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Marginal microhardness of corroded amalgams: a comparative in vitro study
1Department of Prosthodontics, Karolinska Institute, Stockholm, Sweden.
Scandinavian Journal of Dental Research
|August 1, 1990
Summary
High-copper dental amalgams show superior marginal microhardness retention after corrosion. Conventional amalgams experienced greater microhardness reduction due to phase degradation in corrosive sodium chloride environments.
Area of Science:
- Materials Science
- Biomaterials Engineering
- Dental Materials
Background:
- Dental amalgam is a widely used restorative material.
- Understanding its corrosion resistance and mechanical properties is crucial for long-term clinical performance.
- High-copper amalgams were developed to improve corrosion resistance and reduce marginal degradation compared to conventional amalgams.
Purpose of the Study:
- To evaluate the effect of corrosion on the marginal microhardness of conventional and high-copper dental amalgams.
- To compare the corrosion resistance of amalgams in a sodium chloride solution versus a phosphate buffer solution.
- To investigate the microstructural changes and elemental dissolution associated with corrosion.
Main Methods:
- Three dental amalgams (one conventional, two high-copper) were subjected to corrosion in 85 mM NaCl solution for 2 months.
- Control specimens were immersed in 200 mM phosphate buffer solution.
- Marginal microhardness was measured on cross-sections 50 microns from the surface.
- Microstructure was analyzed using Scanning Electron Microscopy (SEM).
- Elemental analysis (Sn, Cu, Zn, Ag, Hg) of corrosion solutions was performed using atomic absorption spectrophotometry.
Main Results:
- Corrosion in NaCl solution resulted in depths of 50-400 microns, while phosphate buffer showed no subsurface corrosion.
- Marginal microhardness decreased in all amalgams after NaCl corrosion.
- High-copper amalgams exhibited greater microhardness than conventional amalgam in both uncorroded and corroded states.
- Degradation of the gamma-2 phase (conventional) and eta' phase (high-copper) was implicated in microhardness reduction.
Conclusions:
- High-copper amalgams demonstrate superior resistance to marginal microhardness loss upon corrosion compared to conventional amalgam.
- The gamma-2 and eta' phases are critical in determining the corrosion-induced microhardness reduction in respective amalgam types.
- Sodium chloride solutions pose a significant corrosive challenge to dental amalgams, impacting their marginal integrity.