PubMed · 284462
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M Scholzen. 1978. [Working with cements].. https://pubmed.ncbi.nlm.nih.gov/284462/
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This study measured the force required to displace four different endodontic posts (an experimental, Para-Post, Flexi-Post, and V Lock) when tensile, torsion, or compressive forces were applied. Extracted mandibular premolars were decoronated at the cementoenamel junction, the roots were divided into groups of similar size, and the pulpal tissue was removed. The canals were enlarged, cleaned, and filled with gutta percha. Post preparations were made, and the posts were cut and cemented into the post spaces with resin cement. The roots were notched with a separating disc and lowered into a metal tube filled with acrylic resin. Two Minim pins were placed into the coronal dentin paralleling the post. Composite resin cores were made around the coronal 4 mm of the posts and the two pins for 10 specimens from each group. The specimens were placed into a standardized fixture and a load applied until failure. The tensile load required to pull the experimental post and resin was significantly less than the load required to remove the threaded posts. Flexi-Posts provided the greatest resistance to torsion and tensile loading. The compressive load required to fracture the core over the V-Lock post was significantly greater than the other post systems.
Aqueous solutions of poly(vinylphosphonic acid) have been found to form polyelectrolyte cements with a wide range of metal oxides. Poly(vinylphosphonic acid), PVPA, has a structure similar to that of poly(acrylic acid), PAA, but contains pendant phosphonic acid,--P(O)(OH)2, groups in place of the carboxylic acid,--COOH, groups of the zinc polycarboxylate, and glass polyalkenoate cements. It is a stronger acid than PAA, with a greatly increased reactivity toward metal oxides. The physical and mechanical properties of a number of metal oxide PVPA cements were studied and compared with those of zinc polycarboxylate cements. The faster acting of the metal oxide PVPA cement seems to produce a cement that is less susceptible to early hydrolysis.
A ball-on-three-ball bi-axial flexure test was used to evaluate the flexure strengths of five kinds of dental cements (zinc phosphate, polycarboxylate, glass ionomer, silicate, and zinc oxide-eugenol cements). The bi-axial flexure strengths of zinc phosphate cement discs of variable dimensions were also measured to determine the size effects of test specimens. Finite element stress analyses were performed on disc specimens which were subjected to both a concentrated load and a uniformly distributed load. The observed values were compared with the theoretical value calculated by the finite element method. A ball-on-three-ball bi-axial flexure test could not be used for thicker specimens, since the fracture origin of these specimens is more likely to occur on the loaded side.