Compressive and Tensile Zones in the Cement Interface of Full Crowns: A Technical Note on the Concept of Resistance

PURPOSE: The objectives of the study were: 1) to map the stresses acting on the cement interface of crown and abutment analogs during loading; and 2) to provide a theoretical basis for the hypothesis that resistance to lateral dislodgment is a function of the distribution of compressive force vectors acting on the cement lute. MATERIALS AND METHODS: Three-dimensional finite element (FE) meshes of crown and abutment analogs were constructed and loaded in a direction perpendicular to the axes of symmetry of the abutments. Three parameters were investigated: taper (10 degrees and 20 degrees of convergence), abutment substrate (Ni-Cr alloy and dentin), and type of cement (zinc oxide eugenol, zinc phosphate, glass ionomer, and composite resin). The tensile and compressive components of the resulting force systems were plotted along two axes (z: parallel to the axis of symmetry of the crown/abutment complex; and y: perpendicular to z, i.e., parallel to the direction of loading). Von Mises stresses were also generated. RESULTS: First, it was shown that the restoration's axis of rotation was located inside the abutment cone and was perpendicular to and intersected the axis of symmetry of the crown/abutment complex. Second, stress distribution was dependent on the three parameters investigated. Varying taper led to shifts due mainly to alterations in specimen geometry, whereas the abutment substrate and the cement type had a bearing on the level of the axis of rotation. The smaller the modulus of elasticity of the abutment substrate or the cement lute, the farther apical the location of the axis of rotation. CONCLUSIONS: Conventional schemes for explaining crown dislodgment in which the restoration rotates around an axis located at the preparation margin should be reassessed. The results of the FE analysis are compatible with the hypothesis that resistance to lateral dislodgment is a function of the distribution of compressive force vectors acting on the cement interface.     

Bioequivalence of two film-coated tablets of imatinib mesylate 400 mg: A randomized,open-label,single-dose,fasting, two-period,two-sequence crossover comparison in healthy male South American volunteers

Background: Imatinib is a tyrosine kinase inhibitor that has been established as a highly effective therapy for chronic myelogenous leukemia and gastrointestinal stromal tumors. A new generic, once-daily 400-mg tablet of imatinib has been developed by a pharmaceutical company in Argentina, where the regulatory standard for marketing authorization of an imatinib generic is in vitro dissolution testing.Objective: The aim of this study was to assess the bioequivalence of a new generic film-coated test tablet formulation versus a film-coated reference tablet formulation of imatinib 400 mg. The local manufacturer seeks to validate the in vitro performance of this new formulation with a bioequivalence study.Methods: A randomized, open-label, single-dose, fasting, 2-period, 2-sequence crossover design with a 2-week washout period was used in this study. The study population consisted of healthy male South American (Uruguayan) volunteers, who were assigned in a 1:1 ratio to a randomized sequence (test-reference or reference-test). In each period, the test or reference formulation was administered after an overnight fast. During the 72-hour follow-up period, participants were monitored for vital signs and symptoms. Blood samples were collected at 15 time points, including baseline, until 72 hours. Physical examination and laboratory tests (blood, urine) were repeated 1 week after study completion. A noncompartmental model was used to determine the pharmacokinetic parameters of imatinib. The 90% CIs of the test/reference ratios for AUC_0-∞ and C_max were determined; the test and reference formulations were considered bioequivalent if the 90% CIs were between 0.80 and 1.25. Adverse events were assessed by a nurse who administered a questionnaire while the healthy volunteers were admitted in the unit.Results: The bioequivalence study was conducted in 30 Uruguayan male volunteers. Demographic characteristics (mean [SD]) included age, 27.8 (6.5) years; weight, 71.2 (9.8) kg; height, 1.71 (0.09) m; and body mass index, 24.3 (3.0) kg/m2. The mean (SD) of AUC_0-∞ was 38,179 (15,504) ng/mL · h^?1 for the test formulation and 40,554 (17,027) ng/mL · h^?1 for the reference formulation. The mean of Cmax for the test formulation was 2472 (933) ng/mL, and the mean Tmax was 3.28 (0.93) hours. The mean of Cmax for the reference formulation was 2566 (963) ng/mL, and the mean T_max was 3.63 (1.20) hours. The point estimates (90% CIs) for the test/reference ratios of the log-transformed AUC- and C_max mean values were 0.95 (0.87–1.03) and 0.97 (0.89–1.05), respectively, which met the regulatory criteria for bioequiv-alence. Thirty-four mild to moderate adverse events were reported (13 with the test formulation and 21 with the reference formulation), and no serious or unexpected adverse events were observed during the study. The adverse events included 16 cases of headache, 13 cases of nausea, 4 cases of vomiting, and 1 episode of diarrhea.Conclusions: The results of this study suggest that the test formulation of imatinib met the regulatory criteria for bioequivalence to the reference formulation in these healthy fasting male volunteers. Both formulations were generally well tolerated and appeared to have a similar adverse-event profile.     

Creation of a Forensic Pathology Biobank in Switzerland: which issues and research opportunities?

A biobank is a collection of biological material associated with health database. The field of biobanking has significantly developed over the past 30 years. Research based on biobank material gives access to data of a large number of people and can often significantly accelerate the understanding of disease and improve the quality of care. In the University Center of Legal Medicine Lausanne-Geneva, samples collected during autopsies are used for forensic investigations. The legal and ethical framework to use these samples for research is often complex and confused, which is unfortunate given the potential of these biospecimens. Indeed, forensic samples are valuable for research because they originate in part from young (including pediatrics cases) and healthy people who are poorly represented in worldwide institutional biobanks. In this context at the beginning of the year 2019, the Forensic Pathology Biobank was created. Creation of a forensic pathology biobank is the best way to standardize local conservation practices and improve personal data management, thus providing a very valuable biological material for scientific projects. Its development gives rise to many questions about technical standards, ethical and legal issues but also many research opportunities.

     

Effect of different surface treatments on the hydrothermal degradation of a 3Y-TZP ceramic for dental implants

Objectives

Implant surface modifications are intended to enhance bone integration. The objective of this study was to assess the effect of different surface treatments on the resistance to hydrothermal degradation, hardness and elastic modulus of a 3Y-TZP ceramic used for dental implants.

Methods

Samples grouped according to their surface morphologies (AS, as-sintered; C, coated; P, dry-polished; R, roughened; PA, polished and annealed; RA, roughened and annealed) were subjected to accelerated hydrothermal degradation (LTD) by exposure to water steam (134 °C, 2 bars) for 100 h. The t–m phase transformation was quantified by grazing incidence X-ray diffraction (GIXDR) and by combined focused ion beam and scanning electron microscopy (FIB-SEM). Elastic modulus and hardness before- and after prolonged aging (100 h) were assessed by nanoindentation.

Results

AS and C specimens presented a better resistance to hydrothermal degradation than P and R samples. After prolonged aging, the depth of the monoclinic transformed layer ranged from 11 μm to 14 μm. Hydrothermal degradation led to a significant decrease of elastic modulus and hardness.

Significance

Surface treatments affected the resistance to hydrothermal degradation of the 3Y-TZP ceramic. Dry mechanical surface modifications should be avoided since a high t–m transformation rate associated to the initial monoclinic content was observed. Annealing was useful to reverse the initial t–m transformation, but did not improve the resistance to hydrothermal degradation.     

Über expositionelle und dispositionelle Verhältnisse bei verschiedenen Formen der Kindertuberkulose

Ohne ZusammenfassungMit 1 Abbildung im Text.     

Fatigue strength of a Au-Pd alloy/585 solder combination.

The S-N diagram (applied stress vs. cycles to failure) for the gold-palladium alloy/585 solder combination was generated. Au-Pd alloy specimens were cast, prepared for soldering, and joined with 585 solder. After milling and polishing of the joint, testing was carried out in a specially designed machine. This device loaded the cantilevered test specimen in a unidirectional mode at a rate of 70 strokes per minute. The applied tensile stress ranged between 294.2 and 686.5 MPa. Three specimens were cycled for each stress level until fracture occurred. The number of fatigue cycles to failure ranged from one cycle (stress level, 686.5 MPa) to 4.83 x 10(6) cycles (stress level, 294.2 MPa). On a logarithmic scale, the relationship between the applied stress and the number of cycles to failure was linear. Under the present (ideal) experimental conditions, the Au-Pd/585 solder combination behaved favorably on the high-cycle end of the diagram. However, no definite endurance limit could be detected within the stress range examined.