Surface characterization of amalgams using X-ray photoelectron spectroscopy

Area of Science:

• Materials Science
• Surface Chemistry
• Dental Materials

Background:

• Dental amalgams are widely used restorative materials.
• Understanding the surface chemistry of aged amalgams is crucial for material longevity and biocompatibility.
• Previous studies have limited insights into the thin surface films formed on aged amalgams.

Purpose of the Study:

• To investigate the composition and structure of surface films on aged amalgams using X-ray photoelectron spectroscopy (XPS).
• To quantitatively determine elemental concentrations and electron binding energies on amalgam surfaces.
• To compare the surface film composition with the bulk composition of amalgams.

Main Methods:

• X-ray photoelectron spectroscopy (XPS, also known as ESCA) was employed to analyze the surfaces of four different amalgams aged for various durations (20 min to 30 days).
• Surface films (less than 10 nm thick) were analyzed directly.
• Bulk composition was analyzed after argon-ion-sputtering to remove approximately 5 nm of surface material.

Main Results:

• XPS analysis revealed that surface films on aged zinc-containing amalgams primarily consisted of hydrated tin and zinc oxy-hydroxide.
• Zinc-free amalgams formed surface films predominantly composed of tin oxide.
• A significant depletion of mercury was observed in the thin surface films of aged amalgams.

Conclusions:

• The formation of tin and zinc oxy-hydroxide or tin oxide surface films is dependent on the presence of zinc in the amalgam.
• Preferential diffusion of tin and/or zinc to the surface, followed by oxidation, likely forms these protective layers.
• Mercury depletion in the surface film may be attributed to surface diffusion and oxidation or partial evaporation during aging.