Influence of various fabrication techniques and porcelain firing on the accuracy of metal-ceramic crowns.

BACKGROUND: The fit of a metal-ceramic restoration is essential to its long-term durability. Regarding marginal and internal fit, there is not enough information about the technologies used in the production of metal-ceramic restorations. The aim of this in vitro study is to compare, both before and after porcelain firing, the marginal, axial, axio-occlusal, and occlusal fit of metal-ceramic restorations manufactured using casting, additive or subtractive computer-aided design, and computer-aided manufacturing techniques (CAD/CAM). METHODS: CAD/CAM were used to create 50 prepared maxillary first molar-shaped Co-Cr die models, which were randomly divided into 5 groups (n = 10). Cobalt-chrome copings were produced by casting (C), hard metal milling (HM), soft metal milling (SM), selective laser melting (SLM), and selective laser sintering (SLS) techniques. Before and after porcelain firing, discrepancies of the copings were measured using the silicone replica technique. The data obtained by measurements with a stereomicroscope at x80 magnification were analyzed statistically in the SPSS program. The ROBUST three-way analysis of variance (ANOVA) method was used to compare the discrepancy values. RESULTS: There were statistically significant differences among fabrication methods (P < .001). The HM method showed the highest discrepancy (90.1 µm), and the C (63 µm) method showed the lowest discrepancy in terms of the die model- crown fit. The C, SLS, and SM methods (63 µm; 61.6 µm; 67.7 µm) were statistically similar (P > .001). The highest discrepancy was observed on the occlusal area (87.1 µm), and the lowest discrepancy was observed on the axial area (47.7 µm) of the coping. Porcelain firing had a decrease in the discrepancy values (P = .001). CONCLUSION: All CAD/CAM techniques are appropriate for clinical use; selective laser sintering and soft milling can be the more recommended methods for the compatibility of metal-porcelain restorations, as they have lower discrepancy values than the SLM and HM methods.

The influence of implant depth, abutment height and mucosal phenotype on peri­implant bone levels: A 2-year clinical trial.

OBJECTIVES: To evaluate the bone changes around equicrestal and subcrestal implants, analyzing the effect of abutment height [short abutments (SA < 2 mm) and long abutments (LA > 2 mm)] and the three components of the peri­implant soft-tissue phenotype. METHODS: Twenty-six patients received 71 implants that were placed according to supracrestal tissue height (STH) in an equicrestal (n = 17), shallow subcrestal ≈1 mm (n = 33), or deep subcrestal ≈2 mm (n = 21) position. After 3 months of healing, rehabilitation was completed using metal-ceramic crowns on multi-unit abutments of 1.5 mm, 2.5 mm, or 3.5 mm in height, depending on the prosthetic space and STH. Longitudinal clinical parameters (STH, mucosal thickness, and keratinized mucosa width) and radiographic data [bone remodelling and marginal bone loss (MBL)] were collected at 3, 6, 12, and 24 months postsurgery. RESULTS: The gain in STH was significantly greater around the implants placed in a subcrestal ≈2 mm position. After 2 years, the mean change in bone remodelling in the SA group was significantly greater than in the LA group. According to the multiple linear regression, bone remodelling depends primarily on abutment height (ß = -0.43), followed by crestal position (ß = 0.34), and keratinized mucosa width (ß = -0.22), while MBL depends on abutment height (ß = -0.37), and the patient's age (ß = -0.36). CONCLUSIONS: Implants placed in an equicrestal or subcrestal ≈1 mm position with LA undergo less bone remodelling, while the lowest level of MBL occurs in subcrestal ≈2 mm implants with LA. Differing soft-tissue thicknesses combined with the use of either SA or LA produced significant intergroup differences in bone remodelling and MBL. CLINICAL SIGNIFICANCE: Abutment height is the most powerful predictor variable affecting bone remodelling and MBL. Depending on the dimensions of the peri­implant soft-tissue phenotype, placing the implants subcrestally may also be a viable option to decrease bone remodelling and, consequently, reduce MBL. CLINICAL TRIAL REGISTRATION: identification number: NCT05670340.

Aesthetic outcomes of different materials for delayed, single-tooth restorations for immediately placed implants. A randomized controlled clinical trial.

OBJECTIVES: The aim of this study is to compare the aesthetic outcomes of metal porcelain (C), lithium disilicate (T1) and porcelain-layered zirconium (T2) immediate implant-supported single crowns in the anterior maxilla. MATERIALS AND METHODS: Forty-five immediate dental implants were provided for 45 patients that required the extraction of a single tooth in the anterior maxilla. A temporary prosthesis was provided at 8 weeks after placement followed by the final prosthesis at 24 weeks post-implantation. The patients were randomly allocated into 3 groups: 15 patients in the control group (C) received a metal-porcelain restoration, 15 patients (T1) received a lithium disilicate (LD) restoration and 15 patients (T2) received a porcelain-layered, zirconium (Z) restoration. Pink (PES) and White (WES) esthetic scores, radiographic bone levels, periodontal parameters and patient's esthetic satisfaction using a visual analogue scale (VAS) were evaluated at the time of final restoration placement (t0) and at 12-months post-loading (t12). RESULTS: No implants were lost during the duration of this study. Statistically significant higher WES and VAS scores (p < 0.05) were recorded in T1 vs C and T1 vs T2 groups respectively. Similar radiographic bone levels and periodontal parameters were recorded in all groups. CONCLUSION: Within the limitations of this study, it was concluded that T1 restorations provided better WES outcomes when compared to C restorations and better VAS scores when compared to T2 restorations at 12 months post-loading. Besides, different material interphases did not have an impact in PES, bone levels or periodontal parameters. CLINICAL RELEVANCE: There is limited data comparing aesthetic outcomes of implant supported single crowns made of different ceramic materials based on accepted and comparable indexes and the evaluation of the patient's perspective regarding these aesthetic outcomes.

Metal-Ceramic Resin-Bonded Fixed Partial Dentures After a Mean Observation Time of 7.5 Years.

PURPOSE: To generate data on the long-term survival of metal-ceramic resin-bonded fixed partial dentures (RBFPDs). MATERIALS AND METHODS: A total of 89 patients received 94 RBFPDs, 5 of whom (women n = 1; men n = 4) received 2 RBFPDs each. All RBFPDs were fabricated as two-retainer end-abutment metal-ceramic restorations. Clinical follow-ups were performed 6 months after cementation and then annually thereafter. The mean observation time was 7.5 years. Cox regression was performed to test the effects of the variables: gender, location, arch, design, use of rubber dam, and adhesive luting system. Survival and success were calculated using Kaplan-Meier curves. As a secondary objective, patient and dentist satisfaction with the esthetics and function of the RBFPDs was evaluated. The significance level was set at α = .05 for all calculations. RESULTS: Estimated Kaplan-Meier failure-free survival was 97.5% (standard error [SE] 1.7) after 5 years and 83.3% (SE 5.3) after 10 years. Calculated intervention-free survival (success) was 90.1% (SE 3.4) after 5 years and 65.5% (SE 6.7) after 10 years. Debonding-free survival was 92.6% (SE 2.9) after 5 years and 80.6% (SE 5.4) after 10 years. Cox regression revealed that none of the four tested variables had a significant effect on the incidence of complications in RBFPDs. Patient and dentist satisfaction with RBFPD esthetics and function was consistently high throughout the observation period. CONCLUSIONS: Within the limitations of an observational study, RBFPDs achieved clinically successful outcomes over a mean observational period of 7.5 years.

Clinical evaluation of posterior zirconia-based and porcelain-fused-to-metal crowns with a vertical preparation technique: an up to 5-year retrospective cohort study.

OBJECTIVE: To evaluate the clinical conditions of single-unit posterior restorations on teeth prepared without finishing line, after 5.6 years of clinical service. MATERIALS AND METHODS: 50 crowns (25 zirconia-based (Zr) and 25 porcelain-fused-to-metal (PFM)) were selected from 34 patients. The restorations were evaluated according to the California Dental Association (CDA) Quality Criteria, and periodontal variables were studied in the abutment teeth compared with the unrestored contralateral teeth. Variables were examined using Mann-Whitney and Pearson´s Chi-Square tests (α = 0.05). The success of the prosthesis was calculated using Kaplan-Meier test. RESULTS: CDA Quality Criteria was considered satisfactory-excellent in all restorations except for one of them, due to chipping on a PFM crown. At, 66 months, the success rates for PFM and Zr crowns were 85.7 % and 100 %, respectively. The plaque index (PI) showed that the restored abutment teeth accumulated significantly less plaque than the control teeth, but the gingival index (GI) was statistically higher in the abutment teeth. In 80 % of cases the probing depth (PB) was ≤3 mm. In addition, in 21 % of the cases, gingival recession was less than 2 mm. The restoration material had a statistically significant effect on GI and PB, with Zr crowns showing less inflammation and less deep pockets than PFM restorations. On the contrary, greater gingival recession was found at the margins of the Zr crowns when compared to the PFM. No statistical differences were found between the two materials in the GI. CONCLUSIONS: Cemented crowns on vertical preparations show good clinical behavior after 5 years. The periodontal parameters (PI, GI, PD) of the Zr restorations are significantly better than those of PFM, with the exception of gingival recession. CLINICAL RELEVANCE: The use of restorations on vertically prepared teeth is a suitable alternative to classical horizontal preparations.

Fracture Resistance and Failure Mode of Monolithic Zirconia, Veneered Zirconia, and Metal-Ceramic Full-Coverage Restorations: A Comparative In Vitro Study.

PURPOSE: To evaluate and compare the fracture mode and strength of monolithic zirconia to veneered zirconia and metal-ceramic full-coverage restorations following artificial aging and to test the performance of translucent zirconia in terms of load-bearing capacity. MATERIALS AND METHODS: Two mandibular first molars were prepared and scanned for their respective groups of full-coverage restorations. A total of 75 full-coverage restorations were fabricated and divided into five groups: two groups for monolithic zirconia, two groups for veneered zirconia, and one group for metal-ceramic. Then, 75 light-cured hybrid composite resin dies were fabricated to serve as abutments. Before cementation, all full-coverage restorations were subjected to accelerated aging. After cementation, all full-coverage restorations were subjected to compressive loading until fracture in an electromechanical universal testing machine. A two-way nested ANOVA and Tukey test were used to analyze the results with 95% confidence levels. RESULTS: Monolithic zirconia full-coverage restorations showed the highest mean fracture resistance of 4,201.0 N, followed by metalceramic full-coverage restorations of 3,609.3 N, and veneered zirconia full-coverage restorations showed the lowest mean fracture resistance of 2,524.6 N. The main mode of failure was cohesive bulk fracture for the monolithic zirconia group, cohesive/adhesive failure with infrastructure damage for the veneered zirconia group, and cohesive/adhesive failure without infrastructure damage for the metal-ceramic group. CONCLUSIONS: Monolithic zirconia full-coverage restorations showed superior resistance to fracture compared to metal-ceramic full-coverage restorations and are highly reliable in terms of load-bearing capacity within the posterior regions of the mouth.

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.

Simulating porcelain firing effect on the structure, corrosion and mechanical properties of Co-Cr-Mo dental alloy fabricated by soft milling.

This study aims at evaluating the effect of simulating porcelain firing on the microstructure, corrosion behavior and mechanical properties of a Co-Cr-Mo alloy fabricated by Metal Soft Milling (MSM). Two groups of Co-28Cr-5Mo specimens (25 × 20 × 3 mm) were prepared by MSM: The as-sintered (AS) specimens and the post-fired (PF) specimens that were subjected to 5 simulating porcelain firing cycles without applying the ceramic mass onto their surface. Phase identification by X-ray Diffraction (XRD), microstructure examination by optical microscopy and Scanning Electron Microscopy combined with Energy-Dispersive X-ray Spectroscopy (SEM/EDX), corrosion testing by cyclic polarization and chronoamperometry in simulated body fluid (SBF), the latter test accompanied by Cr3+ and Cr6+ detection in the electrolyte through the 1.5-diphenylcarbazide (DPC) method and UV/visible spectrophotometry, and mechanical testing by micro-/nano-indentation were conducted to evaluate the effect of the post-firing cycles on the properties of Co-Cr-Mo. The results were statistically analyzed by the t test (p < 0.05: statistically significant). All specimens had a mixed γ-fcc and ε-hcp cobalt-based microstructure with a dispersion of pores filled with SiO2 and a fine M23C6 intergranular presence. PF led to an increase in the ε-Co content and slight grain coarsening. Both AS and PF alloys showed high resistance to general and localized corrosion, whereas neither Cr6+ nor Cr3+ were detected during the passivity-breakdown stage. PF improved the mechanical properties of the AS-alloy, especially the indentation modulus and true hardness (statistically significant differences: p = 0.0009 and 0.006, respectively). MSM and MSM/simulating-porcelain firing have been proven trustworthy fabrication methods of Co-Cr-Mo substrates for metal-ceramic prostheses. Moreover, the post-firing cycles improve the mechanical behavior of Co-Cr-Mo, which is vital under the dynamically changing loads in the oral cavity, whereas they do not degrade the corrosion performance.

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.

Evaluation of the relationship between metallurgical properties and metal-ceramic bond characteristics of Co-Cr alloys manufactured by different techniques.

STATEMENT OF PROBLEM: Metal-ceramic restorations made from cobalt chromium (Co-Cr) alloy have been increasing, but studies on the effects of different manufacturing techniques on metal-ceramic interface characteristics and metal-ceramic bond strength are sparse. PURPOSE: The purpose of this in vitro study was to examine the metal-ceramic interface and the metal-ceramic bond strength of a Co-Cr alloy produced by casting, milling, and selective laser melting (SLM) with or without thermal cycling. MATERIAL AND METHODS: Co-Cr alloys were prepared by casting, milling, and SLM. Two different SLM devices were used. Ninety-six specimens (25×3×0.5 mm) were manufactured. The structure of the oxidation surface of Co-Cr specimens was examined by scanning electron microscopy (SEM) and by X-ray fluorescence spectroscopy (XRFS). After porcelain application, selected specimens were thermal cycled, and the strength of the metal-ceramic bond was measured by the 3-point bend test. All specimens were analyzed for failure type with a stereomicroscope. The elemental composition and morphology of the metal-ceramic interface were examined by XRFS and SEM with energy-dispersive X-ray (EDX). The results of bond strength were analyzed using a 2-way analysis of variance (ANOVA) for manufacturing methods and testing conditions and the Tukey honest significant difference (HSD) test (α=.05). RESULTS: The main effect of the interactions of the testing condition and manufacturing method variables on the bond strength variable was not statistically significantly different. No significant differences were found among the testing conditions tested (P=.638). Significant differences were found among the manufacturing methods tested statistically (P<.001). Statistically significant differences were found in the CAD-CAM and CONSEPT LASER groups, the CAD-CAM and SLM LASER groups, the CAD-CAM and CAST groups, and the CAST-SLM LASER groups (P<.05). Differences were observed among the interface morphologies of casting, milling, and the two SLM groups. CONCLUSIONS: The bond strength between Co-Cr alloy and ceramic is affected by the manufacturing method. The metal-ceramic bond strength is independent of thermal cycling. The bond strength value in all groups was over 25 MPa, which has been considered clinically acceptable. The interface metallurgical structures of Co-Cr alloys were affected by different manufacturing techniques.

Recycling selective laser melting alloy powder on cobalt chromium-to-ceramic bond strength.

STATEMENT OF PROBLEM: Reusing the powder in selective laser melting machines after multiple cycles is a cost-effective procedure for dental laboratories. However, information on the metal-ceramic bond strength of the framework fabricated by using recycled powder is lacking. PURPOSE: The purpose of this in vitro study was to investigate how the bonding agent and repeated alloy powder reuse affected the metal-ceramic bond strength of cobalt chromium frameworks fabricated by using selective laser melting. MATERIAL AND METHODS: Four square and 40-bar-shaped cobalt chromium frameworks were fabricated by selective laser melting. Half were produced by using virgin alloy powder (Group V; nsquare=2, nbar=20), and half with 30-times reused powder (Group R; nsquare=2, nbar=20). The particle size of each powder was measured by using scanning electron microscopy, and its phase composition was characterized by using radiograph diffraction. Each group was divided into 2 subgroups (Group W [Wash Opaque] and Group N [NP-Bond]) according to the brand of bonding agent used. After ceramic application, the metal-ceramic bond strengths were evaluated by using 3-point bend tests. The bonding agents' chemical composition was analyzed by using radiograph fluorescence. Bond strength data were analyzed by using a 2-way analysis of variance (α=.05). RESULTS: Mean ±standard deviation bond strengths did not differ significantly (P>.05) between Groups V (31.25 ±4.65) and R (30.88 ±4.78). Group W (35.34 ±1.78) had significantly higher bond strength than Group N (26.80 ±1.74; P<.001). Radiograph diffraction analysis found that the phase composition of all powders was similar. The bonding agent in Group W contained cerium, whereas, that in Group N did not. CONCLUSIONS: Metal-ceramic bond strength was unaffected by alloy powder reuse. However, the bonding agent brand may affect the bond strength of cobalt chromium frameworks fabricated by using selective laser melting.

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.

Cobalt chromium alloys in fixed prosthodontics: Investigations of mechanical properties and microstructure.

STATEMENT OF PROBLEM: Cobalt chromium (Co-Cr) alloys possess beneficial mechanical properties because alloys, even in thin sections, can resist high mastication forces and exhibit an acceptable bond to the surface porcelain layer. Traditional manufacturing techniques of Co-Cr alloys such as casting have been replaced with newer fabrication techniques, such as milling, laser melting, and presintered milling. Despite scarce documentation, these new manufacturing techniques are being used to fabricate dental and implant constructions. PURPOSE: This in vitro study investigates the hardness, yield strength, elastic modulus, and microstructure of the most commonly used Co-Cr alloys for fixed prosthodontics based on manufacturing technique. In addition, this study investigates the effect of heat treatment on the mechanical properties and microstructure of these materials. MATERIAL AND METHODS: Five Co-Cr alloys were included (dumbbell and rectangular shaped) based on four manufacturing techniques: cast, milled, laser melted, and presintered milled. Commercially pure titanium grade 4 and titanium-6 aluminum-4 vanadium ELI (extra low interstitial) were included for comparison, and yield strength and elongation after fracture were evaluated. The specimens were tested for hardness using the Vickers test and for elastic modulus using a nondestructive impulse excitation technique. The microstructure of selected specimens was analyzed using focused ion beam-scanning electron microscopy (FIB-SEM) and energy dispersive X-ray spectroscopy (EDS). RESULTS: The mechanical properties depend on the manufacturing technique used; the laser-melted and presintered Co-Cr specimens demonstrated the highest mechanical properties, followed by the milled and cast groups. Both the laser-melted and the presintered milled Co-Cr specimens showed smaller grain size compared with the cast and milled Co-Cr specimens. The titanium-6 aluminum-4 vanadium ELI demonstrated higher hardness and yield strength compared to commercially pure titanium grade 4. No major differences were observed for the selected materials regarding the mechanical properties and microstructural appearance after heat treatment. CONCLUSIONS: The laser melting and presintered milling techniques produced higher mechanical properties compared with the cast and milled Co-Cr. These findings were confirmed through microstructural analysis with respect to the grain size, precipitation, and number of pores.

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.

Fundamental Properties and Clinical Application of 3D-Printed Bioglass Porcelain Fused to Metal Dental Restoration.

The purpose of this study is to evaluate the mechanical properties and clinical fitness of 3D-printed bioglass porcelain fused to metal (PFM) dental crowns. To evaluate the mechanical properties, tensile strength, Vickers microhardness, shear bond strength, and surface roughness tests of the SLM printed Co-Cr alloy was conducted. A right mandibular 1st molar tooth was prepared for a single dental crown (n = 10). For a three-unit metal crown and bridge, the right mandibular first premolar and first molar were prepared. Bioglass porcelain was fired to fabricate PFM dental restorations. A clinical gap was observed and measured during each of the four times porcelain was fired. A statistical analysis was conducted. The SLM technique showed the largest statistically significant tensile strength and a 0.2% yield strength value. The milling technique had the lowest statistically significant compressive strength value. The shear bond strength and surface roughness showed no statistically significant difference between the fabricated method. There was a statistically significant change in marginal discrepancy according to the porcelain firing step. The casting technique showed the greatest statistically significant margin discrepancy value. The SLM method showed better fitness than the traditional casting method and showed better mechanical properties as a dental material.

Effects of post-treatment on metal-ceramic bond properties of selective laser melted Co-Cr dental alloy. Part 1: Annealing temperature.

STATEMENT OF PROBLEM: Dental cobalt-chromium (Co-Cr) alloy manufactured by selective laser melting (SLM) is not recommended for clinical applications before annealing because of excessive residual stress. However, limited information is available regarding the relationship between annealing temperature and the metal-ceramic bond properties of SLM Co-Cr alloys. PURPOSE: The purpose of this in vitro study was to investigate the effects of annealing temperature on the metal-ceramic bond properties of SLM Co-Cr alloys. MATERIAL AND METHODS: Four groups with different annealing temperatures (850 °C; 950 °C; 1050 °C; 1150 °C) were prepared by using SLM techniques. Bond strengths were measured by using a 3-point bend test; subsequently, debonded surface morphologies and elements were assessed by using a scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). The area fraction of adherence porcelain (AFAP) value was introduced to analyze fracture characteristics. Microstructural and interfacial characteristics were characterized by SEM/EDS and X-ray diffraction analysis. The coefficient of thermal expansion (CTE) test was used to analyze thermal matching. A 1-way ANOVA and the Tukey honestly significant difference tests were used to analyze bond strengths and AFAP values statistically (α=.05). RESULTS: The mean ±standard deviation values of the metal-ceramic bond strengths were 40.68 ±4.34 MPa for the 850 °C group, 37.54 ±5.34 MPa for the 950 °C group, 45.97 ±2.18 MPa for the 1050 °C group, and 50.79 ±1.79 MPa for the 1150 °C group. Significant differences (P<.05) were observed among all groups. Debonded surfaces and AFAP analysis displayed a mixed fracture mode of adhesive and cohesive fracture, and 1150 °C-annealing specimens exhibited better fracture characteristics close to cohesive fractures. As the temperature increased, native oxide film thicknesses remained unchanged; the 850 °C group had the thinnest diffusion layer, while the other 3 groups had similar thicknesses. Although the 1050 °C and 1150 °C groups displayed higher CTE values, their microstructures were more conducive to atomic diffusion and improved chemical bonding. Microstructure analysis found that ε phase and second-phase precipitates jointly affected metal-ceramic bond strength. CONCLUSIONS: Annealing temperatures affected the metal-ceramic bond strengths of SLM Co-Cr porcelain specimens. 1150 °C annealing SLM Co-Cr specimens displayed higher bond strengths and improved fracture and interface characteristics among the 4 groups.

Effects of hollow structures added by selective laser sintering on the mechanical properties of Co-Cr alloy.

PURPOSE: This study investigates the effects of hollow structures, added by selective laser sintering (SLS), on the mechanical properties of a Co-Cr alloy for providing an optimal structural property to the framework components of removable partial dentures (RPDs). METHODS: The specimens produced using the 3D data of the dumbbell-shaped cylinders were divided into four groups based on the manufacturing method: Cast, Mill, SLS-solid, and SLS-hollow. Tensile tests were performed to measure the mechanical properties of the specimens. The mechanical property values among the four groups were statistically compared using the Kruskal-Wallis test followed by the Steel-Dwass test (α = 0.05). RESULTS: The median elastic modulus was the largest in the Cast, followed by SLS-solid, Mill, and SLS-hollow, with no significant differences observed between all conditions. The median ultimate tensile strength was the largest in the order of SLS-solid, Mill, SLS-hollow, and Cast. The median 0.2% proof stress was the largest in SLS-solid, followed by SLS-hollow, Cast, and Mill. The median elongation was the highest in the order of Mill, SLS-solid, SLS-hollow, and Cast. CONCLUSIONS: With the addition of hollow structures, the elastic modulus decreased while the mechanical strength and proof stress remained high in SLS specimens. In addition, the ISO 22674 standard for dental metals was met, suggesting that SLS may be a possible method to design RPD frameworks with high strength and optimal structural properties.

Evaluation of ceramic adherence to cobalt-chromium alloys fabricated by different manufacturing techniques.

STATEMENT OF PROBLEM: Selective laser melting has been increasingly used in the fabrication of metal-ceramic prostheses. The longevity of the prostheses depends on the strength of the metal-ceramic bond, which may differ with the framework manufacturing technique. PURPOSE: The purpose of this in vitro study was to compare the bond strength of ceramic to cobalt-chromium (Co-Cr) alloys fabricated by different manufacturing methods. MATERIAL AND METHODS: Sixty Ø15×2-mm disk-shaped specimens were prepared and assigned to 3 groups (n=20) with different manufacturing methods: milled Co-Cr (M), selective laser melted Co-Cr (SLM), and cast Co-Cr (C). The disks were ceramic layered with a 2-mm thickness. Half of the specimens from each group were thermocycled. The shear bond strength (SBS) test was applied to all specimens. The microstructure changes after ceramic layering were evaluated by X-ray diffraction (XRD). The specimens' surface morphology was analyzed by using scanning electron microscopy (SEM). RESULTS: Thermocycling had a significant effect on SBS values in the SLM group (P=.017). Considering the registered Fmax (force inducing bonding failure), a significant difference was found between SLM and both M and C groups (P<.001). No significant difference was found between milled and cast Co-Cr (P=.885). The failure types were mostly mixed failures. Ceramic layering induced a crystallization increase in groups C and SLM. CONCLUSIONS: The adhesion strength of ceramic to Co-Cr differed with alloy composition and manufacturing technique. The aging process influenced the results in the SLM group.

The impact of NPK fertilizer on growth and nutrient accumulation in juniper (Juniperus procera) trees grown on fire-damaged and intact soils.

Wildfires significantly alter soil properties and result in vegetation shifts; therefore, rapid reforestation activities are needed in the forests affected by wildfires. The decreased nutrient in the soil is the obvious effect of wildfires; however, little is known about the reforestation of Juniper (Juniperus procera) forests with application of NPK fertilizers. Juniper forests are common in Asir and Taif regions of Saudi Arabia and vulnerable to wildfires; thus, reforestation is needed after the onset of fires. This study assessed the impact of different doses of organic NPK fertilizer (0, 5 and 10 g/L) on growth and nutrient accumulation of Juniper trees grown on fire-damaged and intact soils. Data relating to tree height, number of leaves per plant, fresh and dry biomass accumulation in shoot and root, chlorophyll contents and uptake of N, P, K, and Na were recorded. Individual and interactive effects of soil types and fertilizer doses significantly altered all measured traits with minor exceptions. Overall, higher values of the measured traits were recorded for intact soil and 10 g/L fertilize dose. The increasing fertilizer doses improved the growth and nutrient acquisition and application of 10 g/L fertilizer on intact soil recorded the highest values of growth traits. Juniper trees grown on fire-damaged soil accumulated higher amount of nitrogen than intact soil. Similarly, the trees grown on intact soil accumulated lower amount of Na and maintained comparable K/Na ratio to intact soil. It is concluded that supplying 10 g/L fertilizer could improve the establishment of Juniper trees on fire-damaged soil. Therefore, organic fertilizer can be used to improve the reforestation of wildfire-affected Juniper forests in the Asir province.