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Biomedical subjects

H Lüthy

Publications and source records attributed to H Lüthy.

At least 37 records · Page 2Linked to original sources
PubMed1990

Factors influencing metal-resin tensile bond strength to filled composites.

This study evaluated the effect of metal surface conditioning, application of a silicon layer, water storage, and resin filling on tensile bond strength of a metal-resin system using three experimental composites (un-, micro-, and macrofilled) having the same self-curing resin composed of Bis-GMA and TEGDMA (2:1 wt%). Test specimens were prepared by bonding the resin between pairs of Ni-Cr-Be alloy cast disks (diameter, 8 mm) previously subjected to heat treatments simulating porcelain firing procedures. A specially constructed apparatus facilitated the absolutely parallel alignment and orientation of the disk faces to each other, maintaining a constant resin thickness of 100 microns. Before being bonded, the sand-blasted metal surfaces were either electrolytically etched and/or silicoated. Prior to being tested, assemblies were stored in water at 37 degrees C for one and 30 days. Thereafter, the specimens were processed in a universal testing machine at a cross-head speed of 2 mm/min until failure. Bond strengths ranged from 4.2 to 20.5 MPa. Data were analyzed by ANOVA with a factorial design (conf. level = 99%). The results showed that: (i) bond strength was increased when the metal was silicoated, (ii) the combination of sandblasting/silicoating produced the best values, and (iii) the 30-day water storage combined with silicoating enhanced the strength of the bond. The resin filling had no significant effect, indicating that neither its presence nor type affects bonding strengths to metal.

Analysis of Variance↗
PubMed1990

[Surface and circumference determination in resin-bonded retainer elements: a possibility for long-term prognosis?].

An evaluation of about 300 abutment teeth of resin-bonded bridges (Rochette, electrochemically etched) and resin-bonded extracoronal attachments was performed to determine the surface area and the length of the circumference of the retainers. By using a combined indirect (preparation of the specimen) and direct (automatic image analysis) method for the determination of both parameters a mean value of 50 mm2 for the surface area and 30 mm for the circumference, respectively, was evaluated. In addition, two indices (loading-index (BI): sigma surface area/width of pontic tooth; moisture penetration-index (FPI): sigma surface area/sigma circumferences) as predictors for the longevity of resin-bonded reconstructions were calculated. The loading-index was a good predictor for successful reconstructions: the clinical success was the better, the bigger the retention area, and the smaller the circumference of the retainer and the smaller the pontic tooth.

Dental Abutments↗
PubMed1989

[Tensile loading behavior of different conditioned and bonded metal test samples].

The purpose of this research was to analyze simultaneously the effect of 4 factors (metal conditioning, bonding agent, metal silicoating and water storage) on the tensile behavior of a Bis-GMA resin (microfilled) bonded Ni-Cr-Be alloy by analysis of variance with a multifactorial design. The results showed that metal surface conditioning and the presence of bonding agent had no effect. In contrast, water storage of 33 days or silicoating influenced significantly and positively the tensile bond strength. In addition, 2 significant factor-interactions were detected: a) between silicoating and water storage and b) between metal surface conditioning (sandblasting/etching) and silicoating. Metal sandblasting followed by silicoating reacted more favorably than the combination etching/silicoating. In all cases the mechanochemical adhesion (silicoating technique) resulted in a composite bond strength that was far superior to that of conventional, pure mechanical bonding.

Acid Etching, Dental↗
PubMed1986

Influence of heat treatment on the surface texture of an etched cast nickel-chromium base alloy: an evaluation by profilometric records.

Profilometric measurements were performed to test the electrochemically etched surface roughness of a Ni-Cr-Be alloy in the as-cast state and after porcelain firing simulation. A Student's t test at 5% risk leads to the conclusion that a heat-treated surface is significantly rougher than an as-cast surface after electrolytic etching. The exact cause of the increased roughness and how it improves metal-to-resin bonding must be evaluated by further research.

Acid Etching, Dental↗
PubMed1977

[Reproducibility and accuracy of an optical ssd pointer (author's transl)].

The reproducibility and accuracy of an optical source-surface distance measuring device was systematically examined. The standard deviation of twenty equal distance settings was +/-0,5%. The error in dose-rate caused by one single adjustment did not exceed +/-2%. The position of the effective source-center is defined by a special inverse square plot. A periodical check is recommended.

Mathematics↗
PubMed1976

[Properties of Masonite as phantom material].

The radiophysical properties of the material "Masonit" are examined by experimental methods. Indications are given as to atomic composition, density, effective atomic number, concentration of electrons, and linear attenuation coefficient. A comparison with water shows that "Masonit" is a suitable phantom material especially for the purposes of radiotherapy.

Health Physics↗
PubMed1975

[Dosage measurement of fast electrons using modified Fricke's solution].

A combination of two different modifications indicated in the literature about the ferrosulfate dosimetry has been given. This permits a dose measurement which shows compared to the usual dosimetry of Fricke above all following advantages: dose specification related to water; displacement of the absorption maximum in the perceptible spectral sphere; increase of the sensibility and lower influence of pollutions. The molar coefficient of extinction of the modified solution has been determined from Co-60-gamma irradiation and is epsilonm = 1,46 - 10(4) L - Mol(-1) - cm(-1). The increase of extinction which has been measured with this method after the irradiation with 18 MeV electrons occurs linearly within the studied region to 1200 rd at least, the G-value is 15,5. The indicated method renders possible a relative simple calibration of the ionisation chambers which have been used in the practice.

Cobalt Radioisotopes↗