Fatigue testing and microscopic evaluation of post and core restorations under artificial crowns

Statement of problem. Coronoradicular reconstruction techniques of pulpless teeth include prefabricated post systems that retain a core material such as silver amalgam, composite, glass ionomer, or modified glass ionomer ceme nt. Mechanical properties of these materials are critical to sustain mastic atory forces. Purpose. This in vitro study compared the mechanical resistance of 3 core m aterials (silver amalgam, composite, and silver-reinforced glass ionomer) u nder masticatory conditions. Material and methods. Industrially fabricated teeth were used and a total o f 75 specimens were divided into 3 groups of 25 specimens. Titanium canal p osts were placed, followed by core buildups in amalgam, composite, or glass ionomer. Teeth were prepared for full cast crowns and the crowns were fabr icated and cemented with glass ionomer cement. Twenty specimens from each g roup were placed in a mastication simulator cyclically loading the teeth wi th a 400 N force for 1.5 million cycles. The 5 remaining specimens were use d as controls. Teeth were sectioned and observed macroscopically and micros copically to determine the rate of defects for each material. Observed defe cts were verified with the Kruskal-Wallis test. The 3 core materials were r anked with the Tukey multiple comparison test. Results. Significant differences of mechanical behavior were found for the 3 materials. At P < .01, silver amalgam was significantly superior to compo site and glass ionomer. Composite was significantly superior to glass ionom er. Conclusion. Cores fabricated with amalgam had the lowest rate of defects wh en tested under artificial crowns. Glass ionomer, when used as a core mater ial under artificial crowns, showed the highest rate of defects after an in stantaneous load of 400 N for a 1,500,000 repetition cycle.