Weibull Curves Research Articles

Effect of Quenching Temperature on Microstructure and Rolling Contact Fatigue Behavior of 17Cr2Ni2MoVNb Steel

17Cr2Ni2MoVNb steel is a new type of gear steel in the automotive industry; the rolling contact fatigue behavior is not well documented. In this study, some microscopic analysis methods (optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), and energy dispersive X-ray analysis (EDS)) were used to characterize material microstructure and damage surface. In addition, rolling contact fatigue behavior was evaluated by Weibull curve. The results show that the size of austenite grain increased while the quenching temperature increased. Moreover, the samples with a quenching temperature of 1000 °C exhibited the maximum mean life of 7.33 × 105 cycles. In addition, the failure mode of quenched at 900 °C and 1100 °C were delamination, and pitting was the main failure mode of 1000 °C.

Characteristics of Spatiotemporal Distribution of Sea Surface Wind along the East Coast of Guangdong Province

We analyzed the frequency distribution characteristics of wind speeds occurring at different offshore sites within a range of 0–200 km based on the sea surface wind data captured via buoys and oil platforms located along the east coast of Guangdong Province. The results of the analysis showed that average wind speed measured for each station reached a maximum in winter while minima occurred in summer, corresponding to obvious seasonal variation, and average wind speed increased with offshore distance. The prevailing wind direction at the nearshore site is the easterly wind, and the frequency of winds within 6–10 m s–1 is considerable with that of winds at > 10 m s–1. With the increase of the offshore distance, the winds were less affected by the land, and the prevailing wind direction gradually became northerly winds, predominately those at > 10 m s–1. For areas of shorter offshore distance (< 100 km), surface wind speeds fundamentally conformed to a two-parameter Weibull distribution, but there was a significant difference between wind speed probability distributions and the Weibull distribution in areas more than 100 km offshore. The mean wind speeds and wind speed standard deviations increased with the offshore distance, indicating that with the increase of the wind speed, the pulsation of the winds increased obviously, resulting in an increase in the ratio of the mean wind speed to the standard deviation of wind speed. When the ratio was large, the skewness became negative. When a relatively great degree of dispersion was noted between the observed skewness and the skewness corresponding to the theoretical Weibull curve, the wind speed probability distribution could not be adequately described by a Weibull distribution. This study provides a basis for the verification of the adaptability of Weibull distribution in different sea areas.

The effect of DLC-coating deposition method on the reliability and mechanical properties of abutment’s screws

ObjectiveTo characterize the mechanical properties of different coating methods of DLC (diamond-like carbon) onto dental implant abutment screws, and their effect on the probability of survival (reliability). MethodsSeventy-five abutment screws were allocated into three groups according to the coating method: control (no coating); UMS – DLC applied through unbalanced magnetron sputtering; RFPA-DLC applied through radio frequency plasma-activated (n=25/group). Twelve screws (n=4) were used to determine the hardness and Young’s modulus (YM). A 3D finite element model composed of titanium substrate, DLC-layer and a counterpart were constructed. The deformation (μm) and shear stress (MPa) were calculated. The remaining screws of each group were torqued into external hexagon abutments and subjected to step-stress accelerated life-testing (SSALT) (n=21/group). The probability Weibull curves and reliability (probability survival) were calculated considering the mission of 100, 150 and 200N at 50,000 and 100,000 cycles. ResultsDLC-coated experimental groups evidenced higher hardness than control (p<0.05). In silico analysis depicted that the higher the surface Young’s modulus, the higher the shear stress. Control and RFPA showed β<1, indicating that failures were attributed to materials strength; UMS showed β>1 indicating that fatigue contributed to failure. High reliability was depicted at a mission of 100N. At 200N a significant decrease in reliability was detected for all groups (ranging from 39% to 66%). No significant difference was observed among groups regardless of mission. Screw fracture was the chief failure mode. SignificanceDLC-coating have been used to improve titanium’s mechanical properties and increase the reliability of dental implant-supported restorations.

Fatigue Failure of External Hexagon Connections on Cemented Implant-Supported Crowns

To evaluate the probability of survival and failure modes of different external hexagon connection systems restored with anterior cement-retained single-unit crowns. The postulated null hypothesis was that there would be no differences under accelerated life testing. Fifty-four external hexagon dental implants (∼4 mm diameter) were used for single cement-retained crown replacement and divided into 3 groups: (3i) Full OSSEOTITE, Biomet 3i (n = 18); (OL) OEX P4, Osseolife Implants (n = 18); and (IL) Unihex, Intra-Lock International (n = 18). Abutments were torqued to the implants, and maxillary central incisor crowns were cemented and subjected to step-stress-accelerated life testing in water. Use-level probability Weibull curves and probability of survival for a mission of 100,000 cycles at 200 N (95% 2-sided confidence intervals) were calculated. Stereo and scanning electron microscopes were used for failure inspection. The beta values for 3i, OL, and IL (1.60, 1.69, and 1.23, respectively) indicated that fatigue accelerated the failure of the 3 groups. Reliability for the 3i and OL (41% and 68%, respectively) was not different between each other, but both were significantly lower than IL group (98%). Abutment screw fracture was the failure mode consistently observed in all groups. Because the reliability was significantly different between the 3 groups, our postulated null hypothesis was rejected.

Influence of platform diameter in the reliability and failure mode of extra-short dental implants.

To evaluate the influence of implant diameter in the reliability and failure mode of extra-short dental implants. Sixty-three extra-short implants (5mm-length) were allocated into three groups according to platform diameter: Ø4.0-mm, Ø5.0-mm, and Ø6.0-mm (21 per group). Identical abutments were torqued to the implants and standardized crowns cemented. Three samples of each group were subjected to single-load to failure (SLF) to allow the design of the step-stress profiles, and the remaining 18 were subjected to step-stress accelerated life-testing (SSALT) in water. The use level probability Weibull curves, and the reliability (probability of survival) for a mission of 100,000 cycles at 100MPa, 200MPa, and 300MPa were calculated. Failed samples were characterized in scanning electron microscopy for fractographic inspection. No significant difference was observed for reliability regarding implant diameter for all loading missions. At 100MPa load, all groups showed reliability higher than 99%. A significant decreased reliability was observed for all groups when 200 and 300MPa missions were simulated, regardless of implant diameter. At 300MPa load, the reliability was 0%, 0%, and 5.24%, for Ø4.0mm, Ø5.0mm, and Ø6.0mm, respectively. The mean beta (β) values were lower than 0.55 indicating that failures were most likely influenced by materials strength, rather than damage accumulation. The Ø6.0mm implant showed significantly higher characteristic stress (η = 1,100.91MPa) than Ø4.0mm (1,030.25MPa) and Ø5.0mm implant (η = 1,012.97MPa). Weibull modulus for Ø6.0-mm implant was m = 7.41, m = 14.65 for Ø4.0mm, and m = 11.64 for Ø5.0mm. The chief failure mode was abutment fracture in all groups. The implant diameter did not influence the reliability and failure mode of 5mm extra-short implants.

Fracture strength and probability of survival of narrow and extra-narrow dental implants after fatigue testing: In vitro and in silico analysis

PurposeTo assess the probability of survival (reliability) and failure modes of narrow implants with different diameters. Materials and methodsFor fatigue testing, 42 implants with the same macrogeometry and internal conical connection were divided, according to diameter, as follows: narrow (Ø3.3×10mm) and extra-narrow (Ø2.9×10mm) (21 per group). Identical abutments were torqued to the implants and standardized maxillary incisor crowns were cemented and subjected to step-stress accelerated life testing (SSALT) in water. The use-level probability Weibull curves, and reliability for a mission of 50,000 and 100,000 cycles at 50N, 100, 150 and 180N were calculated. For the finite element analysis (FEA), two virtual models, simulating the samples tested in fatigue, were constructed. Loading at 50N and 100N were applied 30° off-axis at the crown. The von-Mises stress was calculated for implant and abutment. ResultsThe beta (β) values were: 0.67 for narrow and 1.32 for extra-narrow implants, indicating that failure rates did not increase with fatigue in the former, but more likely were associated with damage accumulation and wear-out failures in the latter. Both groups showed high reliability (up to 97.5%) at 50 and 100N. A decreased reliability was observed for both groups at 150 and 180N (ranging from 0 to 82.3%), but no significant difference was observed between groups. Failure predominantly involved abutment fracture for both groups. FEA at 50N-load, Ø3.3mm showed higher von-Mises stress for abutment (7.75%) and implant (2%) when compared to the Ø2.9mm. ConclusionsThere was no significant difference between narrow and extra-narrow implants regarding probability of survival. The failure mode was similar for both groups, restricted to abutment fracture.

Fatigue Failure of Narrow Implants with Different Implant-Abutment Connection Designs.

To evaluate the reliability of narrow diameter dental implants (NDIs) with similar macrogeometry and 3 implant-abutment connection designs. Eighty-four NDIs (3.5 × 10 mm) were selected and divided into 4 groups (n = 21/group) according to implant-abutment connection design, as follows: EH - external hexagon, IH - internal hexagon, IC - internal conical, and IC-M - internal conical connected to a monolithic titanium abutment. Identical abutments were torqued to the implants, and standardized maxillary incisor crowns were cemented and subjected to step-stress accelerated life testing (SSALT) in water. Use of level probability Weibull curves, and reliability for a mission of 50,000 cycles at 75 N and 200 N were calculated. The beta (β) values were: 1.48 for IC, 1.40 for IC-M, 8.54 for EH, and 1.98 for IH, indicating that damage accumulation was an acceleration factor for failure of all groups. At 75 N the probability of survival was not significantly different between groups. A decrease in reliability was observed for all groups at 200 N with no significant differences between IC (81.71%) and IC-M (94.28%), or between EH and IH (0%) which presented the lowest values. EH failures were primarily restricted to the screw, while IH involved screw and implant fracture. IC and IC-M were restricted to prosthetic failures (fracture and bending). Narrow implants with external or internal hexagon connections presented the lowest reliability at high loads compared to internal conical connections. Failure modes differed among connections.

Assessment of wind resources in two parts of Northeast Brazil with the use of numerical models

Assessment of wind resources in two parts of Northeast Brazil with the use of numerical models

Survival and failure modes: platform-switching for internal and external hexagon cemented fixed dental prostheses.

This study evaluated the probability of survival (reliability) of platform-switched fixed dental prostheses (FDPs) cemented on different implant-abutment connection designs. Eighty-four-three-unit FDPs (molar pontic) were cemented on abutments connected to two implants of external or internal hexagon connection. Four groups (n=21 each) were established: external hexagon connection and regular platform (ERC); external hexagon connection and switched platform (ESC); internal hexagon and regular platform (IRC); and internal hexagon and switched platform (ISC). Prostheses were subjected to step-stress accelerated life testing in water. Weibull curves and probability of survival for a mission of 100,000 cycles at 400N (two-sided 90% CI) were calculated. The beta values of 0.22, 0.48, 0.50, and 1.25 for groups ERC, ESC, IRC, and ISC, respectively, indicated a limited role of fatigue in damage accumulation, except for group ISC. Survival decreased for both platform-switched groups (ESC: 74%, and ISC: 59%) compared with the regular matching platform counterparts (ERC: 95%, and IRC: 98%). Characteristic strength was higher only for ERC compared with ESC, but not different between internal connections. Failures chiefly involved the abutment screw. Platform switching decreased the probability of survival of FDPs on both external and internal connections. The absence in loss of characteristic strength observed in internal hexagon connections favor their use compared with platform-switched external hexagon connections.

Comparison of two psychometric functions in analyzing 4-AFC detection results using a task-based structured phantom for digital mammography

Introduction Detectability of spiculated and non-spiculated mass models and microcalcifications, in a structured background phantom of acrylic spheres and water, was studied for digital mammography via the four-alternative forced-choice (4-AFC) paradigm. Purpose To compare the threshold diameters for mass and microcalcification detection using two types of psychometric curves applied on the contrast-detail data. Material and methods Ten images of the structured phantom were acquired on 23 digital mammography systems under automatic exposure control. The 4-AFC study was performed with in-house developed software and 5 medical physicists as observers. Percentage correctly detected lesions (PC) was obtained for each target type. Two psychometric curves (Weibull and Logistic functions) were applied to determine the threshold diameters and number of detected targets (at PC = 62.5%). Results Both fitting procedures were successfully applied on all systems. After averaging over 23 systems, the threshold diameters for spiculated and non-spiculated masses and microcalcifications, with the Weibull psychometric curves, were 4.0 ± 0.3 mm (R2 = 0.61 ± 0.08), 4.6 ± 0.7 mm (R2 = 0.51 ± 0.11), and 0.114 ± 0.003 mm (R2 = 0.91 ± 0.03) respectively, and the values of 4.0 ± 0.4 mm (R2 = 0.61 ± 0.08), 4.7 ± 0.6 mm (R2 = 0.50 ± 0.11), and 0.114 ± 0.003 mm (R2 = 0.91 ± 0.03) were obtained with the Logistic function. The numbers of detected targets assessed from the two functions were not different (3–4 spiculated masses, 1–2 non-spiculated masses, and 4 groups of microcalcifications). If the PC values were not completely covering the lower and upper than 62.5%, there will be possibility different results occurred from these two functions. Conclusion Weibull and Logistic curve fits gave similar and reproducible threshold diameters for the structured phantom.

Modeling and Analysis of Software Fault Detection and Correction Process Through Weibull-Type Fault Reduction Factor, Change Point and Imperfect Debugging

Fault reduction factor (FRF) is one of the most important factors which plays a vital role in software reliability growth. In the past, few studies on the influence of different environmental factors into FRF have been carried out. In these studies, FRF has been defined using some particular functions such as constant, increasing, decreasing and inflection S-shaped. These functions may not be realistic and reasonable to represent the actual behavior of FRF. Therefore, in this study, it has been tried to represent the realistic behavior of FRF using Weibull curve. Moreover, a new approach of software reliability modeling has been proposed in which FRF has been incorporated in fault detection and correction process. Thus, in this paper, a general frame work of software reliability growth model (SRGM) has been proposed considering the fault detection and correction process. The concepts of imperfect debugging and change point have also been incorporated in the present study. Different parameters of the proposed SRGM are estimated using the SPSS and ‘R’ software. Different comparison criteria have been used for comparison of the proposed SRGM with other existing SRGMs. Chi-square goodness-of-fit test has been used for validation of the proposed SRGM.

Resin composite repair for implant-supported crowns.

This study evaluated the reliability of implant-supported crowns repaired with resin composites. Fifty-four titanium abutments were divided in three groups (n=18 each) to support resin nanoceramic molar crowns, as follows: (LU) (Lava Ultimate, 3M ESPE); LU repaired with either a direct or an indirect resin composite. Samples were subjected to mouth-motion accelerated-life testing in water (n=18). Cumulative damage with a use stress of 300N was used to plot Weibull curves for group comparison. Reliability was calculated for a mission of 100,000 cycles at 400N load. Beta values were 0.83 for LU, 0.31 and 0.27 for LU repaired with Filtek and Ceramage, respectively. Weibull modulus for LU was 9.5 and η=1047N, m=6.85, and η=1002N for LU repaired with Ceramage, and m=4.65 and η=766N for LU repaired with Filtek (p<0.10 between LU and LU repaired with Filtek). Reliability at 400N was 100% for both LU and LU repaired with Ceramage which were significantly higher than LU Filtek repair (32%). LU restored crowns failed cohesively. Fractures were confined within the restored material, and detailed fractography is presented. The performance of resin nanoceramic material repaired with an indirect composite was maintained after accelerated-life testing compared to unrepaired controls. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1481-1489, 2017.

Reliability and Failure Modes of a Hybrid Ceramic Abutment Prototype.

A ceramic and metal abutment prototype was fatigue tested to determine the probability of survival at various loads. Lithium disilicate CAD-milled abutments (n = 24) were cemented to titanium sleeve inserts and then screw attached to titanium fixtures. The assembly was then embedded at a 30° angle in polymethylmethacrylate. Each (n = 24) was restored with a resin-cemented machined lithium disilicate all-ceramic central incisor crown. Single load (lingual-incisal contact) to failure was determined for three specimens. Fatigue testing (n = 21) was conducted employing the step-stress method with lingual mouth motion loading. Failures were recorded, and reliability calculations were performed using proprietary software. Probability Weibull curves were calculated with 90% confidence bounds. Fracture modes were classified with a stereomicroscope, and representative samples imaged with scanning electron microscopy. Fatigue results indicated that the limiting factor in the current design is the fatigue strength of the abutment screw, where screw fracture often leads to failure of the abutment metal sleeve and/or cracking in the implant fixture. Reliability for completion of a mission at 200 N load for 50K cycles was 0.38 (0.52% to 0.25 90% CI) and for 100K cycles was only 0.12 (0.26 to 0.05)-only 12% predicted to survive. These results are similar to those from previous studies on metal to metal abutment/fixture systems where screw failure is a limitation. No ceramic crown or ceramic abutment initiated fractures occurred, supporting the research hypothesis. The limiting factor in performance was the screw failure in the metal-to-metal connection between the prototyped abutment and the fixture, indicating that this configuration should function clinically with no abutment ceramic complications. The combined ceramic with titanium sleeve abutment prototype performance was limited by the fatigue degradation of the abutment screw. In fatigue, no ceramic crown or ceramic abutment components failed, supporting the research hypothesis with a reliability similar to that of all-metal abutment fixture systems. A lithium disilcate abutment with a Ti alloy sleeve in combination with an all-ceramic crown should be expected to function clinically in a satisfactory manner.

Forecasting of Fuel cell technology in hybrid and electric vehicles using Gompertz growth curve

This paper is intended to forecast Fuel cell technology using patent literature and technological growth curve models. Technology maturity of the Fuel cell technology is determined from the forecast. Patent data pertaining to Fuel cell technology is extracted from United States Patent and Trademark Office (USPTO) from 1976 to 2012. Fuel cell technology patents are grouped with the help of International Patent Classification (IPC) classes. A demographic analysis is done on World patents pertaining to Fuel cell technology to identify important patent groups and variables for modelling. From the literature study various growth curves in particular Logistic, Gompertz and Weibull Curves are considered to forecast the Fuel cell technology. The upper limit used in this analysis is defined and a formula to evaluate the same is proposed. An algorithm already existing in the literature is used to find the starting year or base year of the normalized cumulative frequency of patent grants plot. After the analysis, Gompertz curve is considered as the best model to forecast Fuel cell technology. The fit of the transformed Gompertz curve is determined with the help of adjusted R-Square value. Parameters of Gompertz curve are estimated using natural logarithmic transformations and regression. These parameters are substituted back in the Gompertz curve and error terms are checked for auto correlation and normality assumptions. Technology Maturity has been evaluated using Gompertz curve and the same is compared with Nonlinear Least Square technique. The forecasting errors over the forecast region are estimated using Root Mean Square Error (RMSE) and Mean Absolute Percentage Error (MAPE).The important aspect of evaluating the technology maturity of a particular technology will be the identification of important patent groups that form the technology and these groups are used to evaluate the upper limit of the technological growth curve. From the Analysis, the Fuel cell technology is categorized as an “EMERGING TECHNOLOGY”. Current forecast of Fuel cell technology maturity is very long and therefore a policy intervention or a subsidy from the Government or a new breakthrough in the Fuel cell research will reduce the forecast time.

Failure and reliability evaluation of turbines used in Nigerian thermal plant

Failure and reliability evaluation of turbines used in Nigerian thermal plant has been undertaken. Data were obtained directly from the operational department of the stations log-book, which were records of the station’s plant generation from each of the operational power generating units. The exponential and Weibull density models were used to evaluate the reliability of six turbines as an individual component in the station. Mean time to failure (MTBF), Mean time to repair (MTTR) and failure rate (λ) are evaluated from the maintenance record book of Sapele thermal power station and used to evaluate the distribution and reliabilities of system components. Each Weibull curve compressed on both axes and the vertical axis showed the density of stretchiness of the reliability of both turbines while the horizontal axis showed the minimum life of turbine or the aging condition in hours. The reliability of ST01 and aging condition of unit drop by 3.5% in every 77 hours from the year 2003 to 2012. ST02 reliability, 3% in 68 hours; ST06 reliability, 3.5% in 76 hour; GT01 reliability 3% in 75 hours; and GT02 reliability 3% in 84 hour. For a power generating station to be reliability the failure rate index must be reduced from unity to 0 as availability is directly proportional to reliability.

Reliability and failure modes of narrow implant systems.

Narrow implants are indicated in areas of limited bone width or when grafting is nonviable. However, the reduction of implant diameter may compromise their performance. This study evaluated the reliability of several narrow implant systems under fatigue, after restored with single-unit crowns. Narrow implant systems were divided (n=18 each), as follows: Astra (ASC); BioHorizons (BSC); Straumann Roxolid (SNC), Intra-Lock (IMC), and Intra-Lock one-piece abutment (ILO). Maxillary central incisor crowns were cemented and subjected to step-stress accelerated life testing in water. Use level probability Weibull curves and reliability for a mission of 100,000 cycles at 130- and 180-N loads (90% two-sided confidence intervals) were calculated. Scanning electron microscopy was used for fractography. Reliability for 100,000 cycles at 130N was ∼99% in group ASC, ∼99% in BSC, ∼96% in SNC, ∼99% in IMC, and ∼100% in ILO. At 180N, reliability of ∼34% resulted for the ASC group, ∼91% for BSC, ∼53% for SNC, ∼70% for IMC, and ∼99% for ILO. Abutment screw fracture was the main failure mode for all groups. Reliability was not different between systems for 100,000 cycles at the 130-N load. A significant decrease was observed at the 180-N load for ASC, SNC, and IMC, whereas it was maintained for BSC and ILO. The investigated narrow implants presented mechanical performance under fatigue that suggests their safe use as single crowns in the anterior region.

Analysis of solder joint reliability of high power LEDs by transient thermal testing and transient finite element simulations

An innovative sensitive test method is developed to detect solder joint cracking for high power LED packages. The method is based on transient thermal analysis and can fully replace the still dominating light-on test. For experimental application of the model, test groups of LED packages were soldered with two different lead free solders (SnAgCu305 and Innolot FL-640) on Aluminum Insulated Metal Substrate (Al-IMS) and exposed to temperature cycles. Transient thermal measurements were performed directly after assembly and after specific cycle numbers. After data processing the increase of the relative thermal resistance between the initial signal at “0” cycles and “n” cycles is obtained and correlated with cracks in the solder joint by cross sections. Based on the CAD and material data of the LED package a finite element (FE) model is set up. The time-resolved temperature curves are properly reproduced by transient thermal simulation. The measured “0” cycle curves are fitted using the FE model by adjusting a few material parameters within their allowed tolerance range. A parameter sensitivity analysis is performed. The impact of a crack in the solder joint between package and printed circuit board (PCB) on the time resolved temperature curve is simulated. The simulated crack propagates from the corner of the package to its center. The experimental measured curves are reproduced. Based on the simulation a failure criteria is defined, representing a crack length between 20% and 30% of the solder joint area, and Weibull curves are calculated. A higher creep resistance for the test group soldered with Innolot FL-640 compared to the test group soldered with SAC305 is observed.

Mechanical Evaluation of Two Grades of Titanium Used in Implant Dentistry.

To investigate the effect of core dental implant materials supporting single crowns on the probability of survival and failure modes. Thirty-six standard external-hex titanium implants (4.0 mm in diameter) were selected to restore single crowns and divided into two groups according to core material: commercially pure grade 2 titanium (G2) and grade 5 titanium-aluminum-vanadium alloy (Ti-6Al-4V) (G5). Abutments were screwed to the implants, and standardized maxillary central incisor metal crowns were cemented and subjected to step-stress accelerated life testing in water. Use-level probability Weibull curves and reliability for missions of 100,000 cycles at 150 N and 200 N (with 90% two-sided confidence intervals [CIs]) were calculated. Polarized light and scanning electron microscopes were used to determine the failure modes. Use-level probability Weibull calculations showed beta values of 0.59 (CI, 0.31 to 1.11) and 1.22 (CI 0.81 to 1.84) for G2 and G5, respectively, and significantly higher characteristic strength and Weibull modulus for G5. The calculated reliability (90% CIs) for a mission of 100,000 cycles at 150 N showed that cumulative damage would lead to survival of 45% of implant-supported crowns of G2 and 98% of G5. At 200 N the probability of survival decreased to 0.03% for G2 and 21% for G5. Abutment screw fracture was the failure mode for all groups. Reliability, characteristic strength, and Weibull modulus were significantly higher for Ti-6Al-4V dental implants than for commercially pure (grade 2) titanium implants. Failure modes were similar for both groups.

Effect of Diamondlike Carbon Coating on Reliability of Implant-Supported Crowns.

To evaluate the effect of diamondlike carbon (DLC) coating on abutments and/or abutment screws on the reliability, characteristic strength, and Weibull modulus of implant-supported single crowns. Seventy-two external hexagon implants (Emfills Implant 4 mm diameter, 10 mm length, Emfills) were divided into four groups (n = 18 each), according to the presence or not of a DLC coating in the abutment and/or abutment screw, as follows: abutment without coating, screw without coating (AwcSwc); abutment without coating with coated screw (AwcSC); abutment coated with noncoated screw (ACSwc), and coated abutment with coated screw (ACSC). Abutments and screws were evaluated with scanning electron microscopy. The specimens were subjected to step-stress accelerated life testing in water. Use-level probability Weibull curves and reliability for a mission of 100,000 cycles at 150 N (90% two-sided confidence intervals) were calculated. Polarized light and scanning electron microscopes were used for fractographic analysis. For a mission of 100,000 cycles at 150 N, reliability was 0.45 (0.20 to 0.67), 0.12 (0.00 to 0.47), 0.56 (0.17 to 0.82), and 0.44 (0.07 to 0.77) for AwcSwc, AwcSC, ACSwc, and ACSC, respectively. The probability Weibull calculation showed a Weibull modulus (m) of m = 5.50, m = 11.64, m = 16.96, and m = 15.08 and the characteristic strengths (η, which indicates the load at which 63.2% of the specimens of each group fail) of η = 202.67 N, ŋ = 206.64 N, ŋ = 192.54 N, and ŋ = 203.59 N for AwcSwc, AwcSC, ACSwc, and ACSC, respectively. Abutment screw fracture was the chief failure outcome in all groups. Characteristic strength values were not different among groups; neither was reliability. However, an increase in Weibull modulus (indicating low variability of the results) was observed with DLC coating of abutment or screw or both.

Probability of survival of implant-supported metal ceramic and CAD/CAM resin nanoceramic crowns

ObjectivesTo evaluate the probability of survival and failure modes of implant-supported resin nanoceramic relative to metal-ceramic crowns. MethodsResin nanoceramic molar crowns (LU) (Lava Ultimate, 3M ESPE, USA) were milled and metal-ceramic (MC) (Co–Cr alloy, Wirobond C+, Bego, USA) with identical anatomy were fabricated (n=21). The metal coping and a burnout-resin veneer were created by CAD/CAM, using an abutment (Stealth-abutment, Bicon LLC, USA) and a milled crown from the LU group as models for porcelain hot-pressing (GC-Initial IQ-Press, GC, USA). Crowns were cemented, the implants (n=42, Bicon) embedded in acrylic-resin for mechanical testing, and subjected to single-load to fracture (SLF, n=3 each) for determination of step-stress profiles for accelerated-life testing in water (n=18 each). Weibull curves (50,000 cycles at 200N, 90% CI) were plotted. Weibull modulus (m) and characteristic strength (η) were calculated and a contour plot used (m versus η) for determining differences between groups. Fractography was performed in SEM and polarized-light microscopy. ResultsSLF mean values were 1871N (±54.03) for MC and 1748N (±50.71) for LU. Beta values were 0.11 for MC and 0.49 for LU. Weibull modulus was 9.56 and η=1038.8N for LU, and m=4.57 and η=945.42N for MC (p>0.10). Probability of survival (50,000 and 100,000 cycles at 200 and 300N) was 100% for LU and 99% for MC. Failures were cohesive within LU. In MC crowns, porcelain veneer fractures frequently extended to the supporting metal coping. ConclusionProbability of survival was not different between crown materials, but failure modes differed. SignificanceIn load bearing regions, similar reliability should be expected for metal ceramics, known as the gold standard, and resin nanoceramic crowns over implants. Failure modes involving porcelain veneer fracture and delamination in MC crowns are less likely to be successfully repaired compared to cohesive failures in resin nanoceramic material.