Composition of clinically aged amalgam restorations.

Twenty-five amalgam restorations ranging in age from two to 25 years were obtained from five subjects. An electron microprobe was used to analyze the specimens for bulk elemental composition and phase composition, and the volume fractions of phases were determined by point-counting on back-scattered electron micrographs. Twenty-one of the specimens were conventional, low-copper amalgams, and the remaining four were high-copper amalgams. The bulk elemental compositions showed little variation from newly prepared amalgams except for the presence of a small amount of chloride and other contaminants. The compositions of the phases were essentially the same as is found in new amalgams, except that there was considerable internal amalgamation of gamma particles. The distribution of phases in the clinically aged amalgams was quite different from that of new amalgams. The low-copper amalgams had decreased amounts of gamma, gamma-1, and gamma-2 phases and increased beta-1 and tin-chloride. The high-copper admixed amalgams had decreased gamma, increased beta-1, and enlarged reaction rings (gamma-1 and eta').

Effect of clinical finishing procedures on amalgam microstructure.

Spherical amalgam specimens were burnished, burnished-polished, polished (wet), or polished (dry). The amalgams were sectioned normal to the prepared surface, elemental analyses were made at a series of depths from the surface with the electron microprobe and the phase fractions were calculated. Significant variations in phase distributions exist within 100 micrometers of the surface.

Electron irradiation effects in the EPMA quantitation of organic specimens.

Electron irradiation of organic specimens adversely affects the validity and reliability of quantitative microanalytical results through the loss of light element constituents of the specimen. Characteristic and continuum x-ray count rates will vary for the duration of the irradiation effects, which require electron doses of 10(-11) to 10(-8) C/micrometer 2. The magnitude of these variations is dependent upon the light element content, thickness and temperature of the specimen and upon the operating conditions used during analysis. The initial count rate at the onset of the electron beam is the most valid count rate to be used in the quantitation of organic specimens, but it can only be accurately determined when the analyzed element exists in high concentration within the specimen or when the beam is grossly defocused. Low temperature analysis will prolong the duration of the mass loss and decrease its magnitude, but erratic count rates, specimen charging due to condensation and inconsistent mass losses have been observed for different specimens. The physics and chemistry of the electron beam-specimen interactions impose limitations upon the potential accuracy in biological microanalysis whic, if ignored, can result in large errors in quantitative projections.

Irradiation effects in the electron microprobe quantitation of mineralized tissues.

The accuracy of absolute quantitation within thick, mineralized tissue specimens is influenced by count rate variations of characteristic X-rays during electron microprobe analysis. The variations occur for electron doses approximately greater than 10(-10) C/micrometer2 and are primarily dependent upon the light element fraction within the irradiated volume. Specimen preparation procedures affect both count rate dynamics and interpretatin of microanalytical results. X-ray intensity data acquird at initial electron exposure and utilized in standard matrix correction schemes will project valid elemental concentrations for known calcium compounds over wide ranges of specimen density. Measurement error could approach +/- 2-3% for the major elemental constituents in mineralized tissues, but only with appropriate control or interpretation of electron irradiation phenomena.

Effect of surface preparation on phase distribution of amalgam surfaces.

Several types of amalgams were prepared with carved, burnished, or polished surfaces. Elemental analyses were made of these surfaces with the electron microprobe and the phase fractions were calculated from these data. The phase distributions were found to vary with the technique of finishing.

Estimation of the phase distribution in dental amalgam with the electron microprobe.

The phase distributions of several dental amalgams have been determined by two methods: calculation from elemental analysis data obtained with the microprobe, and measurement of phase areas on backscattered electron photographs with the image analyzer. The results of these methods agree, in general, with the distributions predicted by the stoichiometric equations.

Scanning electron microscope study of marginal adaptation of amalgam in restoration finishing techniques.

Voids and gaps between the surfaces of the amalgam and the cavity preparation were apparent in the carved and the polished samples. These spaces in the burnished specimens were filled with an amorphous bulk of amalgam apparently caused by the burnishing process. Since the margins of burnished amalgam restorations have been shown to leak less than those of carved and polished specimens, it is hypothesized that this is due to the improved marginal adaptation attained through the burnishing process.

Microstructure of amalgam surfaces.

The polished amalgam surface was smoother than the burnished and the carved surfaces. The burnished surface was smoother than the carved surface. The granular structures on the burnished amalgam surface were found to be of tin-mercury alloy. Polishing appears to be the best finishing technique for amalgam restorations, and there is no substitute for it.