Fabrication of Layered SiC/C/Si/MeSi2/Me Ceramic-Metal Composites via Liquid Silicon Infiltration of Metal-Carbon Matrices.

The growing demand for composite materials capable of enduring prolonged loads in high-temperature and aggressive environments presents pressing challenges for materials scientists. Ceramic materials composed of silicon carbide largely possess high mechanical strength at a relatively low density, even at elevated temperatures. However, they are inherently brittle in nature, leading to concerns about their ability to fracture. The primary objective of this study was to develop a novel technique for fabricating layered composite materials by incorporating SiC-based ceramics, refractory metals, and their silicides as integral constituents. These layered composites were produced through the liquid-phase siliconization method applied to metal-carbon blanks. Analysis of the microstructure of the resultant materials revealed that when a metal element interacts with molten silicon, it leads to the formation of a layer of metal silicide on the metal's surface. Furthermore, three-point bending tests exhibited an enhancement in the bending strength of the layered composite in comparison to the base silicon carbide ceramics. Additionally, the samples demonstrated a quasi-plastic nature during the process of destruction.

Zirconia-ceramic versus metal-ceramic implant-supported multiunit fixed dental prostheses: A systematic review and meta-analysis.

Implant-supported prostheses could serve as a reliable restorative option for partial edentulism. Various restorative materials have been utilized in fabricating these prostheses, impacting both esthetics and peri-implant health. The present systematic review aimed to assess the survival rate and mechanical complications of zirconia ceramic compared to metal-ceramic implant-supported multiunit fixed dental prostheses (FDPs). We conducted searches in online databases such as MEDLINE (PubMed), Scopus, and Cochrane up until December 2022. A risk-of-bias assessment was done for all the included studies. Data extraction was performed based on the following parameters: author, year, study design, number of implants, abutment material, age range, observation period, incidence of mechanical complications, and survival rate. This systematic review included six studies (four randomized controlled trials and two retrospective studies). The meta-analysis significantly favored metal-ceramic restorations regarding mechanical complications with a risk ratio (RR) value of 1.64 and P = 0.001. Meta-analysis showed no difference in metal-ceramic FDPs in prostheses survival rate (P = 0.63; RR: 1.27, 95% confidence interval: 0.52-3.37; heterogeneity: P = 0.65; I2: 0%). While metal-ceramic multiunit implant-supported prostheses exhibited fewer mechanical complications compared to zirconia-ceramic prostheses, there was no significant difference in terms of prosthesis survival rate between the two. Hence, both treatments appear to be viable options for long-term implant-supported prostheses.

Dental ceramic damage associated with incorrect laboratory procedures.

Ceramic is a commonly used material in dentistry for reconstructing missing teeth or their tissues due to its biocompatibility, durability and excellent esthetic properties. Despite these advantages, the ceramic restoration damage remains a significant clinical problem. Its causes can be divided into clinical and laboratory factors. The most known include uneven occlusion, improper preparation, trauma, or parafunctions. This study focuses on characterizing less known laboratory causes of ceramic restoration damage. We reviewed the current literature available in the PubMed and Scopus databases. On the basis of 63 selected studies, 3 basic causes of damage were identified: excessive stresses between the framework and ceramic veneering, poor quality of the connection between the facing layer and the substructure, and defects resulting from the nature of the ceramic material such as defects in the ceramic layer, brittleness and lack of flexibility. The stages of the manufacturing process of various permanent ceramic restorations were presented. By controlling these procedures, we can eliminate the errors, resulting in long-term effective functioning of the ceramic restorations.

Impact of Prosthetic Material and Restoration Type on Peri-Implant Bone Resorption: A Retrospective Analysis in a Romanian Sample.

Background/Objectives: This research investigates the nuanced factors influencing peri-implant bone resorption in implant-supported fixed prostheses, with a focus on age, gender, implant location, time since prosthetic loading, and material characteristics. Methods: Records from a dental clinic in Oradea, Romania, between 1 January 2017 and 1 January 2023, were scrutinized and were selected by means of purposive sampling. All records were analyzed between 1 May 2023 and 15 June 2023. A total of 160 implants were included, and the prosthetic restorations were either metal-ceramic or zirconia. Implants from a single manufacturer were used, and a standardized loading protocol was followed. The study examined variables such as age, gender, implant location, prosthetic material, and time since prosthetic loading. Results: A total of 160 implants were included, with 78 applied to female patients (48.8%) and 82 to male patients (51.2%). The age range of the patients undergoing dental implant procedures was 30 to 79 years. Implants were distributed between the mandible (51.2%) and maxilla (48.8%), with 49.4% placed in the posterior dental arches and 50.6% in the anterior dental arches. The majority of patients received metal-ceramic prosthetic reconstructions (76.9%). Statistical analysis revealed significant differences in resorption patterns between zirconia and metal-ceramic restorations (p < 0.001), with zirconia restorations exhibiting higher resorption in the mesial-vertical and distal-vertical planes compared to metal-ceramic restorations. Age-related factors showed a significant association with distal-vertical resorption (p = 0.017), with patients aged 60-69 years exhibiting higher resorption values compared to those aged 40-49 years. Gender differences were observed in mesial-horizontal resorption (p = 0.036), with male patients displaying higher resorption values compared to female patients. Implant location and time elapsed since implant loading did not show significant associations with resorption patterns. Conclusions: The study provides insights into the multifactorial nature of peri-implant resorption. Age, gender, and material characteristics contribute to variations, informing personalized treatment approaches. The findings facilitate a comprehensive understanding for clinicians, enhancing treatment planning and post-operative care.

Effect of different production techniques on the color of porcelain-fused-to-titanium restorations.

In dentistry, the shade selection of the restoration affects the success of the restoration. For this reason, it may be decisive for clinicians to determine whether the difference in framework production influences color in metal-ceramic restorations. The study examined the effects of different framework production techniques used in porcelain-fused-to-titanium restorations on color changes. 45 square-shaped samples were manufactured using cast, milling, and laser-sintering techniques. Opaque and dentin porcelain were performed, and all samples were glazed. A spectrophotometer was used for color measurements. Before opaque application, after opaque application, and after porcelain + glaze application, it was obtained L*, a*, and b* values. Color differences (ΔE00) were calculated with the CIEDE2000 formula. ANOVA (Post Hoc: Bonferroni) and Shapiro Wilks (Normality) tests were used for statistical analysis (p < 0.05). At the different laboratory steps, the difference between cast&laser-sintered groups and between milled&laser-sintered groups was statistically significant (p < 0.05). Before and after opaque application, the differences in L*, a*, and b* values between cast, milled, and laser-sintered groups were statistically significant (p < 0.05). Different framework production methods influenced the color of porcelain-fused-to-titanium restorations.

A Retrospective Evaluation of 5 Years of Clinical Results of Metal-Ceramic vs. Monolithic Zirconia Superstructures in Maxillary All-on-4TM Concept.

The aim of the current study was to present the clinical and radiological outcomes of monolithic zirconia superstructures compared to the metal-ceramic ones in the All-on-4 concept for the prosthetic rehabilitation of the maxillae. A total of 30 patients were subdivided into groups according to their superstructure type (metal-ceramic (n = 15) or monolithic zirconia (n = 15)). All implants were functionally loaded within 24 h after insertion with provisional acrylic superstructures. Prosthetic complications, marginal bone loss, plaque accumulation, probing pocket depth, bleeding on probing, and bite force were documented over a period of 5 years. Marginal bone loss around the implants of the ceramic group remained well over the five years (1.21 ± 0.23 mm). However, marginal bone loss was significantly lower around the implants in the monolithic zirconia group (0.22 ± 0.14 mm) (p < 0.001). Bleeding on probing, plaque accumulation, and probing pocket depth values were correlated with marginal bone loss. Among all evaluated parameters, no differences could be detected in terms of the angulation of the implants. Detachment or chipping was observed in seven cases in the metal-ceramic superstructure group. In all cases, dentures were removed and repaired in the laboratory. In the monolithic zirconia group, chipping was detected after one year in two cases, after two years in four cases, and after five years in one case and could be managed by polishing in situ. Monolithic zirconia superstructures presented superior results regarding the parameters evaluated.

Digital workflow for monolithic and veneered zirconia and metal-ceramic posterior fixed partial dentures: A five-year prospective randomized clinical trial.

Purpose To evaluate and compare the survival, success rates, and biological and technical complications of three-unit posterior monolithic and veneered zirconia and metal-ceramic (MC) posterior fixed partial dentures (FPDs) fabricated using a digital workflow and computer-aided design and computer-aided manufacturing (CAD/CAM) over a 5-year follow-up.Methods Ninety patients in need of three-unit posterior FPDs were randomized to receive monolithic zirconia (MZ), veneered zirconia (VZ), and MC restorations (n = 30 each). Teeth preparations were scanned using an intraoral scanner, and restorations were milled and cemented with resin cement. Clinical performance and periodontal parameters were assessed at baseline and yearly up to 5 years after insertion. Data analysis was performed using the Kaplan-Meier method, Friedman test, and Wilcoxon signed-rank test with Bonferroni correction and Mann-Whitney U test.Results The 5-year survival rates of the MZ, VZ, and MC FPDs were 87%, 97%, and 100%, respectively (P = 0.04). Most complications were biological in nature. Only one MZ FPD fractured 58 months after placement. All the restorations were assessed as satisfactory at each recall. Differences were found in the gingival index score over time in the VZ and MC groups. The margin index remained stable throughout the follow-up period in both zirconia groups.Conclusions The results of this study suggest that using a digital workflow to fabricate posterior FPDs is an adequate treatment option and that monolithic zirconia could be a viable alternative to metal-ceramic or veneered zirconia. However, further long-term studies are necessary to provide stronger evidence in patients with bruxism.

Comparison of the fracture strengths of single-unit metal-ceramic and monolithic zirconium restorations in the molar region: a systematic review and meta-analysis.

Despite the success of monolithic zirconia restorations (MZ), metal-ceramic restorations (MC) are still considered the gold standard for fixed prosthetics in the posterior region. This systematic review and meta-analysis aimed to compare the fracture strengths of single-unit MC and MZ in the molar region. This review was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA, 2020) statement. All articles were searched from the PubMed and Web of Science databases until November 18, 2022. All in vitro studies evaluating the fracture strengths of MC and MZ were also included. Statistical analysis was performed with the Comprehensive Meta-Analysis program, with a significance level of 0.05. Out of 753 studies, five were selected. The fracture strengths of MZ and MC did not show any statistically significant difference for both tooth (95% CI - 1.589: 2.118, p = 0.779, z = 0.280) and implant (95% CI - 2.215: 2.191, p = 0.992 z = - 0.010) supported restorations. However, different abutment materials (p < 0.001) and aging treatments (p < 0.001) in tooth-supported restorations displayed a significant statistical difference. Additionally, a significant difference was also observed in subgroup analysis considering different cements (p = 0.001) and load speeds (p = 0.001) in implant-supported restorations. Fracture strengths of MZ and MC did not show a significant statistical difference in implant or tooth-supported single-unit posterior restorations. MZ may be a suitable alternative to MC in single-unit posterior restorations. The results should be interpreted with caution, as the included studies were in vitro.

Technical assessment of shear bond strength at ceramo-alloy interface after various surface treatment combinations and application of metal bonding agent.

BACKGROUND: Bonding between metal and ceramic is one of the most important aspects of a successful prosthesis. Various methods have been recommended for preparing the metal surface to enhance the bond between metal and ceramic including the use of a metal bonding agent. OBJECTIVE: This study aims to evaluate and compare the shear bond strength of the metal-ceramic (M-C) interface after combinations of various surface treatments including the application of a metal bonding agent. METHOD: 40 Ni-Cr alloy specimens were made and divided into 4 groups of 10 each based on the combination of surface treatments. Sandblasting, surface grinding, and Oxidation heat treatment (OHT) were performed on specimens from Group 1 (Control). In addition, Group 2 specimens received ultrasonic cleaning, Group 3 steam cleaning, and Group 4 metal bonding agent application. Following surface treatments on all specimens, porcelain build-up was performed, and shear bond strength was tested in a Digital Universal testing machine. The statistical tests used were independent t-test and ANOVA. RESULTS: Results revealed that Group 4 specimens had the highest mean value of shear bond strength of 39.087 MPa while Group 3 specimens showed the least mean shear bond strength of 18.154 MPa with highly statistically significant results (p< 0.001). CONCLUSION: The surface treatments and application of bonding agent to metal prior to porcelain application resulted in increased shear bond strength of the metal-ceramic interface.

[A prospective single-cohort study of implant-supported full-arch metal-ceramic prosthesis with gold-platinum alloy framework for treatment edentulous mandible in elderly patients: 15-year report]. / Implantatsionnoe protezirovanie protyazhennymi metallokeramicheskimi konstruktsiyami s karkasom iz zolotoplatinovogo splava u pozhilykh patsientov: rezul'taty 15-letnego perspektivnogo odnogruppovogo kogortnogo issledovaniya.

OBJECTIVE: To study the effectiveness of implant-supported full-arch metal-ceramic prosthesis with gold-platinum alloy framework in elderly patients. MATERIALS AND METHODS: The study included patients with complete and/or partial loss of teeth and terminal dentition. In 2007-2008, 354 implants were inserted in 27 patients. The age of the patients was 61.31±5.08 years. Mombelli index criteria (mBI [modified Sulcus Bleeding Index]) were used. The plaque index was determined using a modified Löe & Silness method. The state of the peri-implant bone (ΔMBL) was determined by a series of OPG. The Geriatric Oral Health Index (GOHAI) was used to assess oral health in the elderly. RESULTS: Metal-ceramic full-arch implant prostheses with a gold-platinum alloy framework, based on a sufficient and optimal number of implants (6-8), showed high survival rate (100%) after 15 years. Marginal bone loss (ΔMBL) after 15 years was -1.44±1.27 mm. The survival rate of implants was 99.4%. Scores on the GOHAI scale were higher in patients after orthopedic rehabilitation (from 52.7±7.1 to 54.1±8.4, p<0.001). CONCLUSION: After 15 years, all prostheses had mechanical defects, which at the same time allowed them to be used without restrictions. Screw fixation of full-arch implant prostheses, although it was associated with mechanical complications, nevertheless made it possible to perform surgical interventions in a timely manner and stop the development of inflammatory complications. Thus, we do not see any grounds for removing metal-ceramic prostheses and replacing them with new implant prostheses even after a 15-year period of operation. At the same time, it is necessary to take into account the reduction in the possibility of individual oral hygiene in elderly patients, as well as possible restrictions on self-visiting a dentist or dental hygienist.

Comparative Analysis of the Structural Weights of Fixed Prostheses of Zirconium Dioxide, Metal Ceramic, PMMA and 3DPP Printing Resin-Mechanical Implications.

The aim of this study was to determine the mechanical implications of four-unit fixed dental prostheses (FDPs) made of (1) monolithic zirconium dioxide (ZR O2), (2) polymethylmethacrylate (PMMA), (3) metal ceramic (PFM) and (4) impression resin (3DPP). METHODS: Four groups were studied with eight samples for each material (n: 32). Each structure was weighed, subjected to compressive tests and analyzed using 3D FEA. RESULTS: PMMA presented the lowest structural weight (1.33 g), followed by 3DPP (1.98 g), ZR O2 (6.34 g) and PFM (6.44 g). In fracture tests, PMMA presented a compressive strength of 2104.73 N and a tension of 351.752 MPa; followed by PFM, with a strength of 1361.48 N and a tension of 227.521 MPa; ZR O2, with a strength of 1107.63 N and a tension of 185.098 MPa; and 3DPP, with a strength of 1000.88 N and a tension of 143.916 MPa. According to 3D FEA, 3DPP presented the lowest degree of deformation (0.001 mm), followed by PFM (0.011 mm), ZR O2 (0.168 mm) and PMMA (1.035 mm). CONCLUSIONS: The weights of the materials did not have a direct influence on the mean values obtained for strength, stress or strain. Since the performance was related to the tension and forces supported by the structures in critical zones, the importance of considering design factors is clear. In vitro and 3D FEA assays allowed us to simulate different scenarios for the mechanical properties of certain materials before evaluating them clinically. Thus, they can generate predictions that would allow for the design of a better research methodology in future clinical trials.

Metal-Ceramic Compatibility in Dental Restorations According to the Metallic Component Manufacturing Procedure.

In terms of production technology, metal-ceramic systems for dental restorations comply with a concrete algorithm, the efficiency of which is always dependent on the applications for which they are intended. The first stage involves obtaining metal support, followed by firing the ceramic on the surface of the metal to meet the list of functional and aesthetic requirements of a future restoration. The compatibility of the two materials-the metal component and the ceramic component-must be ensured in several respects: chemical compatibility, thermo-chemical compatibility, and mechanical compatibility. Thus, there is a need to simulate the thermal behavior of the metal-ceramic couple in its processing to achieve appropriate dental prostheses. In this study, three types of Co-Cr metal frames were manufactured using three different production technologies: conventional casting, milling (CAM), and selective laser melting (SLM). Composition analyses, scanning electron microscopy (SEM), and microstructural analyses of the metal-ceramic interface for each type of production technology, as well as the determination of the hardness and the thermal expansion coefficients of experimental materials and three-point bending tests, were carried out in this study. Considering all these aspects, we demonstrated the influence of the technology of producing the metallic part of the metal-ceramic bonding process in dental prostheses.

Bond strength of ceramic veneered CAD-milled alloy upon prolonged sintering.

OBJECTIVES: Ceramic-sintering affects bond strength and longevity of metal-ceramic. This study investigated the effect of sintering temperatures and times on metal-ceramic bond strength vis-a-vis interfacial fracture toughness. MATERIALS AND METHODS: One hundred eighty rectangular-shaped (25 × 8 × 1 mm) casting (Auriloy® (CA)) and CAD-milling (Ceramill Sintron® (MA)) alloys were prepared and randomly veneered with ceramic at normal (930 °C; (TN)), increased (940 °C; (TI)), and extremely increased (950 °C; (TE)) sintering temperatures and normal (1 min; (HN)), increased (2 min; (HI)), and extremely increased (3 min; (HE)) sintering time (n = 10/group). Pre-cracked was subjected to four loading-unloading cycles at 0.05 mm/min speed to determine interfacial fracture toughness from strain energy release rate (G). Microstructures were examined with a scanning electron microscope (SEM), energy-dispersive X-ray (EDX), and atomic force microscopy (AFM). ANOVA and Tukey comparisons were determined for significant differences (α = 0.05). RESULTS: Significant differences in G due to the effect of alloy, sintering temperature, and time (p < 0.05) were indicated. MA revealed higher G than CA. Raising temperatures enabled increasing G for CA, not for MA. Extended sintering permitted increasing G for both alloys. Rougher surface of MA than CA was observed. Interfacial ion exchange was differently indicated between CA and MA. CONCLUSIONS: Bond strength was influenced by alloy, sintering temperature, and time. Ceramic has better adhesion to MA than CA. Enhancing bond for CA was succeeded through increasing sintering temperature and time, whereas through extended sintering for MA. CLINICAL RELEVANCE: MA offers stronger bond than CA. Enhancing bond is suggested by extended sintering. Raising temperature can enhance bond for CA, not for MA.

Influence of stress-relieving heat treatments on the efficacy of Co-Cr-Mo-W alloy copings fabricated using selective laser melting.

PURPOSE: This study aimed to evaluate the influence of stress-relieving heat treatments on the metal-ceramic bond strength and fitness accuracy of selective laser melting (SLM)-fabricated Co-Cr alloy copings. METHODS: SLM-manufactured Co-Cr samples were stress-relieved at 750 (Ht-750) and 1150 °C (Ht-1150). The microstructure, surface roughness, metal-ceramic bond strength, marginal and internal fit, Vickers hardness, and residual stress were then compared with those of the non-heat-treated group (As-built). The results were analyzed using one-way ANOVA and post-hoc tests (Tukey's or Student's t test) (P = 0.05). RESULTS: The microstructure of the Ht-1150 samples had a brittle oxide layer and lower surface roughness, resulting in significantly lower bond strength values than those of the other groups. The As-built group exhibited significantly lower marginal gap values than the Ht-750 and Ht-1150 groups. Therefore, the post-heat treatments degraded the marginal fitness. The surface residual stress in all sample groups were compressive because of the sandblasting effect. The compressive stresses were larger in Ht-1150 than in As-built and Ht-750 owing to their low hardness values. CONCLUSIONS: Stress-relief annealing porcelain-fused-to-metal single crowns does not improve bond strength and degrades fitness accuracy because additional post-heat treatments induce thermal distortion. These findings are expected to facilitate the direct application of As-built SLM single crowns in dentistry to minimize post-manufacturing costs and time.

Research on the Role of Surface Treatment of the Metal Surface on the Strength of the Metal-Ceramic Bond.

AIM: The aim of the present study is to investigate the metal-ceramic bond strength as a result of three different surface treatment methods: (1) oxidation, (2) oxidation and sandblasting, and (3) double oxidation on the metal substrate. MATERIALS AND METHODS: A total of 72 metal substrates were made from two different types of metal-ceramic alloys (n = 36): group I, Ni-Cr and group II, Co-Cr alloys. Each group was further divided and subjected to three different surface treatments (n = 12): (1) oxidation in accordance with the manufacturer's instructions; (2) oxidation according to the manufacturer's instructions and then sandblasting with Al2O3, with a grain size of 110 µm, a pressure of 75 psi for 10 sec with a distance of 5 cm and steam cleaning; and (3) double oxidation. The bond strength of the specimens was evaluated with the three-point bending process. The data were recorded, tabulated, and statistically analyzed. RESULTS: For group I, the materials with oxidation based on the specifications, show mean value of 64.02 Nt. The oxidation and sandblasting materials have mean 55.92 Nt. The double oxidation materials have mean 55.47. For group II, the materials with oxidation based on the specifications, show mean value of 58.46 Nt. The oxidation and sandblasting materials have a mean value of 42.56 Nt. The double oxidation materials have mean 42.96 Nt. CONCLUSION: The best method of treatment of the metal substrate is specification oxidation, in terms of the strength of the metal-ceramic bond. Further treatment of the metal substrate reduces the strength of the metal-ceramic bond. CLINICAL SIGNIFICANCE: A prerequisite for clinical success of metal-ceramic prosthetic restorations is the increased strength of the bond between ceramic material and metal substrate. With that in mind, the present research gives important insight into best practices for prosthetic restorations.

Quality of the Ceramic and Ni-Cr Alloy Joint after Al2O3 Abrasive Blasting.

The purpose of this in vitro study was to determine the effect of airborne-particle abrasion process parameters on the strength of the Ni-Cr alloy-ceramic bond. One hundred and forty-four Ni-Cr disks were airborne-particle abraded with 50, 110 and 250 µm Al2O3 at a pressure of 400 and 600 kPa. After treatment, the specimens were bonded to dental ceramics by firing. The strength of the metal-ceramic bond was determined using the shear strength test. The results were analyzed with three-way analysis of variance (ANOVA) and the Tukey honest significant difference (HSD) test (α = 0.05). The examination also considered the thermal loads (5000 cycles, 5-55 °C) to which the metal-ceramic joint is subjected during exploitation. There is a close correlation between the strength of the Ni-Cr alloy-dental ceramic joint and the alloy roughness parameters after abrasive blasting: Rpk (reduced peak height), Rsm (the mean spacing of irregularities), Rsk (skewness of the profile) and RPc (peak density). The highest strength of the Ni-Cr alloy surface bonding with dental ceramics under operating conditions is provided by abrasive blasting under 600 kPa pressure with 110 µm Al2O3 particles (p < 0.05). Both the abrasive blasting pressure and the particle size of the Al2O3 abrasive significantly affect the joint's strength (p < 0.05). The most optimal blasting parameters are 600 kPa pressure with 110 µm Al2O3 particles (p < 0.05). They allow the highest bond strength between the Ni-Cr alloy and dental ceramics to be achieved.

Effect of the CAD-CAM and lost-wax framework fabrication techniques on the fracture strength of porcelain in metal-ceramic restorations.

BACKGROUND: Ceramic fracture is a common problem in metal-ceramic restorations (MCRs). The advent of computer-aided design and computer-aided manufacturing (CAD-CAM) technology eliminated the lost-wax technique, which was responsible for many of the problems associated with framework fabrication. However, the role of the CAD-CAM technology in decreasing porcelain fracture is not yet known. OBJECTIVES: The aim of the present in vitro study was to compare the fracture strength of porcelain in MCRs with metal frameworks fabricated with the use of the lost-wax and CAD-CAM techniques. MATERIAL AND METHODS: Twenty metal dies were prepared with a deep chamfer finish line, with a depth of 1.2 mm and the occlusal taper of the walls of 8°, a 2-millimeter occlusal reduction of the functional cusp, a 1.5-millimeter occlusal reduction of the nonfunctional cusp, and the functional cusp bevel. Ten frameworks were fabricated using the CAD-CAM system and 10 with the lost-wax technique. After porcelain veneering, the specimens underwent thermocycling and cyclic loading to simulate the aging process. The load test was then performed. The fracture strength of porcelain was compared between the 2 groups, and the mode of failure was also determined using a stereomicroscope. RESULTS: Two specimens were excluded from the CAD-CAM group. Thus, 18 specimens were statistically analyzed. The results revealed no significant difference in fracture strength between the 2 groups (p > 0.05). The mode of failure was mixed in all specimens from both groups. CONCLUSIONS: Our results indicated that the fracture strength of porcelain and the mode of failure did not depend on the metal framework fabrication technique (lost-wax or CAD-CAM).

Six-year clinical performance of lithium disilicate glass-ceramic CAD-CAM versus metal-ceramic crowns.

PURPOSE: To assess the clinical performance of monolithic CAD-CAM lithium disilicate glass-ceramic (LDGC) crowns and metal-ceramic (MC) crowns provided by predoctoral students. This study also assessed the effects of patient and provider-related factors on their clinical performance as well as patient preference for these types of crowns. MATERIALS AND METHODS: Twenty-five patients who received 50 crowns (25 LDGC CAD-CAM and 25 MC) provided by predoctoral students were retrospectively examined. LDGC CAD-CAM crowns were milled in-house using the CEREC Bluecam system and cemented with either RelyX Unicem or Calibra Esthetic resin cements. MC crowns were cemented with RelyX Unicem cement. Clinical assessment of the crowns and the supporting periodontal structures were performed following the modified California Dental Association (CDA) criteria. Patients' preference was recorded using a visual analog scale (VAS). The results were statistically analyzed using log-rank test, Pearson Chi-squared test and Kaplan-Meier survival analysis. RESULTS: Twelve complications were observed in the MC crown group (9-esthetic, 2-technical and 1-biological). In comparison, 2 complications in the LDGC CAD-CAM crown group were observed (1-technical and 1-esthetic). The 6-year cumulative survival rates for MC crowns and LDGC CAD-CAM were 90.8% and 96%, respectively, whereas the success rates were 83.4% and 96%, respectively. Overall, patients preferred the esthetic outcomes of LDGC CAD-CAM crowns over MC crowns. CONCLUSION: The high survival and success rates, low number of complications, and the high level of patients' acceptance of monolithic LDGC CAD-CAM crowns lend them well as predictable and viable alternatives to the "gold standard" MC crowns.

X-ray Tomographic Method to Study the Internal Structure of a TiNi-TiB2 Metal Matrix Composite Obtained by Direct Laser Deposition.

The field of additive manufacturing (AM) of various materials is rapidly developing. At the stage of designing and growing products and for the quality control of finished parts, non-destructive methods of analysis, in particular X-ray computed tomography (CT), are in demand. In addition to the advantages of non-destructive imaging of a wide range of materials in three dimensions, modern CT scanners offer a high contrast and high spatial resolution to provide digital information about their three-dimensional geometry and properties. Within the framework of this article, CT was used to follow the structural evolution of a TiNi-TiB2 metal-ceramic composite obtained by direct laser deposition. The relationship has been established between the additive method of production (layered direct laser deposition) and the formed layered structure of the product in the direction of growth. The porosity of the sample was calculated for each scan direction, and the average for the sample was 1.96%. The matrix of the TiNi-TiB2 composite is characterized by the presence of pores of various sizes, shapes and locations. Spherical voids prevail, but keyhole pores are also found. The heterogeneity of the structure was revealed in the form of clearly traced boundaries of the print layers, as well as differences in the density of the inner and outer regions of the composite.

Nanostructure, Plastic Deformation, and Influence of Strain Rate Concerning Ni/Al2O3 Interface System Using a Molecular Dynamic Study (LAMMPS).

The plastic deformation mechanisms of Ni/Al2O3 interface systems under tensile loading at high strain rates were investigated by the classical molecular dynamics (MD) method. A Rahman-Stillinger-Lemberg potential was used for modeling the interaction between Ni and Al atoms and between Ni and O atoms at the interface. To explore the dislocation nucleation and propagation mechanisms during interface tensile failure, two kinds of interface structures corresponding to the terminating Ni layer as buckling layer (Type I) and transition layer (Type II) were established. The fracture behaviors show a strong dependence on interface structure. For Type I interface samples, the formation of Lomer-Cottrell locks in metal causes strain hardening; for Type II interface samples, the yield strength is 40% higher than that of Type I due to more stable Ni-O bonds at the interface. At strain rates higher than 1×109 s-1, the formation of L-C locks in metal is suppressed (Type I), and the formation of Shockley dislocations at the interface is delayed (Type II). The present work provides the direct observation of nucleation, motion, and reaction of dislocations associated with the complex interface dislocation structures of Ni/Al2O3 interfaces and can help researchers better understand the deformation mechanisms of this interface at extreme conditions.