Journal of Dental Research, Vol 64, 470-475, Copyright © 1985 by International & American Associations for Dental Research Online Journals
Creep-fatigue as a possible cause of dental amalgam margin failure
P. T. Williams and G. L. Hedge
Fracture of the margins is the most common cause of failure of dental
amalgam restorations. Both corrosion and creep have been identified as
possible contributors to this type of failure. The stresses that induce
creep may arise from the continued setting expansion of the amalgam, the
formation of corrosion products, mastication, or from the thermal expansion
of the amalgam during ingestion of hot foods. The latter two are
low-frequency cyclic stresses. The amalgams used in dentistry have fusion
temperatures only about 40 degrees C above mouth temperature, and they
experience grain boundary sliding during creep deformation. Since grain
boundary sliding, low-frequency cyclic stresses, and a temperature near the
fusion temperature of the alloy are prerequisites for so-called
"creep-fatigue fracture", this type of fracture may contribute to amalgam
margin failure. Amalgam made from seven different alloys was condensed into
stainless steel dies. After being allowed to set for seven days, the
specimens were thermally cycled between 4 degrees C and 50 degrees C for
500 and 1000 cycles. Amalgam margin integrity was evaluated by scanning
electron microscopy both before and after each cycling period. The amount
of margin fracture was calculated after 1000 cycles. Thermal cycling of
amalgam restorations placed in stainless steel dies resulted in
predominantly intergranular fracturing of the amalgam margins, indicating
that creep-fatigue failure may be a significant contributor to in vivo
margin fracturing.
