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

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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.

Section snippets

Material and Methods

To compare the cytotoxic effects of surplus metal addition to base and high-noble alloys, Ni-Cr, Co-Cr, and Au-Pt alloys were selected. Manufacturers and composition of the metal alloys used are shown in Table I. Sixty disk-shaped (5 × 2 mm) wax specimens (Thowax Sculpturing Wax; Yeti Dentalprodukte GmbH, Engen, Germany) were prepared. Preparation of sprues, investment, burnout, and castings were done according to the manufacturer's instructions. The base-metal alloys (Co-Cr and Ni-Cr) were

Results

The first aim of this study was to examine the effect of adding various amounts of surplus alloy to Co-Cr, Ni-Cr, and Au-Pt alloys on the metabolic activity of HGF cells. Table II summarizes the results of the 2-way ANOVA, which showed that the effects of alloy type on MTT activity depend on the amount of recast alloy addition (P<.001). Significant results were observed for alloy groups (P<.001) and casting procedures (P<.001), indicating that both alloy type and amount of recast alloy addition

Discussion

Because of improved mechanical properties and lower cost, Co-Cr and Ni-Cr base metal alloys have increasingly replaced gold alloys in the fabrication of fixed metal ceramic restorations. In addition, many dental laboratories combine previously cast metal with new alloy for financial reasons. These casting procedures change the chemical composition, microstructure, physical properties, and cytotoxicity of the alloys.9, 55, 56 The results of this study demonstrated that extract solutions from all

Conclusions

Within the limitations of this study, casting procedures decreased the cobalt content (P=.021) and increased the chromium content (P=.048) of Co-Cr alloys. The increased indium content (P<.001) of Au-Pt alloys did not affect the composition of Ni-Cr alloys. However, recast Ni-Cr alloys released higher amounts of nickel than the NA-100 group (P<.001). The cytotoxic ranking of tested alloys was Ni-Cr>Au-Pt>Cr-Co. Adding recast alloy negatively influenced the cellular activity of all tested alloys

Acknowledgments

The authors acknowledge the Research Commission of Baskent University School of Medicine for funding this research and Prof. Ismail Ercan, the director of the Ankara Nuclear Research and Education Center, for permission to perform the spectrophotometric analysis.

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