Biomedical subjects

H W Anselm Wiskott

Publications and source records attributed to H W Anselm Wiskott.

7 recordsLinked to original sources

PubMed2006

Oscillatory shear loading of bovine periodontal ligament--a methodological study.

This study examined the stress response of bovine periodontal ligament (PDL) under sinusoidal straining. The principle of the test consisted in subjecting transverse tooth, PDL and bone sections of known geometries to controlled oscillatory force application. The samples were secured to the actuator by support plates fabricated using a laser sintering technique to fit their contours to the tooth and the alveolar bone. The actuator was attached to the root slices located in the specimen's center. Hence the machine was able to push or pull the root relative to its surrounding alveolar bone. After determining an optimal distraction amplitude, the samples were cyclically loaded first in ramps and then in sinusoidal oscillations at frequencies ranging from 0.2 to 5 Hz. In the present study the following observations were made: (1) Imaging and the laser sintering technique can be used successfully to fabricate custom-made support plates for cross-sectional root-PDL-bone sections using a laser sintering technique, (2) the load-response curves were symmetric in the apical and the coronal directions, (3) both the stress response versus phase angle and the stress response versus. strain curves tended to "straighten" with increasing frequency, and (4) the phase lag between applied strain and resulting stress was small and did not differ in the intrusive and the extrusive directions. As no mechanical or time-dependent anisotropy was demonstrable in the intrusive and extrusive directions, such results may considerably simplify the development of constitutive laws for the PDL.

Animals↗

PubMed2005

In vitro time-dependent response of periodontal ligament to mechanical loading.

This study examined the time-dependent response of bovine periodontal ligament (PDL). Applying linear viscoelastic theory, the objective was 1) to examine the linearity of the PDL's response in terms of its scaling and superposition property and 2) to generate the phase lag-vs.-frequency spectrum graph. PDL specimens were tested under three separate straining conditions: 1) tension ramp tests conducted at different strain rates, 2) pulling step-straining to 0.3 in discrete tests and to 0.3 and 0.6 in one continuous run, and 3) tension-compression sinusoidal oscillations. To this effect, bar-shaped specimens of bovine roots that comprised portions of dentin, PDL tissue, and alveolar bone were produced and strained in a microtensile machine. The experimental data demonstrated that neither the scaling nor the superposition properties were verified and that the viscoelastic response of the PDL was nonlinear. The PDL's elastic response was essentially stiffening, and its viscous component was pseudoplastic. The tangent of the PDL's strain-stress phase lag was in the 0-0.1 range in the tensile direction and in the 0.35-0.45 range in the compressive direction. In line with other biological tissues, the phase lag was largely independent of frequency. By use of the data generated, a mathematical model is outlined that reproduces both the elastic stiffening and viscous thinning of the PDL's response.

Animals↗

PubMed2004

Reversible and irreversible peri-implant lesions: report and etiopathogenic analysis of 7 cases.

The purpose of this report is to review the aberrations in the integration process of cylindrical endosseous implants, though such aberrations are seldom observed. These issues are treated according to the following scheme: (1) infectious lesions, which consist of peri-implantitis, intraosseous infectious foci, and septic voids; (2) transitory lesions; (3) lesions related to occlusal overload; and (4) healing defects. In this report, we illustrate these categories with patient histories and discuss the clinical findings and etiopathogenies.

Adult↗

PubMed2002

In vivo wear of three types of veneering materials using implant-supported restorations: a method evaluation.

In a previous study, we determined the precision and the positional duplicability of a system that used implant connectors to transfer restorations between the oral cavity and the measuring device. The objectives of the present study were to determine whether this testing procedure was suitable for clinical use, and to apply the procedure to the longitudinal assessment of the wear of three types of veneering materials. Ten patients received a total of 12 restorations. The restorations were made either of ceramic (positive control), poly(methylmethacrylate) resin (negative control) or of composite resin. The restorations were profiled at baseline and at 3, 6, 9, 12, 18 and 24 months. For profiling, the restorations were secured to the x-y table of the measuring device using the octagonal connector of the ITI implant system. Numerical analyzes were performed using a commercial array-oriented software package. The ceramic and the composite wore at roughly 12-14 microm yr(-1) (height) 10-12 microm3 microm2 yr(-1) (volume). The resin wore at c. 50 micorm yr(-1) (height) and c. 45 microm3 microm2 yr(-1) (volume). The error of the procedure was estimated at +/- 13%. It was concluded that the procedure was applicable for clinical studies, and that the composite did not differ from the ceramic as to its wear rate.

Algorithms↗

PubMed2001

Mechanical and structural characteristics of commercially pure grade 2 Ti welds and solder joints.

This study aimed at determining whether data previously gathered for a laser welds and IR brazings using a Au-Pd alloy were applicable to titanium joints. As to its resistance under fatigue loading, Au-Pd alloy had shown a poor response to pre-ceramic laser welding and post-ceramic brazing. The present study was designed to assess the mechanical resistance, the microstructure and the elemental diffusion of laser welded, electric arch welded and brazed joints using commercially pure titanium as substrate metal. Mechanical resistance was determined by determining the joints' ultimate tensile strength and their resistance to fatigue loading. Elemental diffusion to and from the joints was assessed using microprobe tracings. Optical micrographs of the joints were also obtained and evaluated. Under monotonic tensile stress, three groups emerged: (1) the GTAW and the native (i.e. as received) substrate, (2) the annealed substrate and the laser welds and (3) the brazed joints. Under fatigue stress, the order was: first the native and annealed substrate, second the brazings and laser welds, third the GTAW joints. No Au-filler brazing withstood the applied fatigue loading. The micrographs showed various patterns, an absence of HAZ cracking and several occurrences of Widmanstätten structures. Elemental diffusion to and from the Ti substrate was substantial in the Ti filler brazings and virtually nil in the Au-based brazings. Under fatigue stress application, the titanium-based brazings as well as the laser- and electric arc welds performed equally well if not better than a previously tested AuPd alloy. There was a definite increase in grain size with increased heat application. However, no feature of the microstructures observed or the elemental analysis could be correlated with the specimen's resistance to fatigue stress application.

Journal Article↗

PubMedDate not supplied

Resistance of ITI implant connectors to multivectorial fatigue load application.

PURPOSE: In an effort to provide patients with mechanically optimized implant connectors, this study was designed to assess the relative fatigue resistance of five types of connectors for the ITI implant system: (1) standard (screw-on) abutments torqued to 35, 70, and 140 Ncm; (2) metal Octa connectors torqued to 35 Ncm; (3) ceramic Octa connectors torqued to 15 and 35 Ncm; (4) cemented cast-on abutments; and (5) an experimental screw-retained composite core. MATERIALS AND METHODS: To duplicate the alternating and multivectorial intraoral loading patterns, the specimens were subjected to the rotating cantilever beam test. The implants, their connectors, and abutments were spun around their longitudinal axes while a perpendicular force was applied to the external end. The objective was to determine the force level at which 50% of the specimens would survive 106 load cycles. The mean force levels at 50% failure and their 95% confidence intervals were determined using staircase analysis. RESULTS: The fatigue resistances of the standard (screw-on) abutment, metal Octa connector, and ceramic Octa connector torqued to 35 Ncm were within a few percent of one another. The fatigue resistance of the cemented cast-on abutment was approximately half that of the screwed connectors, and the experimental screw-retained composite core's resistance was about 30%. Increasing the preload in the standard abutments and ceramic Octa connectors increased their fatigue resistance. CONCLUSION: Preloaded screwed components were mechanically superior to cemented cast-on abutments and screw-retained composite buildups. For the screw-on connectors, augmenting preload (ie, torque) augmented the resistance to fatigue loading.

Cementation↗

PubMedDate not supplied

Fixed prosthodontics centric relation registration technique using resin copings.

The registration of an accurate centric relation is one of the most critical steps in a prosthodontic rehabilitation, yet it sometimes is an uncertain procedure. A technique using resin copings, each supporting an occlusal contact, is presented. By careful, selective addition of resin, the centric relation recording can be controlled. The technique requires a pattern of abutments to provide stability, and is, therefore, primarily applicable to fixed prosthodontics. Nonetheless, it is versatile enough to accommodate a variety of clinical situations.

Dental Occlusion, Centric↗