Microstructures of Pd-containing dispersants for admixed dental amalgams

Effect of heat treatment on structure and properties of dispersed-type dental amalgam

Effect of heat treatment of Ag-Cu-Pd dispersant particles on the structure, mechanical properties and mercury vapor release rate of an Ag-Cu-Sn/Ag-Cu-Pd-based dental amalgam has been investigated. Experimental results indicate that crystallinity of dispersant Ag-Cu-Pd alloy increases with increasing HTT, with most notable increase occurring between 100 and 200 degrees C. Increasing HTT of Ag-Cu-Pd alloy does not change much of the mercury/alloy ratio for amalgamation, but largely reduces working/setting time of the amalgam. The Ag-Cu-Pd particles in 7 d-aged amalgam are comprised primarily of an outer Sn/Cu/Pd-rich zone and an inner Ag/Cu/Pd-rich zone with eutectic-type morphology and chemical distribution. The annealing-enhanced Pd segregation effect is most significantly observed in the amalgam derived from 300 degrees C-annealed Ag-Cu-Pd dispersant. This amalgam also has the highest compressive strength, highest DTS, and lowest creep rate. Higher annealing temperature causes mechanical property of the amalgam to deteriorate. The initial mercury vapor release rates of amalgams derived from 100, 200 and 300 degrees C-annealed Ag-Cu-Pd dispersant are significantly lower than that derived from 400 degrees C-annealed dispersant.

Evaluation of the long-term corrosion behavior of dental amalgams: influence of palladium addition and particle morphology

OBJECTIVES

The purpose of this investigation was to evaluate the long-term corrosion behavior of experimental amalgams as a function of particle morphology and palladium content.

METHODS

Samples of four experimental high copper amalgams were prepared according to ADA specifications. Two of them had the same chemical composition but one had lathe cut particles (LCP) and the other had spherical particles (SP). The two others had spherical powders with an addition of 0.5 wt% of palladium (SP 0.5) and 1 wt% of palladium(SP 1) for the other. Corrosion resistance was evaluated by electrochemical techniques in Ringer's solution in a thermostated cell at 37 degrees C for samples aged 5, 8, 12, 16 months and 10 years. Potentiokinetic curves were drawn and the potential and the current density corresponding to the first anodic peak were registered.

RESULTS

For all the amalgam samples the corrosion behavior improves over the 10-year period. SP samples exhibit a better behavior than LCP. Palladium addition improves corrosion behavior as compared to samples without palladium. No real difference is found regarding the amount of palladium between 0.5 and 1%. The potentials progress from a range between 0 and 20 mV/SCE to a range of 60-80 after 10 years. The stabilization of the potential begins after only 16 months. Except for the LCP, all the values converge to the same level of 80 mV/SCE.

SIGNIFICANCE

The addition of no more than 0.5 wt% Palladium in a high copper amalgam powder improves the corrosion behavior of the amalgam up to a period of 10 years. The potential of the first anodic peak increases for each amalgam, probably in relation to the evolution of the structure of the material. Clinically, it is of interest to consider the good electrochemical behavior of older restorations when contemplating the repair or replacement of such fillings. At the same time, galvanic current can occur when a new amalgam restoration is placed in contact with an old one even if the same amalgam is used. In this situation, the new filling will be anodic and its degradation will be accelerated. The evaluation of the corrosion behavior of dental amalgams has to take into account the age of the samples.

Particle size effect on structure and properties of dispersed Pd-containing dental amalgam

Focus of the study is to evaluate the effect of dispersant particle size on the structure and various properties of spherical matrix, irregular dispersant admixed type Pd amalgams. The results indicate that amalgams prepared from smaller dispersant particles have a shorter setting time (faster amalgamation reaction), smaller setting expansion, higher eta' content and lower early stage gamma2 content. Smaller dispersant particles also lead to a slightly higher compressive strength, lower creep value, more cathodic corrosion potential and less early stage mercury vapor release. The particle size effect on corrosion current density and chemical composition of gamma1 phase in aged amalgam is less significant.

Effect of particle configuration on structure and properties of dispersed Pd-containing dental amalgam

The present work investigates the effect of particle configuration on the structure and properties of four dispersed type Pd-containing amalgams with the same chemical composition. The results indicate that particle configuration plays an important role not only in the structure and chemistry, but also in such properties as compressive strength, creep and mercury release rate. Compromises among the various properties of the present Pd amalgams are needed, when a decision on particle configuration is to be made. As mechanical properties or corrosion resistance is concerned, the amalgam should comprise at least one spherical alloy (matrix or dispersant). As far as mercury release is concerned, the amalgam should comprise irregular dispersant alloy. The amalgam fabricated from irregular dispersant and spherical matrix particles seems to serve all well.

Microstructure and segregation behavior of palladium in silver-copper-palladium alloys

It has been reported that the addition of palladium can modify the microstructure and improve the properties of Ag-Cu eutectic alloy as well as admixed Cu-rich amalgam. The purpose of this work was to study the microstructure and segregation behavior of palladium in a series of Ag-Cu-Pd alloys. All microstructural and microchemical results consistently indicated a strong tendency for palladium to form the ordered Cu3Pd superlattice in the copper-rich phase of the present ternary alloys. Transmission electron microscopic examination indicated that, in addition to the large Cu-rich particles, numerous small (typically tens of nanometers) Cu-rich particles were distributed in the Ag-rich phase. In the alloys containing 10 and 15 wt% Pd, the Cu3Pd superlattice had an L1(2)-type crystal structure. In the alloy containing 20 wt% Pd, the Cu3Pd had a periodic (regular) APB structure. The solubility of palladium in the Cu-rich phase was always much larger than that in the Ag-rich phase. The ratio of the palladium concentration in the copper-rich phase to that in the silver-rich phase decreased with the overall palladium content.