反复熔铸对牙科烤瓷合金显微结构的影响

目的: 探讨反复熔铸对钴铬、纯钛、钯铜镓、金铂烤瓷合金显微结构的影响。方法: 在真空加氩气保护环境下,将4种烤瓷合金单纯反复熔铸1~3次。每次再熔铸前,烤瓷合金均经过课题组前期研究所得“烤瓷合金再熔铸前最佳处理方法”处理,根据金属显微组织检验方法（GB/T13298-2015）,分别对熔铸前、熔铸1~3次后的烤瓷合金进行研磨、抛光、浸蚀,采用金相显微镜或扫描电镜检测金相显微结构。结果: 随着熔铸次数增加,钴铬烤瓷合金晶粒粗化、晶粒间基质和晶界间化合物增多。纯钛烤瓷合金随熔铸次数增加,晶粒粗化明显。2次熔铸后,晶粒有等轴化倾向,3次熔铸则出现针刺状β相。钯铜镓烤瓷合金在2、3次熔铸后,晶粒结构略有长大。金铂烤瓷合金晶粒结构未随熔铸次数发生明显改变。结论: 反复熔铸显著改变钴铬、纯钛、钯铜镓烤瓷合金的显微结构,建议由厂家回收再利用烤瓷合金废旧料。     

The effect of pH on the corrosion of dental metal alloys

The aim of this study was to determine the effects of the oral environment's pH on the corrosion of dental metals and alloys that have different compositions, using electrochemical methods. The corrosion rates and the cathodic Tafel slopes were obtained from the current-potential curves. The effect of pH on the corrosion of dental metals and alloys was dependent on their composition. Dissolution of the ions occurred in all of the tested pH states. The dissolution was moderately low for samples containing titanium because its surface was covered with a protective layer, whereas the dissolution was maximal for the samples containing tin and copper. Addition of cobalt and molybdenum to the alloys improved their corrosion resistance; these cobalt and molybdenum alloys were not effected by changes in the pH. Dissolution of the precious metal alloys increased as the percentage of noble metals increased. The corrosion characteristics of dental metals and alloys are important because the corrosion tendencies of dental alloys in the mouth may cause health hazards, weakening and the aesthetic loss of dental restorations.     

The effect of repeated porcelain firings on corrosion resistance of different dental alloys

PURPOSE

The aim of this study was to evaluate the effects of repeated porcelain firing process on the corrosion rates of the dental alloys.

MATERIALS AND METHODS

Cr-Co, Cr-Ni and Pd-Ag alloys were used for this study. Each metal supported porcelain consisted of 30 specimens of 10 for 7, 9 and 11 firing each. Disc-shaped specimens 10 mm diameter and 3 mm thickness were formed by melting alloys with a propane-oxygen flame and casted with a centrifuge casting machine and then with the porcelain veneer fired onto the metal alloys. Corrosion tests were performed in quintuplicate for each alloy (after repeated porcelain firing) in Fusayama artificial saliva solution (pH = 5) in a low thermal-expansion borosilicate glass cell. Tamhane and Sheffe test was used to compare corrosion differences in the results after repeated firings and among 7, 9 and 11 firing for each alloy. The probability level for statistical significance was set at α=0.05.

RESULTS

The corrosion resistance was higher (30 mV), in case of 7 times firing (Commercial). On the other hand, it was lower in case of 11 times firing (5 mV) (P<.05).

CONCLUSION

Repeated firings decreased corrosion resistance of Pd-Ag, Cr-Co and Cr-Ni alloys. The Pd-Ag alloy exhibited little corrosion in in vitro tests. The Cr-Ni alloy exhibited higher corrosion resistance than Cr-Co alloys in in vitro tests.     

不同氟浓度人工唾液对3种牙用铸造合金表面形貌的影响

目的研究钴铬合金、纯钛及高钴铬钼合金浸泡于不同氟浓度人工唾液发生腐蚀后表面形貌的改变,分析金属的耐腐蚀性。方法将3种金属试件打磨后浸泡于不同氟浓度（0%、0.05%、0.2%）人工唾液中,（37.0±1.0）℃浸泡3周,测量浸泡前后表面粗糙度并观察表面形貌。结果浸泡后金属表面粗糙度随氟浓度升高而增加。在含氟0.05%人工唾液中浸泡后,钴铬合金和纯钛的表面粗糙度与其浸泡前相比差异有统计学意义（P<0.01）;钴铬合金、纯钛与高钴铬钼合金相比差异有统计学意义（P<0.01）;在含氟0.2%人工唾液中浸泡后,3种金属的表面粗糙度较浸泡前差异均有统计学意义（P<0.01）,3种金属间相比较差异均有统计学意义（P<0.01）。结论常使用含氟制品的患者不宜选用纯钛及钴铬合金修复体。口内有这3种金属的患者,不宜长时间使用高氟制品。     

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

summary  There are concerns that tooth bleaching agents may adversely affect dental materials. The aim of this study was to test the hypothesis that increasing concentrations of hydrogen peroxide (HP) are more effective than water at increasing metal ion release from two typical dental casting alloys during bleaching. Discs ( n  =   28 for each alloy) were prepared by casting and heat treated to simulate a typical porcelain-firing cycle. Discs ( n  =   7) of each alloy were immersed in either 0%, 3%, 10% or 30% (w/v) HP solutions for 24 h at 37 °C. Samples were taken for metal ion release determination using inductively coupled plasma-mass spectrometry and the data analysed using a two-way anova followed by a one-way anova . The surface roughness of each disc was measured using a Talysurf contact profilometer before and after bleaching and the data analysed using a paired t -test. With the exception of gold, the differences in metal ion concentration after treatment with 0% (control) and each of 3%, 10% and 30% HP (w/v) were statistically significant ( P  <   0·05). Metal ion release from the two alloys increased with increasing HP concentrations (over 3000% increase in Ni and 1400% increase in Pd ions were recorded when HP concentration increased from 0% to 30%). Surface roughness values of the samples before and after bleaching were not significantly different ( P  > 0·05) Exposure of the two dental casting alloys to HP solutions increased metal ion release of all the elements except gold.     

The effect of abrasion on corrosion of dental Co-Cr alloys. An in vitro study

The effect of abrasion on corrosion of two dental Co-Cr alloys was investigated in vitro. The metals were abraded with a toothbrush and with a piece of tooth enamel. Changes in corrosion potentials and metal release due to the abrasion were measured. Abrasion by tooth enamel caused a persistent drop in corrosion potentials. The release of both chromium and, in particular, cobalt was higher than during brushing. The two alloys tested did not significantly differ with regard to mode and rate of corrosion. It was demonstrated that the corrosion behavior of electrochemically passive dental alloys was affected by abrasion of a magnitude normally encountered during clinical service.     

固定义齿修复材料对MRI图像的影响

目的分析不同口腔固定修复合金材料在MRI图像上产生伪影的大小。方法选择目前临床口腔固定修复最常用的贵金属和非贵金属作为实验材料，通过动物实验的方法对它们在MRI图像上产生伪影的大小作分析。结果不同的金属、同类金属不同的成分在MRI图像上产生的伪影大小不同；镍铬合金产生的伪影面积大，镍含量的差异可能对伪影范围的大小起主要作用；金合金对MRI图像几乎没有影响。结论镍铬合金对MRI有明显影响，金合金对MRI的影响小。     

The burnishability of dental casting alloys.

1. A comparison of Table I with Table IV indicates that all the gold alloys have considerably lower burnishability numbers than are indicated by ADA specification No. 5 for the softened condition. In fact, they are even more burnishable in the hardened condition than specified for Type II alloys. 2. A comparison of Table III with Tables I and II indicates that one of the major advantages of ADA gold alloys is their ease of burnishing. 3. A comparison of Tables III and IV indicates that three of the new alloys (Paliney CB, Albacast, and Alborium) do not meet the burnishability number established from ADA specifications for Type III gold alloys in the softened condition. Moreover, three alloys (Forticast, WLW, and Auralite) probably will require softening heat treatments since their values for conditions of as-cast or hardening heat treatment are much higher than ADA specifications allow for gold alloys. All of these alloys are expected to be either impossible or difficult to burnish in the as-cast state.     

The phenotypic characterization of lymphocyte subpopulations in established human periodontal disease

Phenotypic characterization of lymphoid cell subpopulations in the lesionof established chronic inflammatory periodontal disease in man was carried out using indirect immunofluorescence to dectct the presence of human thymocyte antigen, human myeloid antigen, IgG-and IgM-bearing cells in situ in the lesion. The majority of lymphiod cells were IgM-positive T-cells were found. These results suggest that established chronic infalmmatory periodontal disease in man should be considered as a B-cell lesion. The role of the T-cells in the lesion May be primarily one of helper activity, although cell-mediated immune mechanisms cannot be precluded.     

The safety of nickel containing dental alloys

Nickel is a constituent of many dental alloys. This paper reviews mainly papers published after 1985 with regards to biological reactions to nickel in dentistry. Nickel is an allergen, but there is no evidence that individual patients are at a significant risk of developing sensitivity solely due to contact with nickel-containing dental appliances and restorations. Hypersensitivity reactions to nickel are only likely to occur with prior sensitization from non-dental contacts and even these are rare. Clinical evidence has been presented to show that small doses of nickel, e.g. from dental appliances, may induce tolerance to this allergen. The papers reviewed report low rates of release of nickel from dental alloys. Some nickel compounds, which are mildly cytotoxic, have been implicated as carcinogens by inhalation in industrial settings, but these compounds are not present in dentistry-related operations, including dental technology procedures. Nickel-containing alloys and compounds have not been associated with increased cancer risk by oral or dermal routes of exposure. It is concluded that, subject to use according to established techniques, nickel-containing dental alloys do not pose a risk to patients or members of the dental team.     

The clinical acceptance of dental nickel-chrome alloys

Replacing gold alloys by non-precious ones could save more than 500 million DM per year in German dentistry. However, there are many technical and biological considerations which have to be resolved in evaluating the clinical suitability of non-precious metal alloys. Techniques (e.g. investing, casting, porcelain application) and materials, developed over decades for processing gold alloys, have to be modified in order to achieve complete, sound castings, showing accurate fit and good ceramic-metal bonding. During the 5 years of our clinical studies, no case of localized or generalized tissue reaction due to Ni-Cr alloys was found. The five patients known to suffer from nickel allergy did not show any reaction to Ni-Cr test plates. Although several Ni-Cr alloys are routinely and successfully used in our clinic for single crowns and small bridges as well as for appliances used in complete oral rehabilitation, it should not be assumed that all Ni-Cr based alloys commercially available are equally suitable. There are two main reasons for this: (1) The Ni-Cr alloys comprise a large group; individual alloys exhibit greatly varied composition, microstructure, physical properties and corrosion behaviour. (2) Standards (specifications) by which non-precious metal alloys could be tested, with special regard to their biocompatibility, are lacking. Empirically, some Ni-Cr alloys have turned out to be useful in prosthodontics but further progress will depend upon the development of suitable standards. These are needed urgently.     

The effect of dental restorative materials on dental biofilm

To investigate the arrangement of biofilms formed in vivo, volunteers wore splints with slabs of six different dental materials inserted to collect smooth surface plaque. After 5 d of undisturbed plaque accumulation, the specimens were vital stained and analyzed by the confocal laser scanning microscopy (CLSM) to evaluate the percentage of vital biofilm microflora (VF percentage). Further parameters were the area of the specimens covered by plaque (surface coating; SC, %) and the height of the biofilms (BH, pm). The metals amalgam and gold, the compomer, as well as the glass-ionomer cement harboured an almost entirely dead biofilm (VF <8%). Resin composite led to vitality values between 4 and 21%, while a very thin biofilm on ceramic revealed the highest vitality values (34-86%). SC varied from 6% on glass-ionomer cement to 100% on amalgam. BH reached its highest value on amalgam and gold of 17 and 11 microm, respectively, while heights of between 1 and 6 microm were found on the ceramic, resin composite, compomer and the glass-ionomer cement. Within their limits, the present findings indicate that amalgam, gold, compomer and glass-ionomer cement exert an influence against the adhering biofilm. No general relationship could be established between the different parameters VF percentage, SC percentage and BH (microm).     

3种临床常用烤瓷合金对小鼠成纤维细胞L929的毒性评价

目的:评价3种临床常用牙科烤瓷合金材料的细胞毒性.方法:采用一种能快速评定细胞增殖率和细胞毒性的CCK-8比色法,检测镍铬合金(Ni,77.36%)、钴铬合金(Co,61.0%)、金合金(Au,58.0%)等3种烤瓷合金材料对小鼠成纤维细胞L929相对增殖率的影响;应用单细胞凝胶电泳(彗星电泳),检测3种烤瓷合金材料对小鼠成纤维细胞L929 DNA的损伤情况.采用SAS9.0软件包对数据进行统计学分析.结果:镍铬合金组、钴铬合金组和金合金组细胞的相对增殖率分别为(75.9510±7.6244)%、(84.8920±8.2660)%和(88.5420±12.3611)%.镍铬合金组的细胞毒性显著高于钴铬合金组(P＜0.05)和金合金组(P＜0.05),而钴铬合金组与金合金组之间无显著差异(P＞0.05),但3种材料的细胞毒性分级均为1级,表现为轻微毒性;镍铬合金组DNA损伤程度的彗星数目显著高于钴铬合金组(P＜0.05)和金合金组(P＜0.05).而钴铬合金组与金合金组无显著差异(P＞0.05).结论:钴铬烤瓷合金材料的细胞毒性显著低于镍铬烤瓷合金材料,而与58%金烤瓷合金材料的细胞毒性接近.临床上应尽可能选择钴铬烤瓷合金或58%金烤瓷合金等细胞毒性较低的烤瓷合金材料.     

H2O2对镍铬合金电化学腐蚀性能及离子析出的影响

目的:比较不同浓度H2O2对镍铬合金电化学腐蚀性能及离子析出的影响。方法:应用电化学工作站的电化学阻抗谱法和动电位极化曲线法,对不同浓度H2O2浸泡112 h后的牙科镍铬合金在人工唾液中的腐蚀行为进行比较,并用电感耦合等离子体质谱仪检测电化学腐蚀后人工唾液介质中析出的金属离子浓度。采用SPSS 13.0软件包对数据进行方差分析。结果:0%H2O2浸泡112 h后,镍铬合金在人工唾液中等效电路极化电阻Rct、腐蚀电位Ecorr、点蚀击穿电位Eb以及代表合金表面的"伪钝化"的△E(Ecorr与Eb之差)最大,而30%H2O2浸泡112 h后,镍铬合金在人工唾液中的Rct、Ecorr、Eb以及△E最小,不同浓度H2O2浸泡后镍铬合金耐腐蚀性能顺序为30%<10%<0%(P<0.05);镍铬合金在人工唾液介质中析出的金属离子Ni、Cr、Mo浓度大小顺序为0%<10%<30%(P<0.05)。结论:镍铬合金在不同浓度H2O2中浸泡112 h后,其在人工唾液中的耐腐蚀性能发生了一定变化,随着H2O2浓度的升高,越来越容易腐蚀,且人工唾液介质中析出的金属离子浓度也越来越高。