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Age-hardening mechanisms of dental Ag-Pd-Cu-Au alloys were investigated by means of electron microscopic observations. Hardening was due to the precipitation of the L10 type CuPd-ordered platelet in the grain interior and to the discontinuous precipitation at the grain boundary. The characteristics of age-hardening curves were determined by rates of continuous and discontinuous precipitation.

In this study 96 teeth of 12 patients were restored with either the conventional alloy Premix, the blended non-gamma 2 amalgam Dispersalloy, or one of the spherical alloys Sybraloy and Tytin. To ascertain an objective comparison of the clinical performance of these alloys, two different alloys were used in each of at least two dental arch quadrants in the same patient and consequently were placed in the same oral environment. Clinical performance of the restorations was evaluated by macrophotography and scanning electron microphotography of replicas made after placement and 2, 3, and 5 years thereafter. Standard criteria were used for the evaluation of anatomic form, surface condition, and marginal adaptation of the fillings. In addition, the filling-enamel interface was assessed from the microphotographs. The three high-copper alloys performed better clinically than the conventional alloy, and the spherical alloys had the best qualifications. In addition to visual examination and photographic evaluation of restorations, the micrometric assessment of replica photographs from the scanning electron microscope may render clinical trials of amalgam alloys measurable and less subjective.

Three groups of tensile test pieces were produced using a nickel base partial denture castin alloy and employing induction fusion in each case. The first group was produced from new metal, the second from metal which had been recast four times, and the third from new overheated metal. Samples of alloy were cut from each group and, together with a piece from an original ingot, were mounted, polished, etched, and examined under a metallurgical microscope in order to determine the nature and extent of the metallographic changes resulting from fusion and casting of the alloy.

Dynamic creep tests on specimens of dental amalgam gave a relationship between creep (epsilon), applied dynamic stress (sigma), and number of applied stress cycles (N) as epsilon = AN (m sigma + c) where A, m, and c are constants. This equation can be used to predict creep of amalgam at low levels of stress and extended times. The pattern of results produced for different types of amalgam indicates that the creep process is multifactorial in nature.

Non-noble alloys are available for use in the fabrication of cast restorations. These alloys are not necessarily designed for subsequent application of porcelain. Because they are promoted for use in place of the traditional gold alloys, significant changes in technique and armamentarium are necessary. Casting of acceptable clinical quality can be obtained, but not without additional equipment and personnel training. Obtaining casting of gold alloy quality on a routine basis may not be easily achieved. Casting into detail is possible (see Fig. 5), although greater surface roughness of the casting may be observed with the non-noble alloys. A high polish is possible (Fig. 6), however technicians and clinicians accustomed to and expert in polishing single or multiple gold alloy castings will require time and training to adjust to the somewhat more difficult and time-consuming techniques required in the polishing of non-noble alloys. Well fitting castings of the non-noble alloys require investments capable of greater thermal and/or hygroscopic expansion. The solidification shrinkage in non-noble alloys is greater than that of gold alloys. The clinician may find casting of these alloys to be "tight-fitting" on insertion. At present, because additional time and armamentarioum may be required, laboratory fees for the non-noble metal casting may not be any more economical than those of cast gold alloys. Therefore, the clinician and patient may benefit little with regard to reduced fees for restorations constructed of these alloys. In conclusion, the non-noble metals may find increased use in fixed restorative dentistry as expertise develops to the level at which usage of these products becomes routine. These is still considerable clinical information needed as to the durability and corrosion resistance of these alloys. Some work has been work has been done on the corrosion of these alloys, but much data remains to be obtained. Soldering these alloys is difficult and requires training of the technician in the required usage of special solders. The following facts should be considered in casting and finishing non-noble alloys for single and multiple unit casting in dentistry. 1. Silicate or phosphate bonding investments are required. 2. Recognition of proper casting appearance of the molten alloy is essential. 3. Additional armamentarium is required to obtain casting temperatures necessary. 4. Polishing procedures are more laborious and require harder abrasives. 5...

The biocompatibility of three commercial copper-based dental casting alloys--Duracast MS, Goldent, and Trindium--three experimental copper alloys, and a control gold alloy, Modulay, were investigated. Trindium, Duracast MS, experimental alloys 1 and 2 are aluminum bronzes; Goldent is a hybrid aluminum-brass alloy; and experimental alloy #3 is a high zinc brass alloy. ASTM F813-83 Standard Practice for Direct Contact Cell Culture Evaluation of Materials for Medical Devices, a 3-day direct-contact cell culture regimen and atomic absorption spectroscopy were utilized for evaluating the biocompatibility of these alloys in both Waymouth's and RPMI 1640 complete media. Cellular proliferation assays, using 3H-thymidine uptake, were also conducted in Waymouth's media. In this investigation, only the experimental alloy #3 elicited alterations in morphology and viability of the fibroblast monolayer during the ASTM and 3-day culture tests in either media. Cell cultures exposed to experimental alloy #3 experienced copper concentrations greater than 16.0 ppm in Waymouth's and 10 ppm copper in RPMI 1640 media. Differences in the size of the cytotoxic zone around experimental alloy #3 were also observed, with the larger zone occurring in Waymouth's media. In contrast to the direct cell contact studies, all alloys caused decreases in 3H-thymidine uptake in Waymouth's media at much reduced metal ion concentrations as compared to the controls. Thus, adverse changes in DNA synthesis occurred at much lower copper and zinc concentrations than changes in morphology and viability. Consequently, the assessment of biocompatibility is dependent on the parameters evaluated, and several parameters must be analyzed before a material may be considered biocompatible.

Twelve patients with oral lichen planus (OLP) suspected of dental restorative metal allergy were examined. All patients were patch tested with several metals including six different mercury compounds. One (8%) patient showed a positive patch test to two mercury compounds whereas no mercury allergy was found in a reference group of 17 patients suspected of dental restorative material allergy but without OLP lesions. The mercury allergic OLP patient was further tested on palatal mucosa but no reactions developed. Moreover, the energy dispersive X-ray microanalysis failed to show any contaminating metals in his OLP lesion. Mucosal biopsies were taken in close contact with amalgam fillings from nine OLP patients but these disclosed no evidence of lichenoid or dysplastic alterations. In OLP lesions, the immunofluorescence findings showed fibrinogen deposition, altered basement membrane and elastic fiber staining and intense Ulex europeaus I lectin fluorescence through all epithelial cell layers. Therefore, the present patch tests did not reveal increased frequency of mercury or other metal allergy in OLP patients and the mucosal biopsies failed to show any histologic or immunofluorescence alterations deviating from idiopathic OLP lesions.

Secondary caries formation around restorations is a major cause for their replacement. This in vitro study assessed the capacity of various restorative materials to to resist caries attack. An acidified gel technique was used to produce carieslike lesions around the restored teeth. Assessment of the occurrence and extension of carious lesions was performed using polarized light microscopy. The results showed wide variations in the ability of the restorative materials to resist erosion.

Investigation of dissolution of base metal dental casting alloy constituents in aqueous solutions revealed an unexpectedly high level of beryllium as compared with the other constituents. Analysis of atomic emission spectroscopy is presented here showing the outer surface (0-100 A) is decidedly enriched in beryllium as compared with the bulk composition of the alloy. This localization is consistent in all samples and forms of the alloy tested.

General formulas for wire properties have been derived. These enable comparisons among conventional orthodontic alloys and latest archwire materials. For six common archwire sizes, physical property considerations indicate that Ni-Ti makes the most active "leveling" archwire, the B-Ti is a superior intermediate archwire where flexibility is required, and that S.S. and Co-Cr are the wires of choice for finishing and other applications where stability of form is required. These conclusions are based on the current understanding of equivalent force systems and the mechanical properties of each general classification. Whether these wires or some others are used in future patient care will depend on an uncertain and gloomy economic forecast. The present viewpoint is that the greatest needs are the formulation of empirical equations that better describe the action of triple-stranded archwire in bending and more accurate physical property data for all wires in both the tensile and the torsional states. Such additional information could be very useful to the practitioner in choosing the optimal archwire under changing conditions of cost and availability.

Substitution of gold in part for silver in Ag3Sn alloys is found to result in two separate phases: gamma (Ag3Sn particles) grains with a uniform distribution of gold within the grain and an Au-Sn phase in a form of ring surrounding the gamma grain. The thickness of this ring increases with increasing gold concentration. The phases were identified by using the techniques of x-ray diffraction, optical metallography, scanning electron microscopy, and x-ray energy dispersive spectroscopy.

Nickel-chromium alloy-ceramic couples used in this study exhibited Cr, Ni-Cr, and Ti-Cr interactions with bonding agent-ceramic complexes. Bonding agents may broaden or suppress the width of interaction zones. Metal oxides such as NiO, Cr2O3, or more complex forms such as TiO-Cr2O3 and NiCr2O4 may play a prominent role in controlling ceramic-metal adherence.