How does the piston material affect the in vitro mechanical behavior of dental ceramics?

Statement of problem: Variables involving the indication, manufacturing, and clinical use of ceramic restorations make the standardization of in vitro studies a challenge and raise questions as to the clinical validity of the resulting data. Purpose: The purpose of this in vitro study was to assess the effect of piston material on the fracture behavior of ceramics tested under compressive load. 

Material and methods: Two ceramics were evaluated: a lithium disilicate–based glass-ceramic (D) and a feldspathic porcelain (P). Plate-shaped ceramic specimens (1.5-mm thick) were adhesively cemented onto a dentin analog substrate. The specimens from each ceramic were divided into 4 groups according to the piston material (n=20): metal (M) (stainless steel), composite resin (R) (NEMA-G10, fiber-reinforced epoxy resin), ceramic (C) (lithium disilicate–based glass-ceramic), and human tooth (T) (canine). A gradual compressive load (0.5 mm/min) was applied to the center of the specimen with a universal testing machine. The test was performed in 37°C distilled water, and the initial crack was detected by using an acoustic system. The fracture load values (N) were statistically analyzed with the Kruskal-Wallis and Dunn tests (α=.05). A finite element analysis (FEA) was also performed. 

Results: Piston material had no influence on fracture load and failure mode of ceramic D. Ceramic P showed higher fracture load values when loaded with the composite resin piston. Ceramic P showed more combined failures (cone crack and radial crack) than D. The FEA showed a distinct stress distribution for R piston on P. Pistons C and T resulted in similar stress distribution, fracture load, and failure mode for both ceramics. 

Conclusions: The effect of piston material on the ceramic fracture behavior depends on the ceramic being evaluated.