Flow and Fracture of Dental Alloys Determined by a Microbend Tester
The microstructure of an alloy is the fundamental variable on which the mechanical properties of an alloy depend. For testing the mechanical properties, however, common tests, such as tensile strength or hardness, are generally used. This may be due to the fact that the microstructure study is more complicated and time-consuming. The common method of microstructure study is to perform a series of tensile tests and then obtain the microstructure of the specimens after the tests are completed so as to correlate the structure with the performance data. The actual contribution of each observable microstructure to flow and fracture is rather difficult to detect. When the structure is examined after the fracture has taken place, some of the evidence is lost that would have been available if continuous observation of the structure had been possible. In 1955 Flinn and Trojan' developed an apparatus by means of which the microstructure of an alloy under stress can be studied. The stress can be increased while the microstructure is under observation. Thus any changes that may take place can be detected in any of the phases. When an alloy with a complicated microstructure is studied, the microbend test shows its main advantage, since it is rather difficult to predict how the different phases of a complicated structure will behave under different stresses. With this test the effect of such stress on various phases may be continuously watched under the microscope. The purpose of this study was to observe the behavior of different phases of cobalt-base and gold alloys used in dentistry for partial denture framework when they were subjected to bending stresses.
Brittle Fracture ofDental Amalgam
Thebrittleness ofdental amalgam limits its use tosites inwhichtensile stresses can be keptataminimum. Ifthecauseforthebrittleness couldbeascertained, thenan approach tocorrect thisproblem couldbe devised. Physical properties ofmetalsare ultimately manifested in,andcan beexplained by,their microstructure. Through thework ofseveral researchers,1-3 means ofidentifyingthephases presentinthemicrostructure havebeendeveloped. Inthisstudy, the etching solutions developed bySchmitt1 and Wing2 were employed. Thephases present inamalgam, as shownbythesechemical etches, areidentified as 'y, yri,and72. The y phasecomprises mostoftheoriginal particle whichremains after thereaction ofHg withtheamalgam alloy. The-ypphase isthe reaction product ofmercurywithsilver presentintheoriginal particle andisidentified asAg2Hg3. Thisphase forms a matrix about they phase. Interspersed inthismatrix also aresmall islands ofthe 72 phase, which isformed byreaction ofmercury withthe tincontained intheoriginal particle. Copper andzinc arealso present, butneither their naturenor their location hasbeenestablished. Therefore, themicrostructure of amalgam isknownina general way only. Observing themicrostructure ofan alloy understress, withtheFlinnstrain-viewer,4
Intrapancreatic Accessory Spleen: A Differential Diagnosis to Neuroendocrine Tumors of the Pancreas on Ga-68-DOTATOC PET/CT
A Seventy-three-year-old Caucasian woman underwent a contrast-enhanced computed tomography to clarify a deep venous thrombosis because of a swollen left leg. The CT revealed a contrast-enhancing 18x20 mm sized lesion in the pancreatic tail. It was suspected to be a neuroendocrine tumor and a Ga-68-DOTATOC-PET/CT showed a corresponding strong focal uptake. Laparoscopic spleen-preserving distal pancreatectomy was performed and histopathological examination diagnosed an intrapancreatic accessory spleen. The presence of IPAS should be kept in mind even in case of positive Ga-68-DOTATOC-PET/CT imaging to avoid unnecessary pancreatic resections.