of this study was to examine the correlation between the finish line designs and the marginal adaptation of nonprecious metal alloy coping produced by different digital manufacturing methods. Material and Methods For fabrication of two master models with different finish lines, the master models were designed by 3-D designing software program based on the abutment preparation principle and titanium master models were milled by computer aided manufacturing. Nonprecious metal alloy copings were made respectively from each master model with three different methods, selective laser sintering (SLS), milling and casting by CAD CAM. 12 copings were made by each method resulting in 72 copings in total. The marginal fit was evaluated by measuring the gap between the cavosurface margin of the abutment die and the edge of the crown margin on mesial, buccal, distal and lingual site of each specimen. The measurement was conducted at 40 determined reference points along the circumferential margin with the confocal laser scanning microscope at magnification ×150. Results Mean values of marginal gap of laser sintered copings were 11.8 ± 7.4 μm for deep chamfer margin and 6.3 ± 3.5 μm for rounded shoulder margin and the difference between them was statistically significant (P < 0.0001). Mean values of marginal gap of milled copings were 53.9 ± 27.8 μm for deep chamfer margin and 48.6 ± 30.1 μm for rounded shoulder margin and the difference between them was not significant (P = 0.279). Mean values of marginal gap of casted copings were 18.8 ± 20.2 μm for deep chamfer margin and 33 ± 20.5 μm for rounded shoulder margin and the difference between them was significant (P = 0.0004). Meanwhile, the marginal fit depending on the manufacturing method was significantly different regardless of finish line design. Selective laser sintering group exhibited the best marginal adaptation among three manufacturing methods and digitalized casting group showed better marginal fit than milling group. Conclusions and Clinical Implications (i) The variation of finish line design influences the marginal adaptation of laser sintered metal coping and casted metal coping. (ii) Laser sintered copings with rounded shoulder margin had better marginal fit than deep chamfer margin. (iii) Casted copings with deep chamfer margin had better marginal fit than rounded shoulder margin. (iv) According to the manufacturing method, SLS system showed the best marginal fit among three different methods. Casting and milling method followed that in order.

Evaluation of the fit of metal copings fabricated using stereolithography

Statement of problemRapid prototyping, including stereolithography (SLA), is a more recent technique for fabricating metal frameworks than the conventional lost-wax technique. However, investigations of the marginal discrepancies and internal spacing of cobalt-chromium (Co-Cr) metal copings fabricated using SLA are lacking. PurposeThe purpose of this in vitro study was to evaluate the clinical acceptability of the marginal discrepancies and internal spacing of Co-Cr metal copings fabricated using the SLA technique. Material and methodsA resin tooth of a maxillary right first premolar was prepared with a deep chamfer margin for a metal–ceramic crown. Titanium master dies were milled after scanning the prepared tooth (n=45). In conventional lost wax group (group LW), the conventional lost-wax technique was used to fabricate Co-Cr metal copings (n=15). In milling group (group MC), a computer-aided design (CAD) system was used to design the metal copings, which were milled from Co-Cr alloy (n=15). The CAD system was also used to design the metal copings in a 3D-printed group (group SL), and Co-Cr metal copings were cast from resin patterns fabricated using the SLA device (n=15). Marginal discrepancies and internal spaces were measured using an optical microscope at ×100 magnification at 11 reference points. The values were analyzed statistically with 1-way analysis of variance (α=.05). ResultsThe mean (±SD) overall space was 63.2 ±16.6 μm for group LW, 70.2 ±15.5 μm for group SL, and 130.3 ±13.8 μm for group MC. The overall spaces differed significantly between group MC and the other 2 groups (P<.05). The marginal discrepancy and internal spaces were significantly larger in group MC than in groups LW and SL. (P<.05). Occlusal spaces differed significantly among the 3 study groups (P<.05). ConclusionsCo-Cr metal copings fabricated using an SLA technique showed clinically acceptable marginal discrepancies and internal spaces. These spaces did not differ significantly from those obtained with the conventional lost-wax technique.

Comparison of Fit of Dentures Fabricated by Traditional Techniques Versus CAD/CAM Technology.

To compare the shrinkage of denture bases fabricated by three methods: CAD/CAM, compression molding, and injection molding. The effect of arch form and palate depth was also tested. Nine titanium casts, representing combinations of tapered, ovoid, and square arch forms and shallow, medium, and deep palate depths, were fabricated using electron beam melting (EBM) technology. For each base fabrication method, three poly(vinyl siloxane) impressions were made from each cast, 27 dentures for each method. Compression-molded dentures were fabricated using Lucitone 199 poly methyl methacrylate (PMMA), and injection molded dentures with Ivobase's Hybrid Pink PMMA. For CAD/CAM, denture bases were designed and milled by Avadent using their Light PMMA. To quantify the space between the denture and the master cast, silicone duplicating material was placed in the intaglio of the dentures, the titanium master cast was seated under pressure, and the silicone was then trimmed and recovered. Three silicone measurements per denture were recorded, for a total of 243 measurements. Each silicone measurement was weighed and adjusted to the surface area of the respective arch, giving an average and standard deviation for each denture. Comparison of manufacturing methods showed a statistically significant difference (p = 0.0001). Using a ratio of the means, compression molding had on average 41% to 47% more space than injection molding and CAD/CAM. Comparison of arch/palate forms showed a statistically significant difference (p = 0.023), with shallow palate forms having more space with compression molding. The ovoid shallow form showed CAD/CAM and compression molding had more space than injection molding. Overall, injection molding and CAD/CAM fabrication methods produced equally well-fitting dentures, with both having a better fit than compression molding. Shallow palates appear to be more affected by shrinkage than medium or deep palates. Shallow ovoid arch forms appear to benefit from the use of injection molding compared to CAD/CAM and compression molding.

Modifying ability of titanium-based pelleted master alloys

The problem of enhancing the quality of pressed titanium master alloys is discussed to increase the rate and degree of dissolution of their components and to ensure the formation of a fine-grained structure in aluminum alloys. A technology of producing a pelleted titanium master alloy for effective correction of the chemical composition of an aluminum alloy in casting is developed and tested. Incoming inspection of the component composition and the flux distribution in the volume of pressed pellets of various manufacturers is performed. The rate of dissolution of pressed powder master alloys in the aluminum melt is studied, and their modifying ability is estimated after studying the microstructures of cast blanks. Molasses is used as a binder in a pelleted master alloy. As a result, we achieved a uniform flux distribution over the pellet volume and the formation of uniform pores after annealing as compared pelleted master alloys of other manufacturers. The fabricated alloying briquettes have higher strength characteristics and their dissolution rate in the aluminum melt is higher than those of analogs by 15–20%.

Accuracy of impression scanning compared with stone casts of implant impressions

Statement of problemAccurate virtual implant models are a necessity for the fabrication of precisely fitting superstructures. PurposeThe purpose of this in vitro study was to evaluate different methods with which to build an accurate virtual model of a 3-dimensional implant in the oral cavity; this model would then be used for iterative computer-aided design and computer-aided manufacturing (CAD-CAM) procedures. Material and methodsA titanium master model with 3 rigidly connected implants was manufactured and digitized with a noncontact industrial scanner to obtain a virtual master model. Impressions of the master model with the implant position locators (IPL) were made using vinyl siloxanether material. The impressions were scanned (Impression scanning technique group). For the transfer technique and pick-up technique groups (each group n=20), implant analogs were inserted into the impression copings, impressions were made using polyether, and casts were poured in Type 4 gypsum. The IPLs were screwed into the analogs and scanned. To compare the virtual master model with each virtual test model, a CAD interactive software, ATOS professional, was applied. The Kruskal-Wallis test was subsequently used to determine the overall difference between groups, with the Mann-Whitney U test used for pairwise comparisons. Through Bonferroni correction, the α-level was set to .017. ResultsThe outcome revealed a significant difference among the 3 groups (P<.01) in terms of accuracy. With regard to total deviation, for all axes, the transfer technique generated the greatest divergence, 0.078 mm (±0.022), compared with the master model. Deviation with the pick-up technique was 0.041 mm (±0.009), with impression scanning generating the most accurate models with a deviation of 0.022 mm (±0.007). ConclusionsThe impression scanning method improved the precision of CAD-CAM-fabricated superstructures.

Marginal and internal fit of four-unit zirconia fixed dental prostheses based on digital and conventional impression techniques

The aim of this in vitro study was to evaluate the marginal and internal fit of CAD/CAM-generated four-unit zirconia fixed dental prostheses made with digital and conventional impressions. A titanium master model was used. For group conventional impression (CI), 12 polyether impressions of the master model with Impregum(TM) were made. For group digital impression (DI), 12 digital impressions of the master model using Lava(TM) C.O.S. system were made. The replica technique was applied. The Mann-Whitney U statistical test was applied to detect statistical differences between the groups, in terms of marginal and internal fit. Face-by-face comparisons between groups were also carried out. Groups DI and CI presented mean marginal fit of 63.96 and 65.33 μm, respectively, and showed no statistically significant difference. Groups DI and CI presented significantly different internal fit with mean values of 58.46 and 65.94 μm, respectively. Group DI showed statistically significantly lower values for marginal and internal fit on premolar mesial face, and on molar distal and palatal faces. Frameworks fabricated from digital and conventional impressions showed clinically acceptable marginal fit. Frameworks fabricated from digital impression demonstrated better internal fit than ones fabricated from conventional impression. Reviewing each retainer face, digital impression showed better marginal and internal fit at the premolar mesial and molar distal faces. The results of this in vitro study show that digital impressions made with the Lava(TM) C.O.S. system and its digital workflow are suitable for fabricating four-unit zirconia frameworks, with regard to marginal and internal fit requirements.