ORIGINAL ARTICLE Evaluating The Fracture Toughness and Flexural Strength of Pressable Dental Ceramics: An In Vitro Study Ravi Gurram • C. H. Vamsi Krishna • K. Mahendranadh Reddy • G. V. K. Mohan Reddy • Y. Mahadev Shastry Received: 6 August 2013 / Accepted: 11 October 2013 / Published online: 19 October 2013 Ó Indian Prosthodontic Society 2013 Abstract The study was undertaken to evaluate the biaxial flexural strength, biaxial flexural strength after etching with 9 % HF acid and fracture toughness of three commonly used pressable all ceramic core materials. Ninety glass ceramic specimens were fabricated from three commercially available leucite based core ceramic material (1) Esthetic Empress, (2) Cergo, and (3) Performance Plus. Thirty discs of each material were divided into three groups of 10 discs each. Biaxial flexural strength (30 discs,) Biaxial flexural strength for samples treated with 9 % HF acid (30 discs) and fracture toughness (30 discs) were evaluated. Core material Performance Plus had the lowest biaxial strength of 124.89 MPa, Cergo had strength of 152.22 MPa and the highest value of 163.95 was reported for Esthetic Empress. For samples treated 9 % HF, Per- formance Plus had the lowest biaxial strength of 98.37 MPa, Cergo had strength of 117.42 MPa and the highest value of 143.74 was reported for Esthetic Empress. Core material Performance Plus had the lowest fracture toughness of 1.063 MPa, Cergo had strength of 1.112 MPa and the highest value of 1.225 was reported for Esthetic Empress. The results shows that Esthetic Empress had better mechanical properties compared to Cergo had Per- formance Plus in relation to the parameters tested. Keywords Metal ceramics  Biaxial flexural strength  Fracture toughness Introduction Driven by a debatable need for metal-free restorations, the evolution of all-ceramic systems for dental restorations have been remarkable in last three decades. Processing techniques novel to dentistry have been developed, such as heat pressing, slip-casting and computer aided design computer aided machining (CAD-CAM). Concurrently, all-ceramic materials have been developed to match dental requirements, offering increasingly greater performance from a mechanical standpoint. As opposed to metal- ceramics, all-ceramics contain a significantly greater amount of crystalline phase, which is about 35–99 vol%. This higher level of crystallinity is responsible for an improvement in mechanical properties through various mechanisms, such as crystalline reinforcement or stress induced transformation. The interest of dentists, dental technicians and patients in all-ceramic materials is rapidly increasing as stronger and tougher materials are developed and commercialized along with novel processing technologies. Currently, a wide range of materials and systems are available. How- ever, relatively little is known about their microstructure and toughening mechanisms and their relationship to the mechanical properties of the corresponding ceramic. The present study was undertaken to evaluate the biaxial flex- ural strength [1], biaxial flexural strength after etching with R. Gurram  C. H. V. Krishna (&)  K. M. Reddy  G. V. K. M. Reddy  Y. M. Shastry Department of Prosthodontics, Sri Sai College of Dental Surgery, Kothrepally, Vikarabad, Hyderabad 501101, India e-mail: chvk_guntur@yahoo.co.in R. Gurram e-mail: ravigurram09@gmail.com K. M. Reddy e-mail: mrkareti@gmail.com G. V. K. M. Reddy e-mail: gvkdental@gmail.com Y. M. Shastry e-mail: ymshastry@yahoo.com 123 J Indian Prosthodont Soc (Oct-Dec 2014) 14(4):358–362 DOI 10.1007/s13191-013-0331-1