Flexural Strength of Dental Porcelains with Thermocycling and Different Firing Protocols

Objectives: This is an in vitro study comparing the flexural strength of two dental porcelain after thermocycling, repetitive multiple firings and peak firing temperature (PFT) modifications. Materials and Methods: Two types of dental porcelains were used in this study: Cercon (R) Cream Love and Cercon (R) Cream Kiss (DeguDent, Hanau-Wolfgang/Germany). A total of 50 specimens per porcelain were divided into five groups with ten specimens per group. The first group was fired following the manufacturer's recommendations (control). The second group was fired 10 times repetitively, and the third group was fired and then exposed to 3000 episodes of thermocycling. The fourth group was fired with the PFT modified by + 10 degrees C. The last group was fired with the PFT modified by -10 degrees C. All specimens were tested for flexural strength with the three-point bending test using a universal testing machine (Instron) with a crosshead speed of 0.5 mm/min. Results: The flexural strength, mean (standard deviation [SD]) MPa, of Cercon (R) Ceram Kiss were: Control, 59.6 (7.82); 10 firings, 82.37 (26.32); thermocycling, 68.93 (9.55); PFT (+ 10 degrees C), 75.28 (5.63); and PFT (-10 degrees C), 75.94 (2.85). The results for the flexural strength, mean (SD), of Cercon (R) Ceram Love were: Control, 59.33 (9.9); 10 firings, 106.07 (28.43); thermocycling, 69.87 (11.17); PFT (+ 10 degrees C), 65.7 (10.46); and PFT (-10 degrees C), 51.1 (16.56). Conclusion: There was no difference in the flexural strength between the two veneering porcelains. In addition, repetitive firings significantly improved the flexural strength of both porcelains. Thermocycling significantly increased the flexural strength of both porcelains. There were no significant differences in the flexural strength when changing the PFT for Cercon (R) Ceram Love. Increasing and decreasing the PFT significantly increased the flexural strength of Cercon (R) Ceram Kiss.