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Change in creep rate and microstructure in an aged, low-copper amalgam
Journal of Biomedical Materials Research
|July 1, 1985
Summary
Low-copper dental amalgams aged below 60°C showed reduced creep with increasing gamma-one Ag-Hg grain size. Above 60°C, phase changes significantly impacted creep behavior.
Area of Science:
- Materials Science
- Dental Materials Science
- Metallurgy
Background:
- Dental amalgams are widely used restorative materials.
- Understanding the aging behavior of low-copper amalgams is crucial for predicting their long-term performance.
- The microstructural evolution of amalgams influences their mechanical properties, including creep.
Purpose of the Study:
- To investigate the effect of aging temperature and time on the microstructure and ADA creep of low-copper amalgams.
- To determine the relationship between microstructural changes and creep behavior.
- To elucidate the phase transformations occurring during aging.
Main Methods:
- Low-copper amalgams were aged at temperatures ranging from 37°C to 80°C for 7 and 30 days.
- Scanning electron microscopy and X-ray diffractometry were employed for microstructural analysis.
- Quantitative metallography was used to determine gamma-one Ag-Hg grain size, gamma-two Sn-Hg volume fraction, and surface area.
- American Dental Association (ADA) creep was measured.
Main Results:
- Below 60°C, gamma-one (Ag-Hg) was the predominant matrix phase, with minimal beta-one (Ag-Hg) formation.
- In the temperature range of 60°C and below, both gamma-one grain size and ADA creep followed an Arrhenius law.
- A linear correlation was observed between the logarithm of mean ADA creep and mean gamma-one grain size.
- Above 60°C, gamma-one phases and gamma (Ag-Sn) particles diminished, replaced by beta-one.
- Aging above 60°C led to an increase in gamma-two (Sn-Hg) volume fraction and coarsening, indicated by reduced surface area per unit volume.
- Aging for up to 30 days generally decreased ADA creep.
- At temperatures ≤60°C, decreased creep was attributed to increased gamma-one grain size.
- Above 60°C, reduced creep resulted from multiple factors, including the formation of large beta-one grains.
Conclusions:
- The aging behavior of low-copper amalgams is highly dependent on temperature.
- Microstructural changes, particularly the grain size of gamma-one and the formation of beta-one, significantly influence ADA creep.
- The findings provide insights into the long-term stability and performance of low-copper amalgams under varying thermal conditions.