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Biomedical subjects

A M Weinstein

Publications and source records attributed to A M Weinstein.

89 records · Page 5Linked to original sources
PubMed1977

Fabrication and characterization of porous-rooted polymethylmethacrylate (PMMA) dental implants.

A comparative-agglomeration fabrication technique has been developed to produce polymethylmethacrylate dental implants having a porous coating on the root portion. This process allows control of pore structure enabling ingrowth of either bone or fibrous tissue. The relationships between mechanical properties and pore microstructure have been determined for materials produced by this process. The mechanical properties of the porous coating can be estimated from these relationships.

Dental Implantation↗
PubMed1977

An evaluation of porous alumina ceramic dental implants.

The fabrication, characterization, and clinical results of porous rooted alumina dental implants in animals are presented. Failures of all implants occurred in less than six months and were attributed to the presence of microporosity on the crown and cervical portion of the implant which prevented the establishment of an effective biological seal between the oral cavity and the alveolus.

Aluminum↗
PubMed1976

Electrical stimulation of bone growth into porous A12O3.

Porous, cylindrical, high alumina, ceramic structures were fabricated for implantation in the superior third of canine femoral medullary canals. Implant durations of one, two, four, and eight weeks using three animals per time period were studied. A constant current (10 muA) power supply was used to attempt to stimulate bone growth into the porous ceramic structures. Osseous tissue in-growth was evaluated using a mechanical push-out test, microadiography, and histological thin sectioning. The interfacial shear strength and tissue micro-structure was studied as a function of implant residence site and implant residence site and implant residence time. The results indicate that initially the proximal implants have a higher interfacial shear strength, however, after eight weeks of implantation the distal implants have a shear strength about twice that of the proximal implants. This trend is observed for both the electrically stimulated and nonstimulated specimens. The 10 muA current level used in this investigation was found to have a small but significant effect on shear strength increasing it at implantation times of less than eight weeks.

Aluminum↗
PubMed1976

An evaluation of bone growth into porous high density polyethylene.

The purpose of this investigation was to study bone growth into porous polyethylene rods as a function of time and pore structure. Previous studies have indicated the biocompatibility of solid polyethylene materials which are currently being used clinically. Porous polyethylene rods were implanted in the femurs of mongrel dogs which are sacrificed four, eight, and 16 weeks postoperatively. The implants were then sectioned and examined histologically and microadiographically. Quantitative techniques were employed to determine the amount of bone ingrowth as a function of time and pore size. The pore structures of the materials were evaluated using optical microscopy and mercury intrusion porosimetry. The results of this investigation have demonstrated that porous polyethylene is capable of accepting bone growth into pores as small as 40 mum. The optimum rate of bone ingrowth was observed in pore sizes of approximately 100 to 135 mum, with no increase in the rate of bone ingrowth observed in samples possessing larger pore sizes. No adverse tissue response was found at implant times up to 16 weeks in pore sizes of 100 mum or larger.

Biocompatible Materials↗
PubMedDate not supplied

IRAP--a system for the retrieval and analysis of orthopaedic implant data.

An interactive computer system for the storage, retrieval and analysis of standardized clinical and material characterization data associated with orthopaedic implants is described. The system consists basically of four independent modules. The essence of the system centers on the cross-referencing capabilities which are virtually unlimited. The system has been designed for use by non-computer trained personnel.

Humans↗
PubMedDate not supplied

Insights from mathematical modeling of renal tubular function.

Mathematical models of proximal tubule have been developed which represent the important solute species within the constraints of known cytosolic concentrations, transport fluxes, and overall epithelial permeabilities. In general, model simulations have been used to assess the quantitative feasibility of what appear to be qualitatively plausible mechanisms, or alternatively, to identify incomplete rationalization of experimental observations. The examples considered include: (1) proximal water reabsorption, for which the lateral interspace is a locus for solute-solvent coupling; (2) ammonia secretion, for which the issue is prioritizing driving forces - transport on the Na+/H+ exchanger, on the Na,K-ATPase, or ammoniagenesis; (3) formate-stimulated NaCl reabsorption, for which simple addition of a luminal membrane chloride/formate exchanger fails to represent experimental observation, and (4) balancing luminal entry and peritubular exit, in which ATP-dependent peritubular K+ channels have been implicated, but appear unable to account for the bulk of proximal tubule cell volume homeostasis.

Ammonia↗
PubMedDate not supplied

Stress analysis of porous rooted dental implants.

A model based on a continuously bonded interface predicts high punching stresses at the apex of the implant and low stresses in the cortical plates. A model based on a continuously bonded interface predicts high stiffness and a resultant low implant displacement-load ratio. A model based on a tissue ingrowth-bonded interface predicts uniform distribution of stresses around the implant through the cortical plates. A model based on a tissue ingrowth-bonded interface predicts an implant displacement-load ratio close to the ratio measured with actual implant specimens.

Alveolar Process↗
PubMedDate not supplied

Single-needle venous dialysis: a comparison of three systems.

Single-needle dialysis with femoral vein access was performed on three patient groups using a pressure/time (Vital-Assist) device, a time/time device (Gambro, AK10), and a pressure/pressure device (Cobe Double Blood Pump). Each patient was dialyzed using the same parallel plate dialyzer (PPD 1.3). For each treatment, recirculation was calculated and the clearance of urea and creatinine was determined, both from dialysate content and A-V concentration differences. Recirculation was high (38%) with the Vital-Assist but under 10% with both AK10 and Double Blood Pump. The relatively higher blood flow of the Vital-Assist (180 ml/min) and lower blood flow of the AK10 (100 ml/min) resulted in comparable clearances of urea (80 ml/min) and creatinine (60 ml/min) for these two systems. The Double Blood Pump, with a blood flow of 140 ml/min achieved urea and creatinine clearances of 110 and 80 ml/min. The clearances actually measured were in good agreement with those predicted from theoretical considerations of recirculation and blood flow in a countercurrent dialysis system.

Blood Flow Velocity↗
PubMedDate not supplied

An evaluation of skeletal attachment to LTI pyrolytic carbon, porous titanium, and carbon-coated porous titanium implants.

Porous titanium, carbon-coated porous titanium, and low-temperature isotropic (LTI) pyrolytic carbon transcortical implants were placed in the femora of mongrel dogs. Mechanical and histologic analyses were performed in specimens that remained in situ for six months. Qualitative histologic results indicated that the bone formed a direct appositional interface with as-deposited LTI carbon. The bone tissue response to the two systems with porous coatings was similar. Both systems showed little fibrous tissue interposition and a high degree of mineralized bone ingrowth. The ingrown bone was well organized. However, there was some evidence that the ingrown bone mineral differed significantly from the bulk bone mineral. The only difference between carbon-coated and uncoated porous systems was a significant increase in the percentage of bone ingrowth, with carbon-coated specimens having a 4% increase in bone volume. The strength of appositional attachment to LTI carbon was shown to be at least one order of magnitude weaker than bone ingrowth attachment to the porous systems. The interface shear stiffness of the two porous systems was equivalent; however, the attachment shear strength of bone growth into carbon-coated porous titanium was significantly increased compared with that of bone growth into the uncoated porous titanium. Correlation of the percentage of bone ingrowth and pushout strength was also found to be statistically significant, suggesting that the presence of the carbon coating enhanced bone ingrowth, which resulted in significantly increased shear strengths.

Animals↗
PubMedDate not supplied

The effect of high pressure insertion and antibiotic inclusions upon the mechanical properties of polymethylmethacrylate.

The properties of self-curing polymethylmethacrylate as affected by the admixing of an antibiotic to the powder-liquid mixture and as affected by insertion technique demonstrated that the antibiotic agent may leach from the surface of the acrylic, but not necessarily from the interior. The compressive and tensile strength, determined on two different commercial formulations, suggests that the antibiotic additive is not detrimental to the mechanical properties. A high pressure insertion technique produces a significant improvement in the mechanical properties of the self-curing acrylic material.

Acrylic Resins↗