摘要:

AbstractAs part of the detailed study of the curing of a range of dental elastomeric impression materials, their chemistry was investigated. This information, the dependence of the stress relaxation modulus of the set material on the catalyst/base ratios, and the level of diluent were used to elucidate the network structure. Such information is required before the rheological behavior during cure can be understood. The clinical significance of the recommended catalyst/base ratio is discussed.

ISSN:0021-9304    

DOI:10.1002/jbm.820160402

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractAs part of a detailed study of the curing of a range of dental elastomeric impression materials, a cone and plate rheometer was used to measure the variation in viscosity due to chain growth. The dependence of this behavior on the catalyst/base ratio, retarding and accelerating agents, and alternative initiators was studied and rationalized in terms of the polymerization chemistry investigated previously. Limited success was achieved with the quantitative interpretation of this data in terms of the polymerization kinetics. Of clinical relevance, only the viscosity behavior of the imine‐terminated polyether and one of the thiol‐terminated polysulfides approached that of an ideal impression mater

ISSN:0021-9304    

DOI:10.1002/jbm.820160403

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractAs part of a detailed study of the curing of a range of dental elastomeric impression materials, the 10‐s stress relaxation modulus was measured as a function of the curing time. The influence of the catalyst/base ratio was also investigated and compared with the pregel viscosity previously studied. Using the theory of network formation and an understanding of the chemistry of these materials, the modulus data were interpreted in terms of the polymerization kinetics. The addition silicones exhibited the most abrupt transition between the gel and final set stage, which is close the ideal response. The clinical significant of the results is discusse

ISSN:0021-9304    

DOI:10.1002/jbm.820160404

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe immunoperoxidase technique was applied to observe the electron microscopic presence of human plasma protein on a polymer surface. Two types of polymer material, i.e., Dacron and a newly synthesized heparinized hydrophilic polymer (H‐RSD, Toray Industries, Inc.), showed different reactions to human plasma proteins. The hydrophobic Dacron showed a decreased affinity for plasma albumin, but a greater affinity for fibrinogen, α1‐lipo‐protein, and β‐lipoprotein when compared to H‐RSD. The thrombo‐resistant H‐RSD showed a relatively strong affinity for albumin, but in a spotty or focal manner. Most of the H‐RSD surface did not adsorb albumin. Fibrinogen adsorption was observed in areas smaller than albumin adsorption. The adsorption of fibrinogen appeared to occur through certain material. The α‐lipoprotein and β‐lipoprotein were not adsorbed on the H‐RSD. The immunoperoxidase method is a sensitive and useful technique in studying the interactions between plasma proteins and the sur

ISSN:0021-9304    

DOI:10.1002/jbm.820160405

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractA three‐dimensional finite element stress analysis has been used to investigate the influence that variations in the infrastructural geometry of a blade‐type dental implant have on the stress distribution around LTI carbon and aluminum oxide implants. The finite element model was constructed based upon an analysis of serial sections of a retrieved implant specimen. In addition to the implant, the finite element model contained a three‐unit fixed bridge connected to a natural molar with periodontal membrane. The removal of the bridge allowed for the study of freestanding implants and molar. Variations in the implant blade geometry were found to produce significant changes in the stress distributions around bridged and freestanding aluminum oxide implants. Very little effect, however, was observed around the LTI carbon implants. A comparison of the stresses around the freestanding molar and the stresses around the bridged and freestanding implants was made to determine the implant dessign that came closest to reproducing the stress state around the modeled molar. The LTI carbon system that best achieved this stress state was found to be a full‐blade implant used in conjunction with a tooth as an abutment in a fixed bridge. The aluminum oxide system that best achieved this stress state was found to be of the post or short‐blade design used as a freestandin

ISSN:0021-9304    

DOI:10.1002/jbm.820160406

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractNumerous hypotheses exist to explain observed blood–materials interactions. It is the purpose of this article to test two popular hypotheses, namely, the minimum interfacial free energy hypothesis and the optimum polar/apolar ratio hypothesis. Methacrylate polymers and copolymers were characterized using the captive bubble underwater contact angle method; bulk water content was determined by gravimetric methods; streaming potential measurements were made; and surface roughness and possible particulate contamination were evaluated by reflected light microscopy.In vitroblood tests include whole blood clotting time measurements on polymer‐coated tubes; centrifugal force platelet adhesion on polymer‐coated coverslips; and a measure of the partial thromboplastin time, Russell's viper venom time (Stypven time), and the prothrombin time of native whole blood exposed to polymer‐coated microscope slides. Results suggest that platelet adhesion correlates in the opposite direction of whole blood clotting time and partial thromboplastin time, emphasizing the need for a multiparameter approach to blood–materials testing. Based on these tests the minimum interfacial free energy hypothesis is not supported. In fact, the data suggest the opposite to be true. It is apparent that platelet adhesion can be a misleading indicator of blood compatibility. Neither hypotheses can explain the apparent conflict between the platelet adhesion data and the coagulation

ISSN:0021-9304    

DOI:10.1002/jbm.820160407

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe extent ofin vivoinduced structural alterations were evaluated in 13 retrieved implants ranging from two weeks' to seven years' implantation. A statistically signifiant difference in crystallinity was seen between weight‐bearing and non‐weight‐bearing region, regions of the implants. Further, in the weight‐bearing region, crystallinity was higher in components implanted for two or more years than in those implanted for less than one‐half year. These results were consistent with our priorin vitrostudy on the effects of sterilization and aging. Taken together, the data indicate that UHMW polyethylene is not a static material but is continually undergoing dynamic chang

ISSN:0021-9304    

DOI:10.1002/jbm.820160408

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractA study has been made of the sarcogenicity of particles of cobalt–chromium–molybdenum alloy. The particles were implanted as a dry powder into a surgical incision into the dorsal paraspinal muscle of adult female rats and guinea pigs. Two preparations were used. In one, the particles had a size range of 100–250 μm. This preparation was implanted into 51 Wistar rats. In the other, the particles had a size range of 0.5–50 μm, 85% being in the range 0.5–5 μm. This preparation was implanted into 61 Wistar rats, 53 hooded rats, and 46 Dunkin Hartley guinea pigs. Sham operations were carried out on a control group of 50 Wistar rats. No malignant neoplasms developed at the test or control operation sites during the time periods for which the animals survived. This negative finding contrasts with that from a previous study by Health, Freeman and Swanson, who observed sarcomas in rats at sites of intramuscular injection of cobalt–chromium–molybdenum particles suspended in horse serum. Possible explanations for this difference in resul

ISSN:0021-9304    

DOI:10.1002/jbm.820160409

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThis article reports the morphological observations on the surface changes of poly(glycolic acid) sutures which have been exposed to various dosages of γ irradiation (0, 2.5, 5.0, 10, 20, and 40 Mrad) and duration of immersion (0, 7, 14, 28, 48, 60, and 90 days) in a physiological saline buffer. The most important gross morphological characteristics of PGA suture hydrolytic degradation is the formation of surface cracks on the filaments. The regularity of the surface cracks increased with an increase in the γ irradiation and the duration of hydrolysis. Surface cracks were not observed in irradiated sutures that had not been subjected to hydrolytic degradation. The arrangement of the surface cracks, their orientation on the filaments, and the direction of crack propagation provide very useful information for depicting the mechanism of hydrolytic degradation in this class of fibrous material. The microfibrillar model of fiber structure has been used as the basis for the proposed degradation mechanism of PGAin vitro. It is believed that hydrolysis occurs initially in the amorphous regions sandwiched between two crystalline zones, as tie‐chain segments, free chain ends, and chain folds in these regions degrade into fragments. As degradation proceeds, the size of the fragments reaches the stage at which they can be dissolved into the buffer medium. This dissolution removes the fragments from the amorphous regions, and surface cracks appea

ISSN:0021-9304    

DOI:10.1002/jbm.820160410

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractD(+) tartaric acid is incorporated into glass–ionomer cements to control the setting properties.13C NMR spectroscopy of the fluid cement pastes have shown that tartaric acid reacts more readily than the polyacid with the glass, and hence suppresses the premature gelation of the cement. As the cements set, the pH rises from ca. 1.25 to ca. 3 when tartaric acid is fully complexed. As the polyacid reacts the pH rises further to ca.

ISSN:0021-9304    

DOI:10.1002/jbm.820160411

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY