Correlation between fracture toughness and leucite content in dental porcelains

Objectives: To determine the correlation between fracture toughness and leucite content in dental porcelains. The mechanisms by which leucite influences the fracture toughness of dental porcelains were also investigated. Methods: Six porcelains were tested: A (Ceramco I/Dentsply), B (Ceramco II/Dentsitply), C (Finesse/ Dentsply), D (d.Sign/Ivoctar), Cb (Cerabien/Noritake) and V (Vitadur Alpha/Vita). Bar-shaped specimens were produced, and their fracture toughness was determined by means of the single-edge precracked beam (SEPB) method. The test consisted of fracturing the specimen after a precrack was generated by a bridge-anvil device. K-Ic, was calculated based on fracture force and size of the precrack. Microstructural analysis and determination of the leucite volume fraction were performed on polished specimens etched with 2% HF for 15 s by means of scanning electron microscopy. Fractographic analysis was performed on fracture surfaces. Results: Porcelains A and B presented the highest leucite contents (22%) and similar K-Ic values (1.23 and 1.22 MPa M-1/2, respectively), significantly higher than the other materials. Porcelains C and D presented similar K-Ic values (0.81 and 0.93 MPa m(1/2), respectively), but different leucite contents (6 and 15%, respectively). Porcelain D and D presented higher K-Ic compared to porcelains Cb and V (0.71 and 0.75 MPa m(1/)2, respectively), which presented similar values and the lowest leucite contents (0%). Fractographic analysis showed that porcelains with higher Leucite content presented higher incidence of crack deflection. Conclusions: For the materials evaluated in this study, the leucite content was directly related to K-Ic. The main toughening mechanism observed was crack deflection around leucite particles and clusters. (c) 2005 Elsevier Ltd. All rights reserved.