Jeremy D. Seidt

Load to failure of different zirconia abutments for an internal hexagon implant

STATEMENT OF PROBLEM Various zirconia abutment designs are available to restore implant systems. Fracture resistance is one of the criteria involved in selecting among these options. PURPOSE The purpose of this in vitro study was to measure and compare load to failure for 5 zirconia abutments for an internally hexagon implant. MATERIAL AND METHODS Five 4.1×11.5-mm Zimmer tapered screw-vent implants were individually secured in a loading apparatus, and 3 specimens of each of the 5 different abutments (Zimmer Contour with a Ti ring, anatomic-contour Atlantis-Zr, anatomic-contour Inclusive-Zr, anatomic-contour Astra Tech ZirDesign, Legacy Straight Contoured abutment with Ti core) (N=15) were loaded at a 30-degree angle until the implant abutment complex failed. Data for load to failure were compared with analysis of variance and a Tukey-Kramer post hoc test (α=.05). RESULTS The custom anatomic-contour abutment (Inclusive) showed the lowest load to fracture, and the stock anatomic-contour (AstraTech ZirDesign) the second lowest load to fracture. These were significantly lower than all other abutments (P<.05). The highest overall fracture strength was of a zirconia abutment with a titanium core-hexagon (Legacy Straight Contoured), which was significantly greater than all other abutments (P<.05). Anatomic-contour zirconia abutments fractured at an average of 275 N compared with the average fracture load of 842 N for zirconia abutments with titanium component (P<.05). CONCLUSION The stock zirconia abutment with a titanium ring and the zirconia abutment with a titanium core-hexagon (Legacy Straight Contoured) had significantly greater fracture resistance than that of any of the 1-piece anatomic-contour zirconia abutments tested.

An Energy-Based Method for Uni-Axial Fatigue Life Calculation

An energy based fatigue life prediction framework has been developed for calculation of remaining fatigue life of in-service gas turbine materials. The purpose of the life prediction framework is to account for the material aging effect on fatigue strength of gas turbine engines structural components which are usually designed for infinite life. Previous studies [1–7] indicate the total strain energy dissipated during a monotonic fracture process and a cyclic process is a material property that can be determined by measuring the area underneath the monotonic true stress-strain curve and the sum of the area within each hysteresis loop in the cyclic process, respectively. The energy-based fatigue life prediction framework consists of the following entities: (1) development of a testing procedure to achieve plastic energy dissipation per life cycle and (2) incorporation of an energy-based fatigue life calculation scheme to determine the remaining fatigue life of in-service gas turbine materials. The accuracy of the remaining fatigue life prediction method was verified by comparison between model approximation and experimental results of Aluminum 6061-T6 (Al 6061-T6). The comparison shows promising agreement, thus validating the capability of the framework to produce accurate fatigue life prediction.Copyright

Three-Dimensional Displacement of Nine Different Abutments for an Implant with an Internal Hexagon Platform

PURPOSE Clinicians need to know whether there are any differences among the many abutment options available for restoring a particular implant. This study aims to compare nine abutments for one implant system for positional changes between hand tightening and torqueing. MATERIALS AND METHODS Nine Tapered Screw-Vent (TSV) implants were placed into a resin block. Five specimens of nine different abutments (n = 45) were tried in one of the nine implants. Initially, the abutments were torqued to 20 Ncm to represent hand tightening. Abutments were tightened to 30 Ncm using a torque driver as recommended by the manufacturer for final seating. Images were recorded in 12-second intervals for approximately 10 minutes after the torque was applied. The spatial relationship of the abutments to the resin block was determined using three-dimensional digital image correlation. Commercial image correlation software was used to analyze the displacements. Mean displacements for the nine different abutments were calculated in all three dimensions and for overall displacement in space. A t test with a step-down Bonferroni correction was used for a pairwise comparison of each abutments mean displacements to the other abutments to determine statistical differences (α = .05). RESULTS The Atlantis titanium, Inclusive titanium, and Legacy zirconia abutments showed mean displacements that were statistically significantly higher than other abutments in the horizontal direction. The overall three-dimensional displacement of the Atlantis titanium abutment after an applied 30-Ncm torque was significantly higher than that of six of the other eight abutments (P < .0144). CONCLUSION Within the limitations of this in vitro study, the Zimmer PSA demonstrated less displacement between hand tightening and torqueing than the Atlantis titanium or Inclusive titanium abutments when used to restore a TSV implant.

Strain Measurement at Temperatures Up to 800°C Utilizing Digital Image Correlation

An experimental technique is introduced to measure full field strains using three dimensional digital image correlation at temperatures up to 800°C. Challenges include: thermal air gradients, speckle pattern adhesion, image distortion due to viewing window deformation, camera calibration, and infrared light pollution of the camera sensor. Elements of the test setup are designed to address all of these challenges. The technique is used to measure full-field strains on Ti-6Al-4V specimens as they are loaded to failure in tension. The technique provides substantially more data than traditional elevated temperature strain measurement methods.

Characterization of a Ferritic Stainless Sheet Steel in Simple Shear and Uniaxial Tension at Different Strain Rates

In this study the mechanical properties of ferritic stainless steel EN 1.4521 (AISI 444) were characterized in uniaxial tension and simple shear. The specimen geometries were designed so that tests could be carried out both with a conventional uniaxial materials testing machine and at high strain rates with the Tensile Hopkinson Split Bar method. During the tests, specimen surface deformation was measured using a three dimensional digital image correlation technique based on a two-camera stereovision setup. This technique allowed direct measurement of the specimen gauge section deformation during the test. Test results indicate that the selected approach is suitable for large strain plastic deformation characterization of ductile metals. The stress-strain data obtained from the simple shear tests shows a correlation with the tensile test results according to the von Mises effective stress-strain criterion. Since necking is absent in shear, test data can be obtained at considerably higher plastic strains than in tension. However, the final fracture occurs under a complex loading mode due to the distortion of the specimen geometry and multiaxial loading introduced by the simple shear arrangement. Test results also show that reliable material data can be obtained at high strain rates.Copyright

Research and EducationLoad to failure of different titanium abutments for an internal hexagon implant

STATEMENT OF PROBLEM Several aftermarket abutments are available for a commonly used internal hexagonal connection implant. However, their load to failure performance is unknown when compared with the manufacturers abutment. PURPOSE The purpose of this in vitro study was to conduct a load to failure comparison of 5 different titanium abutments (manufacturers and aftermarket) for cement-retained restorations used on an implant with an internal hexagon connection. MATERIAL AND METHODS Five implants (Tapered Screw-Vent, 4.1×11.5 mm; Zimmer Dental) were individually secured in a loading apparatus, and 3 abutment specimens of each of the 5 different titanium abutments (Atlantis, AstraTech TiDesign, Legacy Straight Contoured, Inclusive Custom, and Zimmer PSA) (n=15 total) were loaded at a 30-degree angle until fracture of the implant abutment complex. Data for load to fracture were compared with analysis of variance and a Tukey-Kramer post hoc test (α=.05). RESULTS Significant differences were noted between the fracture loads of some abutment pairs; Atlantis-AstraTech TiDesign, Atlantis-Legacy Straight Contoured, AstraTech TiDesign-Legacy Straight Contoured, Inclusive Custom-AstraTech TiDesign, and Inclusive Custom-Legacy Straight Contoured (P<.05). The highest overall resistance to fracture was achieved by the Legacy Straight Contoured Abutment, which was significantly greater than all other aftermarket abutments (P<.05). Tested abutments fractured at an average of 649.17 N. The Zimmer PSA abutment was the only abutment that showed no fracture of any of the components before implant failure. CONCLUSION When comparing manufacturers versus aftermarket brands, the manufacturers abutment (Zimmer PSA) was the only abutment without fracture of any of the components. Aftermarket brands experienced screw fractures, which could result in further clinical prosthetic complications. The clinical implications of these findings need further investigation.

Displacement of Implant Abutments Following Initial and Repeated Torqueing.

PURPOSE To measure and compare the three-dimensional (3D) position of nine different abutments manufactured by different manufacturers after repeated torqueing on an internal-hexagon implant. MATERIALS AND METHODS Nine tapered implants were placed into an acrylic resin block. Five specimens each of nine different abutments (n = 45) were placed into one of nine implants. The abutments were handtightened and then torqued to the manufacturer-recommended torque of 30 Ncm. After 10 minutes, 30 Ncm of torque was reapplied. Another 10 minutes elapsed before testing was completed. Images were recorded in 12-second intervals. The spatial relationship of the abutments to the resin block was determined using 3D digital image correlation. Commercial image correlation software was used to analyze the displacements. Mean displacements for the abutments were calculated in three dimensions and overall for both torque applications. Statistical comparisons were done with a t test and a step-down Bonferroni correction. RESULTS The overall 3D displacement of the Atlantis Titanium abutment after the second applied torque was significantly greater than that of two of the eight other abutments. Displacement in all three dimensions for the Atlantis Titanium abutment changed direction between the first and second torque applications. All abutments moved further in the same direction except for the Atlantis Titanium abutment, which moved back toward its original hand-tightened position horizontally after the second torque application. CONCLUSION Re-torqueing of abutments after a 10-minute interval leads to minor displacement of varying degrees between the abutment and a tapered implant. A potential effect of embedment relaxation and/or manufacturing errors should be taken into consideration when selecting an abutment for a cement-retained crown on a tapered implant. Accordingly, clinicians may benefit from adjusting cement-retained implant crowns after re-torqueing the abutments to prevent potential occlusal and interproximal contact problems.

Three-Dimensional Image Correlation Analyses for Strains Generated by Cement and Screw-Retained Implant Prostheses

PURPOSE This study aimed to measure and compare strains generated by splinted implant crowns retained by cement or screws for two implants with applied load. MATERIALS AND METHODS A stereolithic resin model was printed using computed tomography data from a patient missing all mandibular molar teeth. Two 4 × 6 mm implants were consecutively placed in the left side. One set of splinted cement and screw-retained crowns were made to fit the two implants. Image correlation technique was used for full-field measurement of strains using an image correlation software and two synchronized high-resolution digital cameras. A random dot pattern was applied to the model surface. Cameras recorded changes in random dot patterns as prostheses were loaded up to 400 N in vertical and oblique directions using a universal testing machine. Testing was repeated three times for cement and screw-retained prostheses. An image correlation algorithm used the dot pattern to define correlation areas or virtual strain gauge boxes. Three-dimensional coordinates of gauge box centers were determined for each recorded photograph and used to calculate strains. Strain distribution data were compared for major, minor, and von Mises strains for each loading condition, as well as peak and average strains for the field of view using an analysis of variance (α = 0.05). RESULTS Patterns and magnitudes of strain for cement- and screw-retained splinted crowns were similar under vertical loading. Neither peak nor mean strains were significantly different for the two retention methods. For oblique loading, peak strains were lower for the screw-retained crowns; however, there were no statistically significant differences between the two groups when strains were averaged throughout the entire field of view. CONCLUSIONS Cement retention did not improve the magnitude of transferred strains for splinted implant crowns using either loading condition.

Tensile Behavior of Kevlar 49 Woven Fabrics over a Wide Range of Strain Rates

Kevlar and other ballistic fabrics are frequently used in dynamic loading applications such as personnel protective equipment (armor) and soft engine containment systems for fan blade out events in aircraft engines. Numerical simulations of these events require constitutive models that are based on mechanical experiments that approximate the load conditions present in the application. Kevlar 49 fabric is tested in tension at strain rates ranging from 10-4 to 1500 s-1. A servohydraulic load frame is used for low strain rate experiments up to 1 s-1. Experiments at strain rates above 400 s-1 are conducted on a direct-tension split Hopkinson bar apparatus. 3D digital image correlation is used to measure specimen surface displacements and strains.

Characterization of 2024-T351 Aluminum for Dynamic Loading Applications

deformation and failure of 2024-T351 plate stock is studied under a wide range of loading conditions. Uniaxial tension and compression, and pure shear tests have been conducted over a wide range of strain rates and temperatures. The results show no significant strain rate effect on plastic deformation up to strain rates of about 5000 s -1 . Specimen surface finish has a significant effect on strain to failure in tension tests. Specimens with rough surface finish failed at smaller strains than specimens with a smooth finish. Equivalent stress strain curves generated from tension, compression and shear tests do not coincide, which indicate that plasticity models (time independent and time dependent) based on J-2 flow theory will not be suitable for modeling the plastic deformation of the material. Results from testing specimens, machined in different orientations relative to the plate rolling direction, in tension and compression tests show that the plates have anisotropic properties with regard to plasticity and failure. The anisotropic nature of the plate is most apparent in the compression tests where initially round cylindrical specimens are deformed into an elliptical cross section. These data can be used for developing plasticity models that are used for simulations of impact events.