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Abstract

The objective of this work was to manufacture and examine dental amalgam samples joined by the addition of new to old material.

Cylindrical samples 4mm in diameter were prepared from commercial dental amalgam alloys in a split mould. The end surface of the old amalgam was abraded, the sample replaced in the mould and fresh amalgam condensed using experimental vibration techniques developed during the study. Samples were subsequently fractured using 3 point loading.

Although there was considerable scatter in the force to fracture, several experimental procedures produced samples which did not break at the joint. The force to fracture these joined samples generally exceeded that for one- piece samples condensed in a manner similar to that prescribed in BS 2938: 1985.

Notches were machined adjacent to the joint in a selection of joined samples and the central load roller of the 3 point test rig was located opposite. Most fractures commenced at the notch, traversed the joint interface and terminated at the point of applied load. For samples notched at the joint and offset loaded, the fracture path departed from the joint at about halfway. This indicated that the joint was not the weak link in the samples.

The location of the joint was revealed in the microstructure when the parent alloy contained spherical particles: these were cut by the end preparation procedure. Reassembled notched samples after fracture showed the crack to traverse or follow and then depart from the joint. An incomplete copper-tin reaction layer was also seen at the joint on cut spherical silver-copper particles in high copper admixed amalgam.

The range of amalgam alloys which were prepared and tested and where the joint was not weak included conventional, high copper single composition spherical and lathe cut, blended, hybrid and admixed types.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses School of Science & Technology > Engineering

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