The effect of using recast metal on the bond between porcelain and a gold-palladium alloy

Evaluation of the Effect of recasting Nickel-chromium Base Metal Alloy on the Metal-ceramic Bond Strength: An in vitro Study

AIM

The aim of this study was to evaluate the effect of recasting base metal alloy on the metal-ceramic bond strength.

MATERIALS AND METHODS

A total of 60 test samples were prepared from new and recast nickel-chromium alloy and divided into six groups. In group A0, test samples were prepared from 100% new alloy. Groups A1, A2, A3, A4, and A5 were prepared from 50% new alloy and 50% casting remnants (sprue and buttons) of the previous group by weight. All these samples were coated with ceramic (IPS d.SIGN and Ivoclar-Vivadent), and samples were then subjected to three-point bending test to evaluate metal-ceramic bond strength.

RESULTS

The values were analyzed using one-way analysis of variance and Tukey's post hoc test. The mean bond strength of group A0 was higher than that of groups A1, A2, A3, A4, and A5.

CONCLUSION

Metal-ceramic bond strength decreased significantly with multiple recastings.

CLINICAL SIGNIFICANCE

Bond strength between metal and ceramic is a crucial factor for the clinical performance of metal-ceramic restorations. Recasting of alloys may affect the metal oxide layer composition and thickness of metal-ceramic interface, and thereby the metal-ceramic bond.

Influence of recasting different types of dental alloys on gingival fibroblast cytotoxicity

STATEMENT OF PROBLEM

Surplus alloy from the initial casting is commonly reused with the addition of new alloy. This recasting procedure could affect the cytotoxicity of dental alloys.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of repeated casting of high-noble and base metal alloys on gingival fibroblast cytotoxicity.

MATERIAL AND METHODS

Disk-shaped specimens (5 × 2 mm, n=60) of a high-noble (Au-Pt) and 2 base metal (Ni-Cr and Cr-Co, n=20) alloys were prepared with 100% new alloy and 50%, 65%, and 100% once recast alloy. The elemental composition of specimens was analyzed with X-ray energy-dispersive spectroscopy. Five specimens from each group were conditioned in saline with 3% fetal bovine serum albumin. The conditioning media were analyzed for elemental release with atomic absorption spectroscopy. Cytotoxic effects were assessed on human gingival fibroblast with a 3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyl tetrazolium bromide (MTT) colorimetric assay. The data were analyzed with 1-way and 2-way ANOVA and Tukey's HSD multiple comparison test (α-=.05).

RESULTS

Elemental compositions of Co-Cr and Au-Pt alloys were significantly different among casting protocols. Elemental release of Co-Cr and Ni-Cr alloys was significantly different between new and recast specimens (P<.001). Nickel release increased with recast alloy addition. The 2-way ANOVA showed a significant effect of the casting procedure (P<.001) alloy group (P<.001) and their interaction for cytotoxicity (P<.001). The Ni-Cr alloy groups with 65% and 100% recast alloy had lower cellular activity than all other specimens (P<.001).

CONCLUSIONS

The results of this study indicated that alloys containing nickel have increased cytotoxic effects and that composition of the alloys affected the cytotoxicity. Furthermore, recasting nickel-containing alloys with 65% surplus metal addition significantly increased the cytotoxic activity.

Metal ceramic bond after multiple castings of base metal alloy

STATEMENT OF PROBLEM

Remelting previously cast metal can produce a critical change in metal-oxide composition at the dental alloy surface.

PURPOSE

The purpose of this study was to evaluate the effect of multiple castings on bonding of a single selected base metal and a dental ceramic, and to compare results from shear bond and 3-point-bending tests.

MATERIAL AND METHODS

Three groups of dental alloy (Remanium CSe) were prepared by mixing 50% fresh alloy to alloy remnants from previous castings. The specimens in the first casting group used 100% fresh alloy and served as control (C0). The second group consisted of equal amounts of fresh alloy and alloy remnants cast only once (C1). The third and fourth groups contained 50% fresh alloy and alloy cast twice (C2) and 3 times (C3), respectively. The bond load (N) between alloy and dental porcelain (VMK 95 Metal Ceramic) was evaluated, using shear bond and 3-point bending tests. The fracture surfaces of the specimens subjected to testing were analyzed using a stereomicroscope and scanning electron microscope. One-way ANOVA followed by the Tukey multiple comparison test was used for analysis of bond data (alpha=.01).

RESULTS

The mean shear bond load (SD) of C0 (738.0 (77.1) N) was significantly higher than that of C1 (577.8(139.4) N), C2 (494.8 (77.6) N), and C3 (480.5 (60.9) N). Mean peak load for the 3-point-bending test of specimens cast from C0 (39.8 (1.79) N) was significantly higher than for other groups (P<.01). No significant difference was found between C1 (24.4 (5.60) N), C2 (23.2 (4.03) N), and C3 (22.8 (1.79) N) in terms of the shear bond test and the 3-point bending test.

CONCLUSIONS

In general, there was agreement between the 2 bond strength tests to indicate that including re cast base alloy with fresh alloy for metal decreases metal-to-ceramic bond strengths. (J Prosthet Dent 2009;102:165-171)

Influence of recasting palladium-silver alloy on the fit of crowns with different marginal configurations

STATEMENT OF PROBLEM

Dental laboratories may occasionally recast previously cast dental alloy to produce a prosthesis, but this process may have a negative influence on marginal adaptation.

PURPOSE

The aim of this study was to evaluate the cervical and internal fit of complete metal crowns that were cast and recast using palladium-silver alloy and 3 different marginal configurations: straight shoulder, 20-degree bevel shoulder, and 45-degree chamfer.

MATERIAL AND METHODS

Thirty aluminum dies were made, 10 for each marginal configuration. Each group of 10 was further divided into 2 subgroups (n=5), according to the alloy (Pors-on 4) casting history. The dies were waxed using a cylindrical metal matrix to standardize the thickness of the walls. The wax patterns were invested in a phosphate-bonded investment (Deguvest) and cast after heating in an oven (EDG), according to the manufacturer's instruction. The alloy was melted with an oxygen-gas heat source and cooled to room temperature after casting. Afterwards, the specimens were seated on the dies with a static load of 9 kgf for 1 minute. The marginal discrepancy was measured with a metric microscope, using a digital micrometer. All the measurements were done by the same operator. Each crown-die interface was measured 3 times on each of the 4 diametrically opposite points, for a total of 12 measurements for each specimen. Specimens were longitudinally sectioned to obtain 2 hemi-sections for internal discrepancy measurements, measured at 3 points: 1 in the center of the occlusal wall and 2 at each center of each axial wall. Three measurements were made for each point, for a total of 9 measurements per specimen. The results were submitted to parametric statistical 3-way analysis of variance followed by Tukey-Kramer HSD post hoc analysis (alpha=.05).

RESULTS

The new alloy provided significantly better adaptation (P<.001) than the recast alloy for both marginal and internal discrepancy measurements. Marginal designs did not shown any statistical differences when the new metal was used. For recast metal, the straight shoulder showed significantly better adaptation (P<.001) than the 20-degree bevel shoulder and the 45-degree chamfered configurations, which were statistically similar to each other.

CONCLUSION

The results of this study suggest that recasting procedures for crown fabrication should not be used with the palladium-silver alloy tested.

Compositional stability and marginal accuracy of complete cast crowns made with as-received and recast type III gold alloy

STATEMENT OF PROBLEM

The effect of combining new and recast metal on the compositional stability of the alloy used and accuracy of the final restoration is not known.

PURPOSE

This study characterized the elemental compositional stability of as-received and recast type III gold alloy. The effect of combining these alloys on the marginal accuracy of complete cast crowns also was evaluated.

MATERIAL AND METHODS

Sixty standardized type III gold alloy complete crowns were made on epoxy resin dies duplicated from a metal master die with conventional laboratory techniques. Three casting protocols (n = 20 each) were established in relation to the proportion of as-received and recast gold alloys: Group A (100% as-received metal), Group B (50% wt new metal, 50% wt once recast metal), and Group C (100% once recast metal). An elemental analysis was performed at 3 sites along the cast crown (cervical, middle, and occlusal) with x-ray energy-dispersive spectroscopy. Marginal accuracy was measured with a microscope before and after cementation. Results were subjected to 1-way analysis of variance followed by the Ryan-Einot-Gabriel-Welsch multiple-range test at a 1% level of significance.

RESULTS

Elemental composition was significantly different among the casting groups (P<.001). The mean weight percentage values were 72.4% to 75.7% Au, 4.5% to 7.0% Pd, 10.7% to 11.1% Ag, 7.8% to 8.4% Cu, and 1.0% to 1.4% Zn. Statistically but not clinically significant differences also were found for marginal accuracy. The marginal discrepancy was less than 25 microm for all casting conditions, with the lowest value recorded for Group A (7 microm), the highest for Group C (12 microm), and an intermediate value for Group B (9 microm) specimens.

CONCLUSION

Recasting type III gold alloys may adversely affect the marginal accuracy of complete cast crowns. In this study, however, such effects were not clinically significant.

Effects of dental laboratory processing variables and in vitro testing medium on the porcelain adherence of high-palladium casting alloys

PURPOSE

This study assessed the effects of dental laboratory processing variables and testing medium on porcelain adherence of representative high-palladium alloys.

MATERIAL AND METHODS

The processing variables were recasting two and three times, porcelain stripping with hydrofluoric acid and rebuilding, and changing the recommended oxidation procedures. The testing medium was air for these four groups and the nontreatment group. In the last group, the specimens were stored and tested in artificial saliva. The metal ceramic specimens were fractured with biaxial flexure in constant strain. The area fraction of adherent porcelain (%) was calculated with a standardized spectrometric technique. A gold-palladium alloy served as the control.

RESULTS

Recasting without adding new alloy negatively affected some high-palladium alloys. Porcelain stripping did not cause a decrease in adherence of the tested alloys. The alternate oxidation treatment reduced significantly the porcelain adherence of the Au-Pd and one Pd-Cu-Ga alloy. Storage and testing in artificial saliva did not significantly affect the porcelain adherence of the alloys. The Au-Pd alloy exhibited the highest porcelain adherence.

Reuse of silver-palladium ceramic metal

The effect of various percentages of reused silver-palladium alloy on the bond strength of porcelain was considered. All-new metal and once-cast alloy with the addition of 50% new metal produced the highest bond values. Once-cast alloy with less than 50% new metal produced bond strength values that were significantly lower. When using this silver-palladium alloy, 50% new alloy should be added to each casting button, and buttons with questionable casting history should not be used.