Creep of Amalgam at Low Stresses

Abstract

The creep and recovery of dental amalgam were studied with a torsional creep apparatus. The purpose was to investigate viscoelastic behavior in a low stress range that might result from normal chewing forces. The creep of specimens up to six months old was also studied. Four types of alloys for amalgam were used: two single-composition sphericals (SCS), an admixture-lathe-cut eutectic (ALE), and a conventional (CON). Constant torque was applied to dumbbell-shaped specimens for three hr and, after the stress was released, recovery was followed for 50 hr. All measurements were made in water at 37 degrees C after storage of the specimens for one week in 37 degrees C water. Creep was also measured at nine intervals on specimens aged from three hr to six months. The SCS amalgams exhibited the least amount of creep, followed by the ALE amalgam. The CON amalgam had the highest creep. The SCS amalgams approached linear viscoelastic behavior in the shear stress range of 0.78-4.10 MPa at 37 degrees C. They did not exhibit steady-state (viscous) creep at stresses less than 4.10 MPa. Recovery was complete but proceeded more slowly than creep. The ALE and CON amalgams exhibited viscous creep at 1.23 MPa and higher. The steady-state creep rate depended on stress, and the stress exponent ranged from 2.3-3.5. All except the ALE amalgam showed essentially constant creep compliance when aged up to six months, once the amalgamation reaction was completed after 24 to 48 hr. The compliance of the ALE amalgam gradually decreased over the six-month period.

The effect of temperature on viscoelastic properties of glass ionomer cements and compomers

“…In principle, a torsional load will generate an axial deformation in a specimen; however, this has a nonlinear effect, which is negligible at the small torque levels used. Moreover, the method for measuring torsional angular displacement is totally insensitive to any axial deformation that may occur 31…”

The Influence of Sandblasting and Aging on Y-TZP Ceramic During Static and Dynamic Loading

“…The method used generates an axial deformation in the specimen, which is considered negligible for the torsional loads used. In addition the method is totally insensitive to axial deformations [20].…”

“…In addition the frequencies corresponding to the half of the maximum amplitude ν 1 , ν 2 and the resonance full width are calculated. These parameters are integrated in the calculation of tanδ [20].…”

Indentation Creep Behavior of a Direct-filling Silver Alternative to Amalgam

“…The creep tests performed on amalgam generally involved the deformation of the bulk specimen in compression (Her0, 1983), tension (Papadogiannis et al, 1987), and dynamic configurations (McCabe and Carrick, 1987). These tests have provided important information on the time-dependent deformation of amalgam, establishing relationships among creep, microstructure, marginal breakdown, and corrosion.…”