Corrosion of zinc-containing dental amalgam

Abstract – The γ₁ lattice constant of amalgams with and without zinc kept under corrosive and non-corrosive conditions was determined at different times after trituration. Zinc disappeared during 1 d from the γ₁ phase of an amalgam made from 0.9% Zn alloy and during 30 d from an amalgam made from 4% Zn alloy, when powdered amalgam was in contact with a 1% NaCl solution.     

Evaluation of key parameters in a potentiostatic corrosion test for dental amalgam

OBJECTIVES: Participation in a Round Robin study of potentiostatic corrosion test guidelines for dental amalgam was undertaken for the purpose of developing an accurate set of draft guidelines. METHODS: Dispersalloy, sybraloy, aristalloy, phasealloy, and tytin were used as the amalgam specimens. They were prepared following the guidelines, then coupled to a copper wire, cemented into glass tubes, and polished to a 600-grit finish. A corrosion cell was prepared using a carbon counter-electrode, a standard calomel electrode (SCE) as the reference electrode, and amalgam as the working electrode. A 37 degrees C solution of 10 g/l NaCl with a minimum volume of 300 ml was used. Within 5 min of polishing, the open circuit potential (OCP) was recorded for 10 min. Next, the specimen was polarized to 0 mV versus SCE, and the currents were recorded for a 24-h time period. Corrosion results were analyzed statistically with one-way ANOVA (p < 0.05) and the multiple comparisons Student-Newman-Keuls post-hoc test. RESULTS: Problems that occurred with evaporation, beaker size, carbon electrode length, SCE cap removal, glass tube fracture, polishing technique, and fresh electrolyte are easily avoidable with further explanation or reminder notes. Observations made concerning starting time, initial OCP recording, millivoltage, and solution temperature were determined to be necessary for the accuracy of test results. Analysis of results should include clarification of units, and graph interpretations. Finally, the number of specimens per amalgam should be increased from one to three so that statistical analysis can be performed. Using three specimens per amalgam, the method revealed corrosion susceptibility as measured by the improved test: aristalloy > sybraloy > (dispersalloy, phasealloy, tytin). SIGNIFICANCE: Having run the initially proposed guidelines, a number of clarifying changes were made so that the corrosion susceptibilities of five dental amalgams could be clearly differentiated.     

Corrosion products of dental amalgam

Abstract – Corrosion products from five amalgams with different Cu- and Zn-contents were investigated by X-ray diffraction technique. Powdered amalgam samples were treated with 1 % NaCl-solution for up to 1 month. SnO₂, ZnSn(OH)₆ and CuSn(OH)₆ were detected.     

表面粗糙度对牙科银汞合金抗折力的影响

目的比较不同表面粗糙度的牙科银汞合金试件的断裂载荷,探讨试件表面状况对脆性牙科材料抗折力的影响。方法制作直径10mm、厚2mm的圆盘形银汞试件48个．随机分成4组,其中3组分别以220、400、1200号SiC砂纸双面磨平．另一组不经打磨．表面保持试件制作完毕后的自然状态。每组随机抽取5个试件,置于粗糙度测试仪上测量表面粗糙度。试件于（23±1）。C空气中保存7d后置于30％玻璃纤维加强尼龙6．6基底上以20mm直径不锈钢球加载进行赫兹压痕试验,记录初始断裂载荷值并进行统计分析。结果未经打磨、220号、400号、1200号SiC砂纸打磨的试件的表面粗糙度平均值分别为1．77、1．99、1．28、0．66μm,断裂载荷值分别为（656．1±44．1）、（644．9±57．9）、（678.3±40．4）、（721．1±60．1）N。随着粗糙度的降低,初始断裂载荷值逐渐增加,1200号砂纸打磨组与未经打磨组和220号砂纸打磨组之间差异有统计学意义（P〈0．05）。结论脆性材料试件的表面粗糙度对其抗折能力有一定影响．     

Dutch dentists' conceptions of dental silver amalgam

Abstract A sample of 468 dentists completed a questionnaire on their conceptions of amalgam. A minority (1–3%) reported that amalgam often causes toxic, galvanic and/or allergic side-effects. A considerably larger number (10–30%) stated that such side-effects ‘sometimes’ occur, while less respondents (6–11%) said they did not know. 60–80% said that such side-effects do not exist, or rarely. If a patient requested the removal of amalgam, one-third of dentists would do so often for cosmetic or toxic reasons, but only one-fifth in the case of a proven allergy. A very substantial percentage would not remove amalgam except for cosmetic reason. Substantial minorities thought that amalgam should not be used for pregnant women or children, or admitted that they did not know. The use of amalgam was rejected by 5%, while 9% could not decide whether they were for or against its use. Multivariate analysis reveals the existence of two dimensions in the data. The first dimension, referred to as “acceptance-of-amalgam”, makes it possible to distinguish a subsample (about 9%) consisting of “rejectors-of-amalgam”. On the second dimension, referred to as “conviction”, a subsample (almost 20%) of “doubters” can be discerned, alongside “convinced adversaries” (about 4%) and “convinced advocates” (some 25%). The majority of the respondents are thought to be more or less in favour of the use of amulfljiim.     

Creep of dental amalgam as a function of heat treatment

abstract — The creep of dental amalgam was measured as a function of heat treatment of the amalgam. The treatment significantly reduced the creep rate. The β₁ (Ag-Hg) phase was detected in the heat-treated amalgam by X-ray diffraction and metallographic methods, and it appeared that the reduction in creep rate was due to the γ₁→β₁ transformation.     

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

Abstract – 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.     

三种复合树脂表面粗糙度的实验研究

目的：比较3种牙体充填材料的表面用在粗糙度。方法：抛光过程中以粗糙度测试仪分别测试3M Filtek Supreme XT、Venus、ceram XMono试件表面经0.5、1.0、1.5、2.0、2.5、3.0、3.5、4.0min抛光头抛光后的粗糙度值并进行统计学分析。结果：3种充填材料的表面粗糙度程度不等,Venus〉ceram XMono〉3M Filtek Supreme XT。结论：充填材料的表面粗糙度以3M Filtek Supreme XT为最佳。经统计分析,与其他两组充填材料相比有显著性差异。     

Phase content of a high copper dental silver amalgam

abstract – The phase content of a conventional zinc-free silver amalgam and a high copper silver amalgam has been determined by X-ray diffraction and by stoichiometric calculation. The γ2 content in the high copper amalgam is zero for low mercury contents and increases with rising mercury concentration. The γ2 content also rises with prolonged annealing of the alloy.     

The corrosion of dental amalgam in artificial salivas: an electrochemical impedance study

An electrochemical impedance study of the corrosion of Tytin dental amalgam was carried out in electrolytes similar to artificial saliva with or without lactic acid, and in standard inorganic artificial saliva with higher ionic concentration. Spectra were recorded in the presence and absence of dissolved oxygen to show the importance of the formation of oxide film and the adsorption of the organic component, as well as the exposed surface microstructure. The data, supported by open circuit potential and polarisation curve experiments, obtained in the presence and absence of dissolved oxygen are interpreted in the light of possible corrosion mechanisms.     

The environmental effects of dental amalgam

Dental amalgam is one of the most commonly used materials in restorative dentistry. However, one of its major components, mercury, is of particular concern due to its potential adverse effects on humans and the environment. In this review, the environmental impact of dental amalgam will be discussed, with particular reference to the effects attributed to its mercury component. Mercury commonly occurs in nature as sulfides and in a number of minerals. Globally, between 20,000-30,000 tons of mercury are discharged into the environment each year as a result of human activities. According to a recent German report, approximately 46 per cent of the freshly triturated amalgam is inserted as new amalgam restorations and the rest is waste. Depending on the presence of an amalgam separating unit, some of the generated amalgam-contaminated sludge is discharged into the sewage system. Lost or extracted teeth with amalgam fillings and amalgam-contaminated waste, such as trituration capsules and cotton rolls are discharged with the solid waste and, in most instances, are incinerated. Use of disinfectants containing oxidizing substances in dental aspirator kits may contribute to remobilization of mercury and its subsequent release into the environment. Nevertheless, dental mercury contamination is only a small proportion of terrestrial mercury (3-4 per cent), which is quite insignificant compared with industrial pollution and combustion of fossil fuels by vehicles. The environmental impact of dental mercury is mainly due to the poor management of dental amalgam waste. Proper collection of mercury-contaminated solid waste prevents the release of mercury vapour during combustion. In addition, the use of amalgam separating devices reduces the amount of amalgam-contaminated water released from dental clinics.     

Corrosion of dental amalgam and mercury vapor emission in vitro

Abstract – Amalgam specimens were immersed for 30 days in 1) water, 2) 0.9% NaCl in water, 3) 0.9% NaCl and 10 mM phosphate buffer in water, and 4) 0.9% NaCl, 7.7 mM phosphate, and 6.1 mM citric acid in water. The solutions were stored in stoppered glass tubes. Hg-drops were immersed in solutions 1, 2, and 3. The concentration of mercury vapor in the air above the solutions was measured once a day. After 30 days the amounts of Cu, Zn, Hg, and Ag in the solutions were analyzed by atomic absorption spectrophotometry. The results showed that 0.9% NaCl alone or in combination with the additives increased the amounts of elements released into the solutions. The concentration of Hg° in the glass tubes increased with the amount of Hg in the solutions, with the exception of solution No. 3, from which significantly less Hg° evaporated. The results indicate that the composition of the saliva, oral hygiene and dietary factors may be determinants of Hg° emission from amalgams in the oral cavity.     

Reasons for replacement of amalgam dental restorations

abstract — Recurrent caries appears to be the most frequently occurring reason for replacement of amalgam dental restorations. Recent developments of amalgam alloys have improved the clinical appearance of such fillings but the possible influence on their durability is uncertain.     

抛光和自上釉对陶瓷表面平滑度的影响

目的：比较研究抛光和自上釉这两种不同的陶瓷表面处理方法，对陶瓷表面平滑度产生的影响。方法：分别以SEM和粗糙度测试仪，对抛光组和自上釉组的试件表面进行定量测试分析。试件的制作及处理均按照临床所用的常规方法。结果：SEM观察表明抛光组的平滑度与自上釉相似。经粗糙度测试仪测得的Ra值，抛光组为0.412μm，自上釉组为0．417μg。两者比较未见显著性差异（P＞0．05），且SEM的检查与Ra值的测定具有一致性。结论：采用抛光处理可以获得与自上釉相同平滑度的陶瓷表面。     

Flow and creep of dental amalgam

The intention of the study was to assess the differences in results obtained from creep and flow measurements of dental amalgams. Flow registers deformation during setting. Creep denotes the deformation of the set amalgam. The present study did not demonstrate a correlation between flow and creep, and creep is considered a more desirable parameter to include in a standard.     

Surface roughness of acrylic resins submitted to mechanical and chemical polishing

Surface roughness is extremely important as it influences micro-organism accumulation and consequently oral health. The aim of the present study was to evaluate the influence of mechanical polishing (MP) and chemical polishing (CP) on surface roughness of four heat-cured denture base acrylic resins. Twenty sample discs were prepared for each of the following acrylic resins: Classico (CL), QC 20 (QC), Acron MC (AC) and Onda Cryl (ON). The first two are boiling cured resins and the latter two are microwave cured. After curing and deflasking, samples were ground and subdivided into two groups: MP, which received pumice slurry, chalk powder, soft brush and felt cone, at a bench vice; and CP, which received fluid specifically for chemical polisher. Surface roughness was measured using a Surf Corder SE 1700 rugosimeter. Data collected were statistically analysed by analysis of variance followed by Tukey's test. Surface roughness means in mum were: CL-MP: 0.0350; CL-CP: 0.2298; QC-MP: 0.0307; QC-CP: 0.1792; AC-MP: 0.0312; AC-CP: 0.2700; ON-MP: 0.0321; ON-CP: 0.2949. It can be concluded that MP produced significantly smoother surfaces than CP and that surface roughness because of MP was not influenced by acrylic resin type, whereas this was not true of CP.     

The effect of hydrogen peroxide concentration on metal ion release from dental amalgam

OBJECTIVES: The aim of this study was to investigate the effect of hydrogen peroxide (HP) concentration on metal ion release from dental amalgam. METHODS: Dental amalgam discs (n=25) were prepared by packing amalgam into cylindrical plastic moulds (10 mm diameter and 2 mm height). The discs were divided into five equal groups and each group was immersed in 20 ml of either 0%, 1%, 3%, 10% or 30% HP solution for 24 h at 37 degrees C. Samples were taken for metal ion release determination (Hg, Ag, Sn and Cu) using inductively coupled plasma mass spectrometry (ICP-MS). The surface roughness of each disc was measured before and after bleaching. RESULTS: The differences in concentration of metal ions released after treatment with 0% (control) and each of 1%, 3%, 10% and 30% HP were statistically significant (p<0.05). Metal ion release for the elements (Hg, Ag, Sn and Cu) increased with exposure to increasing concentrations of HP. Surface roughness measurements of the samples before and after treatments with HP solutions were not significantly different (p>0.05). CONCLUSIONS: Exposure to HP bleaching agent was associated with increased metal ion released from dental amalgams compared to treatment with a control solution. Ion release was in proportion to the peroxide concentration tested, with the highest concentration associated with the greatest metal ion release for all elements investigated.     

A case of high mercury exposure from dental amalgam

This report describes a patient who suffered from several complaints, which by herself were attributed to her amalgam fillings. Analysis of mercury in plasma and urine showed unexpectedly high concentrations. 63 and 223 nmol/l. respectively. Following removal of the amalgam fillings, the urinary excretion of mercury became gradually normalized, and her symptoms declined.     

不同抛光方法对钴铬合金铸造义齿表面粗糙度及精度的影响

目的研究不同抛光方法对钴铬合金铸造义齿表面粗糙度及精度的影响。方法(1)制作30个30mm×10mm×1.5mm钴铬合金试件,选择1组作为对照组,其余各组分别用5种方法抛光光整技术、电解、打磨、打磨后再电解、打磨后再光整,测量其表面粗糙度;(2)铸造钴铬合金基托30个,选择1组作为对照组,其余各组用5种方法抛光,在相当于上颌第二磨牙远中部位切断义齿基托与标准模型,测量基托组织面与标准模型间5个部位的间隙。用SPSS13.0软件对数据进行方差分析。结果(1)抛光前,试件表面粗糙度值最大(Ra3.38μm),手工打磨后再光整组粗糙度值最小(Ra0.19μm)。除光整组、电解组试件之间的差别无统计学意义外(P>0.05),其余各组差别均有极显著统计学意义(P<0.01)。(2)各组试件的精度值在抛光前、后无统计学差异(P>0.05)。结论手工打磨后再进行光整的铸件表面粗糙度最低,光整抛光方法对上颌铸造基托的精度无影响。     

Electrochemical potentials of amalgam restorations in vivo

Abstract The potentials of 407 amalgam restorations have been determined in vivo. The measurements were performed with very high impedance equipment, and relative to a Ag/AgCl reference electrode. The readings varied from — 23 mV to —595 mV, with 90% of the readings confined to within — 127 mV to —431 mV and a mean value of —226.1 mV. Of the restorations, 394 were measured twice, and no significant difference could be found between the first and the second reading. During the study, eight new restorations were inserted. Their potentials varied from —180 mV to —565 mV, with a mean of —339.4 mV, which was significantly lower than that of the older restorations.