Clinical evaluation of fixed partial dentures made in Sweden and China.

The aim of this study was to compare the quality of fixed partial dentures (FPDs) made in a Chinese dental laboratory with corresponding FPDs made in Swedish dental laboratories. Twenty-one patients were fitted with FPDs between March 2007 and December 2008. Single crowns and prostheses of up to seven units were made. All dentures, gold and CoCr alloys covered with ceramic, were produced in duplicate: one by a dental technician in China and the other by a dental technician in Sweden. The dentures were blind-tested with regard to marginal integrity, anatomic form and color, approximal and occlusal contacts, and time taken for adjustments. The composition of dentures was analyzed, and the material used, framework weight, compliance of the laboratories, and costs (material and labour) were recorded. There was no difference in the quality of marginal integrity, anatomic form, color, approximal and occlusal contacts, or in the time taken for adjustments. The bridge frameworks made in China were thinner and lighter (p<0.01) than those made in Sweden. Three FPDs from China showed elastic deformation when tested clinically and were considered too thin for clinical use. In 11 out of 14 orders from the Chinese laboratory, the gold alloy specified was not delivered and the cobalt-chromium alloy contained small amounts (0.19%) of nickel.The prostheses with gold-alloy frameworks from China cost 47% of those from Sweden (p<0.01) and those with cobalt/chromium frameworks 44% (p<0.01). In conclusion, the quality of the FPDs made in Sweden and China was comparable, with the exception of the dimension of the Chinese bridges, which in some cases was considered too weak. The gold alloy ordered from the Chinese laboratory was often not the alloy delivered and the CoCr alloy contained small amounts of nickel. FPDs from China cost less than half the price of those from Sweden.

In search of a gold standard.

This is a review article of relevant research to offer best-practice advice to the practitioner regarding the choice of intracoronal indirect restorative materials. The paper reviews the use of cast gold, a variety of porcelain materials and indirect composite resin materials as inlay materials. Subjects reviewed are the effects on tooth strength, the effect of bonding the material on tooth strength, stress analysis on teeth using different restorative material choice of luting material, wear of the material and its antagonist surface and clinical research outcomes and conclusions.

Metal-ceramic bridges from commercial dental laboratories: alloy composition, cost and quality of fit.

The quality of construction of fixed bridge prostheses directly affects their long-term survival. The cost, alloy composition and marginal fit of bridges made by 30 commercial dental laboratories is assessed. Duplicate models of a three unit bridge preparation were sent to 30 different laboratories, as if required for a patient receiving treatment under the General Dental Service. Material was sent via general dental practitioners, requesting metal-ceramic bridges made from 45% Au alloy, precious metal or non-precious metal. Proximal contacts were overbuilt at 65% of sites and pontic tissue contacts were excessive in all but one bridge. Eight laboratories did not use alloys corresponding to the request made. The mean marginal gaps of non-precious metal bridges (145 microns) were significantly greater than those for 45% gold alloy (106 microns). Marginal fit was poor and a number of factors have been observed, with other postulated, which may have contributed to this problem.

[Radiographic evaluation of 12% Au-Ag-Pd alloy cast lower denture plates constructed by dental student as a laboratory exercise].

We evaluated 12% Au-Ag-Pd alloy cast lower denture plates prepared by dental students in laboratory exercises for casting defects. First, we determined the most suitable exposure conditions for nondestructive radiographic test of 12% Au-Ag-Pd alloy. Subsequently, 130 plates were nondestructively evaluated by radiography under the most suitable exposure conditions. In radiographic testing using X-Omat RP films (Eastman Kodak Co.) and X-Omatic Fine Screen (Eastman Kodak Co.), the most suitable exposure conditions involved a target-to-film distance of 1.9 m, tube voltage of 148 Kvp, tube current of 10 mA, and exposure time of 1.5 sec. Preliminary radiographic examination of artificial casting defects revealed semispherical defects in the diameter of 0.25 mm in 1.6 mm-thick 12% Au-Ag-Pd alloy plates and detects of 0.26 mm in 2.4 mm thick plates. In the 130 cast plates, 56 casting defects were detected. These defects were found at the left webbing part in 40 (30.8%), right webbing part in 36 (27.7%), lingual bar in 7 (5.4%), I-bar in 4 (3.0%), and at other regions of the metal frames in 3 (2.3%) cases. These results indicate that nondestructive radiographic testing is as effective in detection of casting defects in 12% Au-Ag-Pd alloy cast plates as it is in Co-Cr and Ni-Cr alloy plates. This method was also found to be effective in evaluation of the practice metal frames constructed by dental students.

Corrosion evaluation of gold-based dental alloys.

Three commercial gold-based dental alloys and three constant-nobility ternary alloys (Au-Ag-Cu) were evaluated for corrosion using a quantitative test battery. Integration of the current density, in a de-aerated solution of 1% NaCl along the approximate potential range found in the mouth (-300 mV to +300 mV vs. SCE), yields a quantitative rank ordering of the test alloys. The results are combined with prior findings on other commercial alloys to demonstrate the interaction of nobility and microstructure. Nobility determines the overall corrosion resistance for gold-based alloys. However, because of mutual insolubility, alloying with copper induces silver segregation, resulting in a higher corrosion rate at a given nobility. Thus, microstructure has an influence on corrosion, but heat treatments are largely ineffective in altering the basic corrosion characteristics. The test techniques, in combination with tarnish evaluations, provide a quantitative battery for alloy evaluation. The results indicate the combinations of nobility, microstructure, and environment most likely to avoid corrosion difficulties.

Status report on low-gold-content alloys for fixed prostheses. Council on Dental Materials, Instruments, and Equipment.

Because of their savings in cost and comparable mechanical and handling properties, low-gold-content dental casting alloys will remain an attractive alternative to high-gold-content alloys. Certain compositions perform well in the corrosive oral environment; others do not. Accurate information on such performance is currently unavailable. Accurate prediction of tarnish and ocrrosion behavior awaits development and acceptance of reliable and valid performance tests. There is adequate evidence that not only the Ag, Cu, and Pd ratios are important for resistance to corrosion but also the addition of minor amounts of other elements may be important for adequate clinical performance.

A quantitative and subjective characterization of tarnishing in low-gold alloys.

1. The quantitative objective characterization of tarnish gave results which are identical with those obtained from a blind subjective analysis. 2. The low-gold alloys fall into three classes. The alloy Ney Cast III is superior in performance to the other low golds and approximately equivalent to the high-gold alloy Firmilay. The intermediate alloys, including Midacast, Stabilor G, Mowrey No. 46, Tiffany, and Midas are similar in performance to the high-gold alloy Rx O.R.Y. The low-gold alloys Dent Cast 44, Minigold, and Progold tarnish in a manner which, in our opinion, makes them unacceptable.

[A study of the ageing process in dental Ag-Pd-Cu-Au alloys by anisothermal annealing method (author's transl)].

The ageing processes in dental Ag-Pd-Cu-Au alloy were investigated by means of electrical resistivity measurements during anisothermal annealing. The main results obtained are as follows; (1) There are two obvious precipitation processes (stage I and stage II) during anisothermal annealing after quenching from above critical temperature. And the apparent difference in stage I attribute to solution treatment temperature. (2) Stage I occured at lower temperature, is one ageing process by the migration and annihilation of quenched-in excess vacancies. Another is stage II at higher temperature by the diffusion of equilibrium vacancies.

[Studies on Au-Ag-Pd-Cu alloys. (Part 1) Effects of Au component on some properties of alloys (author's transl)].

Au-Ag-Pd-Cu quaternary dental alloys were studied to find out the more favourable Au content. Pd and Cu content were fixed to 20 wt% respectively but Au content were changed from 10 wt% to 40 wt% and Ag content were balanced. Tensile, hardness, corrosion and castability test were carried out. Results were as follows. 1) The tensile strength and elongation of swaged specimen showed highest value at 30 wt% Au but in case of casted specimen, tensile strength was highest as 20 wt% and elongation was minimum at 30 wt% Au. Those differences between swaged and cast specimens were seemed to depend on the casting porosities. 2) The Vickers hardness test showed that the hardness gradually increased with Au content and showed the highest value at 30 wt% Au. 3) The corrosion test in the 0.1% Na2S solution indicated that the corrosion resistance was increased with Au content but the rate of increment was slow down at 30 wt% Au. 4) The castability test showed that no significant difference was found out one another. These experimental results seemed to indicate that 30 wt% Au was the favourable composition for Au-Ag-Pd-Cu dental alloys.