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At least 991 records · Page 55Linked to original sources
PubMed1983

Fracture toughness of dental amalgams.

The fracture toughness of selected low and high copper content amalgams has been determined using three testing methods. A miniature single edge notched three point bend specimen, based on BS 5447, was found to give the most reliable values of fracture toughness, determined both as the work of fracture and as the opening mode plane strain critical stress intensity factor. The conventional low copper amalgam, Aristaloy, proved to be tougher under all test conditions than the high copper amalgams. It is suggested that time-dependent plastic flow mechanisms are responsible for this behaviour.

Biomechanical Phenomena↗
PubMed1995

The effect of matrix phase morphology on the structure of Ag-Cu-Pd dispersed phase dental amalgam.

The effect of an Ag-Cu-Pd dispersant alloy on the structure of amalgams fabricated with two different particle types of low-copper amalgam matrices was investigated. In amalgams L and L (0), a low-copper lathe-cut amalgam Aristalloy was used as the matrix. In amalgams S and S(0), the matrix used was Spheralloy, a low-copper spherical amalgam. X-ray diffraction was used to analyse the relative content of the phases in the amalgams. The presence of Pd in the dispersant of amalgams L and S resulted in a decrease in the amount of eta' (Cu6Sn5) and an increase in the amount of unreacted particles when compared to the controls L(0) and S(0). Amalgams fabricated with a spherical alloy matrix (S and S(0)) showed a greater effect than amalgams fabricated with a lathe-cut matrix alloy (L and L(0)).

Chemical Phenomena↗
PubMed1998

Mercury vapor release from dental amalgam after laser treatment.

The aim of this in vitro study was to determine whether the treatment of amalgam with different lasers leads to an increased release of mercury (Hg) vapor. In the case of CO2-lasers in pulse and continuous-wave mode, there was no effect visible on the amalgam surface and no Hg vapor could be detected. Using an Nd:YAG, Er:YAG or Nd:YLF laser, crater formation could be observed on the amalgam surfaces. With the solid state lasers tested, however, the Hg vapor measurements taken indicated that pulses applied to amalgam cause a substantially increased release of Hg vapor. This vapor may contribute to the patient's total mercury exposure.

Aluminum Silicates↗
PubMed1985

Strength and creep of dental amalgam: the effects of deviation from recommended preparation procedure.

The effects of deviations from recommended preparation procedures on the compressive strength, modulus of elasticity, plastic deformation, toughness, and creep of four commercial amalgam alloys have been investigated. Deviations included changes in trituration time, mercury/alloy ratio, and condensation pressure. With regard to both compressive strength and creep, there were great differences in the susceptibility of different amalgam alloys to variations in manipulation. One conventional alloy showed almost no variation in compressive strength as a result of the deviations from the recommended preparation procedure. This material also showed much greater plastic deformation and fracture toughness than the other materials, making it less brittle and probably more resistant to bending forces. Dispersalloy exhibited both increased and decreased strength as a result of the deviations, while ANA 2000 and Revalloy only showed decreased strength. Some of the alterations for ANA 2000 and Revalloy resulted in a decrease in strength below an acceptable clinical level. Regarding the modulus of elasticity, only the conventional alloys were affected by the alterations in the preparation procedure. However, for the plastic deformation, the results were reversed; only the high-copper alloys were affected. The toughness of the specimens was decreased for all the alloys with the exception of one, which was insensitive to changes in the preparation procedure as far as compressive strength was concerned. One of the high-copper alloys showed the least change in creep relative to deviations in preparation procedures. Lowered condensation pressure increased the creep value for all the amalgams; and for the conventional alloys a lowered mercury/alloy ratio also resulted in increased creep.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical Phenomena↗
PubMed1986

Influence of submerged electrical welding/cutting on dental amalgam in Swedish divers.

Professional commercial divers working with electrical cutting and welding sometimes experience a metallic taste phenomenon. An enquéte study among divers showed no influence of different equipment on the occurrence of such metallic taste, but it seems to occur less frequently in low salinity water. It has been suggested that this metallic taste phenomenon is due to increased corrosion rate of dental restorations, especially of amalgam. Experimental results recording the potential of amalgam specimens placed in the oral cavity of divers during welding, showed influence on the potential, and thus probably on the corrosion rate, during welding only when the diver came into direct contact with the water, e.g. through leakage in the suit.

Adult↗
PubMed1991

Corrosion of five different dental amalgams.

The purpose of this study was to determine the gamma-2 presence in two South African amalgams (Amalgaphase and Silvalloy) and to compare this data with that obtained from tests on a well-known gamma-2 containing amalgam (Amalcap) and on two products with a reportedly low gamma-2 content (Dispersalloy and Permite-C). Samples were prepared according to standard ISO procedures in special sample holders. The rotating disc electrode technique (similar to the technique described by Gal-Or, Bruckenstein and Carter, 1978) was used to determine the presence of gamma-2. All samples were evaluated after one and again after nine days. Results indicated that only Dispersalloy displayed no reaction at day one; in other words no gamma-2 could be detected after 24 hours. All other amalgams showed a definite peak on the polarization plot between -200 and -250 mV indicating electrochemical activity (corrosion) in that region. On day nine, only Amalcap (the gamma-2 containing amalgam) still exhibited a reaction peak. Thorough clinical studies will have to be undertaken to evaluate the durability of the South African products.

Corrosion↗
PubMed1976

Marginal fracture of dental amalgams.

The purpose of this study was to determine the marginal fracture of different amalgams, using a semiclinical method which facilitates standardization and minimizes the observation time, in 10 patients receiving complete dentures. Cavities were cut occlusally in acrylic premolars and molars. The margin was then beveled to 45 degrees with a cone-shaped diamond. Two dispersion-strengthened amalgams and one conventional amalgam were used in each mouth. The cavities of each quadrant were filled with the same amalgam. Thus, conventional amalgam fillings were always placed in opposing quadrants to those filled with a dispersion-strengthened amalgam. The degree of marginal fracture was evaluated from the prints (magnification X 5-7) by five dentists separately and blindly. After 6 months' service, severe marginal fracturing was frequently seen.

Acrylic Resins↗
PubMedDate not supplied

Influence of alloy composition on the hardening of silver-tin dental amalgam.

The objective of the investigation was to examine the reactions of mercury with silver-tin alloys with compositions spanning the phase fields beta, (beta + gamma), gamma, and (gamma + Sn). The experimental methods employed include the application of light microscopy, scanning electron microscopy, and electron probe microanalysis. These techniques were used to investigate the mechanisms of reaction and to identify the nature and morphology of the reaction products formed on bulk specimens of the alloys. The progress and characteristics of the reactions that occur during hardening of amalgams prepared from powders of these alloys were monitored using a high-sensitivity dilatometer. These results were correlated with direct observations on the development of the microstructures. The reaction of mercury with the beta-phase alloy occurred rapidly and resulted in a very marked and rapid expansion during the initial stages of hardening. gamma-Phase alloys, on the other hand, reacted more slowly and contracted markedly during hardening. The behavior of amalgams made from alloys with compositions lying between these two extremes appeared to be explicable in terms of the characteristics of the separate phases from which they were constituted.

Absorption↗
PubMed1978

Creep and beta1 formation in dental amalgam.

Measurements of creep, beta1 phase content and gamma1 lattice parameter were performed on four conventional amalgams stored at 37 degrees C up to 2 years. The creep values and lattice parameters decreased and the beta1 content increased during this period; the most prominent alterations took place within the first 6 months.

Dental Amalgam↗
PubMed1977

Creep and phase transformation in dental amalgam.

Creep measurements were performed on different types of amalgams as a function of heat treatment after specimen preparation before testing. The types of amalgams included lathecut, spherical, nonpreamalgamated amalgams, and an amalgam containing Ag-Cu particles. Heat treatment significantly reduced the creep of all alloy types studied. Creep reduction was associated with the phase and transformation gamma1 leads to beta1 (Ag-Hg), which was detected by metallographic and microprobe analysis.

Chemical Phenomena↗
PubMed1995

Mercury release from dental amalgams: an in vitro study under controlled chewing and brushing in an artificial mouth.

The release of mercury vapor from class I amalgam restorations prepared in human molar teeth was studied during chewing simulations in an artificial mouth of a bi-axial servo-hydraulic mechanical test system. So that the total mercury released from the restoration over a fixed time could be determined, a closed chamber surrounded the envelope of chewing motion. In addition, the influence of sampling frequency on mercury release was corrected by the use of different sampling frequencies over a fixed time interval of mercury release measurement and extrapolation to zero sampling time. Thus, a combination of a closed environment and an extrapolation method to determine the mercury release under continuous sampling was used to determine the mercury released under normal breathing conditions. The measured mercury release rate data were used to calculate the potential daily mercury dose in a patient due to a single amalgam restoration, following the method previously outlined by Berglund. The mercury release from both a conventional and a high-copper amalgam was evaluated at different age intervals after the restoration was placed in the teeth. The results show that while the age of the amalgam and the amalgam type influence the extent of mercury release during the initial non-steady-state conditions, the steady-state value of mercury daily dose due to a single amalgam filling is 0.03 micrograms/day, which is well below the calculated threshold-limiting value (TLV) of 82.29 micrograms/day considered dangerous for occupational exposure in the United States.

Air Pollution, Indoor↗
PubMed1982

High copper alloys for dental amalgam.

The nature, physical properties and clinical performance of amalgams made from alloys containing copper in excess of 6 per cent by weight are reviewed. There are two basic types of high copper alloy: (a) mixtures of 'spherical' silver/copper or silver/tin/copper particles with low copper low copper lathe-cut or 'spherical' and (b) single composition silver/tin/copper spherical or lathe-cut particles. Copper contents range from 8.5 per cent to 30 per cent. In amalgams made from high copper alloys the soft corrodible gamma 2 (Sn7Hg) phase is reduced or eliminated by preferential formation of the eta (Cu6Sn5) phase. Improved clinical performance (less marginal breakdown) has been related to low creep, little or no gamma 2 phase and the presence of zinc. The possible roles played by these factors in the mechanism of marginal breakdown are discussed. Physical properties are not a reliable guide to the clinical performance of amalgams. Although high copper amalgams as a group show 'superior' physical properties and clinical performance to low copper amalgams, a high copper content does not necessarily mean improved clinical performance. Indeed, certain well-manipulated low copper amalgams can show clinical results comparable with some high copper amalgams, but not as good as the best high copper amalgams. In most clinical studies the silver/copper plus lathe-cut (dispersed phase) alloys and some of the single composition high copper alloys show the greatest clinical durability. The most significant factor in clinical performance is the choice of alloy.

Chemical Phenomena↗
PubMed2004

Childhood urine mercury excretion: dental amalgam and fish consumption as exposure factors.

The authors investigated the effect of amalgam fillings and fish consumption on urine mercury level (UHg), in children aged 4-8 years old inclusive. Using a sample of 60 children, we found that children with amalgam fillings had significantly higher UHg levels than children without amalgams (geometric mean=1.412microg Hg/g versus 0.436 microg Hg/g, respectively, P = 0.0001). Subjects with reported higher fish consumption also had significantly higher UHgs (P = 0.004). Univariate analyses provide evidence of an association between elevated UHg level and young age (P = 0.009), short height (P = 0.024), and low weight (P = 0.049) in children with amalgam chewing surfaces. We also found a negative correlation between urine mercury and age (-0.378), height (-0.418), and weight (-0.391). A multiple logistic regression model shows that the presence of amalgam fillings leads to increased odds of high UHg in children (OR=47.18), even after adjusting for high fish consumption (OR=8.66) and height (OR=11.36).

Age Factors↗
PubMed1999

[In vitro evaluation of mercury leakage from dental amalgam using atomic absorption spectrophotometry].

OBJECTIVE: The use of silver amalgam as a tooth filler is under constant critical review because of its mercury content. After a review of the literature on this subject, in vitro spectrophotometry was used to assay the release of mercury by these amalgams in basal conditions. METHODS: The experiment was conducted in two phases using standard doses of amalgam. In Phase 1 Black Class I cavities were created in extracted teeth that were big enough to take the required dose of amalgam. In some cases the material was inserted in a single operation, while in others the amalgam was introduced in three stages. Some of the cavities were cleansed with cotton buds bathed in ethyl alcohol, while others were not. All the drilled teeth were imbued in a bath of artificial saliva held at a constant temperature. In the second experiment, crushed amalgam was immersed in a similar bath of artificial saliva but otherwise untreated. The saliva was assayed after different time lapses using atomic absorption spectrophotometry and the FIAS technique. RESULTS: The results showed extremely variable but always modest quantities of free mercury in the artificial saliva. CONCLUSIONS: The findings suggest that not all the mercury available in the amalgamation phase is involved in the formation of the crystalline reticulum and that the percentage of mercury bonded is different every time. While the titre of free mercury encountered was always extremely low and hard to predict, it cannot be ignored.

Dental Amalgam↗
PubMed1978

Corrosion and creep of dental amalgam.

The influence of stress on corrosion was investigated by a potentiostatic technique. Amalgrams with low creep, both with and without gamma2-phase, revealed small increases in current with stress application while alloys with high creep exhibited large increases in current. Rupture of protective oxide due to increased strain for high creep alloys may explain the phenomenon.

Corrosion↗