A Titration Method for the Determination of Acid and Alkali Production by Micro-Organisms

The purpose of this investigation was to study the influence of changing the precondensation mercury content (initial mercury content) on the early and final transverse strength of different amalgams. The material consisted of five conventional lathe cut alloys, two of which were zinc free, of one dispersion strengthened and one spherical alloy and of three lathe cut preamalgamated alloys. The amalgam was mixed with mercury using three different alloy-mercury ratios. Thus the precondensation mercury content of Mix I was about 50 per cent, of Mix II about 54 and of Mix HI about 59 per cent for all amalgams except the spherical brand. Rectangular amalgam test pieces, measuring 2 × 2 × 12 mm, were condensed by hand using a load of about 17 kg/cm². The transverse strength test was performed either after one hour or one week using three point loading. The results show that for some of the amalgams an increase of the precondensation mercury content resulted in a slight reduction of the early strength. Furthermore the results show that the early strength was lower for the preamalgamated amalgams than for the other amalgams. Increasing the precondensation mercury content did not significantly effect the final strength of six amalgam brands but increased the strength of three brands and reduced the strength of one brand. It was concluded that it is safer to use a moderate excess of initial mercury in clinical amalgam work than to try to reduce the initial mercury content as much as possible.     

Mercury evaporation from amalgams with varied mercury contents

This study examined the relationship between mercury content and mercury evaporation from amalgams during setting. Two different types of commercial high-copper amalgams (single composition and admixed types) were used. Cylindrical specimens of each amalgam were prepared with five different mercury contents according to ADA Specification No.1. Specimens were also prepared by hand condensation. Mercury evaporation from amalgam specimens maintained at 37 degrees C was measured using a gold film mercury analyzer from 10 min after the end of trituration until the mercury concentration in air reached an undetectable level. The mercury content more clearly influenced the mercury evaporation from the admixed type amalgam specimens when the mercury content decreased below the manufacturers' recommended trituration conditions. Triturating with less mercury than the manufacturers' recommended amount cannot lower the evaporation of mercury from freshly made amalgam. Proper condensing procedures can minimize the mercury evaporation from the amalgam surface.     

Effect of free mercury on the strengths of dental amalgams

A previous study of several different Ag?Sn, Ag?Cu, and Ag?Sn?Cu alloys revealed that some of these alloys were susceptible to mercury embrittlement. The present study was undertaken to determine the extent to which embrittlement of alloy particles in amalgam affects the strength of the material. Specimens of low copper amalgam (O), high copper admixed amalgam (D), and high copper single composition amalgams (S and T) were condensed into 2 mm×4 mm×15 mm molds using a pressure of 14 MPa. After aging the specimens for 7 days at 37°C, mercury was coated on each specimen either by electro-plating mercury or by immersion in mercury. In each method, mercury was applied for 15 s or 1 min. At 30 s after coating, each specimen was placed in a 3-point fracture fixture and immediately loaded at 0.25 and 2.54 mm/min until fracture occurred. As controls, specimens of each amalgam without mercury coating were also tested. Ten specimens per experimental condition were tested. Fractured surfaces were examined using a scanning electron microscope. Strength reductions as high as 60% for O amalgam, 44% for D amalgam, and 31% for T amalgam were found. Two observations suggest that embrittlement of unconsumed alloy particles is primarily responsible for the strength reduction: 1) the amalgams showing susceptibility to mercury embrittlement in the present study contain alloy particles of alloys that were shown to be susceptible to embrittlement in an earlier study, and 2) the amalgam S, which showed the least susceptibility to mercury embrittlement, contains unconsumed alloy particles of an alloy that showed no significant embrittlement in the earlier study. Experimental evidence supports the hypothesis that free mercury released during corrosion or aging of amalgam restorations can contribute to the weakening of these restorations.     

Polishability of dental amalgam as influenced by condensation pressure and primary mercury content

The polishability of some amalgam products was studied by determining the roughness (Rs) of metallographically polished specimens. The surface porosity of the specimens was also measured and was found to be closely correlated with the roughness. Two manipulative variables, condensation pressure and primary (precondensation) mercury content, were examined with respect to their effect on porosity and polishability. For the condensation pressures 14 and 20 MPa no differences could be observed in the effect on the surface properties studied. The primary mercury content was varied in three steps--the normal, recommended level and 5% more and less than this. For those products having a recommended precondensation mercury content of 50% or less, the 5% decrease in mercury resulted in a pronounced increase in porosity and Rs. The results indicate that polishability is for some products markedly improved by avoiding a dry mix.     

The Influence of the Condensation Pressure Upon Crushing Strength and Mercury Content of Amalgam

This is a study of the effect of condensation pressure upon crushing strength and mercury content at various amalgams, and of the relation between crushing strength and mercury content. The results are presented in Tables 1 and 2, and in Figures 1, 2, and 3. The experiments show that and increase of the condensation pressure from 0.8 to 9.4 kg/mm² results in a continued increase of the crushing strength and a reduction of the mercury content (Figures 1 and 2). The experiments also show (Figure 3) that a reduction of the mercury content of the amalgams below 50% will result in an increase of the crushing strength from 40 to 75 kg/cm²/%.     

Modulus of elasticity in bending of composites and amalgams

In this study, the modulus of elasticity in bending (a measure of rigidity) and transverse strength (a measure of edge strength) were determined for composites and amalgams. the results were as follows. The modulus of elasticity of microfilled composites is approximately one-third that of the macrofiller-containing composites. Composites containing a relatively coarse-sized macrofiller have a higher elastic modulus than those containing a finer macrofiller. The transverse strength of microfilled composites is approximately one half that of the macrofiller-containing composite, which, in turn, is close in value to the transverse strength of amalgam. High-copper amalgams are substantially more rigid than the traditional low-copper amalgams, but do not show large differences among themselves. The transverse strength among various amalgams does not appear to be related to amalgam type but does correlate to final Hg content. The modulus of elasticity of composites most likely to be used in posterior teeth is approximately one third of the modulus of elasticity of amalgam; that is, amalgams are three times more rigid.     

Flow stress and deformation hardening of triturated amalgam

The proper adaptation of dental amalgam to the cavity wall is important to reduce the risk of secondary caries. The condensation properties of amalgam can be expected to be dependent on the flow stress of the material. The resistance to plastic deformation has been investigated by analyzing load-deformation curves in extrusion and indentation experiments for 5 different types of amalgam and a wax. The results indicate that the flow stress of triturated amalgam, in contrast to wax, increases primarily with the deformation time. The reason for this relationship is suggested to be continuous displacements between alloy particles and mercury leading to increased direct contact and reaction rates. The reduction of the pore volume in both processes, and the mercury being squeezed out in indentation, are likely to make a minor contribution to the initial deformation hardening, but cannot explain the effect of deformation time on flow stress. It can be predicted that condensation should be carried out with as rapid compression movements as possible in order to avoid too early development of a hard amalgam mix. Approximate calculations of the flow stress in extrusion and indentation have been carried out. The flow stress of amalgams was found to increase with the alloy:mercury ratio.     

Effects of palladium addition on emission of mercury vapor from dental amalgam

OBJECTIVES: The purpose of this investigation was to test the hypothesis that palladium causes a reduction in mercury emission when added to dental amalgam during condensation. METHODS: Mercury vapor release was measured in a closed bottle system and an Intraoral Flow device(IOF). Conventional amalgam restorations were modified by addition of various palladium pellets. 1.57 mm diameter palladium pellets with different porosities were fabricated. These pellets were then placed in amalgam restoration using typical condensation and carving procedures. The samples were stored in a closed bottle and mercury measurements were taken from the bottles at 30 min, 1, 3, 5, 24 and 48 h and 7 days after trituration using a Jerome 411 Mercury Vapor Analyzer (Arizona Instrument Corp., Jerome, AZ). The palladium pellets identified as the most effective in mercury vapor reduction were further tested in an IOF device. Data were analyzed by two-way ANOVA followed by Tukey HSD pairwise analysis for significant findings (alpha = 0.05). RESULTS: The palladium containing amalgams when tested in the closed bottle system yielded significantly lower (p < 0.05) mercury vapor release than the controls. Pellets fabricated with the highest porosity yielded the greatest reduction in overall mercury vapor release. In the IOF device the overall amount of mercury vapor released from the palladium containing amalgams was also significantly less than the control (p < 0.05). SIGNIFICANCE: Mercury vapor emission from dental amalgam was greatly reduced by adding palladium pellets to amalgam during condensation. These techniques require only slight modifications of the standard operative procedures.     

Porosity, strength, and mercury content of amalgam made by different dentists in their own practice

Fifty-nine dentists made Class I-like amalgam fillings in plastic blocks in their own practices using their usual routines and products. The amalgam specimens were subjected to porosity determination at the marginal and central portions of the amalgam surface. In addition, diametral tensile strength and mercury content were measured. The results demonstrated substantial variations in the properties of the amalgams made by different dentists. Generally, the margin of the fillings were more porous than the central parts. Six cases (10%) had marginal porosity exceeding 10%. Fillings made from spherical products exhibited the most extreme results, and their median values for strength and mercury content were lower than those of the lathe-cut products.     

Recent developments in alloys for dental amalgams: their properties and proper use.

Since the development more than ten years ago of a new type of amalgam alloy that will react with mercury without forming the unfavourable gamma2 (Sn7-8Hg) phase, several new alloy brands with a similar reaction pattern have been presented. This new generation of amalgam alloy is called non-gamma2 alloy as distinct from the conventional alloys. Three of the new alloys studied contain approximately three volume percent gamma2 and should be classified as modified concentional amalgams. The non-gamma2 amalgams may be characterized in the following way: (1) instead of gamma2 they contain a reaction product of copper and tin (Cu6Sn5), the so-called eta1 phase. (2) They are significantly more resistant to corrosion than the conventional amalgams but do in time produce sufficient solid corrosion products to seal the micro-fissures between filling and cavity walls. (3) When corroding, they do not release metallic mercury, and the solid corrosion products formed and precipitated on the free surface of the fillings seem relatively little resistant to the organic acids of the plaque. (4) Most of them have relatively low creep and tensile strength, but high compressive strength. (5) Clinically the non-gamma2 amalgams are remarkable for superior marginal integrity and, seemingly, also for improved persistence of surface lustre.     

The contribution of dental amalgam to mercury in blood

We determined the exposure to mercury from dental amalgam by comparison of blood levels of mercury before and after removal of all amalgams from ten subjects. Baseline concentrations of mercury in whole blood were measured weekly for four to 18 weeks (median = 6.6 weeks) prior to removal. All amalgams were removed in a single appointment. The subjects had an average of 14 surfaces of amalgam, seven of which were occlusal surfaces. Weekly blood sampling was continued for five to 18 weeks (median = 7.6 weeks) after the amalgams were removed. The mean baseline concentration of total mercury in whole blood of the ten subjects was 2.18 (SD = 0.90) ng Hg/mL before the amalgams were removed. The baseline mercury levels were related to the number of amalgam surfaces. The linear correlation coefficient was 0.724 with number of occlusal surfaces, and 0.433 with total number of surfaces. After removal of the amalgams, nine of the ten subjects exhibited a statistically significant decrease in blood mercury at the 95% level of confidence. The mean decrease in mercury was 1.13 (SD = 0.60) ng Hg/mL. The half-time for elimination of mercury from blood after amalgam removal was 30.2 (SD = 5.8) days. Removal of the amalgams provided an additional exposure of 1.46 (SD = 1.17) ng Hg/mL that was rapidly cleared from the blood with a half-time of 2.9 days. The daily intake of mercury from amalgam in the subjects was estimated to be at least 1.3 micrograms.     

Effect of ball milling on structures and properties of dispersed-type dental amalgam

Objectives

The purpose of the present study was to investigate the effect of ball milling on the initial mercury vapor release rate and mechanical properties such as compressive strength, diametral tensile strength and creep value, of the dispersed-type dental amalgam, and comparison was made with respect to two commercial amalgam alloys.

Methods

Ball milling was employed to modify the configuration of the originally spherical-shaped Ag-Cu-Pd dispersant alloy particles. Improvement in mechanical properties while maintaining a low early-stage mercury vapor release rate of the amalgam is attempted.

Results

The experimental results show that the amalgam (AmB10) which was made from Ag-Cu-Pd dispersant alloy particles that were ball-milled for 10 min and heat-treated at 300 °C for 2 days exhibited a low initial mercury vapor release rate of 69 pg/mm²/s, which was comparable with that of commercial amalgam alloy Tytin (68 pg/mm²/s), and was lower than that of Dispersalloy (73 pg/mm²/s). As for mechanical properties, amalgam AmB10 exhibited the highest 1 h compressive strength (228 MPa), which was higher than that of commercial amalgam alloy Dispersalloy by 72%; while its 24 h diametral tensile strength was also the highest (177 MPa), and was higher than that of Dispersalloy by 55%. Furthermore, the creep value of the amalgams made from Ag-Cu-Pd alloy particles with 10 min ball-milling and heat treatment at 300 °C for 2 days was measured to be 0.12%, which was about 20% that of Dispersalloy.

Significance

It is found that ball milling of the dispersant Ag-Cu-Pd alloy particles for 10 min was able to modify the configuration of the alloy particles into irregular-shapes. Subsequently, heat treatment at 300 °C significantly lowered the initial mercury vapor release rate, increased its 1 h compressive strength and 1 h diametral tensile strength, and lowered its creep value.     

A comparison of methods for determining setting rate of amalgam

A bstract — Four methods were compared for determining the setting rate of amalgams. The resultant order of preference as a standard method was compressive strength at 30 minutes after preparation of the specimen, the time to the last transverse cut on a cylindrical specimen with a "guillotine" blade and the time to non-fracture of a ball of amalgam with a final set Gillmore needle. A mercury absorption method was unacceptable. Alloys labelled fast and standard setting could be separated and limits between fast and standard alloys have been examined for each method.     

Initial corrosion of amalgams in vitro

Abstract – The amounts of copper, mercury, silver or zinc released from two brands of freshly prepared, lathe cut amalgams and from one brand of dispersed phase type amalgam into artificial saliva have been measured. Samples were immersed in the solution a few minutes after the end of trituration and exposed statically for periods of up to about 4 days. The initial mercury release from such specimens could exceed the long term mercury release from old amalgams by more than two orders of magnitude. The measurements indicate that during the first day after insertion of two amalgam fillings, each with an assumed surface area of 1 cm² and under presumably static conditions, mercury at the level of more than twice the mercury food and drink intake could be released in the oral cavity. This is, however, a situation which appears infrequently, e.g. following dental treatment once a year. The amounts of copper and zinc released initially were considerably lower than the corresponding food and drink intake values, while silver might be on the same level. The measurements were conducted using nuclear tracer techniques.     

Effect of manifacturing technology on the resistance to corrosion of amalgam fillings and speed of mercury emission

The study investigates the influence of the various manufacturing technological alternatives of a given alloy on the corrosion properties, as well as it evaluates the quantity of mercury release from the amalgam filling having the same alloy. The resistance of dental amalgams to corrosion is the function of their precious metal (mercury and silver) content. The release speed of the mercury depends on the original condition of the alloy. The highest values were given for filing amalgam. When investigating the composition of amalgam mainly in spherical form, a significant decrease could be here determined.     

Cytotoxicity of amalgams, alloys, and their elements and phases

The purpose of this study was to compare the relative cytotoxicity of amalgams, alloys, and their constituent elements and phases, by means of a rapid and sensitive in vitro cell culture test. Pure copper and zinc showed intensive cytotoxicity, significantly greater than that of pure silver and mercury. Pure tin was non-cytotoxic. The gamma-one phase (Ag2Hg3) revealed moderate cytotoxicity, which was significantly decreased by the addition of 1.5% and 5% Sn. However, the addition of 1.5% Zn to gamma 1 containing 1.5% Sn dramatically increased the cytotoxicity of gamma 1 to the same level as that of pure zinc. Whenever zinc was present in amalgams, higher cytotoxicity was revealed. High-copper amalgams showed the same cytotoxicity as a zinc-free low-copper amalgam. The addition of selenium did not reduce the cytotoxicity of amalgam. The cytotoxicity of amalgams was reduced after 24 h. The results of this study suggest that the major contributor to the cytotoxicity of alloy for amalgam is probably copper, while that for amalgam is zinc.     

Decrease of γ1 lattice constant with time in dental silver amalgam

Abstract— As a measure of the mercury content of the γ₁ phase in dental silver amalgam, the lattice constant of this phase in different amalgams was determined at various times after trituration. The lattice constants of amalgams prepared from alloys with a high silver content have lower values and show a steeper decline with time than amalgams with a low Ag-content. Therefore, since a higher lattice constant presumably is associated with increased mercury vapor, the mercury vapor emission from amalgams with a low Ag-content probably is greater than from amalgams with a high Ag-content, especially during the first weeks after trituration.     

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)     

Effect of admixed indium on mercury vapor release from dental amalgam

The purpose of this study was to evaluate the effect of admixed indium on the amount of mercury vapor released from dental amalgam. We made amalgam specimens according to ADA Specification Number 1. We added various amounts (0-14% by weight) of indium to the alloy powder. We also tested the commercial amalgams Dispersalloy, Valiant, and Indiloy. Specimens were held at 37 degrees C and 100% humidity. We used a Jerome Mercury Vapor Analyzer (model 411) to measure the mercury vapor released. We analyzed the data by means of ANOVA and Student-Newman-Keuls procedures. Admixed indium significantly decreased the amount of mercury vapor released from dental amalgams; the period of the greatest effect on mercury vapor released was during the setting phase of amalgam; and dental amalgams with greater than or equal to 8% admixed indium released the least amount of mercury vapor.     

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

summary 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 η'(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)).