Compressive stress-strain behaviour of cast dental restorations in relation to luting cement distribution

This work is concerned with the performance, under dynamic compression, of the adhesives used to simulate cementation of gold crowns onto nickel chromium dies. A measurement system, based on the mounting of strain gauges onto the outer surface of the crowns, has been developed, which allows a semi-quantitative estimate of the state of adhesion. A preliminary study was carried out where miniature gauges were bonded onto the buccal, lingual, mesial and distal surfaces of gold crowns cast to fit onto a chromium-cobalt die, as a precursor to the final design of the instrumented crown. The crowns were then loaded in compression periodically measuring the strain at all four gauges. The results showed the load-strain relationship in fully, partially and uncemented crowns, along with repeated load-unload behaviour to close to the ultimate strength of the bond. The load-strain relationship is linear and repeatable and the slope varies over a factor of about 30 between the un-cemented and fully cemented crown, demonstrating that there is significant sensitivity to bond integrity. These results were used to determine the parameters for a systematic study of S-N relationships in restorative dentistry crowns.